scPharmaceuticals (SCPH) 10-Q 16 May 22 2022 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	May 31, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Trading Symbol	SCPH
Entity Registrant Name	SCPHARMACEUTICALS INC.
Entity Central Index Key	0001604950
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.0001
Security Exchange Name	NASDAQ
Entity File Number	001-38293
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5184075
Entity Address, Address Line One	2400 District Avenue
Entity Address, Address Line Two	Suite 310
Entity Address, City or Town	Burlington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01803
City Area Code	617
Local Phone Number	517-0730
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		27,371,488

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 51,630	$ 74,268
Restricted cash	182	182
Short-term investments	13,788	1,010
Prepaid expenses	2,567	2,791
Other current assets	59	24
Total current assets	68,226	78,275
Property and equipment, net	66	69
Right-of-use lease assets - operating, net	318	410
Deposits and other assets	283	283
Total assets	68,893	79,037
Current liabilities
Accounts payable	445	544
Accrued expenses	3,477	3,995
Term loan, short-term	9,826	9,805
Lease obligation - operating, short-term	356	476
Other current liabilities	71	26
Total current liabilities	14,175	14,846
Term loan, long-term	4,913	7,354
Lease obligation - operating, long-term	10
Other liabilities	402	367
Total liabilities	19,500	22,567
Commitments and contingencies (Note 11)
Stockholders’ equity
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued and outstanding
Common stock, $0.0001 par value; 150,000,000 shares authorized as of March 31, 2022; 27,366,707 and 27,371,488 shares issued and outstanding as of December 31, 2021 and March 31, 2022, respectively	3	3
Additional paid-in capital	246,823	246,166
Accumulated deficit	(197,429)	(189,698)
Accumulated other comprehensive loss	(4)	(1)
Total stockholders’ equity	49,393	56,470
Total liabilities and stockholders’ equity	$ 68,893	$ 79,037

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	27,371,488	27,366,707
Common stock, shares outstanding	27,371,488	27,366,707

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating expenses:
Research and development	$ 4,347	$ 4,009
General and administrative	2,893	2,732
Total operating expenses	7,240	6,741
Loss from operations	(7,240)	(6,741)
Other income	14	255
Interest income	13	20
Interest expense	(518)	(636)
Net loss	$ (7,731)	$ (7,102)
Net loss per share — basic and diluted	$ (0.28)	$ (0.26)
Weighted average common shares outstanding — basic and diluted	27,368,354	27,336,724
Other comprehensive loss:
Unrealized loss on short-term investments	$ (3)	$ (2)
Comprehensive loss	$ (7,734)	$ (7,104)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Other Comprehensive Income
Beginning Balance at Dec. 31, 2020	$ 82,170	$ 3	$ 243,830	$ (161,664)	$ 1
Beginning Balance, Shares at Dec. 31, 2020		27,325,959
Net loss	(7,102)			(7,102)
Issuance of common stock upon exercise of stock options	9		9
Issuance of common stock upon exercise of stock options, Shares		2,500
Vesting of restricted stock	(81)		(81)
Vesting of restricted stock, Shares		26,994
Stock-based compensation	521		521
Unrealized loss on short-term investments	(2)				(2)
Ending Balance at Mar. 31, 2021	75,515	$ 3	244,279	(168,766)	(1)
Ending Balance, Shares at Mar. 31, 2021		27,355,453
Beginning Balance at Dec. 31, 2021	56,470	$ 3	246,166	(189,698)	(1)
Beginning Balance, Shares at Dec. 31, 2021		27,366,707
Net loss	(7,731)			(7,731)
Issuance of common stock upon exercise of stock options	$ 21		21
Issuance of common stock upon exercise of stock options, Shares	4,781	4,781
Stock-based compensation	$ 636		636
Unrealized loss on short-term investments	(3)				(3)
Ending Balance at Mar. 31, 2022	$ 49,393	$ 3	$ 246,823	$ (197,429)	$ (4)
Ending Balance, Shares at Mar. 31, 2022		27,371,488

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities
Net loss	$ (7,731,000)	$ (7,102,000)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation expense	9,000	8,000
Amortization expense - right-of-use leased assets - operating	93,000	98,000
Accretion expense	4,000	79,000
Stock-based compensation	636,000	521,000
Non-cash interest expense	114,000	127,000
Changes in operating assets and liabilities
Prepaid expenses and other assets	187,000	(119,000)
Accounts payable, accrued expenses and other liabilities	(681,000)	(2,227,000)
Net cash used in operating activities	(7,369,000)	(8,615,000)
Cash flows from investing activities
Purchases of property and equipment	(6,000)
Maturities of short-term investments		16,700,000
Purchases of short-term investments	(12,784,000)	(3,995,000)
Net cash provided by (used in) investing activities	(12,790,000)	12,705,000
Cash flows from financing activities
Principal payments on term loan	(2,500,000)
Proceeds from the exercise of vested stock options	21,000	9,000
Settlements of restricted stock units for tax withholding obligations		(81,000)
Net cash used in financing activities	(2,479,000)	(72,000)
Net increase (decrease) in cash, cash equivalents and restricted cash	(22,638,000)	4,018,000
Cash, cash equivalents and restricted cash at beginning of period	74,450,000	72,001,000
Cash, cash equivalents and restricted cash at end of period	51,812,000	76,019,000
Supplemental cash flow information
Interest paid	425,000	597,000
Taxes paid	$ 36,000	$ 42,000

