TRACON Pharmaceuticals (TCON) 10-K 5 Mar 24 2023 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 01, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Registrant Name	TRACON Pharmaceuticals, Inc.
Entity Central Index Key	0001394319
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 7.6
Entity Common Stock, Shares Outstanding		45,504,501
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	TCON
Security Exchange Name	NASDAQ
Entity File Number	001-36818
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	34-2037594
Entity Address, Address Line One	4350 La Jolla Village Drive
Entity Address, Address Line Two	Suite 800
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92122
City Area Code	858
Local Phone Number	550-0780
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	San Diego, California

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 8,564,000	$ 17,433,000
Prepaid and other assets	526,000	795,000
Total current assets	9,090,000	18,228,000
Property and equipment, net	37,000	51,000
Restricted cash	73,000	67,000
Other assets	905,000	1,123,000
Total assets	10,105,000	19,469,000
Current liabilities:
Accounts payable	2,544,000	3,923,000
Accrued expenses	7,211,000	7,184,000
Accrued compensation and related expenses	427,000	1,457,000
Long-term debt, current portion		9,807,000
Total current liabilities	10,182,000	22,371,000
Other long-term liabilities	732,000	969,000
Arbitration financing payable	0	3,280,000
Commitments and contingencies (Note 5)
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value, authorized shares - 10,000,000 at December 31, 2023 andDecember 31,2022; issued and outstanding shares - none
Common stock, $0.001 par value; authorized shares - 60,000,000 and 40,000,000 at December 31, 2023 and December 31, 2022, respectively; issued and outstanding shares - 44,269,976 and 23,125,250 at December 31, 2023 and December 31, 2022, respectively	44,000	23,000
Additional paid-in capital	239,646,000	229,737,000
Accumulated deficit	(240,499,000)	(236,911,000)
Total stockholders' deficit	(809,000)	(7,151,000)
Total liabilities and stockholders' deficit	$ 10,105,000	$ 19,469,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
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 (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	60,000,000	40,000,000
Common stock, shares issued	44,269,976	23,125,250
Common stock, shares outstanding	44,269,976	23,125,250

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Revenue	$ 12,045		$ 346
Revenue, Product and Service [Extensible Enumeration]	us-gaap:CollaborativeArrangementMember		us-gaap:CollaborativeArrangementMember
Operating expenses:
Research and development	$ 12,277	$ 13,888	$ 11,146
General and administrative	6,666	14,006	17,547
Arbitration success fees	2,375
Total operating expenses	21,318	27,894	28,693
Loss from operations	(9,273)	(27,894)	(28,347)
Other income (expense):
Interest expense, net	(7,304)	(994)	(318)
Other income (expense), net	12,989	(247)	(2)
Total other income (expense)	5,685	(1,241)	(320)
Net loss	$ (3,588)	$ (29,135)	$ (28,667)
Net loss per share, basic	$ (0.11)	$ (1.39)	$ (1.66)
Net loss per share, diluted	$ (0.11)	$ (1.39)	$ (1.66)
Weighted-average shares outstanding, basic	32,745,708	20,919,118	17,252,637
Weighted-average shares outstanding diluted	32,745,708	20,919,118	17,252,637

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2020	$ 25,072	$ 15	$ 204,166	$ (179,109)
Balance (in Shares) at Dec. 31, 2020		15,478,787
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	149		149
Issuance of common stock under equity plans (in shares)		40,414
Stock-based compensation expense	1,775		1,775
Issuance of common stock, net of offering costs	13,385	$ 4	13,381
Issuances of common stock, net of offering costs (in shares)		3,926,702
Net loss	(28,667)			(28,667)
Balance at Dec. 31, 2021	11,714	$ 19	219,471	(207,776)
Balance (in Shares) at Dec. 31, 2021		19,445,903
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	95		95
Issuance of common stock under equity plans (in shares)		56,261
Stock-based compensation expense	2,041		2,041
Issuance of common stock and warrants, net of offering costs	7,874	$ 3	7,871
Issuance of common stock and warrants, net of offering costs (in shares)		3,232,418
Issuance of common stock upon cashless exercise of pre-funded warrants	1	$ 1
Issuance of common stock upon cashless exercise of pre-funded warrants, shares		390,668
Issuance of common stock warrants in connection with debt financing	259		259
Net loss	(29,135)			(29,135)
Balance at Dec. 31, 2022	(7,151)	$ 23	229,737	(236,911)
Balance (in Shares) at Dec. 31, 2022		23,125,250
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	45		45
Issuance of common stock under equity plans (in shares)		45,569
Stock-based compensation expense	1,969		1,969
Issuance of common stock and warrants, net of offering costs	7,916	$ 14	7,902
Issuance of common stock and warrants, net of offering costs (in shares)		14,231,653
Issuance of common stock upon cashless exercise of pre-funded warrants		$ 7	(7)
Issuance of common stock upon cashless exercise of pre-funded warrants, shares		6,867,504
Net loss	(3,588)			(3,588)
Balance at Dec. 31, 2023	$ (809)	$ 44	$ 239,646	$ (240,499)
Balance (in Shares) at Dec. 31, 2023		44,269,976

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net loss	$ (3,588)	$ (29,135)	$ (28,667)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation	1,969	2,041	1,775
Depreciation and amortization	14	16	14
Noncash interest	88	343	61
Amortization of debt discount	7,325	435	21
Amortization of premium/discount on short-term investments			(1)
Lease asset amortization and liability accretion, net	20	54	(73)
Equity ownership license revenue			(246)
Impairment of private company equity ownership		246
Changes in assets and liabilities:
Prepaid expenses and other assets	269	69	(80)
Accounts payable and accrued expenses	(1,391)	(233)	4,683
Accrued compensation and related expenses	(1,030)	(75)	(58)
Net cash provided by (used in) operating activities	3,676	(26,239)	(22,571)
Cash flows from investing activities
Purchase of property and equipment		(17)	(48)
Proceeds from the maturity of short-term investments			4,000
Net cash (used in) provided by investing activities		(17)	3,952
Cash flows from financing activities
Proceeds from long-term debt and arbitration financing		13,390
Repayment of long-term debt and arbitration financing payable	(20,500)	(1,680)	(2,800)
Proceeds from sale of common stock and warrants, net of offering costs	7,916	7,879	13,211
Proceeds from issuance of common stock under equity plans	45	95	149
Net cash (used in) provided by financing activities	(12,539)	19,684	10,560
Change in cash, cash equivalents, and restricted cash	(8,863)	(6,572)	(8,059)
Cash, cash equivalents, and restricted cash at beginning of period	17,500	24,072	32,131
Cash, cash equivalents, and restricted cash at end of period	8,637	17,500	24,072
Supplemental disclosure of cash flow information
Interest paid	$ 7,491	359	$ 266
Supplemental schedule of noncash investing and financing activities
Issuance of common stock warrants in connection with long-term debt		$ 259

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (3,588)	$ (29,135)	$ (28,667)

