Applied Therapeutics (APLT) S-1 21 Jan 20 IPO registration Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2019
Document and Entity Information [Abstract]
Document Type	S-1
Entity Registrant Name	Applied Therapeutics Inc.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Central Index Key	0001697532
Amendment Flag	false

Condensed Balance Sheets

Condensed Balance Sheets $ in Thousands	Dec. 31, 2018USD ($)
CURRENT ASSETS:
Cash and cash equivalents	$ 18,748
Prepaid expenses and other current assets	1,498
Total current assets	20,246
TOTAL ASSETS	20,246
CURRENT LIABILITIES:
Accounts payable	3,015
Accrued expenses and other current liabilities	1,413
Total current liabilities	4,428
Total liabilities	4,428
Convertible preferred stock	35,410
STOCKHOLDERS' EQUITY (DEFICIT):
Common Stock, $0.0001 par value, 11,049,720 and 20,441,982 shares authorized at December 31, 2017 and 2018, respectively; 5,458,450 and 5,513,531 shares issued and outstanding at December 31, 2017 and 2018, respectively; 12,609,277 shares issued and outstanding, pro forma as of December 31, 2018 (unaudited)
Additional paid-in capital	1,665
Accumulated deficit	(21,257)
Total stockholders' equity (deficit)	(19,592)
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT)	20,246
Pro Forma
CURRENT ASSETS:
Cash and cash equivalents	18,748
Prepaid expenses and other current assets	1,498
Total current assets	20,246
TOTAL ASSETS	20,246
CURRENT LIABILITIES:
Accounts payable	3,015
Accrued expenses and other current liabilities	1,413
Total current liabilities	4,428
Total liabilities	4,428
STOCKHOLDERS' EQUITY (DEFICIT):
Common Stock, $0.0001 par value, 11,049,720 and 20,441,982 shares authorized at December 31, 2017 and 2018, respectively; 5,458,450 and 5,513,531 shares issued and outstanding at December 31, 2017 and 2018, respectively; 12,609,277 shares issued and outstanding, pro forma as of December 31, 2018 (unaudited)
Additional paid-in capital	37,075
Accumulated deficit	(21,257)
Total stockholders' equity (deficit)	15,818
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT)	20,246
Series A Convertible Preferred Stock
CURRENT LIABILITIES:
Convertible preferred stock	6,254
STOCKHOLDERS' EQUITY (DEFICIT):
Total stockholders' equity (deficit)	6,254
Series A Convertible Preferred Stock | Pro Forma
CURRENT LIABILITIES:
Convertible preferred stock
Series B Convertible Preferred Stock
CURRENT LIABILITIES:
Convertible preferred stock	29,156
STOCKHOLDERS' EQUITY (DEFICIT):
Total stockholders' equity (deficit)	29,156
Series B Convertible Preferred Stock | Pro Forma
CURRENT LIABILITIES:
Convertible preferred stock

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	May 16, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Convertible preferred stock, par value (in dollars per share)				$ 0.0001
Convertible preferred stock, authorized (in shares)				10,883,950				3,535,910
Convertible preferred stock, issued (in shares)				7,095,746				3,093,898
Convertible preferred stock, outstanding (in shares)	0	0		7,095,746
Convertible preferred stock, liquidation preference (in dollars)				$ 36,964				$ 7,000
Common Stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Common Stock, authorized (in shares)	100,000,000			20,441,982				11,049,720
Common Stock, issued (in shares)	17,134,190			5,513,531				5,458,450
Common stock, outstanding (in shares)	17,134,190			5,513,531				5,458,450
Series A Convertible Preferred Stock
Convertible preferred stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, authorized (in shares)	0			3,093,898				3,535,910
Convertible preferred stock, issued (in shares)	0			3,093,898				3,093,898
Convertible preferred stock, outstanding (in shares)	0		3,093,898	3,093,898	3,093,898	3,093,898	3,093,898	3,093,898
Convertible preferred stock, liquidation preference (in dollars)	$ 0			$ 7,000				$ 7,000
Series B Convertible Preferred Stock
Convertible preferred stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, authorized (in shares)	0			7,790,052				0
Convertible preferred stock, issued (in shares)	0			4,001,848				0
Convertible preferred stock, outstanding (in shares)	0		4,444,773	4,001,848				0
Convertible preferred stock, liquidation preference (in dollars)	$ 0			$ 29,964				$ 0
Pro Forma
Common Stock, issued (in shares)				12,609,277				12,609,277
Pro Forma | Series A Convertible Preferred Stock
Convertible preferred stock, issued (in shares)				0				0
Convertible preferred stock, outstanding (in shares)				0				0
Pro Forma | Series B Convertible Preferred Stock
Convertible preferred stock, issued (in shares)				0				0
Convertible preferred stock, outstanding (in shares)				0				0

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
OPERATING EXPENSES:
Research and development	$ 7,453			$ 2,726			$ 18,582	$ 6,111	$ 11,471	$ 3,703
General and administrative	3,294			598			9,331	1,418	2,047	582
Total operating expenses	10,747			3,324			27,913	7,529	13,518	4,285
LOSS FROM OPERATIONS	(10,747)			(3,324)			(27,913)	(7,529)	(13,518)	(4,285)
OTHER INCOME (EXPENSE), NET:
Interest income (expense), net	34			(584)			33	(1,400)	(1,642)	3
Loss on extinguishment of debt									(221)
Other expense				(373)				(873)	(1,140)
Total other income (expense), net	34			(957)			33	(2,273)	(3,003)	3
Net loss	$ (10,713)	$ (8,437)	$ (8,730)	$ (4,281)	$ (3,185)	$ (2,335)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.63)			$ (0.78)			$ (1.98)	$ (1.79)	$ (3.01)	$ (0.79)
Weighted-average common stock outstanding—basic and diluted	17,095,870			5,497,871			14,085,579	5,473,414	5,483,149	5,406,513
Pro Forma
OTHER INCOME (EXPENSE), NET:
Net loss per share attributable to common stockholders-basic and diluted									$ (1.80)
Weighted-average common stock outstanding—basic and diluted									9,163,087

Condensed Statement of Converti

Condensed Statement of Convertible Preferred Stock - USD ($) $ in Thousands	Feb. 05, 2018	Feb. 28, 2019	Jan. 31, 2017	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Temporary Equity
Balance at beginning of period					$ 35,410	$ 6,254
Balance at beginning of period (in shares)					7,095,746
Balance at end of period				$ 35,410		$ 35,410	$ 6,254
Balance at end of period (in shares)				7,095,746		7,095,746
Series A Convertible Preferred Stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period					$ 6,254	$ 6,254
Balance at beginning of period (in shares)					3,093,898	3,093,898
Issuance of convertible preferred stock for cash, net of issuance costs							$ 6,254
Issuance of convertible preferred stock for cash, net of issuance costs (in shares)			3,093,898				3,093,898
Balance at end of period				$ 6,254	$ 6,254	$ 6,254	$ 6,254
Balance at end of period (in shares)				3,093,898	3,093,898	3,093,898	3,093,898
Series B Convertible Preferred Stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period					$ 29,156
Balance at beginning of period (in shares)					4,001,848	0
Issuance of convertible preferred stock for cash, net of issuance costs					$ 3,051	$ 20,937
Issuance of convertible preferred stock for cash, net of issuance costs (in shares)		442,930		2,904,127	442,925	2,904,127
Issuance of convertible preferred stock on extinguishment of convertible promissory notes	$ 8,200					$ 8,219
Issuance of convertible preferred stock on extinguishment of convertible promissory notes (in shares)	1,097,721					1,097,721
Balance at end of period				$ 29,156	$ 32,207	$ 29,156
Balance at end of period (in shares)				4,001,848	4,444,773	4,001,848	0

Condensed Statement of Conver_2

Condensed Statement of Convertible Preferred Stock (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Series A Convertible Preferred Stock
Issuance of convertible preferred stock for cash, issuance costs	$ 746

Condensed Statement of Stockhol

Condensed Statement of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common Stock Par value $0.0001	Additional Paid-in Capital	Accumulated Deficit	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Total
Balance at Dec. 31, 2016		$ 41	$ (454)			$ (413)
Balance (in shares) at Dec. 31, 2016	4,972,373
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in exchange for license		486				486
Issuance of common stock in exchange for license (in shares)	486,077
Issuance of common stock warrants in connection with the issuance of convertible preferred stock		216				216
Stock-based compensation expense		32				32
Net loss			(4,282)			(4,282)
Balance at Dec. 31, 2017		775	(4,736)	$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017	5,458,450			3,093,898
Increase (Decrease) in Stockholders' Equity
Stock-based compensation expense		26
Net loss			(2,335)			(2,335)
Balance at Mar. 31, 2018		801	(7,071)			(6,296)
Balance (in shares) at Mar. 31, 2018	5,458,450
Balance at Dec. 31, 2017		775	(4,736)	$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017	5,458,450			3,093,898
Increase (Decrease) in Stockholders' Equity
Net loss						(9,802)
Balance at Sep. 30, 2018		992	(14,537)			(13,571)
Balance (in shares) at Sep. 30, 2018	5,504,360
Balance at Dec. 31, 2017		775	(4,736)	$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017	5,458,450			3,093,898
Increase (Decrease) in Stockholders' Equity
Issuance of convertible preferred stock on extinguishment of convertible promissory notes		101				101
Issuance of common stock warrants in connection with the issuance of convertible promissory notes		242				242
Issuance of common stock warrants in connection with the issuance of convertible preferred stock		228				228
Exercise of options for common stock issued under Equity Incentive Plan		47				$ 47
Exercise of options for common stock issued under Equity Incentive Plan (in shares)	55,081					55,081
Stock-based compensation expense		272				$ 272
Net loss			(16,521)			(16,521)
Balance at Dec. 31, 2018		1,665	(21,257)	$ 6,254	$ 29,156	(19,592)
Balance (in shares) at Dec. 31, 2018	5,513,531			3,093,898	4,001,848
Balance at Mar. 31, 2018		801	(7,071)			(6,296)
Balance (in shares) at Mar. 31, 2018	5,458,450
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan		9				9
Exercise of options for common stock issued under Equity Incentive Plan (in shares)	9,171
Stock-based compensation expense		76				76
Net loss			(3,185)			(3,185)
Balance at Jun. 30, 2018		886	(10,256)			(9,396)
Balance (in shares) at Jun. 30, 2018	5,467,621
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan		28				28
Exercise of options for common stock issued under Equity Incentive Plan (in shares)	36,739
Stock-based compensation expense		78				78
Net loss			(4,281)			(4,281)
Balance at Sep. 30, 2018		992	(14,537)			(13,571)
Balance (in shares) at Sep. 30, 2018	5,504,360
Balance at Dec. 31, 2018		1,665	(21,257)	$ 6,254	$ 29,156	(19,592)
Balance (in shares) at Dec. 31, 2018	5,513,531			3,093,898	4,001,848
Increase (Decrease) in Stockholders' Equity
Issuance of common stock warrants in connection with the issuance of Series B convertible preferred stock		80				80
Stock-based compensation expense		325				325
Net loss			(8,730)			(8,730)
Balance at Mar. 31, 2019		2,070	(29,987)			(27,917)
Balance (in shares) at Mar. 31, 2019	5,513,531
Balance at Dec. 31, 2018		1,665	(21,257)	$ 6,254	$ 29,156	$ (19,592)
Balance (in shares) at Dec. 31, 2018	5,513,531			3,093,898	4,001,848
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan (in shares)						81,988
Net loss						$ (27,880)
Balance at Sep. 30, 2019	$ 1	79,872	(49,137)			30,747
Balance (in shares) at Sep. 30, 2019	17,134,190
Balance at Mar. 31, 2019		2,070	(29,987)			(27,917)
Balance (in shares) at Mar. 31, 2019	5,513,531
Increase (Decrease) in Stockholders' Equity
Stock-based compensation expense		3,279				3,279
Net loss			(8,437)			(8,437)
Balance at Jun. 30, 2019	$ 1	78,427	(38,424)			40,004
Balance (in shares) at Jun. 30, 2019	17,052,202
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan		226				226
Exercise of options for common stock issued under Equity Incentive Plan (in shares)	81,988
Stock-based compensation expense		1,219				1,219
Net loss			(10,713)			(10,713)
Balance at Sep. 30, 2019	$ 1	$ 79,872	$ (49,137)			$ 30,747
Balance (in shares) at Sep. 30, 2019	17,134,190

Condensed Statement of Stockh_2

Condensed Statement of Stockholders' (Deficit) Equity (Parenthetical) - $ / shares	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity
Common Stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Common Stock Par value $0.0001
Increase (Decrease) in Stockholders' Equity
Common Stock, par value (in dollars per share)	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (16,521)	$ (4,282)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	272	32
Issuance of common stock in exchange for license		486
Non-cash interest expense	1,642
Change in fair value of derivative liability	972
Change in fair value of warrant liability	168
Loss on extinguishment of debt	221
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,179)	(9)
Accounts payable	2,302	499
Accrued expenses and other current liabilities	941	79
Net cash used in operating activities	(11,182)	(3,195)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible promissory notes, net of cash issuance costs of $440	5,560
Payment of offering costs	(119)
Exercise of stock options for common stock under Equity Incentive Plan	47
Net cash provided by financing activities	26,653	6,470
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	15,471	3,275
Cash and cash equivalents at beginning of period	3,277	2
Cash and cash equivalents at end of period	18,748	3,277
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITY:
Derivative liability in connection with issuance of convertible promissory notes	1,896
Extinguishment of convertible promissory notes	4,646
Extinguishment of derivative liability in connection with extinguishment of convertible promissory notes	2,868
Deferred offering costs in accrued expenses	191
2018 Notes
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITY:
Issuance of warrants	242
Series A Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible preferred stock, net of cash issuance costs		6,470
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITY:
Issuance of warrants		$ 216
Series B Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible preferred stock, net of cash issuance costs	21,165
SUPPLEMENTAL DISCLOSURE OF NONCASH FINANCING ACTIVITY:
Issuance of warrants	228
Issuance of convertible preferred stock upon extinguishment of convertible promissory notes	$ 8,219

Condensed Statements of Cash _2

Condensed Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash issuance cost, Convertible promissory notes	$ 440
Series A Convertible Preferred Stock
Cash issuance costs, Convertible preferred stock		$ 530
Series B Convertible Preferred Stock
Cash issuance costs, Convertible preferred stock	$ 584

ORGANIZATION AND SUMMARY OF SIG

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Operations and Business Applied Therapeutics, Inc. (the “Company”) is a clinical-stage biopharmaceutical company developing a pipeline of novel product candidates against validated molecular targets in indications of high unmet medical need. In particular, the Company is currently targeting treatments for cardiovascular disease, galactosemia and diabetic complications. The Company was incorporated in Delaware on January 20, 2016 and is headquartered in New York, New York. On May 16, 2019, the Company completed an initial public offering (“IPO”) in which the Company issued and sold 4,000,000 shares of its common stock at a public offering price of $10.00 per share, for aggregate gross proceeds of $40.0 million. The Company received net of proceeds $34.6 million, after deducting underwriting discounts and commissions and offering costs. Prior to the completion of the IPO, the Company primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 8). In connection with the IPO, the Company effected a 55.2486-for-1 stock split of its issued and outstanding shares of common stock and convertible preferred stock. The stock split became effective on April 26, 2019. Stockholders entitled to fractional shares as a result of the forward stock split received cash payment in lieu of receiving fractional shares. All share and per share amounts for all periods presented in the accompanying condensed financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect this stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately increased and the respective per share value and exercise prices, if applicable, were proportionately decreased in accordance with the terms of the agreements governing such securities. Upon the closing of the IPO on May 16, 2019, all of the then-outstanding shares of convertible preferred stock automatically converted into 7,538,671 shares of common stock on a one-for-one basis. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. The accompanying unaudited condensed financial statements as of September 30, 2019 and for the three and nine months ended September 30, 2019 and 2018 have been prepared by the Company in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and, pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2018 included in the Company’s final prospectus that forms a part of the Company’s Registration Statement on Form S-1 (Reg. No. 333-230838), filed with the SEC pursuant to Rule 424(b)(4) on May 14, 2019 (the “Prospectus”). The unaudited condensed financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited condensed financial statements contain all adjustments which are necessary for a fair presentation of the Company’s financial position as of September 30, 2019, results of operations for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2019. Liquidity The Company has incurred, and expects to continue to incur, significant operating losses and negative cash flows for at least the next several years as it continues to develop its drug candidates. To date, the Company has not generated any revenue, and it does not expect to generate revenue unless and until it successfully completes development and obtains regulatory approval for one of its product candidates. Management believes that the Company’s existing cash, together with the net proceeds from the IPO, will allow the Company to continue its operations for at least 12 months from the issuance date of these financial statements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant Accounting Policies The significant accounting policies and estimates used in preparation of the condensed financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus. Except as detailed below, there have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2019. Stock‑Based Compensation The Company accounts for its stock-based compensation as expense in the condensed statements of operations based on the awards' grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black-Scholes option pricing model with the exception of stock options that include service, performance and market conditions, which are valued using the Monte-Carlo simulation model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company has historically been a private company and lacks company-specific historical and implied volatility information. Therefore, the Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission ("SEC") Staff Accounting Bulletin ("SAB") No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. A Monte-Carlo simulation is an analytical method used to estimate fair value by performing a large number of simulations or trial runs and thereby determining a value based on the possible outcomes from these trial runs based on the specific vesting conditions. The fair value of stock-based payments is recognized as expense over the requisite service period which is generally the vesting period, with the exception of the fair value of stock-based payments for awards that include service, performance and market conditions, which is recognized as expense over the derived service period determined using the Monte-Carlo simulation. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. Upon closing the IPO in May 2019, $2.6 million in deferred offering costs were reclassified from prepaid and other current assets and recorded against the IPO proceeds reducing additional paid-in capital. As of September 30, 2019, the Company did not have any deferred offering costs recorded in prepaid and other current assets. Investments We have investments in marketable debt securities. We determine the appropriate classification of our investments at the date of purchase and reevaluate the classifications at the balance sheet date. Marketable debt securities with maturities of 12 months or less are classified as short-term. Marketable debt securities with maturities greater than 12 months are classified as long-term. The Company’s marketable securities are accounted for as available for sale (“AFS”). AFS securities are reported at fair value. Unrealized gains and losses, after applicable income taxes, are reported in accumulated other comprehensive income/(loss). We conduct an other-than-temporary impairment (“OTTI”) analysis on a quarterly basis or more often if a potential loss-triggering event occurs. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and whether we intend to sell. For AFS securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Recently Adopted Accounting Pronouncements The new accounting pronouncements recently adopted by the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus as filed with the SEC on May 14, 2019. Except as described below, there have been no new accounting pronouncements adopted by the Company during the nine months ended September 30, 2019. In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) , which requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases on their balance sheet date (“ASU No. 2016-02”). ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018. In July 2018, an amendment was made that allows companies the option of using the effective date of the new standard as the initial application date (at the beginning of the period in which the new standard is adopted, rather than at the beginning of the earliest comparative period). This update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize the associated lease assets and lease liabilities on its balance sheet. Additionally, in March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements (“ASU No. 2019-01”). ASU No. 2019-01 clarifies the transition guidance related to interim disclosures provided in the year of adoption. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease did not significantly change from previous U.S. GAAP. The modified retrospective method includes several optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. The Company adopted Topic 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance under ASC 840. In adopting Topic 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease; ii) the lease classification of existing or expired leases; and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election not to recognize assets or related lease liabilities with a lease term of twelve months or less in its condensed balance sheet. The adoption of this standard did not have an impact on the Company’s condensed balance sheet as all of the Company’s leases are for terms that are less than 12 months. Additionally, the adoption of this standard did not have a material impact on the Company’s condensed statements of operations or condensed statement of cash flows. On August 6, 2019 the Company entered into a lease for approximately 6,579 square feet of new office space in New York City (the “Lease”). The Lease will commence upon delivery of the premise after certain improvements are made, which is anticipated to be on or about November 1, 2019 (the “Commencement Date”), for a five-year period. Under the Lease, the Company will pay monthly rent of approximately $38,000 for the first year following the Commencement Date, and such rent will increase by a nominal percentage every year following the first anniversary of the Commencement Date. The Company will also pay a real estate tax escalation, as additional rent, over a base year. Total lease obligation over the term of the lease will be approximately $2.4 million. Recently Issued Accounting Pronouncements The FASB issued authoritative guidance that amends guidance on reporting credit losses for assets, including available-for-sale marketable securities and any other financial assets not excluded from the scope that have the contractual right to receive cash. For available-for-sale marketable securities, credit losses should be measured in a manner similar to current generally accepted accounting standards; however, ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , will require that credit losses be presented as an allowance rather than as a write-down. We are currently in the process of evaluating the impact of this guidance on our condensed financial statements.	Applied Therapeutics, Inc. Notes to the Financial Statements 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Operations and Business Applied Therapeutics, Inc. (the “Company”) is a clinical‑stage biopharmaceutical company developing a pipeline of novel product candidates against validated molecular targets in indications of high unmet medical need. In particular, the Company is currently targeting treatments for cardiovascular disease, galactosemia and diabetic complications. The Company was incorporated in Delaware on January 20, 2016 and is headquartered in New York, New York. Going Concern The Company has evaluated whether there are conditions and events considered in the aggregate that raise substantial doubt about the Company’s ability to continue as a going concern. Through December 31, 2018, the Company has primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 6). The Company has incurred recurring losses from operations since its inception, including net losses of $4.3 million and $16.5 million for the years ended December 31, 2017 and December 31, 2018, respectively, and has used cash in operations of $3.2 million and $11.2 million for the years ended December 31, 2017 and December 31, 2018, respectively. In addition, as of December 31, 2018, the Company had an accumulated deficit of $21.3 million. The Company expects its operating losses and negative cash flows to continue into the foreseeable future as it continues to develop, manufacture, and commercialize its product candidates. The Company is seeking to complete an initial public offering (“IPO”) of its common stock. In the event the Company does not complete an IPO, and even after the completion of an IPO, the Company expects to seek additional funding through private or public equity financings, debt financings, collaborations, or other strategic transactions. The Company may not be able to obtain funding on acceptable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Based on the operating losses incurred since inception, the expectation of continuing operating losses for the foreseeable future, and the need to raise additional capital to finance its operations, the Company has concluded that there is substantial doubt about its ability to continue as a going concern within one year after the date that the financial statements are issued. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. The financial statements do not include any adjustments that might be necessary if the Company is unable to continue as a going concern. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Unaudited Pro Forma Information The accompanying unaudited pro forma balance sheet as of December 31, 2018 has been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding convertible preferred stock into 7,095,746 shares of common stock. The accompanying unaudited pro forma basic and diluted net loss per share attributable to common stockholders in the statements of operations for the year ended December 31, 2018 have been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding shares of convertible preferred stock into shares of common stock as of December 31, 2018. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third‑party fees that are directly associated with in‑process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of convertible preferred stock and stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. The Company recorded deferred offering costs of $0.3 million as of December 31, 2018 in prepaid expenses and other current assets. Fair Value Measurements Certain assets and liabilities are reported on a recurring basis at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1—Quoted prices in active markets for identical assets or liabilities. Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. Cash and Cash Equivalents The Company considers all short‑term, highly liquid investments, with an original maturity of three months or less, to be cash equivalents. The Company maintains its cash in bank deposit accounts which, at times, may exceed federally insured limits. The Company has not experienced any losses in these accounts and does not believe it is exposed to any significant credit risk on cash and cash equivalents. Common Stock Valuation The Company utilizes significant estimates and assumptions in determining the fair value of its common stock. The Company has utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately‑Held Company Equity Securities Issued as Compensation (the “Practice Aid”), to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time of, and the likelihood of, achieving a liquidity event, such as an IPO or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date. Convertible Preferred Stock The Company records shares of its convertible preferred stock at their respective fair values on the dates of issuance less issuance costs. The Company classifies shares of its convertible preferred stock outside of stockholders’ deficit when the redemption of such units or shares is outside the Company’s control. The Company does not adjust the carrying values of the convertible preferred units or convertible preferred stock to the liquidation preferences of such units or shares until such time as a deemed liquidation event is probable of occurring. Research and Development The Company expenses all costs incurred in performing research and development activities. Research and development expenses include salaries and other related costs, materials and supplies, preclinical expenses, manufacturing expenses, contract services and other outside expenses. As part of the process of preparing the financial statements, the Company is required to estimate their accrued research and development expenses. The Company makes estimates of the accrued expenses as of each balance sheet date in the financial statements based on facts and circumstances known at that time. In addition, there may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense in which case such amounts are reflected as prepaid expenses and other current assets. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual or the amount of prepaid expenses accordingly. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized in prepaid expenses and other current assets. The capitalized amounts are expensed as the related goods are delivered or the services are performed. General and Administrative General and administrative expenses consist primarily of salaries and other related costs, including stock‑based compensation, for personnel in the Company’s executive and finance functions. General and administrative expenses also include professional fees for legal, accounting, auditing, tax and consulting services; travel expenses; and facility‑related expenses, which include allocated expenses for rent and maintenance of facilities and other operating costs. Stock‑Based Compensation The Company accounts for its stock‑based compensation as expense in the statements of operations based on the awards’ grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company‑specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, Share‑Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of stock‑based payments is recognized as expense over the requisite service period which is generally the vesting period. Income Taxes The Company uses the asset and liability method of accounting for deferred income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the carrying amounts and the tax basis of assets and liabilities at currently enacted tax rates. These temporary differences primarily relate to net operating loss carryforwards available to offset future taxable income. Valuation allowances are established, if necessary, to reduce a deferred tax asset to the amount that will more likely than not be realized. The Company recognizes tax liabilities from an uncertain tax position only if it is more likely than not that the tax position will not be sustained upon examination by the taxing authorities, based on the technical merits of the tax position. There are no uncertain tax positions that have been recognized in the accompanying financial statements. The Company is required to file tax returns in the U.S. federal jurisdiction and in the state of New York. The Company’s policy is to recognize interest and penalties related to uncertain tax benefits, if any, as part of income tax expense. No such interest and penalties have been accrued as of December 31, 2017 and 2018. Net Loss per Share and Unaudited Pro Forma Net Loss per Share Basic net loss per share is calculated by dividing net loss available to common stockholders by the weighted‑average common stock outstanding. Diluted net loss per share is calculated similarly, except that it includes the dilutive effect of the assumed exercise of securities, including outstanding warrants and the effect of shares issuable under the Company’s stock‑based compensation plan, if such effect is dilutive. Unaudited pro forma net loss per share attributable to common stockholders is computed using the weighted‑average number of common shares outstanding after giving effect to the conversion of all outstanding convertible preferred stock into shares of common stock as if such conversion had occurred at January 1, 2018, or the date of original issuance, if later. Segment Information Operating segments are defined as components of an enterprise for which separate discrete information is available for evaluation by the chief operating decision‑maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision‑maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment, which is the business of discovering and developing its product candidates. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014‑09, Revenue from Contracts with Customers (Topic 606) (“ASU No. 2014‑09”), which modifies how all entities recognize revenue, and consolidates into one Accounting Standards Codification (“ASC”) (ASC Topic 606, Revenue from Contracts with Customers ), the current guidance found in ASC Topic 605, and various other revenue accounting standards for specialized transactions and industries. ASU No. 2014‑09 outlines a comprehensive five‑step revenue recognition model based on the principle that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU No. 2015‑14, Revenue from Contracts with Customers (Topic 606): Deferral of Effective Date (“ASU No. 2015‑14”), which defers the effective date of ASU No. 2014‑09 by one year. Early adoption is permitted for annual periods beginning after December 15, 2016. To date, the Company has not had any arrangements that are within the scope of ASU No. 2014‑09, or its predecessor, ASC Topic 605. The Company adopted these pronouncements on January 1, 2017, which did not have any impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Improvements to Employee Share‑Based Payment Accounting (“ASU No. 2016‑09”), which simplifies share‑based payment accounting through a variety of amendments. The Company elected to early adopt this guidance effective January 1, 2016, and has elected to account for forfeitures as incurred and therefore no forfeiture estimate is utilized in the year ended December 31, 2017. Adoption of ASU No. 2016‑09 did not have a material impact on the Company’s financial statements. In May 2017, the FASB issued ASU No. 2017‑09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU No. 2017‑09”), which clarifies when to account for a change to the terms or conditions of a share‑based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The standard is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted ASU No. 2017‑09 as of January 1, 2018, which did not have a material impact on the Company’s financial statements. In June 2018, the FASB issued ASU No. 2018‑07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share‑Based Payment Accounting (“ASU No. 2018‑07”). These amendments expand the scope of Topic 718, Compensation—Stock Compensation , which currently only includes share‑based payments to employees, to include share‑based payments issued to nonemployees for goods or services. Consequently, the accounting for share‑based payments to nonemployees and employees will be substantially aligned. This ASU supersedes Subtopic 505‑50, Equity—Equity‑Based Payments to Non‑Employees . This standard is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted as long as ASU No. 2014‑09 has been adopted by the Company. The Company adopted ASU No. 2018‑07 as of January 1, 2017, which did not have a material impact on the Company’s financial statements. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) , which requires lessees to recognize assets and liabilities for leases with lease terms greater than 12 months in the statement of financial position. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016‑02 also requires improved disclosures to help users of financial statements better understand the amount, timing and uncertainty of cash flows arising from leases. The update is effective for fiscal years beginning after December 15, 2018, including interim reporting periods within that reporting period. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2016‑02 will have on its financial statements. In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement . which, eliminates, modifies, and adds disclosure requirements on fair value measurements. The standard is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2018‑13 will have on its financial statements.

