Applied Therapeutics (APLT) 10-Q 12 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 10, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-38898
Entity Registrant Name	Applied Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-3405262
Entity Address, Address Line One	545 Fifth Avenue
Entity Address, Address Line Two	Suite 1400
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10017
City Area Code	212
Local Phone Number	220-9226
Title of 12(b) Security	Common Stock
Trading Symbol	APLT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		26,215,514
Entity Central Index Key	0001697532
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 70,207	$ 57,466
Investments	38,595	39,363
Prepaid expenses and other current assets	8,141	5,764
Total current assets	116,943	102,593
Operating lease right-of-use asset	1,404	1,712
Security deposits and leasehold improvements	200	201
TOTAL ASSETS	118,547	104,506
CURRENT LIABILITIES:
Current portion of operating lease liabilities	436	406
Accounts payable	9,170	640
Accrued expenses and other current liabilities	21,237	20,189
Total current liabilities	30,843	21,235
NONCURRENT LIABILITIES:
Noncurrent portion of operating lease liabilities	1,003	1,332
Total noncurrent liabilities	1,003	1,332
Total liabilities	31,846	22,567
STOCKHOLDERS' EQUITY:
Common stock, $0.0001 par value; 100,000,000 shares authorized as of September 30, 2021 and December 31, 2020; 26,214,399 shares and 22,493,661 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	3	2
Additional paid-in capital	326,108	242,780
Accumulated other comprehensive loss	(254)	(112)
Accumulated deficit	(239,156)	(160,731)
Total stockholders' equity	86,701	81,939
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 118,547	$ 104,506

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Condensed Balance Sheets
Common Stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common Stock, authorized (in shares)	100,000,000	100,000,000
Common Stock, issued (in shares)	26,214,399	22,493,661
Common stock, outstanding (in shares)	26,214,399	22,493,661

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
OPERATING EXPENSES:
Research and development	$ 17,597	$ 19,945	$ 46,846	$ 47,974
General and administrative	10,833	10,020	31,658	22,744
Total operating expenses	28,430	29,965	78,504	70,718
LOSS FROM OPERATIONS	(28,430)	(29,965)	(78,504)	(70,718)
OTHER INCOME (EXPENSE), NET:
Interest income (expense), net	76	131	321	435
Other income (expense)	(64)	(10)	(242)	11
Total other income (expense), net	12	121	79	446
Net loss	(28,418)	(29,844)	(78,425)	(70,272)
Net loss attributable to common stockholders-basic	(28,418)	(29,844)	(78,425)	(70,272)
Net loss attributable to common stockholders- diluted	$ (28,418)	$ (29,844)	$ (78,425)	$ (70,272)
Net loss per share attributable to common stockholders-basic	$ (1.09)	$ (1.33)	$ (3.08)	$ (3.22)
Net loss per share attributable to common stockholders-diluted	$ (1.09)	$ (1.33)	$ (3.08)	$ (3.22)
Weighted-average common stock outstanding-basic	26,177,079	22,426,203	25,472,590	21,790,207
Weighted-average common stock outstanding-diluted	26,177,079	22,426,203	25,472,590	21,790,207

Condensed Statements of Compreh

Condensed Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Statements of Comprehensive Income (Loss)
Net Loss	$ (28,418)	$ (29,844)	$ (78,425)	$ (70,272)
Other comprehensive income (loss)
Unrealized gain (loss) on marketable securities	(69)	(65)	(142)	(92)
Other comprehensive gain (loss), net of tax	(69)	(65)	(142)	(92)
Comprehensive income (loss), net of tax	$ (28,487)	$ (29,909)	$ (78,567)	$ (70,364)

Condensed Statements of Stockho

Condensed Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common StockSecondary Public Offering 2020	Common StockFebruary Offering 2021	Common Stock	Additional Paid-in CapitalPrivate Placement	Additional Paid-in CapitalSecondary Public Offering 2020	Additional Paid-in CapitalFebruary Offering 2021	Additional Paid-in CapitalRegistration of Form S-3 offering/Shelf Offering	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Private Placement	Secondary Public Offering 2020	February Offering 2021	Registration of Form S-3 offering/Shelf Offering	Total
Balance at Dec. 31, 2019			$ 1					$ 99,378	$ (66,770)	$ (2)					$ 32,607
Balance (in shares) at Dec. 31, 2019			18,531,560
Increase (Decrease) in Stockholders' Equity
Issuance of common stock	$ 1				$ 134,127							$ 134,128
Issuance of common stock (in shares)	3,152,712
Issuance costs				$ (41)							$ (41)
Exercise of options for common stock issued under equity incentive plan								81							81
Exercise of options for common stock issued under equity incentive plan (in shares)			35,027
Exercise of warrants of common stock (in shares)			249,978
Stock-based compensation expense								1,331							1,331
Net loss									(12,369)						(12,369)
Other comprehensive income (loss)										91					91
Balance at Mar. 31, 2020			$ 2					234,876	(79,139)	89					155,828
Balance (in shares) at Mar. 31, 2020			21,969,277
Balance at Dec. 31, 2019			$ 1					99,378	(66,770)	(2)					32,607
Balance (in shares) at Dec. 31, 2019			18,531,560
Increase (Decrease) in Stockholders' Equity
Net loss															(70,272)
Balance at Sep. 30, 2020			$ 2					240,074	(137,042)	(94)					102,940
Balance (in shares) at Sep. 30, 2020			22,456,686
Balance at Mar. 31, 2020			$ 2					234,876	(79,139)	89					155,828
Balance (in shares) at Mar. 31, 2020			21,969,277
Increase (Decrease) in Stockholders' Equity
Issuance costs				$ (6)	$ (25)		$ (495)				$ (6)	$ (25)		$ (495)
Exercise of options for common stock issued under equity incentive plan								1,342							1,342
Exercise of options for common stock issued under equity incentive plan (in shares)			324,614
Exercise of warrants of common stock (in shares)			37,251
Stock-based compensation expense								1,737							1,737
Net loss									(28,059)						(28,059)
Other comprehensive income (loss)										(118)					(118)
Balance at Jun. 30, 2020			$ 2					237,429	(107,198)	(29)					130,204
Balance (in shares) at Jun. 30, 2020			22,331,142
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under equity incentive plan								242							242
Exercise of options for common stock issued under equity incentive plan (in shares)			125,544
Stock-based compensation expense								2,403							2,403
Net loss									(29,844)						(29,844)
Other comprehensive income (loss)										(65)					(65)
Balance at Sep. 30, 2020			$ 2					240,074	(137,042)	(94)					102,940
Balance (in shares) at Sep. 30, 2020			22,456,686
Balance at Dec. 31, 2020			$ 2					242,780	(160,731)	(112)					81,939
Balance (in shares) at Dec. 31, 2020			22,493,661
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		$ 1				$ 74,386							$ 74,387
Issuance of common stock (in shares)		3,450,000
Exercise of options for common stock issued under equity incentive plan								67							67
Exercise of options for common stock issued under equity incentive plan (in shares)			37,400
Exercise of options for common stock not yet issued								(1)							(1)
Exercise of options for common stock not yet issued (in shares)			(465)
Restricted Stock Unit released for common stock issued under Equity Incentive Plan (in shares)			1,988
Exercise of warrants of common stock								69							69
Exercise of warrants of common stock (in shares)			27,855
Stock-based compensation expense								2,981							2,981
Net loss									(24,179)						(24,179)
Other comprehensive income (loss)										(42)					(42)
Balance at Mar. 31, 2021			$ 3					320,282	(184,910)	(154)					135,221
Balance (in shares) at Mar. 31, 2021			26,010,439
Balance at Dec. 31, 2020			$ 2					242,780	(160,731)	(112)					$ 81,939
Balance (in shares) at Dec. 31, 2020			22,493,661
Increase (Decrease) in Stockholders' Equity
Exercise of options for common stock issued under equity incentive plan (in shares)															190,436
Net loss															$ (78,425)
Balance at Sep. 30, 2021			$ 3					326,108	(239,156)	(254)					86,701
Balance (in shares) at Sep. 30, 2021			26,214,399
Balance at Mar. 31, 2021			$ 3					320,282	(184,910)	(154)					135,221
Balance (in shares) at Mar. 31, 2021			26,010,439
Increase (Decrease) in Stockholders' Equity
Secondary public offering issuance costs						$ 35							$ 35
Issuance of common stock for options exercised in prior periods under Equity Incentive Plan								1							1
Issuance of common stock for options exercised in prior periods under Equity Incentive Plan (in shares)			465
Exercise of options for common stock issued under equity incentive plan								341							341
Exercise of options for common stock issued under equity incentive plan (in shares)			82,668
Exercise of options for common stock not yet issued								(1)							(1)
Exercise of options for common stock not yet issued (in shares)			(920)
Restricted Stock Unit released for common stock issued under Equity Incentive Plan (in shares)			37,884
Stock-based compensation expense								2,702							2,702
Net loss									(25,828)						(25,828)
Other comprehensive income (loss)										(31)					(31)
Balance at Jun. 30, 2021			$ 3					323,360	(210,738)	(185)					112,440
Balance (in shares) at Jun. 30, 2021			26,130,536
Increase (Decrease) in Stockholders' Equity
Issuance of common stock for options exercised in prior periods under Equity Incentive Plan								1							1
Issuance of common stock for options exercised in prior periods under Equity Incentive Plan (in shares)			920
Exercise of options for common stock issued under equity incentive plan								103							103
Exercise of options for common stock issued under equity incentive plan (in shares)			70,368
Exercise of options for common stock not yet issued								(1)							(1)
Exercise of options for common stock not yet issued (in shares)			(115)
Restricted Stock Unit released for common stock issued under Equity Incentive Plan (in shares)			12,690
Stock-based compensation expense								2,645							2,645
Net loss									(28,418)						(28,418)
Other comprehensive income (loss)										(69)					(69)
Balance at Sep. 30, 2021			$ 3					$ 326,108	$ (239,156)	$ (254)					$ 86,701
Balance (in shares) at Sep. 30, 2021			26,214,399