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Organization And Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	1. Organization and Summary of Significant Accounting Policies Organization and Business TRACON Pharmaceuticals, Inc. (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer, and utilizes its cost efficient, contract research organization (CRO) independent product development platform to partner with other life science companies to develop and commercialize innovative products in the United States. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, TRACON Pharma Limited and TRACON Pharma International Limited, which were formed in September 2015 and January 2019, respectively, and are currently inactive. All significant intercompany accounts and transactions have been eliminated. Basis of Presentation As of December 31, 2023, the Company has devoted substantially all its efforts to product development, raising capital, and building infrastructure and has not realized revenues from its planned principal operations. The Company has incurred operating losses since inception. As of December 31, 2023 , the Company had an accumulated deficit of $ 240.5 million. The Company anticipates that it will continue to incur net losses into the foreseeable future as it continues the development and commercialization of its product candidates and works to develop additional product candidates through research and development programs. At December 31, 2023, the Company had cash and cash equivalents of $ 8.6 million, of which $ 0.1 million is classified as restricted cash as it is pledged as collateral for the Company’s obligations under its corporate headquarters facility lease. The Company’s ability to execute its operating plan through 2024 and beyond depends on its ability to obtain additional funding through equity offerings, debt financings, or potential licensing and collaboration arrangements. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, based on the Company’s current working capital, anticipated operating expenses and net losses, and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, management believes that there is substantial doubt about its ability to continue as a going concern for a period of 12 months following the date that these consolidated financial statements are issued. The consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through its existing cash and cash equivalents, as well as through future equity offerings, debt financings, other third-party funding, and potential licensing or collaboration arrangements. In addition, the Company may fund its losses from operations through the Capital on Demand TM Sales Agreement (the Sales Agreement) the Company entered into with JonesTrading in December 2020, as amended in March 2022, pursuant to which the Company may sell, at its option, up to an aggregate of $ 50.0 million of the Company’s common stock, $ 41.5 million of which remained available for sale as of December 31, 2023 , and the common stock purchase agreement (the LPC Purchase Agreement) the Company entered into with Lincoln Park Capital Fund, LLC (Lincoln Park) in May 2023, pursuant to which the Company may sell, at its option, up to an aggregate of $ 26.0 million of the Company’s common stock, $ 25.0 million of which remained available for sale as of December 31, 2023 . There can be no assurance that additional funds will be available when needed from any source or, if available, will be available on terms that are acceptable to the Company. Risks and Uncertainties Global economic and business activities continue to face widespread macroeconomic uncertainties, including labor shortages, inflation and monetary supply shifts, recession risks and potential disruptions from the Russia-Ukraine conflict. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business . Use of Estimates The Company’s consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenue, and expenses. The most significant estimates in the Company’s consolidated financial statements relate to expenses incurred for clinical trials. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company’s assets or liabilities as of the date of this filing. Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of three months or less at the date of purchase. The carrying amounts approximate fair value due to the short maturities of these investments. Cash and cash equivalents include cash in readily available checking and money market funds. Restricted Cash Restricted cash consists of money market funds held by the Company’s financial institution as collateral for the Company’s obligations under its facility lease for the Company’s corporate headquarters in San Diego, California. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Property and Equipment Property and equipment is stated at cost and depreciated using the straight-line method over the estimated useful life of the related assets, which is generally five years . Leasehold improvements are amortized over the shorter of the lease term or estimated useful life of the related assets. Repairs and maintenance costs are charged to expense as incurred. Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are recorded as other assets, accounts payable and accrued expenses, and other long-term liabilities within the consolidated balance sheet. The Company currently does not have any finance leases. Operating lease right-of-use (ROU) assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term. Revenue Recognition To date, the Company’s revenue has been derived from license and collaboration agreements. The terms of these arrangements included payments to the Company for the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. In accordance with Accounting Standards Codification (ASC) 606, Revenue from Contracts with Customers (ASC 606), the Company performs the following five steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the contract(s) with a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services transferred to the customer. Once a contract is determined to be within the scope of ASC 606, at contract inception the Company assesses the goods or services promised within the contract to determine those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization, and regulatory milestone payments, the Company evaluates whether the achievement of the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. Performance milestone payments represent a form of variable consideration. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Achievement of milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable until the approvals are achieved. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis and the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations at the outset of the arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its collaborators based on billing schedules established in each contract. Up-front and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Clinical Trial Expense Accruals As part of the process of preparing the Company’s consolidated financial statements, the Company is required to estimate expenses resulting from its obligations under contracts with vendors, clinical sites, and consultants in connection with conducting clinical trials. The financial terms of these contracts vary and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its consolidated financial statements by recording those expenses in the period in which services are performed and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with the clinical sites and applicable personnel and outside service providers as to the progress or state of consummation of trials. During a clinical trial, the Company adjusts the clinical expense recognition if actual results differ from its estimates. The Company makes estimates of accrued expenses as of each balance sheet date based on the facts and circumstances known at that time. The Company’s clinical trial accruals are dependent upon accurate reporting by clinical sites and other third-party vendors. Although the Company does not expect its estimates to differ materially from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting amounts that are too high or too low for any particular period. For the three years ended December 31, 2023 , there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. Research and Development Costs Research and development costs, including license fees, are expensed as incurred. Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain. Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of employee stock option grants, employee restricted stock unit grants (RSUs), and employee stock purchase plan (ESPP) rights recognized as expense over the requisite service period of the awards (usually the vesting period) on a straight-line basis. The Company estimates the fair value of stock option grants and ESPP rights using the Black-Scholes option pricing model. The fair value of RSUs is based on the closing sales price for such stock on the date of grant. Equity award forfeitures are recorded as they occur. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than‑not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average shares of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of shares of common stock outstanding that are subject to repurchase. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): December 31, 2023 2022 Warrants to purchase common stock 1,533,293 6,766,246 Common stock options 3,121,152 2,246,310 ESPP shares 10,444 3,387 4,664,889 9,015,943 Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Financial Instruments and Fair

Financial Instruments and Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Financial Instruments and Fair Value Measurements	2. Financial Instruments and Fair Value Measurements Cash equivalents, which are classified as equity securities, and restricted cash consisted of the following (in thousands): December 31, 2023 December 31, 2022 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 3,689 $ — $ — $ 3,689 $ 10,150 $ — $ — $ 10,150 Classified as: Cash equivalents $ 3,616 $ 10,083 Restricted cash 73 67 Total cash equivalents and restricted cash $ 3,689 $ 10,150 As of December 31, 2023 and 2022, the Company had no investments. The carrying amounts of cash and cash equivalents, prepaid and other assets, accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. The fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets Other Significant for Identical Observable Unobservable Assets Inputs Inputs Total (Level 1) (Level 2) (Level 3) At December 31, 2023 Money market funds $ 3,689 $ — $ 3,689 $ — At December 31, 2022 Money market funds $ 10,150 $ — $ 10,150 $ —

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	3. Balance Sheet Details Property and Equipment Property and equipment consisted of the following (in thousands): December 31, December 31, 2023 2022 Computer and office equipment $ 203 $ 203 Furniture and fixtures 19 19 Leasehold improvements 21 21 243 243 Less accumulated depreciation and amortization ( 206 ) ( 192 ) $ 37 $ 51 Depreciation and amortization expense related to property and equipment totaled approximately $ 14,000 , $ 16,000 and $ 14,000 for the years ended December 31, 2023, 2022 and 2021, respectively. Accounts payable and accrued expenses Accounts payable and accrued expenses consisted of the following (in thousands): December 31, December 31, 2023 2022 Accounts payable $ 2,544 $ 3,923 Accrued clinical related expenses 6,736 6,091 Accrued legal and accounting 199 299 Accrued long-term debt terminal interest — 425 Current portion of operating lease liability 236 198 Other accruals 40 171 $ 9,755 $ 11,107

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Long-Term Debt	4. Long-Term Debt Arbitration Financing Investment Agreement In December 2022, the Company entered into a non-recourse financing agreement (the Investment Agreement) with certain investors (collectively, the Investors) pursuant to which the Investors agreed to pay the Company a maximum aggregate amount (Maximum Capital) equal to $ 30.0 million or a lesser amount based on the amount awarded (Arbitration Award), if any, to the Company in connection with its arbitration proceeding (the Arbitration) with I-Mab Biopharma (I-Mab). Of the Maximum Capital, (i) $ 3.5 million (Initial Capital) was paid to the Company shortly after execution, (ii) 25 % was to be paid to the Company within 15 business days of issuance of an Arbitration Award, subject to the Arbitration Award size exceeding a prespecified threshold and satisfaction of other conditions set forth in the Investment Agreement, and (iii) the remainder was to be paid to the Company in tranches over a multi-year period, subject to the issuance of an Arbitration Award and the Arbitration Award size exceeding a prespecified threshold and satisfaction of other conditions set forth in the Investment Agreement. In connection with the execution of the Investment Agreement and funding of the Initial Capital amount, the Company paid a closing fee in the amount of 2 %. In April 2023, the Company received notification of the Arbitration Award resulting from the Arbitration. As the Arbitration Award did not exceed the prespecified thresholds under the Investment Agreement, the Company will not receive any additional funds under the Investment Agreement such that, as of date of the Arbitration Award, the Maximum Capital is equal to the Initial Capital. Subject to and contingent on the Company’s actual recovery of proceeds from an Arbitration Award or any contemporaneously resolved settlements with I-Mab and following the payment of applicable attorney’s fees (the Proceeds), the Company was required to pay the Investors an amount (Repayment Amount) equal to the sum of (i) all amounts paid by the Investors to or on behalf of the Company pursuant to the Investment Agreement, plus (ii) a low sub-single digit to low single digit multiple calculated on each tranche of Maximum Capital actually paid by the Investors to or on behalf of the Company with the applicable multiple being based on the timing of payment from the Company and whether certain events relating to the Arbitration occurred, plus (iii) a mid-teen percentage annual rate of return on the amounts set forth in clauses (i) and (ii) that begins to accrue if the amounts are not paid by the Company to the Investors within a multi-month period specified in the Investment Agreement. If the amount of Proceeds are less than the Repayment Amount, then the Company was only required to pay to the Investors the Proceeds recovered (other than in circumstances in which the Company accepts a settlement offer that resolves the Arbitration for an amount less than the Repayment Amount without the prior written consent of the Investors), and in the circumstance in which there are no Proceeds then the Company was not required to pay the Investors any Repayment Amounts and the Investors have no right of recourse or right of action against the Company. In December 2022, the Investors funded the Initial Capital amount of $ 3.5 million which was recorded as arbitration financing payable on the consolidated balance sheets, net of debt discount, including the Initial Capital closing fee, and amortized over the estimated term of the agreement using the effective interest method. In July 2023, the Company agreed to and collected a settlement of $ 22.0 million in full satisfaction of the Arbitration Award. The Company determined an effective interest rate and term over which the related debt discount was amortized based on the known timing of collection of the proceeds from the Arbitration Award resulting in $ 7.2 million o f interest being recognized during the year ended December 31, 2023. At December 31, 2023, the arbitration financing investment agreement was paid in full and no future amounts were owed. Runway Growth Finance Corp. Loan and Security Agreement In September 2022, the Company entered into a loan and security agreement (the RGC Loan Agreement) with Runway Growth Finance Corp. (RGC). The RGC Loan Agreement was a long-term debt facility that provided a term loan commitment in an aggregate principal amount of up to $ 35.0 million in three tranches: (i) a Term A loan in an aggregate principal amount of $ 10.0 million, with the full amount funded in a single disbursement on closing of the RGC Loan Agreement and repaid in January 2023 in connection with the Investment Agreement; (ii) a Term B loan in an aggregate principal amount of up to $ 15.0 million to be funded in one or more disbursements at the request of the Company on or prior to June 30, 2024, subject to certain conditions being met; and (iii) a Term C loan in an aggregate principal amount of up to $ 10.0 million that may be disbursed in a single disbursement in the lender’s sole discretion upon the Company’s request at any time from closing of the RGC Loan Agreement through and including December 31, 2024. In December 2022, the Company and RGC amended the RGC Loan Agreement (the RGC Loan Amendment) under which: (i) the Company repaid all amounts of principal and accrued but unpaid interest in respect of the Term A Loan (as defined in the RGC Loan Agreement) on January 3, 2023 without the obligation for the Company to pay the final payment fee or the prepayment fee described in the RGC Loan Agreement; (ii) on or before March 31, 2023, at the Company’s request, if the Company has raised at least $ 25.0 million in net cash proceeds from certain equity or debt transactions (including amounts raised in connection with the Investment Agreement) prior to making such request, RGC will loan to the Company an aggregate principal amount of $ 10.0 million, with the full amount funded in a single disbursement; (iii) the Company will not issue an additional warrant to RGC in connection with the loan, if any, described in clause (ii) above; and (iv) RGC’s security interest in Specific Collateral was subordinated to the arbitration financing Investors’ security interest in the Specific Collateral. If the loan described in clause (ii) above is not made by March 31, 2023, the RGC Loan Agreement will terminate on that date, and the Company will not be obligated to pay the prepayment fee described in the RGC Loan Agreement but the final payment fee of 4.25 % of the aggregate principal amount of the funded term loans as described in the RCG Loan Agreement will become immediately due and payable. All other material terms and conditions of the RGC Loan Agreement remained unchanged and the transaction was accounted for as a debt modification. On April 5, 2023, the Company and RGC amended the RGC Loan Agreement effective March 31, 2023 such that the Company would have until April 15, 2023 to raise at least $ 25.0 million in net cash proceeds from certain equity or debt transactions prior to making a request of RGC to redraw an aggregate principal amount of $ 10.0 million under the RGC Loan Agreement, which RGC may, in its sole and absolute discretion, allow or deny. On April 20, 2023, the Company and RGC amended the RGC Loan Agreement effective April 15, 2023 to extend the time period described in the foregoing sentence from April 15, 2023 to April 28, 2023. The Company did not redraw the $ 10.0 million under the RGC Loan Agreement, as amended, by April 28, 2023, resulting in the RGC Loan Agreement terminating and the final payment fee becoming immediately due and payable on that date. In connection with the funding of the Term A loan, the Company issued RGC warrants to purchase 150,753 shares of its common stock (the RGC Term A Warrants) at an exercise price of $ 1.99 per underlying share of the Company’s common stock. The RGC Term A Warrants are fully exercisable in whole or in part at the option of the holder, payable in cash or on a cashless basis according to the formula set forth in the RGC Term A Warrants, and expire September 2, 2032 . The fair value of the warrant at the grant date was determined utilizing a Black-Scholes pricing model, recorded as a component of the total debt discount and stockholders’ deficit within additional paid-in capital on the consolidated balance sheets, and was amortized to interest expense using the effective interest method over the term of the debt. As of December 31, 2022, long-term debt and unamortized debt discount balances associated with the RGC Loan Agreement were as follows (in thousands): December 31, 2022 Long-term debt $ 10,000 Less debt discount, net of current portion — Long-term debt, net of debt discount 10,000 Less current portion of long-term debt ( 10,000 ) Long-term debt, net of current portion $ — Current portion of long-term debt $ 10,000 Current portion of debt discount ( 193 ) Current portion of long-term debt, net $ 9,807 At December 31, 2023, the RGC Loan Agreement was paid in full and no future amounts were owed. Silicon Valley Bank Loan and Security Agreement In May 2018, the Company entered into a third amendment to its Amended and Restated Loan and Security Agreement with Silicon Valley Bank (the 2018 Amended SVB Loan) under which the Company borrowed $ 7.0 million, all of which was immediately used to repay the Company’s then existing loan with SVB. The 2018 Amended SVB Loan matured in June 2022 and in accordance with its terms, the Company paid a final payment of $ 0.3 million associated with the payoff of the 2018 Amended SVB Loan. In August 2022, the Company terminated the 2018 Amended SVB Loan. At December 31, 2023, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 12,938