LICENSE AGREEMENT

LICENSE AGREEMENT	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
LICENSE AGREEMENT
LICENSE AGREEMENT	2. LICENSE AGREEMENT Columbia University In October 2016, the Company entered into a license agreement (the “2016 Columbia Agreement”) with the Trustees of Columbia University (“Columbia University”) to obtain an exclusive royalty-bearing sublicensable license in respect to certain patents. As part of the consideration for entering into the 2016 Columbia Agreement, the Company issued to Columbia University shares equal to 5% of its outstanding common stock on a fully diluted basis at the time of issue. The common stock had a fair value of $0.5 million at the time of issuance. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2016 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid-six figures beginning on the 10th anniversary of the effective date of the 2016 Columbia Agreement. The Company has not granted any sublicenses under the 2016 Columbia Agreement. However, if the Company sublicenses the rights granted under the 2016 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 20%, depending on the stage of development at the time such revenue is received from such third parties. In January 2019, the Company entered into a second license agreement with Columbia University (the “2019 Columbia Agreement”). Pursuant to the 2019 Columbia Agreement, Columbia University granted the Company a royalty-bearing, sublicensable license that is exclusive with respect to certain patents, and non-exclusive with respect to certain know-how, in each case to develop, manufacture and commercialize PI3k inhibitor products. The license grant is worldwide. Under the 2019 Columbia Agreement, the Company is obligated to use commercially reasonable efforts to research, discover, develop and market licensed products for commercial sale in the licensed territory, and to comply with certain obligations to meet specified development and funding milestones within defined time periods. Columbia University retains the right to conduct, and grant third parties the right to conduct, non-clinical academic research using the licensed technology; provided that such research is not funded by a commercial entity or for-profit entity or results in rights granted to a commercial or for-profit entity. As consideration for entering into the 2019 Columbia Agreement, the Company made a nominal upfront payment to Columbia University. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2019 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low- to mid-single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid-six figures beginning on the tenth anniversary of the effective date of the 2019 Columbia Agreement. The Company has not granted any sublicenses under the 2019 Columbia Agreement. However, if the Company sublicenses the rights granted under the 2019 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 50%, depending on the stage of development at the time such revenue is received from such third parties. The 2019 Columbia Agreement will terminate upon the expiration of all the Company’s royalty payment obligations in all countries. The Company may terminate the 2019 Columbia Agreement for convenience upon 90 days’ written notice to Columbia University. At its election, Columbia University may terminate the 2019 Columbia Agreement, or convert the licenses granted to the Company into non-exclusive, non-sublicensable licenses, in the case of (a) the Company’s uncured material breach upon 30 days’ written notice (which shall be extended to 90 days if the Company is diligently attempting to cure such material breach), (b) the Company’s failure to achieve the specified development and funding milestone events, or (c) the Company’s insolvency . In March 2019, and in connection with the 2016 Columbia Agreement, the Company entered into a research services agreement (the “2019 Columbia Research Agreement” and collectively with the 2016 Columbia Agreement and 2019 Columbia Agreement, the “Columbia Agreements”) with Columbia University with the purpose of analyzing structural and functional changes in brain tissue in an animal model of galactosemia, and the effects of certain compounds whose intellectual property rights were licensed to the Company as part of the 2016 Columbia Agreement on any such structural and functional changes. The 2019 Columbia Research Agreement has a term of 12 months from its effective date; provided that the Company can terminate the 2019 Columbia Research Agreement without cause with at least 30 days’ prior written notice. The services covered by the 2019 Columbia Research Agreement will be performed by Columbia University in two parts consisting of six months. The decision to proceed with Part 2 of the 2019 Columbia Research Agreement shall be made solely by the Company and will be contingent on the success of the research performed in Part 1. In consideration for the services performed by Columbia University in Part 1, the Company will be required to pay $0.1 million to Columbia University for staffing, supplies and indirect costs. If the Company decides to continue the research defined in Part 2, the Company will be required to pay an additional $0.2 million to Columbia University. During the three and nine months ended September 30, 2019, the Company recorded $17,000 and $42,000, respectively, in research and development expense and $28,000 and $0.3 million, respectively, in general and administrative expense related to the Columbia Agreements. During the three and nine months ended September 30, 2018, the Company recorded $0.1 million and $0.2 million, respectively, in research and development expense and $43,000 and $98,000, respectively, in general and administrative expense related to the Columbia Agreements. In aggregate, the Company has incurred $1.7 million in expense from the execution of the Columbia Agreements through September 30, 2019. As of September 30, 2019, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable. As of December 31, 2018, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable.	2. LICENSE AGREEMENT Columbia University In October 2016, the Company entered into a license agreement (the “Columbia Agreement”) with The Trustees of Columbia University in the City of New York (“Columbia University”). Pursuant to the Columbia Agreement, Columbia University granted the Company a royalty‑bearing, sublicensable license that is exclusive with respect to certain patents, and non‑exclusive with respect to certain know‑how, in each case to develop, manufacture and commercialize aldose reductase inhibitor products, including AT‑001, AT‑003 and AT‑007. The license grant is worldwide with the exception of a single patent family covering AT‑001 and AT‑003 for which the license grant excludes China, Taiwan, Hong Kong and Macao. Under the Columbia Agreement, the Company is obligated to use commercially reasonable efforts to research, discover, develop and market licensed products for commercial sale in the licensed territory, and to comply with certain obligations to meet specified development and funding milestones within defined time periods. Columbia University retains the right to conduct, and grant third parties the right to conduct, non‑clinical academic research using the licensed technology, provided that such research is not funded by a commercial entity or for‑profit entity or results in rights granted to a commercial or for‑profit entity. As consideration for entering into the Columbia Agreement, the Company made a nominal upfront payment to Columbia University and, following the occurrence of certain trigger events, issued to Columbia University shares equal to 5% of its outstanding common stock on a fully diluted basis at the time of issue. The common stock had a fair value of $0.5 million, which was recognized as research and development expense for the year ended December 31, 2017. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid six figures beginning on the 10th anniversary of the effective date of the Columbia Agreement. The Company has not granted any sublicenses under the Columbia Agreement. However, if the Company sublicenses the rights granted under the Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 20%, depending on the stage of development at the time such revenue is received from such third parties. The Columbia Agreement will terminate upon the expiration of all the Company’s royalty payment obligations in all countries. The Company may terminate the Columbia Agreement for convenience upon 90 days’ written notice to Columbia University. At its election, Columbia University may terminate the Columbia Agreement, or convert the licenses granted to the Company into non‑exclusive, non‑sublicensable licenses, in the case of (a) the Company’s uncured material breach upon 30 days’ written notice (which shall be extended to 90 days if the Company is diligently attempting to cure such material breach), (b) the Company’s failure to achieve the specified development and funding milestone events, or (c) the Company’s insolvency. The Company recorded research and development expense related to the Columbia Agreement of $0.6 million and $0.5 million for the years ended December 31, 2017 and 2018, respectively, and $1.4 million from the execution of the Columbia Agreement through December 31, 2018. Columbia University is a related party as they have been issued shares of the Company’s common stock. As of December 31, 2017, the Company had $0.2 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable. As of December 31, 2018, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	3. FAIR VALUE MEASUREMENTS The following table summarizes, as of September 30, 2019, the Company's financial assets and liabilities that are measured at fair value on a recurring basis, according to the fair value hierarchy described in the significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus. As of December 31, 2018, the Company did not have financial assets or liabilities that are measured at fair value on a recurring basis (in thousands). As of September 30, 2019 Level 1 Level 2 Level 3 Total Cash $ 12,933 $ — $ — $ 12,933 Money market funds 133 — — 133 Total cash and cash equivalents $ 13,065 $ — $ — $ 13,065 Commercial paper and corporate bonds — 7,522 — 7,522 U.S. government agency debt securities — 12,367 — 12,367 Total marketable securities $ — $ 19,889 $ — $ 19,889 Total financial assets measured at fair value on a recurring basis $ 13,065 $ 19,889 $ — $ 32,954 Investments in commercial paper, corporate bonds, and U.S. government agency debt securities have been classified as Level 2 as they are valued using quoted prices in less active markets or other directly or indirectly observable inputs. Fair values of corporate bonds and U.S. government agency debt securities were derived from a consensus or weighted average price based on input of market prices from multiple sources at each reporting period. With regard to commercial paper, all of the securities had high credit ratings and one year or less to maturity; therefore, fair value was derived from accretion of purchase price to face value over the term of maturity or quoted market prices for similar instruments if available. During the three and nine months ended September 30, 2019, there were no transfers of financial assets between Level 1 and Level 2. During the three and nine months ended September 30, 2018, the Company had Level 1 financial assets (cash) and Level 3 financial liabilities that were measured at fair value on a recurring basis. The Company's convertible promissory notes issued on February 5, 2018 (the "2018 Notes") (see Note 4), contained certain features which met the criteria to be bifurcated and accounted for separately from the 2018 Notes (the "Derivative Liability"). Also in connection with the issuance of the 2018 Notes, the Company had a contingent obligation to issue common stock warrants ("2018 Notes Warrants") upon the conversion of the 2018 Notes into Series B convertible preferred stock ("Series B Preferred Stock") (the "Warrant Liability"). The Derivative Liability and the Warrant Liability were initially recorded at fair value of $1.9 million and $0.1 million, respectively, and were subsequently remeasured at fair value at each reporting period. In November 2018, the Derivative Liability was settled in connection with the extinguishment of the 2018 Notes (see Note 4). The following table provides a roll forward of the aggregate fair values of the Derivative Liability and Warrant Liability as of September 30, 2018, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 180 6 Balance as of March 31, 2018 $ 2,076 $ 80 Change in fair value 294 21 Balance as of June 30, 2018 $ 2,370 $ 101 Change in fair value 335 38 Balance as of September 30, 2018 $ 2,704 $ 139 Changes in the fair value of the Derivative Liability and Warrant Liability were recognized in other income (expense), net in the condensed statement of operations. The Company recognized other expense in connection with the Derivative Liability of $0.3 million and $0.8 million during the three and nine months ended September 30, 2018, respectively. The Company recognized other income in connection with the Warrant Liability of $38 thousand and $65 thousand during the three and nine months ended September 30, 2018, respectively.	3. FAIR VALUE MEASUREMENTS During the year ended December 31, 2018, the Company had level 3 financial liabilities that were measured at fair value on a recurring basis that were no longer outstanding as of December 31, 2018. There were no transfers between fair value hierarchy levels during the year ended December 31, 2018. There were no financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017. Derivative Liability The Company’s convertible promissory notes issued on February 5, 2018 (the “2018 Notes”) (see Note 4), contained certain features which met the criteria to be bifurcated and accounted for separately from the 2018 Notes (the “Derivative Liability”). The Derivative Liability was recorded at fair value of $1.9 million upon the issuance of the 2018 Notes and was subsequently remeasured at fair value at each reporting period and immediately before extinguishment. Changes in the fair value of the Derivative Liability were recognized as a component of other income (expense), net in the statement of operations. The Derivative Liability was initially valued and remeasured using a “with‑and‑without” method. The “with‑and‑without” methodology involves valuing the whole instrument on an as‑is basis and then valuing the instrument without the individual embedded derivative. The difference between the entire instrument with the embedded derivative compared to the instrument without the embedded derivative is the fair value of the derivative, recorded as the Derivative Liability. The Derivative Liability is settled when the underlying debt instrument is settled either through conversion or extinguishment into equity at a variable price, which is a redemption feature, or held to maturity. In November 2018, the Derivative Liability was settled in connection with the extinguishment of the 2018 Notes. Warrant Liability In connection with the issuance of the 2018 Notes, the Company had a contingent obligation to issue common stock warrants (“2018 Notes Warrants”) upon the conversion of the 2018 Notes into Series B convertible preferred stock (“Series B Preferred Stock”) (see Note 6 and Note 7). As the obligation to issue the 2018 Notes Warrants was not initially for a fixed number of warrants, it was recorded as a liability (the “Warrant Liability”) at fair value of $0.1 million upon the issuance of the 2018 Notes and was subsequently remeasured at fair value each reporting period and immediately before the 2018 Notes were extinguished. Changes in the fair value of the Warrant Liability were recognized in other income (expense), net in the statement of operations. In November 2018, in connection with the conversion of the 2018 Notes into Series B Preferred Stock, the 2018 Notes Warrants were issued and reclassified to equity. The 2018 Notes Warrants were initially valued and remeasured using a Black‑Scholes option pricing model with the range of assumptions as follows: Contractual term (in years) 10.0 Volatility 74.48% - 76.56% Risk-free interest rate 2.85% - 3.20% Dividend yield 0.00% The following table provides a roll forward of the aggregate fair values of the Company’s Derivative Liability and Warrant Liability, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 972 168 Extinguishment of Derivative Liability in connection with extinguishment of 2018 Notes (2,868) — Reclassification of Warrant Liability into 2018 Notes Warrants — (242) Balance as of December 31, 2018 $ — $ — The inputs utilized by management to value the Derivative Liability and 2018 Notes Warrants are highly subjective. The assumptions used in calculating the fair value of the Derivative Liability and 2018 Notes Warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the Derivative Liability and 2018 Notes Warrants may be materially different in the future.

CONVERTIBLE PROMISSORY NOTES

CONVERTIBLE PROMISSORY NOTES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
CONVERTIBLE PROMISSORY NOTES
CONVERTIBLE PROMISSORY NOTES	5. CONVERTIBLE PROMISSORY NOTES There were no convertible promissory notes outstanding as of September 30, 2019 and December 31, 2018. On February 5, 2018, the Company issued the 2018 Notes in the aggregate principal amount of $6.0 million. The 2018 Notes bore interest at a rate of 15.0% per annum, were unsecured and were due and payable, including accrued interest, on August 8, 2019. In the event of a qualified sale of preferred stock to one or more investors resulting in gross proceeds to the Company of at least $8.0 million, all principal and accrued and unpaid interest under the 2018 Notes was automatically convertible into a number of shares of the Company’s preferred stock issued in such a financing equal to the outstanding principal and accrued but unpaid interest under the 2018 Notes, divided by an amount equal to 80% of the lowest price per share of the preferred stock sold in the financing. In the event of a corporate transaction or change of control event, the 2018 Notes contained a put option whereby the Company was required to pay to the holders of 2018 Notes an amount equal to (i) the principal amount then outstanding under the 2018 Notes plus any accrued but unpaid interest, plus (ii) an amount equal to 30% of the outstanding principal amount. The terms of the 2018 Notes provided that: (i) all outstanding principal and interest was due and payable in cash upon an event of acceleration, as defined in the 2018 Notes agreement; (ii) amounts outstanding under the notes were not prepayable without the written consent of the holders of more than 50% of the outstanding principal of the notes, and in addition to the balance the Company will prepay, the Company will also pay the noteholders an amount equal to 15% of the principal amount of the notes that the Company is prepaying; and (iii) with respect to subordination, the Company has no outstanding indebtedness for borrowed money or any other liabilities, other than accounts payable arrangements with vendors entered into in the ordinary course of business and consistent with usual trade terms and will not issue or incur additional indebtedness for borrowed money while the 2018 Notes remain outstanding. There were no financial or negative covenants associated with the convertible promissory notes. The Derivative Liability represents the conversion feature in the event of a qualified financing and the put option, each of which met the definition of an embedded derivative and were required to be combined and accounted for as a separate unit of accounting. The Company recorded the issuance-date fair value of the Derivative Liability of $1.9 million as a debt discount and Derivative Liability in the Company’s balance sheet (see Note 3) . In connection with the 2018 Notes, the Company paid legal costs and bank fees of $0.4 million and were obligated to issue the 2018 Notes Warrants (see Note 3 and Note 9) with an initial fair value of $0.1 million, which were capitalized and recorded as a debt discount. The debt discount, which included the Derivative Liability and 2018 Notes Warrants, was amortized at an effective interest rate of 54.9% using the effective interest method over the term of the loan. In connection with the 2018 Notes, the Company recognized interest expense of $0.6 million and $1.4 million during the three and nine months ended September 30, 2018, respectively. The interest expense includes amortization of the debt discount of $0.8 million and $0.3 million for the three and nine months ended September 30, 2018 , respectively . In November 2018, in connection with the Company’s issuance and sale of Series B Preferred Stock, all of the then-outstanding principal and accrued interest under the 2018 Notes, totaling $6.6 million, was automatically converted into 1,097,721 shares of Series B Preferred Stock at a price equal to 80% of the $7.49 per share price paid by investors in the Series B Preferred Stock financing.	4. CONVERTIBLE PROMISSORY NOTES On February 5, 2018, the Company issued the 2018 Notes in the aggregate principal amount of $6.0 million. The 2018 Notes bore interest at a rate of 15.0% per annum, were unsecured and were due and payable, including accrued interest, on August 8, 2019. In the event of a qualified sale of preferred stock to one or more investors resulting in gross proceeds to the Company of at least $8.0 million, all principal and accrued and unpaid interest under the 2018 Notes was automatically convertible into a number of shares of the Company’s preferred stock issued in such a financing equal to the outstanding principal and accrued but unpaid interest under the 2018 Notes, divided by an amount equal to 80% of the lowest price per share of the preferred stock sold in the financing. In the event of a corporate transaction or change of control event, the 2018 Notes contained a put option whereby the Company was required to pay to the holders of 2018 Notes an amount equal to (i) the principal amount then outstanding under the 2018 Notes plus any accrued but unpaid interest, plus (ii) an amount equal to 30% of the outstanding principal amount. The terms of the 2018 Notes provided that (i) all outstanding principal and interest was due and payable in cash upon an event of acceleration, as defined in the 2018 Notes agreement; (ii) amounts outstanding under the 2018 Notes were not prepayable without the written consent of the holders of more than 50% of the outstanding principal of the 2018 Notes, and in addition to the balance the Company will prepay, the Company will also pay the noteholders an amount equal to 15% of the principal amount of the 2018 Notes that the Company is prepaying; and (iii) with respect to subordination, the Company has no outstanding indebtedness for borrowed money or any other liabilities, other than accounts payable arrangements with vendors entered into in the ordinary course of business and consistent with usual trade terms and will not issue or incur additional indebtedness for borrowed money while the 2018 Notes remain outstanding. There were no financial or negative covenants associated with the 2018 Notes. The Derivative Liability represents the conversion feature in the event of a qualified financing and the put option, which each met the definition of an embedded derivative and were required to be combined and accounted for as a separate unit of accounting. The Company recorded the issuance‑date fair value of the Derivative Liability of $1.9 million as a debt discount and Derivative Liability in the Company’s balance sheet. In connection with the 2018 Notes, the Company paid legal costs and bank fees of $0.4 million and was obligated to issue the 2018 Notes Warrants (see Note 3 and Note 7) with an initial fair value of $0.1 million, which were capitalized and recorded as a debt discount. The debt discount, which included legal costs, bank fees, the Derivative Liability and 2018 Notes Warrants, was amortized using the effective interest method over the term of the loan. The Company recognized interest expense of $1.6 million, including amortization of the debt discount of $0.9 million, during the year ended December 31, 2018 in connection with the 2018 Notes. In November 2018, in connection with the Company’s issuance and sale of Series B Preferred Stock, all of the outstanding principal and accrued interest under the 2018 Notes, totaling $6.6 million, was automatically converted into 1,097,721 shares of Series B Preferred Stock at a price equal to 80% of the $7.49 per share price paid by investors in the Series B Preferred Stock financing. The Company accounted for the conversion of the 2018 Notes as a debt extinguishment and recognized a loss on extinguishment of debt of $0.2 million within other income (expense), net in the Company’s statement of operations and $0.1 million within additional paid‑in‑capital related to the amount of unpaid and accrued interest as of the extinguishment date that was not converted into Series B Preferred Stock. The loss on extinguishment was calculated as the difference between (i) the fair value of the 1,097,721 shares of Series B convertible preferred stock issued to settle the 2018 Notes of $8.2 million and (ii) the carrying value of the 2018 Notes, net of the unamortized debt discount, of $5.1 million plus the then‑current fair value of the Derivative Liability associated with the 2018 Notes at the time of the extinguishment of $2.9 million.

STOCK BASED COMPENSATION

STOCK BASED COMPENSATION	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCK BASED COMPENSATION
STOCK BASED COMPENSATION	8 . STOCK‑BASED COMPENSATION Equity Incentive Plans In May 2019, the Company's board of directors (the "Board") adopted its 2019 Equity Incentive Plan ("2019 Plan"), which was subsequently approved by its stockholders and became effective on May 13, 2019. As a result, no additional awards under the Company's 2016 Equity Incentive Plan, as amended (the "2016 Plan") will be granted and all outstanding stock awards granted under the 2016 Plan that are repurchased, forfeited, expired or are cancelled will become available for grant under the 2019 Plan in accordance with its terms. The 2016 Plan will continue to govern outstanding equity awards granted thereunder. The 2019 Plan provides for the issuance of incentive stock options ("ISOs") to employees, and for the grant of nonstatutory stock options ("NSOs"), stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards and other forms of stock awards to the Company's employees, officers and directors, as well as non- employees, consultants and affiliates to the Company. Under the terms of the 2019 Plan, stock options may not be granted at an exercise price less than fair market value of the Company's common stock on the date of the grant. The 2019 Plan will be administered by the Compensation Committee of the Company's Board. Initially, subject to adjustments as provided in the 2019 Plan, the maximum number of the Company's common stock that may be issued under the 2019 Plan is 4,530,000 shares, which is the sum of (i) 1,618,841 new shares, plus (ii) the number of shares (not to exceed 2,911,159 shares) that remained available for the issuance of awards under the 2016 Plan, at the time the 2019 Plan became effective, and (iii) any shares subject to outstanding stock options or other stock awards granted under the 2016 Plan that are forfeited, expired, or reacquired. The 2019 Plan provides that the number of shares reserved and available for issuance under the 2019 Plan will automatically increase each January 1, beginning on January 1, 2020, by 5% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. Subject to certain changes in capitalization of the Company, the aggregate maximum number of shares of common stock that may be issued pursuant to the exercise of ISOs shall be equal to 13,000,000 shares of common stock. Stock options awarded under the 2019 Plan expire 10 years after grant and typically vest over four years. As of September 30, 2019, there were options to purchase 3,767,571 shares of common stock outstanding under the 2016 Plan and 2019 Plan and 680,441 shares of common stock were available for future issuance under the 2019 Plan. Stock-Based Compensation Expense Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2019 and 2018 was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 495 $ 38 $ 2,087 $ 88 General and administrative 724 39 2,736 92 Total stock-based compensation expense $ 1,219 $ 78 $ 4,823 $ 180 During the nine months ended September 30, 2019, the Company granted options to purchase 2,657,628 shares of common stock. The Company recorded stock-based compensation expense for options granted during the three and nine months ended September 30, 2019 of $1.2 million and $4.8 million, respectively. As of September 30, 2019 and December 31, 2018, there were 3,767,571 and 1,202,979 options outstanding, respectively. The weighted‑average fair value of options granted during the nine months ended September 30, 2019 and 2018 was $4.71 and $1.03 per share, respectively. As of September 30, 2019, the total unrecognized stock‑based compensation balance for unvested options was $9.8 million expected to be recognized over a period of 1.8 years. The following table summarizes the information about options outstanding at September 30, 2019 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Options granted 2,657,628 7.34 Options exercised (81,988) 2.77 — Forfeited (11,048) 4.70 Expired — — Outstanding at September 30, 2019 3,767,571 $ 5.54 9.19 $ 20,860 Exercisable at September 30, 2019 1,364,658 $ 2.80 8.84 $ 11,174 Nonvested at September 30, 2019 2,402,913 $ 7.09 9.39 $ 9,686 In April 2019, the Company modified certain stock options, originally granted under the 2016 Plan. As a result of this modification, the Company accelerated the vesting for some of the stock options. There was no incremental stock-based compensation expense as a result of this modification as the fair-value-based measures of the modified awards immediately after the modification were less than the fair-value-based measures of the original awards immediately before the modification. Stock Options Granted to Employees that Contain Service, Performance and Market Conditions Included in the stock options granted during the nine months ended September 30, 2019 were 159,501 stock options that contain service-, performance- and market-based vesting conditions granted to the Company's interim Chief Financial Officer ("CFO") with a fair value at the grant date of $0.5 million, valued using the Monte-Carlo simulation model. The derived service period, calculated using the Monte-Carlo simulation model, ranged from one day to three years. The assumptions used in the Monte-Carlo simulation model were as follows: Nine Months Ended September 30, 2019 Time to expiration (in years) 10.0 Volatility 68.54 % Risk-free interest rate 2.64 % Dividend yield 0.00 % Cost of equity 24.00 % Fair value of underlying common stock (as of valuation date) $ 5.85 The compensation expense for these awards is recognized over the derived service period, or, if earlier, until the vesting condition is met. The condition for the performance-based stock options was based on the Company's completion of its IPO and the condition for the market-based stock options was based on the future price of the Company's common stock trading at or above a specified threshold. During the nine months ended September 30, 2019, 79,778 of the stock options containing service-, and performance-based vesting conditions were vested following the satisfaction of service- and performance-based conditions. In May 2019, the Company entered into a severance agreement, effective on May 31, 2019 ("Termination Date"), with the interim CFO. As part of this severance arrangement and as of the Termination Date, the Company accelerated the vesting of 79,723 unvested options, which were originally granted to the former CFO under the 2016 Plan. As a result of this modification, the Company recorded stock-based compensation expense of $0.6 million included in general and administrative expense for the three months and nine months ended September 30, 2019. The Company accounted for this modification as a Type III modification since, at the modification date, the expectation of the award vesting changed from improbable to probable. As a result, the stock-based compensation expense recognized was based on the modification-date fair value. As of September 30, 2019 there were no outstanding stock options containing service-, performance-, and market-based vesting conditions. During the three and nine months ended September 30, 2019, the Company incurred $0.7 million and $0.8 million, respectively, in stock-based compensation expense relating to the vesting of stock options containing service-, performance- and market-based vesting conditions, which includes the stock-based compensation expense resulting from the modification of these options in May 2019 and were included in general and administrative expense as of September 30, 2019. 2019 Employee Stock Purchase Plan In May 2019, the Company’s Board and its stockholders approved the 2019 Employee Stock Purchase Plan (the “2019 ESPP”), which became effective as of May 13, 2019. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares of common stock initially reserved for issuance under the ESPP was 180,000 shares. The ESPP provides for an annual increase on the first day of each year beginning in 2020 and ending in 2029, in each case subject to the approval of the Board, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the calendar month before the date of the automatic increase and (ii) 360,000 shares; provided that prior to the date of any such increase, the Board may determine that such increase will be less than the amount set forth in clauses (i) and (ii). As of September 30, 2019, no shares of common stock had been issued under the ESPP. The first offering period has not yet been decided by the Board.	5. STOCK‑BASED COMPENSATION In 2016, the Company adopted, and its stockholders approved, the 2016 Equity Incentive Plan, as amended (the “2016 Plan”), which provides for the granting of options at the discretion of the board of directors or any subcommittee of the Board to its employees, officers and independent contractors. Under the terms of the 2016 Plan, options may not be granted at an exercise price less than fair market value of the Company’s common stock on the date of the grant. As of December 31, 2017 and 2018, there were 1,345,469 shares and 2,966,241 shares, respectively, reserved by the Company to grant under the 2016 Plan and an aggregate of 1,083,041 shares and 1,708,179 shares, respectively remained available for future grants. Stock options awarded under the 2016 Plan expire 10 years after the grant and typically vest over three years. Total stock‑based compensation expense recorded for employees, directors and non‑employees during the years ended December 31, 2017 and 2018 was as follows (in thousands): Year Ended December 31, 2017 2018 Research and development $ — $ 140 General and administrative 32 132 Total stock-based compensation expense $ 32 $ 272 The weighted‑average fair value of options granted during the year ended December 31, 2017 and 2018 was $0.66 per share and $1.54 per share, respectively. As of December 31, 2017 and 2018, the total unrecognized stock‑based compensation balance for unvested options was $0.1 million and $1.3 million, respectively, which is expected to be recognized over 2.1 years as of each date. The total fair value of options vested during the year ended December 31, 2017 and 2018 was less than $1,000 and approximately $40,000, respectively. The following table summarizes the information about options outstanding at December 31, 2018 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2017 262,427 $ 0.90 9.09 $ 27 Options granted 995,633 $ 1.44 Options exercised (55,081) $ 0.84 33 Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Exercisable at December 31, 2018 73,692 $ 0.88 8.01 $ 282 Nonvested at December 31, 2018 1,129,287 $ 1.38 9.22 $ 3,747 Valuation Assumptions The fair value of each option award granted is estimated on the date of the grant using the Black‑Scholes option valuation model based on the weighted average assumptions noted in the table below for those options granted in the years ended December 31, 2017 and 2018. Year Ended December 31, December 31, 2017 2018 Expected term (in years) 6.0 5.9 Volatility 75.06 % 71.78 % Risk-free interest rate 2.09 % 2.71 % Dividend yield 0.00 % 0.00 %

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019
STOCKHOLDERS’ EQUITY
STOCKHOLDERS' EQUITY	9. STOCKHOLDERS’ EQUITY Common Stock The holders of the common stock are entitled to one vote for each share of common stock held at all meetings of the stockholders. There are no cumulative voting rights. Preferred Stock In February 2019, the Company issued 442,930 shares of Series B Preferred Stock at $7.49 per share for gross proceeds of approximately $3.3 million. Issuance costs were $0.3 million, which included the obligation to issue warrants to purchase common stock (see Note 10). Upon completion of the IPO, all 7,538,671 shares of outstanding Series A Preferred Stock (“Series A Preferred Stock”) and Series B Preferred Stock (collectively , "the Preferred Stock") was converted into common stock on a one-to-one basis. As of September 30, 2019, there were no shares of preferred stock outstanding. As of December 31, 2018, the Preferred Stock consisted of the following (in thousands, except share data): December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746 The rights and privileges of the preferred stockholders were as follows: Voting The holders of Preferred Stock had the right to one vote for each share of common stock into which such Preferred Stock could be converted and will vote together with the holders of common stock as a single class. Dividends Dividends were payable to holders of Preferred Stock prior to payment of any dividend to holders of common stock. Dividends were payable when and if declared out of funds legally available and such dividends were not cumulative. In the event the Board declared a dividend payable on the common stock, the holders of the Preferred Stock were entitled to receive the amount of dividends per share of Preferred Stock that would be payable on the number of whole shares of the common stock into which each share of such Preferred Stock held by each holder could be converted into. Liquidation Prior to the IPO, in the event of any liquidation, dissolution or winding up of the Company, or a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding would have been entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock by reason of their ownership thereof, in an amount per share equal to the greater of (i) the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) plus any dividends declared but unpaid thereon or (ii) such amount per share as would have been payable had each series of Preferred Stock been converted into common stock immediately prior to a liquidation, dissolution or winding up of the Company or Deemed Liquidation Event. If upon any such liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, the proceeds would have been insufficient to pay the holders of shares of Preferred Stock the full amount to which they shall be entitled, the holders of shares of Preferred Stock would have shared ratably in any distribution of the proceeds in proportion to the respective amounts which would have otherwise been payable in respect of the shares of Preferred Stock held by them upon such distribution if all amounts payable with respect to such shares were paid in full. After the payment of all preferential amounts to be paid to the holders of shares of Preferred Stock, the remaining proceeds would have been distributed among the holders of shares of common stock pro rata based on the number of shares held by each such holder. A Deemed Liquidation Event was defined as: (i) a merger where the Company is a constituent party or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to such merger or consolidation, except any such merger or consolidation involving the Company or a subsidiary in which the shares of capital stock of the Company outstanding immediately prior to such merger or consolidation continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following such merger or consolidation, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such merger or consolidation, the parent corporation of such surviving or resulting corporation; or (ii) the sale, lease, transfer, exclusive license or other disposition, in a single transaction or series of related transactions, by the Company or any subsidiary of the Company of all or substantially all the assets of the Company and its subsidiaries taken as a whole, or the sale or disposition (whether by merger or otherwise) of one or more subsidiaries of the Company if substantially all of the assets of the Company and its subsidiaries taken as a whole are held by such subsidiary or subsidiaries, except where such sale, lease, transfer, exclusive license or other disposition is to a wholly owned subsidiary of the Company. Protective Provisions Prior to the IPO, at any time when any shares of Preferred Stock remained outstanding, the Company could not take any of the following actions without the vote or written consent of the holders of a majority of the then outstanding shares of Preferred Stock separately as a class: (i) liquidate, dissolve or wind-up the business and affairs of the Company, effect any merger, consolidation or any other Deemed Liquidation Event, or consent to any of the foregoing, in each case other than in the event that such event would provide the holders of the Preferred Stock a return per each share of Preferred Stock, including all distributions and dividends paid to such holders prior to such event by the Company, if any, of at least two (2) times the Series B original issue price in the twenty-four (24) months following the Series B original issue date (November 5, 2018) or three (3) times the Series B original issue price thereafter; (ii) amend, alter, or repeal any provision of the Certificate of Incorporation or the Company’s bylaws in a manner that adversely affects the powers, preferences or rights of the Preferred Stock; (iii) create, or authorize the creation of, or issue or obligate itself to issue shares of, any additional class or series of capital stock unless the same ranks junior to the Preferred Stock with respect to the distribution of assets on the liquidation, dissolution or winding up of the Company, the payment of dividends and rights of redemption, or increase the authorized number of shares of Preferred Stock; (iv) purchase or redeem (or permit any subsidiary to purchase or redeem) or pay or declare any dividend or make any distribution on, any shares of capital stock of the Company other than (a) redemptions of or dividends or distributions on the Preferred Stock as expressly authorized herein, (b) dividends or other distributions payable on the common stock solely in the form of additional shares of common stock and (c) repurchases of stock from former employees, officers, directors, consultants or other persons who performed services for the Company or any subsidiary in connection with the cessation of such employment or service at the lower of the original purchase price or the then-current fair market value thereof; (v) create, or authorize the creation of, or issue, or authorize the issuance of any debt security, or permit any subsidiary to take any such action with respect to any debt security, if the aggregate indebtedness of the Company and its subsidiaries for borrowed money following such action would exceed $2.0 million other than equipment leases or bank lines of credit; (vi) create, or hold capital stock in, any subsidiary that is not wholly owned (either directly or through one or more other subsidiaries) by the Company, or sell, transfer or otherwise dispose of any capital stock of any direct or indirect subsidiary of the Company, or permit any direct or indirect subsidiary to sell, lease, transfer, exclusively license or otherwise dispose (in a single transaction or series of related transactions) of all or substantially all of the assets of such subsidiary; or (vi) increase or decrease the authorized number of directors of the Company. Optional Conversion Rights Each share of Preferred Stock was convertible, at the option of the holder thereof, at any time and from time to time after issuance, and without the payment of additional consideration into such number of fully paid and nonassessable shares of common stock as is determined by dividing the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) by the series conversion price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) in effect at the time of conversion. Mandatory Conversion Rights All outstanding shares of Preferred Stock were to be automatically converted into shares of common stock, at the then effective conversion rate, upon either (a) the closing of the sale of shares of common stock to the public in a firm-commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, resulting in at least $30.0 million of proceeds, net of the underwriting discount and commissions, to the Company, or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of at least a majority of the then outstanding shares of Preferred Stock. Redemption The Preferred Stock was redeemable upon the occurrence of a Deemed Liquidation Event, which would not be solely in control of the Company. Therefore, the Preferred Stock was classified as temporary equity.	6. STOCKHOLDERS’ EQUITY As of December 31, 2018, the authorized capital stock of the Company consists of 20,441,982 shares of common stock, par value $0.0001 per share, and 10,883,950 shares of convertible preferred stock, par value $0.0001 per share, of which 3,093,898 are designated as Series A convertible preferred stock (“Series A Preferred Stock”) and 7,790,052 are designated as Series B Preferred Stock (collectively, with the Series A Preferred Stock, the “Preferred Stock”). As of December 31, 2017, the Company had 5,458,450 shares of common stock issued and outstanding and 3,093,898 shares of Series A Preferred Stock issued and outstanding. As of December 31, 2018, the Company had 5,513,531 shares of common stock issued and outstanding, 3,093,898 shares of Series A Preferred Stock issued and outstanding and 4,001,848 shares of Series B Preferred Stock issued and outstanding. Common Stock In February 2017, the Company issued 486,077 shares of common stock, with a fair value of $0.5 million, as consideration pursuant to a license agreement with Columbia University (see Note 2). Voting The holders of the common stock are entitled to one vote for each share of common stock held at all meetings of the stockholders. There is no cumulative voting. Preferred Stock In January 2017, the Company issued 3,093,898 shares of Series A Preferred Stock at $2.26 per share for gross proceeds of $7.0 million. Issuance costs were $0.7 million, which included the issuance of warrants to purchase common stock (see Note 7). Between November and December 2018, the Company issued an aggregate of 2,904,127 shares of its Series B Preferred Stock at $7.49 per share for gross proceeds of $21.7 million. Issuance costs were $0.8 million, which included the obligation to issue warrants to purchase common stock (see Note 7). In addition, all of the outstanding principal and accrued interest under the 2018 Notes were automatically converted into an aggregate of 1,097,721 shares of its Series B Preferred Stock. As of December 31, 2017 and 2018, Preferred Stock consisted of the following (in thousands, except share data): December 31, 2017 Preferred Preferred Stock Issued Common Stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 Total 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 Total 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746 The following is a summary of the rights and privileges of the common and preferred stockholders as of December 31, 2018: Voting The holders of Preferred Stock have the right to one vote for each share of common stock into which such Preferred Stock could be converted and will vote together with the holders of common stock as a single class. Dividends Dividends are payable to holders of Preferred Stock prior to payment of any dividend to holders of common stock. Dividends are payable when and if declared out of funds legally available and such dividends are not cumulative. In the event the board of directors of the Company declares a dividend payable on the common stock, the holders of the Preferred Stock would be entitled to receive the amount of dividends per share of Preferred Stock that would be payable on the number of whole shares of the common stock into which each share of such Preferred Stock held by each holder could be converted into. Liquidation In the event of any liquidation, dissolution or winding up of the Company, or a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding are entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock by reason of their ownership thereof, in an amount per share equal to the greater of (i) the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) plus any dividends declared but unpaid thereon or (ii) such amount per share as would have been payable had each series of Preferred Stock been converted into common stock immediately prior to a liquidation, dissolution or winding up of the Company or Deemed Liquidation Event. If upon any such liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, the proceeds shall be insufficient to pay the holders of shares of Preferred Stock the full amount to which they shall be entitled, the holders of shares of Preferred Stock shall share ratably in any distribution of the proceeds in proportion to the respective amounts which would otherwise be payable in respect of the shares of Preferred Stock held by them upon such distribution if all amounts payable with respect to such shares were paid in full. After the payment of all preferential amounts to be paid to the holders of shares of Preferred Stock, the remaining proceeds shall be distributed among the holders of shares of common stock pro rata based on the number of shares held by each such holder. A Deemed Liquidation Event is defined as: (i) a merger where the Company is a constituent party or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to such merger or consolidation, except any such merger or consolidation involving the Company or a subsidiary in which the shares of capital stock of the Company outstanding immediately prior to such merger or consolidation continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following such merger or consolidation, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such merger or consolidation, the parent corporation of such surviving or resulting corporation; or (ii) the sale, lease, transfer, exclusive license or other disposition, in a single transaction or series of related transactions, by the Company or any subsidiary of the Company of all or substantially all the assets of the Company and its subsidiaries taken as a whole, or the sale or disposition (whether by merger or otherwise) of one or more subsidiaries of the Company if substantially all of the assets of the Company and its subsidiaries taken as a whole are held by such subsidiary or subsidiaries, except where such sale, lease, transfer, exclusive license or other disposition is to a wholly owned subsidiary of the Company. Protective Provisions At any time when any shares of Preferred Stock remain outstanding, the Company shall not take any of the following actions without the vote or written consent of the holders of a majority of the then outstanding shares of Preferred Stock separately as a class: (i) liquidate, dissolve or wind‑up the business and affairs of the Company, effect any merger, consolidation or any other Deemed Liquidation Event, or consent to any of the foregoing, in each case other than in the event that such event would provide the holders of the Preferred Stock a return per each share of Preferred Stock, including all distributions and dividends paid to such holders prior to such event by the Company, if any, of at least two (2) times the Series B Original Issue Price in the twenty‑four (24) months following the Series B Original Issue Date (November 5, 2018) or three (3) times the Series B Original Issue Price thereafter; (ii) amend, alter, or repeal any provision of the Certificate of Incorporation or the Company’s bylaws in a manner that adversely affects the powers, preferences or rights of the Preferred Stock; (iii) create, or authorize the creation of, or issue or obligate itself to issue shares of, any additional class or series of capital stock unless the same ranks junior to the Preferred Stock with respect to the distribution of assets on the liquidation, dissolution or winding up of the Company, the payment of dividends and rights of redemption, or increase the authorized number of shares of Preferred Stock; (iv) purchase or redeem (or permit any subsidiary to purchase or redeem) or pay or declare any dividend or make any distribution on, any shares of capital stock of the Company other than (a) redemptions of or dividends or distributions on the Preferred Stock as expressly authorized herein, (b) dividends or other distributions payable on the common stock solely in the form of additional shares of common stock and (c) repurchases of stock from former employees, officers, directors, consultants or other persons who performed services for the Company or any subsidiary in connection with the cessation of such employment or service at the lower of the original purchase price or the then‑current fair market value thereof; (v) create, or authorize the creation of, or issue, or authorize the issuance of any debt security, or permit any subsidiary to take any such action with respect to any debt security, if the aggregate indebtedness of the Company and its subsidiaries for borrowed money following such action would exceed $2.0 million other than equipment leases or bank lines of credit; (vi) create, or hold capital stock in, any subsidiary that is not wholly owned (either directly or through one or more other subsidiaries) by the Company, or sell, transfer or otherwise dispose of any capital stock of any direct or indirect subsidiary of the Company, or permit any direct or indirect subsidiary to sell, lease, transfer, exclusively license or otherwise dispose (in a single transaction or series of related transactions) of all or substantially all of the assets of such subsidiary; or (vi) increase or decrease the authorized number of directors of the Company. Optional Conversion Rights Each share of Preferred Stock is convertible, at the option of the holder thereof, at any time and from time to time after issuance, and without the payment of additional consideration into such number of fully paid and nonassessable shares of common stock as is determined by dividing the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) by the series conversion price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) in effect at the time of conversion. As of December 31, 2018, the Preferred Stock is convertible in to common stock on a one‑for‑one basis. Mandatory Conversion Rights All outstanding shares of Preferred Stock shall automatically be converted into shares of common stock, at the then effective conversion rate, upon either (a) the closing of the sale of shares of common stock to the public in a firm‑commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, resulting in at least $30.0 million of proceeds, net of the underwriting discount and commissions, to the Company, or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of at least a majority of the then outstanding shares of Preferred Stock. Redemption The Preferred Stock is redeemable upon the occurrence of a Deemed Liquidation Event, which is not solely in control of the Company. Therefore, the Preferred Stock has been classified as temporary equity.