Condensed Statements of Stock_2

Condensed Statements of Stockholders' (Deficit) Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity
Common Stock, par value (in dollars per share)			$ 0.0001
Secondary Public Offering 2020
Increase (Decrease) in Stockholders' Equity
Stock issuance cost		$ 714
February Offering 2021
Increase (Decrease) in Stockholders' Equity
Stock issuance cost	$ 203
Common Stock
Increase (Decrease) in Stockholders' Equity
Common Stock, par value (in dollars per share)			$ 0.0001	$ 0.0001

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
OPERATING ACTIVITIES:
Net loss	$ (78,425)	$ (70,272)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,328	5,471
Amortization of operating lease right-of-use assets	308	281
Change in operating lease liability	(299)	(263)
Changes in operating assets and liabilities:
Financed insurance premium	(4,434)
Prepaid expenses	(1,107)	3,396
Accounts payable	8,530	(6,739)
Accrued expenses and other current liabilities	149	11,127
Amortization of leasehold improvements	1
Amortization of insurance premium	3,163	1,540
Net cash used in operating activities	(63,786)	(55,459)
INVESTING ACTIVITIES:
Purchase of available-for-sale securities	(109,119)	(127,558)
Proceeds from sale of available-for-sale securities	5,539	17,109
Proceeds from maturities of available-for-sale securities	104,206	62,536
Net cash used in investing activities	626	(47,913)
FINANCING ACTIVITIES:
Proceeds from stock issuance, net of cash issuance costs	74,420	134,102
Proceeds from financed insurance premium	4,434
Financed insurance premium down payment		(793)
Repayments of short-term borrowings	(3,534)	(1,074)
Exercise of stock options for common stock under Equity Incentive Plan	512	1,665
Exercise of Warrants	69
Net cash provided by financing activities	75,901	133,201
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	12,741	29,829
Cash and cash equivalents at beginning of period	57,466	18,850
Cash and cash equivalents at end of period	70,207	48,679
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Insurance premium obtained in exchange for a short-term loan		(4,015)
Unrealized gain (loss) on marketable securities	$ (142)	92
Private Placement
FINANCING ACTIVITIES:
Payment of offering costs		(206)
Registration of Form S-3 offering/Shelf Offering
FINANCING ACTIVITIES:
Payment of offering costs		(493)
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Stock issuance costs in accrued expenses		$ 2

Condensed Statements of Cash _2

Condensed Statements of Cash Flows (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Condensed Statements of Cash Flows
Cash issuance costs	$ 702

ORGANIZATION AND SUMMARY OF SIG

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2021
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 rare metabolic diseases such as Galactosemia, Sorbitol Dehydrogenase deficiency, (“SORD” deficiency), and diabetic complications including diabetic cardiomyopathy. 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 (the “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 proceeds of $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). On November 12, 2019, the Company completed a private placement (the “Private Placement”), pursuant to which it issued and sold 1,380,344 shares of the Company’s common stock at a price of $14.50 per share, for net proceeds of $18.4 million after deducting placement agent discounts and commissions and offering costs. On January 28, 2020, the Company completed its secondary public offering (the “Secondary Public Offering”), pursuant to which it issued and sold 2,741,489 shares of common stock at a public offering price of $45.50 per share, with an additional 411,223 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares. The aggregate net proceeds received by the Company from the offering, after deducting underwriting discounts and commissions and offering costs, were $134.1 million. On June 4, 2020, the Company filed a shelf registration statement on Form S-3 (the “Shelf Registration Statement”) under which the Company may, from time to time, sell securities in one or more offerings having an aggregate offering price of up to $300.0 million. The Shelf Registration Statement was declared effective as of June 15, 2020. On June 12, 2020, the Company entered into an equity distribution agreement (the “Equity Distribution Agreement”) with Goldman Sachs & Co. LLC (“Goldman”), as a sales agent to sell shares of the Company’s common stock, from time to time, having an aggregate offering price of up to $100 million. Goldman may act as an agent on the Company’s behalf or purchase shares of the Company’s common stock as a principal. As of September 30, 2021, the Company has not sold any shares of common stock pursuant to the Equity Distribution Agreement. In February 2021, the Company completed an underwritten public offering of 3,450,000 shares of common stock (the “February Offering”), including the exercise in full of the underwriters’ option to purchase 450,000 additional shares of common stock, which option closed on February 19, 2021. The shares were offered at a price to the public of $23.00 per share, resulting in aggregate net proceeds of approximately $74.4 million, after deducting underwriting discounts and commissions and offering expenses . ​ The accompanying unaudited condensed financial statements 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, 2020 included in the Annual Report, filed with the SEC on March 18, 2021 (the “Annual Report”). 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, 2021, results of operations for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2021, are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021. 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, cash equivalents, and investments together with the net proceeds from the February Offering, 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 may 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, 2020, and the notes thereto, which are included in the Annual Report. There have been no material changes to the Company’s significant accounting policies during the three and nine months ended September 30, 2021. Recent Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes: Simplifying the Accounting for Income Taxes. primarily be made prospectively, with some changes to be made retrospectively. The Company adopted the amendment in January 2021 with no impact on the financial statements. ​

LICENSE AGREEMENT

LICENSE AGREEMENT	9 Months Ended
	Sep. 30, 2021
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. The 2016 Columbia Agreement will terminate upon the expiration of all the Company’s royalty payment obligations in all countries. The Company may terminate the 2016 Columbia Agreement for convenience upon 90 days’ written notice to Columbia University. At its election, Columbia University may terminate the 2016 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 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 In March 2019, and in connection with the 2016 Columbia Agreement, the Company entered into a research services agreement (the “2019 Columbia Research Agreement”) 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 had a term of from its effective date and expired in accordance with its terms. On October 3, 2019, and in connection with the 2019 Columbia Agreement, the Company entered into a research services agreement (the “PI3k Columbia Research Agreement” and collectively with the 2016 Columbia Agreement, 2019 Columbia Agreement and 2019 Columbia Research Agreement, the “Columbia Agreements”) with Columbia University with the purpose of analyzing PI3k inhibitors for the treatment of lymphoid malignancies. The PI3k Columbia Research Agreement had a term of 18 months from its effective date and expired in accordance with its term. ​ During the three and nine months ended September 30, 2021, the Company recorded $0 and $0, respectively, in research and development expense and $46,000 and $0.2 million, respectively, in general and administrative expense related to the Columbia Agreements. During the three and nine months ended September 30, 2020, the Company recorded $0 and $0.3 million, respectively, in research and development expense and $33,000 and $0.1 million, respectively, in general and administrative expense related to the Columbia Agreements. In aggregate, the Company has incurred $2.5 million in expense from the execution of the Columbia Agreements through September 30, 2021. As of September 30, 2021, 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, 2020, the Company had $0.1 million due to Columbia University included in accrued expenses. ​ University of Miami 2020 Miami License Agreement On October 28, 2020, the Company entered into a license agreement with the University of Miami (the “2020 Miami License Agreement”) relating to certain technology that is co-owned by the University of Miami (UM), the University of Rochester (UR) and University College London (UCL). UM was granted an exclusive agency from UR and UCL to license each of their rights in the technology. Pursuant to the 2020 Miami License Agreement, UM, on behalf of itself and UR and UCL, granted the Company a royalty-bearing, sublicensable license that is exclusive with respect to certain patent applications and patents that may grant from the applications, and non-exclusive with respect to certain know-how, in each case to research, develop, make, have made, use, sell and import products for use in treating and/or detecting certain inherited neuropathies, in particular those caused by mutation in the sorbitol dehydrogenase (SORD) gene. The license grant is worldwide. Under the 2020 Miami License Agreement, the Company is obligated to use commercially reasonable efforts to develop, manufacture, market and sell licensed products in the licensed territory, and to comply with certain obligations to meet specified development milestones within defined time periods. UM retains for itself, UR, and UCL the right to use the licensed patent rights and licensed technology for their internal non- commercial educational, research and clinical patient care purposes, including in sponsored research and collaboration with commercial entities. ​ Under the terms of the 2020 Miami License Agreement, the Company was obligated to pay UM an up-front non-refundable license fee of $1.1 million, and a second non-refundable license fee of $0.5 million due on the first anniversary of the date of the license. The Company will be required to make further payments to UM of up to an aggregate $2.2 million for the achievement of specified patenting and development milestones, and up to an aggregate of $4.1 million for achievement of late stage regulatory milestones. The Company will also be required to pay royalties ranging from 0.88% - 5% on the Company’s, the Company’s affiliates’ and the Company’s sublicensees’ net sales of licensed products. If the Company sublicenses the rights granted under the 2020 Miami License Agreement to one or more third parties, the Company will be required to pay to UM a portion of the non-royalty sublicensing revenue received from such third parties ranging from 15% – 25%. ​ The 2020 Miami License Agreement terminates upon the later of the expiration of all issued patents and filed patent applications or 10 years after the first commercial sale of the last product or process for which a royalty is due, unless earlier terminated. In addition, the 2020 Miami License Agreement may be terminated by the Company at any time upon 60 days prior written notice to UM, and may be terminated by either the Company or UM upon material breach of an obligation if action to cure the breach is not initiated within 60 days of receipt of written notice. During the three and nine months ended September 30, 2021, the Company recorded $0.2 million in research and development expense related to the 2020 Miami License Agreement. In aggregate, the Company has incurred $2.3 million in expense from execution of the 2020 Miami License Agreement through September 30, 2021. The Company had $0.7 million and $1.6 million due to UM included in accrued expenses as of September 30, 2021 and December 31, 2020, respectively, relating to the 2020 Miami License Agreement. ​ 2020 Miami Option Agreement ​ On October 28, 2020, the Company entered into an option agreement with the University of Miami (the “2020 Miami Option Agreement”) concerning certain research activities and technology relating to SORD neuropathy that may be pursued and developed by UM. Under the 2020 Miami Option Agreement, if UM conducts such research activities, then UM is obligated to grant the Company certain option rights to access and use the research results and to obtain licenses to any associated patent rights upon the Company making specified payments to UM within specified time limits. If the Company elects to obtain option rights the Company will be required to make payments to UM in the low-six figures to the low-seven figures, depending upon the rights the Company elects to obtain, and the Company will be obligated to make certain milestone payments in the high-six figures to mid-seven figures if UM conducts and completes certain research activities within specified time periods and the Company elects to receive rights to use the results of that research. ​ ​ 2020 Miami Sponsored Research Agreement ​ On December 14, 2020, the Company entered into a research agreement with the University of Miami (the “2020 Miami Research Agreement”), under which the University of Miami will conduct a research study relating to SORD neuropathy and deliver a final report on the study to the Company. The term of the research agreement is from December 14, 2020 through December 30, 2021. The consideration for the 2020 Miami Research Agreement was ​ During the three and nine months ended September 30, 2021, the Company recorded $0.1 million and $0.2 million, respectively, in research and development expense in relation to the 2020 Miami Research Agreement. The Company recorded $0.2 million and $3,740 as of September 30, 2021 and December 31, 2020, respectively, in accrued expense in relation to the 2020 Miami Research Agreement. ​ Bayh-Dole Act Some of the intellectual property rights the Company has licensed, including certain rights licensed in the agreements described above, may have been generated through the use of U.S. government funding. As a result, the U.S. government may have certain rights to intellectual property embodied in the Company’s current or future product candidates under the Bayh-Dole Act of 1980, or Bayh-Dole Act, including the grant to the government of a non-exclusive, worldwide, freedom to operate license under any patents, and the requirement, absent a waiver, to manufacture products substantially in the United States. To the extent any of the Company’s current or future intellectual property is generated through the use of U.S. government funding, the provisions of the Bayh-Dole Act may similarly apply. ​