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies License Agreements The Company has entered into various license agreements pursuant to which the Company acquired licenses to certain intellectual property. The agreements generally required an upfront license fee and, in some cases, reimbursement of patent costs. Additionally, under each agreement, the Company may be required to pay annual maintenance fees, royalties, milestone payments and sublicensing fees. Each license agreement is generally cancelable by the Company, given appropriate prior written notice. At December 31, 2023, potential future milestone payments under these agreements totaled an aggregate of $ 9.6 million.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2023
Stockholders' Equity Note [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Lincoln Park Common Stock Purchase Agreement In May 2023, the Company and Lincoln Park entered into the LPC Purchase Agreement, which provides that, upon the terms and subject to the conditions and limitations set forth therein, Lincoln Park is committed to purchase up to an aggregate of $ 26.0 million of the Company's shares of common stock from time to time and at the Company’s sole discretion over the term of the LPC Purchase Agreement, $ 25.0 million of which remained available for sale as of December 31, 2023. In consideration for entering into the LPC Purchase Agreement, concurrently with the execution of the LPC Purchase Agreement, the Company issued to Lincoln Park 599,216 shares of its common stock as a commitment fee, which was recorded as a component of stockholders’ deficit within additional paid-in capital on the consolidated balance sheets. Concurrently with entering into the LPC Purchase Agreement, the Company also entered into a Registration Rights Agreement in which the Company agreed to file one or more registration statements as permissible and necessary to register under the Securities Act for resale of the shares of its common stock that may be issued to Lincoln Park under the LPC Purchase Agreement, which occurred in May 2023. In May 2023, the Company also issued and sold 1,735,207 shares (the Initial Purchase Shares) of the Company’s common stock to Lincoln Park pursuant to the LPC Purchase Agreement at a purchase price of $ 0.5763 per Initial Purchase Share resulting in net proceeds of $ 1.0 million. At the Company's special meeting of stockholders held in September 2023, stockholder approval, in accordance with applicable rules of the Nasdaq Stock Market, was obtained for the potential future sale and issuance of shares of the Company’s common stock to Lincoln Park in accordance with the pricing terms set forth in the LPC Purchase Agreement that could result in Lincoln Park owning in excess of 19.99 % of the shares of the Company’s common stock outstanding immediately after giving effect to such sale. Sale of Common Stock and Pre-Funded Warrants In March 2023, the Company issued and sold 174,508 shares of its common stock at a purchase price of $ 1.38 per share and pre-funded warrants to purchase 2,013,999 shares of its common stock at a purchase price of $ 1.37 per share of underlying common stock with an exercise price of $ 0.01 per share of underlying common stock (the 2023 Pre-Funded Warrants) for net proceeds of approximately $ 3.0 million in a private placement (the Private Placement) with an accredited institutional healthcare-focused fund. In accordance with their terms, the 2023 Pre-Funded Warrants may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 % of the shares of the Company’s common stock outstanding immediately after giving effect to such exercise, unless approval by the Company's stockholders is obtained as required under the Nasdaq listing standards, including Nasdaq Listing Rules 5635(b) and (d). The 2023 Pre-Funded Warrants were recorded as a component of stockholders’ deficit within additional paid-in capital on the consolidated balance sheets. In June 2022, the Company issued and sold 841,989 shares of its common stock at a purchase price of $ 1.32 per share and pre-funded warrants to purchase 2,205,018 shares of its common stock at a purchase price of $ 1.31 per share of underlying common stock with an exercise price of $ 0.01 per share of underlying common stock (the 2022 Pre-Funded Warrants) for net proceeds of approximately $ 3.9 million in a registered direct offering (the Offering) with an accredited institutional healthcare-focused fund. In accordance with their terms, the 2022 Pre-Funded Warrants may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 % of the shares of the Company’s common stock outstanding immediately after giving effect to such exercise, unless approval by the Company's stockholders is obtained as required under the Nasdaq listing standards, including Nasdaq Listing Rules 5635(b) and (d). The 2022 Pre-Funded Warrants were recorded as a component of stockholders’ deficit within additional paid-in capital on the consolidated balance sheets. In connection with the Offering, the Company amended two existing pre-funded warrants to purchase shares of the Company’s common stock held by the same institutional healthcare-focused fund to extend the exercise periods and to permit exercise in excess of a similar 19.99 % limit following approval of the Company’s stockholders of such exercise. At the Company's 2023 Annual Meeting held in April 2023, stockholder approval, in accordance with applicable rules of the Nasdaq Stock Market, was obtained for the issuance of shares of common stock upon the potential future exercise of certain outstanding warrants held by this accredited institutional healthcare-focused fund, including the 2023 Pre-Funded Warrants and the 2022 Pre-Funded Warrants, that would result in it and its affiliates owning in excess of 19.99 % of the shares of common stock outstanding immediately after giving effect to such exercise. At-The-Market Issuance Sales Agreement In December 2020, as amended in March 2022, the Company entered into a Capital on Demand TM Sales Agreement (the Sales Agreement) with JonesTrading, pursuant to which it may sell from time to time, at its option, up to an aggregate of $ 50.0 million of the Company’s common stock through JonesTrading, as sales agent or principal, $ 41.5 million of which remained available for sale as of December 31, 2023. Sales of the Company’s common stock made pursuant to the Sales Agreement with JonesTrading, if any, will be made on the Nasdaq Capital Market under the Company’s effective registration statement on Form S-3, subject to limitations on the amount of securities the Company may sell pursuant to its effective registration statement on Form S-3 within any 12-month period, by means of ordinary brokers’ transactions at market prices. Additionally, under the terms of the Sales Agreement, the Company may also sell shares of its common stock through JonesTrading, on the Nasdaq Capital Market or otherwise, at negotiated prices or at prices related to the prevailing market price. JonesTrading will use its commercially reasonable efforts to sell the Company’s common stock from time to time, based upon the Company’s instructions (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company is required to pay JonesTrading 2.5 % of gross proceeds for the common stock sold through the Sales Agreement. Common Stock Warrants As of December 31, 2023, the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 September 2, 2032 150,753 $ 1.99 1,533,293 During the year ended December 31, 2023, the Company issued 6,867,504 shares of its common stock upon the cashless exercise of 7,245,984 pre-funded warrants. During the year ended December 31, 2022, the Company issued 390,668 shares of its common stock upon the cashless exercise of 398,093 pre-funded warrants. Stock Compensation Plans Effective January 1, 2015, the Company’s Board adopted the 2015 Equity Incentive Plan (2015 Plan). Under the 2015 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company or its subsidiaries. Initially, a total of 80,103 shares of common stock were reserved for issuance under the 2015 Plan. In addition, pursuant to the June 10, 2021 amendment, the number of shares of common stock available for issuance under the 2015 Plan will be annually increased on the first day of each fiscal year during the term of the 2015 Plan, as amended, beginning with the 2022 fiscal year until (and including) January 1, 2031, by an amount equal to 5 % of the total number of shares of common stock outstanding on December 31 of the preceding calendar year or such lesser amount as the Company’s Board may determine. The maximum term of the options granted under the 2015 Plan is no more than ten years . Grants generally vest at 25 % one year from the vesting commencement date and ratably each month thereafter for a period of 36 months, subject to continuous service. In addition, pursuant to a June 2021 amendment, the 2015 Plan was amended to allow an additional aggregate 200,000 shares of common stock to be used exclusively for the grant of equity awards as a material inducement for individuals to commence employment at the Company in compliance with Nasdaq Listing Rule 5635(c)(4). Stock Options Stock option activity under all Plans is summarized as follows: Weighted- Number of Average Options Exercise Price Balance at December 31, 2022 2,246,310 $ 9.07 Granted 1,089,400 1.71 Exercised — — Forfeited ( 214,558 ) 8.59 Balance at December 31, 2023 3,121,152 $ 6.53 Information about the Company’s outstanding stock options as of December 31, 2023 is as follows: Weighted- Average Weighted- Remaining Average Contractual Aggregate Number of Exercise Term Intrinsic Shares Price (in years) Value Options outstanding 3,121,152 $ 6.53 7.36 $ — Options vested and expected to vest 3,121,152 $ 6.53 7.36 $ — Options exercisable 1,446,873 $ 11.11 6.47 $ — The weighted-average grant date fair value per share of employee option grants during the years ended December 31, 2023, 2022 and 2021 was $ 1.31 , $ 1.65 , and $ 6.05 , respectively. The aggregate intrinsic value used in the above table of options at December 31, 2023 is based on the Company’s closing market price per common share on December 29, 2023, the last business day of the 2023 fiscal year, of $ 0.1751 . No stock options were exercised during the years ended December 31, 2023 and 2022. The total grant-date fair value of options that vested during the years ended December 31, 2023, 2022 and 2021 was $ 1.9 million, $ 2.6 million, and $ 0.8 million, respectively. Employee Stock Purchase Plan (ESPP) On January 1, 2015, the Company’s Board adopted the ESPP, which became effective upon the pricing of the Company’s initial public offering on January 29, 2015. The ESPP permits participants to purchase common stock through payroll deductions of up to 15 % of their eligible compensation. Initially, a total of 18,346 shares of common stock was reserved for issuance under the ESPP. In addition, pursuant to the June 10, 2021 amendment, the number of shares of common stock available for issuance under the ESPP will be annually increased on the first day of each fiscal year during the term of the ESPP, beginning with the 2022 fiscal year, by an amount equal to the lesser of: (i) 250,000 shares; (ii) 1 % of the total number of shares of common stock outstanding on December 31 of the preceding calendar year; or (iii) such other amount as the Company’s Board may determine. Stock compensation expense for the years ended December 31, 2023, 2022 and 2021 related to the ESPP was immaterial. Stock-Based Compensation Expense The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Year Ended December 31, 2023 2022 2021 Risk-free interest rate 3.5 % 1.9 % 0.8 % Expected volatility 90.1 % 89.8 % 90.3 % Expected term (in years) 6.2 6.2 6.2 Expected dividend yield — % — % — % Risk-free interest rate. The Company bases the risk‑free interest rate assumption on the U.S. Treasury’s rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. Expected volatility. The Company considers its historical volatility when determining the expected volatility. Expected term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, it determines the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period. Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends. The allocation of stock-based compensation expense was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development $ 935 $ 830 $ 628 General and administrative 1,034 1,211 1,147 $ 1,969 $ 2,041 $ 1,775 As of December 31, 2023 and 2022, the unrecognized compensation cost related to outstanding time-based options was $ 2.8 million and $ 3.6 million, respectively, and is expected to be recognized as expense over approximately 2.4 years and 2.5 years, respectively. Common Stock Reserved for Future Issuance Common stock reserved for future issuance was as follows: December 31, 2023 2022 Common stock warrants 1,533,293 6,766,246 Common stock options granted and outstanding 3,121,152 2,246,310 Awards available under the 2015 Plan 431,755 150,335 Shares available under the Employee Stock Purchase Plan 429,500 243,817 5,515,700 9,406,708

