Unity Biotechnology (UBX) 10-Q 14 May 24 2024 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2024	May 10, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Trading Symbol	UBX
Entity Registrant Name	Unity Biotechnology, Inc.
Entity Central Index Key	0001463361
Current Fiscal Year End Date	--12-31
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		16,789,577
Entity Shell Company	false
Entity File Number	001-38470
Entity Tax Identification Number	26-4726035
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	285 East Grand Ave.
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	416-1192
Title of 12(b) Security	Common Stock, par value $0.0001
Security Exchange Name	NASDAQ

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 7,430	$ 19,803	[1]
Short-term marketable securities	28,902	23,398	[1]
Prepaid expenses and other current assets	2,187	3,404	[1]
Total current assets	38,519	46,605	[1]
Property and equipment, net	4,851	5,082	[1]
Operating lease right-of-use assets	12,441	12,981	[1]
Long-term marketable securities	1,952	0	[1]
Long-term restricted cash	896	896	[1]
Other long-term assets	204	126	[1]
Total assets	58,863	65,690	[1]
Current liabilities:
Accounts payable	1,398	1,380	[1]
Accrued compensation	1,154	1,841	[1]
Accrued and other current liabilities	5,180	4,619	[1]
Total current liabilities	7,732	7,840	[1]
Operating lease liability, net of current portion	22,606	23,539	[1]
Warrant liability	4,537	5,913	[1]
Total liabilities	34,875	37,292	[1]
Commitments and contingencies (Note 6)
Stockholders’ equity:
Convertible preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding	0	0	[1]
Common stock, $0.0001 par value; 300,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 16,786,647 and 16,784,969 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively	2	2	[1]
Additional paid-in capital	514,167	512,773	[1]
Accumulated other comprehensive loss	(38)	(24)	[1]
Accumulated deficit	(490,143)	(484,353)	[1]
Total stockholders’ equity	23,988	28,398	[1]
Total liabilities and stockholders’ equity	$ 58,863	$ 65,690	[1]
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	10,000,000	10,000,000
Convertible preferred stock, shares issued	0	0
Convertible preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	16,786,647	16,784,969
Common stock, shares outstanding	16,786,647	16,784,969

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 3,721	$ 5,760
General and administrative	3,878	4,798
Total operating expenses	7,599	10,558
Loss from operations	(7,599)	(10,558)
Interest income	513	855
Interest expense	0	(1,002)
Gain (loss) on warrant liability	1,376	5,491
Other income (expense), net	(80)	(65)
Net loss	(5,790)	(5,279)
Other comprehensive (loss) gain
Unrealized gain (loss) on marketable debt securities	(14)	101
Comprehensive loss	$ (5,804)	$ (5,178)
Net loss per share, basic	$ (0.34)	$ (0.37)
Net loss per share, diluted	$ (0.34)	$ (0.37)
Weighted-average number of shares used in computing net loss per share, basic	16,785,090	14,312,887
Weighted-average number of shares used in computing net loss per share, diluted	16,785,090	14,312,887

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total		ATM Equity Offering Program	Common Stock	Common Stock ATM Equity Offering Program	Additional Paid-In Capital	Additional Paid-In Capital ATM Equity Offering Program	Accumulated Other Comprehensive (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2022	$ 56,084			$ 1		$ 500,827		$ (251)	$ (444,493)
Beginning balance, (in shares) at Dec. 31, 2022				14,215,302
Issuance of common stock, net of issuance costs			$ 274				$ 274
Issuance of common stock (in shares)					106,781
Vesting of restricted stock units, (in shares)				37,131
Stock-based compensation	2,175					2,175
Unrealized (gain) loss on available-for-sale marketable securities	101							101
Net loss	(5,279)								(5,279)
Ending balance at Mar. 31, 2023	53,355			$ 1		503,276		(150)	(449,772)
Ending balance, (in shares) at Mar. 31, 2023				14,359,214
Beginning balance at Dec. 31, 2023	$ 28,398	[1]		$ 2		512,773		(24)	(484,353)
Beginning balance, (in shares) at Dec. 31, 2023	16,784,969			16,784,969
Repurchase of early exercised shares (in shares)				(3,336)
Vesting of restricted stock units, (in shares)				5,014
Stock-based compensation	$ 1,394					1,394
Unrealized (gain) loss on available-for-sale marketable securities	(14)							(14)
Net loss	(5,790)								(5,790)
Ending balance at Mar. 31, 2024	$ 23,988			$ 2		$ 514,167		$ (38)	$ (490,143)
Ending balance, (in shares) at Mar. 31, 2024	16,786,647			16,786,647
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities
Net loss	$ (5,790)	$ (5,279)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	227	329
Amortization of debt issuance costs	0	314
Net accretion and amortization of premium and discounts on marketable securities	(261)	(433)
Gain on disposal of property and equipment	(16)	0
Stock-based compensation	1,394	2,175
Non-cash rent expense	(300)	(270)
Gain (loss) on warrant liability	(1,376)	(5,491)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	1,217	(1,249)
Other long-term assets	(78)	23
Accounts payable	19	(320)
Accrued compensation	(687)	(1,037)
Accrued liabilities and other current liabilities	468	(78)
Net cash used in operating activities	(5,183)	(11,316)
Investing activities
Purchase of marketable securities	(13,459)	(5,973)
Maturities of marketable securities	6,250	27,251
Sale of property and equipment	19	0
Net cash provided by (used in) investing activities	(7,190)	21,278
Financing activities
Net cash provided by financing activities	0	274
Net increase (decrease) in cash, cash equivalents and restricted cash	(12,373)	10,236
Cash, cash equivalents and restricted cash at beginning of the period	20,699	13,632
Cash, cash equivalents and restricted cash at end of the period	8,326	23,868
Supplemental Disclosures of Cash Flow Information:
Cash paid for interest	0	680
Cash and cash equivalents	7,430	22,972
Restricted cash	896	896
Total cash, cash equivalents and restricted cash	8,326	23,868
ATM Offering Program
Financing activities
Proceeds from issuance of common stock, net of issuance costs	$ 0	$ 274

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (5,790)	$ (5,279)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	On January 5, 2024 and in compliance with the Company's Insider Trading Compliance Policy, our Chief Financial Officer and our Chief Legal Officer adopted a Rule 10b5-1 to cover tax withholding obligations incurred in connection with the vesting of restricted stock units. The amount of shares to be sold to satisfy the Company’s tax withholding obligations under these arrangements is dependent on future events which cannot be known at this time, including the future trading price of Company shares. The expiration date relating to these arrangements is dependent on future events which cannot be known at this time, including the final vest date of the applicable time-vesting restricted stock units and the officers’ termination of service.
Title	Chief Financial Officer and our Chief Legal Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	January 5, 2024