WARRANTS

WARRANTS	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
WARRANTS
WARRANTS	10. WARRANTS Warrants Issued with the 2018 Notes On January 18, 2018, the Company entered into a placement agent agreement through which it became obligated to issue common stock warrants in connection with the issuance of the 2018 Notes. The obligation to issue the 2018 Notes Warrants was recorded as a liability at its fair value (see Note 3), which was initially $0.1 million, and was included in the issuance costs of the 2018 Notes (see Note 4). On November 5, 2018, in connection with the extinguishment of the 2018 Notes into shares of Series B Preferred Stock, the Company issued the 2018 Notes Warrants, which were equity‑classified warrants upon issuance, to purchase 76,847 shares of common stock, valued at $0.3 million. The 2018 Notes Warrants vested immediately upon issuance and have an exercise price of $6.59 per share and expire on November 4, 2028. Warrants Issued with Series B Preferred Stock In November and December 2018, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue warrants to purchase 72,261 shares of common stock (collectively the “2018 Warrants”), valued in the aggregate at $0.2 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 8). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2018 Warrants was estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 % In February 2019, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue warrants to purchase 23,867 shares of common stock (collectively the “2019 Warrants”), valued in the aggregate at $0.1 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 8). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2019 Warrants was estimated using the Black-Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 % The inputs utilized by management to value the warrants are highly subjective. The assumptions used in calculating the fair value of the warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the warrants may be materially different in the future.	7. WARRANTS Warrants Issued with Series A Preferred Stock On January 26, 2017, in connection with the sale and issuance of the Series A Preferred Stock, the Company issued equity‑classified warrants to purchase 309,389 shares of common stock (the “2017 Warrants”), valued at $0.2 million, and included in the issuance costs of the Series A Preferred Stock (see Note 4). The warrants vested immediately and have an exercise price of $2.49 per share and expire on March 13, 2027. The fair value of warrants issued is estimated using the Black‑Scholes option pricing model with the following assumptions for the 2017 Warrants. Contractual term (in years) 10.0 Volatility 76.95 % Risk-free interest rate 2.62 % Dividend yield 0.00 % Warrants Issued with the 2018 Notes On January 18, 2018, the Company entered into a placement agent agreement through which it became obligated to issue common stock warrants in connection with the issuance of the 2018 Notes. The obligation to issue the 2018 Notes Warrants was recorded as a liability at its fair value (see Note 3), which was initially $0.1 million, and was included in the issuance costs of the 2018 Notes (see Note 4). On November 5, 2018, in connection with the extinguishment of the 2018 Notes into shares of Series B Preferred Stock, the Company issued the 2018 Notes Warrants, which were equity‑classified warrants upon issuance, to purchase 76,847 shares of common stock, valued at $0.3 million. The 2018 Notes Warrants vested immediately upon issuance and have an exercise price of $6.59 per share and expire on November 4, 2028. Warrants Issued with Series B Preferred Stock In November and December 2018, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue equity‑classified warrants to purchase 72,261 shares of common stock (collectively the “2018 Warrants”), valued in the aggregate at $0.2 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 6). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2018 Warrants is estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 % The inputs utilized by management to value the warrants are highly subjective. The assumptions used in calculating the fair value of the warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the warrants may be materially different in the future.

INCOME TAXES

INCOME TAXES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
INCOME TAXES
INCOME TAXES	11. INCOME TAXES During the three and nine months ended September 30, 2019 and the year ended December 31, 2018, the Company recorded a full valuation allowance on federal and state deferred tax assets since management does not forecast the Company to be in a profitable position in the near future.	8. INCOME TAXES The Company’s current tax provision for the years ended December 31, 2017 and 2018 is $0 and $0, respectively. The Company’s deferred tax provision for the years ended December 31, 2017 and 2018 is $0. Deferred income tax assets and liabilities consist of the following (in thousands): Year ended December 31, 2017 2018 Deferred tax assets Accrued expenses $ 335 $ — Stock‑based compensation 11 98 Capitalized startup costs 38 35 Net operating losses 1,200 6,176 Total deferred tax assets 1,584 6,309 Less: valuation allowance (1,584) (6,309) Net deferred tax asset (liability) $ — $ — Deferred tax assets result primarily from unutilized net operating losses, capitalized startup costs and timing differences as a result of the Company reporting its income tax returns. As of December 31, 2018, the Company had approximately $3.6 million of federal and state net operating losses (“NOLs”) carried forward expiring through 2037. Additionally, the Company generated approximately $14.2 million of NOLs in 2018 which, for federal income tax purposes, do not expire but are limited to offsetting up to 80% of future taxable income. The NOL carry forwards are subject to review and possible adjustment by the U.S. and state tax authorities. NOL carry forwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders, as defined under Sections 382 Internal Revenue Code. This could limit the amount of NOLs that the Company can utilize annually to offset future taxable income or tax liabilities. As of December 31, 2018, the Company has not performed such an analysis. Subsequent ownership changes and proposed future changes to tax rules in respect of the utilization of losses carried forward may further affect the limitation in future years. In assessing the realizability of the Company’s deferred tax assets, management considers whether or not it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company’s assessment is based on the weight of available evidence, including cumulative losses since inception and expected future losses and, as such, the Company does not believe it is more likely than not that the deferred tax assets will be realized. Accordingly, a full valuation allowance has been established and no deferred tax assets and related tax benefit have been recognized in the accompanying financial statements. At December 31, 2017 and 2018, the Company recorded valuation allowances of $1.6 million and $6.3 million, respectively, representing an increase in the valuation allowance of $4.7 million in 2018 due to the uncertainty regarding the realization of such deferred tax assets, to offset the benefits of net operating losses generated during those years. The U.S. federal statutory corporate tax rate reconciles to the Company’s effective tax rate for the years ended December 31, 2017 and 2018: Year Ended December 31, 2017 2018 Federal statutory rate 34.0 % 21.0 % State and local taxes net of federal tax benefit 11.3 13.5 Tax rate change (13.8) 0.3 Change in valuation allowance (32.2) (28.5) Permanently disallowed interest expense — (6.3) Other 0.7 — Total % % On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act (“Tax Act”), which made significant changes to the U.S. federal income tax law. The Tax Act affected 2018 and forward, including but not limited to a reduction in the federal corporate rate from 35.0% to 21.0%, elimination of the corporate alternative minimum tax, a new limitation on the deductibility of certain executive compensation, limitations on NOLs generated after December 31, 2017 and various other items. These changes did not have a material impact on the Company’s financial statements due to the accumulated NOLs in the United States.

BENEFIT PLANS

BENEFIT PLANS	12 Months Ended
	Dec. 31, 2018
BENEFIT PLANS
BENEFIT PLANS	9. BENEFIT PLANS The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code in 2018. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre‑tax basis. Matching contributions to the plan may be made at the discretion of the Company’s board of directors. The Company made approximately $11,000 in matching contributions to the plan during the year ended December 31, 2018.

NET LOSS PER COMMON SHARE

NET LOSS PER COMMON SHARE	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
NET LOSS PER COMMON SHARE
NET LOSS PER COMMON SHARE	12. NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing the net loss available to common stockholders by the weighted‑average number of shares of common stock outstanding during the period. Diluted net loss per common share is computed by giving the effect of all potential shares of common stock, including stock options, preferred shares, warrants and instruments convertible into common stock, to the extent dilutive. Basic and diluted net loss per common share was the same for the three and nine months ended September 30, 2019 and 2018, as the inclusion of all potential common shares outstanding would have been anti‑dilutive. The following table sets forth the computation of basic and diluted net loss per common share for the three and nine months ended September 30, 2019 and 2018 (in thousands, except share and per share data): Three Months Ended September 30, 2019 2018 Numerator: Net loss $ (10,713) $ (4,281) Denominator: Weighted-average common stock outstanding 17,095,870 5,497,871 Net loss per share attributable to common stockholders - basic and diluted $ (0.63) $ (0.78) Nine Months Ended September 30, 2019 2018 Numerator: Net loss $ (27,880) $ (9,802) Denominator: Weighted-average common stock outstanding 14,085,579 5,473,414 Net loss per share attributable to common stockholders - basic and diluted $ (1.98) $ (1.79) The Company’s potentially dilutive securities, which include Preferred Stock, stock options, and warrants, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted‑average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding for the three and nine months ended September 30, 2019 and 2018, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti‑dilutive effect: As of September 30, 2019 2018 Preferred Stock — 3,093,898 Options to purchase common stock 3,767,571 1,035,466 Warrants to purchase common stock 482,364 309,389	10. NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing the net loss available to common stockholders by the weighted‑average number of shares of common stock outstanding during the period. Diluted net loss per common share is computed by giving the effect of all potential shares of common stock, including stock options, preferred shares, warrants and instruments convertible into common stock, to the extent dilutive. Basic and diluted net loss per common share was the same for the years ended December 2017 and 2018, as the inclusion of all potential common shares outstanding would have been anti‑dilutive. The following table sets forth the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Years Ended December 31, 2017 2018 Numerator: Net loss $ (4,282) $ (16,521) Denominator: Weighted-average common stock outstanding 5,406,513 5,483,149 Net loss per share, basic and diluted $ (0.79) $ (3.01) The Company’s potential dilutive securities, which include Preferred Stock, stock options and warrants, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted‑average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at December 31, 2017 and 2018, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti‑dilutive effect: As of December 31, 2017 2018 Preferred Stock 3,093,898 7,095,746 Options to purchase common stock 262,427 1,202,979 Warrants to purchase common stock 309,389 458,497 Unaudited Pro Forma Net Loss Per Share The unaudited pro forma basic and diluted net loss per share attributable to common stockholders for the year ended December 31, 2018 has been prepared to give effect to adjustments arising upon the completion of a qualified IPO. The unaudited pro forma basic and diluted weighted‑average common shares outstanding used in the calculation of unaudited pro forma basic and diluted net loss per share attributable to common stockholders for the year ended December 31, 2018 has been prepared to give effect, upon a qualified IPO, to the conversion of all outstanding shares of Preferred Stock into common stock as if the proposed IPO had occurred on the later of January 1, 2018 or the issuance date of the preferred stock. Unaudited pro forma basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2018 (unaudited) Numerator: Net loss attributable to common stockholders—basic and diluted $ (16,521) Pro forma net loss attributable to common stockholders—basic and diluted $ (16,521) Denominator: Weighted‑average common stock outstanding—basic and diluted 5,483,149 Pro forma adjustment to reflect conversion of convertible preferred stock to common stock upon the completion of the proposed initial public offering 3,679,938 Pro forma weighted‑average common stock outstanding—basic and diluted 9,163,087 Pro forma net loss per share attributable to common stockholders—basic and diluted $ (1.80)

RELATED PARTIES

RELATED PARTIES	12 Months Ended
	Dec. 31, 2018
RELATED PARTIES
RELATED PARTIES	11. RELATED PARTIES In December 2018, the Company entered into an agreement (the “LaunchLabs Agreement”) with ARE‑LaunchLabs NYC LLC (“Alexandria LaunchLabs”), a subsidiary of Alexandria Real Estate Equities, Inc. for use of specified premises within the Alexandria LaunchLabs space. A member of the Company’s board of directors is the founder and executive chairman of Alexandria Real Estate Equities, Inc. During the year ended December 31, 2018, the Company made payments to Alexandria LaunchLabs of approximately $13,000 under the LaunchLabs Agreement, which was recognized in research and development expenses. As of December 31, 2018, there were no amounts due to Alexandria LaunchLabs under the LaunchLabs Agreement.

SUBSEQUENT EVENT

SUBSEQUENT EVENT	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
SUBSEQUENT EVENT
SUBSEQUENT EVENTS	13. SUBSEQUENT EVENT On October 3, 2019, and in connection with the 2019 Columbia Agreement, the Company entered into a research services agreement with Columbia University with the purpose of analyzing certain compounds for the treatment of lymphoid malignancies. The research service agreement has a term of 18 months from is effective date; provided that the Company can terminate the research service agreement without cause with at least 30 days prior written notice. In consideration for the services performed by Columbia University, the Company will be required to pay $0.4 million to Columbia University for staffing, supplies and indirect costs. On November 7, 2019, the Company entered into a definitive Securities Purchase Agreement (the “Securities Purchase Agreement”) for a private placement (the “Private Placement”) with a select group of accredited investors (collectively, the “Purchasers”). Pursuant to the Securities Purchase Agreement, the Purchasers have agreed to purchase 1,380,344 shares of the Company’s common stock, par value $0.0001 per share (the “Shares”), which resulted in gross proceeds to the Company of approximately $20.0 million at a price of $14.50 per share before deducting placement agent commissions and other offering expenses. The Private Placement closed on November 12, 2019 .	12. SUBSEQUENT EVENTS Issuance of Series B Preferred Stock In February 2019, the Company issued an aggregate of 442,925 shares of its Series B Preferred Stock to investors and certain members of its board of directors at a price per share of $7.49 for proceeds of $3.1 million, net of issuance costs of $0.2 million. The rights and privileges of the Series B Preferred Stock are the same as the rights and privileges of the Series B Preferred Stock issued in earlier closings. In connection with the Series B Preferred Stock issuance, the Company is obligated to issue warrants to purchase shares of common stock to the placement agent. Columbia University In January 2019, the Company entered into a license agreement with Columbia University (“2019 Columbia Agreement”). Pursuant to the 2019 Columbia Agreement, Columbia University granted the Company a royalty‑bearing, sublicensable license that is exclusive with respect to certain patents, and non‑exclusive with respect to certain know‑how, in each case to develop, manufacture and commercialize PI3K inhibitor products. As consideration, the Company made a nominal upfront payment to Columbia University. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2019 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid six figures beginning on the 10th anniversary of the effective date of the 2019 Columbia Agreement. If the Company sublicenses the rights granted under the 2019 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such sublicensees, at percentages ranging from 10% to 50%, depending on the passage of time or the stage of development of the applicable product at the time such revenue is received from such sublicenses. Forward Stock Split In April 2019, the board of directors and the stockholders of the Company approved a 55.2486‑for‑1 forward stock split of the Company’s outstanding common stock and Preferred Stock, which was effected on April 26, 2019. Stockholders entitled to fractional shares as a result of the forward stock split will receive a cash payment in lieu of receiving fractional shares. The Company’s historical share and per share information has been retroactively adjusted to give effect to this forward stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately increased and the respective per share value and exercise prices, if applicable, were proportionately decreased in accordance with the terms of the agreements governing such securities. Modification of Certain Stock Option Grants On April 22, 2019, the Board of Directors approved a modification to the vesting conditions of certain outstanding stock option grants to certain employees and directors. The Company is evaluating the impact this modification will have to its 2019 financial statements.

ORGANIZATION AND SUMMARY OF S_2

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Liquidity	Liquidity The Company has incurred, and expects to continue to incur, significant operating losses and negative cash flows for at least the next several years as it continues to develop its drug candidates. To date, the Company has not generated any revenue, and it does not expect to generate revenue unless and until it successfully completes development and obtains regulatory approval for one of its product candidates. Management believes that the Company’s existing cash, together with the net proceeds from the IPO, will allow the Company to continue its operations for at least 12 months from the issuance date of these financial statements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.	Going Concern The Company has evaluated whether there are conditions and events considered in the aggregate that raise substantial doubt about the Company’s ability to continue as a going concern. Through December 31, 2018, the Company has primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 6). The Company has incurred recurring losses from operations since its inception, including net losses of $4.3 million and $16.5 million for the years ended December 31, 2017 and December 31, 2018, respectively, and has used cash in operations of $3.2 million and $11.2 million for the years ended December 31, 2017 and December 31, 2018, respectively. In addition, as of December 31, 2018, the Company had an accumulated deficit of $21.3 million. The Company expects its operating losses and negative cash flows to continue into the foreseeable future as it continues to develop, manufacture, and commercialize its product candidates. The Company is seeking to complete an initial public offering (“IPO”) of its common stock. In the event the Company does not complete an IPO, and even after the completion of an IPO, the Company expects to seek additional funding through private or public equity financings, debt financings, collaborations, or other strategic transactions. The Company may not be able to obtain funding on acceptable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Based on the operating losses incurred since inception, the expectation of continuing operating losses for the foreseeable future, and the need to raise additional capital to finance its operations, the Company has concluded that there is substantial doubt about its ability to continue as a going concern within one year after the date that the financial statements are issued. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. The financial statements do not include any adjustments that might be necessary if the Company is unable to continue as a going concern.
Risk and Uncertainties	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers.	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.
Unaudited Pro Forma Information		Unaudited Pro Forma Information The accompanying unaudited pro forma balance sheet as of December 31, 2018 has been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding convertible preferred stock into 7,095,746 shares of common stock. The accompanying unaudited pro forma basic and diluted net loss per share attributable to common stockholders in the statements of operations for the year ended December 31, 2018 have been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding shares of convertible preferred stock into shares of common stock as of December 31, 2018.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. Upon closing the IPO in May 2019, $2.6 million in deferred offering costs were reclassified from prepaid and other current assets and recorded against the IPO proceeds reducing additional paid-in capital. As of September 30, 2019, the Company did not have any deferred offering costs recorded in prepaid and other current assets.	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third‑party fees that are directly associated with in‑process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of convertible preferred stock and stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. The Company recorded deferred offering costs of $0.3 million as of December 31, 2018 in prepaid expenses and other current assets.
Fair Value Measurements		Fair Value Measurements Certain assets and liabilities are reported on a recurring basis at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1—Quoted prices in active markets for identical assets or liabilities. Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all short‑term, highly liquid investments, with an original maturity of three months or less, to be cash equivalents. The Company maintains its cash in bank deposit accounts which, at times, may exceed federally insured limits. The Company has not experienced any losses in these accounts and does not believe it is exposed to any significant credit risk on cash and cash equivalents.
Common Stock Valuation		Common Stock Valuation The Company utilizes significant estimates and assumptions in determining the fair value of its common stock. The Company has utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately‑Held Company Equity Securities Issued as Compensation (the “Practice Aid”), to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time of, and the likelihood of, achieving a liquidity event, such as an IPO or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.
Convertible Preferred Stock		Convertible Preferred Stock The Company records shares of its convertible preferred stock at their respective fair values on the dates of issuance less issuance costs. The Company classifies shares of its convertible preferred stock outside of stockholders’ deficit when the redemption of such units or shares is outside the Company’s control. The Company does not adjust the carrying values of the convertible preferred units or convertible preferred stock to the liquidation preferences of such units or shares until such time as a deemed liquidation event is probable of occurring.
Research and Development		Research and Development The Company expenses all costs incurred in performing research and development activities. Research and development expenses include salaries and other related costs, materials and supplies, preclinical expenses, manufacturing expenses, contract services and other outside expenses. As part of the process of preparing the financial statements, the Company is required to estimate their accrued research and development expenses. The Company makes estimates of the accrued expenses as of each balance sheet date in the financial statements based on facts and circumstances known at that time. In addition, there may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense in which case such amounts are reflected as prepaid expenses and other current assets. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual or the amount of prepaid expenses accordingly. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized in prepaid expenses and other current assets. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
General and Administrative		General and Administrative General and administrative expenses consist primarily of salaries and other related costs, including stock‑based compensation, for personnel in the Company’s executive and finance functions. General and administrative expenses also include professional fees for legal, accounting, auditing, tax and consulting services; travel expenses; and facility‑related expenses, which include allocated expenses for rent and maintenance of facilities and other operating costs.
Stock-Based Compensation	Stock‑Based Compensation The Company accounts for its stock-based compensation as expense in the condensed statements of operations based on the awards' grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black-Scholes option pricing model with the exception of stock options that include service, performance and market conditions, which are valued using the Monte-Carlo simulation model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company has historically been a private company and lacks company-specific historical and implied volatility information. Therefore, the Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission ("SEC") Staff Accounting Bulletin ("SAB") No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. A Monte-Carlo simulation is an analytical method used to estimate fair value by performing a large number of simulations or trial runs and thereby determining a value based on the possible outcomes from these trial runs based on the specific vesting conditions. The fair value of stock-based payments is recognized as expense over the requisite service period which is generally the vesting period, with the exception of the fair value of stock-based payments for awards that include service, performance and market conditions, which is recognized as expense over the derived service period determined using the Monte-Carlo simulation.	Stock‑Based Compensation The Company accounts for its stock‑based compensation as expense in the statements of operations based on the awards’ grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company‑specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, Share‑Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of stock‑based payments is recognized as expense over the requisite service period which is generally the vesting period.
Income Taxes		Income Taxes The Company uses the asset and liability method of accounting for deferred income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the carrying amounts and the tax basis of assets and liabilities at currently enacted tax rates. These temporary differences primarily relate to net operating loss carryforwards available to offset future taxable income. Valuation allowances are established, if necessary, to reduce a deferred tax asset to the amount that will more likely than not be realized. The Company recognizes tax liabilities from an uncertain tax position only if it is more likely than not that the tax position will not be sustained upon examination by the taxing authorities, based on the technical merits of the tax position. There are no uncertain tax positions that have been recognized in the accompanying financial statements. The Company is required to file tax returns in the U.S. federal jurisdiction and in the state of New York. The Company’s policy is to recognize interest and penalties related to uncertain tax benefits, if any, as part of income tax expense. No such interest and penalties have been accrued as of December 31, 2017 and 2018.
Net Loss per Share and Unaudited Pro Forma Net Loss per Share		Net Loss per Share and Unaudited Pro Forma Net Loss per Share Basic net loss per share is calculated by dividing net loss available to common stockholders by the weighted‑average common stock outstanding. Diluted net loss per share is calculated similarly, except that it includes the dilutive effect of the assumed exercise of securities, including outstanding warrants and the effect of shares issuable under the Company’s stock‑based compensation plan, if such effect is dilutive. Unaudited pro forma net loss per share attributable to common stockholders is computed using the weighted‑average number of common shares outstanding after giving effect to the conversion of all outstanding convertible preferred stock into shares of common stock as if such conversion had occurred at January 1, 2018, or the date of original issuance, if later.
Segment Information		Segment Information Operating segments are defined as components of an enterprise for which separate discrete information is available for evaluation by the chief operating decision‑maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision‑maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment, which is the business of discovering and developing its product candidates.
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements The new accounting pronouncements recently adopted by the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus as filed with the SEC on May 14, 2019. Except as described below, there have been no new accounting pronouncements adopted by the Company during the nine months ended September 30, 2019. In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) , which requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases on their balance sheet date (“ASU No. 2016-02”). ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018. In July 2018, an amendment was made that allows companies the option of using the effective date of the new standard as the initial application date (at the beginning of the period in which the new standard is adopted, rather than at the beginning of the earliest comparative period). This update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize the associated lease assets and lease liabilities on its balance sheet. Additionally, in March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements (“ASU No. 2019-01”). ASU No. 2019-01 clarifies the transition guidance related to interim disclosures provided in the year of adoption. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease did not significantly change from previous U.S. GAAP. The modified retrospective method includes several optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. The Company adopted Topic 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance under ASC 840. In adopting Topic 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease; ii) the lease classification of existing or expired leases; and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election not to recognize assets or related lease liabilities with a lease term of twelve months or less in its condensed balance sheet. The adoption of this standard did not have an impact on the Company’s condensed balance sheet as all of the Company’s leases are for terms that are less than 12 months. Additionally, the adoption of this standard did not have a material impact on the Company’s condensed statements of operations or condensed statement of cash flows. On August 6, 2019 the Company entered into a lease for approximately 6,579 square feet of new office space in New York City (the “Lease”). The Lease will commence upon delivery of the premise after certain improvements are made, which is anticipated to be on or about November 1, 2019 (the “Commencement Date”), for a five-year period. Under the Lease, the Company will pay monthly rent of approximately $38,000 for the first year following the Commencement Date, and such rent will increase by a nominal percentage every year following the first anniversary of the Commencement Date. The Company will also pay a real estate tax escalation, as additional rent, over a base year. Total lease obligation over the term of the lease will be approximately $2.4 million. Recently Issued Accounting Pronouncements The FASB issued authoritative guidance that amends guidance on reporting credit losses for assets, including available-for-sale marketable securities and any other financial assets not excluded from the scope that have the contractual right to receive cash. For available-for-sale marketable securities, credit losses should be measured in a manner similar to current generally accepted accounting standards; however, ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , will require that credit losses be presented as an allowance rather than as a write-down. We are currently in the process of evaluating the impact of this guidance on our condensed financial statements.	Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014‑09, Revenue from Contracts with Customers (Topic 606) (“ASU No. 2014‑09”), which modifies how all entities recognize revenue, and consolidates into one Accounting Standards Codification (“ASC”) (ASC Topic 606, Revenue from Contracts with Customers ), the current guidance found in ASC Topic 605, and various other revenue accounting standards for specialized transactions and industries. ASU No. 2014‑09 outlines a comprehensive five‑step revenue recognition model based on the principle that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU No. 2015‑14, Revenue from Contracts with Customers (Topic 606): Deferral of Effective Date (“ASU No. 2015‑14”), which defers the effective date of ASU No. 2014‑09 by one year. Early adoption is permitted for annual periods beginning after December 15, 2016. To date, the Company has not had any arrangements that are within the scope of ASU No. 2014‑09, or its predecessor, ASC Topic 605. The Company adopted these pronouncements on January 1, 2017, which did not have any impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Improvements to Employee Share‑Based Payment Accounting (“ASU No. 2016‑09”), which simplifies share‑based payment accounting through a variety of amendments. The Company elected to early adopt this guidance effective January 1, 2016, and has elected to account for forfeitures as incurred and therefore no forfeiture estimate is utilized in the year ended December 31, 2017. Adoption of ASU No. 2016‑09 did not have a material impact on the Company’s financial statements. In May 2017, the FASB issued ASU No. 2017‑09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU No. 2017‑09”), which clarifies when to account for a change to the terms or conditions of a share‑based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The standard is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted ASU No. 2017‑09 as of January 1, 2018, which did not have a material impact on the Company’s financial statements. In June 2018, the FASB issued ASU No. 2018‑07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share‑Based Payment Accounting (“ASU No. 2018‑07”). These amendments expand the scope of Topic 718, Compensation—Stock Compensation , which currently only includes share‑based payments to employees, to include share‑based payments issued to nonemployees for goods or services. Consequently, the accounting for share‑based payments to nonemployees and employees will be substantially aligned. This ASU supersedes Subtopic 505‑50, Equity—Equity‑Based Payments to Non‑Employees . This standard is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted as long as ASU No. 2014‑09 has been adopted by the Company. The Company adopted ASU No. 2018‑07 as of January 1, 2017, which did not have a material impact on the Company’s financial statements. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) , which requires lessees to recognize assets and liabilities for leases with lease terms greater than 12 months in the statement of financial position. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016‑02 also requires improved disclosures to help users of financial statements better understand the amount, timing and uncertainty of cash flows arising from leases. The update is effective for fiscal years beginning after December 15, 2018, including interim reporting periods within that reporting period. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2016‑02 will have on its financial statements. In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement . which, eliminates, modifies, and adds disclosure requirements on fair value measurements. The standard is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2018‑13 will have on its financial statements.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Schedule of Company's Derivative Liability and Warrant Liability	The following table provides a roll forward of the aggregate fair values of the Derivative Liability and Warrant Liability as of September 30, 2018, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 180 6 Balance as of March 31, 2018 $ 2,076 $ 80 Change in fair value 294 21 Balance as of June 30, 2018 $ 2,370 $ 101 Change in fair value 335 38 Balance as of September 30, 2018 $ 2,704 $ 139	The following table provides a roll forward of the aggregate fair values of the Company’s Derivative Liability and Warrant Liability, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 972 168 Extinguishment of Derivative Liability in connection with extinguishment of 2018 Notes (2,868) — Reclassification of Warrant Liability into 2018 Notes Warrants — (242) Balance as of December 31, 2018 $ — $ —
Warrants Issued with the 2018 Notes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Schedule of fair value of warrants using the Black Scholes option pricing model		Contractual term (in years) 10.0 Volatility 74.48% - 76.56% Risk-free interest rate 2.85% - 3.20% Dividend yield 0.00%