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2021
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	3. FAIR VALUE MEASUREMENTS The following tables summarize, as of September 30, 2021, 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 in the Company’s audited financial statements as of and for the year ended December 31, 2020, and the notes thereto, which are included in the Annual Report. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 (in thousands) ​ Level 1 ​ Level 2 ​ Level 3 ​ Total Cash ​ $ 17,309 ​ $ — ​ $ — ​ $ 17,309 Money market funds ​ ​ 52,898 ​ ​ — ​ ​ — ​ ​ 52,898 Total cash and cash equivalents ​ $ 70,207 ​ $ — ​ $ — ​ $ 70,207 U.S. government agency debt securities ​ ​ — ​ ​ 38,595 ​ ​ — ​ ​ 38,595 Total marketable securities ​ $ — ​ $ 38,595 ​ $ — ​ $ 38,595 Total financial assets measured at fair value on a recurring basis ​ $ 70,207 ​ $ 38,595 ​ $ — ​ $ 108,802 ​ Investments in U.S. government agency debt securities Fair values of U.S. government agency debt securities 2

INVESTMENTS

INVESTMENTS	9 Months Ended
	Sep. 30, 2021
INVESTMENTS
INVESTMENTS	4. INVESTMENTS Marketable Securities Marketable securities, which the Company classifies as available-for-sale securities, primarily consist of 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 balance sheets. The following tables provide the Company’s marketable securities by security type (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Unrealized Unrealized Estimated ​ ​ Unrealized Unrealized Estimated (in thousands) ​ Cost ​ Gains ​ Losses ​ Fair Value ​ Cost ​ Gains ​ Losses ​ Fair Value US government agency debt security ​ ​ 38,849 ​ ​ 2 ​ ​ (256) ​ ​ 38,595 ​ ​ 39,475 ​ ​ 11 ​ ​ (123) ​ ​ 39,363 Total ​ $ 38,849 ​ $ 2 ​ $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 ​ $ (123) ​ $ 39,363 ​ As of September 30, 2021, the Company’s investment portfolio reported an unrealized loss of $0.3 million. Based on its evaluations, the Company determined that a credit loss allowance is not required since the decline was not related to underlying credit issues of the counterparties. The counterparties to these investments have high credit quality with investment grade ratings of at least AA+ or above, along with a history of no defaults. No single investment in the portfolio had an individually material unrealized loss and in the aggregate. The total amount of unrealized losses of $0.3 million as of September 30, 2021 was only 0.65% of the total amortized costs basis of the investment portfolio. In addition, the Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost bases. Accordingly, based on the foregoing evaluation, the Company did not record any credit losses during the three and nine months ended September 30, 2021 and the entire amount of the decline in fair value below the amortized cost basis was recorded as an unrealized loss, net of tax, in other comprehensive loss in the Statements of Comprehensive Loss. Unrealized gains are also reflected, net of tax, as other comprehensive income (loss) in the Statements of Comprehensive Loss. Contractual maturities of the Company’s marketable securities are summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ ​ Unrealized ​ Unrealized Estimated ​ ​ ​ ​ Unrealized ​ Unrealized Estimated (in thousands) ​ Cost Gains Losses Fair Value Cost Gains Losses Fair Value Due in one year or less ​ $ 38,849 ​ $ 2 ​ $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 ​ $ (123) ​ $ 39,363 Due in one through two years ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total ​ $ 38,849 ​ $ 2 $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 $ (123) ​ $ 39,363 ​ At September 30, 2021, the Company had $2,000 of gross unrealized gains and $0.3 million of gross unrealized losses primarily due to fluctuations in the fair value of certain U.S. government agency debt securities. During the three and nine months ended September 30, 2021, the Company recorded gross realized losses of $64,000 and $0.2 million, respectively, and gross realized gains of $0 and $0, respectively, from the sale of marketable securities. ​ The unrealized losses and fair values of available-for-sale securities that have been in an unrealized loss position for a period of less than and greater than 12 months as of September 30, 2021 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Securities in an unrealized loss position less than 12 months ​ Securities in an unrealized loss position greater than 12 months ​ Total ​ ​ Unrealized Estimated Unrealized Estimated Unrealized Estimated (in thousands) ​ Losses ​ Fair Value ​ Losses ​ Fair Value ​ Losses ​ Fair Value US government agency debt security ​ ​ (256) ​ ​ 28,356 ​ ​ — ​ ​ — ​ ​ (256) ​ ​ 28,356 Total ​ $ (256) ​ $ 28,356 ​ $ — ​ $ — ​ $ (256) ​ $ 28,356 ​ The unrealized losses and fair values of available-for-sale securities that have been in an unrealized loss position for a period of less than and greater than 12 months as of December 31, 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2020 ​ ​ Securities in an unrealized loss position less than 12 months ​ Securities in an unrealized loss position greater than 12 months ​ Total ​ ​ Unrealized Estimated Unrealized Estimated Unrealized Estimated (in thousands) ​ Losses ​ Fair Value ​ Losses ​ Fair Value ​ Losses ​ Fair Value US government agency debt security ​ ​ (123) ​ ​ 14,073 ​ ​ — ​ ​ — ​ ​ (123) ​ ​ 14,073 Total ​ $ (123) ​ $ 14,073 ​ $ — ​ $ — ​ $ (123) ​ $ 14,073 ​

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	9 Months Ended
	Sep. 30, 2021
PREPAID EXPENSES AND OTHER CURRENT ASSETS
PREPAID EXPENSES AND OTHER CURRENT ASSETS	5. PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, (in thousands) ​ 2021 ​ 2020 Prepaid research and development expenses ​ $ 3,925 ​ $ 2,349 Insurance premium asset ​ ​ 2,733 ​ ​ 1,463 Prepaid rent expenses ​ 74 ​ 108 Prepaid insurance expenses ​ 86 ​ 91 Prepaid commercial and patient advocacy ​ ​ 523 ​ ​ 968 Research and development tax credit receivable ​ 279 ​ 500 Interest receivable ​ ​ 48 ​ ​ 5 Other prepaid expenses and current assets ​ ​ 473 ​ ​ 280 Total prepaid expenses & other current assets ​ $ 8,141 ​ $ 5,764 ​