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2023
Collaborations Disclosure [Abstract]
Collaboration and License Agreements	7. Collaboration and License Agreements Inhibrx, Inc.(Inhibrx) License Agreement In November 2023, the Company granted a non-exclusive, non-sublicensable, non-transferable (except in the event of the transfer or sale of all or substantially all of the business or assets of Inhibrx) worldwide perpetual license of its’ CRO-independent product development platform (PDP) to Inhibrx for a nonrefundable upfront fee of $ 3.0 million plus an additional $ 0.2 million upon the completion of certain training. The Company is obligated to be available over a six-month period beginning on the date of license transfer to provide up to 500 hours of training to Inhibrx. The PDP license allows Inhibrx to use the Company’s configuration documentation with a widely used software package in addition to use the Company’s validation and qualification of the software package and the Company’s standard operation procedure documents, policies, work instructions, and clinical operation templates in the administration of clinical trials and related research and development activities. Under the terms of the agreement, Inhibrx has sole responsibility for funding and conducting any such clinical trials and related research and development activities. The Company is not obligated to tailor any of the related documentation and is not involved in conducting any of the related clinical trials or research and development activities. The Company assessed this agreement and identified multiple promised goods and services, which included at contract inception: (1) the PDP license and (2) up to 500 hours of training over a six-month period. Management evaluated these promised goods and services and determined each was a separate performance obligation. The transaction price at contract inception included fixed consideration of the $ 3.0 million upfront payment and $ 0.2 million payment due upon the earlier of the completion of 500 hours of training or six months. The total $ 3.2 million transaction price was allocated to each performance obligation based on relative standalone selling price. The $ 3.0 million amount allocated to the PDP license performance obligation was recognized at the point in time Inhibrx could first use and benefit from the license, which occurred in the fourth quarter of 2023. The $ 0.2 million amount allocated to the training performance obligation will be recognized over the six-month period in which the Company is obligated to be available to provide training. Eucure and Biocytogen Collaborative Development and Commercialization Agreement In October 2021, the Company, Eucure (Beijing) Biopharma Co., Ltd. (Eucure) and Biocytogen Pharmaceuticals (Beijing) Co., Ltd. (Biocytogen), Eucure’s controlling affiliate, entered into a collaborative development and commercialization agreement (the YH001 Collaboration Agreement) for the development of YH001, a monospecific investigational CTLA-4 antibody. Pursuant to the YH001 Collaboration Agreement, the Company was granted an exclusive (including with respect to Eucure and its affiliates), nontransferable, license to develop and commercialize YH001 in North America for the treatment, through administration of YH001 by intravenous or subcutaneous means, of multiple human indications, including sarcoma, microsatellite stable colorectal cancer, renal cell carcinoma (RCC), and K-ras positive non-small cell lung cancer (collectively, the Initial Indications) or one or more of bladder cancer, endometrial cancer, and melanoma as substitute indications, which may be substituted for Initial Indications at the Company’s discretion (each upon such substitution, a Substitute Indication). The Company is responsible for, and will bear the costs of, preparing and filing all regulatory submissions and conducting any Phase 1, Phase 2, Phase 3, or post-approval clinical trials in North America for YH001 in the Initial Indications and potentially the Substitute Indications, while Eucure is responsible for conducting, and will bear the costs of, the preparation of chemistry, manufacturing and controls activities for YH001. Eucure has agreed to manufacture and supply, or to arrange for a third party manufacturer to manufacture and supply, YH001 to the Company for clinical trials pursuant to the terms of a clinical supply and quality agreement to be separately negotiated. During a specified period, the Company has the option, subject to Eucure’s prior written approval, to expand the license to include the development and commercialization of YH001 for the treatment, through administration by intravenous or subcutaneous means, of all human and veterinary therapeutic indications in North America for a payment to Eucure in the low single digit millions. The Company will be responsible for commercializing YH001 in North America, including booking of sales revenue in the Initial and Substitute Indications. The Company will owe Eucure escalating double digit royalties on net sales of YH001 in North America ranging from the mid-twenties to mid-double digits; provided that until the end of the first full calendar year following the first commercial sale of YH001, royalties will range from the lower double digits to the mid-double digits. If sales of YH001 exceed a pre-determined sales threshold in the first full year of sales following first commercial sale, the Company will owe a milestone to Eucure in the high single digit millions. Payment obligations under the YH001 Collaboration Agreement continue on a country-by-country basis until the latest of (i) expiration of the last to expire licensed patent covering YH001, (ii) expiration of marketing or regulatory exclusivity covering YH001 and (iii) 10 years from the first commercial sale of YH001 in such country in North America. Eucure has agreed to manufacture and supply, or to arrange for a third party manufacturer to manufacture and supply, YH001 to the Company at cost plus a low double digit markup for commercial sales pursuant to the terms of a commercial supply and quality agreement to be separately negotiated. 3D Medicines and Alphamab Collaboration and Clinical Trial Agreement In December 2019, the Company, 3D Medicines Co., Ltd. (3D Medicines), and Jiangsu Alphamab Biopharmaceuticals Co., Ltd. (Alphamab) entered into a collaboration and clinical trial agreement (the Envafolimab Collaboration Agreement) for the development of envafolimab, also known as KN035, an investigational PD-L1 single-domain antibody (sdAb), or nanobody, administered by subcutaneous injection, for the treatment of sarcoma in North America. No consideration was exchanged in the Envafolimab Collaboration Agreement. Given no consideration was exchanged, no value was assigned to the Envafolimab Collaboration Agreement in the accompanying consolidated balance sheets. Pursuant to the Envafolimab Collaboration Agreement, the Company was granted an exclusive license to develop and commercialize envafolimab for the treatment of sarcoma in North America. The Company is responsible for conducting, and will bear the costs of Phase 1, Phase 2, and Phase 3 or post-approval clinical trials in North America for envafolimab in the indications of refractory and first line treatment of sarcoma. 3D Medicines and Alphamab are responsible for conducting, and will bear the costs of, investigational new drug (IND)-enabling studies (other than those specific to the sarcoma indication) and the preparation of chemistry, manufacturing and controls (CMC) activities sections of an IND application for envafolimab. 3D Medicines and Alphamab have agreed to manufacture and supply, or to arrange for a third party manufacturer to manufacture and supply, envafolimab to the Company at pre-negotiated prices that vary based on clinical or commercial use. 3D Medicines and Alphamab retained the right to develop envafolimab in all territories outside of North America as well as within North America for all indications other than sarcoma. The Company will be responsible for commercializing envafolimab for sarcoma in North America, including booking of sales revenue, unless (a) envafolimab is first approved in North America for an indication other than sarcoma and launched in North America, or (b) envafolimab is first approved in North America for sarcoma and subsequently approved in North America for an additional non-orphan indication and sold commercially by 3D Medicines and/or Alphamab, or a licensee, in which case 3D Medicines and Alphamab will be responsible for commercializing envafolimab for sarcoma in North America, including booking of sales revenue. If 3D Medicines and Alphamab become responsible for commercialization under the Envafolimab Collaboration Agreement, the Company has the option to co-market envafolimab for sarcoma in North America. In the event that envafolimab is first approved in North America for sarcoma and within three years of the commercial launch of envafolimab in North America for sarcoma 3D Medicines and Alphamab replace the Company as the party responsible for commercialization, and the Company elects and 3D Medicines and Alphamab agree for the Company to not co-market envafolimab for sarcoma in North America, then 3D Medicine and Alphamab will be required to compensate the Company for its costs associated with preparing for and conducting commercial activities. If the Company has the responsibility for commercialization under the Envafolimab Collaboration Agreement, the Company will owe 3D Medicines and Alphamab tiered double digit royalties on net sales of envafolimab for sarcoma in North America ranging from the teens to mid-double digits. If 3D Medicines and Alphamab have responsibility for commercialization under the Envafolimab Collaboration Agreement, the Company will be entitled to (a) escalating double digit royalties on net sales of envafolimab for sarcoma in North America ranging from the teens to mid-double digits if the Company has chosen to not co-market envafolimab in sarcoma or (b) a 50 % royalty on net sales of envafolimab for sarcoma in North America if the Company has chosen to co-market envafolimab in sarcoma. Payment obligations under the Envafolimab Collaboration Agreement continue on a country-by-country basis until the last to expire licensed patent covering envafolimab expires. 3D Medicines and Alphamab retain the right to reacquire the rights to envafolimab for sarcoma in North America in connection with an arm’s length sale to a third party, provided that the sale may not occur prior to completion of a pivotal trial of envafolimab in sarcoma without the Company’s written consent and the parties must negotiate in good faith and agree to fair compensation to be paid to the Company for the value of and opportunity represented by the required rights. Each party agreed that during the term of the Envafolimab Collaboration Agreement, it would not develop or license from any third party a monospecific inhibitor to PD-L1 or PD-1 in sarcoma. The term of the Envafolimab Collaboration Agreement continues until the later of the date the parties cease further development and commercialization of envafolimab for sarcoma in North America or the expiration of all payment obligations. The Envafolimab Collaboration Agreement may be terminated earlier by a party in the event of an uncured material breach by the other party or bankruptcy of the other party, or for safety reasons related to envafolimab. In the event the Company elects, or a joint steering committee determines, to cease further development or commercialization of envafolimab, or if the Company fails to use commercially reasonable efforts to develop (including progress in clinical trials) and commercialize envafolimab and does not cure such failure within a specified time period, then the Company’s rights and obligations under the Envafolimab Collaboration Agreement will revert to 3D Medicines and Alphamab. I-Mab Collaboration Agreements In November 2018, the Company and I-Mab entered into separate strategic collaboration and clinical trial agreements (the I-Mab Collaboration Agreements) for the development of programs for multiple immuno-oncology product candidates, including I-Mab’s proprietary CD73 antibody TJ004309 (the TJ004309 Agreement) as well as up to five proprietary bispecific antibodies currently under development by I-Mab (the Bispecific Agreement). Pursuant to the TJ004309 Agreement, the Company and I-Mab were collaborating on developing the TJ004309 antibody, with the Company bearing the costs of filing an IND and for Phase 1 clinical trials, with the parties sharing costs equally for Phase 2 clinical trials, and with the Company and I-Mab bearing 40 % and 60 %, respectively, of the costs for pivotal clinical trials. I-Mab was responsible for the cost of certain non-clinical activities, the drug supply of TJ004309, and any reference drugs used in the clinical trials. The Company would be entitled to receive escalating portions of royalty and non-royalty consideration and a royalty based on net sales if I-Mab licenses TJ004309 in certain territories or commercializes TJ004309, respectively. The TJ004309 Agreement was terminatable by either party in the event of an uncured material breach by the other party or bankruptcy of the other party, for safety reasons related to TJ004309 or by I-Mab if the Company causes certain delays in completing a Phase 1 clinical trial. In addition, the TJ004309 Agreement was terminatable by I-Mab for any reason within 90 days following the completion of the first Phase 1 clinical trial, in which case the Company would be entitled to a minimum termination fee of $ 9.0 million, or following the completion of the first Phase 2 clinical trial, in which case the Company would be entitled to a pre-specified termination fee of $ 15.0 million and either a percentage of non-royalty consideration I-Mab may receive as part of a license to a third party or an additional payment if TJ004309 is approved for marketing outside Greater China before a third-party license is executed, in addition to a double digit percentage of royalty consideration. As previously disclosed, in June 2020, I-Mab commenced an arbitration proceeding under the Rules of Arbitration of the International Chamber of Commerce before an arbitration tribunal seated in New York City (the Tribunal) after the Company invoked contractual dispute resolution provisions asserting that I-Mab had breached its contractual obligations under the TJ004309 Agreement and the Bispecific Agreement. In April 2023, the Company received notification from the Tribunal of the Arbitration Award. The Tribunal found in favor of the Company for certain claims and declared the Phase 1 clinical trial of TJ004309 Agreement “Complete,” as that term is defined in the TJ004309 Agreement as of January 2022. The Arbitration Award included the $ 9.0 million prespecified termination fee payable by I-Mab under the TJ004309 Agreement, which was collected in July 2023. The Company re-evaluated the transaction price as of the end of the reporting period and concluded the $ 9.0 million variable consideration associated with the prespecified termination fee was no longer fully constrained as it was determined to be probable that a significant reversal would not occur if the Company recognized the variable consideration as revenue in the current period. Accordingly, the Company recognized the $ 9.0 million as collaboration revenue within the accompanying consolidated statements of operations for the year ended December 31, 2023. In connection with the resolution of the arbitration, the TJ004309 Agreement and the Bispecific Agreement have been terminated and no further revenue will be recognized associated with these agreements. The $ 13.0 million gain associated with the collection of the Arbitration Award in July 2023 consisted of the $ 22.0 million collected amount less the $ 9.0 million TJ004309 termination fee recognized as collaboration revenue. The gain has been included within other income, net within the accompanying consolidated statements of operations. Additionally, in connection with the Arbitration, the Company entered into a contingency fee arrangement with its legal counsels whereby counsels agreed to defer a portion of their legal fees (Success Fees) and would receive payment of the Success Fees in full or at a low single digit multiple depending on the amount awarded and contingent upon recovery of proceeds from an Arbitration Award. Success Fees in the amount of $ 2.4 million were paid in 2023 and have been included within arbitration success fees within the accompanying consolidated statements of operations. In connection with the settlement, legal counsels also forgave approximately $ 0.3 million in related legal invoices.