STOCK BASED COMPENSATION (Table

STOCK BASED COMPENSATION (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCK BASED COMPENSATION
Schedule of stock-based compensation expenses	Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2019 and 2018 was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 495 $ 38 $ 2,087 $ 88 General and administrative 724 39 2,736 92 Total stock-based compensation expense $ 1,219 $ 78 $ 4,823 $ 180	Total stock‑based compensation expense recorded for employees, directors and non‑employees during the years ended December 31, 2017 and 2018 was as follows (in thousands): Year Ended December 31, 2017 2018 Research and development $ — $ 140 General and administrative 32 132 Total stock-based compensation expense $ 32 $ 272
Schedule of options outstanding	The following table summarizes the information about options outstanding at September 30, 2019 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Options granted 2,657,628 7.34 Options exercised (81,988) 2.77 — Forfeited (11,048) 4.70 Expired — — Outstanding at September 30, 2019 3,767,571 $ 5.54 9.19 $ 20,860 Exercisable at September 30, 2019 1,364,658 $ 2.80 8.84 $ 11,174 Nonvested at September 30, 2019 2,402,913 $ 7.09 9.39 $ 9,686	The following table summarizes the information about options outstanding at December 31, 2018 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2017 262,427 $ 0.90 9.09 $ 27 Options granted 995,633 $ 1.44 Options exercised (55,081) $ 0.84 33 Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Exercisable at December 31, 2018 73,692 $ 0.88 8.01 $ 282 Nonvested at December 31, 2018 1,129,287 $ 1.38 9.22 $ 3,747
Schedule of valuation assumptions	Nine Months Ended September 30, 2019 Time to expiration (in years) 10.0 Volatility 68.54 % Risk-free interest rate 2.64 % Dividend yield 0.00 % Cost of equity 24.00 % Fair value of underlying common stock (as of valuation date) $ 5.85	Year Ended December 31, December 31, 2017 2018 Expected term (in years) 6.0 5.9 Volatility 75.06 % 71.78 % Risk-free interest rate 2.09 % 2.71 % Dividend yield 0.00 % 0.00 %

STOCKHOLDER EQUITY (Tables)

STOCKHOLDER EQUITY (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCKHOLDER EQUITY
Summary of Preferred Stock	As of December 31, 2018, the Preferred Stock consisted of the following (in thousands, except share data): December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746	As of December 31, 2017 and 2018, Preferred Stock consisted of the following (in thousands, except share data): December 31, 2017 Preferred Preferred Stock Issued Common Stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 Total 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 Total 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746

WARRANTS (Tables)

WARRANTS (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
2017 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model		Contractual term (in years) 10.0 Volatility 76.95 % Risk-free interest rate 2.62 % Dividend yield 0.00 %
2018 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	The fair value of the 2018 Warrants was estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 %	Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 %

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
INCOME TAXES
Summary of deferred income tax assets and liabilities	Deferred income tax assets and liabilities consist of the following (in thousands): Year ended December 31, 2017 2018 Deferred tax assets Accrued expenses $ 335 $ — Stock‑based compensation 11 98 Capitalized startup costs 38 35 Net operating losses 1,200 6,176 Total deferred tax assets 1,584 6,309 Less: valuation allowance (1,584) (6,309) Net deferred tax asset (liability) $ — $ —
Schedule of the U.S. federal statutory corporate tax rate reconciles to the Company's effective tax rate	Year Ended December 31, 2017 2018 Federal statutory rate 34.0 % 21.0 % State and local taxes net of federal tax benefit 11.3 13.5 Tax rate change (13.8) 0.3 Change in valuation allowance (32.2) (28.5) Permanently disallowed interest expense — (6.3) Other 0.7 — Total % %

NET LOSS PER COMMON SHARE (Tabl

NET LOSS PER COMMON SHARE (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
NET LOSS PER COMMON SHARE
Schedule of computation of basic and diluted net loss per common share	The following table sets forth the computation of basic and diluted net loss per common share for the three and nine months ended September 30, 2019 and 2018 (in thousands, except share and per share data): Three Months Ended September 30, 2019 2018 Numerator: Net loss $ (10,713) $ (4,281) Denominator: Weighted-average common stock outstanding 17,095,870 5,497,871 Net loss per share attributable to common stockholders - basic and diluted $ (0.63) $ (0.78) Nine Months Ended September 30, 2019 2018 Numerator: Net loss $ (27,880) $ (9,802) Denominator: Weighted-average common stock outstanding 14,085,579 5,473,414 Net loss per share attributable to common stockholders - basic and diluted $ (1.98) $ (1.79)	The following table sets forth the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Years Ended December 31, 2017 2018 Numerator: Net loss $ (4,282) $ (16,521) Denominator: Weighted-average common stock outstanding 5,406,513 5,483,149 Net loss per share, basic and diluted $ (0.79) $ (3.01)
Schedule of potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	As of September 30, 2019 2018 Preferred Stock — 3,093,898 Options to purchase common stock 3,767,571 1,035,466 Warrants to purchase common stock 482,364 309,389	As of December 31, 2017 2018 Preferred Stock 3,093,898 7,095,746 Options to purchase common stock 262,427 1,202,979 Warrants to purchase common stock 309,389 458,497
Schedule of calculation of unaudited pro forma basic and diluted net loss per share attributable to common stockholders		Unaudited pro forma basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2018 (unaudited) Numerator: Net loss attributable to common stockholders—basic and diluted $ (16,521) Pro forma net loss attributable to common stockholders—basic and diluted $ (16,521) Denominator: Weighted‑average common stock outstanding—basic and diluted 5,483,149 Pro forma adjustment to reflect conversion of convertible preferred stock to common stock upon the completion of the proposed initial public offering 3,679,938 Pro forma weighted‑average common stock outstanding—basic and diluted 9,163,087 Pro forma net loss per share attributable to common stockholders—basic and diluted $ (1.80)

ORGANIZATION AND SUMMARY OF S_3

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Going Concern (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Net loss	$ (10,713)	$ (8,437)	$ (8,730)	$ (4,281)	$ (3,185)	$ (2,335)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Cash used in operations							(23,900)	$ (5,313)	(11,182)	(3,195)
Accumulated deficit	$ (49,137)						$ (49,137)		$ (21,257)	$ (4,736)
Substantial Doubt about Going Concern, within One Year									true

ORGANIZATION AND SUMMARY OF S_4

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Pro Forma (Details)	Dec. 31, 2018shares
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Common stock issued	7,095,746

ORGANIZATION AND SUMMARY OF S_5

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Offering Costs (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Deferred offering cost
Deferred offering costs	$ 0	$ 0.3

ORGANIZATION AND SUMMARY OF S_6

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Dividend yield (as a percent)	0.00%	0.00%

ORGANIZATION AND SUMMARY OF S_7

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Uncertain tax positions	$ 0	$ 0
Accrued interest and penalties	$ 0	$ 0

LICENSE AGREEMENT (Details)

LICENSE AGREEMENT (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended		27 Months Ended	36 Months Ended
	Jan. 31, 2019	Feb. 28, 2017	Oct. 31, 2016	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2019
Agreements
Fair value of stock issued					$ 34,618
Research and development				$ 7,453		$ 2,726	$ 18,582	$ 6,111	$ 11,471	$ 3,703
General and administrative				3,294		598	9,331	1,418	2,047	582
Operating expenses				10,747		3,324	27,913	7,529	13,518	4,285
Accrued expenses and other current liabilities				4,829			4,829		1,413	280	$ 1,413	$ 4,829
Accounts payable				1,688			1,688		3,015	713	3,015	1,688
Columbia University
Agreements
Research and development				17		100	42	200	500	600	1,400
General and administrative				28		$ 43	300	$ 98
Operating expenses												1,700
Accrued expenses and other current liabilities				100			100		100		100	100
Accounts payable				$ 100			$ 100		100		100	$ 100
License agreement | Columbia University | Accrued expenses
Agreements
Due to related party									100	200	100
License agreement | Columbia University | Accounts payable
Agreements
Due to related party									$ 100	$ 100	$ 100
2016 license agreement | Columbia University
Agreements
Percentage of outstanding common stock issued			5.00%
Fair value of stock issued		$ 500	$ 500
Written notice period for termination of agreement			90 days
Written notice period for termination of agreement, uncured material breach			30 days
Extended written notice period for termination of agreement, attempt to cure material breach			90 days
2016 license agreement | Columbia University | Minimum
Agreements
Percentage of sublicensing revenue, if sublicenses rights granted			10.00%
2016 license agreement | Columbia University | Maximum
Agreements
Payment on achievement of specified development and regulatory milestones			$ 1,300
Payment on achievement of specified level of aggregate annual net sales			$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted			20.00%
2019 license agreement | Columbia University
Agreements
Written notice period for termination of agreement	90 days
Written notice period for termination of agreement, uncured material breach	30 days
Extended written notice period for termination of agreement, attempt to cure material breach	90 days
2019 license agreement | Columbia University | Minimum
Agreements
Percentage of sublicensing revenue, if sublicenses rights granted	10.00%
2019 license agreement | Columbia University | Maximum
Agreements
Payment on achievement of specified development and regulatory milestones	$ 1,300
Payment on achievement of specified level of aggregate annual net sales	$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted	50.00%

FAIR VALUE MEASUREMENTS - Trans

FAIR VALUE MEASUREMENTS - Transfers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Feb. 05, 2018
FAIR VALUE MEASUREMENTS
Assets, transfer from level 1 to level 2	$ 0	$ 0	$ 0
Assets, transfer from level 2 to level 1	0	0	$ 0
Assets, level 3 transfer	0	0
Liabilities, transfer from level 1 to level 2	0	0
Liabilities, transfer from level 2 to level 1	0	0
Liabilities, level 3 transfer	$ 0	$ 0
Fair value of derivative liability				$ 1,900
Fair value of warrant liability				$ 100

FAIR VALUE MEASUREMENTS - Assum

FAIR VALUE MEASUREMENTS - Assumptions (Details)	Dec. 31, 2018YRate
Volatility | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.7448
Volatility | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.7656
Warrants Issued with the 2018 Notes | Contractual term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input | Y	10
Warrants Issued with the 2018 Notes | Risk-free interest rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0285
Warrants Issued with the 2018 Notes | Risk-free interest rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0320
Warrants Issued with the 2018 Notes | Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0

FAIR VALUE MEASUREMENTS - Level

FAIR VALUE MEASUREMENTS - Level 3 roll forward (Details) - USD ($) $ in Thousands	Feb. 05, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Derivative Liability
Fair Value
Initial fair value	$ 1,900			$ 1,896		$ 1,896
Change in fair value		$ 335	$ 294	180	$ 800	972
Extinguishment of Derivative Liability in connection with extinguishment of 2018 Notes						(2,868)
Warrants Liability
Fair Value
Initial fair value	$ 100			74		74
Change in fair value		$ 38	$ 21	$ 6	$ 65	168
Reclassification of Warrant Liability into 2018 Notes Warrants						$ (242)

CONVERTIBLE PROMISSORY NOTES (D

CONVERTIBLE PROMISSORY NOTES (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 05, 2018	Nov. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Feb. 28, 2019	Jan. 18, 2018
Debt
Outstanding notes			$ 0			$ 0	$ 0
Loss on extinguishment of debt						(221)
Amount of unpaid and accrued interest recognized in additional paid-in capital						$ 101
Fair value of derivative liability	$ 1,900
Series B Convertible Preferred Stock
Debt
Debt converted into shares			1,097,721
Issue price (in dollars per share)		$ 7.49	$ 7.49			$ 7.49		$ 7.49
Amount of unpaid and accrued interest recognized in additional paid-in capital	$ 100
Preferreds stock issued (in shares)	1,097,721					1,097,721
Preferreds stock issued	$ 8,200					$ 8,219
Warrants Issued with the 2018 Notes
Debt
Initial fair value recorded as debt discount (in dollars)	100								$ 100
2018 Notes
Debt
Outstanding notes		$ 6,600
Aggregate principal amount	$ 6,000
Interest rate (as a percent)	15.00%
Threshold proceeds from sale of preferred stock	$ 8,000
Preferred stock conversion price as a percentage of lowest price per share of preferred stock sold in financing	80.00%	80.00%
Percentage of outstanding principal amount payable in event of corporate transaction or change of control event	30.00%
Minimum percentage of outstanding principal amount written consent required for prepayment	50.00%
Additional percentage of outstanding principal payable on prepayment	15.00%
Legal costs and bank fees	$ 400
Interest expense				$ 600	$ 1,400	1,600
Amortization of debt discount				$ 800	$ 300	$ 900
Debt converted into shares		1,097,721
Loss on extinguishment of debt	(200)
Carrying value, net of unamortized debt discount	5,100
2018 Notes | Derivative Liability
Debt
Initial fair value recorded as debt discount (in dollars)	$ 1,900
Fair value of derivative liability		$ 2,900

STOCK BASED COMPENSATION - Plan

STOCK BASED COMPENSATION - Plans (Details) - shares	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2019	Dec. 31, 2017
Stock-based compensation
Options outstanding (in shares)	1,202,979	3,767,571	262,427
2016 Plan
Stock-based compensation
Shares reserved (in shares)	2,966,241		1,345,469
Expiration period	10 years
Vesting period	3 years
Number of shares available for future issuance	1,708,179		1,083,041

STOCK BASED COMPENSATION - Stoc

STOCK BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Total stock-based compensation expense	$ 1,219	$ 78	$ 4,823	$ 180	$ 32	$ 272
Research and development
Stock-based compensation
Total stock-based compensation expense	495	38	2,087	88		140
General and administrative
Stock-based compensation
Total stock-based compensation expense	$ 724	$ 39	$ 2,736	$ 92	$ 32	$ 132

STOCK BASED COMPENSATION - Othe

STOCK BASED COMPENSATION - Other details (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Weighted-average fair value of options granted (in dollars per share)	$ 4.71	$ 1.03
Unrecognized stock-based compensation balance for unvested options	$ 9,800,000
2016 Plan
Stock-based compensation
Weighted-average fair value of options granted (in dollars per share)			$ 1.54	$ 0.66
Unrecognized stock-based compensation balance for unvested options			$ 1,300,000	$ 100,000
Unrecognized stock-based compensation balance for unvested options expected to be recognized (in years)			2 years 1 month 6 days	2 years 1 month 6 days
Total fair value of options vested			$ 40,000
Maximum | 2016 Plan
Stock-based compensation
Total fair value of options vested				$ 1,000

STOCK BASED COMPENSATION - Opti

STOCK BASED COMPENSATION - Options outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Options Outstanding
Outstanding at beginning of period (in shares)	1,202,979	262,427
Options granted (in shares)	2,657,628	995,633
Options exercised (in shares)	(81,988)	(55,081)
Outstanding at end of period (in shares)	3,767,571	1,202,979	262,427
Exercisable at end of period (in shares)	1,364,658	73,692
Nonvested at end of period (in shares)	2,402,913	1,129,287
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 1.35	$ 0.90
Options granted (in dollars per share)	7.34	1.44
Options exercised (in dollars per share)	2.77	0.84
Outstanding at end of period (in dollars per share)	5.54	1.35	$ 0.90
Exercisable at end of period (in dollars per share)	2.80	0.88
Nonvested at end of period (in dollars per share)	$ 7.09	$ 1.38
Weighted-Average Remaining Contractual Term-in years
Outstanding	9 years 2 months 9 days	9 years 1 month 21 days	9 years 1 month 2 days
Exercisable	8 years 10 months 2 days	8 years 4 days
Nonvested	9 years 4 months 21 days	9 years 2 months 19 days
Aggregate Intrinsic Value
Options exercised (in dollars)		$ 33
Outstanding (in dollars)	$ 20,860	4,029	$ 27
Exercisable (in dollars)	11,174	282
Nonvested (in dollars)	$ 9,686	$ 3,747

STOCK BASED COMPENSATION - Valu

STOCK BASED COMPENSATION - Valuation assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Valuation Assumptions
Time to expiration (in years)	5 years 10 months 24 days	6 years
Volatility	71.78%	75.06%
Risk-free interest rate	2.71%	2.09%
Dividend yield (as a percent)	0.00%	0.00%

STOCKHOLDERS' EQUITY - Authoriz

STOCKHOLDERS' EQUITY - Authorized, issued and outstanding and Common Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	9 Months Ended
	Feb. 28, 2017USD ($)Voteshares	Oct. 31, 2016USD ($)	Jun. 30, 2019USD ($)$ / sharesshares	Sep. 30, 2019Vote$ / sharesshares	May 16, 2019shares	Mar. 31, 2019$ / sharesshares	Dec. 31, 2018$ / sharesshares	Sep. 30, 2018$ / sharesshares	Jun. 30, 2018$ / sharesshares	Mar. 31, 2018$ / sharesshares	Dec. 31, 2017$ / sharesshares
STOCKHOLDERS' EQUITY
Common Stock, authorized (in shares)				100,000,000			20,441,982				11,049,720
Common Stock, par value (in dollars per share) | $ / shares				$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, authorized (in shares)							10,883,950				3,535,910
Convertible preferred stock, par value (in dollars per share) | $ / shares							$ 0.0001
Common Stock, issued (in shares)				17,134,190			5,513,531				5,458,450
Common stock, outstanding (in shares)				17,134,190			5,513,531				5,458,450
Convertible preferred stock, issued (in shares)							7,095,746				3,093,898
Convertible preferred stock, outstanding (in shares)				0	0		7,095,746
Fair value of stock issued | $			$ 34,618
Series A Convertible Preferred Stock
STOCKHOLDERS' EQUITY
Convertible preferred stock, authorized (in shares)				0			3,093,898				3,535,910
Convertible preferred stock, par value (in dollars per share) | $ / shares				$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, issued (in shares)				0			3,093,898				3,093,898
Convertible preferred stock, outstanding (in shares)				0		3,093,898	3,093,898	3,093,898	3,093,898	3,093,898	3,093,898
Series B Convertible Preferred Stock
STOCKHOLDERS' EQUITY
Convertible preferred stock, authorized (in shares)				0			7,790,052				0
Convertible preferred stock, par value (in dollars per share) | $ / shares				$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, issued (in shares)				0			4,001,848				0
Convertible preferred stock, outstanding (in shares)				0		4,444,773	4,001,848				0
Common Stock Par value $0.0001
STOCKHOLDERS' EQUITY
Common Stock, par value (in dollars per share) | $ / shares			$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Shares issued (in shares)			4,000,000
Fair value of stock issued | $			$ 1
Number of votes per common stock | Vote	1			1
Columbia University | 2016 license agreement
STOCKHOLDERS' EQUITY
Shares issued (in shares)	486,077
Fair value of stock issued | $	$ 500	$ 500

STOCKHOLDERS' EQUITY - Common S

STOCKHOLDERS' EQUITY - Common Stock (Details) - Vote	1 Months Ended	9 Months Ended
	Feb. 28, 2017	Sep. 30, 2019
Common Stock Par value $0.0001
STOCKHOLDERS' EQUITY
Number of votes per common stock	1	1

STOCKHOLDERS' EQUITY - Preferre

STOCKHOLDERS' EQUITY - Preferred stock issued (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2019	Jan. 31, 2017	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	May 16, 2019	Nov. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Preferred Stock
Preferred Stock Outstanding			7,095,746		7,095,746		0	0
Series A Convertible Preferred Stock
Preferred Stock
Issuance of convertible preferred stock (in shares)		3,093,898				3,093,898
Issue price (in dollars per share)		$ 2.26	$ 2.26		$ 2.26
Gross proceeds from issuance of convertible preferred stock		$ 7
Issuance costs		$ 0.7
Preferred Stock Outstanding			3,093,898	3,093,898	3,093,898	3,093,898	0			3,093,898	3,093,898	3,093,898
Series B Convertible Preferred Stock
Preferred Stock
Issuance of convertible preferred stock (in shares)	442,930		2,904,127	442,925	2,904,127
Issue price (in dollars per share)	$ 7.49		$ 7.49		$ 7.49				$ 7.49
Gross proceeds from issuance of convertible preferred stock	$ 3.3		$ 21.7
Debt converted into shares			1,097,721
Issuance costs	$ 0.3		$ 0.8
Preferred Stock Outstanding			4,001,848	4,444,773	4,001,848	0	0

STOCKHOLDERS' EQUITY - Prefer_2

STOCKHOLDERS' EQUITY - Preferred stock summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	May 16, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Preferred Stock
Preferred Stock Authorized				10,883,950				3,535,910
Preferred Stock Issued				7,095,746				3,093,898
Preferred Stock Outstanding	0	0		7,095,746
Carrying Value				$ 35,410				$ 6,254
Liquidation Value				$ 36,964				$ 7,000
Common Stock Issuable Upon Conversion				7,095,746				3,093,898
Series A Convertible Preferred Stock
Preferred Stock
Preferred Stock Authorized	0			3,093,898				3,535,910
Preferred Stock Issued	0			3,093,898				3,093,898
Preferred Stock Outstanding	0		3,093,898	3,093,898	3,093,898	3,093,898	3,093,898	3,093,898
Carrying Value			$ 6,254	$ 6,254	$ 6,254	$ 6,254	$ 6,254	$ 6,254
Liquidation Value	$ 0			$ 7,000				$ 7,000
Common Stock Issuable Upon Conversion				3,093,898				3,093,898
Series B Convertible Preferred Stock
Preferred Stock
Preferred Stock Authorized	0			7,790,052				0
Preferred Stock Issued	0			4,001,848				0
Preferred Stock Outstanding	0		4,444,773	4,001,848				0
Carrying Value			$ 32,207	$ 29,156
Liquidation Value	$ 0			$ 29,964				$ 0
Common Stock Issuable Upon Conversion				4,001,848

STOCKHOLDERS' EQUITY - Prefer_3

STOCKHOLDERS' EQUITY - Preferred stock other information (Details) $ / shares in Units, $ in Millions	May 16, 2019$ / shares	Nov. 05, 2018	Dec. 31, 2018USD ($)Vote$ / shares	Feb. 28, 2019$ / shares	Nov. 30, 2018$ / shares	Jan. 31, 2017$ / shares
Preferred Stock
Number of votes for each share of common stock into which temporary equity could be converted | Vote			1
Threshold debt obligations | $			$ 2
Conversion ratio (as a percent)			1.00%
Minimum proceeds from conversion of preferred stock if converted | $			$ 30
Series A Convertible Preferred Stock
Preferred Stock
Original issue price (in dollars per share)			$ 2.26			$ 2.26
Stock conversion price (in dollars per share)	$ 2.26		$ 2.26
Series B Convertible Preferred Stock
Preferred Stock
Dividend multiple to be paid within twenty-four months following the original issue date		2
Dividend multiple to be paid thereafter following the original issue date		3	3
Original issue price (in dollars per share)			$ 7.49	$ 7.49	$ 7.49
Stock conversion price (in dollars per share)	$ 7.49		$ 7.49

WARRANTS - Issued with Series A

WARRANTS - Issued with Series A Preferred Stock (Details) $ / shares in Units, $ in Thousands	Jan. 26, 2017USD ($)$ / sharesshares	Mar. 31, 2019USD ($)	Dec. 31, 2017YRate
Warrants
Warrants to purchase common stock (in dollars) | $		$ 80
Warrants Issued with Series A Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares	309,389
Warrants to purchase common stock (in dollars) | $	$ 200
Exercise price (in dollars per share) | $ / shares	$ 2.49
2017 Warrants | Warrants Issued with Series A Preferred Stock | Contractual term (in years)
Warrants
Measurement input | Y			10
2017 Warrants | Warrants Issued with Series A Preferred Stock | Volatility
Warrants
Measurement input			0.7695
2017 Warrants | Warrants Issued with Series A Preferred Stock | Risk-free interest rate
Warrants
Measurement input			0.0262
2017 Warrants | Warrants Issued with Series A Preferred Stock | Dividend yield
Warrants
Measurement input			0

WARRANTS - Issued with the 2018

WARRANTS - Issued with the 2018 Notes (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 05, 2018	Mar. 31, 2019	Feb. 05, 2018	Jan. 18, 2018
Warrants
Warrants to purchase common stock (in dollars)		$ 80
Warrants Issued with the 2018 Notes
Warrants
Initial fair value recorded as debt discount (in dollars)			$ 100	$ 100
Warrants to purchase common stock (in shares)	76,847
Warrants to purchase common stock (in dollars)	$ 300
Exercise price (in dollars per share)	$ 6.59

WARRANTS - Issued with Series B

WARRANTS - Issued with Series B Preferred Stock (Details) $ / shares in Units, $ in Thousands	Jan. 26, 2017USD ($)$ / sharesshares	Feb. 28, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)YRate$ / sharesshares	Mar. 31, 2019USD ($)	Sep. 30, 2019YRate
Warrants
Warrants to purchase common stock (in dollars)				$ 80
Warrants Issued with Series A Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares	309,389
Warrants to purchase common stock (in dollars)	$ 200
Exercise price (in dollars per share) | $ / shares	$ 2.49
Warrants Issued with Series B Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares		23,867	72,261
Warrants to purchase common stock (in dollars)		$ 100	$ 200
Exercise price (in dollars per share) | $ / shares		$ 8.24	$ 8.24
Expiration term		10 years	10 years
2018 Warrants | Warrants Issued with Series B Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares			72,261
Warrants to purchase common stock (in dollars)			$ 200
Exercise price (in dollars per share) | $ / shares			$ 8.24
Expiration term			10 years
2018 Warrants | Warrants Issued with Series B Preferred Stock | Contractual term (in years)
Warrants
Measurement input | Y			10		10
2018 Warrants | Warrants Issued with Series B Preferred Stock | Volatility
Warrants
Measurement input | Rate			0.7322		0.7448
2018 Warrants | Warrants Issued with Series B Preferred Stock | Risk-free interest rate
Warrants
Measurement input | Rate			0.0270		0.0320
2018 Warrants | Warrants Issued with Series B Preferred Stock | Dividend yield
Warrants
Measurement input | Rate			0		0

INCOME TAXES - Provision (Detai

INCOME TAXES - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
INCOME TAXES
Current tax provision	$ 0	$ 0
Deferred tax provision	$ 0	$ 0

INCOME TAXES - Deferred taxes (

INCOME TAXES - Deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Accrued expenses		$ 335
Stock-based compensation	$ 98	11
Capitalized startup costs	35	38
Net operating losses	6,176	1,200
Total deferred tax assets	6,309	1,584
Less: valuation allowance	$ (6,309)	$ (1,584)

INCOME TAXES - NOL (Details)

INCOME TAXES - NOL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
INCOME TAXES
Operating loss carryforwards expiring through 2037	$ 3,600
Operating loss carryforwards do not expire	$ 14,200
Threshold offsetting percentage of future taxable income	80.00%
Less: valuation allowance	$ 6,309	$ 1,584
Increase in valuation allowance	$ 4,700

INCOME TAXES - Income tax rate

INCOME TAXES - Income tax rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Tax rate reconciliation
Federal statutory rate (as a percent)	21.00%	34.00%
State and local taxes net of federal tax benefit (as a percent)	13.50%	11.30%
Tax rate change (as a percent)	0.30%	(13.80%)
Change in valuation allowance (as a percent)	(28.50%)	(32.20%)
Permanently disallowed interest expense (as a percent)	(6.30%)
Other (as a percent)		0.70%
Total (as a percent)	0.00%	0.00%
Maximum
Tax rate reconciliation
Federal statutory rate (as a percent)		35.00%

BENEFIT PLANS (Details)

BENEFIT PLANS (Details)	12 Months Ended
	Dec. 31, 2018USD ($)
BENEFIT PLANS
Employer matching contributions to the plan	$ 11,000

NET LOSS PER COMMON SHARE - EPS

NET LOSS PER COMMON SHARE - EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss attributable to common stockholders-basic	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Net loss attributable to common stockholders- diluted	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Denominator:
Weighted-average common stock outstanding	17,095,870	5,497,871	14,085,579	5,473,414	5,483,149	5,406,513
Net loss per share attributable to common stockholders-basic and diluted	$ (0.63)	$ (0.78)	$ (1.98)	$ (1.79)	$ (3.01)	$ (0.79)

NET LOSS PER COMMON SHARE - Ant

NET LOSS PER COMMON SHARE - Anti-dilutive securities (Details) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders		3,093,898	7,095,746	3,093,898
Options
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	3,767,571	1,035,466	1,202,979	262,427
Warrants Liability
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	482,364	309,389	458,497	309,389

NET LOSS PER COMMON SHARE - Pro

NET LOSS PER COMMON SHARE - Pro Forma Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
NET LOSS PER COMMON SHARE
Net loss attributable to common stockholders-basic	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Net loss attributable to common stockholders- diluted	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Weighted-average common stock outstanding—basic and diluted	17,095,870	5,497,871	14,085,579	5,473,414	5,483,149	5,406,513
Pro forma adjustment to reflect conversion of convertible preferred stock to common stock upon the completion of the proposed initial public offering					3,679,938
Pro forma weighted-average common stock outstanding-diluted					9,163,087
Pro forma net loss per share attributable to common stockholders-diluted					$ (1.80)

RELATED PARTIES (Details)

RELATED PARTIES (Details) - LaunchLabs Agreement	12 Months Ended
	Dec. 31, 2018USD ($)
Related Party Transaction [Line Items]
Payments to related party	$ 13,000
Due to related parties	$ 0

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) $ / shares in Units, $ in Thousands	1 Months Ended			9 Months Ended
	Apr. 30, 2019	Feb. 28, 2019USD ($)$ / sharesshares	Jan. 31, 2019USD ($)	Sep. 30, 2019USD ($)
Subsequent event
Proceeds from issuance of convertible preferred stock, net of cash issuance costs				$ 3,131
Cash issuance costs, Convertible preferred stock				$ 186
2019 license agreement | Columbia University | Minimum
Subsequent event
Percentage of sublicensing revenue, if sublicenses rights granted			10.00%
2019 license agreement | Columbia University | Maximum
Subsequent event
Payment on achievement of specified development and regulatory milestones			$ 1,300
Payment on achievement of specified level of aggregate annual net sales			$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted			50.00%
Subsequent Event.
Subsequent event
Stock split ratio	55.2486
Subsequent Event. | 2019 license agreement | Columbia University | Minimum
Subsequent event
Percentage of sublicensing revenue, if sublicenses rights granted			10.00%
Subsequent Event. | 2019 license agreement | Columbia University | Maximum
Subsequent event
Payment on achievement of specified development and regulatory milestones			$ 1,300
Payment on achievement of specified level of aggregate annual net sales			$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted			50.00%
Subsequent Event. | Series B Preferred Stock
Subsequent event
Issuance of convertible preferred stock (in shares) | shares		442,925
Issue price (in dollars per share) | $ / shares		$ 7.49
Proceeds from issuance of convertible preferred stock, net of cash issuance costs		$ 3,100
Cash issuance costs, Convertible preferred stock		$ 200

Condensed Balance Sheets_2

Condensed Balance Sheets $ in Thousands	Sep. 30, 2019USD ($)
CURRENT ASSETS:
Cash and cash equivalents	$ 13,065
Prepaid expenses and other current assets	4,080
Investments	19,889
Total current assets	37,034
Other assets	230
TOTAL ASSETS	37,264
CURRENT LIABILITIES:
Accounts payable	1,688
Accrued expenses and other current liabilities	4,829
Total current liabilities	6,517
Total liabilities	6,517
STOCKHOLDERS’ EQUITY (DEFICIT):
Common stock, $0.0001 par value; 100,000,000 and 20,441,982 shares authorized as of September 30, 2019 and December 31, 2018, respectively; 17,134,190 shares and 5,513,531 shares issued and outstanding as of September 30, 2019 and December 31, 2018, respectively	1
Additional paid-in capital	79,872
Accumulated other comprehensive loss	11
Accumulated deficit	(49,137)
Total stockholders' equity (deficit)	30,747
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT)	$ 37,264