Organization

Organization	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Description of Business Unity Biotechnology, Inc. (the “Company”) is a biotechnology company engaged in the research and development of therapeutics to slow, halt, or reverse diseases of aging. The Company devotes substantially all of its time and efforts to performing research and development and raising capital. The Company’s headquarters are located in South San Francisco, California. The Company was incorporated in the State of Delaware in 2009. Liquidity The accompanying unaudited condensed financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The Company has incurred operating losses and has an accumulated deficit as a result of ongoing efforts to develop drug product candidates, including conducting preclinical and clinical trials and providing general and administrative support for these operations. The Company had an accumulated deficit of $ 490.1 million and $ 484.4 million as of March 31, 2024 and December 31, 2023, respectively. The Company had net losses of $ 5.8 million and $ 5.3 million for the three months ended March 31, 2024 and 2023, respectively, and net cash used in operating activities of $ 5.2 million and $ 11.3 million for the three months ended March 31, 2024 and 2023, respectively. To date, none of the Company’s drug product candidates have been approved for sale, and therefore, the Company has no t generated any product revenue and does not expect positive cash flows from operations in the foreseeable future. The Company has financed its operations primarily through private placements of preferred stock and promissory notes, public equity issuances and more recently, from its ATM Offering Programs, an Equity Purchase Agreement, the sale of common stock and warrants under a Follow-On Offering and the Inducement Offer and will continue to be dependent upon equity and/or debt financing until the Company is able to generate positive cash flows from its operations. The Company anticipates operating losses and negative operating cash flows to continue for the foreseeable future. The Company had cash, cash equivalents, and marketable securities of $ 38.3 million as of March 31, 2024. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing. If sufficient funds on acceptable terms are not available when needed, the Company could be further required to significantly reduce its operating expenses and delay, reduce the scope of, or eliminate one or more of its development programs. Failure to manage discretionary spending or raise additional financing, as needed, may adversely impact the Company’s ability to achieve its intended business objectives, or the Company may be forced to liquidate assets where possible, or to cease operations or file for bankruptcy protection. The Company expects that its cash, cash equivalents, and marketable securities will be sufficient to fund its operations for a period of at least one year from the date the accompanying unaudited condensed financial statements are filed with the Securities and Exchange Commission ("SEC").

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and the rules and regulations of the United States SEC for interim reporting. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, the unaudited condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC. Unaudited Condensed Financial Statements The accompanying financial information for the three months ended March 31, 2024 and 2023 are unaudited. The unaudited condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of March 31, 2024 and its results of operations for the three months ended March 31, 2024 and 2023 and cash flows for the three months ended March 31, 2024 and 2023. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other periods. Use of Estimates The condensed financial statements have been prepared in accordance with GAAP, which requires management to make estimates and assumptions that affect the amounts and disclosures reported in the condensed financial statements and accompanying notes. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s condensed balance sheets and the amount of expenses and income reported for each of the periods presented are affected by estimates and assumptions, which are used for, but are not limited to, determining the fair value of assets and liabilities, the fair value of right-of-use assets and lease liabilities, and stock-based compensation. Actual results could differ from such estimates or assumptions. Estimating fair values of liability-classified financial instruments requires the development of estimates that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors. As liability-classified financial instruments are initially and subsequently carried at fair value, the Company’s financial results will reflect the volatility in these estimate and assumption changes. Changes in estimated fair value are recognized as a component of "Other expense, net" in the Statements of Operations and Comprehensive Loss. Segments The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources. Recently Issued Accounting Pronouncements Not Yet Adopted There have been no new accounting pronouncements issued or effective that are expected to have a material impact on the Company's condensed financial statements.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The carrying amounts of financial instruments such as cash and cash equivalents, restricted cash, prepaid expenses and other current assets, accounts payable, accrued compensation, accrued and other current liabilities approximate the related fair values due to the short maturities of these instruments. The Company’s financial assets and liabilities subject to fair value measurements and the level of inputs used in such measurements were as follows (in thousands): March 31, 2024 Total Level 1 Level 2 Level 3 Assets: Cash equivalents: Money market funds $ 6,327 $ 6,327 $ — $ — Total cash equivalents 6,327 6,327 — — Short-term marketable securities: U.S. treasuries 12,451 — 12,451 — U.S. government debt securities 16,451 — 16,451 — Total short-term marketable securities 28,902 — 28,902 — Long-term marketable securities: U.S. treasuries 1,952 — 1,952 — Total long-term marketable securities 1,952 — 1,952 — Restricted cash equivalents: Money market funds 896 896 — — Total restricted cash equivalents 896 896 — — Total assets subject to fair value measurements $ 38,077 $ 7,223 $ 30,854 $ — Liabilities: Warrant Liability $ 4,537 $ — $ — $ 4,537 Total liabilities subject to fair value measurements $ 4,537 $ — $ — $ 4,537 December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents: Money market funds $ 12,864 $ 12,864 $ — $ — U.S. treasuries 2,989 — 2,989 — Total cash equivalents 15,853 12,864 2,989 — Short-term marketable securities: U.S. treasuries 7,849 — 7,849 — U.S. government debt securities 15,549 — 15,549 — Total short-term marketable securities 23,398 — 23,398 — Restricted cash equivalents: Money market funds 896 896 — — Total restricted cash equivalents 896 896 — — Total assets subject to fair value measurements $ 40,147 $ 13,760 $ 26,387 $ — Liabilities: Warrant Liability $ 5,913 $ — $ — $ 5,913 Total liabilities subject to fair value measurements 5,913 — — 5,913 The Company estimates the fair value of its money market funds, U.S. treasuries, and U.S. government debt securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data; and other observable inputs. August 2022 Warrants ("Existing Warrants") The common stock warrants are classified as a liability on the Balance Sheets and are measured at fair value with the change in fair value recorded within “Gain (loss) on warrant liability” on the Statement of Operations and Comprehensive Loss. The estimated fair value of the outstanding common warrants was $ 2.1 million and $ 2.8 million as of March 31, 2024 and December 31, 2023, respectively. The Company estimates the fair value of its warrant liability using a Monte Carlo simulation model based on significant inputs not observable in the market, which represents a Level 3 measurement. The Company used the following key assumptions within its valuation. In all scenarios, the Company also applied the likelihood of a fundamental transaction and the related impact on the Company’s common stock price and volatility. March 31, 2024 Common stock price $ 1.64 Exercise price per share $ 8.50 Estimated volatility 80.0 % Risk-free interest rate 4.36 % Contractual term (in years) 3.39 November 2023 Inducement Offer ('New Warrants') In November 2023, the Company issued common stock warrants to purchase an aggregate of 2,143,000 shares of common stock at an exercise price of $ 1.92 per warrant. Additionally, 128,580 common stock warrants were issued to the Placement Agent ("Placement Agent Warrants") at an exercise price of $ 2.5563 per warrant. The New Warrants and Placement Agent Warrants are recorded for as a liability on the Balance Sheet and are adjusted to estimated fair value at period end through “Gain (loss) on warrant liability” on the Statement of Operations and Comprehensive Loss. The estimated fair value of the New Warrants was $ 2.5 million and $ 3.1 million as of March 31, 2024 and December 31, 2023, respectively. The Company estimates the fair value of its Level 3 warrant liabilities using a Monte Carlo simulation model. The Company used the following key assumptions within its valuation. In all scenarios, the Company also applied the likelihood of a fundamental transaction and the related impact on the Company’s common stock price and volatility. March 31, 2024 Common stock price $ 1.64 Exercise price per share $ 1.92 - 2.5563 Expected volatility 80.0 % Risk-free interest rate 4.25 % Contractual term (in years) 4.62 The following is a roll forward of the fair value of Level 3 warrants for the three months ended March 31, 2024 (in thousands): Warrant Liability Balance at December 31, 2023 $ 5,913 Change in fair value ( 1,376 ) Balance at March 31, 2024 $ 4,537