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	8. Leases The Company’s operating lease obligations relate to its corporate headquarters as the Company leases its office space under a non-cancelable operating lease. The Company amended its lease in August 2021 extending the lease term to April 2027 . The lease is subject to base lease payments and additional charges for common area maintenance and other costs and includes certain lease incentives and tenant improvement allowances. Operating lease expense was $ 0.4 million for each of the three years ended December 31, 2023, 2022 and 2021. As of December 31, 2023, the Company did not have any finance leases, nor any other operating leases. Supplemental cash flow information related to operating leases was as follows (in thousands): Years Ended December 31, 2023 2022 2021 Cash paid within operating cash flows $ 320 $ 285 $ 461 ROU assets recognized in exchange for new lease obligations $ — $ — $ 1,117 Supplemental balance sheet information related to operating leases was as follows (in thousands, except lease term and discount rate): December 31, 2023 2022 Reported as: Other assets (ROU asset) $ 905 $ 1,123 Accounts payable and accrued expenses (lease liability) $ 236 $ 198 Other long-term liabilities (lease liability) 732 969 Total lease liabilities $ 968 $ 1,167 Weighted average remaining lease term 3.3 4.3 Weighted average discount rate 11.3 % 11.3 % As of December 31, 2023, the maturities of the Company’s operating lease liabilities are as follows (in thousands): 2024 $ 334 2025 349 2026 365 2027 123 Total lease payments 1,171 Less imputed interest ( 203 ) Total operating lease liabilities $ 968 Und er the terms of the lease agreement, the Company provided the lessor with an irrevocable letter of credit in the amount of $ 73,000 . Th e lessor is entitled to draw on the letter of credit in the event of any default by the Company under the terms of the lease.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands): Years Ended December 31, 2023 2022 2021 Federal income taxes $ ( 754 ) $ ( 6,118 ) $ ( 6,020 ) State income taxes, net of federal benefit ( 182 ) ( 1,962 ) ( 1,889 ) Permanent items 56 81 93 Uncertain tax positions 344 2,477 494 Research and development credits ( 1,569 ) ( 2,119 ) ( 1,661 ) Other, net ( 40 ) 125 28 Stock compensation 246 78 203 Change in valuation allowance 1,899 7,438 8,752 Provision for income taxes $ — $ — $ — Significant components of the Company’s deferred tax assets and deferred tax liabilities are summarized as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 50,103 $ 50,779 Research and development credits and Orphan Drug Credit 12,960 11,928 Depreciation and amortization 210 236 Right-of-use liability 204 245 Section 174 capitalized research expense 4,253 2,503 Other, net 1,720 1,906 Total deferred tax assets 69,450 67,597 Right-of-use asset ( 190 ) ( 236 ) Total deferred tax liabilities ( 190 ) ( 236 ) Total net deferred 69,260 67,361 Valuation allowance ( 69,260 ) ( 67,361 ) Net deferred tax assets $ — $ — The Company has net deferred tax assets relating primarily to net operating loss (NOL) carryforwards and research and development and Orphan Drug credit carryforwards. Beginning in 2022, the Tax Cuts and Jobs Act of 2017 requires taxpayers to capitalize and amortize research and development expenditures over five years for domestic research and 15 years for foreign research pursuant to Section 174 of the Internal Revenue Code (Code). Subject to certain limitations, the Company may use these deferred tax assets to offset taxable income in future periods. Due to the Company’s history of losses and uncertainty regarding future earnings, a full valuation allowance has been recorded against the Company’s deferred tax assets, as it is more likely than not that such assets will not be realized. The net change in the total valuation allowance for the years ended December 31, 2023, 2022 and 2021 was $ 1.9 million, $ 7.4 million, and $ 8.8 million, respectively. As of December 31, 2023, the Company had federal and California NOL carryforwards of $ 190.2 million and $ 146.9 million, respectively. The federal and California NOL carryforwards will begin to expire in 2030 and 2033 , respectively, if not utilized. The federal NOL generated after 2017 of $ 106.9 million will carryforward indefinitely, but the deductibility of such federal NOLs is limited to 80 % of taxable income. As of December 31, 2023, the Company also had federal research and development and Orphan Drug tax credit carryforwards of $ 15.1 million and California research and development tax credit carryforwards of $ 3.3 million. The federal research and development and Orphan Drug tax credit carryforwards will begin expiring in 2031 and 2036 , respectively, if not utilized. The California research credit will carry forward indefinitely under current law. Pursuant to Sections 382 and 383 of the Code, the annual use of the Company’s NOL and research and development credit carryforwards may be limited in the event that a cumulative change in ownership of more than 50 % occurs within a three-year period. The Company previously completed a Section 382/383 analysis regarding the limitation of NOL and research and development credit carryforwards as of December 31, 2018 and did not identify any change in ownership of more than 50 % within the preceding three-year period since an ownership change was determined to have occurred at the time of the Company’s initial public offering in January 2015. The Company has not completed a study to assess whether an ownership change has occurred or whether there have been multiple ownership changes since December 31, 2018. If the Company has experienced an ownership change at any time since December 31, 2018, utilization of the NOL or R&D credit carryforwards would be subject to an annual limitation under Section 382 of the Code. Any limitation may result in expiration of a portion of the NOL or R&D credit carryforwards before utilization. Any carryforwards that will expire prior to utilization as a result of such limitations will be removed from deferred tax assets with a corresponding reduction of the valuation allowance with no net effect on income tax expense or the effective tax rate. The Inflation Reduction Act of 2022, which incorporates a Corporate Alternative Minimum Tax (CAMT), was signed on August 16, 2022 and changes became effective for tax years beginning after December 31, 2022. The new tax will require companies to compute two separate calculations for federal income tax purposes and pay the greater of the new minimum tax or their regular tax liability. The act is not expected to have a significant impact on the Company's financial position, results of operations or cash flows. The changes in the Company’s unrecognized tax benefits are summarized as follows (in thousands): Balance at December 31, 2020 $ 6,610 Change related to prior year positions 1 Increase related to current year positions 506 Balance at December 31, 2021 7,117 Change related to prior year positions ( 5 ) Increase related to current year positions 2,984 Balance at December 31, 2022 10,096 Change related to prior year positions — Increase related to current year positions 532 Balance at December 31, 2023 $ 10,628 The Company’s policy is to include interest and penalties related to unrecognized income tax benefits as a component of income tax expense. The Company has no accruals for interest or penalties in the accompanying consolidated balance sheets as of December 31, 2023 and 2022 and has no t recognized interest or penalties in the accompanying consolidated statements of operations for the three years in the period ended December 31, 2023. Due to the valuation allowance recorded against the Company’s deferred tax assets, future changes in unrecognized tax benefits will not impact the Company’s effective tax rate. The Company does not expect its unrecognized tax benefits to change significantly in the next 12 months. The Company is subject to taxation in the United States and California. Due to the net operating loss carryforwards, the U.S. federal and California returns are open to examination for all years since inception. The Company has not been, nor is it currently, under examination by the federal or any state tax authority.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
401(k) Plan	10. 401(k) Plan The Company maintains a defined contribution 401(k) plan available to eligible employees. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under federal tax regulations. The Company, at its discretion, may make certain matching contributions to the 401(k) plan. Matching contributions for the years ended December 31, 2023, 2022 and 2021 totaled $ 0.2 million, $ 0.2 million, and $ 0.1 million, respectively.