Condensed Balance Sheets (Par_2

Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	May 16, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Convertible preferred stock, par value (in dollars per share)				$ 0.0001
Convertible preferred stock, authorized (in shares)				10,883,950				3,535,910
Convertible preferred stock, issued (in shares)				7,095,746				3,093,898
Convertible preferred stock, outstanding (in shares)	0	0		7,095,746
Convertible preferred stock, liquidation preference (in dollars)				$ 36,964				$ 7,000
Common Stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Common Stock, authorized (in shares)	100,000,000			20,441,982				11,049,720
Common Stock, issued (in shares)	17,134,190			5,513,531				5,458,450
Common stock, outstanding (in shares)	17,134,190			5,513,531				5,458,450
Series A Convertible Preferred Stock
Convertible preferred stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, authorized (in shares)	0			3,093,898				3,535,910
Convertible preferred stock, issued (in shares)	0			3,093,898				3,093,898
Convertible preferred stock, outstanding (in shares)	0		3,093,898	3,093,898	3,093,898	3,093,898	3,093,898	3,093,898
Convertible preferred stock, liquidation preference (in dollars)	$ 0			$ 7,000				$ 7,000
Series B Convertible Preferred Stock
Convertible preferred stock, par value (in dollars per share)	$ 0.0001			$ 0.0001				$ 0.0001
Convertible preferred stock, authorized (in shares)	0			7,790,052				0
Convertible preferred stock, issued (in shares)	0			4,001,848				0
Convertible preferred stock, outstanding (in shares)	0		4,444,773	4,001,848				0
Convertible preferred stock, liquidation preference (in dollars)	$ 0			$ 29,964				$ 0

Condensed Statements of Opera_2

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
OPERATING EXPENSES:
Research and development	$ 7,453			$ 2,726			$ 18,582	$ 6,111	$ 11,471	$ 3,703
General and administrative	3,294			598			9,331	1,418	2,047	582
Total operating expenses	10,747			3,324			27,913	7,529	13,518	4,285
LOSS FROM OPERATIONS	(10,747)			(3,324)			(27,913)	(7,529)	(13,518)	(4,285)
OTHER INCOME (EXPENSE), NET:
Interest income (expense), net	34			(584)			33	(1,400)	(1,642)	3
Other expense				(373)				(873)	(1,140)
Total other income (expense), net	34			(957)			33	(2,273)	(3,003)	3
Net loss	(10,713)	$ (8,437)	$ (8,730)	(4,281)	$ (3,185)	$ (2,335)	(27,880)	(9,802)	(16,521)	(4,282)
Net loss attributable to common stockholders—basic	(10,713)			(4,281)			(27,880)	(9,802)	(16,521)	(4,282)
Net loss attributable to common stockholders— diluted	$ (10,713)			$ (4,281)			$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.63)			$ (0.78)			$ (1.98)	$ (1.79)	$ (3.01)	$ (0.79)
Weighted-average common stock outstanding—basic and diluted	17,095,870			5,497,871			14,085,579	5,473,414	5,483,149	5,406,513

Condensed Statement of Comprehe

Condensed Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Stament of Comprehensive Income
Net loss	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)
Other comprehensive income (loss)
Unrealized gain (loss) on marketable securities	11		11
Other comprehensive income (loss), net of tax	11		11
Comprehensive income (loss), net of tax	$ (10,702)	$ (4,281)	$ (27,869)	$ (9,802)

Condensed Statement of Conver_3

Condensed Statement of Convertible Preferred Stock $ in Thousands	3 Months Ended
	Jun. 30, 2019USD ($)shares
Series A Convertible Preferred Stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period | $	$ 6,254
Balance at beginning of period (in shares) | shares	3,093,898
Conversion of convertible preferred stock into common stock upon closing of initial public offering | $	$ (6,254)
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares) | shares	(3,093,898)
Series B Convertible Preferred Stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period | $	$ 32,207
Balance at beginning of period (in shares) | shares	4,444,773
Conversion of convertible preferred stock into common stock upon closing of initial public offering | $	$ (32,207)
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares) | shares	(4,444,773)

Condensed Statement of Conver_4

Condensed Statement of Convertible Preferred Stock (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Series B Convertible Preferred Stock
Issuance of convertible preferred stock for cash, issuance costs	$ 266	$ 812

Condensed Statement of Stockh_3

Condensed Statement of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common Stock Par value $0.0001Series A Convertible Preferred Stock	Common Stock Par value $0.0001Series B Convertible Preferred Stock	Common Stock Par value $0.0001	Additional Paid-in CapitalSeries A Convertible Preferred Stock	Additional Paid-in CapitalSeries B Convertible Preferred Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Total
Balance at Dec. 31, 2016						$ 41	$ (454)				$ (413)
Balance (in shares) at Dec. 31, 2016			4,972,373
Increase (Decrease) in Stockholders' Equity
Stock-based compensation expense						32					32
Net loss							(4,282)				(4,282)
Balance at Dec. 31, 2017						775	(4,736)		$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017			5,458,450						3,093,898
Increase (Decrease) in Stockholders' Equity
Stock-based compensation expense						26
Net loss							(2,335)				(2,335)
Balance at Mar. 31, 2018						801	(7,071)				(6,296)
Balance (in shares) at Mar. 31, 2018			5,458,450
Balance at Dec. 31, 2017						775	(4,736)		$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017			5,458,450						3,093,898
Increase (Decrease) in Stockholders' Equity
Net loss											(9,802)
Balance at Sep. 30, 2018						992	(14,537)				(13,571)
Balance (in shares) at Sep. 30, 2018			5,504,360
Balance at Dec. 31, 2017						775	(4,736)		$ 6,254		(3,961)
Balance (in shares) at Dec. 31, 2017			5,458,450						3,093,898
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan						47					$ 47
Exercise of options for common stock issued under Equity Incentive Plan (in shares)			55,081								55,081
Stock-based compensation expense						272					$ 272
Net loss							(16,521)				(16,521)
Balance at Dec. 31, 2018						1,665	(21,257)		$ 6,254	$ 29,156	(19,592)
Balance (in shares) at Dec. 31, 2018			5,513,531						3,093,898	4,001,848
Balance at Mar. 31, 2018						801	(7,071)				(6,296)
Balance (in shares) at Mar. 31, 2018			5,458,450
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan						9					9
Exercise of options for common stock issued under Equity Incentive Plan (in shares)			9,171
Stock-based compensation expense						76					76
Net loss							(3,185)				(3,185)
Balance at Jun. 30, 2018						886	(10,256)				(9,396)
Balance (in shares) at Jun. 30, 2018			5,467,621
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan						28					28
Exercise of options for common stock issued under Equity Incentive Plan (in shares)			36,739
Stock-based compensation expense						78					78
Net loss							(4,281)				(4,281)
Balance at Sep. 30, 2018						992	(14,537)				(13,571)
Balance (in shares) at Sep. 30, 2018			5,504,360
Balance at Dec. 31, 2018						1,665	(21,257)		$ 6,254	$ 29,156	(19,592)
Balance (in shares) at Dec. 31, 2018			5,513,531						3,093,898	4,001,848
Increase (Decrease) in Stockholders' Equity
Issuance of common stock warrants in connection with the issuance of Series B convertible preferred stock						80					80
Stock-based compensation expense						325					325
Net loss							(8,730)				(8,730)
Balance at Mar. 31, 2019						2,070	(29,987)				(27,917)
Balance (in shares) at Mar. 31, 2019			5,513,531
Balance at Dec. 31, 2018						1,665	(21,257)		$ 6,254	$ 29,156	$ (19,592)
Balance (in shares) at Dec. 31, 2018			5,513,531						3,093,898	4,001,848
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan (in shares)											81,988
Conversion of convertible preferred stock into common stock upon closing of initial public offering											$ 38,461
Net loss											(27,880)
Balance at Sep. 30, 2019			$ 1			79,872	(49,137)	$ 11			30,747
Balance (in shares) at Sep. 30, 2019			17,134,190
Balance at Mar. 31, 2019						2,070	(29,987)				(27,917)
Balance (in shares) at Mar. 31, 2019			5,513,531
Increase (Decrease) in Stockholders' Equity
Conversion of convertible preferred stock into common stock upon closing of initial public offering				$ 6,254	$ 32,207				$ 6,254	$ 32,207
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)	3,093,898	4,444,773
Issuance of common stock upon initial public offering, net of issuance costs of $5,383			$ 1			34,617					34,618
Issuance of common stock upon initial public offering, net of issuance costs of $5,383 (in shares)			4,000,000
Stock-based compensation expense						3,279					3,279
Net loss							(8,437)				(8,437)
Balance at Jun. 30, 2019			$ 1			78,427	(38,424)				40,004
Balance (in shares) at Jun. 30, 2019			17,052,202
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under Equity Incentive Plan						226					226
Exercise of options for common stock issued under Equity Incentive Plan (in shares)			81,988
Stock-based compensation expense						1,219					1,219
Net loss							(10,713)				(10,713)
Other comprehensive income (loss)								11			11
Balance at Sep. 30, 2019			$ 1			$ 79,872	$ (49,137)	$ 11			$ 30,747
Balance (in shares) at Sep. 30, 2019			17,134,190

Condensed Statement of Stockh_4

Condensed Statement of Stockholders' (Deficit) Equity (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2019USD ($)$ / shares
Increase (Decrease) in Stockholders' Equity
Issuance costs | $	$ 5,383
Common Stock Par value $0.0001
Increase (Decrease) in Stockholders' Equity
Common Stock, par value (in dollars per share) | $ / shares	$ 0.0001

Condensed Statements of Cash _3

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,823	180	272	32
Non-cash interest expense		1,399	1,642
Payment of security deposit for long-term lease	(230)
Change in fair value of derivative liability		809	972
Change in fair value of warrant liability		64	168
Changes in operating assets and liabilities:
Prepaid expenses	(2,702)	(1,097)	(1,179)	(9)
Accounts payable	(1,327)	1,833	2,302	499
Accrued expenses and other current liabilities	3,416	1,301	941	79
Net cash used in operating activities	(23,900)	(5,313)	(11,182)	(3,195)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of available-for-sale securities	(19,878)
Net cash used in investing activities	(19,878)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of Series B convertible preferred stock, net of cash issuance costs of $186	3,131
Proceeds from issuance of convertible promissory notes, net of cash issuance costs of $440		5,560	5,560
Payment of offering costs	(2,463)		(119)
Proceeds from the initial public offering, net of underwriter commissions	37,200
Exercise of stock options for common stock under Equity Incentive Plan	227	37	47
Net cash provided by financing activities	38,095	5,597	26,653	6,470
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(5,683)	284	15,471	3,275
Cash and cash equivalents at beginning of period	18,748	3,277	3,277	2
Cash and cash equivalents at end of period	13,065	3,561	18,748	3,277
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Derivative liability in connection with issuance of convertible promissory notes		1,896	1,896
Conversion of Preferred Stock to Equity Following IPO	38,461
2018 Notes
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Issuance of warrants		$ 74	242
Series A Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of Series B convertible preferred stock, net of cash issuance costs of $186				6,470
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Issuance of warrants				$ 216
Series B Convertible Preferred Stock
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of Series B convertible preferred stock, net of cash issuance costs of $186			21,165
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Issuance of warrants	$ 80		$ 228

Condensed Statements of Cash _4

Condensed Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Condensed Statements of Cash Flows
Cash issuance costs, Convertible preferred stock	$ 186
Cash issuance cost, Convertible promissory notes		$ 440	$ 440

ORGANIZATION AND SUMMARY OF S_8

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Operations and Business Applied Therapeutics, Inc. (the “Company”) is a clinical-stage biopharmaceutical company developing a pipeline of novel product candidates against validated molecular targets in indications of high unmet medical need. In particular, the Company is currently targeting treatments for cardiovascular disease, galactosemia and diabetic complications. The Company was incorporated in Delaware on January 20, 2016 and is headquartered in New York, New York. On May 16, 2019, the Company completed an initial public offering (“IPO”) in which the Company issued and sold 4,000,000 shares of its common stock at a public offering price of $10.00 per share, for aggregate gross proceeds of $40.0 million. The Company received net of proceeds $34.6 million, after deducting underwriting discounts and commissions and offering costs. Prior to the completion of the IPO, the Company primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 8). In connection with the IPO, the Company effected a 55.2486-for-1 stock split of its issued and outstanding shares of common stock and convertible preferred stock. The stock split became effective on April 26, 2019. Stockholders entitled to fractional shares as a result of the forward stock split received cash payment in lieu of receiving fractional shares. All share and per share amounts for all periods presented in the accompanying condensed financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect this stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately increased and the respective per share value and exercise prices, if applicable, were proportionately decreased in accordance with the terms of the agreements governing such securities. Upon the closing of the IPO on May 16, 2019, all of the then-outstanding shares of convertible preferred stock automatically converted into 7,538,671 shares of common stock on a one-for-one basis. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. The accompanying unaudited condensed financial statements as of September 30, 2019 and for the three and nine months ended September 30, 2019 and 2018 have been prepared by the Company in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and, pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2018 included in the Company’s final prospectus that forms a part of the Company’s Registration Statement on Form S-1 (Reg. No. 333-230838), filed with the SEC pursuant to Rule 424(b)(4) on May 14, 2019 (the “Prospectus”). The unaudited condensed financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited condensed financial statements contain all adjustments which are necessary for a fair presentation of the Company’s financial position as of September 30, 2019, results of operations for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2019. Liquidity The Company has incurred, and expects to continue to incur, significant operating losses and negative cash flows for at least the next several years as it continues to develop its drug candidates. To date, the Company has not generated any revenue, and it does not expect to generate revenue unless and until it successfully completes development and obtains regulatory approval for one of its product candidates. Management believes that the Company’s existing cash, together with the net proceeds from the IPO, will allow the Company to continue its operations for at least 12 months from the issuance date of these financial statements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Significant Accounting Policies The significant accounting policies and estimates used in preparation of the condensed financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus. Except as detailed below, there have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2019. Stock‑Based Compensation The Company accounts for its stock-based compensation as expense in the condensed statements of operations based on the awards' grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black-Scholes option pricing model with the exception of stock options that include service, performance and market conditions, which are valued using the Monte-Carlo simulation model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company has historically been a private company and lacks company-specific historical and implied volatility information. Therefore, the Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission ("SEC") Staff Accounting Bulletin ("SAB") No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. A Monte-Carlo simulation is an analytical method used to estimate fair value by performing a large number of simulations or trial runs and thereby determining a value based on the possible outcomes from these trial runs based on the specific vesting conditions. The fair value of stock-based payments is recognized as expense over the requisite service period which is generally the vesting period, with the exception of the fair value of stock-based payments for awards that include service, performance and market conditions, which is recognized as expense over the derived service period determined using the Monte-Carlo simulation. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. Upon closing the IPO in May 2019, $2.6 million in deferred offering costs were reclassified from prepaid and other current assets and recorded against the IPO proceeds reducing additional paid-in capital. As of September 30, 2019, the Company did not have any deferred offering costs recorded in prepaid and other current assets. Investments We have investments in marketable debt securities. We determine the appropriate classification of our investments at the date of purchase and reevaluate the classifications at the balance sheet date. Marketable debt securities with maturities of 12 months or less are classified as short-term. Marketable debt securities with maturities greater than 12 months are classified as long-term. The Company’s marketable securities are accounted for as available for sale (“AFS”). AFS securities are reported at fair value. Unrealized gains and losses, after applicable income taxes, are reported in accumulated other comprehensive income/(loss). We conduct an other-than-temporary impairment (“OTTI”) analysis on a quarterly basis or more often if a potential loss-triggering event occurs. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and whether we intend to sell. For AFS securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Recently Adopted Accounting Pronouncements The new accounting pronouncements recently adopted by the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus as filed with the SEC on May 14, 2019. Except as described below, there have been no new accounting pronouncements adopted by the Company during the nine months ended September 30, 2019. In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) , which requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases on their balance sheet date (“ASU No. 2016-02”). ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018. In July 2018, an amendment was made that allows companies the option of using the effective date of the new standard as the initial application date (at the beginning of the period in which the new standard is adopted, rather than at the beginning of the earliest comparative period). This update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize the associated lease assets and lease liabilities on its balance sheet. Additionally, in March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements (“ASU No. 2019-01”). ASU No. 2019-01 clarifies the transition guidance related to interim disclosures provided in the year of adoption. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease did not significantly change from previous U.S. GAAP. The modified retrospective method includes several optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. The Company adopted Topic 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance under ASC 840. In adopting Topic 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease; ii) the lease classification of existing or expired leases; and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election not to recognize assets or related lease liabilities with a lease term of twelve months or less in its condensed balance sheet. The adoption of this standard did not have an impact on the Company’s condensed balance sheet as all of the Company’s leases are for terms that are less than 12 months. Additionally, the adoption of this standard did not have a material impact on the Company’s condensed statements of operations or condensed statement of cash flows. On August 6, 2019 the Company entered into a lease for approximately 6,579 square feet of new office space in New York City (the “Lease”). The Lease will commence upon delivery of the premise after certain improvements are made, which is anticipated to be on or about November 1, 2019 (the “Commencement Date”), for a five-year period. Under the Lease, the Company will pay monthly rent of approximately $38,000 for the first year following the Commencement Date, and such rent will increase by a nominal percentage every year following the first anniversary of the Commencement Date. The Company will also pay a real estate tax escalation, as additional rent, over a base year. Total lease obligation over the term of the lease will be approximately $2.4 million. Recently Issued Accounting Pronouncements The FASB issued authoritative guidance that amends guidance on reporting credit losses for assets, including available-for-sale marketable securities and any other financial assets not excluded from the scope that have the contractual right to receive cash. For available-for-sale marketable securities, credit losses should be measured in a manner similar to current generally accepted accounting standards; however, ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , will require that credit losses be presented as an allowance rather than as a write-down. We are currently in the process of evaluating the impact of this guidance on our condensed financial statements.	Applied Therapeutics, Inc. Notes to the Financial Statements 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Operations and Business Applied Therapeutics, Inc. (the “Company”) is a clinical‑stage biopharmaceutical company developing a pipeline of novel product candidates against validated molecular targets in indications of high unmet medical need. In particular, the Company is currently targeting treatments for cardiovascular disease, galactosemia and diabetic complications. The Company was incorporated in Delaware on January 20, 2016 and is headquartered in New York, New York. Going Concern The Company has evaluated whether there are conditions and events considered in the aggregate that raise substantial doubt about the Company’s ability to continue as a going concern. Through December 31, 2018, the Company has primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 6). The Company has incurred recurring losses from operations since its inception, including net losses of $4.3 million and $16.5 million for the years ended December 31, 2017 and December 31, 2018, respectively, and has used cash in operations of $3.2 million and $11.2 million for the years ended December 31, 2017 and December 31, 2018, respectively. In addition, as of December 31, 2018, the Company had an accumulated deficit of $21.3 million. The Company expects its operating losses and negative cash flows to continue into the foreseeable future as it continues to develop, manufacture, and commercialize its product candidates. The Company is seeking to complete an initial public offering (“IPO”) of its common stock. In the event the Company does not complete an IPO, and even after the completion of an IPO, the Company expects to seek additional funding through private or public equity financings, debt financings, collaborations, or other strategic transactions. The Company may not be able to obtain funding on acceptable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Based on the operating losses incurred since inception, the expectation of continuing operating losses for the foreseeable future, and the need to raise additional capital to finance its operations, the Company has concluded that there is substantial doubt about its ability to continue as a going concern within one year after the date that the financial statements are issued. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. The financial statements do not include any adjustments that might be necessary if the Company is unable to continue as a going concern. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Unaudited Pro Forma Information The accompanying unaudited pro forma balance sheet as of December 31, 2018 has been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding convertible preferred stock into 7,095,746 shares of common stock. The accompanying unaudited pro forma basic and diluted net loss per share attributable to common stockholders in the statements of operations for the year ended December 31, 2018 have been prepared to give effect, upon the closing of a qualified IPO, to the conversion of all outstanding shares of convertible preferred stock into shares of common stock as of December 31, 2018. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third‑party fees that are directly associated with in‑process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of convertible preferred stock and stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. The Company recorded deferred offering costs of $0.3 million as of December 31, 2018 in prepaid expenses and other current assets. Fair Value Measurements Certain assets and liabilities are reported on a recurring basis at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1—Quoted prices in active markets for identical assets or liabilities. Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. Cash and Cash Equivalents The Company considers all short‑term, highly liquid investments, with an original maturity of three months or less, to be cash equivalents. The Company maintains its cash in bank deposit accounts which, at times, may exceed federally insured limits. The Company has not experienced any losses in these accounts and does not believe it is exposed to any significant credit risk on cash and cash equivalents. Common Stock Valuation The Company utilizes significant estimates and assumptions in determining the fair value of its common stock. The Company has utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately‑Held Company Equity Securities Issued as Compensation (the “Practice Aid”), to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time of, and the likelihood of, achieving a liquidity event, such as an IPO or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date. Convertible Preferred Stock The Company records shares of its convertible preferred stock at their respective fair values on the dates of issuance less issuance costs. The Company classifies shares of its convertible preferred stock outside of stockholders’ deficit when the redemption of such units or shares is outside the Company’s control. The Company does not adjust the carrying values of the convertible preferred units or convertible preferred stock to the liquidation preferences of such units or shares until such time as a deemed liquidation event is probable of occurring. Research and Development The Company expenses all costs incurred in performing research and development activities. Research and development expenses include salaries and other related costs, materials and supplies, preclinical expenses, manufacturing expenses, contract services and other outside expenses. As part of the process of preparing the financial statements, the Company is required to estimate their accrued research and development expenses. The Company makes estimates of the accrued expenses as of each balance sheet date in the financial statements based on facts and circumstances known at that time. In addition, there may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense in which case such amounts are reflected as prepaid expenses and other current assets. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual or the amount of prepaid expenses accordingly. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized in prepaid expenses and other current assets. The capitalized amounts are expensed as the related goods are delivered or the services are performed. General and Administrative General and administrative expenses consist primarily of salaries and other related costs, including stock‑based compensation, for personnel in the Company’s executive and finance functions. General and administrative expenses also include professional fees for legal, accounting, auditing, tax and consulting services; travel expenses; and facility‑related expenses, which include allocated expenses for rent and maintenance of facilities and other operating costs. Stock‑Based Compensation The Company accounts for its stock‑based compensation as expense in the statements of operations based on the awards’ grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company‑specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, Share‑Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of stock‑based payments is recognized as expense over the requisite service period which is generally the vesting period. Income Taxes The Company uses the asset and liability method of accounting for deferred income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the carrying amounts and the tax basis of assets and liabilities at currently enacted tax rates. These temporary differences primarily relate to net operating loss carryforwards available to offset future taxable income. Valuation allowances are established, if necessary, to reduce a deferred tax asset to the amount that will more likely than not be realized. The Company recognizes tax liabilities from an uncertain tax position only if it is more likely than not that the tax position will not be sustained upon examination by the taxing authorities, based on the technical merits of the tax position. There are no uncertain tax positions that have been recognized in the accompanying financial statements. The Company is required to file tax returns in the U.S. federal jurisdiction and in the state of New York. The Company’s policy is to recognize interest and penalties related to uncertain tax benefits, if any, as part of income tax expense. No such interest and penalties have been accrued as of December 31, 2017 and 2018. Net Loss per Share and Unaudited Pro Forma Net Loss per Share Basic net loss per share is calculated by dividing net loss available to common stockholders by the weighted‑average common stock outstanding. Diluted net loss per share is calculated similarly, except that it includes the dilutive effect of the assumed exercise of securities, including outstanding warrants and the effect of shares issuable under the Company’s stock‑based compensation plan, if such effect is dilutive. Unaudited pro forma net loss per share attributable to common stockholders is computed using the weighted‑average number of common shares outstanding after giving effect to the conversion of all outstanding convertible preferred stock into shares of common stock as if such conversion had occurred at January 1, 2018, or the date of original issuance, if later. Segment Information Operating segments are defined as components of an enterprise for which separate discrete information is available for evaluation by the chief operating decision‑maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision‑maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment, which is the business of discovering and developing its product candidates. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014‑09, Revenue from Contracts with Customers (Topic 606) (“ASU No. 2014‑09”), which modifies how all entities recognize revenue, and consolidates into one Accounting Standards Codification (“ASC”) (ASC Topic 606, Revenue from Contracts with Customers ), the current guidance found in ASC Topic 605, and various other revenue accounting standards for specialized transactions and industries. ASU No. 2014‑09 outlines a comprehensive five‑step revenue recognition model based on the principle that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU No. 2015‑14, Revenue from Contracts with Customers (Topic 606): Deferral of Effective Date (“ASU No. 2015‑14”), which defers the effective date of ASU No. 2014‑09 by one year. Early adoption is permitted for annual periods beginning after December 15, 2016. To date, the Company has not had any arrangements that are within the scope of ASU No. 2014‑09, or its predecessor, ASC Topic 605. The Company adopted these pronouncements on January 1, 2017, which did not have any impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Improvements to Employee Share‑Based Payment Accounting (“ASU No. 2016‑09”), which simplifies share‑based payment accounting through a variety of amendments. The Company elected to early adopt this guidance effective January 1, 2016, and has elected to account for forfeitures as incurred and therefore no forfeiture estimate is utilized in the year ended December 31, 2017. Adoption of ASU No. 2016‑09 did not have a material impact on the Company’s financial statements. In May 2017, the FASB issued ASU No. 2017‑09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU No. 2017‑09”), which clarifies when to account for a change to the terms or conditions of a share‑based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The standard is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted ASU No. 2017‑09 as of January 1, 2018, which did not have a material impact on the Company’s financial statements. In June 2018, the FASB issued ASU No. 2018‑07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share‑Based Payment Accounting (“ASU No. 2018‑07”). These amendments expand the scope of Topic 718, Compensation—Stock Compensation , which currently only includes share‑based payments to employees, to include share‑based payments issued to nonemployees for goods or services. Consequently, the accounting for share‑based payments to nonemployees and employees will be substantially aligned. This ASU supersedes Subtopic 505‑50, Equity—Equity‑Based Payments to Non‑Employees . This standard is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted as long as ASU No. 2014‑09 has been adopted by the Company. The Company adopted ASU No. 2018‑07 as of January 1, 2017, which did not have a material impact on the Company’s financial statements. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) , which requires lessees to recognize assets and liabilities for leases with lease terms greater than 12 months in the statement of financial position. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016‑02 also requires improved disclosures to help users of financial statements better understand the amount, timing and uncertainty of cash flows arising from leases. The update is effective for fiscal years beginning after December 15, 2018, including interim reporting periods within that reporting period. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2016‑02 will have on its financial statements. In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement . which, eliminates, modifies, and adds disclosure requirements on fair value measurements. The standard is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2018‑13 will have on its financial statements.

LICENSE AGREEMENT_2

LICENSE AGREEMENT	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
LICENSE AGREEMENT
LICENSE AGREEMENT	2. LICENSE AGREEMENT Columbia University In October 2016, the Company entered into a license agreement (the “2016 Columbia Agreement”) with the Trustees of Columbia University (“Columbia University”) to obtain an exclusive royalty-bearing sublicensable license in respect to certain patents. As part of the consideration for entering into the 2016 Columbia Agreement, the Company issued to Columbia University shares equal to 5% of its outstanding common stock on a fully diluted basis at the time of issue. The common stock had a fair value of $0.5 million at the time of issuance. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2016 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid-six figures beginning on the 10th anniversary of the effective date of the 2016 Columbia Agreement. The Company has not granted any sublicenses under the 2016 Columbia Agreement. However, if the Company sublicenses the rights granted under the 2016 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 20%, depending on the stage of development at the time such revenue is received from such third parties. In January 2019, the Company entered into a second license agreement with Columbia University (the “2019 Columbia Agreement”). Pursuant to the 2019 Columbia Agreement, Columbia University granted the Company a royalty-bearing, sublicensable license that is exclusive with respect to certain patents, and non-exclusive with respect to certain know-how, in each case to develop, manufacture and commercialize PI3k inhibitor products. The license grant is worldwide. Under the 2019 Columbia Agreement, the Company is obligated to use commercially reasonable efforts to research, discover, develop and market licensed products for commercial sale in the licensed territory, and to comply with certain obligations to meet specified development and funding milestones within defined time periods. Columbia University retains the right to conduct, and grant third parties the right to conduct, non-clinical academic research using the licensed technology; provided that such research is not funded by a commercial entity or for-profit entity or results in rights granted to a commercial or for-profit entity. As consideration for entering into the 2019 Columbia Agreement, the Company made a nominal upfront payment to Columbia University. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2019 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low- to mid-single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid-six figures beginning on the tenth anniversary of the effective date of the 2019 Columbia Agreement. The Company has not granted any sublicenses under the 2019 Columbia Agreement. However, if the Company sublicenses the rights granted under the 2019 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 50%, depending on the stage of development at the time such revenue is received from such third parties. The 2019 Columbia Agreement will terminate upon the expiration of all the Company’s royalty payment obligations in all countries. The Company may terminate the 2019 Columbia Agreement for convenience upon 90 days’ written notice to Columbia University. At its election, Columbia University may terminate the 2019 Columbia Agreement, or convert the licenses granted to the Company into non-exclusive, non-sublicensable licenses, in the case of (a) the Company’s uncured material breach upon 30 days’ written notice (which shall be extended to 90 days if the Company is diligently attempting to cure such material breach), (b) the Company’s failure to achieve the specified development and funding milestone events, or (c) the Company’s insolvency . In March 2019, and in connection with the 2016 Columbia Agreement, the Company entered into a research services agreement (the “2019 Columbia Research Agreement” and collectively with the 2016 Columbia Agreement and 2019 Columbia Agreement, the “Columbia Agreements”) with Columbia University with the purpose of analyzing structural and functional changes in brain tissue in an animal model of galactosemia, and the effects of certain compounds whose intellectual property rights were licensed to the Company as part of the 2016 Columbia Agreement on any such structural and functional changes. The 2019 Columbia Research Agreement has a term of 12 months from its effective date; provided that the Company can terminate the 2019 Columbia Research Agreement without cause with at least 30 days’ prior written notice. The services covered by the 2019 Columbia Research Agreement will be performed by Columbia University in two parts consisting of six months. The decision to proceed with Part 2 of the 2019 Columbia Research Agreement shall be made solely by the Company and will be contingent on the success of the research performed in Part 1. In consideration for the services performed by Columbia University in Part 1, the Company will be required to pay $0.1 million to Columbia University for staffing, supplies and indirect costs. If the Company decides to continue the research defined in Part 2, the Company will be required to pay an additional $0.2 million to Columbia University. During the three and nine months ended September 30, 2019, the Company recorded $17,000 and $42,000, respectively, in research and development expense and $28,000 and $0.3 million, respectively, in general and administrative expense related to the Columbia Agreements. During the three and nine months ended September 30, 2018, the Company recorded $0.1 million and $0.2 million, respectively, in research and development expense and $43,000 and $98,000, respectively, in general and administrative expense related to the Columbia Agreements. In aggregate, the Company has incurred $1.7 million in expense from the execution of the Columbia Agreements through September 30, 2019. As of September 30, 2019, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable. As of December 31, 2018, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable.	2. LICENSE AGREEMENT Columbia University In October 2016, the Company entered into a license agreement (the “Columbia Agreement”) with The Trustees of Columbia University in the City of New York (“Columbia University”). Pursuant to the Columbia Agreement, Columbia University granted the Company a royalty‑bearing, sublicensable license that is exclusive with respect to certain patents, and non‑exclusive with respect to certain know‑how, in each case to develop, manufacture and commercialize aldose reductase inhibitor products, including AT‑001, AT‑003 and AT‑007. The license grant is worldwide with the exception of a single patent family covering AT‑001 and AT‑003 for which the license grant excludes China, Taiwan, Hong Kong and Macao. Under the Columbia Agreement, the Company is obligated to use commercially reasonable efforts to research, discover, develop and market licensed products for commercial sale in the licensed territory, and to comply with certain obligations to meet specified development and funding milestones within defined time periods. Columbia University retains the right to conduct, and grant third parties the right to conduct, non‑clinical academic research using the licensed technology, provided that such research is not funded by a commercial entity or for‑profit entity or results in rights granted to a commercial or for‑profit entity. As consideration for entering into the Columbia Agreement, the Company made a nominal upfront payment to Columbia University and, following the occurrence of certain trigger events, issued to Columbia University shares equal to 5% of its outstanding common stock on a fully diluted basis at the time of issue. The common stock had a fair value of $0.5 million, which was recognized as research and development expense for the year ended December 31, 2017. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid six figures beginning on the 10th anniversary of the effective date of the Columbia Agreement. The Company has not granted any sublicenses under the Columbia Agreement. However, if the Company sublicenses the rights granted under the Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such third parties, at percentages between 10% and 20%, depending on the stage of development at the time such revenue is received from such third parties. The Columbia Agreement will terminate upon the expiration of all the Company’s royalty payment obligations in all countries. The Company may terminate the Columbia Agreement for convenience upon 90 days’ written notice to Columbia University. At its election, Columbia University may terminate the Columbia Agreement, or convert the licenses granted to the Company into non‑exclusive, non‑sublicensable licenses, in the case of (a) the Company’s uncured material breach upon 30 days’ written notice (which shall be extended to 90 days if the Company is diligently attempting to cure such material breach), (b) the Company’s failure to achieve the specified development and funding milestone events, or (c) the Company’s insolvency. The Company recorded research and development expense related to the Columbia Agreement of $0.6 million and $0.5 million for the years ended December 31, 2017 and 2018, respectively, and $1.4 million from the execution of the Columbia Agreement through December 31, 2018. Columbia University is a related party as they have been issued shares of the Company’s common stock. As of December 31, 2017, the Company had $0.2 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable. As of December 31, 2018, the Company had $0.1 million due to Columbia University included in accrued expenses and $0.1 million included in accounts payable.