Description of Business and Bas

Description of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	1. Description of Business and Basis of Presentation Description of Business scPharmaceuticals LLC was formed as a limited liability company under the laws of the State of Delaware on February 19, 2013. On March 24, 2014, scPharmaceuticals LLC was converted to a Delaware corporation and changed its name to scPharmaceuticals Inc. (“the Company”). The Company is a pharmaceutical company focused on developing and commercializing products that have the potential to optimize the delivery of infused therapies, advance patient care and reduce healthcare costs. The Company’s strategy is designed to enable the subcutaneous administration of therapies that have previously been limited to intravenous (“IV”) delivery. The Company’s headquarters and primary place of business is Burlington, Massachusetts. Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) for interim financial information and have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. The condensed consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary, scPharmaceuticals Securities Corporation. Certain information and disclosures normally included in financial statements in accordance with U.S. GAAP have been condensed or omitted. Accordingly, these condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and related notes for the year ended December 31, 2021 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 22, 2022. The Company has determined that it operates in one segment. The accompanying condensed consolidated balance sheet as of March 31, 2022, the condensed consolidated statements of operations and comprehensive loss and stockholders’ equity for the three months ended March 31, 2021 and 2022 and condensed consolidated statements of cash flows for the three months ended March 31, 2021 and 2022 are unaudited. The unaudited condensed consolidated financial statements have been prepared on a basis consistent with that used to prepare the Company’s audited annual financial statements and include, in the opinion of management, adjustments, consisting of normal recurring items, necessary for the fair statement of the condensed consolidated financial statements. The operating results for the three months ended March 31, 2022 are not necessarily indicative of the results expected for the full year ending December 31, 2022. Liquidity As of March 31, 2022, the Company had an accumulated deficit of approximately $ 197.4 million. Management expects to continue to incur operating losses for the foreseeable future. The Company has financed its operations to date from proceeds from the sale of common stock, preferred stock and the incurrence of debt. As of March 31, 2022 , the Company had cash, cash equivalents, restricted cash, and short-term investments of $ 65.6 million. The Company's existing cash, cash equivalents, restricted cash and short-term investments will be sufficient to meet its cash commitments for at least the next 12 months after the date that the interim condensed consolidated financial statements are issued. Additionally, the Company expects to have access to funds pursuant to an at-the-market offering program with Cowen and Company, LLC (Note 9), or could otherwise seek additional funding through a combination of public or private equity offerings or debt financing if it believes additional resources are needed. Additional financing may not be available on a timely basis on terms acceptable to the Company, or at all.

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies 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 the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reported periods. Actual results could differ from those estimates. Cash, Cash Equivalents and Restricted Cash Cash, cash equivalents and restricted cash consists of bank deposits and money market accounts with financial institutions. Cash equivalents are carried at cost which approximates fair value due to their short-term nature and which the Company believes do not have a material exposure to credit risk. The Company considers all highly liquid investments with maturities of three months or less from the date of purchase to be cash equivalents. The Company’s cash and cash equivalent accounts, at times, may exceed federally insured limits. The Company has not experienced any losses in such accounts. As of March 31, 2022 , the Company classified $ 182,000 as restricted cash related to a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate office facilities (Note 11). Cash, cash equivalents and restricted cash consists of the following (in thousands): December 31, March 31, Cash and cash equivalents $ 74,268 $ 51,630 Restricted cash 182 182 Cash, cash equivalents and restricted cash $ 74,450 $ 51,812 Concentration of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents and short-term investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s short-term investments consist of United States Treasury securities, corporate debt securities and commercial paper. The Company has adopted an investment policy that limits the amounts the Company may invest in any one type of investment and requires all investments held by the Company to hold a minimum rating, thereby reducing credit risk exposure. Investments The Company invests excess cash balances in available-for-sale debt securities. The Company determines the appropriate classification of these securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company reports available-for-sale investments at fair value at each balance sheet date and includes any unrealized gains and losses in accumulated other comprehensive income (loss), a component of stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in the value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other than temporary,” including the intention to sell and, if so, marks the investment to market through a charge to the Company’s consolidated statements of operations and comprehensive loss. Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in right-of-use (“ROU”) lease assets, current portion of lease obligations, and long-term lease obligations on the Company’s balance sheets. ROU lease assets represent the Company’s right to use an underlying asset for the lease term and lease obligations represent the Company’s obligation to make lease payments arising from the lease. Operating ROU lease assets and obligations are recognized at the commencement date based on the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The ROU lease asset excludes lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. Income Taxes The Company accounts for income taxes in accordance with the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes. Deferred tax assets and liabilities are recorded to reflect the impact of temporary differences between amounts of assets and liabilities for financial reporting purposes and such amounts as measured under enacted tax laws. A valuation allowance is required to offset any net deferred tax assets if, based upon the available evidence, it is more likely than not that some or all of the deferred tax asset will not be realized. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is “more likely than not” to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. At March 31, 2022 , the Company had no such accruals. As part of the Tax Cuts and Jobs Act of 2017 (TCJA), beginning with the Company’s fiscal year ending December 31, 2022, the Company is required to capitalize research and development expenses, as defined under section 174 of the Internal Revenue Code of 1986, as amended. For expenses that are incurred for research and development in the United States, the amounts will be amortized over 5 years, and expenses that are incurred for research and experimentation outside the United States will be amortized over 15 years. The Company already capitalizes its research and development expenses for income tax purposes as it is a start-up company, so there is no material impact forecasted for this change in legislation in 2022.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Net Loss per Share	3. Net Loss per Share Net Loss per Share Attributable to Common Stockholders The following table sets forth the computation of basic and diluted net loss per share of common stock (in thousands, except share and per share data): Three Months Ended March 31, 2021 2022 Net loss $ ( 7,102 ) $ ( 7,731 ) Weighted-average shares used in computing net loss per share 27,336,724 27,368,354 Net loss per share, basic and diluted $ ( 0.26 ) $ ( 0.28 ) The Company’s potentially dilutive securities, which include stock options and unvested restricted stock units, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect. Three Months Ended March 31, 2021 2022 Stock options to purchase common stock 2,805,029 3,442,152 Unvested restricted stock units 42,250 42,250 Total 2,847,279 3,484,402