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	9 Months Ended
	Sep. 30, 2021
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	6. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, (in thousands) ​ 2021 ​ 2020 Accrued pre-clinical and clinical expenses ​ $ 13,102 ​ $ 13,742 Short-term insurance financing note ​ ​ 1,974 ​ ​ 1,074 Accrued professional fees ​ 740 ​ 511 Accrued compensation and benefits ​ 1,852 ​ 2,103 Accrued commercial expenses ​ ​ 2,114 ​ ​ 502 Accrued patent expenses ​ 798 ​ 1,704 Other ​ 657 ​ 553 Total accrued expenses & other current liabilities ​ $ 21,237 ​ $ 20,189 ​

STOCK BASED COMPENSATION

STOCK BASED COMPENSATION	9 Months Ended
	Sep. 30, 2021
STOCK BASED COMPENSATION
STOCK BASED COMPENSATION	7. 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, 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 is 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 was 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, 2021, there were 809,071 shares of common stock available for issuance under the 2019 Plan. Stock-Based Compensation Expense Total stock-based compensation expense recorded for employees, directors and non-employees (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, (in thousands) 2021 2020 2021 2020 Research and development ​ $ 642 ​ $ 638 ​ $ 1,974 ​ $ 1,911 General and administrative ​ 2,003 ​ 1,765 ​ 6,354 ​ 3,560 Total stock-based compensation expense ​ $ 2,645 ​ $ 2,403 ​ $ 8,328 ​ $ 5,471 ​ Stock Option Activity During the nine months ended September 30, 2021 the Company granted 231,081 options to shares of common stock. For the three and nine months ended September 30, 2021 and 2020, amortization of stock compensation of options amounted to $2.2 million and $7.0 million, respectively, and $2.0 million and $4.9 million, respectively. ​ The following table summarizes the information about options outstanding at September 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Weighted- Remaining Aggregate ​ ​ Options Average Contractual Intrinsic (in thousands, except for share data) ​ Outstanding ​ Exercise Price Term (in years) ​ Value Outstanding at December 31, 2020 4,529,675 ​ $ 12.87 ​ 8.5 ​ $ 51,103 Options granted 231,081 ​ ​ 16.72 ​ ​ ​ ​ ​ Options exercised (190,436) ​ ​ 2.68 ​ ​ ​ ​ 2,973 Forfeited (27,872) ​ ​ 20.67 ​ ​ ​ ​ ​ Expired (95) ​ ​ 44.02 ​ ​ ​ ​ ​ Outstanding at September 30, 2021 4,542,353 ​ $ 13.44 ​ 7.9 ​ $ 31,778 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Exercisable at September 30, 2021 2,895,866 ​ $ 8.60 ​ 7.4 ​ $ 28,630 Nonvested at September 30, 2021 1,646,487 ​ $ 21.65 ​ 8.7 ​ $ 3,148 ​ ​ Valuation of Stock Options Granted to Employees that Contain Service Conditions Only The fair value of each option award granted with service-based vesting 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 nine months ended September 30, 2021 and 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ 2021 2020 ​ Expected term (in years) ​ ​ 5.6 ​ ​ 6.0 ​ Volatility ​ 70.99 % ​ 69.30 % Risk-free interest rate ​ 0.91 % ​ 0.54 % Dividend yield ​ ​ — % ​ — % ​ Restricted Stock Unit Activity During the nine months ended September 30, 2021 the Company granted 93,645 RSUs to shares of common stock. For the three months ended September 30, 2021 and 2020, amortization of stock compensation of RSUs amounted to $0.5 million and $0.4 million, respectively. For the nine months ended September 30, 2021 and 2020, amortization of stock compensation of RSU’s amounted to $1.3 million and $0.6 million, respectively. As of September 30, 2021 and 2020, the unamortized compensation costs associated with non-vested restricted stock awards were $5.1 million and $5.5 million, respectively, with a weighted-average remaining amortization period of 2.9 and 3.6 years, respectively. ​ The following table summarizes the information about restricted stock units outstanding at September 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date Aggregate (in thousands, except for share data) ​ Shares Fair Value ​ Intrinsic Value Outstanding at December 31, 2020 206,529 ​ $ 36.08 ​ $ 4,546 Awarded 93,645 ​ ​ 14.82 ​ ​ ​ Released (52,562) ​ ​ 33.52 ​ ​ ​ Forfeited (24,919) ​ ​ 34.98 ​ ​ ​ Outstanding at September 30, 2021 222,693 ​ $ 27.87 ​ $ 3,697 Nonvested at September 30, 2021 222,693 ​ $ 27.87 ​ $ 3,697 ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Recognition Period (in years) ​ 2.9 ​ ​ ​ ​ ​ ​ ​ ​ 2019 Employee Stock Purchase Plan In May 2019, the Company’s Board and its stockholders approved the 2019 Employee Stock Purchase Plan (the “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, 2021, no shares of common stock had been issued under the ESPP. The first offering period has not yet been decided by the Board.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended
	Sep. 30, 2021
STOCKHOLDERS' EQUITY
STOCKHOLDERS' EQUITY	8. STOCKHOLDERS’ EQUITY As of September 30, 2021, and December 31, 2020, the authorized capital stock of the Company consists of 100,000,000 shares of common stock, par value $0.0001 per share and 10,000,000 shares of preferred stock, par value $0.0001 per share. Common Stock Equity Distribution Agreement In June 2020, the Company entered into the Equity Distribution Agreement with Goldman to sell shares of the Company’s common stock, from time to time, having an aggregate offering price of up to $100.0 million. The issuance and sale of shares of common stock by the Company pursuant to the Equity Distribution Agreement is deemed an “at-the-market” offering under the Securities Act of 1933, as amended, or the Securities Act. Goldman is entitled to compensation for its services equal to up to of the gross offering proceeds of all shares of the Company’s common stock sold through it as a sales agent pursuant to the Equity Distribution Agreement. As of September 30, 2021, the Company had received

WARRANTS

WARRANTS	9 Months Ended
	Sep. 30, 2021
WARRANTS
WARRANTS	9. 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. 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 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 % ​ On February 21, 2020, two warrantholders exercised 185,634 warrants in a cashless exercise at net, and the Company issued 176,092 shares of common stock. On February 24, 2020, a warrantholder exercised 72,818 warrants in a cashless exercise at net, and the Company issued 69,094 shares of common stock. On February 5, 2021, a warrantholder exercised 27,855 warrants on a cash basis and received 27,855 shares of common stock. The Company received $69,000 in cash proceeds for the exercise of these 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 convertible promissory notes, issued on February 5, 2018 (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. 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. On February 24, 2020, a warrantholder exercised 386 warrants in a cashless exercise at net, and the Company issued 333 shares of common stock. On June 24, 2020, a warrantholder exercised 20,331 warrants in a cashless exercise at net, and the Company issued 17,369 shares of common stock. 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. 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 73.22 % Risk-free interest rate 2.70 % 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. The warrants vested 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. ​ On January 14, 2020, a warrantholder exercised 220 warrants in a cashless exercise at net, and the Company issued 146 shares of common stock. On February 24, 2020, a warrantholder exercised 5,193 warrants in a cashless exercise at net, and the Company issued 4,313 shares of common stock. On June 24, 2020, a warrantholder exercised 24,309 warrants in a cashless exercise at net, and the Company issued 19,882 shares of common stock. ​ A summary of the Company’s outstanding common stock warrants as of September 30, 2021 is as follows: ​ ​ ​ ​ ​ ​ ​ Warrants Outstanding as of December 31, 2020 ​ ​ 153,473 Warrants granted and issued ​ — Warrants exercised ​ (27,855) Warrants exchanged ​ — Balance as of September 30, 2021 ​ ​ 125,618 ​

LEASES

LEASES	9 Months Ended
	Sep. 30, 2021
LEASES
LEASES	10. LEASES The following table summarizes the Company’s lease related costs for the nine months ended September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating (in thousands) Lease Cost ​ Statement of Operations Location ​ ​ 2021 ​ ​ 2020 Operating Lease Cost ​ General and administrative ​ $ 126 ​ $ 121 Total Lease Cost ​ ​ ​ $ 126 ​ $ 121 ​ Average lease terms and discount rates for the Company’s operating leases were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ Other Information 2021 ​ 2020 ​ Weighted-average remaining lease term ​ ​ ​ ​ ​ ​ ​ Operating leases ​ ​ 3.00 years ​ ​ 4.08 years ​ Weighted-average discount rate ​ ​ ​ ​ ​ ​ ​ Operating leases ​ ​ 5.69% ​ ​ 5.69% ​ ​ The following table summarizes the maturities of lease liabilities as of September 30, 2021: ​ ​ ​ ​ ​ ​ Operating Year ​ (in thousands) 2021 ​ $ 128 2022 ​ ​ 507 2023 ​ ​ 515 2024 ​ ​ 423 Thereafter ​ ​ — Total lease payments ​ ​ 1,573 Less: interest ​ ​ 134 Total lease liabilities ​ $ 1,439 ​

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2021
INCOME TAXES
INCOME TAXES	11. INCOME TAXES On March 27, 2020, Congress enacted the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) to provide certain relief as a result of the Covid-19 pandemic. The CARES Act provides numerous tax provisions and other stimulus measures, including temporary changes regarding the prior and future utilization of net operating losses, temporary changes to the prior and future limitations on interest deductions, temporary suspension of certain payment requirements for the employer portion of social security taxes, technical corrections from prior tax legislation for tax depreciation of certain qualified improvement property and the creation of certain refundable employee retention credits. The CARES Act did not have a material impact on our financial statements for the three and nine months ended September 30, 2021. The Company continues to monitor any effects that may result from the CARES Act. ​ During the nine months ended September 30, 2021 and the year ended December 31, 2020, 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.