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Organization And Accounting Policies [Abstract]
Organization and Business	Organization and Business TRACON Pharmaceuticals, Inc. (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer, and utilizes its cost efficient, contract research organization (CRO) independent product development platform to partner with other life science companies to develop and commercialize innovative products in the United States. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, TRACON Pharma Limited and TRACON Pharma International Limited, which were formed in September 2015 and January 2019, respectively, and are currently inactive. All significant intercompany accounts and transactions have been eliminated.
Basis of Presentation	Basis of Presentation As of December 31, 2023, the Company has devoted substantially all its efforts to product development, raising capital, and building infrastructure and has not realized revenues from its planned principal operations. The Company has incurred operating losses since inception. As of December 31, 2023 , the Company had an accumulated deficit of $ 240.5 million. The Company anticipates that it will continue to incur net losses into the foreseeable future as it continues the development and commercialization of its product candidates and works to develop additional product candidates through research and development programs. At December 31, 2023, the Company had cash and cash equivalents of $ 8.6 million, of which $ 0.1 million is classified as restricted cash as it is pledged as collateral for the Company’s obligations under its corporate headquarters facility lease. The Company’s ability to execute its operating plan through 2024 and beyond depends on its ability to obtain additional funding through equity offerings, debt financings, or potential licensing and collaboration arrangements. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, based on the Company’s current working capital, anticipated operating expenses and net losses, and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, management believes that there is substantial doubt about its ability to continue as a going concern for a period of 12 months following the date that these consolidated financial statements are issued. The consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through its existing cash and cash equivalents, as well as through future equity offerings, debt financings, other third-party funding, and potential licensing or collaboration arrangements. In addition, the Company may fund its losses from operations through the Capital on Demand TM Sales Agreement (the Sales Agreement) the Company entered into with JonesTrading in December 2020, as amended in March 2022, pursuant to which the Company may sell, at its option, up to an aggregate of $ 50.0 million of the Company’s common stock, $ 41.5 million of which remained available for sale as of December 31, 2023 , and the common stock purchase agreement (the LPC Purchase Agreement) the Company entered into with Lincoln Park Capital Fund, LLC (Lincoln Park) in May 2023, pursuant to which the Company may sell, at its option, up to an aggregate of $ 26.0 million of the Company’s common stock, $ 25.0 million of which remained available for sale as of December 31, 2023 . There can be no assurance that additional funds will be available when needed from any source or, if available, will be available on terms that are acceptable to the Company.
Risks And Uncertainties	Risks and Uncertainties Global economic and business activities continue to face widespread macroeconomic uncertainties, including labor shortages, inflation and monetary supply shifts, recession risks and potential disruptions from the Russia-Ukraine conflict. The Company continues to actively monitor the impact of these macroeconomic factors on its financial condition, liquidity, operations, and workforce. The extent of the impact of these factors on the Company’s operational and financial performance, including its ability to execute its business strategies and initiatives in the expected time frame, will depend on future developments, which are uncertain and cannot be predicted; however, any continued or renewed disruption resulting from these factors could negatively impact the Company’s business .
Use of Estimates	Use of Estimates The Company’s consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenue, and expenses. The most significant estimates in the Company’s consolidated financial statements relate to expenses incurred for clinical trials. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company’s assets or liabilities as of the date of this filing.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of three months or less at the date of purchase. The carrying amounts approximate fair value due to the short maturities of these investments. Cash and cash equivalents include cash in readily available checking and money market funds.
Restricted Cash	Restricted Cash Restricted cash consists of money market funds held by the Company’s financial institution as collateral for the Company’s obligations under its facility lease for the Company’s corporate headquarters in San Diego, California.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Property and Equipment	Property and Equipment Property and equipment is stated at cost and depreciated using the straight-line method over the estimated useful life of the related assets, which is generally five years . Leasehold improvements are amortized over the shorter of the lease term or estimated useful life of the related assets. Repairs and maintenance costs are charged to expense as incurred.
Leases	Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are recorded as other assets, accounts payable and accrued expenses, and other long-term liabilities within the consolidated balance sheet. The Company currently does not have any finance leases. Operating lease right-of-use (ROU) assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term.
Revenue Recognition	Revenue Recognition To date, the Company’s revenue has been derived from license and collaboration agreements. The terms of these arrangements included payments to the Company for the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. In accordance with Accounting Standards Codification (ASC) 606, Revenue from Contracts with Customers (ASC 606), the Company performs the following five steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the contract(s) with a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services transferred to the customer. Once a contract is determined to be within the scope of ASC 606, at contract inception the Company assesses the goods or services promised within the contract to determine those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization, and regulatory milestone payments, the Company evaluates whether the achievement of the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. Performance milestone payments represent a form of variable consideration. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Achievement of milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable until the approvals are achieved. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis and the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations at the outset of the arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its collaborators based on billing schedules established in each contract. Up-front and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.
Clinical Trial Expense Accruals	Clinical Trial Expense Accruals As part of the process of preparing the Company’s consolidated financial statements, the Company is required to estimate expenses resulting from its obligations under contracts with vendors, clinical sites, and consultants in connection with conducting clinical trials. The financial terms of these contracts vary and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its consolidated financial statements by recording those expenses in the period in which services are performed and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with the clinical sites and applicable personnel and outside service providers as to the progress or state of consummation of trials. During a clinical trial, the Company adjusts the clinical expense recognition if actual results differ from its estimates. The Company makes estimates of accrued expenses as of each balance sheet date based on the facts and circumstances known at that time. The Company’s clinical trial accruals are dependent upon accurate reporting by clinical sites and other third-party vendors. Although the Company does not expect its estimates to differ materially from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting amounts that are too high or too low for any particular period. For the three years ended December 31, 2023 , there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials.
Research and Development Costs	Research and Development Costs Research and development costs, including license fees, are expensed as incurred.
Patent Costs	Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of employee stock option grants, employee restricted stock unit grants (RSUs), and employee stock purchase plan (ESPP) rights recognized as expense over the requisite service period of the awards (usually the vesting period) on a straight-line basis. The Company estimates the fair value of stock option grants and ESPP rights using the Black-Scholes option pricing model. The fair value of RSUs is based on the closing sales price for such stock on the date of grant. Equity award forfeitures are recorded as they occur.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than‑not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average shares of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of shares of common stock outstanding that are subject to repurchase. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): December 31, 2023 2022 Warrants to purchase common stock 1,533,293 6,766,246 Common stock options 3,121,152 2,246,310 ESPP shares 10,444 3,387 4,664,889 9,015,943
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Organization And Accounting Policies [Abstract]
Schedule of potentially dilutive securities not included in the calculation of diluted net loss per share	Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): December 31, 2023 2022 Warrants to purchase common stock 1,533,293 6,766,246 Common stock options 3,121,152 2,246,310 ESPP shares 10,444 3,387 4,664,889 9,015,943