Investments

Investments	3 Months Ended
	Mar. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Investments	4. Investments Cash in excess of the Company’s immediate requirements is invested in accordance with the Company’s investment policy that primarily seeks to maintain adequate liquidity and preserve capital. A summary of the Company’s available-for-sale classified investments as of December 31, 2021 and March 31, 2022 consisted of the following (in thousands): At December 31, 2021 Investments - Current: Cost Basis Accumulated Unrealized Gains Accumulated Unrealized Losses Fair Value Corporate debt securities $ 1,011 $ - $ ( 1 ) $ 1,010 Total $ 1,011 $ - $ ( 1 ) $ 1,010 At March 31, 2022 Investments - Current: Cost Basis Accumulated Unrealized Gains Accumulated Unrealized Losses Fair Value United States Treasury securities $ 8,987 $ - $ ( 1 ) $ 8,986 Corporate debt securities 2,813 - ( 3 ) 2,810 Commercial paper 1,992 - - 1,992 Total $ 13,792 $ - $ ( 4 ) $ 13,788 The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of March 31, 2022 consisted of the following (in thousands): Amortized Cost Fair Value Due in one year or less $ 13,792 $ 13,788 Total $ 13,792 $ 13,788

Property and Equipment

Property and Equipment	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment	5. Property and Equipment Purchased property and equipment consist of the following (dollars in thousands): ESTIMATED December 31, March 31, Office equipment 5 years $ 10 $ 6 Office furniture 7 years 126 126 Computer equipment 3 years 8 8 Leasehold improvements Life of lease 95 95 239 235 Less: Accumulated depreciation ( 170 ) ( 169 ) Property and equipment, net $ 69 $ 66 Depreciation expense for the three months ended March 31, 2021 and March 31, 2022 was $ 8,000 and $ 9,000 , respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2022
Accrued Liabilities, Current [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consist of the following (in thousands): December 31, March 31, Contract research and development $ 2,350 $ 2,199 Employee compensation and related costs 1,152 707 Consulting and professional service fees 265 335 Interest 154 132 Financing related costs 60 60 State taxes 5 44 Other 9 - Total accrued expenses $ 3,995 $ 3,477

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	7. Fair Value of Financial Instruments FASB ASC Topic, Fair Value Measurements and Disclosures (“ASC 820”), provides a fair value hierarchy, which classifies fair value measurements based on the inputs used in measuring fair value. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below: Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and observable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying values of the Company’s cash and restricted cash, prepaid expenses and deposits approximate their fair values due to their short-term nature. The carrying value of the Company’s loan payable is considered a reasonable estimate of fair value because the Company’s interest rate is near current market rates for instruments with similar characteristics. The following tables summarize the Company’s assets that are measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): As of December 31, 2021 TOTAL Quoted Prices Significant Significant Assets: Cash equivalents $ 72,449 $ 72,449 $ — $ — Total cash equivalents 72,449 72,449 — — Corporate debt securities 1,010 — 1,010 — Investments 1,010 — 1,010 — Total $ 73,459 $ 72,449 $ 1,010 $ — As of March 31, 2022 TOTAL Quoted Prices Significant Significant Assets: Cash equivalents $ 49,666 $ 47,866 $ 1,800 $ — Total cash equivalents 49,666 47,866 1,800 — United States Treasury securities 8,986 8,986 — — Corporate debt securities 2,810 — 2,810 Commercial paper 1,992 — 1,992 — Investments 13,788 8,986 4,802 — Total $ 63,454 $ 56,852 $ 6,602 $ —

Term Loan

Term Loan	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Term Loan	8. Term Loan In May 2017, the Company entered into a loan and security agreement (the “2017 Loan Agreement”), with SLR Investment Corp. (f/k/a Solar Capital Ltd.) and Silicon Valley Bank (together, the “Lenders”), for $ 10.0 million. In September 2019, the Company replaced the 2017 Loan Agreement with a new $ 20.0 million term loan with the Lenders (the “2019 Loan Agreement”). The 2019 Loan Agreement extends the term of the credit facility until September 17, 2023 . Debt issuance costs for the 2019 Loan Agreement, including unamortized issuance costs for the 2017 Loan Agreement, will be amortized to interest expense over the remaining term of the 2019 Loan Agreement using the effective-interest method. The interest rate under the 2019 Loan Agreement is the higher of (i) LIBOR plus 7.95 % or (ii) 10.18 % and there was an interest-only period until September 30, 2021. The rate at March 31, 2022 was 10.18 %. Pursuant to the 2019 Loan Agreement, the Company provided a first priority security interest in substantially all of the Company’s assets, including intellectual property, subject to certain exceptions. The Company entered into an Exit Agreement in connection with the 2019 Loan Agreement which provides for an aggregate payment of 4 % of the loan commitment, or $ 800,000 , to the lenders upon the occurrence of an exit event (the “Exit Fee”). The Company paid the Exit Fee during 2020 in conjunction with the Company’s public offering, which was deemed to be an exit event pursuant to the Exit Agreement. As of March 31, 2022 , unpaid borrowings under the 2019 Loan Agreement totaled $ 15.0 million. For the three months ended March 31, 2022 , the Company recorded $ 80,000 related to the amortization of debt discount associated with the 2019 Loan Agreement. For the three months ended March 31, 2021 , the Company recorded $ 87,000 related to the amortization of debt discount associated with the 2019 Loan Agreement. The 2019 Loan Agreement allows the Company to voluntarily prepay all (but not less than all) of the outstanding principal at any time. A prepayment premium of 3 % or 1 % through the one-year anniversary and the two-year anniversary, respectively, would be assessed on the outstanding principal. After the two-year anniversary, a 0.5 % prepayment premium would be assessed on the outstanding principal. A final payment fee of $ 500,000 is due upon the earlier to occur of the maturity date or prepayment of such borrowings. For the three months ended March 31, 2022 , the Company recorded $ 34,000 related to the amortization of the final payment fee associated with the 2019 Loan Agreement. For the three months ended March 31, 2021 , the Company recorded $ 40,000 related to the amortization of the final payment fee associated with the 2019 Loan Agreement. In an event of default under the 2019 Loan Agreement, the interest rate will be increased by 5 % and the balance under the loan may become immediately due and payable at the option of the lenders. The 2019 Loan Agreement includes restrictions on, among other things, the Company’s ability to incur additional indebtedness, change the name or location of the Company’s business, merge with or acquire other entities, pay dividends or make other distributions to holders of its capital stock, make certain investments, engage in transactions with affiliates, create liens, sell assets or pay subordinated debt. Total term loan and unamortized debt discount balances are as follows (in thousands): March 31, Face value $ 15,000 Less: discount ( 261 ) Total $ 14,739 Less: current portion ( 9,826 ) Long-term portion $ 4,913 As of March 31, 2022, future principal payments due under the 2019 Loan Agreement are as follows (in thousands): Year ended: December 31, 2022 $ 7,500 December 31, 2023 7,500 Total $ 15,000