FAIR VALUE MEASUREMENTS_2

FAIR VALUE MEASUREMENTS	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	3. FAIR VALUE MEASUREMENTS The following table summarizes, as of September 30, 2019, the Company's financial assets and liabilities that are measured at fair value on a recurring basis, according to the fair value hierarchy described in the significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus. As of December 31, 2018, the Company did not have financial assets or liabilities that are measured at fair value on a recurring basis (in thousands). As of September 30, 2019 Level 1 Level 2 Level 3 Total Cash $ 12,933 $ — $ — $ 12,933 Money market funds 133 — — 133 Total cash and cash equivalents $ 13,065 $ — $ — $ 13,065 Commercial paper and corporate bonds — 7,522 — 7,522 U.S. government agency debt securities — 12,367 — 12,367 Total marketable securities $ — $ 19,889 $ — $ 19,889 Total financial assets measured at fair value on a recurring basis $ 13,065 $ 19,889 $ — $ 32,954 Investments in commercial paper, corporate bonds, and U.S. government agency debt securities have been classified as Level 2 as they are valued using quoted prices in less active markets or other directly or indirectly observable inputs. Fair values of corporate bonds and U.S. government agency debt securities were derived from a consensus or weighted average price based on input of market prices from multiple sources at each reporting period. With regard to commercial paper, all of the securities had high credit ratings and one year or less to maturity; therefore, fair value was derived from accretion of purchase price to face value over the term of maturity or quoted market prices for similar instruments if available. During the three and nine months ended September 30, 2019, there were no transfers of financial assets between Level 1 and Level 2. During the three and nine months ended September 30, 2018, the Company had Level 1 financial assets (cash) and Level 3 financial liabilities that were measured at fair value on a recurring basis. The Company's convertible promissory notes issued on February 5, 2018 (the "2018 Notes") (see Note 4), contained certain features which met the criteria to be bifurcated and accounted for separately from the 2018 Notes (the "Derivative Liability"). Also in connection with the issuance of the 2018 Notes, the Company had a contingent obligation to issue common stock warrants ("2018 Notes Warrants") upon the conversion of the 2018 Notes into Series B convertible preferred stock ("Series B Preferred Stock") (the "Warrant Liability"). The Derivative Liability and the Warrant Liability were initially recorded at fair value of $1.9 million and $0.1 million, respectively, and were subsequently remeasured at fair value at each reporting period. In November 2018, the Derivative Liability was settled in connection with the extinguishment of the 2018 Notes (see Note 4). The following table provides a roll forward of the aggregate fair values of the Derivative Liability and Warrant Liability as of September 30, 2018, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 180 6 Balance as of March 31, 2018 $ 2,076 $ 80 Change in fair value 294 21 Balance as of June 30, 2018 $ 2,370 $ 101 Change in fair value 335 38 Balance as of September 30, 2018 $ 2,704 $ 139 Changes in the fair value of the Derivative Liability and Warrant Liability were recognized in other income (expense), net in the condensed statement of operations. The Company recognized other expense in connection with the Derivative Liability of $0.3 million and $0.8 million during the three and nine months ended September 30, 2018, respectively. The Company recognized other income in connection with the Warrant Liability of $38 thousand and $65 thousand during the three and nine months ended September 30, 2018, respectively.	3. FAIR VALUE MEASUREMENTS During the year ended December 31, 2018, the Company had level 3 financial liabilities that were measured at fair value on a recurring basis that were no longer outstanding as of December 31, 2018. There were no transfers between fair value hierarchy levels during the year ended December 31, 2018. There were no financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017. Derivative Liability The Company’s convertible promissory notes issued on February 5, 2018 (the “2018 Notes”) (see Note 4), contained certain features which met the criteria to be bifurcated and accounted for separately from the 2018 Notes (the “Derivative Liability”). The Derivative Liability was recorded at fair value of $1.9 million upon the issuance of the 2018 Notes and was subsequently remeasured at fair value at each reporting period and immediately before extinguishment. Changes in the fair value of the Derivative Liability were recognized as a component of other income (expense), net in the statement of operations. The Derivative Liability was initially valued and remeasured using a “with‑and‑without” method. The “with‑and‑without” methodology involves valuing the whole instrument on an as‑is basis and then valuing the instrument without the individual embedded derivative. The difference between the entire instrument with the embedded derivative compared to the instrument without the embedded derivative is the fair value of the derivative, recorded as the Derivative Liability. The Derivative Liability is settled when the underlying debt instrument is settled either through conversion or extinguishment into equity at a variable price, which is a redemption feature, or held to maturity. In November 2018, the Derivative Liability was settled in connection with the extinguishment of the 2018 Notes. Warrant Liability In connection with the issuance of the 2018 Notes, the Company had a contingent obligation to issue common stock warrants (“2018 Notes Warrants”) upon the conversion of the 2018 Notes into Series B convertible preferred stock (“Series B Preferred Stock”) (see Note 6 and Note 7). As the obligation to issue the 2018 Notes Warrants was not initially for a fixed number of warrants, it was recorded as a liability (the “Warrant Liability”) at fair value of $0.1 million upon the issuance of the 2018 Notes and was subsequently remeasured at fair value each reporting period and immediately before the 2018 Notes were extinguished. Changes in the fair value of the Warrant Liability were recognized in other income (expense), net in the statement of operations. In November 2018, in connection with the conversion of the 2018 Notes into Series B Preferred Stock, the 2018 Notes Warrants were issued and reclassified to equity. The 2018 Notes Warrants were initially valued and remeasured using a Black‑Scholes option pricing model with the range of assumptions as follows: Contractual term (in years) 10.0 Volatility 74.48% - 76.56% Risk-free interest rate 2.85% - 3.20% Dividend yield 0.00% The following table provides a roll forward of the aggregate fair values of the Company’s Derivative Liability and Warrant Liability, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 972 168 Extinguishment of Derivative Liability in connection with extinguishment of 2018 Notes (2,868) — Reclassification of Warrant Liability into 2018 Notes Warrants — (242) Balance as of December 31, 2018 $ — $ — The inputs utilized by management to value the Derivative Liability and 2018 Notes Warrants are highly subjective. The assumptions used in calculating the fair value of the Derivative Liability and 2018 Notes Warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the Derivative Liability and 2018 Notes Warrants may be materially different in the future.

INVESTMENTS

INVESTMENTS	9 Months Ended
	Sep. 30, 2019
INVESTMENTS
INVESTMENTS	4. INVESTMENTS Marketable Securities Marketable securities, which the Company classifies as available-for-sale securities, primarily consist of high quality commercial paper, corporate bonds, and U.S. government debt obligations. Marketable securities with remaining effective maturities of twelve months or less from the balance sheet date are classified as short-term; otherwise, they are classified as long-term on the condensed consolidated balance sheets. The following tables provide the Company’s marketable securities by security type as of September 30, 2019 and December 31, 2018 (in thousands): As of September 30, 2019 Gross Gross Unrealized Unrealized Estimated Cost Gains Losses Fair Value Commercial Paper and corporate bonds $ 7,527 $ — $ (5) $ 7,522 US government agency debt security 12,351 16 — 12,367 Total $ 19,878 $ 16 $ (5) $ 19,889 Contractual maturities of the Company’s marketable securities as of September 30, 2019 and December 31, 2018 are summarized as follows (in thousands): As of September 30, 2019 Gross Gross Unrealized Unrealized Estimated Cost Gains Losses Fair Value Due in one year or less $ 19,878 $ 16 $ (5) $ 19,889 Total $ 19,878 $ 16 $ (5) $ 19,889 At September 30, 2019, the Company had $11 thousand of net unrealized gains primarily due to an increase in the fair value of certain U.S. government agency debt securities. During the three and nine months ended September 30, 2019, the Company recorded no net realized gains or losses from the sale of marketable securities. As of September 30, 2019, we did not intend to sell and it was not likely that we would be required to sell these investments before recovery of their amortized cost basis, which may be at maturity. Unrealized losses related to these investments are primarily due to interest rate fluctuations as opposed to changes in credit quality. Therefore, as of September 30, 2019, we have recognized no other-than-temporary impairment loss.

CONVERTIBLE PROMISSORY NOTES_2

CONVERTIBLE PROMISSORY NOTES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
CONVERTIBLE PROMISSORY NOTES
CONVERTIBLE PROMISSORY NOTES	5. CONVERTIBLE PROMISSORY NOTES There were no convertible promissory notes outstanding as of September 30, 2019 and December 31, 2018. On February 5, 2018, the Company issued the 2018 Notes in the aggregate principal amount of $6.0 million. The 2018 Notes bore interest at a rate of 15.0% per annum, were unsecured and were due and payable, including accrued interest, on August 8, 2019. In the event of a qualified sale of preferred stock to one or more investors resulting in gross proceeds to the Company of at least $8.0 million, all principal and accrued and unpaid interest under the 2018 Notes was automatically convertible into a number of shares of the Company’s preferred stock issued in such a financing equal to the outstanding principal and accrued but unpaid interest under the 2018 Notes, divided by an amount equal to 80% of the lowest price per share of the preferred stock sold in the financing. In the event of a corporate transaction or change of control event, the 2018 Notes contained a put option whereby the Company was required to pay to the holders of 2018 Notes an amount equal to (i) the principal amount then outstanding under the 2018 Notes plus any accrued but unpaid interest, plus (ii) an amount equal to 30% of the outstanding principal amount. The terms of the 2018 Notes provided that: (i) all outstanding principal and interest was due and payable in cash upon an event of acceleration, as defined in the 2018 Notes agreement; (ii) amounts outstanding under the notes were not prepayable without the written consent of the holders of more than 50% of the outstanding principal of the notes, and in addition to the balance the Company will prepay, the Company will also pay the noteholders an amount equal to 15% of the principal amount of the notes that the Company is prepaying; and (iii) with respect to subordination, the Company has no outstanding indebtedness for borrowed money or any other liabilities, other than accounts payable arrangements with vendors entered into in the ordinary course of business and consistent with usual trade terms and will not issue or incur additional indebtedness for borrowed money while the 2018 Notes remain outstanding. There were no financial or negative covenants associated with the convertible promissory notes. The Derivative Liability represents the conversion feature in the event of a qualified financing and the put option, each of which met the definition of an embedded derivative and were required to be combined and accounted for as a separate unit of accounting. The Company recorded the issuance-date fair value of the Derivative Liability of $1.9 million as a debt discount and Derivative Liability in the Company’s balance sheet (see Note 3) . In connection with the 2018 Notes, the Company paid legal costs and bank fees of $0.4 million and were obligated to issue the 2018 Notes Warrants (see Note 3 and Note 9) with an initial fair value of $0.1 million, which were capitalized and recorded as a debt discount. The debt discount, which included the Derivative Liability and 2018 Notes Warrants, was amortized at an effective interest rate of 54.9% using the effective interest method over the term of the loan. In connection with the 2018 Notes, the Company recognized interest expense of $0.6 million and $1.4 million during the three and nine months ended September 30, 2018, respectively. The interest expense includes amortization of the debt discount of $0.8 million and $0.3 million for the three and nine months ended September 30, 2018 , respectively . In November 2018, in connection with the Company’s issuance and sale of Series B Preferred Stock, all of the then-outstanding principal and accrued interest under the 2018 Notes, totaling $6.6 million, was automatically converted into 1,097,721 shares of Series B Preferred Stock at a price equal to 80% of the $7.49 per share price paid by investors in the Series B Preferred Stock financing.	4. CONVERTIBLE PROMISSORY NOTES On February 5, 2018, the Company issued the 2018 Notes in the aggregate principal amount of $6.0 million. The 2018 Notes bore interest at a rate of 15.0% per annum, were unsecured and were due and payable, including accrued interest, on August 8, 2019. In the event of a qualified sale of preferred stock to one or more investors resulting in gross proceeds to the Company of at least $8.0 million, all principal and accrued and unpaid interest under the 2018 Notes was automatically convertible into a number of shares of the Company’s preferred stock issued in such a financing equal to the outstanding principal and accrued but unpaid interest under the 2018 Notes, divided by an amount equal to 80% of the lowest price per share of the preferred stock sold in the financing. In the event of a corporate transaction or change of control event, the 2018 Notes contained a put option whereby the Company was required to pay to the holders of 2018 Notes an amount equal to (i) the principal amount then outstanding under the 2018 Notes plus any accrued but unpaid interest, plus (ii) an amount equal to 30% of the outstanding principal amount. The terms of the 2018 Notes provided that (i) all outstanding principal and interest was due and payable in cash upon an event of acceleration, as defined in the 2018 Notes agreement; (ii) amounts outstanding under the 2018 Notes were not prepayable without the written consent of the holders of more than 50% of the outstanding principal of the 2018 Notes, and in addition to the balance the Company will prepay, the Company will also pay the noteholders an amount equal to 15% of the principal amount of the 2018 Notes that the Company is prepaying; and (iii) with respect to subordination, the Company has no outstanding indebtedness for borrowed money or any other liabilities, other than accounts payable arrangements with vendors entered into in the ordinary course of business and consistent with usual trade terms and will not issue or incur additional indebtedness for borrowed money while the 2018 Notes remain outstanding. There were no financial or negative covenants associated with the 2018 Notes. The Derivative Liability represents the conversion feature in the event of a qualified financing and the put option, which each met the definition of an embedded derivative and were required to be combined and accounted for as a separate unit of accounting. The Company recorded the issuance‑date fair value of the Derivative Liability of $1.9 million as a debt discount and Derivative Liability in the Company’s balance sheet. In connection with the 2018 Notes, the Company paid legal costs and bank fees of $0.4 million and was obligated to issue the 2018 Notes Warrants (see Note 3 and Note 7) with an initial fair value of $0.1 million, which were capitalized and recorded as a debt discount. The debt discount, which included legal costs, bank fees, the Derivative Liability and 2018 Notes Warrants, was amortized using the effective interest method over the term of the loan. The Company recognized interest expense of $1.6 million, including amortization of the debt discount of $0.9 million, during the year ended December 31, 2018 in connection with the 2018 Notes. In November 2018, in connection with the Company’s issuance and sale of Series B Preferred Stock, all of the outstanding principal and accrued interest under the 2018 Notes, totaling $6.6 million, was automatically converted into 1,097,721 shares of Series B Preferred Stock at a price equal to 80% of the $7.49 per share price paid by investors in the Series B Preferred Stock financing. The Company accounted for the conversion of the 2018 Notes as a debt extinguishment and recognized a loss on extinguishment of debt of $0.2 million within other income (expense), net in the Company’s statement of operations and $0.1 million within additional paid‑in‑capital related to the amount of unpaid and accrued interest as of the extinguishment date that was not converted into Series B Preferred Stock. The loss on extinguishment was calculated as the difference between (i) the fair value of the 1,097,721 shares of Series B convertible preferred stock issued to settle the 2018 Notes of $8.2 million and (ii) the carrying value of the 2018 Notes, net of the unamortized debt discount, of $5.1 million plus the then‑current fair value of the Derivative Liability associated with the 2018 Notes at the time of the extinguishment of $2.9 million.

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	9 Months Ended
	Sep. 30, 2019
PREPAID EXPENSES AND OTHER CURRENT ASSETS
PREPAID EXPENSES AND OTHER CURRENT ASSETS	6. PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2019 2018 Deferred offering costs $ — $ 310 Prepaid research and development expenses 1,543 1,044 Prepaid rent expenses 78 65 Prepaid insurance expenses 1,934 1 Other prepaid expenses and current assets 525 78 Total prepaid expenses & other current assets $ 4,080 $ 1,498

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	9 Months Ended
	Sep. 30, 2019
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	7. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2019 2018 Accrued pre-clinical and clinical expenses $ 3,684 $ 865 Accrued professional fees 248 312 Accrued compensation and benefits 640 56 Accrued patent expenses 65 126 Other 192 54 Total accrued expenses & other current liabilities $ 4,829 $ 1,413

STOCK BASED COMPENSATION_2

STOCK BASED COMPENSATION	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCK BASED COMPENSATION
STOCK BASED COMPENSATION	8 . STOCK‑BASED COMPENSATION Equity Incentive Plans In May 2019, the Company's board of directors (the "Board") adopted its 2019 Equity Incentive Plan ("2019 Plan"), which was subsequently approved by its stockholders and became effective on May 13, 2019. As a result, no additional awards under the Company's 2016 Equity Incentive Plan, as amended (the "2016 Plan") will be granted and all outstanding stock awards granted under the 2016 Plan that are repurchased, forfeited, expired or are cancelled will become available for grant under the 2019 Plan in accordance with its terms. The 2016 Plan will continue to govern outstanding equity awards granted thereunder. The 2019 Plan provides for the issuance of incentive stock options ("ISOs") to employees, and for the grant of nonstatutory stock options ("NSOs"), stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards and other forms of stock awards to the Company's employees, officers and directors, as well as non- employees, consultants and affiliates to the Company. Under the terms of the 2019 Plan, stock options may not be granted at an exercise price less than fair market value of the Company's common stock on the date of the grant. The 2019 Plan will be administered by the Compensation Committee of the Company's Board. Initially, subject to adjustments as provided in the 2019 Plan, the maximum number of the Company's common stock that may be issued under the 2019 Plan is 4,530,000 shares, which is the sum of (i) 1,618,841 new shares, plus (ii) the number of shares (not to exceed 2,911,159 shares) that remained available for the issuance of awards under the 2016 Plan, at the time the 2019 Plan became effective, and (iii) any shares subject to outstanding stock options or other stock awards granted under the 2016 Plan that are forfeited, expired, or reacquired. The 2019 Plan provides that the number of shares reserved and available for issuance under the 2019 Plan will automatically increase each January 1, beginning on January 1, 2020, by 5% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. Subject to certain changes in capitalization of the Company, the aggregate maximum number of shares of common stock that may be issued pursuant to the exercise of ISOs shall be equal to 13,000,000 shares of common stock. Stock options awarded under the 2019 Plan expire 10 years after grant and typically vest over four years. As of September 30, 2019, there were options to purchase 3,767,571 shares of common stock outstanding under the 2016 Plan and 2019 Plan and 680,441 shares of common stock were available for future issuance under the 2019 Plan. Stock-Based Compensation Expense Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2019 and 2018 was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 495 $ 38 $ 2,087 $ 88 General and administrative 724 39 2,736 92 Total stock-based compensation expense $ 1,219 $ 78 $ 4,823 $ 180 During the nine months ended September 30, 2019, the Company granted options to purchase 2,657,628 shares of common stock. The Company recorded stock-based compensation expense for options granted during the three and nine months ended September 30, 2019 of $1.2 million and $4.8 million, respectively. As of September 30, 2019 and December 31, 2018, there were 3,767,571 and 1,202,979 options outstanding, respectively. The weighted‑average fair value of options granted during the nine months ended September 30, 2019 and 2018 was $4.71 and $1.03 per share, respectively. As of September 30, 2019, the total unrecognized stock‑based compensation balance for unvested options was $9.8 million expected to be recognized over a period of 1.8 years. The following table summarizes the information about options outstanding at September 30, 2019 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Options granted 2,657,628 7.34 Options exercised (81,988) 2.77 — Forfeited (11,048) 4.70 Expired — — Outstanding at September 30, 2019 3,767,571 $ 5.54 9.19 $ 20,860 Exercisable at September 30, 2019 1,364,658 $ 2.80 8.84 $ 11,174 Nonvested at September 30, 2019 2,402,913 $ 7.09 9.39 $ 9,686 In April 2019, the Company modified certain stock options, originally granted under the 2016 Plan. As a result of this modification, the Company accelerated the vesting for some of the stock options. There was no incremental stock-based compensation expense as a result of this modification as the fair-value-based measures of the modified awards immediately after the modification were less than the fair-value-based measures of the original awards immediately before the modification. Stock Options Granted to Employees that Contain Service, Performance and Market Conditions Included in the stock options granted during the nine months ended September 30, 2019 were 159,501 stock options that contain service-, performance- and market-based vesting conditions granted to the Company's interim Chief Financial Officer ("CFO") with a fair value at the grant date of $0.5 million, valued using the Monte-Carlo simulation model. The derived service period, calculated using the Monte-Carlo simulation model, ranged from one day to three years. The assumptions used in the Monte-Carlo simulation model were as follows: Nine Months Ended September 30, 2019 Time to expiration (in years) 10.0 Volatility 68.54 % Risk-free interest rate 2.64 % Dividend yield 0.00 % Cost of equity 24.00 % Fair value of underlying common stock (as of valuation date) $ 5.85 The compensation expense for these awards is recognized over the derived service period, or, if earlier, until the vesting condition is met. The condition for the performance-based stock options was based on the Company's completion of its IPO and the condition for the market-based stock options was based on the future price of the Company's common stock trading at or above a specified threshold. During the nine months ended September 30, 2019, 79,778 of the stock options containing service-, and performance-based vesting conditions were vested following the satisfaction of service- and performance-based conditions. In May 2019, the Company entered into a severance agreement, effective on May 31, 2019 ("Termination Date"), with the interim CFO. As part of this severance arrangement and as of the Termination Date, the Company accelerated the vesting of 79,723 unvested options, which were originally granted to the former CFO under the 2016 Plan. As a result of this modification, the Company recorded stock-based compensation expense of $0.6 million included in general and administrative expense for the three months and nine months ended September 30, 2019. The Company accounted for this modification as a Type III modification since, at the modification date, the expectation of the award vesting changed from improbable to probable. As a result, the stock-based compensation expense recognized was based on the modification-date fair value. As of September 30, 2019 there were no outstanding stock options containing service-, performance-, and market-based vesting conditions. During the three and nine months ended September 30, 2019, the Company incurred $0.7 million and $0.8 million, respectively, in stock-based compensation expense relating to the vesting of stock options containing service-, performance- and market-based vesting conditions, which includes the stock-based compensation expense resulting from the modification of these options in May 2019 and were included in general and administrative expense as of September 30, 2019. 2019 Employee Stock Purchase Plan In May 2019, the Company’s Board and its stockholders approved the 2019 Employee Stock Purchase Plan (the “2019 ESPP”), which became effective as of May 13, 2019. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares of common stock initially reserved for issuance under the ESPP was 180,000 shares. The ESPP provides for an annual increase on the first day of each year beginning in 2020 and ending in 2029, in each case subject to the approval of the Board, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the calendar month before the date of the automatic increase and (ii) 360,000 shares; provided that prior to the date of any such increase, the Board may determine that such increase will be less than the amount set forth in clauses (i) and (ii). As of September 30, 2019, no shares of common stock had been issued under the ESPP. The first offering period has not yet been decided by the Board.	5. STOCK‑BASED COMPENSATION In 2016, the Company adopted, and its stockholders approved, the 2016 Equity Incentive Plan, as amended (the “2016 Plan”), which provides for the granting of options at the discretion of the board of directors or any subcommittee of the Board to its employees, officers and independent contractors. Under the terms of the 2016 Plan, options may not be granted at an exercise price less than fair market value of the Company’s common stock on the date of the grant. As of December 31, 2017 and 2018, there were 1,345,469 shares and 2,966,241 shares, respectively, reserved by the Company to grant under the 2016 Plan and an aggregate of 1,083,041 shares and 1,708,179 shares, respectively remained available for future grants. Stock options awarded under the 2016 Plan expire 10 years after the grant and typically vest over three years. Total stock‑based compensation expense recorded for employees, directors and non‑employees during the years ended December 31, 2017 and 2018 was as follows (in thousands): Year Ended December 31, 2017 2018 Research and development $ — $ 140 General and administrative 32 132 Total stock-based compensation expense $ 32 $ 272 The weighted‑average fair value of options granted during the year ended December 31, 2017 and 2018 was $0.66 per share and $1.54 per share, respectively. As of December 31, 2017 and 2018, the total unrecognized stock‑based compensation balance for unvested options was $0.1 million and $1.3 million, respectively, which is expected to be recognized over 2.1 years as of each date. The total fair value of options vested during the year ended December 31, 2017 and 2018 was less than $1,000 and approximately $40,000, respectively. The following table summarizes the information about options outstanding at December 31, 2018 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2017 262,427 $ 0.90 9.09 $ 27 Options granted 995,633 $ 1.44 Options exercised (55,081) $ 0.84 33 Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Exercisable at December 31, 2018 73,692 $ 0.88 8.01 $ 282 Nonvested at December 31, 2018 1,129,287 $ 1.38 9.22 $ 3,747 Valuation Assumptions The fair value of each option award granted is estimated on the date of the grant using the Black‑Scholes option valuation model based on the weighted average assumptions noted in the table below for those options granted in the years ended December 31, 2017 and 2018. Year Ended December 31, December 31, 2017 2018 Expected term (in years) 6.0 5.9 Volatility 75.06 % 71.78 % Risk-free interest rate 2.09 % 2.71 % Dividend yield 0.00 % 0.00 %