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities Marketable securities, which are classified as available-for-sale, consisted of the following as of March 31, 2024 (in thousands): Amortized Unrealized Unrealized Fair Cash equivalents: Money market funds $ 6,327 $ — $ — $ 6,327 Total cash equivalents 6,327 — — 6,327 Short-term marketable securities: U.S. treasuries 12,474 — ( 23 ) 12,451 U.S. government debt securities 16,464 — ( 13 ) 16,451 Total short-term marketable securities 28,938 — ( 36 ) 28,902 Long-term marketable securities: U.S. treasuries 1,954 — ( 2 ) 1,952 Total long-term marketable securities 1,954 — ( 2 ) 1,952 Restricted Cash equivalents: Money market funds 896 — — 896 Total restricted cash equivalents 896 — — 896 Total $ 38,115 $ — $ ( 38 ) $ 38,077 Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2023 (in thousands): Amortized Unrealized Unrealized Fair Cash equivalents: Money market funds $ 12,864 $ — $ — $ 12,864 U.S. treasuries 2,989 — — 2,989 Total cash equivalents 15,853 — — 15,853 Short-term marketable securities: U.S. treasuries 7,853 4 ( 7 ) 7,850 U.S. government debt securities 15,570 1 ( 22 ) 15,549 Total short-term marketable securities 23,423 5 ( 29 ) 23,399 Restricted Cash equivalents: Money market funds 896 — — 896 Total restricted cash equivalents 896 — — 896 Total $ 40,172 $ 5 $ ( 29 ) $ 40,148 At March 31, 2024, the remaining contractual maturities of available-for-sale securities were less than two years . There have been no significant realized gains or losses on available-for-sale securities for the periods presented. As of March 31, 2024, the Company did not hold any individual securities in an unrealized loss position for 12 months or greater. The Company has the ability and intent to hold all marketable securities that have been in a continuous loss position until maturity or recovery. No significant facts or circumstances have arisen to indicate that there has been any significant deterioration in the creditworthiness of the issuers of the securities held by the Company. The Company considered the current and expected future economic and market conditions and determined that the estimate of credit losses was not significantly impacted. Thus, there has been no change in estimate of expected credit loss during the three ended March 31, 2024 and no allowance for credit loss was recorded at March 31, 2024. The Company will continue to assess the current and expected future economic and market conditions as further development arises.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	3 Months Ended
	Mar. 31, 2024
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following: March 31, 2024 December 31, 2023 Prepaid research and development expenses $ 60 $ 415 Prepaid insurance expenses 150 541 Tax credit receivable 1,493 1,493 Interest receivable 121 84 Other prepaid expenses and current assets 363 871 Total prepaid expenses & other current assets $ 2,187 $ 3,404

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases In February 2019, the Company entered into a lease agreement for new office and laboratory space in South San Francisco, California. The term of the lease agreement commenced in May 2019 . The lease has an initial term from occupancy of approximately ten years ending on December 31, 2029 with an option to extend the term for an additional eight years at then-market rental rates . The total base rent payment escalates annually based on a fixed percentage beginning from the 13 th month of the lease agreement. The Company will also be responsible for the operating expenses and real estate taxes allocated to the building and common areas. Pursuant to the lease agreement, the landlord provided the Company with a tenant improvement allowance of $ 10.7 million, which was included in deferred rent and leasehold improvements on the balance sheet at December 31, 2019. In connection with the execution of the lease agreement, the Company delivered a letter of credit of approximately $ 0.9 million to the landlord. The Company’s operating leases include various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature. In June 2021, the Company entered into an agreement to sublease a portion of the first floor of the South San Francisco, California facility, consisting of approximately 23,000 square feet, to Freenome Holdings, Inc., through June 30, 2024 . The base sublease rent rate is $ 6.25 per rental square foot per month and will increase annually by 3.5 % through expiration of the agreement. Additionally, the subtenant is required to pay approximately 37 % of operating expenses and property management fees that the Company is required to pay under the lease for the South San Francisco, California facility. The Company incurred initial direct costs of $ 0.2 million in sublease commissions related to entering into the agreements to sublease the South San Francisco, California facility. To account for the commissions, the Company capitalized the total commissions amount and will amortize the balance over the term of the sublease. Sublease income was $ 0.7 million and $ 0.6 million for the three months ended March 31, 2024 and 2023, respectively, which was offset against total rent expense. In May 2022, the Company entered into an agreement to sublease a portion of the second floor of the South San Francisco, California facility, consisting of approximately 15,000 square feet, to Initial Therapeutics, Inc. ("Initial Therapeutics"). The original sublease term commenced on July 1, 2022 and continued through June 30, 2024 and further extended through June 30, 2026 upon execution of an amendment as defined below. The base sublease rent rate is $ 7.80 per rental square foot per month and will increase by 3.5 % annually through the expiration of the agreement. Additionally, the subtenant is required to pay approximately 24 % of operating expenses and property management fees that the Company is required to pay under the lease for the South San Francisco, California facility. The Company incurred initial direct costs of $ 0.1 million in sublease commissions related to entering into the agreements to sublease the South San Francisco, California facility. To account for the commissions, the Company capitalized the total commissions amount and will amortize the balance over the term of the sublease. On September 15, 2023, the Company entered into an amendment with Initial Therapeutics to sublease the remainder of the second floor of the South San Francisco, California facility, consisting of an additional 17,000 square feet. The sublease term will commence on October 1, 2023 and extends the existing sublease agreement that commenced on July 1, 2022 through June 30, 2026 . The additional space will be subleased at a monthly rent rate of $ 1.00 per square foot starting a month after Initial Therapeutics first takes possession of the additional space through June 30, 2024. Starting July 1, 2024, the rent rate for the entirety of Initial Therapeutics' subleased space will be $ 6.02 per rental square foot per month and will increase 3.5 % on December 1, 2024 and 2025. Additionally, Initial Therapeutics will be required to pay approximately 51 % of operating expenses and property management fees that the Company is required to pay under the lease for the South San Francisco, California facility. The Company incurred initial direct costs of $ 0.3 million in sublease commissions. Sublease income from Initial Therapeutics, Inc. was $ 0.8 million and $ 0.4 million for the three months ended March 31, 2024 and 2023, respectively, which was offset against total rent expense. The following table summarizes the components of lease expense and sublease income, which are included in operating expenses in the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2024 2023 Operating lease cost $ 938 $ 930 Variable lease cost 272 203 Sublease income ( 1,472 ) ( 963 ) Total lease (income) cost $ ( 262 ) $ 170 Variable lease payments include amounts relating to common area maintenance, real estate taxes and insurance and are recognized in the condensed statements of operations and comprehensive loss as incurred. The following table summarizes the maturities of lease liabilities as of March 31, 2024 (in thousands): Amount 2024 (remaining 9 months) $ 3,726 2025 5,123 2026 5,287 2027 5,457 2028 5,633 Thereafter 5,801 Total future minimum lease payments 31,027 Less: Amount representing interest ( 4,877 ) Present value of future minimum lease payments 26,150 Less: Current portion of operating lease liability ( 3,544 ) Noncurrent portion of operating lease liability $ 22,606 On September 15, 2023, the Company entered into a sub-sublease agreement with GT Biopharma, Inc. to sublease a portion of its first floor at 8000 Marina Boulevard, Brisbane, California, consisting of 4,500 square feet. The sub-sublease term will commence on October 6, 2023 through June 30, 2024 . The space will be subleased at a rent rate of $ 2.00 per rent square feet. Indemnifications The Company indemnifies each of its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with the Company’s amended and restated certificate of incorporation and bylaws. The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of risk associated with the Company’s exposure and may enable the Company to recover a portion of any future amounts paid. The Company believes that the fair value of these potential indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.