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity 2021 At-the-Market Issuance Sales Agreement On March 23, 2021, the Company entered into an Open Market Sale Agreement SM (the “2021 ATM Agreement”) with Cowen and Company, LLC (“Cowen”) with respect to an at-the-market offering program (the “2021 ATM Program”) under which the Company could offer and sell shares of its common stock (the “2021 ATM Shares”), having an aggregate offering price of up to $ 50.0 million through Cowen as its sales agent. The Company agreed to pay Cowen a commission up to 3.0 % of the gross sales proceeds of such 2021 ATM Shares. As of March 31, 2022 , the Company had received no proceeds from the sale of shares of common stock pursuant to the 2021 ATM Agreement.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	10. Stock-Based Compensation Stock Options The Company’s 2017 Stock Option and Incentive Plan (the “2017 Stock Plan”) became effective in November 2017 , upon the closing of the Company’s initial public offering and will expire in October 2027 . Under the 2017 Stock Plan, the Company may grant incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. The Company’s 2014 Stock Incentive Plan (the “2014 Stock Plan”) was terminated in November 2017 effective upon the completion of the Company’s initial public offering and no further options will be granted under the 2014 Stock Plan. At March 31, 2022 , there were 598,619 options outstanding under the 2014 Stock Plan. As of March 31, 2022 , there were 6,143,876 shares of the Company’s common stock authorized for issuance under the 2017 Stock Plan, including 359,652 options that have been forfeited from the 2014 Stock Plan. At March 31, 2022 , there were 3,228,289 options available for issuance under the 2017 Stock Plan, 2,843,533 options outstanding and 42,250 RSUs outstanding. Awards granted under the 2017 Stock Plan have a term of ten years . Vesting of awards under the 2017 Stock Plan is determined by the board of directors, but is generally over one to four-year terms. The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions: Three Months Ended 2021 2022 Risk-free interest rate 0.50 % - 0.72 % 1.67 % - 1.90 % Expected dividend yield 0 % 0 % Expected life 5.5 - 6.7 years 5.6 - 6.7 years Expected volatility 72 %- 74 % 70 %- 72 % Weighted-average grant date fair value $ 4.36 $ 2.93 The following table summarizes information about stock option activity during the three months ended March 31, 2022 (in thousands, except share and per share data): NUMBER OF WEIGHTED- WEIGHTED- AGGREGATE Outstanding, December 31, 2021 2,662,752 $ 6.28 Granted 795,119 4.61 Exercised ( 4,781 ) 4.42 Forfeited ( 10,938 ) 8.32 Outstanding, March 31, 2022 3,442,152 $ 5.89 7.83 $ 2,389 Vested and exercisable, March 31, 2022 1,582,865 $ 6.18 6.33 $ 1,356 Vested and expected to vest, March 31, 2022 2,777,959 $ 5.95 7.52 $ 1,997 The following table summarizes information about RSU activity during the three months ended March 31, 2022: RSUs AVERAGE GRANT Outstanding, December 31, 2021 42,250 $ 3.25 Granted — — Vested — — Forfeited — — RSUs outstanding at March 31, 2022 42,250 $ 3.25 Unrecognized compensation expense related to unvested options as of March 31, 2022 was $ 3.8 million and will be recognized over the remaining vesting periods of the underlying awards. The weighted-average period over which such compensation is expected to be recognized is 2.6 years. Unrecognized compensation expense related to unvested RSUs as of March 31, 2022 was $ 18,000 and will be recognized over the remaining vesting periods of the underlying awards. The weighted-average period over which such compensation is expected to be recognized is 6 months. Employee Stock Purchase Plan In October 2017, the board of directors approved the 2017 Employee Stock Purchase Plan ("the ESPP") which became effective in November 2017, upon the closing of the Company's IPO. As part of the ESPP, eligible employees may acquire an ownership interest in the Company by purchasing common stock, at a discount, through payroll deductions. Eligible employees who elected to participate were able to participate in the ESPP beginning September 1, 2021. As of March 31, 2022, there were 1,188,629 shares of common stock available for issuance under the ESPP. The Company recorded stock-based compensation expense in the following expense categories of its accompanying condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2022 (in thousands): Three Months Ended March 31, 2021 2022 Research and development $ 226 $ 254 General and administrative 295 382 Total $ 521 $ 636