STOCKHOLDERS' EQUITY_2

STOCKHOLDERS' EQUITY	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019
STOCKHOLDERS’ EQUITY
STOCKHOLDERS’ EQUITY	9. STOCKHOLDERS’ EQUITY Common Stock The holders of the common stock are entitled to one vote for each share of common stock held at all meetings of the stockholders. There are no cumulative voting rights. Preferred Stock In February 2019, the Company issued 442,930 shares of Series B Preferred Stock at $7.49 per share for gross proceeds of approximately $3.3 million. Issuance costs were $0.3 million, which included the obligation to issue warrants to purchase common stock (see Note 10). Upon completion of the IPO, all 7,538,671 shares of outstanding Series A Preferred Stock (“Series A Preferred Stock”) and Series B Preferred Stock (collectively , "the Preferred Stock") was converted into common stock on a one-to-one basis. As of September 30, 2019, there were no shares of preferred stock outstanding. As of December 31, 2018, the Preferred Stock consisted of the following (in thousands, except share data): December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746 The rights and privileges of the preferred stockholders were as follows: Voting The holders of Preferred Stock had the right to one vote for each share of common stock into which such Preferred Stock could be converted and will vote together with the holders of common stock as a single class. Dividends Dividends were payable to holders of Preferred Stock prior to payment of any dividend to holders of common stock. Dividends were payable when and if declared out of funds legally available and such dividends were not cumulative. In the event the Board declared a dividend payable on the common stock, the holders of the Preferred Stock were entitled to receive the amount of dividends per share of Preferred Stock that would be payable on the number of whole shares of the common stock into which each share of such Preferred Stock held by each holder could be converted into. Liquidation Prior to the IPO, in the event of any liquidation, dissolution or winding up of the Company, or a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding would have been entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock by reason of their ownership thereof, in an amount per share equal to the greater of (i) the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) plus any dividends declared but unpaid thereon or (ii) such amount per share as would have been payable had each series of Preferred Stock been converted into common stock immediately prior to a liquidation, dissolution or winding up of the Company or Deemed Liquidation Event. If upon any such liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, the proceeds would have been insufficient to pay the holders of shares of Preferred Stock the full amount to which they shall be entitled, the holders of shares of Preferred Stock would have shared ratably in any distribution of the proceeds in proportion to the respective amounts which would have otherwise been payable in respect of the shares of Preferred Stock held by them upon such distribution if all amounts payable with respect to such shares were paid in full. After the payment of all preferential amounts to be paid to the holders of shares of Preferred Stock, the remaining proceeds would have been distributed among the holders of shares of common stock pro rata based on the number of shares held by each such holder. A Deemed Liquidation Event was defined as: (i) a merger where the Company is a constituent party or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to such merger or consolidation, except any such merger or consolidation involving the Company or a subsidiary in which the shares of capital stock of the Company outstanding immediately prior to such merger or consolidation continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following such merger or consolidation, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such merger or consolidation, the parent corporation of such surviving or resulting corporation; or (ii) the sale, lease, transfer, exclusive license or other disposition, in a single transaction or series of related transactions, by the Company or any subsidiary of the Company of all or substantially all the assets of the Company and its subsidiaries taken as a whole, or the sale or disposition (whether by merger or otherwise) of one or more subsidiaries of the Company if substantially all of the assets of the Company and its subsidiaries taken as a whole are held by such subsidiary or subsidiaries, except where such sale, lease, transfer, exclusive license or other disposition is to a wholly owned subsidiary of the Company. Protective Provisions Prior to the IPO, at any time when any shares of Preferred Stock remained outstanding, the Company could not take any of the following actions without the vote or written consent of the holders of a majority of the then outstanding shares of Preferred Stock separately as a class: (i) liquidate, dissolve or wind-up the business and affairs of the Company, effect any merger, consolidation or any other Deemed Liquidation Event, or consent to any of the foregoing, in each case other than in the event that such event would provide the holders of the Preferred Stock a return per each share of Preferred Stock, including all distributions and dividends paid to such holders prior to such event by the Company, if any, of at least two (2) times the Series B original issue price in the twenty-four (24) months following the Series B original issue date (November 5, 2018) or three (3) times the Series B original issue price thereafter; (ii) amend, alter, or repeal any provision of the Certificate of Incorporation or the Company’s bylaws in a manner that adversely affects the powers, preferences or rights of the Preferred Stock; (iii) create, or authorize the creation of, or issue or obligate itself to issue shares of, any additional class or series of capital stock unless the same ranks junior to the Preferred Stock with respect to the distribution of assets on the liquidation, dissolution or winding up of the Company, the payment of dividends and rights of redemption, or increase the authorized number of shares of Preferred Stock; (iv) purchase or redeem (or permit any subsidiary to purchase or redeem) or pay or declare any dividend or make any distribution on, any shares of capital stock of the Company other than (a) redemptions of or dividends or distributions on the Preferred Stock as expressly authorized herein, (b) dividends or other distributions payable on the common stock solely in the form of additional shares of common stock and (c) repurchases of stock from former employees, officers, directors, consultants or other persons who performed services for the Company or any subsidiary in connection with the cessation of such employment or service at the lower of the original purchase price or the then-current fair market value thereof; (v) create, or authorize the creation of, or issue, or authorize the issuance of any debt security, or permit any subsidiary to take any such action with respect to any debt security, if the aggregate indebtedness of the Company and its subsidiaries for borrowed money following such action would exceed $2.0 million other than equipment leases or bank lines of credit; (vi) create, or hold capital stock in, any subsidiary that is not wholly owned (either directly or through one or more other subsidiaries) by the Company, or sell, transfer or otherwise dispose of any capital stock of any direct or indirect subsidiary of the Company, or permit any direct or indirect subsidiary to sell, lease, transfer, exclusively license or otherwise dispose (in a single transaction or series of related transactions) of all or substantially all of the assets of such subsidiary; or (vi) increase or decrease the authorized number of directors of the Company. Optional Conversion Rights Each share of Preferred Stock was convertible, at the option of the holder thereof, at any time and from time to time after issuance, and without the payment of additional consideration into such number of fully paid and nonassessable shares of common stock as is determined by dividing the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) by the series conversion price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) in effect at the time of conversion. Mandatory Conversion Rights All outstanding shares of Preferred Stock were to be automatically converted into shares of common stock, at the then effective conversion rate, upon either (a) the closing of the sale of shares of common stock to the public in a firm-commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, resulting in at least $30.0 million of proceeds, net of the underwriting discount and commissions, to the Company, or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of at least a majority of the then outstanding shares of Preferred Stock. Redemption The Preferred Stock was redeemable upon the occurrence of a Deemed Liquidation Event, which would not be solely in control of the Company. Therefore, the Preferred Stock was classified as temporary equity.	6. STOCKHOLDERS’ EQUITY As of December 31, 2018, the authorized capital stock of the Company consists of 20,441,982 shares of common stock, par value $0.0001 per share, and 10,883,950 shares of convertible preferred stock, par value $0.0001 per share, of which 3,093,898 are designated as Series A convertible preferred stock (“Series A Preferred Stock”) and 7,790,052 are designated as Series B Preferred Stock (collectively, with the Series A Preferred Stock, the “Preferred Stock”). As of December 31, 2017, the Company had 5,458,450 shares of common stock issued and outstanding and 3,093,898 shares of Series A Preferred Stock issued and outstanding. As of December 31, 2018, the Company had 5,513,531 shares of common stock issued and outstanding, 3,093,898 shares of Series A Preferred Stock issued and outstanding and 4,001,848 shares of Series B Preferred Stock issued and outstanding. Common Stock In February 2017, the Company issued 486,077 shares of common stock, with a fair value of $0.5 million, as consideration pursuant to a license agreement with Columbia University (see Note 2). Voting The holders of the common stock are entitled to one vote for each share of common stock held at all meetings of the stockholders. There is no cumulative voting. Preferred Stock In January 2017, the Company issued 3,093,898 shares of Series A Preferred Stock at $2.26 per share for gross proceeds of $7.0 million. Issuance costs were $0.7 million, which included the issuance of warrants to purchase common stock (see Note 7). Between November and December 2018, the Company issued an aggregate of 2,904,127 shares of its Series B Preferred Stock at $7.49 per share for gross proceeds of $21.7 million. Issuance costs were $0.8 million, which included the obligation to issue warrants to purchase common stock (see Note 7). In addition, all of the outstanding principal and accrued interest under the 2018 Notes were automatically converted into an aggregate of 1,097,721 shares of its Series B Preferred Stock. As of December 31, 2017 and 2018, Preferred Stock consisted of the following (in thousands, except share data): December 31, 2017 Preferred Preferred Stock Issued Common Stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 Total 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 Total 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746 The following is a summary of the rights and privileges of the common and preferred stockholders as of December 31, 2018: Voting The holders of Preferred Stock have the right to one vote for each share of common stock into which such Preferred Stock could be converted and will vote together with the holders of common stock as a single class. Dividends Dividends are payable to holders of Preferred Stock prior to payment of any dividend to holders of common stock. Dividends are payable when and if declared out of funds legally available and such dividends are not cumulative. In the event the board of directors of the Company declares a dividend payable on the common stock, the holders of the Preferred Stock would be entitled to receive the amount of dividends per share of Preferred Stock that would be payable on the number of whole shares of the common stock into which each share of such Preferred Stock held by each holder could be converted into. Liquidation In the event of any liquidation, dissolution or winding up of the Company, or a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding are entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock by reason of their ownership thereof, in an amount per share equal to the greater of (i) the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) plus any dividends declared but unpaid thereon or (ii) such amount per share as would have been payable had each series of Preferred Stock been converted into common stock immediately prior to a liquidation, dissolution or winding up of the Company or Deemed Liquidation Event. If upon any such liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, the proceeds shall be insufficient to pay the holders of shares of Preferred Stock the full amount to which they shall be entitled, the holders of shares of Preferred Stock shall share ratably in any distribution of the proceeds in proportion to the respective amounts which would otherwise be payable in respect of the shares of Preferred Stock held by them upon such distribution if all amounts payable with respect to such shares were paid in full. After the payment of all preferential amounts to be paid to the holders of shares of Preferred Stock, the remaining proceeds shall be distributed among the holders of shares of common stock pro rata based on the number of shares held by each such holder. A Deemed Liquidation Event is defined as: (i) a merger where the Company is a constituent party or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to such merger or consolidation, except any such merger or consolidation involving the Company or a subsidiary in which the shares of capital stock of the Company outstanding immediately prior to such merger or consolidation continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following such merger or consolidation, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such merger or consolidation, the parent corporation of such surviving or resulting corporation; or (ii) the sale, lease, transfer, exclusive license or other disposition, in a single transaction or series of related transactions, by the Company or any subsidiary of the Company of all or substantially all the assets of the Company and its subsidiaries taken as a whole, or the sale or disposition (whether by merger or otherwise) of one or more subsidiaries of the Company if substantially all of the assets of the Company and its subsidiaries taken as a whole are held by such subsidiary or subsidiaries, except where such sale, lease, transfer, exclusive license or other disposition is to a wholly owned subsidiary of the Company. Protective Provisions At any time when any shares of Preferred Stock remain outstanding, the Company shall not take any of the following actions without the vote or written consent of the holders of a majority of the then outstanding shares of Preferred Stock separately as a class: (i) liquidate, dissolve or wind‑up the business and affairs of the Company, effect any merger, consolidation or any other Deemed Liquidation Event, or consent to any of the foregoing, in each case other than in the event that such event would provide the holders of the Preferred Stock a return per each share of Preferred Stock, including all distributions and dividends paid to such holders prior to such event by the Company, if any, of at least two (2) times the Series B Original Issue Price in the twenty‑four (24) months following the Series B Original Issue Date (November 5, 2018) or three (3) times the Series B Original Issue Price thereafter; (ii) amend, alter, or repeal any provision of the Certificate of Incorporation or the Company’s bylaws in a manner that adversely affects the powers, preferences or rights of the Preferred Stock; (iii) create, or authorize the creation of, or issue or obligate itself to issue shares of, any additional class or series of capital stock unless the same ranks junior to the Preferred Stock with respect to the distribution of assets on the liquidation, dissolution or winding up of the Company, the payment of dividends and rights of redemption, or increase the authorized number of shares of Preferred Stock; (iv) purchase or redeem (or permit any subsidiary to purchase or redeem) or pay or declare any dividend or make any distribution on, any shares of capital stock of the Company other than (a) redemptions of or dividends or distributions on the Preferred Stock as expressly authorized herein, (b) dividends or other distributions payable on the common stock solely in the form of additional shares of common stock and (c) repurchases of stock from former employees, officers, directors, consultants or other persons who performed services for the Company or any subsidiary in connection with the cessation of such employment or service at the lower of the original purchase price or the then‑current fair market value thereof; (v) create, or authorize the creation of, or issue, or authorize the issuance of any debt security, or permit any subsidiary to take any such action with respect to any debt security, if the aggregate indebtedness of the Company and its subsidiaries for borrowed money following such action would exceed $2.0 million other than equipment leases or bank lines of credit; (vi) create, or hold capital stock in, any subsidiary that is not wholly owned (either directly or through one or more other subsidiaries) by the Company, or sell, transfer or otherwise dispose of any capital stock of any direct or indirect subsidiary of the Company, or permit any direct or indirect subsidiary to sell, lease, transfer, exclusively license or otherwise dispose (in a single transaction or series of related transactions) of all or substantially all of the assets of such subsidiary; or (vi) increase or decrease the authorized number of directors of the Company. Optional Conversion Rights Each share of Preferred Stock is convertible, at the option of the holder thereof, at any time and from time to time after issuance, and without the payment of additional consideration into such number of fully paid and nonassessable shares of common stock as is determined by dividing the original issue price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) by the series conversion price ($2.26 per share for Series A Preferred Stock and $7.49 per share for Series B Preferred Stock) in effect at the time of conversion. As of December 31, 2018, the Preferred Stock is convertible in to common stock on a one‑for‑one basis. Mandatory Conversion Rights All outstanding shares of Preferred Stock shall automatically be converted into shares of common stock, at the then effective conversion rate, upon either (a) the closing of the sale of shares of common stock to the public in a firm‑commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, resulting in at least $30.0 million of proceeds, net of the underwriting discount and commissions, to the Company, or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of at least a majority of the then outstanding shares of Preferred Stock. Redemption The Preferred Stock is redeemable upon the occurrence of a Deemed Liquidation Event, which is not solely in control of the Company. Therefore, the Preferred Stock has been classified as temporary equity.

WARRANTS_2

WARRANTS	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
WARRANTS
WARRANTS	10. WARRANTS Warrants Issued with the 2018 Notes On January 18, 2018, the Company entered into a placement agent agreement through which it became obligated to issue common stock warrants in connection with the issuance of the 2018 Notes. The obligation to issue the 2018 Notes Warrants was recorded as a liability at its fair value (see Note 3), which was initially $0.1 million, and was included in the issuance costs of the 2018 Notes (see Note 4). On November 5, 2018, in connection with the extinguishment of the 2018 Notes into shares of Series B Preferred Stock, the Company issued the 2018 Notes Warrants, which were equity‑classified warrants upon issuance, to purchase 76,847 shares of common stock, valued at $0.3 million. The 2018 Notes Warrants vested immediately upon issuance and have an exercise price of $6.59 per share and expire on November 4, 2028. Warrants Issued with Series B Preferred Stock In November and December 2018, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue warrants to purchase 72,261 shares of common stock (collectively the “2018 Warrants”), valued in the aggregate at $0.2 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 8). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2018 Warrants was estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 % In February 2019, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue warrants to purchase 23,867 shares of common stock (collectively the “2019 Warrants”), valued in the aggregate at $0.1 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 8). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2019 Warrants was estimated using the Black-Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 % The inputs utilized by management to value the warrants are highly subjective. The assumptions used in calculating the fair value of the warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the warrants may be materially different in the future.	7. WARRANTS Warrants Issued with Series A Preferred Stock On January 26, 2017, in connection with the sale and issuance of the Series A Preferred Stock, the Company issued equity‑classified warrants to purchase 309,389 shares of common stock (the “2017 Warrants”), valued at $0.2 million, and included in the issuance costs of the Series A Preferred Stock (see Note 4). The warrants vested immediately and have an exercise price of $2.49 per share and expire on March 13, 2027. The fair value of warrants issued is estimated using the Black‑Scholes option pricing model with the following assumptions for the 2017 Warrants. Contractual term (in years) 10.0 Volatility 76.95 % Risk-free interest rate 2.62 % Dividend yield 0.00 % Warrants Issued with the 2018 Notes On January 18, 2018, the Company entered into a placement agent agreement through which it became obligated to issue common stock warrants in connection with the issuance of the 2018 Notes. The obligation to issue the 2018 Notes Warrants was recorded as a liability at its fair value (see Note 3), which was initially $0.1 million, and was included in the issuance costs of the 2018 Notes (see Note 4). On November 5, 2018, in connection with the extinguishment of the 2018 Notes into shares of Series B Preferred Stock, the Company issued the 2018 Notes Warrants, which were equity‑classified warrants upon issuance, to purchase 76,847 shares of common stock, valued at $0.3 million. The 2018 Notes Warrants vested immediately upon issuance and have an exercise price of $6.59 per share and expire on November 4, 2028. Warrants Issued with Series B Preferred Stock In November and December 2018, in connection with the sale and issuance of the Series B Preferred Stock, the Company was obligated to issue equity‑classified warrants to purchase 72,261 shares of common stock (collectively the “2018 Warrants”), valued in the aggregate at $0.2 million, which was included in the issuance costs for the Series B Preferred Stock (see Note 6). The warrants vest immediately upon issuance, have an exercise price of $8.24 per share and expire 10 years from the date of issuance. The fair value of the 2018 Warrants is estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 % The inputs utilized by management to value the warrants are highly subjective. The assumptions used in calculating the fair value of the warrants represent the Company’s best estimates, but these estimates involve inherent uncertainties and the application of management judgment. As a result, if factors change and the Company uses different assumptions, the fair value of the warrants may be materially different in the future.

INCOME TAXES_2

INCOME TAXES	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
INCOME TAXES
INCOME TAXES	11. INCOME TAXES During the three and nine months ended September 30, 2019 and the year ended December 31, 2018, the Company recorded a full valuation allowance on federal and state deferred tax assets since management does not forecast the Company to be in a profitable position in the near future.	8. INCOME TAXES The Company’s current tax provision for the years ended December 31, 2017 and 2018 is $0 and $0, respectively. The Company’s deferred tax provision for the years ended December 31, 2017 and 2018 is $0. Deferred income tax assets and liabilities consist of the following (in thousands): Year ended December 31, 2017 2018 Deferred tax assets Accrued expenses $ 335 $ — Stock‑based compensation 11 98 Capitalized startup costs 38 35 Net operating losses 1,200 6,176 Total deferred tax assets 1,584 6,309 Less: valuation allowance (1,584) (6,309) Net deferred tax asset (liability) $ — $ — Deferred tax assets result primarily from unutilized net operating losses, capitalized startup costs and timing differences as a result of the Company reporting its income tax returns. As of December 31, 2018, the Company had approximately $3.6 million of federal and state net operating losses (“NOLs”) carried forward expiring through 2037. Additionally, the Company generated approximately $14.2 million of NOLs in 2018 which, for federal income tax purposes, do not expire but are limited to offsetting up to 80% of future taxable income. The NOL carry forwards are subject to review and possible adjustment by the U.S. and state tax authorities. NOL carry forwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders, as defined under Sections 382 Internal Revenue Code. This could limit the amount of NOLs that the Company can utilize annually to offset future taxable income or tax liabilities. As of December 31, 2018, the Company has not performed such an analysis. Subsequent ownership changes and proposed future changes to tax rules in respect of the utilization of losses carried forward may further affect the limitation in future years. In assessing the realizability of the Company’s deferred tax assets, management considers whether or not it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company’s assessment is based on the weight of available evidence, including cumulative losses since inception and expected future losses and, as such, the Company does not believe it is more likely than not that the deferred tax assets will be realized. Accordingly, a full valuation allowance has been established and no deferred tax assets and related tax benefit have been recognized in the accompanying financial statements. At December 31, 2017 and 2018, the Company recorded valuation allowances of $1.6 million and $6.3 million, respectively, representing an increase in the valuation allowance of $4.7 million in 2018 due to the uncertainty regarding the realization of such deferred tax assets, to offset the benefits of net operating losses generated during those years. The U.S. federal statutory corporate tax rate reconciles to the Company’s effective tax rate for the years ended December 31, 2017 and 2018: Year Ended December 31, 2017 2018 Federal statutory rate 34.0 % 21.0 % State and local taxes net of federal tax benefit 11.3 13.5 Tax rate change (13.8) 0.3 Change in valuation allowance (32.2) (28.5) Permanently disallowed interest expense — (6.3) Other 0.7 — Total % % On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act (“Tax Act”), which made significant changes to the U.S. federal income tax law. The Tax Act affected 2018 and forward, including but not limited to a reduction in the federal corporate rate from 35.0% to 21.0%, elimination of the corporate alternative minimum tax, a new limitation on the deductibility of certain executive compensation, limitations on NOLs generated after December 31, 2017 and various other items. These changes did not have a material impact on the Company’s financial statements due to the accumulated NOLs in the United States.

NET LOSS PER COMMON SHARE_2

NET LOSS PER COMMON SHARE	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
NET LOSS PER COMMON SHARE
NET LOSS PER COMMON SHARE	12. NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing the net loss available to common stockholders by the weighted‑average number of shares of common stock outstanding during the period. Diluted net loss per common share is computed by giving the effect of all potential shares of common stock, including stock options, preferred shares, warrants and instruments convertible into common stock, to the extent dilutive. Basic and diluted net loss per common share was the same for the three and nine months ended September 30, 2019 and 2018, as the inclusion of all potential common shares outstanding would have been anti‑dilutive. The following table sets forth the computation of basic and diluted net loss per common share for the three and nine months ended September 30, 2019 and 2018 (in thousands, except share and per share data): Three Months Ended September 30, 2019 2018 Numerator: Net loss $ (10,713) $ (4,281) Denominator: Weighted-average common stock outstanding 17,095,870 5,497,871 Net loss per share attributable to common stockholders - basic and diluted $ (0.63) $ (0.78) Nine Months Ended September 30, 2019 2018 Numerator: Net loss $ (27,880) $ (9,802) Denominator: Weighted-average common stock outstanding 14,085,579 5,473,414 Net loss per share attributable to common stockholders - basic and diluted $ (1.98) $ (1.79) The Company’s potentially dilutive securities, which include Preferred Stock, stock options, and warrants, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted‑average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding for the three and nine months ended September 30, 2019 and 2018, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti‑dilutive effect: As of September 30, 2019 2018 Preferred Stock — 3,093,898 Options to purchase common stock 3,767,571 1,035,466 Warrants to purchase common stock 482,364 309,389	10. NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing the net loss available to common stockholders by the weighted‑average number of shares of common stock outstanding during the period. Diluted net loss per common share is computed by giving the effect of all potential shares of common stock, including stock options, preferred shares, warrants and instruments convertible into common stock, to the extent dilutive. Basic and diluted net loss per common share was the same for the years ended December 2017 and 2018, as the inclusion of all potential common shares outstanding would have been anti‑dilutive. The following table sets forth the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Years Ended December 31, 2017 2018 Numerator: Net loss $ (4,282) $ (16,521) Denominator: Weighted-average common stock outstanding 5,406,513 5,483,149 Net loss per share, basic and diluted $ (0.79) $ (3.01) The Company’s potential dilutive securities, which include Preferred Stock, stock options and warrants, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted‑average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at December 31, 2017 and 2018, from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti‑dilutive effect: As of December 31, 2017 2018 Preferred Stock 3,093,898 7,095,746 Options to purchase common stock 262,427 1,202,979 Warrants to purchase common stock 309,389 458,497 Unaudited Pro Forma Net Loss Per Share The unaudited pro forma basic and diluted net loss per share attributable to common stockholders for the year ended December 31, 2018 has been prepared to give effect to adjustments arising upon the completion of a qualified IPO. The unaudited pro forma basic and diluted weighted‑average common shares outstanding used in the calculation of unaudited pro forma basic and diluted net loss per share attributable to common stockholders for the year ended December 31, 2018 has been prepared to give effect, upon a qualified IPO, to the conversion of all outstanding shares of Preferred Stock into common stock as if the proposed IPO had occurred on the later of January 1, 2018 or the issuance date of the preferred stock. Unaudited pro forma basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Year Ended December 31, 2018 (unaudited) Numerator: Net loss attributable to common stockholders—basic and diluted $ (16,521) Pro forma net loss attributable to common stockholders—basic and diluted $ (16,521) Denominator: Weighted‑average common stock outstanding—basic and diluted 5,483,149 Pro forma adjustment to reflect conversion of convertible preferred stock to common stock upon the completion of the proposed initial public offering 3,679,938 Pro forma weighted‑average common stock outstanding—basic and diluted 9,163,087 Pro forma net loss per share attributable to common stockholders—basic and diluted $ (1.80)

SUBSEQUENT EVENT_2

SUBSEQUENT EVENT	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
SUBSEQUENT EVENT
SUBSEQUENT EVENTS	13. SUBSEQUENT EVENT On October 3, 2019, and in connection with the 2019 Columbia Agreement, the Company entered into a research services agreement with Columbia University with the purpose of analyzing certain compounds for the treatment of lymphoid malignancies. The research service agreement has a term of 18 months from is effective date; provided that the Company can terminate the research service agreement without cause with at least 30 days prior written notice. In consideration for the services performed by Columbia University, the Company will be required to pay $0.4 million to Columbia University for staffing, supplies and indirect costs. On November 7, 2019, the Company entered into a definitive Securities Purchase Agreement (the “Securities Purchase Agreement”) for a private placement (the “Private Placement”) with a select group of accredited investors (collectively, the “Purchasers”). Pursuant to the Securities Purchase Agreement, the Purchasers have agreed to purchase 1,380,344 shares of the Company’s common stock, par value $0.0001 per share (the “Shares”), which resulted in gross proceeds to the Company of approximately $20.0 million at a price of $14.50 per share before deducting placement agent commissions and other offering expenses. The Private Placement closed on November 12, 2019 .	12. SUBSEQUENT EVENTS Issuance of Series B Preferred Stock In February 2019, the Company issued an aggregate of 442,925 shares of its Series B Preferred Stock to investors and certain members of its board of directors at a price per share of $7.49 for proceeds of $3.1 million, net of issuance costs of $0.2 million. The rights and privileges of the Series B Preferred Stock are the same as the rights and privileges of the Series B Preferred Stock issued in earlier closings. In connection with the Series B Preferred Stock issuance, the Company is obligated to issue warrants to purchase shares of common stock to the placement agent. Columbia University In January 2019, the Company entered into a license agreement with Columbia University (“2019 Columbia Agreement”). Pursuant to the 2019 Columbia Agreement, Columbia University granted the Company a royalty‑bearing, sublicensable license that is exclusive with respect to certain patents, and non‑exclusive with respect to certain know‑how, in each case to develop, manufacture and commercialize PI3K inhibitor products. As consideration, the Company made a nominal upfront payment to Columbia University. The Company will be required to make further payments to Columbia University of up to an aggregate of $1.3 million for the achievement of specified development and regulatory milestones, and up to an aggregate of $1.0 million for the achievement of a specified level of aggregate annual net sales, in each case in connection with products covered by the 2019 Columbia Agreement. The Company will also be required to pay tiered royalties to Columbia University in the low‑ to mid‑single digit percentages on the Company’s, its affiliates’ and its sublicensees’ net sales of licensed products, subject to specified offsets and reductions. In addition, the Company is required to make specified annual minimum royalty payments to Columbia University, which is contingent upon the approval of the licensed products, in the mid six figures beginning on the 10th anniversary of the effective date of the 2019 Columbia Agreement. If the Company sublicenses the rights granted under the 2019 Columbia Agreement to one or more third parties, it will be required to pay Columbia University a portion of the net sublicensing revenue received from such sublicensees, at percentages ranging from 10% to 50%, depending on the passage of time or the stage of development of the applicable product at the time such revenue is received from such sublicenses. Forward Stock Split In April 2019, the board of directors and the stockholders of the Company approved a 55.2486‑for‑1 forward stock split of the Company’s outstanding common stock and Preferred Stock, which was effected on April 26, 2019. Stockholders entitled to fractional shares as a result of the forward stock split will receive a cash payment in lieu of receiving fractional shares. The Company’s historical share and per share information has been retroactively adjusted to give effect to this forward stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately increased and the respective per share value and exercise prices, if applicable, were proportionately decreased in accordance with the terms of the agreements governing such securities. Modification of Certain Stock Option Grants On April 22, 2019, the Board of Directors approved a modification to the vesting conditions of certain outstanding stock option grants to certain employees and directors. The Company is evaluating the impact this modification will have to its 2019 financial statements.

ORGANIZATION AND SUMMARY OF S_9

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Basis of Accounting	Operations and Business Applied Therapeutics, Inc. (the “Company”) is a clinical-stage biopharmaceutical company developing a pipeline of novel product candidates against validated molecular targets in indications of high unmet medical need. In particular, the Company is currently targeting treatments for cardiovascular disease, galactosemia and diabetic complications. The Company was incorporated in Delaware on January 20, 2016 and is headquartered in New York, New York. On May 16, 2019, the Company completed an initial public offering (“IPO”) in which the Company issued and sold 4,000,000 shares of its common stock at a public offering price of $10.00 per share, for aggregate gross proceeds of $40.0 million. The Company received net of proceeds $34.6 million, after deducting underwriting discounts and commissions and offering costs. Prior to the completion of the IPO, the Company primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 8). In connection with the IPO, the Company effected a 55.2486-for-1 stock split of its issued and outstanding shares of common stock and convertible preferred stock. The stock split became effective on April 26, 2019. Stockholders entitled to fractional shares as a result of the forward stock split received cash payment in lieu of receiving fractional shares. All share and per share amounts for all periods presented in the accompanying condensed financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect this stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately increased and the respective per share value and exercise prices, if applicable, were proportionately decreased in accordance with the terms of the agreements governing such securities. Upon the closing of the IPO on May 16, 2019, all of the then-outstanding shares of convertible preferred stock automatically converted into 7,538,671 shares of common stock on a one-for-one basis. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. The accompanying unaudited condensed financial statements as of September 30, 2019 and for the three and nine months ended September 30, 2019 and 2018 have been prepared by the Company in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and, pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2018 included in the Company’s final prospectus that forms a part of the Company’s Registration Statement on Form S-1 (Reg. No. 333-230838), filed with the SEC pursuant to Rule 424(b)(4) on May 14, 2019 (the “Prospectus”). The unaudited condensed financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited condensed financial statements contain all adjustments which are necessary for a fair presentation of the Company’s financial position as of September 30, 2019, results of operations for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2019.
Liquidity	Liquidity The Company has incurred, and expects to continue to incur, significant operating losses and negative cash flows for at least the next several years as it continues to develop its drug candidates. To date, the Company has not generated any revenue, and it does not expect to generate revenue unless and until it successfully completes development and obtains regulatory approval for one of its product candidates. Management believes that the Company’s existing cash, together with the net proceeds from the IPO, will allow the Company to continue its operations for at least 12 months from the issuance date of these financial statements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.	Going Concern The Company has evaluated whether there are conditions and events considered in the aggregate that raise substantial doubt about the Company’s ability to continue as a going concern. Through December 31, 2018, the Company has primarily funded its operations with proceeds from the sale of convertible preferred stock (see Note 6). The Company has incurred recurring losses from operations since its inception, including net losses of $4.3 million and $16.5 million for the years ended December 31, 2017 and December 31, 2018, respectively, and has used cash in operations of $3.2 million and $11.2 million for the years ended December 31, 2017 and December 31, 2018, respectively. In addition, as of December 31, 2018, the Company had an accumulated deficit of $21.3 million. The Company expects its operating losses and negative cash flows to continue into the foreseeable future as it continues to develop, manufacture, and commercialize its product candidates. The Company is seeking to complete an initial public offering (“IPO”) of its common stock. In the event the Company does not complete an IPO, and even after the completion of an IPO, the Company expects to seek additional funding through private or public equity financings, debt financings, collaborations, or other strategic transactions. The Company may not be able to obtain funding on acceptable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Based on the operating losses incurred since inception, the expectation of continuing operating losses for the foreseeable future, and the need to raise additional capital to finance its operations, the Company has concluded that there is substantial doubt about its ability to continue as a going concern within one year after the date that the financial statements are issued. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. The financial statements do not include any adjustments that might be necessary if the Company is unable to continue as a going concern.
Risk and Uncertainties	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers.	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and reliance on third‑party manufacturers.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.
Stock-Based Compensation	Stock‑Based Compensation The Company accounts for its stock-based compensation as expense in the condensed statements of operations based on the awards' grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black-Scholes option pricing model with the exception of stock options that include service, performance and market conditions, which are valued using the Monte-Carlo simulation model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company has historically been a private company and lacks company-specific historical and implied volatility information. Therefore, the Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission ("SEC") Staff Accounting Bulletin ("SAB") No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. A Monte-Carlo simulation is an analytical method used to estimate fair value by performing a large number of simulations or trial runs and thereby determining a value based on the possible outcomes from these trial runs based on the specific vesting conditions. The fair value of stock-based payments is recognized as expense over the requisite service period which is generally the vesting period, with the exception of the fair value of stock-based payments for awards that include service, performance and market conditions, which is recognized as expense over the derived service period determined using the Monte-Carlo simulation.	Stock‑Based Compensation The Company accounts for its stock‑based compensation as expense in the statements of operations based on the awards’ grant date fair values. The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards. The Company estimates the fair value of options granted using the Black‑Scholes option pricing model. The Black‑Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk‑free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company‑specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company uses the simplified method as allowed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin (“SAB”) No. 107, Share‑Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of stock‑based payments is recognized as expense over the requisite service period which is generally the vesting period.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. Upon closing the IPO in May 2019, $2.6 million in deferred offering costs were reclassified from prepaid and other current assets and recorded against the IPO proceeds reducing additional paid-in capital. As of September 30, 2019, the Company did not have any deferred offering costs recorded in prepaid and other current assets.	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third‑party fees that are directly associated with in‑process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the statement of convertible preferred stock and stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations. The Company recorded deferred offering costs of $0.3 million as of December 31, 2018 in prepaid expenses and other current assets.
Investments	Investments We have investments in marketable debt securities. We determine the appropriate classification of our investments at the date of purchase and reevaluate the classifications at the balance sheet date. Marketable debt securities with maturities of 12 months or less are classified as short-term. Marketable debt securities with maturities greater than 12 months are classified as long-term. The Company’s marketable securities are accounted for as available for sale (“AFS”). AFS securities are reported at fair value. Unrealized gains and losses, after applicable income taxes, are reported in accumulated other comprehensive income/(loss). We conduct an other-than-temporary impairment (“OTTI”) analysis on a quarterly basis or more often if a potential loss-triggering event occurs. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and whether we intend to sell. For AFS securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis and (ii) the amortized cost basis cannot be recovered as a result of credit losses.
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements The new accounting pronouncements recently adopted by the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Prospectus as filed with the SEC on May 14, 2019. Except as described below, there have been no new accounting pronouncements adopted by the Company during the nine months ended September 30, 2019. In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) , which requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases on their balance sheet date (“ASU No. 2016-02”). ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018. In July 2018, an amendment was made that allows companies the option of using the effective date of the new standard as the initial application date (at the beginning of the period in which the new standard is adopted, rather than at the beginning of the earliest comparative period). This update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize the associated lease assets and lease liabilities on its balance sheet. Additionally, in March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements (“ASU No. 2019-01”). ASU No. 2019-01 clarifies the transition guidance related to interim disclosures provided in the year of adoption. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease did not significantly change from previous U.S. GAAP. The modified retrospective method includes several optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. The Company adopted Topic 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance under ASC 840. In adopting Topic 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease; ii) the lease classification of existing or expired leases; and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election not to recognize assets or related lease liabilities with a lease term of twelve months or less in its condensed balance sheet. The adoption of this standard did not have an impact on the Company’s condensed balance sheet as all of the Company’s leases are for terms that are less than 12 months. Additionally, the adoption of this standard did not have a material impact on the Company’s condensed statements of operations or condensed statement of cash flows. On August 6, 2019 the Company entered into a lease for approximately 6,579 square feet of new office space in New York City (the “Lease”). The Lease will commence upon delivery of the premise after certain improvements are made, which is anticipated to be on or about November 1, 2019 (the “Commencement Date”), for a five-year period. Under the Lease, the Company will pay monthly rent of approximately $38,000 for the first year following the Commencement Date, and such rent will increase by a nominal percentage every year following the first anniversary of the Commencement Date. The Company will also pay a real estate tax escalation, as additional rent, over a base year. Total lease obligation over the term of the lease will be approximately $2.4 million. Recently Issued Accounting Pronouncements The FASB issued authoritative guidance that amends guidance on reporting credit losses for assets, including available-for-sale marketable securities and any other financial assets not excluded from the scope that have the contractual right to receive cash. For available-for-sale marketable securities, credit losses should be measured in a manner similar to current generally accepted accounting standards; however, ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , will require that credit losses be presented as an allowance rather than as a write-down. We are currently in the process of evaluating the impact of this guidance on our condensed financial statements.	Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014‑09, Revenue from Contracts with Customers (Topic 606) (“ASU No. 2014‑09”), which modifies how all entities recognize revenue, and consolidates into one Accounting Standards Codification (“ASC”) (ASC Topic 606, Revenue from Contracts with Customers ), the current guidance found in ASC Topic 605, and various other revenue accounting standards for specialized transactions and industries. ASU No. 2014‑09 outlines a comprehensive five‑step revenue recognition model based on the principle that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU No. 2015‑14, Revenue from Contracts with Customers (Topic 606): Deferral of Effective Date (“ASU No. 2015‑14”), which defers the effective date of ASU No. 2014‑09 by one year. Early adoption is permitted for annual periods beginning after December 15, 2016. To date, the Company has not had any arrangements that are within the scope of ASU No. 2014‑09, or its predecessor, ASC Topic 605. The Company adopted these pronouncements on January 1, 2017, which did not have any impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016‑09, Improvements to Employee Share‑Based Payment Accounting (“ASU No. 2016‑09”), which simplifies share‑based payment accounting through a variety of amendments. The Company elected to early adopt this guidance effective January 1, 2016, and has elected to account for forfeitures as incurred and therefore no forfeiture estimate is utilized in the year ended December 31, 2017. Adoption of ASU No. 2016‑09 did not have a material impact on the Company’s financial statements. In May 2017, the FASB issued ASU No. 2017‑09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU No. 2017‑09”), which clarifies when to account for a change to the terms or conditions of a share‑based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The standard is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted ASU No. 2017‑09 as of January 1, 2018, which did not have a material impact on the Company’s financial statements. In June 2018, the FASB issued ASU No. 2018‑07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share‑Based Payment Accounting (“ASU No. 2018‑07”). These amendments expand the scope of Topic 718, Compensation—Stock Compensation , which currently only includes share‑based payments to employees, to include share‑based payments issued to nonemployees for goods or services. Consequently, the accounting for share‑based payments to nonemployees and employees will be substantially aligned. This ASU supersedes Subtopic 505‑50, Equity—Equity‑Based Payments to Non‑Employees . This standard is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted as long as ASU No. 2014‑09 has been adopted by the Company. The Company adopted ASU No. 2018‑07 as of January 1, 2017, which did not have a material impact on the Company’s financial statements. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) , which requires lessees to recognize assets and liabilities for leases with lease terms greater than 12 months in the statement of financial position. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016‑02 also requires improved disclosures to help users of financial statements better understand the amount, timing and uncertainty of cash flows arising from leases. The update is effective for fiscal years beginning after December 15, 2018, including interim reporting periods within that reporting period. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2016‑02 will have on its financial statements. In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement . which, eliminates, modifies, and adds disclosure requirements on fair value measurements. The standard is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU 2018‑13 will have on its financial statements.