Equity Financing

Equity Financing	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Equity Financing	7. Equity Financing The Company has 10,000,000 shares of convertible preferred stock authorized for issuance, par value of $ 0.0001 per share. As of March 31, 2024 and December 31, 2023, no shares of preferred stock were issued and outstanding. The Company has 300,000,000 shares of common stock authorized for issuance, par value of $ 0.0001 per share. Holders of the Company’s common stock are entitled to one vote per share. As of March 31, 2024 and December 31, 2023, there were 16,786,647 and 16,784,969 shares, respectively, of common stock issued and outstanding. Follow-On Offering In August 2022, the Company closed an underwritten offering (the “Follow-On Offering”) in which the Company issued and sold an aggregate of 6,428,571 of the Company’s common stock together with warrants (the "Existing Warrants”) to purchase up to 6,428,572 of the Company’s common stock at an offering price of at an aggregate offering price of $ 7.00 per unit. The Existing Warrants have an exercise price of $ 8.50 per warrant. The gross proceeds to the Company were $ 45.0 million before deducting underwriting discounts and commissions and other offering expenses. The net proceeds of the Follow-On Offering were approximately $ 41.7 million. The Existing Warrants are exercisable at any time after their original issuance and on or prior to the five-year anniversary of the original issuance date. A holder of Existing Warrants may not exercise the warrant if the holder, together with its affiliates, would beneficially own more than 4.99 % of the number of shares of common stock outstanding immediately after giving effect to such exercise. As of March 31, 2024, 2,143,000 warrants have been exercised. The Company recorded the Existing Warrants as liabilities based upon the guidance of ASC 480 and ASC 815. The Company evaluated the Existing Warrants under ASC 815-40 and concluded that they do not meet the criteria to be classified in stockholders’ equity. Specifically, the settlement value in a scenario of a fundamental transaction precluded the Existing Warrants from being indexed to the Company’s own stock and Company believes that the scope exception related to the occurrence of a fundamental transaction in ASC 815-40 is not met. Since the Existing Warrants meet the definition of a derivative, they are recorded as liabilities and measured at fair value at initial recognition. Any subsequent changes in their respective fair values is recognized in the Statement of Operations and Comprehensive Loss at each reporting date. At March 31, 2024 and December 31, 2023, the Company updated the estimated fair value of the outstanding Existing Warrants using a Monte-Carlo valuation model resulting in an estimated fair value of $ 2.1 million and $ 2.8 million (subsequent to the exercise of the Existing Warrants as described in the section below ), respectively. The change in fair value for the three months ended March 31, 2024 and 2023 of $ 0.7 million and $ 5.5 million, respectively, was recorded as the Gain (loss) on warrant liability in the condensed Statements of Operations and Comprehensive Loss. Inducement Offer On November 9, 2023, the Company entered into an inducement offer letter agreement (the “Inducement Offer”) with certain holders (collectively, the “Holders”) of the Company's Existing Warrants to purchase up to an aggregate of 2,143,000 shares of common stock. The Holders agreed to exercise for cash their Existing Warrants to purchase an aggregate of 2,143,000 shares of common stock at a reduced exercise price of $ 2.045 per share in consideration of the Company’s agreement to issue new unregistered common stock purchase warrants (the “New Warrants”) to purchase up to an aggregate of 2,143,000 shares of the Company’s common stock. Each New Warrant will have an exercise price equal to $ 1.92 per share. The New Warrants will be exercisable on or after the initial issue date until the five-year anniversary of such date. The exercise price and number of New Warrant Shares issuable upon exercise of the New Warrants is subject to appropriate adjustment in the event of stock dividends, stock splits, subsequent rights offerings, pro rata distributions, reorganizations, or similar events affecting the Company’s common stock and the exercise price. The Company engaged H.C. Wainwright & Co., LLC (the “Placement Agent”) to act as its exclusive placement agent in connection with the transactions summarized above. The Company also issued to the Placement Agent or its designees warrants to purchase up to 128,580 shares of common stock. The Placement Agent Warrants have substantially the same terms as the New Warrants, except that the Placement Agent Warrants have an exercise price equal to $ 2.5563 per share. The Company recorded the New Warrants and Placement Agent Warrants (together “2023 Warrants”) as liabilities based upon the guidance of ASC 480 and ASC 815. The Company evaluated the 2023 Warrants under ASC 815-40 and concluded that they do not meet the criteria to be classified in stockholders’ equity. Specifically, the settlement value in a scenario of a fundamental transaction precludes the 2023 Warrants from being indexed to the Company’s own stock and Company believes that the scope exception related to the occurrence of a fundamental transaction in ASC 815-40 is not met. Since the 2023 Warrants are recorded as liabilities on the Balance Sheet at fair value, any subsequent changes in their respective fair values are recognized in the Statement of Operations and Comprehensive Loss at each reporting date. The Company received aggregate gross proceeds of $ 4.4 million from the exercise of the Existing Warrants by the Holders (the “Exercise”), before deducting placement agent fees and other offering expenses payable by the Company. At March 31, 2024 and December 31, 2023, the Company updated the estimated fair value of the outstanding New Warrants using a Monte-Carlo valuation model resulting in an estimated fair value of $ 2.5 million and $ 3.1 million (subsequent to the exercise of the Existing Warrants as described in the section below ), respectively. The change in fair value for the three months ended March 31, 2024 and 2023 of $ 0.6 million and zero , respectively, was recorded as the Gain (loss) on warrant liability in the condensed statements of operations and comprehensive loss.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	8 . Stock-Based Compensation Stock Options and Restricted Stock Units (RSUs) Activity A summary of the Company’s stock option activity under the 2013 Equity Incentive Plan, 2018 Incentive Award Plan (the "2018 Plan"), and 2020 Employment Inducement Incentive Plan for the three months ended March 31, 2024 is as follows: Number of Weighted- Balances at December 31, 2023 1,913,345 $ 14.23 Granted 621,834 $ 1.67 Canceled ( 159,095 ) $ 6.02 Balances at March 31, 2024 2,376,084 $ 11.49 A summary of the Company’s restricted stock units (“RSUs”), performance stock units (“PSUs”), and restricted stock awards (“RSAs”) activity for the three months ended March 31, 2024 is as follows: Number of Weighted- Unvested at December 31, 2023 41,225 $ 30.18 Granted 407,725 $ 1.67 Vested ( 5,014 ) $ 31.02 Canceled ( 20,000 ) $ 1.67 Unvested at March 31, 2024 423,936 $ 4.09 Stock Based Compensation Expense The following table sets forth the total stock-based compensation expense for all options granted to employees and nonemployees, including shares sold through the issuance of non-recourse promissory notes which are considered to be options for accounting purposes, and costs associated with the Company’s 2018 Employee Stock Purchase Plan (“2018 ESPP”) included in the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2024 2023 Research and development $ 321 $ 682 General and administrative 1,073 1,493 Total $ 1,394 $ 2,175