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Operating Leases The Company leases office facilities and equipment under long-term, non-cancelable operating lease agreements. The leases expire at various dates through 2025 and do not include renewal options. Certain leases provide for increases in future minimum annual rental payments as defined in the lease agreements. The leases generally also include real estate taxes and common area maintenance charges in the annual rental payments. Pursuant to the terms of its lease agreement for the Company’s headquarters, the Company obtained a letter of credit in the amount of approximately $ 182,000 as security on the lease obligation. The letter of credit is listed as restricted cash on the Company’s consolidated balance sheets. Short-term leases are leases having a term of twelve months or less. The Company recognizes short-term leases on a straight-line basis and does no t record a related lease asset or liability for such leases. The following is a maturity analysis of the annual undiscounted cash flows of the operating lease liabilities as of March 31, 2022 (in thousands): Year ended: December 31, 2022 $ 369 December 31, 2023 9 December 31, 2024 9 December 31, 2025 1 Total minimum lease payments 388 Less imputed interest ( 22 ) Total $ 366 Three Months Ended 2021 2022 Lease cost: Operating lease cost $ 122 $ 118 Short-term lease cost - 13 Sublease income ( 13 ) ( 13 ) Total lease cost $ 109 $ 118 Other information Cash paid for amounts included in the measurement of lease liabilities $ 141 $ 140 Operating cash flows from operating leases $ ( 14 ) $ ( 18 ) Weighted-average remaining lease term - operating leases 1.7 years 0.8 years Weighted-average discount rate - operating leases 10.1 % 10.1 % Research and Development Agreements As part of the Company’s research and development efforts, the Company enters into research and development agreements with certain companies. These agreements contain varying terms and provisions which include fees and milestones to be paid by the Company. Some of these agreements also contain provisions which require the Company to make payments for exclusivity in the development of products in the area of loop diuretics.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. On April 11, 2022, the Company signed an amendment to the lease for its facility located in Burlington, Massachusetts. The lease commenced on September 1, 2017 and was scheduled to expire on November 30, 2022. The amendment extends the original lease term for a period of 12 months through November 30, 2023 and does not contain any options to extend beyond that term. The amendment results in future minimum lease payments of approximately $ 640,000 .

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
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 the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reported periods. Actual results could differ from those estimates.
Cash Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Cash, cash equivalents and restricted cash consists of bank deposits and money market accounts with financial institutions. Cash equivalents are carried at cost which approximates fair value due to their short-term nature and which the Company believes do not have a material exposure to credit risk. The Company considers all highly liquid investments with maturities of three months or less from the date of purchase to be cash equivalents. The Company’s cash and cash equivalent accounts, at times, may exceed federally insured limits. The Company has not experienced any losses in such accounts. As of March 31, 2022 , the Company classified $ 182,000 as restricted cash related to a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate office facilities (Note 11). Cash, cash equivalents and restricted cash consists of the following (in thousands): December 31, March 31, Cash and cash equivalents $ 74,268 $ 51,630 Restricted cash 182 182 Cash, cash equivalents and restricted cash $ 74,450 $ 51,812
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents and short-term investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s short-term investments consist of United States Treasury securities, corporate debt securities and commercial paper. The Company has adopted an investment policy that limits the amounts the Company may invest in any one type of investment and requires all investments held by the Company to hold a minimum rating, thereby reducing credit risk exposure.
Investments	Investments The Company invests excess cash balances in available-for-sale debt securities. The Company determines the appropriate classification of these securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company reports available-for-sale investments at fair value at each balance sheet date and includes any unrealized gains and losses in accumulated other comprehensive income (loss), a component of stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in the value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other than temporary,” including the intention to sell and, if so, marks the investment to market through a charge to the Company’s consolidated statements of operations and comprehensive loss.
Leases	Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in right-of-use (“ROU”) lease assets, current portion of lease obligations, and long-term lease obligations on the Company’s balance sheets. ROU lease assets represent the Company’s right to use an underlying asset for the lease term and lease obligations represent the Company’s obligation to make lease payments arising from the lease. Operating ROU lease assets and obligations are recognized at the commencement date based on the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The ROU lease asset excludes lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term.
Income Taxes	Income Taxes The Company accounts for income taxes in accordance with the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes. Deferred tax assets and liabilities are recorded to reflect the impact of temporary differences between amounts of assets and liabilities for financial reporting purposes and such amounts as measured under enacted tax laws. A valuation allowance is required to offset any net deferred tax assets if, based upon the available evidence, it is more likely than not that some or all of the deferred tax asset will not be realized. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is “more likely than not” to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. At March 31, 2022 , the Company had no such accruals. As part of the Tax Cuts and Jobs Act of 2017 (TCJA), beginning with the Company’s fiscal year ending December 31, 2022, the Company is required to capitalize research and development expenses, as defined under section 174 of the Internal Revenue Code of 1986, as amended. For expenses that are incurred for research and development in the United States, the amounts will be amortized over 5 years, and expenses that are incurred for research and experimentation outside the United States will be amortized over 15 years. The Company already capitalizes its research and development expenses for income tax purposes as it is a start-up company, so there is no material impact forecasted for this change in legislation in 2022.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents and Restricted Cash	As of March 31, 2022 , the Company classified $ 182,000 as restricted cash related to a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate office facilities (Note 11). Cash, cash equivalents and restricted cash consists of the following (in thousands): December 31, March 31, Cash and cash equivalents $ 74,268 $ 51,630 Restricted cash 182 182 Cash, cash equivalents and restricted cash $ 74,450 $ 51,812

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share of Common Stock	The following table sets forth the computation of basic and diluted net loss per share of common stock (in thousands, except share and per share data): Three Months Ended March 31, 2021 2022 Net loss $ ( 7,102 ) $ ( 7,731 ) Weighted-average shares used in computing net loss per share 27,336,724 27,368,354 Net loss per share, basic and diluted $ ( 0.26 ) $ ( 0.28 )
Schedule of Antidilutive Securities Excluded from Computation of Net Loss Per Share	The Company’s potentially dilutive securities, which include stock options and unvested restricted stock units, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect. Three Months Ended March 31, 2021 2022 Stock options to purchase common stock 2,805,029 3,442,152 Unvested restricted stock units 42,250 42,250 Total 2,847,279 3,484,402