BENEFIT PLANS

BENEFIT PLANS	9 Months Ended
	Sep. 30, 2021
BENEFIT PLANS
BENEFIT PLANS	12. 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 $ 0.2 million and $ 0.1 million in matching contributions to the plan during the nine months ended September 30, 2021 and 2020, respectively.

NET LOSS PER COMMON SHARE

NET LOSS PER COMMON SHARE	9 Months Ended
	Sep. 30, 2021
NET LOSS PER COMMON SHARE
NET LOSS PER COMMON SHARE	13. 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, 2021 and 2020, as the inclusion of all potential common shares outstanding would have been anti-dilutive. The following tables set forth the computation of basic and diluted net loss per common share for the three and nine months ended September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ September 30, (in thousands, except for share data) 2021 2020 Numerator: ​ ​ ​ ​ ​ Net loss ​ $ (28,418) ​ $ (29,844) Denominator: ​ ​ ​ ​ ​ Weighted-average common stock outstanding ​ 26,177,079 ​ ​ 22,426,203 Net loss per share attributable to common stockholders - basic and diluted ​ $ (1.09) ​ $ (1.33) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ September 30, ​ 2021 2020 Numerator: ​ ​ Net loss ​ $ (78,425) ​ $ (70,272) Denominator: ​ ​ ​ ​ ​ Weighted-average common stock outstanding ​ 25,472,590 ​ ​ 21,790,207 Net loss per share attributable to common stockholders - basic and diluted ​ $ (3.08) ​ $ (3.22) ​ The Company’s potentially dilutive securities, which include restricted stock units, 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 nine months ended September 30, 2021 and 2020, 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, ​ 2021 2020 Options to purchase common stock 4,542,353 ​ 3,942,536 Restricted stock units ​ 222,693 ​ 145,126 Warrants to purchase common stock 125,618 ​ 153,473 ​

RELATED PARTIES

RELATED PARTIES	9 Months Ended
	Sep. 30, 2021
RELATED PARTIES
RELATED PARTIES	14. 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 on a month-to-month basis. A member of the Company’s board of directors is the founder and executive chairman of Alexandria Real Estate Equities, Inc. During the three and nine months ended September 30, 2021, and 2020, the Company made payments to Alexandria LaunchLabs of approximately $23,000, $30,000, $70,000, and $66,000 respectively, under the LaunchLabs Agreement, which was recognized in research and development expenses. As of September 30, 2021, there were no amounts due to Alexandria LaunchLabs under the LaunchLabs Agreement.

ORGANIZATION AND SUMMARY OF S_2

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2021
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Operations and Business	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 rare metabolic diseases such as Galactosemia, Sorbitol Dehydrogenase deficiency, (“SORD” deficiency), and diabetic complications including diabetic cardiomyopathy. 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 (the “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 proceeds of $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). On November 12, 2019, the Company completed a private placement (the “Private Placement”), pursuant to which it issued and sold 1,380,344 shares of the Company’s common stock at a price of $14.50 per share, for net proceeds of $18.4 million after deducting placement agent discounts and commissions and offering costs. On January 28, 2020, the Company completed its secondary public offering (the “Secondary Public Offering”), pursuant to which it issued and sold 2,741,489 shares of common stock at a public offering price of $45.50 per share, with an additional 411,223 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares. The aggregate net proceeds received by the Company from the offering, after deducting underwriting discounts and commissions and offering costs, were $134.1 million. On June 4, 2020, the Company filed a shelf registration statement on Form S-3 (the “Shelf Registration Statement”) under which the Company may, from time to time, sell securities in one or more offerings having an aggregate offering price of up to $300.0 million. The Shelf Registration Statement was declared effective as of June 15, 2020. On June 12, 2020, the Company entered into an equity distribution agreement (the “Equity Distribution Agreement”) with Goldman Sachs & Co. LLC (“Goldman”), as a sales agent to sell shares of the Company’s common stock, from time to time, having an aggregate offering price of up to $100 million. Goldman may act as an agent on the Company’s behalf or purchase shares of the Company’s common stock as a principal. As of September 30, 2021, the Company has not sold any shares of common stock pursuant to the Equity Distribution Agreement. In February 2021, the Company completed an underwritten public offering of 3,450,000 shares of common stock (the “February Offering”), including the exercise in full of the underwriters’ option to purchase 450,000 additional shares of common stock, which option closed on February 19, 2021. The shares were offered at a price to the public of $23.00 per share, resulting in aggregate net proceeds of approximately $74.4 million, after deducting underwriting discounts and commissions and offering expenses . ​ The accompanying unaudited condensed financial statements 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, 2020 included in the Annual Report, filed with the SEC on March 18, 2021 (the “Annual Report”). 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, 2021, results of operations for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2021, are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021.
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, cash equivalents, and investments together with the net proceeds from the February Offering, 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 may 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.
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.
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.
Significant Accounting Policies	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, 2020, and the notes thereto, which are included in the Annual Report. There have been no material changes to the Company’s significant accounting policies during the three and nine months ended September 30, 2021.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes: Simplifying the Accounting for Income Taxes. primarily be made prospectively, with some changes to be made retrospectively. The Company adopted the amendment in January 2021 with no impact on the financial statements.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
FAIR VALUE MEASUREMENTS
Schedule of financial assets or liabilities measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 (in thousands) ​ Level 1 ​ Level 2 ​ Level 3 ​ Total Cash ​ $ 17,309 ​ $ — ​ $ — ​ $ 17,309 Money market funds ​ ​ 52,898 ​ ​ — ​ ​ — ​ ​ 52,898 Total cash and cash equivalents ​ $ 70,207 ​ $ — ​ $ — ​ $ 70,207 U.S. government agency debt securities ​ ​ — ​ ​ 38,595 ​ ​ — ​ ​ 38,595 Total marketable securities ​ $ — ​ $ 38,595 ​ $ — ​ $ 38,595 Total financial assets measured at fair value on a recurring basis ​ $ 70,207 ​ $ 38,595 ​ $ — ​ $ 108,802

INVESTMENTS (Tables)

INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
INVESTMENTS
Schedule of marketable securities by security type	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Unrealized Unrealized Estimated ​ ​ Unrealized Unrealized Estimated (in thousands) ​ Cost ​ Gains ​ Losses ​ Fair Value ​ Cost ​ Gains ​ Losses ​ Fair Value US government agency debt security ​ ​ 38,849 ​ ​ 2 ​ ​ (256) ​ ​ 38,595 ​ ​ 39,475 ​ ​ 11 ​ ​ (123) ​ ​ 39,363 Total ​ $ 38,849 ​ $ 2 ​ $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 ​ $ (123) ​ $ 39,363
Schedule of contractual maturities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ ​ ​ ​ Unrealized ​ Unrealized Estimated ​ ​ ​ ​ Unrealized ​ Unrealized Estimated (in thousands) ​ Cost Gains Losses Fair Value Cost Gains Losses Fair Value Due in one year or less ​ $ 38,849 ​ $ 2 ​ $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 ​ $ (123) ​ $ 39,363 Due in one through two years ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total ​ $ 38,849 ​ $ 2 $ (256) ​ $ 38,595 ​ $ 39,475 ​ $ 11 $ (123) ​ $ 39,363
Unrealized Gain (Loss) on Investments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Securities in an unrealized loss position less than 12 months ​ Securities in an unrealized loss position greater than 12 months ​ Total ​ ​ Unrealized Estimated Unrealized Estimated Unrealized Estimated (in thousands) ​ Losses ​ Fair Value ​ Losses ​ Fair Value ​ Losses ​ Fair Value US government agency debt security ​ ​ (256) ​ ​ 28,356 ​ ​ — ​ ​ — ​ ​ (256) ​ ​ 28,356 Total ​ $ (256) ​ $ 28,356 ​ $ — ​ $ — ​ $ (256) ​ $ 28,356 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2020 ​ ​ Securities in an unrealized loss position less than 12 months ​ Securities in an unrealized loss position greater than 12 months ​ Total ​ ​ Unrealized Estimated Unrealized Estimated Unrealized Estimated (in thousands) ​ Losses ​ Fair Value ​ Losses ​ Fair Value ​ Losses ​ Fair Value US government agency debt security ​ ​ (123) ​ ​ 14,073 ​ ​ — ​ ​ — ​ ​ (123) ​ ​ 14,073 Total ​ $ (123) ​ $ 14,073 ​ $ — ​ $ — ​ $ (123) ​ $ 14,073

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2021
PREPAID EXPENSES AND OTHER CURRENT ASSETS
Summary of prepaid expenses and other current assets	​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, (in thousands) ​ 2021 ​ 2020 Prepaid research and development expenses ​ $ 3,925 ​ $ 2,349 Insurance premium asset ​ ​ 2,733 ​ ​ 1,463 Prepaid rent expenses ​ 74 ​ 108 Prepaid insurance expenses ​ 86 ​ 91 Prepaid commercial and patient advocacy ​ ​ 523 ​ ​ 968 Research and development tax credit receivable ​ 279 ​ 500 Interest receivable ​ ​ 48 ​ ​ 5 Other prepaid expenses and current assets ​ ​ 473 ​ ​ 280 Total prepaid expenses & other current assets ​ $ 8,141 ​ $ 5,764