Financial Instruments and Fai_2

Financial Instruments and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Available-for-sale Securities and Equity Securities	Cash equivalents, which are classified as equity securities, and restricted cash consisted of the following (in thousands): December 31, 2023 December 31, 2022 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 3,689 $ — $ — $ 3,689 $ 10,150 $ — $ — $ 10,150 Classified as: Cash equivalents $ 3,616 $ 10,083 Restricted cash 73 67 Total cash equivalents and restricted cash $ 3,689 $ 10,150
Schedule of assets and liabilities measured at fair value on a recurring basis	The fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets Other Significant for Identical Observable Unobservable Assets Inputs Inputs Total (Level 1) (Level 2) (Level 3) At December 31, 2023 Money market funds $ 3,689 $ — $ 3,689 $ — At December 31, 2022 Money market funds $ 10,150 $ — $ 10,150 $ —

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Schedule Of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, December 31, 2023 2022 Computer and office equipment $ 203 $ 203 Furniture and fixtures 19 19 Leasehold improvements 21 21 243 243 Less accumulated depreciation and amortization ( 206 ) ( 192 ) $ 37 $ 51
Schedule Of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consisted of the following (in thousands): December 31, December 31, 2023 2022 Accounts payable $ 2,544 $ 3,923 Accrued clinical related expenses 6,736 6,091 Accrued legal and accounting 199 299 Accrued long-term debt terminal interest — 425 Current portion of operating lease liability 236 198 Other accruals 40 171 $ 9,755 $ 11,107

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Schedule of Long-term debt and unamortized debt discount balances	As of December 31, 2022, long-term debt and unamortized debt discount balances associated with the RGC Loan Agreement were as follows (in thousands): December 31, 2022 Long-term debt $ 10,000 Less debt discount, net of current portion — Long-term debt, net of debt discount 10,000 Less current portion of long-term debt ( 10,000 ) Long-term debt, net of current portion $ — Current portion of long-term debt $ 10,000 Current portion of debt discount ( 193 ) Current portion of long-term debt, net $ 9,807
Schedule of exercisable outstanding warrants for purchase of common stock issued	At December 31, 2023, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 12,938 As of December 31, 2023, the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 September 2, 2032 150,753 $ 1.99 1,533,293

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2023
Stockholders' Equity Note [Abstract]
Schedule of exercisable outstanding warrants for purchase of common stock issued	At December 31, 2023, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 12,938 As of December 31, 2023, the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 June 4, 2024 2,906 $ 77.40 May 3, 2025 5,363 $ 26.10 September 2, 2032 150,753 $ 1.99 1,533,293
Schedule of stock option activity	Stock option activity under all Plans is summarized as follows: Weighted- Number of Average Options Exercise Price Balance at December 31, 2022 2,246,310 $ 9.07 Granted 1,089,400 1.71 Exercised — — Forfeited ( 214,558 ) 8.59 Balance at December 31, 2023 3,121,152 $ 6.53
Schedule of outstanding stock options	Information about the Company’s outstanding stock options as of December 31, 2023 is as follows: Weighted- Average Weighted- Remaining Average Contractual Aggregate Number of Exercise Term Intrinsic Shares Price (in years) Value Options outstanding 3,121,152 $ 6.53 7.36 $ — Options vested and expected to vest 3,121,152 $ 6.53 7.36 $ — Options exercisable 1,446,873 $ 11.11 6.47 $ —
Summary of weighted-average assumptions used Black-Scholes option pricing model to determine the fair value	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Year Ended December 31, 2023 2022 2021 Risk-free interest rate 3.5 % 1.9 % 0.8 % Expected volatility 90.1 % 89.8 % 90.3 % Expected term (in years) 6.2 6.2 6.2 Expected dividend yield — % — % — %
Summary of allocation of stock-based compensation expense	The allocation of stock-based compensation expense was as follows (in thousands): Year Ended December 31, 2023 2022 2021 Research and development $ 935 $ 830 $ 628 General and administrative 1,034 1,211 1,147 $ 1,969 $ 2,041 $ 1,775
Schedule of common stock reserved for future issuance	Common stock reserved for future issuance was as follows: December 31, 2023 2022 Common stock warrants 1,533,293 6,766,246 Common stock options granted and outstanding 3,121,152 2,246,310 Awards available under the 2015 Plan 431,755 150,335 Shares available under the Employee Stock Purchase Plan 429,500 243,817 5,515,700 9,406,708

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to operating leases was as follows (in thousands): Years Ended December 31, 2023 2022 2021 Cash paid within operating cash flows $ 320 $ 285 $ 461 ROU assets recognized in exchange for new lease obligations $ — $ — $ 1,117
Schedule of Supplemental Balance Sheet Information Related to Operating Leases	Supplemental balance sheet information related to operating leases was as follows (in thousands, except lease term and discount rate): December 31, 2023 2022 Reported as: Other assets (ROU asset) $ 905 $ 1,123 Accounts payable and accrued expenses (lease liability) $ 236 $ 198 Other long-term liabilities (lease liability) 732 969 Total lease liabilities $ 968 $ 1,167 Weighted average remaining lease term 3.3 4.3 Weighted average discount rate 11.3 % 11.3 %
Schedule of Maturities of Operating Lease Liabilities	As of December 31, 2023, the maturities of the Company’s operating lease liabilities are as follows (in thousands): 2024 $ 334 2025 349 2026 365 2027 123 Total lease payments 1,171 Less imputed interest ( 203 ) Total operating lease liabilities $ 968

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of reconciliation of effective tax rate and federal statutory tax rate	A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands): Years Ended December 31, 2023 2022 2021 Federal income taxes $ ( 754 ) $ ( 6,118 ) $ ( 6,020 ) State income taxes, net of federal benefit ( 182 ) ( 1,962 ) ( 1,889 ) Permanent items 56 81 93 Uncertain tax positions 344 2,477 494 Research and development credits ( 1,569 ) ( 2,119 ) ( 1,661 ) Other, net ( 40 ) 125 28 Stock compensation 246 78 203 Change in valuation allowance 1,899 7,438 8,752 Provision for income taxes $ — $ — $ —
Schedule of components of deferred tax assets and deferred tax Liabilities	Significant components of the Company’s deferred tax assets and deferred tax liabilities are summarized as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 50,103 $ 50,779 Research and development credits and Orphan Drug Credit 12,960 11,928 Depreciation and amortization 210 236 Right-of-use liability 204 245 Section 174 capitalized research expense 4,253 2,503 Other, net 1,720 1,906 Total deferred tax assets 69,450 67,597 Right-of-use asset ( 190 ) ( 236 ) Total deferred tax liabilities ( 190 ) ( 236 ) Total net deferred 69,260 67,361 Valuation allowance ( 69,260 ) ( 67,361 ) Net deferred tax assets $ — $ —
Schedule of changes in unrecognized tax benefits	The changes in the Company’s unrecognized tax benefits are summarized as follows (in thousands): Balance at December 31, 2020 $ 6,610 Change related to prior year positions 1 Increase related to current year positions 506 Balance at December 31, 2021 7,117 Change related to prior year positions ( 5 ) Increase related to current year positions 2,984 Balance at December 31, 2022 10,096 Change related to prior year positions — Increase related to current year positions 532 Balance at December 31, 2023 $ 10,628