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Classified Investments	A summary of the Company’s available-for-sale classified investments as of December 31, 2021 and March 31, 2022 consisted of the following (in thousands): At December 31, 2021 Investments - Current: Cost Basis Accumulated Unrealized Gains Accumulated Unrealized Losses Fair Value Corporate debt securities $ 1,011 $ - $ ( 1 ) $ 1,010 Total $ 1,011 $ - $ ( 1 ) $ 1,010 At March 31, 2022 Investments - Current: Cost Basis Accumulated Unrealized Gains Accumulated Unrealized Losses Fair Value United States Treasury securities $ 8,987 $ - $ ( 1 ) $ 8,986 Corporate debt securities 2,813 - ( 3 ) 2,810 Commercial paper 1,992 - - 1,992 Total $ 13,792 $ - $ ( 4 ) $ 13,788
Summary of Amortized Cost and Fair Value of Available-for-Sale Investments by Contract Maturity	The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of March 31, 2022 consisted of the following (in thousands): Amortized Cost Fair Value Due in one year or less $ 13,792 $ 13,788 Total $ 13,792 $ 13,788

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Purchased Property and Equipment	Purchased property and equipment consist of the following (dollars in thousands): ESTIMATED December 31, March 31, Office equipment 5 years $ 10 $ 6 Office furniture 7 years 126 126 Computer equipment 3 years 8 8 Leasehold improvements Life of lease 95 95 239 235 Less: Accumulated depreciation ( 170 ) ( 169 ) Property and equipment, net $ 69 $ 66

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2022
Accrued Liabilities, Current [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): December 31, March 31, Contract research and development $ 2,350 $ 2,199 Employee compensation and related costs 1,152 707 Consulting and professional service fees 265 335 Interest 154 132 Financing related costs 60 60 State taxes 5 44 Other 9 - Total accrued expenses $ 3,995 $ 3,477

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	The following tables summarize the Company’s assets that are measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): As of December 31, 2021 TOTAL Quoted Prices Significant Significant Assets: Cash equivalents $ 72,449 $ 72,449 $ — $ — Total cash equivalents 72,449 72,449 — — Corporate debt securities 1,010 — 1,010 — Investments 1,010 — 1,010 — Total $ 73,459 $ 72,449 $ 1,010 $ — As of March 31, 2022 TOTAL Quoted Prices Significant Significant Assets: Cash equivalents $ 49,666 $ 47,866 $ 1,800 $ — Total cash equivalents 49,666 47,866 1,800 — United States Treasury securities 8,986 8,986 — — Corporate debt securities 2,810 — 2,810 Commercial paper 1,992 — 1,992 — Investments 13,788 8,986 4,802 — Total $ 63,454 $ 56,852 $ 6,602 $ —

Term Loan (Tables)

Term Loan (Tables)	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Schedule of Total Term Loan and Unamortized Debt Discount	Total term loan and unamortized debt discount balances are as follows (in thousands): March 31, Face value $ 15,000 Less: discount ( 261 ) Total $ 14,739 Less: current portion ( 9,826 ) Long-term portion $ 4,913
Schedule of Future Principal Payments Due	As of March 31, 2022, future principal payments due under the 2019 Loan Agreement are as follows (in thousands): Year ended: December 31, 2022 $ 7,500 December 31, 2023 7,500 Total $ 15,000

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
Schedule of Estimated Fair Value of Options Valuation Assumptions	The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions: Three Months Ended 2021 2022 Risk-free interest rate 0.50 % - 0.72 % 1.67 % - 1.90 % Expected dividend yield 0 % 0 % Expected life 5.5 - 6.7 years 5.6 - 6.7 years Expected volatility 72 %- 74 % 70 %- 72 % Weighted-average grant date fair value $ 4.36 $ 2.93
Summary of Information about Stock Option Activity	The following table summarizes information about stock option activity during the three months ended March 31, 2022 (in thousands, except share and per share data): NUMBER OF WEIGHTED- WEIGHTED- AGGREGATE Outstanding, December 31, 2021 2,662,752 $ 6.28 Granted 795,119 4.61 Exercised ( 4,781 ) 4.42 Forfeited ( 10,938 ) 8.32 Outstanding, March 31, 2022 3,442,152 $ 5.89 7.83 $ 2,389 Vested and exercisable, March 31, 2022 1,582,865 $ 6.18 6.33 $ 1,356 Vested and expected to vest, March 31, 2022 2,777,959 $ 5.95 7.52 $ 1,997
Schedule of RSU Activity	The following table summarizes information about RSU activity during the three months ended March 31, 2022: RSUs AVERAGE GRANT Outstanding, December 31, 2021 42,250 $ 3.25 Granted — — Vested — — Forfeited — — RSUs outstanding at March 31, 2022 42,250 $ 3.25
Summary of Stock-Based Compensation Expense	The Company recorded stock-based compensation expense in the following expense categories of its accompanying condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2022 (in thousands): Three Months Ended March 31, 2021 2022 Research and development $ 226 $ 254 General and administrative 295 382 Total $ 521 $ 636

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Schedule of Maturity Analysis of Annual Undiscounted Cash Flows of Operating Lease Liabilities	The following is a maturity analysis of the annual undiscounted cash flows of the operating lease liabilities as of March 31, 2022 (in thousands): Year ended: December 31, 2022 $ 369 December 31, 2023 9 December 31, 2024 9 December 31, 2025 1 Total minimum lease payments 388 Less imputed interest ( 22 ) Total $ 366
Schedule of Lease Cost and Other Information of Operating Lease Liabilities	Three Months Ended 2021 2022 Lease cost: Operating lease cost $ 122 $ 118 Short-term lease cost - 13 Sublease income ( 13 ) ( 13 ) Total lease cost $ 109 $ 118 Other information Cash paid for amounts included in the measurement of lease liabilities $ 141 $ 140 Operating cash flows from operating leases $ ( 14 ) $ ( 18 ) Weighted-average remaining lease term - operating leases 1.7 years 0.8 years Weighted-average discount rate - operating leases 10.1 % 10.1 %

Description of Business and B_2

Description of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (197,429)	$ (189,698)
Cash, cash equivalents, restricted cash, and short-term investments	$ 65,600