Net Loss per Common Share

Net Loss per Common Share	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Net Loss per Common Share	9. Net Loss per Common Share Basic net loss per share is calculated by dividing net loss by the weighted-average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of shares of common stock and potential dilutive common stock equivalents outstanding during the period if the effect is dilutive. The calculation of diluted earnings (loss) per share also requires the consideration of the effect of dilutive potential common shares outstanding during the period determined using the treasury-stock related to the warrants outstanding. A reconciliation of the numerators and denominators used in computing net loss from continuing operations per share is as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2024 2023 Numerator: Net loss $ ( 5,790 ) $ ( 5,279 ) Denominator: Weighted-average number of shares 16,785,090 14,312,887 Net loss per share—basic and diluted $ ( 0.34 ) $ ( 0.37 ) Since the Company was in a net loss position for all periods presented, basic net loss per common share is the same as diluted net loss per common share as the inclusion of all potential common shares outstanding would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Three Months Ended March 31, 2024 2023 Options to purchase common stock 2,376,084 1,603,958 Outstanding warrants to purchase common stock 6,557,152 6,428,572 Early exercised common stock subject to future vesting — 3,336 RSUs subject to future vesting 423,936 108,452 Shares subject to future vesting relating to the 2018 ESPP 46,046 65,939 Total 9,403,218 8,210,257 Up to 3,390 shares may be contingently issued, if certain performance conditions are met under the Company’s in-licensing agreements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and the rules and regulations of the United States SEC for interim reporting. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, the unaudited condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC.
Unaudited Condensed Financial Statements	Unaudited Condensed Financial Statements The accompanying financial information for the three months ended March 31, 2024 and 2023 are unaudited. The unaudited condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of March 31, 2024 and its results of operations for the three months ended March 31, 2024 and 2023 and cash flows for the three months ended March 31, 2024 and 2023. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other periods.
Use of Estimates	Use of Estimates The condensed financial statements have been prepared in accordance with GAAP, which requires management to make estimates and assumptions that affect the amounts and disclosures reported in the condensed financial statements and accompanying notes. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s condensed balance sheets and the amount of expenses and income reported for each of the periods presented are affected by estimates and assumptions, which are used for, but are not limited to, determining the fair value of assets and liabilities, the fair value of right-of-use assets and lease liabilities, and stock-based compensation. Actual results could differ from such estimates or assumptions. Estimating fair values of liability-classified financial instruments requires the development of estimates that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors. As liability-classified financial instruments are initially and subsequently carried at fair value, the Company’s financial results will reflect the volatility in these estimate and assumption changes. Changes in estimated fair value are recognized as a component of "Other expense, net" in the Statements of Operations and Comprehensive Loss.
Segments	Segments The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted There have been no new accounting pronouncements issued or effective that are expected to have a material impact on the Company's condensed financial statements.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements	The Company’s financial assets and liabilities subject to fair value measurements and the level of inputs used in such measurements were as follows (in thousands): March 31, 2024 Total Level 1 Level 2 Level 3 Assets: Cash equivalents: Money market funds $ 6,327 $ 6,327 $ — $ — Total cash equivalents 6,327 6,327 — — Short-term marketable securities: U.S. treasuries 12,451 — 12,451 — U.S. government debt securities 16,451 — 16,451 — Total short-term marketable securities 28,902 — 28,902 — Long-term marketable securities: U.S. treasuries 1,952 — 1,952 — Total long-term marketable securities 1,952 — 1,952 — Restricted cash equivalents: Money market funds 896 896 — — Total restricted cash equivalents 896 896 — — Total assets subject to fair value measurements $ 38,077 $ 7,223 $ 30,854 $ — Liabilities: Warrant Liability $ 4,537 $ — $ — $ 4,537 Total liabilities subject to fair value measurements $ 4,537 $ — $ — $ 4,537 December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents: Money market funds $ 12,864 $ 12,864 $ — $ — U.S. treasuries 2,989 — 2,989 — Total cash equivalents 15,853 12,864 2,989 — Short-term marketable securities: U.S. treasuries 7,849 — 7,849 — U.S. government debt securities 15,549 — 15,549 — Total short-term marketable securities 23,398 — 23,398 — Restricted cash equivalents: Money market funds 896 896 — — Total restricted cash equivalents 896 896 — — Total assets subject to fair value measurements $ 40,147 $ 13,760 $ 26,387 $ — Liabilities: Warrant Liability $ 5,913 $ — $ — $ 5,913 Total liabilities subject to fair value measurements 5,913 — — 5,913
Summary of Assumptions used in Fair Value Estimates of Level 3 Warrant Liabilities	The Company estimates the fair value of its warrant liability using a Monte Carlo simulation model based on significant inputs not observable in the market, which represents a Level 3 measurement. The Company used the following key assumptions within its valuation. In all scenarios, the Company also applied the likelihood of a fundamental transaction and the related impact on the Company’s common stock price and volatility. March 31, 2024 Common stock price $ 1.64 Exercise price per share $ 8.50 Estimated volatility 80.0 % Risk-free interest rate 4.36 % Contractual term (in years) 3.39 The Company estimates the fair value of its Level 3 warrant liabilities using a Monte Carlo simulation model. The Company used the following key assumptions within its valuation. In all scenarios, the Company also applied the likelihood of a fundamental transaction and the related impact on the Company’s common stock price and volatility. March 31, 2024 Common stock price $ 1.64 Exercise price per share $ 1.92 - 2.5563 Expected volatility 80.0 % Risk-free interest rate 4.25 % Contractual term (in years) 4.62
Sumarry of Roll forward of the fair value of level 3 Warrants	The following is a roll forward of the fair value of Level 3 warrants for the three months ended March 31, 2024 (in thousands): Warrant Liability Balance at December 31, 2023 $ 5,913 Change in fair value ( 1,376 ) Balance at March 31, 2024 $ 4,537