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2021
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
Summary of accrued expenses and other current liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, (in thousands) ​ 2021 ​ 2020 Accrued pre-clinical and clinical expenses ​ $ 13,102 ​ $ 13,742 Short-term insurance financing note ​ ​ 1,974 ​ ​ 1,074 Accrued professional fees ​ 740 ​ 511 Accrued compensation and benefits ​ 1,852 ​ 2,103 Accrued commercial expenses ​ ​ 2,114 ​ ​ 502 Accrued patent expenses ​ 798 ​ 1,704 Other ​ 657 ​ 553 Total accrued expenses & other current liabilities ​ $ 21,237 ​ $ 20,189

STOCK BASED COMPENSATION (Table

STOCK BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2021
Stock-based compensation
Schedule of stock-based compensation expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, (in thousands) 2021 2020 2021 2020 Research and development ​ $ 642 ​ $ 638 ​ $ 1,974 ​ $ 1,911 General and administrative ​ 2,003 ​ 1,765 ​ 6,354 ​ 3,560 Total stock-based compensation expense ​ $ 2,645 ​ $ 2,403 ​ $ 8,328 ​ $ 5,471
Schedule of options outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Weighted- Remaining Aggregate ​ ​ Options Average Contractual Intrinsic (in thousands, except for share data) ​ Outstanding ​ Exercise Price Term (in years) ​ Value Outstanding at December 31, 2020 4,529,675 ​ $ 12.87 ​ 8.5 ​ $ 51,103 Options granted 231,081 ​ ​ 16.72 ​ ​ ​ ​ ​ Options exercised (190,436) ​ ​ 2.68 ​ ​ ​ ​ 2,973 Forfeited (27,872) ​ ​ 20.67 ​ ​ ​ ​ ​ Expired (95) ​ ​ 44.02 ​ ​ ​ ​ ​ Outstanding at September 30, 2021 4,542,353 ​ $ 13.44 ​ 7.9 ​ $ 31,778 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Exercisable at September 30, 2021 2,895,866 ​ $ 8.60 ​ 7.4 ​ $ 28,630 Nonvested at September 30, 2021 1,646,487 ​ $ 21.65 ​ 8.7 ​ $ 3,148
Schedule of restricted stock units outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date Aggregate (in thousands, except for share data) ​ Shares Fair Value ​ Intrinsic Value Outstanding at December 31, 2020 206,529 ​ $ 36.08 ​ $ 4,546 Awarded 93,645 ​ ​ 14.82 ​ ​ ​ Released (52,562) ​ ​ 33.52 ​ ​ ​ Forfeited (24,919) ​ ​ 34.98 ​ ​ ​ Outstanding at September 30, 2021 222,693 ​ $ 27.87 ​ $ 3,697 Nonvested at September 30, 2021 222,693 ​ $ 27.87 ​ $ 3,697 ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average Remaining Recognition Period (in years) ​ 2.9 ​ ​ ​ ​ ​ ​
Stock options - Service conditions only
Stock-based compensation
Schedule of valuation assumptions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ 2021 2020 ​ Expected term (in years) ​ ​ 5.6 ​ ​ 6.0 ​ Volatility ​ 70.99 % ​ 69.30 % Risk-free interest rate ​ 0.91 % ​ 0.54 % Dividend yield ​ ​ — % ​ — %

WARRANTS (Tables)

WARRANTS (Tables)	9 Months Ended
	Sep. 30, 2021
Warrants
Schedule of warrants outstanding	​ ​ ​ ​ ​ ​ ​ Warrants Outstanding as of December 31, 2020 ​ ​ 153,473 Warrants granted and issued ​ — Warrants exercised ​ (27,855) Warrants exchanged ​ — Balance as of September 30, 2021 ​ ​ 125,618
Warrants Issued with Series A Preferred Stock | 2017 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	​ ​ ​ ​ ​ Contractual term (in years) 10.0 Volatility 74.48 % Risk-free interest rate 3.20 % Dividend yield 0.00 %
Warrants Issued with Series B Preferred Stock | 2018 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	​ ​ ​ ​ ​ Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 %
Warrants Issued with Series B Preferred Stock | 2019 Warrants
Warrants
Schedule of fair value of warrants using the Black Scholes option pricing model	​ ​ ​ ​ ​ Contractual term (in years) 10.0 Volatility 73.22 % Risk-free interest rate 2.70 % Dividend yield 0.00 %

LEASES (Tables)

LEASES (Tables)	9 Months Ended
	Sep. 30, 2021
LEASES
Summary of lease related costs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating (in thousands) Lease Cost ​ Statement of Operations Location ​ ​ 2021 ​ ​ 2020 Operating Lease Cost ​ General and administrative ​ $ 126 ​ $ 121 Total Lease Cost ​ ​ ​ $ 126 ​ $ 121
Summary of lease terms and discount rates	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ Other Information 2021 ​ 2020 ​ Weighted-average remaining lease term ​ ​ ​ ​ ​ ​ ​ Operating leases ​ ​ 3.00 years ​ ​ 4.08 years ​ Weighted-average discount rate ​ ​ ​ ​ ​ ​ ​ Operating leases ​ ​ 5.69% ​ ​ 5.69% ​
Summary of maturities of lease liabilities	​ ​ ​ ​ ​ ​ Operating Year ​ (in thousands) 2021 ​ $ 128 2022 ​ ​ 507 2023 ​ ​ 515 2024 ​ ​ 423 Thereafter ​ ​ — Total lease payments ​ ​ 1,573 Less: interest ​ ​ 134 Total lease liabilities ​ $ 1,439

NET LOSS PER COMMON SHARE (Tabl

NET LOSS PER COMMON SHARE (Tables)	9 Months Ended
	Sep. 30, 2021
NET LOSS PER COMMON SHARE
Schedule of computation of basic and diluted net loss per common share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ September 30, (in thousands, except for share data) 2021 2020 Numerator: ​ ​ ​ ​ ​ Net loss ​ $ (28,418) ​ $ (29,844) Denominator: ​ ​ ​ ​ ​ Weighted-average common stock outstanding ​ 26,177,079 ​ ​ 22,426,203 Net loss per share attributable to common stockholders - basic and diluted ​ $ (1.09) ​ $ (1.33) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ September 30, ​ 2021 2020 Numerator: ​ ​ Net loss ​ $ (78,425) ​ $ (70,272) Denominator: ​ ​ ​ ​ ​ Weighted-average common stock outstanding ​ 25,472,590 ​ ​ 21,790,207 Net loss per share attributable to common stockholders - basic and diluted ​ $ (3.08) ​ $ (3.22) ​
Schedule of potential dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ September 30, ​ 2021 2020 Options to purchase common stock 4,542,353 ​ 3,942,536 Restricted stock units ​ 222,693 ​ 145,126 Warrants to purchase common stock 125,618 ​ 153,473

ORGANIZATION AND SUMMARY OF S_3

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock issued (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 12, 2020	Jun. 04, 2020	Jan. 28, 2020	Nov. 12, 2019	May 16, 2019	Feb. 28, 2021	Sep. 30, 2021	Sep. 30, 2020
IPO
Proceeds from stock issuance, net of cash issuance costs							$ 74,420	$ 134,102
IPO
IPO
Issuance of common stock (in shares)					4,000,000
Issue price (in dollars per share)					$ 10
Aggregate gross proceeds from issuance					$ 40,000
Net proceeds after deducting underwriting discounts and commissions and offering costs					$ 34,600
Private Placement
IPO
Issuance of common stock (in shares)				1,380,344
Issue price (in dollars per share)				$ 14.50
Proceeds from stock issuance, net of cash issuance costs				$ 18,400
Secondary Public Offering 2020
IPO
Issue price (in dollars per share)			$ 45.50
Proceeds from stock issuance, net of cash issuance costs			$ 134,100
Secondary public offering, excluding underwriters' option
IPO
Issuance of common stock (in shares)			2,741,489
February Offering 2021
IPO
Issuance of common stock (in shares)						3,450,000
Issue price (in dollars per share)						$ 23
Proceeds from stock issuance, net of cash issuance costs						$ 74,400
Underwriters' option
IPO
Issuance of common stock (in shares)			411,223			450,000
Registration of Form S-3 offering/Shelf Offering
IPO
Maximum value of shares authorized to be sold in stock offering.		$ 300,000
Equity Distribution Agreement
IPO
Maximum value of shares authorized to be sold in stock offering.	$ 100,000

LICENSE AGREEMENT - Columbia (D

LICENSE AGREEMENT - Columbia (Details) - USD ($) $ in Thousands	Oct. 03, 2019	Mar. 31, 2019	Jan. 31, 2019	Oct. 31, 2016	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Agreements
Research and development					$ 17,597	$ 19,945	$ 46,846	$ 47,974
General and administrative					10,833	10,020	31,658	22,744
Operating expenses					28,430	29,965	78,504	70,718
Accrued expenses and other current liabilities					21,237		21,237		$ 21,237	$ 20,189
Accounts payable					9,170		9,170		9,170	640
Columbia University
Agreements
Research and development					0	0	0	300
General and administrative					46	$ 33	200	$ 100
Operating expenses									2,500
Accrued expenses and other current liabilities					100		100		100	$ 100
Accounts payable					$ 100		$ 100		$ 100
2016 license agreement | Columbia University
Agreements
Percentage of outstanding common stock issued				5.00%
Fair value of stock issued				$ 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
P13k Research agreement | Columbia University
Agreements
Agreement term	18 months