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Schedule Of Accounting Policies [Line Items]
Restricted cash	$ 182,000	$ 182,000
Potential interest and penalties associated with uncertain tax positions, accruals	$ 0
Amortized period for expenses incurred for research and development in united states	5 years
Amortized period for expenses incurred for research and development outside united states	15 years
Letter of Credit
Schedule Of Accounting Policies [Line Items]
Restricted cash	$ 182,000

Significant Accounting Polici_5

Significant Accounting Policies - Schedule of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 51,630	$ 74,268
Restricted cash	182	182
Cash, cash equivalents and restricted cash	$ 51,812	$ 74,450	$ 76,019	$ 72,001

Net Loss per Share - Computatio

Net Loss per Share - Computation of Basic and Diluted Net Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (7,731)	$ (7,102)
Weighted-average shares used in computing net loss per share	27,368,354	27,336,724
Net loss per share, basic and diluted	$ (0.28)	$ (0.26)

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,484,402	2,847,279
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,442,152	2,805,029
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	42,250	42,250

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Classified Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Cost Basis	$ 13,792	$ 1,011
Accumulated Unrealized Gains	0	0
Accumulated Unrealized Losses	(4)	(1)
Fair Value	13,788	1,010
United States Treasury Securities
Marketable Securities [Line Items]
Cost Basis	8,987
Accumulated Unrealized Gains	0
Accumulated Unrealized Losses	(1)
Fair Value	8,986
Corporate Debt Securities
Marketable Securities [Line Items]
Cost Basis	2,813	1,011
Accumulated Unrealized Gains	0	0
Accumulated Unrealized Losses	(3)	(1)
Fair Value	2,810	$ 1,010
Commercial Paper
Marketable Securities [Line Items]
Cost Basis	1,992
Accumulated Unrealized Gains	0
Accumulated Unrealized Losses	0
Fair Value	$ 1,992

Investments - Summary of Amorti

Investments - Summary of Amortized Cost and Fair Value of Available-for-Sale Investments by Contract Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 13,792
Amortized Cost, Total	13,792	$ 1,011
Fair Value, Due in one year or less	13,788
Fair Value, Total	$ 13,788	$ 1,010

Property and Equipment - Schedu

Property and Equipment - Schedule of Purchased Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 235	$ 239
Less: Accumulated depreciation	(169)	(170)
Property and equipment, net	$ 66	69
Office Equipment
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	5 years
Property and equipment, gross	$ 6	10
Office Furniture
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	7 years
Property and equipment, gross	$ 126	126
Computer Equipment
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	3 years
Property and equipment, gross	$ 8	8
Leasehold Improvements
Property Plant And Equipment [Line Items]
ESTIMATED USEFUL LIFE	Life of lease
Property and equipment, gross	$ 95	$ 95

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 9,000	$ 8,000

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Contract research and development	$ 2,199	$ 2,350
Employee compensation and related costs	707	1,152
Consulting and professional service fees	335	265
Interest	132	154
Financing related costs	60	60
State taxes	44	5
Other		9
Total accrued expenses	$ 3,477	$ 3,995

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets:
Cash equivalents	$ 49,666	$ 72,449
Investments	13,788	1,010
Total	63,454	73,459
United States Treasury Securities
Assets:
Investments	8,986
Corporate Debt Securities
Assets:
Investments	2,810	1,010
Commercial Paper
Assets:
Investments	1,992
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	47,866	72,449
Investments	8,986
Total	56,852	72,449
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Cash equivalents	1,800
Investments	4,802
Total	6,602	1,010
Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities
Assets:
Investments	2,810	$ 1,010
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper
Assets:
Investments	$ 1,992

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - SLR Investment Corp. and Silicon Valley Bank - USD ($)	1 Months Ended	3 Months Ended
	Sep. 30, 2019	Mar. 31, 2022	Mar. 31, 2021	May 31, 2017
2017 Loan Agreement
Debt Instrument [Line Items]
Unpaid borrowings				$ 10,000,000
2019 Loan Agreement
Debt Instrument [Line Items]
Loan agreement, maturity date	Sep. 17, 2023
Debt instrument, interest rate terms		The interest rate under the 2019 Loan Agreement is the higher of (i) LIBOR plus 7.95% or (ii) 10.18%
Debt instrument, effective interest rate		10.18%
Exit fee, percentage		4.00%
Exit fee		$ 800,000
Unpaid borrowings	$ 20,000,000	15,000,000
Amortization of debt discount		$ 80,000	$ 87,000
Prepayment premium percentage after year two		0.50%
Final payment fee		$ 500,000
Amortization of final payment fee		$ 34,000	$ 40,000
Increase in interest rate on default		5.00%
2019 Loan Agreement | Minimum
Debt Instrument [Line Items]
Interest rate, minimum		10.18%
Prepayment premium percentage two		0.01
2019 Loan Agreement | Maximum
Debt Instrument [Line Items]
Prepayment premium percentage one		0.03
2019 Loan Agreement | Libor
Debt Instrument [Line Items]
Basis spread on variable base rate		7.95%

Term Loan - Schedule of Total T

Term Loan - Schedule of Total Term Loan and Unamortized Debt Discount (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2019
Debt Instrument [Line Items]
Less: current portion	$ (9,826)	$ (9,805)
Long-term portion	4,913	$ 7,354
2019 Loan Agreement | SLR Investment Corp. and Silicon Valley Bank
Debt Instrument [Line Items]
Loan and security agreement, amount	15,000		$ 20,000
Less: discount	(261)
Total	14,739
Less: current portion	(9,826)
Long-term portion	$ 4,913

Term Loan - Schedule of Future

Term Loan - Schedule of Future Principal Payments Due (Details) - 2019 Loan Agreement - SLR Investment Corp. and Silicon Valley Bank - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2019
Debt Instrument [Line Items]
December 31, 2022	$ 7,500
December 31, 2023	7,500
Total	$ 15,000	$ 20,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - 2021 ATM Agreement - Cowen - Common Stock - USD ($)	Mar. 23, 2021	Mar. 31, 2022
Stockholders Equity Note [Line Items]
Proceeds from sale of shares,Net		$ 0
Maximum
Stockholders Equity Note [Line Items]
Aggregate offering price	$ 50,000,000
Percentage of commission on gross sales proceeds	3.00%