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Securities Classified as Available-for-Sale	Marketable securities, which are classified as available-for-sale, consisted of the following as of March 31, 2024 (in thousands): Amortized Unrealized Unrealized Fair Cash equivalents: Money market funds $ 6,327 $ — $ — $ 6,327 Total cash equivalents 6,327 — — 6,327 Short-term marketable securities: U.S. treasuries 12,474 — ( 23 ) 12,451 U.S. government debt securities 16,464 — ( 13 ) 16,451 Total short-term marketable securities 28,938 — ( 36 ) 28,902 Long-term marketable securities: U.S. treasuries 1,954 — ( 2 ) 1,952 Total long-term marketable securities 1,954 — ( 2 ) 1,952 Restricted Cash equivalents: Money market funds 896 — — 896 Total restricted cash equivalents 896 — — 896 Total $ 38,115 $ — $ ( 38 ) $ 38,077 Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2023 (in thousands): Amortized Unrealized Unrealized Fair Cash equivalents: Money market funds $ 12,864 $ — $ — $ 12,864 U.S. treasuries 2,989 — — 2,989 Total cash equivalents 15,853 — — 15,853 Short-term marketable securities: U.S. treasuries 7,853 4 ( 7 ) 7,850 U.S. government debt securities 15,570 1 ( 22 ) 15,549 Total short-term marketable securities 23,423 5 ( 29 ) 23,399 Restricted Cash equivalents: Money market funds 896 — — 896 Total restricted cash equivalents 896 — — 896 Total $ 40,172 $ 5 $ ( 29 ) $ 40,148

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	3 Months Ended
	Mar. 31, 2024
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following: March 31, 2024 December 31, 2023 Prepaid research and development expenses $ 60 $ 415 Prepaid insurance expenses 150 541 Tax credit receivable 1,493 1,493 Interest receivable 121 84 Other prepaid expenses and current assets 363 871 Total prepaid expenses & other current assets $ 2,187 $ 3,404

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Summary of Components of Lease Expense	The following table summarizes the components of lease expense and sublease income, which are included in operating expenses in the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2024 2023 Operating lease cost $ 938 $ 930 Variable lease cost 272 203 Sublease income ( 1,472 ) ( 963 ) Total lease (income) cost $ ( 262 ) $ 170
Summary of Maturities of Lease Liabilities	The following table summarizes the maturities of lease liabilities as of March 31, 2024 (in thousands): Amount 2024 (remaining 9 months) $ 3,726 2025 5,123 2026 5,287 2027 5,457 2028 5,633 Thereafter 5,801 Total future minimum lease payments 31,027 Less: Amount representing interest ( 4,877 ) Present value of future minimum lease payments 26,150 Less: Current portion of operating lease liability ( 3,544 ) Noncurrent portion of operating lease liability $ 22,606

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Summary of Stock Option Activity	A summary of the Company’s stock option activity under the 2013 Equity Incentive Plan, 2018 Incentive Award Plan (the "2018 Plan"), and 2020 Employment Inducement Incentive Plan for the three months ended March 31, 2024 is as follows: Number of Weighted- Balances at December 31, 2023 1,913,345 $ 14.23 Granted 621,834 $ 1.67 Canceled ( 159,095 ) $ 6.02 Balances at March 31, 2024 2,376,084 $ 11.49
Summary of Restricted Stock Units, Performance Stock Units and Restricted Stock Awards Activity	A summary of the Company’s restricted stock units (“RSUs”), performance stock units (“PSUs”), and restricted stock awards (“RSAs”) activity for the three months ended March 31, 2024 is as follows: Number of Weighted- Unvested at December 31, 2023 41,225 $ 30.18 Granted 407,725 $ 1.67 Vested ( 5,014 ) $ 31.02 Canceled ( 20,000 ) $ 1.67 Unvested at March 31, 2024 423,936 $ 4.09
Summary of Stock-based Compensation Expense	The following table sets forth the total stock-based compensation expense for all options granted to employees and nonemployees, including shares sold through the issuance of non-recourse promissory notes which are considered to be options for accounting purposes, and costs associated with the Company’s 2018 Employee Stock Purchase Plan (“2018 ESPP”) included in the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2024 2023 Research and development $ 321 $ 682 General and administrative 1,073 1,493 Total $ 1,394 $ 2,175

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share	A reconciliation of the numerators and denominators used in computing net loss from continuing operations per share is as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2024 2023 Numerator: Net loss $ ( 5,790 ) $ ( 5,279 ) Denominator: Weighted-average number of shares 16,785,090 14,312,887 Net loss per share—basic and diluted $ ( 0.34 ) $ ( 0.37 )
Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Three Months Ended March 31, 2024 2023 Options to purchase common stock 2,376,084 1,603,958 Outstanding warrants to purchase common stock 6,557,152 6,428,572 Early exercised common stock subject to future vesting — 3,336 RSUs subject to future vesting 423,936 108,452 Shares subject to future vesting relating to the 2018 ESPP 46,046 65,939 Total 9,403,218 8,210,257

Organization - Additional Infor

Organization - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	[1]
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (490,143)		$ (484,353)
Net loss	(5,790)	$ (5,279)
Cash used in operations	(5,183)	(11,316)
Product revenue	0	$ 0
Cash, cash equivalents and marketable securities	$ 38,300
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2024 Segment
Number of operating segment	1