LICENSE AGREEMENT - Miami Unive

LICENSE AGREEMENT - Miami University (Details) - USD ($)	Dec. 14, 2020	Oct. 28, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Agreements
Research and development			$ 17,597,000	$ 19,945,000	$ 46,846,000	$ 47,974,000
Operating expenses			28,430,000	29,965,000	78,504,000	70,718,000
General and administrative			10,833,000	$ 10,020,000	31,658,000	$ 22,744,000
Accrued expenses and other current liabilities			21,237,000		21,237,000		$ 21,237,000	$ 20,189,000
Accounts payable			9,170,000		9,170,000		9,170,000	640,000
2020 license agreement | University of Miami
Agreements
Amount of first payment to be made for license issue fee		$ 1,100,000
Amount of second payment to be made for license issue fee, due on first anniversary of the date of license		500,000
Payment to be made on achievement of specified patenting and development milestones		2,200,000
Payment to be made on achievement of late stage regulatory milestones		$ 4,100,000
Agreement term		10 years
Written notice period for termination of agreement		60 days
Written notice period of material breach leading to termination		60 days
Research and development			200,000		200,000
Operating expenses							2,300,000
Accrued expenses and other current liabilities			700,000		700,000		700,000	1,600,000
2020 license agreement | University of Miami | Minimum
Agreements
Royalties payment (as a percent)		0.88%
Non-royalty sublicensing revenue payment (as a percent)		15.00%
2020 license agreement | University of Miami | Maximum
Agreements
Royalties payment (as a percent)		5.00%
Non-royalty sublicensing revenue payment (as a percent)		25.00%
2020 Research Agreement | University of Miami
Agreements
Consideration	$ 300,000
Research and development			100,000		200,000
Accrued expenses and other current liabilities			$ 200,000		$ 200,000		$ 200,000	$ 3,740

FAIR VALUE MEASUREMENTS - FV hi

FAIR VALUE MEASUREMENTS - FV hierarchy (Details) - Fair Value, Recurring $ in Thousands	Sep. 30, 2021USD ($)
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	$ 70,207
Marketable securities	38,595
Total financial assets measured at fair value on a recurring basis	108,802
Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	70,207
Total financial assets measured at fair value on a recurring basis	70,207
Level 2
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	38,595
Total financial assets measured at fair value on a recurring basis	38,595
Cash
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	17,309
Cash | Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	17,309
Money market funds
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	52,898
Money market funds | Level 1
Financial assets or liabilities measured at fair value on a recurring basis
Cash and cash equivalents	52,898
U.S. government agency debt securities
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	38,595
U.S. government agency debt securities | Level 2
Financial assets or liabilities measured at fair value on a recurring basis
Marketable securities	$ 38,595

FAIR VALUE MEASUREMENTS - Trans

FAIR VALUE MEASUREMENTS - Transfers (Details) $ in Thousands	Sep. 30, 2021USD ($)
FAIR VALUE MEASUREMENTS
Assets, transfer from level 1 to level 2	$ 0
Assets, transfer from level 2 to level 1	$ 0

INVESTMENTS - By type (Details)

INVESTMENTS - By type (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable securities by type
Cost	$ 38,849	$ 39,475
Gross Unrealized Gains	2	11
Gross Unrealized Losses	(256)	(123)
Estimated Fair Value	38,595	39,363
U.S. government agency debt securities
Marketable securities by type
Cost	38,849	39,475
Gross Unrealized Gains	2	11
Gross Unrealized Losses	(256)	(123)
Estimated Fair Value	$ 38,595	$ 39,363

INVESTMENTS - Additional Inform

INVESTMENTS - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
INVESTMENTS
Gross unrealized loss	$ 256	$ 123
Unrealized loss as a percentage of total amortized costs basis of corporate bond portfolio	0.65%

INVESTMENTS - By contractual ma

INVESTMENTS - By contractual maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
INVESTMENTS
Due in one year or less - Cost	$ 38,849	$ 39,475
Due in on year or less - Gross Unrealized Gains	2	11
Due in one through two years - Gross Unrealized Losses	(256)	(123)
Due in one year or less - Estimated Fair Value	38,595	39,363
Cost	38,849	39,475
Gross Unrealized Gains	2	11
Gross Unrealized Losses	(256)	(123)
Estimated Fair Value	$ 38,595	$ 39,363

INVESTMENTS - Realized gains an

INVESTMENTS - Realized gains and losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Marketable securities realized gain (loss) recorded
Gross realized gain from sale of marketable securities	$ 0	$ 0
Gross realized loss from sale of marketable securities	$ 64	$ 200

INVESTMENTS - Unrealized losses

INVESTMENTS - Unrealized losses and fair values of available-for-sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Securities in an unrealized loss position less than 12 months
Unrealized Losses Less Than 12 months	$ (256)	$ (123)
Estimated Fair Value Less Than 12 Months	28,356	14,073
Total Unrealized Losses	(256)	(123)
Total Estimated Fair Value	28,356	14,073
U.S. government agency debt securities
Securities in an unrealized loss position less than 12 months
Unrealized Losses Less Than 12 months	(256)	(123)
Estimated Fair Value Less Than 12 Months	28,356	14,073
Total Unrealized Losses	(256)	(123)
Total Estimated Fair Value	$ 28,356	$ 14,073

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
PREPAID EXPENSES AND OTHER CURRENT ASSETS
Prepaid research and development expenses	$ 3,925	$ 2,349
Insurance premium asset	2,733	1,463
Prepaid rent expenses	74	108
Prepaid insurance expenses	86	91
Prepaid commercial and patient advocacy	523	968
Research and development tax credit receivable	279	500
Interest receivable	48	5
Other prepaid expenses and current assets	473	280
Total prepaid expenses & other current assets	$ 8,141	$ 5,764

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES
Accrued pre-clinical and clinical expenses	$ 13,102	$ 13,742
Short-term insurance financing note	1,974	1,074
Accrued professional fees	740	511
Accrued compensation and benefits	1,852	2,103
Accrued commercial expenses	2,114	502
Accrued patent expenses	798	1,704
Other	657	553
Total accrued expenses & other current liabilities	$ 21,237	$ 20,189

STOCK BASED COMPENSATION - Plan

STOCK BASED COMPENSATION - Plans (Details) - 2019 Plan - shares	1 Months Ended
	May 31, 2019	Sep. 30, 2021
Stock-based compensation
Shares reserved (in shares)	4,530,000
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%
Number of shares available for future issuance		809,071
Options
Stock-based compensation
Maximum number of shares authorized for issuance	13,000,000
Expiration period	10 years
Vesting period	4 years

STOCK BASED COMPENSATION - Stoc

STOCK BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-based compensation
Total stock-based compensation expense	$ 2,645	$ 2,403	$ 8,328	$ 5,471
Research and development
Stock-based compensation
Total stock-based compensation expense	642	638	1,974	1,911
General and administrative
Stock-based compensation
Total stock-based compensation expense	$ 2,003	$ 1,765	$ 6,354	$ 3,560

STOCK BASED COMPENSATION - Opti

STOCK BASED COMPENSATION - Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-based compensation
Options granted (in shares)			231,081
Stock-based compensation expense	$ 2,645	$ 2,403	$ 8,328	$ 5,471
Weighted-average fair value of options granted (in dollars per share)			$ 10.01	$ 24.74
Unrecognized stock-based compensation balance for unvested options	20,200		$ 20,200
Options
Stock-based compensation
Stock-based compensation expense	$ 2,200	$ 2,000	$ 7,000	$ 4,900
Unrecognized stock-based compensation balance for unvested options expected to be recognized (in years)			2 years 6 months

STOCK BASED COMPENSATION - Op_2

STOCK BASED COMPENSATION - Options activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Options Outstanding
Outstanding at beginning of period (in shares) | shares	4,529,675
Options granted (in shares) | shares	231,081
Options exercised (in shares) | shares	(190,436)
Forfeited (in shares) | shares	(27,872)
Expired (in shares) | shares	(95)
Outstanding at end of period (in shares) | shares	4,542,353	4,529,675
Exercisable at end of period (in shares) | shares	2,895,866
Nonvested at end of period (in shares) | shares	1,646,487
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 12.87
Options granted (in dollars per share) | $ / shares	16.72
Options exercised (in dollars per share) | $ / shares	2.68
Options forfeited (in dollars per share) | $ / shares	20.67
Options expired (in dollars per share) | $ / shares	44.02
Outstanding at end of period (in dollars per share) | $ / shares	13.44	$ 12.87
Exercisable at end of period (in dollars per share) | $ / shares	8.60
Nonvested at end of period (in dollars per share) | $ / shares	$ 21.65
Weighted-Average Remaining Contractual Term-in years
Outstanding	7 years 10 months 24 days	8 years 6 months
Exercisable	7 years 4 months 24 days
Nonvested	8 years 8 months 12 days
Aggregate Intrinsic Value
Options exercised (in dollars) | $	$ 2,973
Outstanding (in dollars) | $	31,778	$ 51,103
Exercisable (in dollars) | $	28,630
Nonvested (in dollars) | $	$ 3,148