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional options granted	795,119
Stock option, number of shares outstanding	3,442,152	2,662,752
Unrecognized compensation expense	$ 3,800,000
Recognition period (in years)	2 years 7 months 6 days
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense	$ 18,000
Recognition period (in years)	6 months
2017 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option and incentive plan effective date	Nov. 30, 2017
Stock option and incentive plan expiration date	Oct. 31, 2027
Stock option, number of shares outstanding	2,843,533
Number of common shares authorized for issuance	6,143,876
Stock options, available for issuance	3,228,289
Term of option granted	10 years
2017 Stock Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term	1 year
2017 Stock Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting term	4 years
2017 Stock Plan | Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of restricted stock units outstanding	42,250
2014 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional options granted	0
Stock option and incentive plan expiration date	Nov. 30, 2017
Stock option, number of shares outstanding	598,619
Number of options forfeited	359,652
2017 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock shares available for issuance	1,188,629

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Estimated Fair Value of Options Valuation Assumptions (Details) - $ / shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.67%	0.50%
Risk-free interest rate, maximum	1.90%	0.72%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	70.00%	72.00%
Expected volatility, maximum	72.00%	74.00%
Weighted-average grant date fair value	$ 2.93	$ 4.36
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 7 months 6 days	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 8 months 12 days	6 years 8 months 12 days

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Information about Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)$ / sharesshares
NUMBER OF SHARES
Number of shares outstanding, beginning balance | shares	2,662,752
Additional options granted | shares	795,119
Number of shares exercised | shares	(4,781)
Number of shares forfeited | shares	(10,938)
Number of shares outstanding, ending balance | shares	3,442,152
Vested and exercisable, ending balance | shares	1,582,865
Vested and expected to vest, ending balance | shares	2,777,959
WEIGHTED-AVERAGE EXERCISE PRICE
Weighted average exercise prices, outstanding beginning balance | $ / shares	$ 6.28
Weighted average exercise prices, granted | $ / shares	4.61
Weighted average exercise prices, exercised | $ / shares	4.42
Weighted average exercise prices, forfeited | $ / shares	8.32
Weighted average exercise prices, outstanding ending balance | $ / shares	5.89
Weighted average exercise prices, vested and exercisable ending balance | $ / shares	6.18
Weighted average exercise prices, vested and expected to vest ending balance | $ / shares	$ 5.95
WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM
Weighted average remaining contractual term, outstanding	7 years 9 months 29 days
Weighted average remaining contractual term, vested and exercisable	6 years 3 months 29 days
Weighted average remaining contractual term, vested and expected to vest	7 years 6 months 7 days
AGGREGATE INTRINSIC VALUE
Aggregate intrinsic value, outstanding ending balance | $	$ 2,389
Aggregate intrinsic value, vested and exercisable ending balance | $	1,356
Aggregate intrinsic value, vested and expected to vest ending balance | $	$ 1,997

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of RSU Activity (Details) - Restricted Stock Units (RSUs)	3 Months Ended
	Mar. 31, 2022$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
RSUs Outstanding, December 31, 2021 | shares	42,250
RSUs Granted | shares	0
RSUs Vested | shares	0
RSUs Forfeited | shares	0
RSUs outstanding at March 31, 2022 | shares	42,250
AVERAGE GRANT DATE FAIR VALUE, Outstanding, December 31, 2021 | $ / shares	$ 3.25
AVERAGE GRANT DATE FAIR VALUE, Granted | $ / shares	0
AVERAGE GRANT DATE FAIR VALUE, Vested | $ / shares	0
AVERAGE GRANT DATE FAIR VALUE, Forfeited | $ / shares	0
AVERAGE GRANT DATE FAIR VALUE, RSUs outstanding at March 31, 2022 | $ / shares	$ 3.25

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 636	$ 521
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	254	226
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 382	$ 295

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Commitments And Contingencies [Line Items]
Operating leases expire	2025
Restricted cash	$ 182,000	$ 182,000
Short-term lease asset	318,000	410,000
Short-term lease liability	356,000	$ 476,000
Short-term Leases Recognized on Straight-line Basis
Commitments And Contingencies [Line Items]
Short-term lease asset	0
Short-term lease liability	0
Letter of Credit
Commitments And Contingencies [Line Items]
Restricted cash	182,000
Letter of Credit | Lease Agreement Require Standby Letter of Credit
Commitments And Contingencies [Line Items]
Restricted cash	$ 182,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Maturity Analysis of Annual Undiscounted Cash Flows of Operating Lease Liabilities (Details) $ in Thousands	Mar. 31, 2022USD ($)
Year ended:
December 31, 2022	$ 369
December 31, 2023	9
December 31, 2024	9
December 31, 2025	1
Total minimum lease payments	388
Less imputed interest	(22)
Total	$ 366

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Lease Cost and Other Information of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Lease cost:
Operating lease cost	$ 118	$ 122
Short-term lease cost	13	0
Sublease income	(13)	(13)
Total lease cost	118	109
Other information
Cash paid for amounts included in the measurement of lease liabilities	140	141
Operating cash flows from operating leases	$ (18)	$ (14)
Weighted-average remaining lease term - operating leases	9 months 18 days	1 year 8 months 12 days
Weighted-average discount rate - operating leases	10.10%	10.10%

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Apr. 11, 2022	Mar. 31, 2022
Subsequent Event [Line Items]
Future minimum lease payments		$ 388,000
Subsequent Events | Burlington, Massachusetts
Subsequent Event [Line Items]
Operating leases expiration date	Nov. 30, 2023
Lease term	12 months
Future minimum lease payments	$ 640,000