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Short-term marketable securities	$ 28,902	$ 23,398	[1]
Long-term marketable securities	1,952	0	[1]
Restricted cash equivalents	896	896	[1]
Fair Value, Recurring
Assets:
Cash equivalents	6,327	15,853
Short-term marketable securities	28,902	23,398
Long-term marketable securities	1,952
Restricted cash equivalents	896	896
Total assets subject to fair value measurements	38,077	40,147
Total liabilities subject to fair value measurements on a recurring basis	4,537	5,913
Fair Value, Recurring | Level 1
Assets:
Cash equivalents	6,327	12,864
Restricted cash equivalents	896	896
Total assets subject to fair value measurements	7,223	13,760
Fair Value, Recurring | Level 2
Assets:
Cash equivalents		2,989
Short-term marketable securities	28,902	23,398
Long-term marketable securities	1,952
Total assets subject to fair value measurements	30,854	26,387
Fair Value, Recurring | Level 3
Assets:
Total liabilities subject to fair value measurements on a recurring basis	4,537	5,913
Money market funds | Fair Value, Recurring
Assets:
Cash equivalents	6,327	12,864
Restricted cash equivalents	896	896
Money market funds | Fair Value, Recurring | Level 1
Assets:
Cash equivalents	6,327	12,864
Restricted cash equivalents	896	896
U.S. Treasuries | Fair Value, Recurring
Assets:
Cash equivalents		2,989
Short-term marketable securities	12,451	7,849
Long-term marketable securities	1,952
U.S. Treasuries | Fair Value, Recurring | Level 2
Assets:
Cash equivalents		2,989
Short-term marketable securities	12,451	7,849
Long-term marketable securities	1,952
U.S. government debt securities | Fair Value, Recurring
Assets:
Short-term marketable securities	16,451	15,549
U.S. government debt securities | Fair Value, Recurring | Level 2
Assets:
Short-term marketable securities	16,451	15,549
Warrant Liability | Fair Value, Recurring
Assets:
Total liabilities subject to fair value measurements on a recurring basis	4,537	5,913
Warrant Liability | Fair Value, Recurring | Level 3
Assets:
Total liabilities subject to fair value measurements on a recurring basis	$ 4,537	$ 5,913
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Nov. 30, 2023
August 2022 Warrants ('Existing Warrants')
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of warrant liability	$ 2.1	$ 2.8
November 2023 Inducement Offer ('New Warrants')
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants issued to purchase common stock			2,143,000
Exercise price for warrant			$ 1.92
November 2023 Inducement Offer ('New Warrants') | Warrant Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of warrant liability	$ 2.5	$ 3.1
November 2023 Inducement Offer ('New Warrants') | Placement Agent | Placement Agent Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants issued to purchase common stock			128,580
Exercise price for warrant			$ 2.5563

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Assumptions used in Fair Value Estimates of Level 3 Warrant Liabilities (Details) - Level 3 - Fair Value, Recurring	Mar. 31, 2024 $ / shares
August 2022 Warrants ('Existing Warrants')
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock price	$ 1.64
Exercise price per share	$ 8.5
Contractual terms	3 years 4 months 20 days
August 2022 Warrants ('Existing Warrants') | Estimated Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.80
August 2022 Warrants ('Existing Warrants') | Risk-free Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.0436
November 2023 Inducement Offer ('New Warrants')
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock price	$ 1.64
Contractual terms	4 years 7 months 13 days
November 2023 Inducement Offer ('New Warrants') | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exercise price per share	$ 1.92
November 2023 Inducement Offer ('New Warrants') | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exercise price per share	$ 2.5563
November 2023 Inducement Offer ('New Warrants') | Estimated Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.80
November 2023 Inducement Offer ('New Warrants') | Risk-free Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.0425

Fair Value Measurements - Sumar

Fair Value Measurements - Sumarry of Roll forward of the fair value of level 3 Warrants (Details) - Level 3 - Warrant Liability $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2023	$ 5,913
Change in fair value	(1,376)
Balance at March 31, 2024	$ 4,537

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 38,115	$ 40,172
Unrealized Gains	0	5
Unrealized Losses	(38)	(29)
Fair Value	38,077	40,148
Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	6,327	15,853
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,327	15,853
Cash Equivalents | Money market funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	6,327	12,864
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,327	12,864
Cash Equivalents | U S Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		2,989
Unrealized Gains		0
Unrealized Losses		0
Fair Value		2,989
Short Term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	28,938	23,423
Unrealized Gains	0	5
Unrealized Losses	(36)	(29)
Fair Value	28,902	23,399
Short Term Marketable Securities | U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	16,464	15,570
Unrealized Gains	0	1
Unrealized Losses	(13)	(22)
Fair Value	16,451	15,549
Short Term Marketable Securities | U S Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	12,474	7,853
Unrealized Gains	0	4
Unrealized Losses	(23)	(7)
Fair Value	12,451	7,850
Long Term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	1,954
Unrealized Gains	0
Unrealized Losses	(2)
Fair Value	1,952
Long Term Marketable Securities | U S Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	1,954
Unrealized Gains	0
Unrealized Losses	(2)
Fair Value	1,952
Restricted Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	896	896
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	896	896
Restricted Cash Equivalents | Money market funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	896	896
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 896	$ 896

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Realized gains or losses on available-for-sale debt securities	$ 0	$ 0
Allowance for credit loss	$ 0
Maximum
Marketable Securities [Line Items]
Available-for sale securities, remaining contractual maturity	2 years

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 60	$ 415
Prepaid insurance expenses	150	541
Tax credit receivable	1,493	1,493
Interest receivable	121	84
Other prepaid expenses and current assets	363	871
Total prepaid expenses & other current assets	$ 2,187	$ 3,404	[1]
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

License Revenue and Agreements

License Revenue and Agreements - Additional Information (Details) - shares	Mar. 31, 2024	Dec. 31, 2023
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock, shares issued	16,786,647	16,784,969

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands		1 Months Ended			3 Months Ended
	Sep. 15, 2023 USD ($) ft² $ / ft²	May 31, 2022 USD ($) ft² $ / ft²	Jun. 30, 2021 USD ($) ft² $ / ft²	Feb. 28, 2019 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)
Commitments And Contingencies [Line Items]
Sublease income					$ 1,472	$ 963
South San Francisco, California
Commitments And Contingencies [Line Items]
Lessee, operating lease, description					In February 2019, the Company entered into a lease agreement for new office and laboratory space in South San Francisco, California. The term of the lease agreement commenced in May 2019. The lease has an initial term from occupancy of approximately ten years ending on December 31, 2029 with an option to extend the term for an additional eight years at then-market rental rates
Operating lease, initial lease term				10 years
Operating lease, renewal term				8 years
Tenant improvement allowance				$ 10,700
Letter of credit, delivered in connection of lease agreement				$ 900
Lease commencement date				2019-05
Operating lease, option to extend description					option to extend the term for an additional eight years
Operating lease, existence of option to extend				true
Lease expiration date				Dec. 31, 2029
South San Francisco, California | Office and Laboratory Space, Second Floor
Commitments And Contingencies [Line Items]
Space subleased (in square feet) | ft²	17,000	15,000
Sublease start date	Oct. 01, 2023	Jul. 01, 2022
Sublease expiration date	Jun. 30, 2026	Jun. 30, 2026
Sublease rent per square foot | $ / ft²	1	7.8
Annual percentage increase in sublease base rent	3.50%	3.50%
Increase in sublease rent per square foot | $ / ft²	6.02
Percentage of operating expenses and property management fees to be paid by subtenant	51%	24%
Incurred initial direct costs of sublease	$ 300	$ 100
Sublease income					$ 800	400
Original sublease expiration date		Jun. 30, 2024
Existing sublease start date	Jul. 01, 2022
South San Francisco, California | Office And Laboratory Space First Floor
Commitments And Contingencies [Line Items]
Space subleased (in square feet) | ft²			23,000
Sublease expiration date			Jun. 30, 2024
Sublease rent per square foot | $ / ft²			6.25
Annual percentage increase in sublease base rent			3.50%
Percentage of operating expenses and property management fees to be paid by subtenant			37%
Incurred initial direct costs of sublease			$ 200
Sublease income					$ 700	$ 600
Brisbane, California | Office And Laboratory Space First Floor
Commitments And Contingencies [Line Items]
Space subleased (in square feet) | ft²	4,500
Sublease start date	Oct. 06, 2023
Sublease expiration date	Jun. 30, 2024
Sublease rent per square foot | $ / ft²	2