STOCK BASED COMPENSATION - Valu

STOCK BASED COMPENSATION - Valuation assumptions (Details) - Stock options - Service conditions only	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Valuation Assumptions
Expected term/Time to expiration (in years)	5 years 7 months 6 days	6 years
Volatility	70.99%	69.30%
Risk-free interest rate	0.91%	0.54%

STOCK BASED COMPENSATION - RSUs

STOCK BASED COMPENSATION - RSUs (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Stock-based compensation
Stock-based compensation expense	$ 2,645	$ 2,403	$ 8,328	$ 5,471
Restricted Stock Units (RSUs)
Stock-based compensation
Stock-based compensation expense	500	400	1,300	600
Unamortized stock-based compensation costs for unvested awards	$ 5,100	$ 5,500	$ 5,100	$ 5,500
Summary of restricted stock units outstanding
Outstanding at beginning of period ( in shares)			206,529
Awarded (in shares)			93,645
Released (in shares)			(52,562)
Forfeited (in shares)			(24,919)
Outstanding at end of period ( in shares)	222,693		222,693
Nonvested at end of period (in shares)	222,693		222,693
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)			$ 36.08
Awarded (in dollars per share)			14.82
Released (in dollars per share)			33.52
Forfeited (in dollars per share)			34.98
Outstanding at end of period (in dollars per share)	$ 27.87		27.87
Nonvested at end of period (in dollars per share)	$ 27.87		$ 27.87
Aggregate Intrinsic Value
Outstanding at end of period (in dollars)	$ 3,697		$ 3,697		$ 4,546
Nonvested at end of period (in dollars)	$ 3,697		$ 3,697
Unrecognized stock-based compensation balance for unvested options expected to be recognized (in years)			2 years 10 months 24 days	3 years 7 months 6 days

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, 2021
Stock-based compensation
Shares authorized (in shares)	180,000
Shares issued under ESPP		0
Maximum
Stock-based compensation
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 - Authoriz

STOCKHOLDERS' EQUITY - Authorized stock (Details) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
STOCKHOLDERS' EQUITY
Common Stock, authorized (in shares)	100,000,000	100,000,000
Common Stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred Stock, authorized (in shares)	10,000,000	10,000,000
Preferred Stock, par value (in dollars per share)	$ 0.0001	$ 0.0001

STOCKHOLDERS' EQUITY - Common S

STOCKHOLDERS' EQUITY - Common Stock and Equity Distribution Agreement (Details) - Equity Distribution Agreement - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2021
STOCKHOLDERS' EQUITY
Offering price	$ 100
Maximum amount paid to Goldman (as a percent)	3.00%
Proceeds from stock issuance		$ 0

WARRANTS - Issued with Series A

WARRANTS - Issued with Series A Preferred Stock (Details) $ / shares in Units, $ in Thousands	Feb. 05, 2021USD ($)shares	Feb. 24, 2020shares	Feb. 21, 2020itemshares	Jan. 26, 2017USD ($)$ / sharesshares	Sep. 30, 2021USD ($)Yshares
Warrants
Warrants exercised (in shares)					27,855
Proceeds from exercise of warrants | $					$ 69
2017 Warrants | Warrants Issued with Series A Preferred Stock
Warrants
Warrants to purchase common stock (in shares)				309,389
Warrants to purchase common stock (in dollars) | $				$ 200
Exercise price (in dollars per share) | $ / shares				$ 2.49
Number of warrant holders that exercised options | item			2
Warrants exercised (in shares)	27,855	72,818	185,634
Stock issued in exercise of warrants (in shares)	27,855	69,094	176,092
Proceeds from exercise of warrants | $	$ 69
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					0.7448
2017 Warrants | Warrants Issued with Series A Preferred Stock | Risk-free interest rate
Warrants
Measurement input					0.0320
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 Millions	Jun. 24, 2020	Feb. 24, 2020	Nov. 05, 2018	Sep. 30, 2021	Jan. 18, 2018
Warrants
Warrants exercised (in shares)				27,855
Warrants Issued with the 2018 Notes
Warrants
Initial fair value recorded as debt discount (in dollars)					$ 0.1
Warrants to purchase common stock (in shares)			76,847
Warrants to purchase common stock (in dollars)			$ 0.3
Exercise price (in dollars per share)			$ 6.59
Warrants exercised (in shares)	20,331	386
Stock issued in exercise of warrants (in shares)	17,369	333

WARRANTS - Issued with Series B

WARRANTS - Issued with Series B Preferred Stock (Details) $ / shares in Units, $ in Millions	Jun. 24, 2020shares	Feb. 24, 2020shares	Jan. 14, 2020shares	Feb. 28, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2021RateYshares
Class of Warrant or Right [Line Items]
Warrants exercised (in shares) | shares						27,855
Warrants Issued with Series B Preferred Stock
Class of Warrant or Right [Line Items]
Warrants exercised (in shares) | shares	24,309	5,193	220
Stock issued in exercise of warrants (in shares) | shares	19,882	4,313	146
Warrants Issued with Series B Preferred Stock | 2018 Warrants
Class of Warrant or Right [Line Items]
Warrants to purchase common stock (in shares) | shares					72,261
Warrants to purchase common stock (in dollars) | $					$ 0.2
Exercise price (in dollars per share) | $ / shares					$ 8.24
Expiration term					10 years
Warrants Issued with Series B Preferred Stock | 2018 Warrants | Contractual term (in years)
Class of Warrant or Right [Line Items]
Measurement input | Y						10
Warrants Issued with Series B Preferred Stock | 2018 Warrants | Volatility
Class of Warrant or Right [Line Items]
Measurement input						0.7322
Warrants Issued with Series B Preferred Stock | 2018 Warrants | Risk-free interest rate
Class of Warrant or Right [Line Items]
Measurement input | Rate						0.0270
Warrants Issued with Series B Preferred Stock | 2018 Warrants | Dividend yield
Class of Warrant or Right [Line Items]
Measurement input | Rate						0
Warrants Issued with Series B Preferred Stock | 2019 Warrants
Class of Warrant or Right [Line Items]
Warrants to purchase common stock (in shares) | shares				23,867
Warrants to purchase common stock (in dollars) | $				$ 0.1
Exercise price (in dollars per share) | $ / shares				$ 8.24
Expiration term				10 years
Warrants Issued with Series B Preferred Stock | 2019 Warrants | Contractual term (in years)
Class of Warrant or Right [Line Items]
Measurement input | Y						10
Warrants Issued with Series B Preferred Stock | 2019 Warrants | Volatility
Class of Warrant or Right [Line Items]
Measurement input | Rate						0.7322
Warrants Issued with Series B Preferred Stock | 2019 Warrants | Risk-free interest rate
Class of Warrant or Right [Line Items]
Measurement input | Rate						0.0270
Warrants Issued with Series B Preferred Stock | 2019 Warrants | Dividend yield
Class of Warrant or Right [Line Items]
Measurement input | Rate						0

WARRANTS - Warrant Activity (De

WARRANTS - Warrant Activity (Details)	9 Months Ended
	Sep. 30, 2021shares
WARRANTS
Outstanding as of beginning of period	153,473
Warrants exercised	(27,855)
Outstanding as of end of period	125,618

LEASES - Lease Cost (Details)

LEASES - Lease Cost (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases
Operating Lease Cost	$ 126	$ 121
General and administrative
Leases
Operating Lease Cost	$ 126	$ 121

LEASES - Lease terms and discou

LEASES - Lease terms and discount rates (Details)	Sep. 30, 2021	Sep. 30, 2020
LEASES
Weighted-average remaining lease term - operating leases	3 years	4 years 29 days
Weighted-average discount rate - operating leases	5.69%	5.69%

LEASES - Maturities of Lease Li

LEASES - Maturities of Lease Liabilities (Details) $ in Thousands	Sep. 30, 2021USD ($)
LEASES
2021	$ 128
2022	507
2023	515
2024	423
Total lease payments	1,573
Less: interest	134
Total lease liabilities	$ 1,439

BENEFIT PLANS (Details)

BENEFIT PLANS (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
BENEFIT PLANS
Employer matching contributions to the plan	$ 0.2	$ 0.1

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
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss attributable to common stockholders-basic	$ (28,418)	$ (29,844)	$ (78,425)	$ (70,272)
Net loss attributable to common stockholders- diluted	$ (28,418)	$ (29,844)	$ (78,425)	$ (70,272)
Denominator:
Weighted-average common stock outstanding-basic	26,177,079	22,426,203	25,472,590	21,790,207
Weighted-average common stock outstanding-diluted	26,177,079	22,426,203	25,472,590	21,790,207
Net loss per share attributable to common stockholders-basic	$ (1.09)	$ (1.33)	$ (3.08)	$ (3.22)
Net loss per share attributable to common stockholders-diluted	$ (1.09)	$ (1.33)	$ (3.08)	$ (3.22)

NET LOSS PER COMMON SHARE - Ant

NET LOSS PER COMMON SHARE - Anti-dilutive securities (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
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	4,542,353	3,942,536
Restricted Stock Units (RSUs)
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	222,693	145,126
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	125,618	153,473

RELATED PARTIES (Details)

RELATED PARTIES (Details) - LaunchLabs Agreement - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Related Party Transaction [Line Items]
Payments to related party	$ 23	$ 30	$ 70	$ 66
Due to related parties	$ 0		$ 0