FAIR VALUE MEASUREMENTS (Tabl_2

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
FAIR VALUE MEASUREMENTS
Schedule of financial assets or liabilities measured at fair value on a recurring basis	As of December 31, 2018, the Company did not have financial assets or liabilities that are measured at fair value on a recurring basis (in thousands). As of September 30, 2019 Level 1 Level 2 Level 3 Total Cash $ 12,933 $ — $ — $ 12,933 Money market funds 133 — — 133 Total cash and cash equivalents $ 13,065 $ — $ — $ 13,065 Commercial paper and corporate bonds — 7,522 — 7,522 U.S. government agency debt securities — 12,367 — 12,367 Total marketable securities $ — $ 19,889 $ — $ 19,889 Total financial assets measured at fair value on a recurring basis $ 13,065 $ 19,889 $ — $ 32,954
Schedule of Company’s Derivative Liability and Warrant Liability	The following table provides a roll forward of the aggregate fair values of the Derivative Liability and Warrant Liability as of September 30, 2018, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 180 6 Balance as of March 31, 2018 $ 2,076 $ 80 Change in fair value 294 21 Balance as of June 30, 2018 $ 2,370 $ 101 Change in fair value 335 38 Balance as of September 30, 2018 $ 2,704 $ 139	The following table provides a roll forward of the aggregate fair values of the Company’s Derivative Liability and Warrant Liability, for which fair value is determined using Level 3 inputs (in thousands): Derivative Warrant Liability Liability Balance as of January 1, 2018 $ — $ — Initial fair value of Derivative Liability 1,896 — Initial fair value of Warrant Liability — 74 Change in fair value 972 168 Extinguishment of Derivative Liability in connection with extinguishment of 2018 Notes (2,868) — Reclassification of Warrant Liability into 2018 Notes Warrants — (242) Balance as of December 31, 2018 $ — $ —

INVESTMENTS (Tables)

INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2019
INVESTMENTS
Schedule of marketable securities by security type	The following tables provide the Company’s marketable securities by security type as of September 30, 2019 and December 31, 2018 (in thousands): As of September 30, 2019 Gross Gross Unrealized Unrealized Estimated Cost Gains Losses Fair Value Commercial Paper and corporate bonds $ 7,527 $ — $ (5) $ 7,522 US government agency debt security 12,351 16 — 12,367 Total $ 19,878 $ 16 $ (5) $ 19,889
Schedule of contractual maturities	Contractual maturities of the Company’s marketable securities as of September 30, 2019 and December 31, 2018 are summarized as follows (in thousands): As of September 30, 2019 Gross Gross Unrealized Unrealized Estimated Cost Gains Losses Fair Value Due in one year or less $ 19,878 $ 16 $ (5) $ 19,889 Total $ 19,878 $ 16 $ (5) $ 19,889

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2019
PREPAID EXPENSES AND OTHER CURRENT ASSETS
Summary of prepaid expenses and other current assets	Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, 2019 2018 Deferred offering costs $ — $ 310 Prepaid research and development expenses 1,543 1,044 Prepaid rent expenses 78 65 Prepaid insurance expenses 1,934 1 Other prepaid expenses and current assets 525 78 Total prepaid expenses & other current assets $ 4,080 $ 1,498

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2019
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
Summary of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2019 2018 Accrued pre-clinical and clinical expenses $ 3,684 $ 865 Accrued professional fees 248 312 Accrued compensation and benefits 640 56 Accrued patent expenses 65 126 Other 192 54 Total accrued expenses & other current liabilities $ 4,829 $ 1,413

STOCK BASED COMPENSATION (Tab_2

STOCK BASED COMPENSATION (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCK BASED COMPENSATION
Schedule of stock-based compensation expenses	Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2019 and 2018 was as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 495 $ 38 $ 2,087 $ 88 General and administrative 724 39 2,736 92 Total stock-based compensation expense $ 1,219 $ 78 $ 4,823 $ 180	Total stock‑based compensation expense recorded for employees, directors and non‑employees during the years ended December 31, 2017 and 2018 was as follows (in thousands): Year Ended December 31, 2017 2018 Research and development $ — $ 140 General and administrative 32 132 Total stock-based compensation expense $ 32 $ 272
Schedule of options outstanding	The following table summarizes the information about options outstanding at September 30, 2019 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Options granted 2,657,628 7.34 Options exercised (81,988) 2.77 — Forfeited (11,048) 4.70 Expired — — Outstanding at September 30, 2019 3,767,571 $ 5.54 9.19 $ 20,860 Exercisable at September 30, 2019 1,364,658 $ 2.80 8.84 $ 11,174 Nonvested at September 30, 2019 2,402,913 $ 7.09 9.39 $ 9,686	The following table summarizes the information about options outstanding at December 31, 2018 (in thousands, except share and per share data): Weighted-Average Weighted- Remaining Aggregate Options Average Contractual Intrinsic Outstanding Exercise Price Term (in years) Value Outstanding at December 31, 2017 262,427 $ 0.90 9.09 $ 27 Options granted 995,633 $ 1.44 Options exercised (55,081) $ 0.84 33 Outstanding at December 31, 2018 1,202,979 $ 1.35 9.14 $ 4,029 Exercisable at December 31, 2018 73,692 $ 0.88 8.01 $ 282 Nonvested at December 31, 2018 1,129,287 $ 1.38 9.22 $ 3,747
Schedule of valuation assumptions	Nine Months Ended September 30, 2019 Time to expiration (in years) 10.0 Volatility 68.54 % Risk-free interest rate 2.64 % Dividend yield 0.00 % Cost of equity 24.00 % Fair value of underlying common stock (as of valuation date) $ 5.85	Year Ended December 31, December 31, 2017 2018 Expected term (in years) 6.0 5.9 Volatility 75.06 % 71.78 % Risk-free interest rate 2.09 % 2.71 % Dividend yield 0.00 % 0.00 %

STOCKHOLDER EQUITY (Tables)_2

STOCKHOLDER EQUITY (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
STOCKHOLDER EQUITY
Summary of Preferred Stock	As of December 31, 2018, the Preferred Stock consisted of the following (in thousands, except share data): December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746	As of December 31, 2017 and 2018, Preferred Stock consisted of the following (in thousands, except share data): December 31, 2017 Preferred Preferred Stock Issued Common Stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 Total 3,535,910 3,093,898 $ 6,254 $ 7,000 3,093,898 December 31, 2018 Preferred Preferred Stock Issued Common stock Stock and Carrying Liquidation Issuable Upon Authorized Outstanding Value Value Conversion Series A Preferred Stock 3,093,898 3,093,898 $ 6,254 $ 7,000 3,093,898 Series B Preferred Stock 7,790,052 4,001,848 29,156 29,964 4,001,848 Total 10,883,950 7,095,746 $ 35,410 $ 36,964 7,095,746

WARRANTS (Tables)_2

WARRANTS (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
2018 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	The fair value of the 2018 Warrants was estimated using the Black‑Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 %	Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 %
2019 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	The fair value of the 2019 Warrants was estimated using the Black-Scholes option pricing model with the following assumptions: Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 %

NET LOSS PER COMMON SHARE (Ta_2

NET LOSS PER COMMON SHARE (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
NET LOSS PER COMMON SHARE
Schedule of computation of basic and diluted net loss per common share	The following table sets forth the computation of basic and diluted net loss per common share for the three and nine months ended September 30, 2019 and 2018 (in thousands, except share and per share data): Three Months Ended September 30, 2019 2018 Numerator: Net loss $ (10,713) $ (4,281) Denominator: Weighted-average common stock outstanding 17,095,870 5,497,871 Net loss per share attributable to common stockholders - basic and diluted $ (0.63) $ (0.78) Nine Months Ended September 30, 2019 2018 Numerator: Net loss $ (27,880) $ (9,802) Denominator: Weighted-average common stock outstanding 14,085,579 5,473,414 Net loss per share attributable to common stockholders - basic and diluted $ (1.98) $ (1.79)	The following table sets forth the computation of basic and diluted net loss per common share (in thousands, except share and per share data): Years Ended December 31, 2017 2018 Numerator: Net loss $ (4,282) $ (16,521) Denominator: Weighted-average common stock outstanding 5,406,513 5,483,149 Net loss per share, basic and diluted $ (0.79) $ (3.01)
Schedule of potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	As of September 30, 2019 2018 Preferred Stock — 3,093,898 Options to purchase common stock 3,767,571 1,035,466 Warrants to purchase common stock 482,364 309,389	As of December 31, 2017 2018 Preferred Stock 3,093,898 7,095,746 Options to purchase common stock 262,427 1,202,979 Warrants to purchase common stock 309,389 458,497

ORGANIZATION AND SUMMARY OF _10

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - IPO (Details) $ / shares in Units, $ in Millions	May 16, 2019USD ($)$ / sharesshares	Apr. 26, 2019	Sep. 30, 2019shares	Dec. 31, 2018shares
IPO
Convertible preferred stock, outstanding (in shares)	0		0	7,095,746
IPO
IPO
Shares issued (in shares)	4,000,000
Issue price (in dollars per share) | $ / shares	$ 10
Aggregate gross proceeds from issuance | $	$ 40
Net proceeds after deducting underwriting discounts and commissions and estimated offering costs | $	$ 34.6
Stock split ratio		55.2486
Number of shares into which convertible preferred stock are converted	7,538,671
Number of shares issued for each share of convertible preferred stock converted	1

ORGANIZATION AND SUMMARY OF _11

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-based compensation (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Dividend yield (as a percent)		0.00%	0.00%
Options
Stock-based compensation
Dividend yield (as a percent)	0.00%

ORGANIZATION AND SUMMARY OF _12

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred Offering Costs (Details) - USD ($) $ in Millions	1 Months Ended
	May 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Deferred offering cost
Reclassification of deferred offering costs	$ 2.6
Deferred offering costs		$ 0	$ 0.3

ORGANIZATION AND SUMMARY OF _13

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recent Accounting Pronouncements (Details)	Jan. 01, 2019
Recently Adopted Accounting Pronouncements
Lease, Practical Expedients, Package	true
ASC Topic 842, Leases
Recently Adopted Accounting Pronouncements
Change in Accounting Principle, Accounting Standards Update, Adopted	true

ORGANIZATION AND SUMMARY OF _14

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leases (Details) - Office $ in Thousands	Aug. 06, 2019USD ($)ft²
Leases
Leased area | ft²	6,579
Lease term not yet commenced	5 years
Monthly lease rent	$ 38
Total lease obligation	$ 2,400

LICENSE AGREEMENT (Details)_2

LICENSE AGREEMENT (Details) $ in Thousands	1 Months Ended				3 Months Ended			9 Months Ended		12 Months Ended		27 Months Ended	36 Months Ended
	Mar. 31, 2019USD ($)item	Jan. 31, 2019USD ($)	Feb. 28, 2017USD ($)	Oct. 31, 2016USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)
Agreements
Fair value of stock issued						$ 34,618
Research and development					$ 7,453		$ 2,726	$ 18,582	$ 6,111	$ 11,471	$ 3,703
General and administrative					3,294		598	9,331	1,418	2,047	582
Operating expenses					10,747		3,324	27,913	7,529	13,518	4,285
Accrued expenses and other current liabilities					4,829			4,829		1,413	280	$ 1,413	$ 4,829
Accounts payable					1,688			1,688		3,015	713	3,015	1,688
Common Stock Par value $0.0001
Agreements
Fair value of stock issued						$ 1
Columbia University
Agreements
Research and development					17		100	42	200	500	$ 600	1,400
General and administrative					28		$ 43	300	$ 98
Operating expenses													1,700
Accrued expenses and other current liabilities					100			100		100		100	100
Accounts payable					$ 100			$ 100		$ 100		$ 100	$ 100
2016 license agreement | Columbia University
Agreements
Percentage of outstanding common stock issued				5.00%
Fair value of stock issued			$ 500	$ 500
Written notice period for termination of agreement				90 days
Written notice period for termination of agreement, uncured material breach				30 days
Extended written notice period for termination of agreement, attempt to cure material breach				90 days
2016 license agreement | Columbia University | Minimum
Agreements
Percentage of sublicensing revenue, if sublicenses rights granted				10.00%
2016 license agreement | Columbia University | Maximum
Agreements
Payment on achievement of specified development and regulatory milestones				$ 1,300
Payment on achievement of specified level of aggregate annual net sales				$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted				20.00%
2019 license agreement | Columbia University
Agreements
Written notice period for termination of agreement		90 days
Written notice period for termination of agreement, uncured material breach		30 days
Extended written notice period for termination of agreement, attempt to cure material breach		90 days
2019 license agreement | Columbia University | Minimum
Agreements
Percentage of sublicensing revenue, if sublicenses rights granted		10.00%
2019 license agreement | Columbia University | Maximum
Agreements
Payment on achievement of specified development and regulatory milestones		$ 1,300
Payment on achievement of specified level of aggregate annual net sales		$ 1,000
Percentage of sublicensing revenue, if sublicenses rights granted		50.00%
2019 research agreement | Columbia University
Agreements
Agreement term	12 months
Written notice period for termination of agreement	30 days
Number of parts | item	2
2019 research agreement - Part I | Columbia University
Agreements
Agreement term	6 months
Payment to be made	$ 100
2019 research agreement - Part II | Columbia University
Agreements
Agreement term	6 months
Payment to be made	$ 200

FAIR VALUE MEASUREMENTS - FV hi

FAIR VALUE MEASUREMENTS - FV hierarchy (Details) - Fair Value, Recurring $ in Thousands	Sep. 30, 2019USD ($)
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	$ 13,065
Marketable securities	19,889
Total financial assets measured at fair value on a recurring basis	32,954
Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	13,065
Total financial assets measured at fair value on a recurring basis	13,065
Level 2
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	19,889
Total financial assets measured at fair value on a recurring basis	19,889
Cash
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	12,933
Cash | Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	12,933
Money market funds
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	133
Money market funds | Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	133
Commercial paper and corporate bonds
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	7,522
Commercial paper and corporate bonds | Level 2
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	7,522
U.S. government agency debt securities
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	12,367
U.S. government agency debt securities | Level 2
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	$ 12,367

FAIR VALUE MEASUREMENTS - Tra_2

FAIR VALUE MEASUREMENTS - Transfers (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
FAIR VALUE MEASUREMENTS
Assets, transfer from level 1 to level 2	$ 0	$ 0	$ 0
Assets, transfer from level 2 to level 1	$ 0	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Lev_2

FAIR VALUE MEASUREMENTS - Level 3 roll forward (Details) - USD ($) $ in Thousands	Feb. 05, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Fair Value
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Income					us-gaap:NonoperatingIncomeExpense
Derivative Liability
Fair Value
Balance at beginning of period		$ 2,370	$ 2,076
Initial fair value	$ 1,900			$ 1,896		$ 1,896
Change in fair value		335	294	180	$ 800	972
Balance at end of period		2,704	2,370	2,076	2,704
Warrants Liability
Fair Value
Balance at beginning of period		101	80
Initial fair value	$ 100			74		74
Change in fair value		38	21	6	65	$ 168
Balance at end of period		$ 139	$ 101	$ 80	$ 139

INVESTMENTS - By type (Details)

INVESTMENTS - By type (Details) $ in Thousands	Sep. 30, 2019USD ($)
Marketable securities by type
Cost	$ 19,878
Gross Unrealized Gains	16
Gross Unrealized Losses	(5)
Estimated Fair Value	19,889
Commercial paper and corporate bonds
Marketable securities by type
Cost	7,527
Gross Unrealized Losses	(5)
Estimated Fair Value	7,522
U.S. government agency debt securities
Marketable securities by type
Cost	12,351
Gross Unrealized Gains	16
Estimated Fair Value	$ 12,367

INVESTMENTS - By contractual ma

INVESTMENTS - By contractual maturity (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
INVESTMENTS
Due in one year or less - Cost	$ 19,878	$ 19,878
Due in one year or less - Estimated Fair Value	19,889	19,889
Cost	19,878	19,878
Gross Unrealized Gains	16	16
Gross Unrealized Losses	(5)	(5)
Estimated Fair Value	19,889	19,889
Net unrealized gains	11	11
Marketable securities realized gain (loss) recorded
Net realized gain from sale of marketable securities	0	0
Net realized loss from sale of marketable securities	$ 0	0
Other-than-temporary impairment loss
Other-than-temporary impairment loss recognized		$ 0

CONVERTIBLE PROMISSORY NOTES _2

CONVERTIBLE PROMISSORY NOTES (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 05, 2018	Nov. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Feb. 28, 2019	Jan. 18, 2018
Debt
Outstanding notes			$ 0			$ 0	$ 0
Series B Convertible Preferred Stock
Debt
Debt converted into shares			1,097,721
Issue price (in dollars per share)		$ 7.49	$ 7.49			$ 7.49		$ 7.49
Warrants Issued with the 2018 Notes
Debt
Initial fair value recorded as debt discount (in dollars)	$ 100								$ 100
2018 Notes
Debt
Outstanding notes		$ 6,600
Aggregate principal amount	$ 6,000
Interest rate (as a percent)	15.00%
Threshold proceeds from sale of preferred stock	$ 8,000
Preferred stock conversion price as a percentage of lowest price per share of preferred stock sold in financing	80.00%	80.00%
Percentage of outstanding principal amount payable in event of corporate transaction or change of control event	30.00%
Minimum percentage of outstanding principal amount written consent required for prepayment	50.00%
Additional percentage of outstanding principal payable on prepayment	15.00%
Legal costs and bank fees	$ 400
Effective interest rate (as a percent)	54.90%
Interest expense				$ 600	$ 1,400	$ 1,600
Amortization of debt discount				$ 800	$ 300	$ 900
Debt converted into shares		1,097,721
2018 Notes | Derivative Liability
Debt
Initial fair value recorded as debt discount (in dollars)	$ 1,900

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
PREPAID EXPENSES AND OTHER CURRENT ASSETS
Deferred offering costs		$ 310
Prepaid research and development expenses	$ 1,543	1,044
Prepaid rent expenses	78	65
Prepaid insurance expenses	1,934	1
Other prepaid expenses and current assets	525	78
Total prepaid expenses & other current assets	$ 4,080	$ 1,498	$ 9

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
Accrued pre-clinical and clinical expenses	$ 3,684	$ 865
Accrued professional fees	248	312
Accrued compensation and benefits	640	56
Accrued patent expenses	65	126
Other	192	54
Total accrued expenses & other current liabilities	$ 4,829	$ 1,413

STOCK BASED COMPENSATION - Pl_2

STOCK BASED COMPENSATION - Plans (Details) - shares	1 Months Ended
	May 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Options outstanding (in shares)		3,767,571	1,202,979	262,427
2019 Plan
Stock-based compensation
New shares reserved (in shares)	1,618,841
Reserved shares available from 2016 Plan (in shares)	2,911,159
Increase in number of shares reserved and available for issuance (as a percent)	5.00%
Expiration period	10 years
Vesting period	4 years
Number of shares available for future issuance		680,441
2019 Plan | Maximum
Stock-based compensation
Shares reserved (in shares)	4,530,000
2019 Plan | Options
Stock-based compensation
Maximum number of shares authorized for issuance	13,000,000

STOCK BASED COMPENSATION - St_2

STOCK BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Total stock-based compensation expense	$ 1,219	$ 78	$ 4,823	$ 180	$ 32	$ 272
Research and development
Stock-based compensation
Total stock-based compensation expense	495	38	2,087	88		140
General and administrative
Stock-based compensation
Total stock-based compensation expense	$ 724	$ 39	$ 2,736	$ 92	$ 32	$ 132

STOCK BASED COMPENSATION - Op_2

STOCK BASED COMPENSATION - Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Options granted (in shares)			2,657,628		995,633
Stock-based compensation expense	$ 1,219	$ 78	$ 4,823	$ 180	$ 32	$ 272
Options outstanding (in shares)	3,767,571		3,767,571		1,202,979	262,427
Weighted-average fair value of options granted (in dollars per share)			$ 4.71	$ 1.03
Unrecognized stock-based compensation balance for unvested options	$ 9,800		$ 9,800
Options
Stock-based compensation
Unrecognized stock-based compensation balance for unvested options expected to be recognized (in years)			1 year 9 months 18 days
Options | Award date, Three months ended September 30, 2019
Stock-based compensation
Stock-based compensation expense	$ 1,200
Options | Award date, Nine months ended September 30, 2019
Stock-based compensation
Stock-based compensation expense			$ 4,800

STOCK BASED COMPENSATION - Op_3

STOCK BASED COMPENSATION - Options outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Options Outstanding
Outstanding at beginning of period (in shares)	1,202,979	262,427
Options granted (in shares)	2,657,628	995,633
Options exercised (in shares)	(81,988)	(55,081)
Forfeited (in shares)	(11,048)
Outstanding at end of period (in shares)	3,767,571	1,202,979	262,427
Exercisable at end of period (in shares)	1,364,658	73,692
Nonvested at end of period (in shares)	2,402,913	1,129,287
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 1.35	$ 0.90
Options granted (in dollars per share)	7.34	1.44
Options exercised (in dollars per share)	2.77	0.84
options forfeited(in dollars per share)	4.70
Outstanding at end of period (in dollars per share)	5.54	1.35	$ 0.90
Exercisable at end of period (in dollars per share)	2.80	0.88
Nonvested at end of period (in dollars per share)	$ 7.09	$ 1.38
Weighted-Average Remaining Contractual Term-in years
Outstanding	9 years 2 months 9 days	9 years 1 month 21 days	9 years 1 month 2 days
Exercisable	8 years 10 months 2 days	8 years 4 days
Nonvested	9 years 4 months 21 days	9 years 2 months 19 days
Aggregate Intrinsic Value
Outstanding (in dollars)	$ 20,860	$ 4,029	$ 27
Exercisable (in dollars)	11,174	282
Nonvested (in dollars)	$ 9,686	$ 3,747

STOCK BASED COMPENSATION - Op_4

STOCK BASED COMPENSATION - Options that Contain Service, Performance and Market Conditions (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Stock-based compensation
Options granted (in shares)	2,657,628	995,633
Stock Options that Contain Service, Performance and Market Conditions
Stock-based compensation
Options granted (in shares)	159,501
Fair value at grant date	$ 0.5
Stock Options that Contain Service, Performance and Market Conditions | Minimum
Stock-based compensation
Derived service period	P1D
Stock Options that Contain Service, Performance and Market Conditions | Maximum
Stock-based compensation
Derived service period	P3Y

STOCK BASED COMPENSATION - Va_2

STOCK BASED COMPENSATION - Valuation assumptions (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Assumptions
Time to expiration (in years)		5 years 10 months 24 days	6 years
Volatility		71.78%	75.06%
Risk-free interest rate		2.71%	2.09%
Dividend yield (as a percent)		0.00%	0.00%
Stock Options that Contain Service, Performance and Market Conditions
Valuation Assumptions
Time to expiration (in years)	10 years
Volatility	68.54%
Risk-free interest rate	2.64%
Dividend yield (as a percent)	0.00%
Cost of equity	24.00%
Fair value of underlying common stock (as of valuation date)	$ 5.85

STOCK BASED COMPENSATION -Servi

STOCK BASED COMPENSATION -Service, Performance and Market Condition Option Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Stock-based compensation expense		$ 1,219	$ 78	$ 4,823	$ 180	$ 32	$ 272
Options outstanding (in shares)		3,767,571		3,767,571		1,202,979	262,427
Stock Options that Contain Service, Performance and Market Conditions
Stock-based compensation
Options vested (in shares)				79,778
Stock-based compensation expense		$ 700		$ 800
Options outstanding (in shares)		0		0
Former Interim Chief Financial Officer | Stock Options that Contain Service, Performance and Market Conditions
Stock-based compensation
Options vested (in shares)	79,723
General and administrative
Stock-based compensation
Stock-based compensation expense		$ 724	$ 39	$ 2,736	$ 92	$ 32	$ 132
General and administrative | Former Interim Chief Financial Officer | Stock Options that Contain Service, Performance and Market Conditions
Stock-based compensation
Stock-based compensation expense		$ 600		$ 600

STOCK BASED COMPENSATION - 2019

STOCK BASED COMPENSATION - 2019 Employee Stock Purchase Plan (Details) - 2019 ESPP - shares	1 Months Ended	9 Months Ended
	May 31, 2019	Sep. 30, 2019
Stock-based compensation
Shares issued under ESPP		0
Maximum
Stock-based compensation
Shares authorized (in shares)	180,000
Increase in number of shares reserved and available for issuance (as a percent)	1.00%
Increase in number of shares reserved and available for issuance (in shares)	360,000

STOCKHOLDERS' EQUITY - Common_2

STOCKHOLDERS' EQUITY - Common Stock (Details) - Vote	1 Months Ended	9 Months Ended
	Feb. 28, 2017	Sep. 30, 2019
Common Stock Par value $0.0001
STOCKHOLDERS' EQUITY
Number of votes per common stock	1	1

STOCKHOLDERS' EQUITY - Prefer_4

STOCKHOLDERS' EQUITY - Preferred stock issued (Details) - USD ($) $ / shares in Units, $ in Millions	May 16, 2019	Feb. 28, 2019	Jan. 31, 2017	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Nov. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Preferred Stock
Preferred Stock Outstanding	0			7,095,746		7,095,746		0
IPO
Preferred Stock
Issue price (in dollars per share)	$ 10
Number of shares into which convertible preferred stock are converted	7,538,671
Number of shares issued for each share of convertible preferred stock converted	1
Series A Convertible Preferred Stock
Preferred Stock
Issuance of convertible preferred stock (in shares)			3,093,898				3,093,898
Issue price (in dollars per share)			$ 2.26	$ 2.26		$ 2.26
Gross proceeds from issuance of convertible preferred stock			$ 7
Issuance costs			$ 0.7
Preferred Stock Outstanding				3,093,898	3,093,898	3,093,898	3,093,898	0		3,093,898	3,093,898	3,093,898
Series B Convertible Preferred Stock
Preferred Stock
Issuance of convertible preferred stock (in shares)		442,930		2,904,127	442,925	2,904,127
Issue price (in dollars per share)		$ 7.49		$ 7.49		$ 7.49			$ 7.49
Gross proceeds from issuance of convertible preferred stock		$ 3.3		$ 21.7
Debt converted into shares				1,097,721
Issuance costs		$ 0.3		$ 0.8
Preferred Stock Outstanding				4,001,848	4,444,773	4,001,848	0	0

STOCKHOLDERS' EQUITY - Prefer_5

STOCKHOLDERS' EQUITY - Preferred stock summary (Details) - USD ($) $ in Thousands	Sep. 30, 2019	May 16, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Preferred Stock
Preferred Stock Authorized				10,883,950				3,535,910
Preferred Stock Issued				7,095,746				3,093,898
Preferred Stock Outstanding	0	0		7,095,746
Carrying Value				$ 35,410				$ 6,254
Liquidation Value				$ 36,964				$ 7,000
Common Stock Issuable Upon Conversion				7,095,746				3,093,898
Series A Convertible Preferred Stock
Preferred Stock
Preferred Stock Authorized	0			3,093,898				3,535,910
Preferred Stock Issued	0			3,093,898				3,093,898
Preferred Stock Outstanding	0		3,093,898	3,093,898	3,093,898	3,093,898	3,093,898	3,093,898
Carrying Value			$ 6,254	$ 6,254	$ 6,254	$ 6,254	$ 6,254	$ 6,254
Liquidation Value	$ 0			$ 7,000				$ 7,000
Common Stock Issuable Upon Conversion				3,093,898				3,093,898
Series B Convertible Preferred Stock
Preferred Stock
Preferred Stock Authorized	0			7,790,052				0
Preferred Stock Issued	0			4,001,848				0
Preferred Stock Outstanding	0		4,444,773	4,001,848				0
Carrying Value			$ 32,207	$ 29,156
Liquidation Value	$ 0			$ 29,964				$ 0
Common Stock Issuable Upon Conversion				4,001,848

STOCKHOLDERS' EQUITY - Prefer_6

STOCKHOLDERS' EQUITY - Preferred stock other information (Details) $ / shares in Units, $ in Millions	May 16, 2019$ / shares	Nov. 05, 2018	Dec. 31, 2018USD ($)Vote$ / shares	Feb. 28, 2019$ / shares	Nov. 30, 2018$ / shares	Jan. 31, 2017$ / shares
Preferred Stock
Number of votes for each share of common stock into which temporary equity could be converted | Vote			1
Threshold debt obligations | $			$ 2
Minimum proceeds from conversion of preferred stock if converted | $			$ 30
Series A Convertible Preferred Stock
Preferred Stock
Original issue price (in dollars per share)			$ 2.26			$ 2.26
Stock conversion price (in dollars per share)	$ 2.26		$ 2.26
Series B Convertible Preferred Stock
Preferred Stock
Dividend multiple to be paid within twenty-four months following the original issue date		2
Dividend multiple to be paid thereafter following the original issue date		3	3
Original issue price (in dollars per share)			$ 7.49	$ 7.49	$ 7.49
Stock conversion price (in dollars per share)	$ 7.49		$ 7.49

WARRANTS - Issued with the 20_2

WARRANTS - Issued with the 2018 Notes (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 05, 2018	Mar. 31, 2019	Feb. 05, 2018	Jan. 18, 2018
Warrants
Warrants to purchase common stock (in dollars)		$ 80
Warrants Issued with the 2018 Notes
Warrants
Initial fair value recorded as debt discount (in dollars)			$ 100	$ 100
Warrants to purchase common stock (in shares)	76,847
Warrants to purchase common stock (in dollars)	$ 300
Exercise price (in dollars per share)	$ 6.59

WARRANTS - Issued with Series_2

WARRANTS - Issued with Series B Preferred Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended
	Feb. 28, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)YRate$ / sharesshares	Mar. 31, 2019USD ($)	Sep. 30, 2019YRate
Warrants
Warrants to purchase common stock (in dollars) | $			$ 80
Warrants Issued with Series B Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares	23,867	72,261
Warrants to purchase common stock (in dollars) | $	$ 100	$ 200
Exercise price (in dollars per share) | $ / shares	$ 8.24	$ 8.24
Expiration term	10 years	10 years
2018 Warrants | Warrants Issued with Series B Preferred Stock
Warrants
Warrants to purchase common stock (in shares) | shares		72,261
Warrants to purchase common stock (in dollars) | $		$ 200
Exercise price (in dollars per share) | $ / shares		$ 8.24
Expiration term		10 years
2018 Warrants | Warrants Issued with Series B Preferred Stock | Contractual term (in years)
Warrants
Measurement input | Y		10		10
2018 Warrants | Warrants Issued with Series B Preferred Stock | Volatility
Warrants
Measurement input		0.7322		0.7448
2018 Warrants | Warrants Issued with Series B Preferred Stock | Risk-free interest rate
Warrants
Measurement input		0.0270		0.0320
2018 Warrants | Warrants Issued with Series B Preferred Stock | Dividend yield
Warrants
Measurement input		0		0
2019 Warrants | Warrants Issued with Series B Preferred Stock | Contractual term (in years)
Warrants
Measurement input | Y				10
2019 Warrants | Warrants Issued with Series B Preferred Stock | Volatility
Warrants
Measurement input				0.7322
2019 Warrants | Warrants Issued with Series B Preferred Stock | Risk-free interest rate
Warrants
Measurement input				0.0270
2019 Warrants | Warrants Issued with Series B Preferred Stock | Dividend yield
Warrants
Measurement input				0

NET LOSS PER COMMON SHARE - E_2

NET LOSS PER COMMON SHARE - EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss attributable to common stockholders—basic	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Net loss attributable to common stockholders— diluted	$ (10,713)	$ (4,281)	$ (27,880)	$ (9,802)	$ (16,521)	$ (4,282)
Denominator:
Weighted-average common stock outstanding	17,095,870	5,497,871	14,085,579	5,473,414	5,483,149	5,406,513
Net loss per share attributable to common stockholders—basic and diluted	$ (0.63)	$ (0.78)	$ (1.98)	$ (1.79)	$ (3.01)	$ (0.79)

NET LOSS PER COMMON SHARE - A_2

NET LOSS PER COMMON SHARE - Anti-dilutive securities (Details) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders		3,093,898	7,095,746	3,093,898
Options
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	3,767,571	1,035,466	1,202,979	262,427
Warrants Liability
Antidilutive securities excluded from computation of loss per share
Potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	482,364	309,389	458,497	309,389

SUBSEQUENT EVENT (Details)

SUBSEQUENT EVENT (Details) - USD ($) $ / shares in Units, $ in Millions	Nov. 12, 2019	Oct. 03, 2019	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent event
Common Stock, par value (in dollars per share)			$ 0.0001	$ 0.0001	$ 0.0001
Subsequent Event. | Private Placement
Subsequent event
Shares issued (in shares)	1,380,344
Common Stock, par value (in dollars per share)	$ 0.0001
Proceeds from issuance of common stock	$ 20
Issue price (in dollars per share)	$ 14.50
Subsequent Event. | Research services agreement | Columbia University
Subsequent event
Agreement term		18 months
Written notice period for termination of agreement		30 days
Payment to be made		$ 0.4