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Lease, Cost [Abstract]
Operating lease cost	$ 938	$ 930
Variable lease cost	272	203
Sublease income	(1,472)	(963)
Total lease (income) cost	$ (262)	$ 170

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	[1]
Commitments and Contingencies Disclosure [Abstract]
2024 (remaining 9 months)	$ 3,726
2025	5,123
2026	5,287
2027	5,457
2028	5,633
Thereafter	5,801
Total future minimum lease payments	31,027
Less: Amount representing interest	(4,877)
Present value of future minimum lease payments	26,150
Less: Current portion of operating lease liability	(3,544)
Noncurrent portion of operating lease liability	$ 22,606	$ 23,539
[1] The balance sheet as of December 31, 2023 is derived from the audited financial statements as of that date.

Term Loan Facility - Additional

Term Loan Facility - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Line Items]
Interest expense	$ 0	$ 1,002

Equity Financing - Additional I

Equity Financing - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Nov. 09, 2023	Aug. 31, 2022	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Subsidiary Sale Of Stock [Line Items]
Number of stock, authorized for issuance			10,000,000		10,000,000
Number of stock, par value per share			$ 0.0001		$ 0.0001
Number of stock, shares issued			0		0
Number of stock, shares outstanding			0		0
Common stock, shares authorized			300,000,000		300,000,000
Common stock, par value per share			$ 0.0001		$ 0.0001
Common stock, shares issued			16,786,647		16,784,969
Common stock, shares outstanding			16,786,647		16,784,969
Gain (loss) on warrant liability			$ 1,376	$ 5,491
Inducement Offer
Subsidiary Sale Of Stock [Line Items]
Gain (loss) on warrant liability			600	$ 0
Estimated Fair Value of Common Warrants Outstanding			$ 2,500		$ 3,100
Common Stock
Subsidiary Sale Of Stock [Line Items]
Common stock, shares outstanding			16,786,647	14,359,214	16,784,969	14,215,302
Existing Warrants | Holders | Inducement Offer
Subsidiary Sale Of Stock [Line Items]
Warrants issued to purchase ordinary shares	2,143,000
Reduced exercise price of warrant	$ 2.045
Expected aggregate gross proceeds from exercise of warrants	$ 4,400
New Warrants | Holders | Inducement Offer
Subsidiary Sale Of Stock [Line Items]
Exercise price for warrant	$ 1.92
Warrants issued to purchase ordinary shares	2,143,000
New Warrants | Holders | Inducement Offer | Maximum
Subsidiary Sale Of Stock [Line Items]
Warrants exercisable term	5 years
Placement Agent Warrants | H.C. Wainwright & Co.
Subsidiary Sale Of Stock [Line Items]
Exercise price for warrant	$ 2.5563
Warrants issued to purchase ordinary shares	128,580
Follow-On Offering
Subsidiary Sale Of Stock [Line Items]
Gross proceeds		$ 45,000
Gain (loss) on warrant liability			$ 700	$ 5,500
Proceeds from sale of common stock		$ 41,700
Number of warrants exercised			2,143,000
Estimated Fair Value of Common Warrants Outstanding			$ 2,100		$ 2,800
Follow-On Offering | Maximum
Subsidiary Sale Of Stock [Line Items]
Warrants exercisable term		5 years
Warrant exercise percentage of ordinary shares outstanding beneficially owned		4.99%
Follow-On Offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares)		6,428,571
Share purchase price		$ 7
Follow-On Offering | Existing Warrants
Subsidiary Sale Of Stock [Line Items]
Exercise price for warrant		$ 8.5
Warrants issued to purchase ordinary shares		6,428,572

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Number of Shares
Balances at December 31, 2023 | shares	1,913,345
Granted | shares	621,834
Canceled | shares	(159,095)
Balances at March 31, 2024 | shares	2,376,084
Weighted-Average Exercise Price
Balances at December 31, 2023 | $ / shares	$ 14.23
Granted | $ / shares	1.67
Canceled | $ / shares	6.02
Balances at March 31, 2024 | $ / shares	$ 11.49

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Restricted Stock Units, Performance Stock Units and Restricted Stock Awards Activity (Details) - RSU, RSA and PSU	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested at December 31, 2023 | shares	41,225
Shares, Granted | shares	407,725
Shares, Vested | shares	(5,014)
Shares, Canceled | shares	(20,000)
Shares, Unvested at March 31, 2024 | shares	423,936
Weighted-Average Grant Date Fair Value, Unvested at December 31, 2023 | $ / shares	$ 30.18
Weighted-Average Grant Date Fair Value, Granted | $ / shares	1.67
Weighted-Average Grant Date Fair Value, Vested | $ / shares	31.02
Weighted-Average Grant Date Fair Value, Canceled | $ / shares	1.67
Weighted-Average Grant Date Fair Value, Unvested at March 31, 2024 | $ / shares	$ 4.09

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,394	$ 2,175
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	321	682
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,073	$ 1,493

Net Loss per Common Share - Sch

Net Loss per Common Share - Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net loss	$ (5,790)	$ (5,279)
Denominator:
Weighted average number of shares outstanding-basic	16,785,090	14,312,887
Weighted average number of shares outstanding-diluted	16,785,090	14,312,887
Net loss per share-basic	$ (0.34)	$ (0.37)
Net loss per share-diluted	$ (0.34)	$ (0.37)

Net Loss per Common Share - Sum

Net Loss per Common Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	9,403,218	8,210,257
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,376,084	1,603,958
Outstanding warrants to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	6,557,152	6,428,572
Early Exercised Common Stock Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		3,336
RSUs subject to future vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	423,936	108,452
Shares subject to future vesting relating to the 2018 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	46,046	65,939

Net Loss per Common Share - Add

Net Loss per Common Share - Additional Information (Details)	3 Months Ended
	Mar. 31, 2024 shares
Maximum
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares contingently issued	3,390

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Subsequent Event [Line Items]
Common stock, par value per share	$ 0.0001	$ 0.0001