Organization and Summary of S_4

Organization and Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Basis of Presentation
Accumulated deficit	$ (240,499,000)	$ (236,911,000)
Cash, cash equivalents	8,600,000
Restricted cash	$ 73,000	$ 67,000
Property and Equipment
Estimated useful life	5 years
Segment reporting
Number of reportable segments | Segment	1
Jones Trading Institutional Services LLC | Capital on Demand Sales Agreement | Common Stock
Basis of Presentation
Maximum aggregate value of stock to be sold	$ 50,000,000
Remaining amount available under the Sales Agreement	41,500,000
Lincoln Park Capital Fund, LLC | Capital on Demand Sales Agreement | Common Stock
Basis of Presentation
Maximum aggregate value of stock to be sold	26,000,000
Remaining amount available under the Sales Agreement	$ 25,000,000

Organization and Summary of S_5

Organization and Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive securities
Antidilutive securities	4,664,889	9,015,943
Warrants to Purchase Common Stock
Antidilutive securities
Antidilutive securities	1,533,293	6,766,246
Common Stock Options
Antidilutive securities
Antidilutive securities	3,121,152	2,246,310
ESPP Shares
Antidilutive securities
Antidilutive securities	10,444	3,387

Financial Instruments and Fai_3

Financial Instruments and Fair Value Measurements - Schedule of Available-for-sale Securities and Equity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cash equivalents	$ 3,616	$ 10,083
Restricted cash	73	67
Total cash equivalents, restricted cash, and other assets	3,689	10,150
Money market funds
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	3,689	10,150
Estimated Fair Value	$ 3,689	$ 10,150

Financial Instruments and Fai_4

Financial Instruments and Fair Value Measurements - Additional Information (Details)	Dec. 31, 2023 USD ($)
Fair Value Disclosures [Abstract]
Short-term investments	$ 0
Amount of transfers between levels	$ 0

Financial Instruments and Fai_5

Financial Instruments and Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - Money market funds - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Fair value, assets	$ 3,689	$ 10,150
Level 2
Assets:
Fair value, assets	$ 3,689	$ 10,150

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule Of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Public Utilities Inventory [Line Items]
Property and equipment	$ 243	$ 243
Less accumulated depreciation and amortization	(206)	(192)
Property and equipment, net	37	51
Computer And Office Equipment [Member]
Public Utilities Inventory [Line Items]
Property and equipment	203	203
Furniture and Fixtures [Member]
Public Utilities Inventory [Line Items]
Property and equipment	19	19
Leasehold Improvements [Member]
Public Utilities Inventory [Line Items]
Property and equipment	$ 21	$ 21

Balance Sheet Details - Additio

Balance Sheet Details - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Depreciation and amortization expense related to property and equipment	$ 14,000	$ 16,000	$ 14,000

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule Of Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Public Utilities Inventory [Line Items]
Accounts payable	$ 2,544	$ 3,923
Accrued clinical related expenses	6,736	6,091
Accrued legal and accounting	199	299
Accrued long-term debt terminal interest		425
Current portion of operating lease liability	968	1,167
Other accruals	40	171
Total	9,755	11,107
Other Current Liabilities
Public Utilities Inventory [Line Items]
Current portion of operating lease liability	$ 236	$ 198

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details)		1 Months Ended				3 Months Ended	12 Months Ended
	Apr. 05, 2023 USD ($)	Jul. 31, 2023 USD ($)	Dec. 30, 2022 USD ($)	Sep. 30, 2022 USD ($) Tranche $ / shares shares	May 31, 2018 USD ($)	Mar. 31, 2023	Dec. 31, 2023 USD ($) shares	Apr. 20, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Maximum capital contribution			$ 30,000,000
Initial capital contribution from investors			$ 3,500,000
Percentage of Initial Capital Contribution From Investors			25%
Percentage of closing fee amount			2%
Arbitration financing payable			$ 3,500,000				$ 0		$ 3,280,000
Settlement received		$ 22,000,000
Interest							$ 7,200,000
Conversion of warrants to purchase shares | shares							1,533,293
Silicon Valley Bank
Debt Instrument [Line Items]
Conversion of warrants to purchase shares | shares							12,938
RGC Loan Agreement
Debt Instrument [Line Items]
Principal and interest payment							$ 0
Loan And Security Agreement | Runway Growth Finance Corp
Debt Instrument [Line Items]
Long term debt, principal amount				$ 10,000,000
Proceeds from sale of debt and equity securities	$ 25,000,000		$ 25,000,000
Percentage of final payment fee						4.25%
Loan And Security Agreement | Runway Growth Finance Corp | Term Loan
Debt Instrument [Line Items]
Number of tranche | Tranche				3
Loan And Security Agreement | Runway Growth Finance Corp | Term Loan | Maximum
Debt Instrument [Line Items]
Long term debt, principal amount				$ 35,000,000
Loan And Security Agreement | Runway Growth Finance Corp | Term Loan A
Debt Instrument [Line Items]
Long term debt, principal amount				10,000,000
Loan And Security Agreement | Runway Growth Finance Corp | Term Loan B | Maximum
Debt Instrument [Line Items]
Long term debt, principal amount				15,000,000
Loan And Security Agreement | Runway Growth Finance Corp | Term Loan C | Maximum
Debt Instrument [Line Items]
Long term debt, principal amount	$ 10,000,000			$ 10,000,000				$ 10,000,000
Warrants | Runway Growth Finance Corp | Term Loan A
Debt Instrument [Line Items]
Conversion of warrants to purchase shares | shares				150,753
Exercise price (per share) | $ / shares				$ 1.99
Expiration date				Sep. 02, 2032
2018 SVB Loan | Silicon Valley Bank
Debt Instrument [Line Items]
Proceeds from long-term debt					$ 7,000,000
Final payment on payoff					$ 300,000

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt and Unamortized Debt Discount Balances (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 10,000
Long-term debt, net of debt discount	10,000
Less current portion of long-term debt	(10,000)
Current portion of long-term debt	10,000
Current portion of debt discount	(193)
Current portion of long-term debt, net	$ 9,807

Long-Term Debt - Schedule of Ex

Long-Term Debt - Schedule of Exercisable Outstanding Warrants for Purchase of Common Stock Issued (Details)	Dec. 31, 2023 $ / shares shares
Debt Instrument [Line Items]
Conversion of warrants to purchase shares	1,533,293
Silicon Valley Bank
Debt Instrument [Line Items]
Conversion of warrants to purchase shares	12,938
Silicon Valley Bank | January 25, 2024
Debt Instrument [Line Items]
Conversion of warrants to purchase shares	4,669
Exercise price (per share) | $ / shares	$ 51.4
Silicon Valley Bank | June 4, 2024
Debt Instrument [Line Items]
Conversion of warrants to purchase shares	2,906
Exercise price (per share) | $ / shares	$ 77.4
Silicon Valley Bank | May 3, 2025
Debt Instrument [Line Items]
Conversion of warrants to purchase shares	5,363
Exercise price (per share) | $ / shares	$ 26.1

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	Dec. 31, 2023 USD ($)
Research and development arrangement
Commitments and Contingencies
Potential milestone payable	$ 9.6

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	May 31, 2023	Mar. 31, 2023	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jun. 30, 2023
Class Of Stock [Line Items]
Conversion of warrants to purchase shares				1,533,293
Net proceeds				$ 45,000	$ 95,000	$ 149,000
Lincoln Park Purchase Agreement
Class Of Stock [Line Items]
Aggregate value of shares committed to purchase	$ 26,000,000
Common stock purchase price per share	$ 0.5763
Net proceeds	$ 1,000,000
Percentage of common stock outstanding owned after sale agreement				19.99%
2022 Pre-Funded Warrants
Class Of Stock [Line Items]
Maximum percentage of holders ownership interest in common stock after exercise			19.99%
2023 Pre-Funded Warrants
Class Of Stock [Line Items]
Maximum percentage of holders ownership interest in common stock after exercise		19.99%
Common Stock
Class Of Stock [Line Items]
Cashless exercise of pre-funded warrants to purchase common stock				7,245,984	398,093
Issuance of common stock upon cashless exercise of pre-funded warrants				6,867,504	390,668
Common Stock | Lincoln Park Purchase Agreement
Class Of Stock [Line Items]
Common stock issued and sold	1,735,207			599,216
Remaining amount available under the Sales Agreement				$ 25,000,000
Common Stock | Private Placement
Class Of Stock [Line Items]
Net proceeds from common stock issuance		$ 3,000,000
Common Stock | Direct Offerings
Class Of Stock [Line Items]
Net proceeds from common stock issuance			$ 3,900,000
Common Stock | Capital on Demand Sales Agreement | Jones Trading Institutional Services LLC
Class Of Stock [Line Items]
Maximum aggregate value of stock to be sold				50,000,000
Remaining amount available under the Sales Agreement				$ 41,500,000
Percentage of gross proceeds, required to pay for common stock sold through sales agreement				2.50%
Common Stock | 2022 Pre-Funded Warrants | Direct Offerings
Class Of Stock [Line Items]
Exercise price (per share)							$ 0.01
Common Stock | 2023 Pre-Funded Warrants | Private Placement
Class Of Stock [Line Items]
Exercise price (per share)		$ 0.01
Common Stock | Purchase Price Of $1.38 Per Share | Private Placement
Class Of Stock [Line Items]
Common stock issued and sold		174,508
Common stock purchase price per share		$ 1.38
Common Stock | Purchase Price Of $1.37 Per Share | 2023 Pre-Funded Warrants | Private Placement
Class Of Stock [Line Items]
Common stock issued and sold		2,013,999
Common stock purchase price per share		$ 1.37
Common Stock | Purchase Price of $1.32 Per Share | Direct Offerings
Class Of Stock [Line Items]
Common stock issued and sold			841,989
Common stock purchase price per share							1.32
Common Stock | Purchase Price of $1.31 Per Share | 2022 Pre-Funded Warrants | Direct Offerings
Class Of Stock [Line Items]
Common stock issued and sold			2,205,018
Common stock purchase price per share							$ 1.31

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Outstanding Warrants for Purchase of Common Stock Issued (Details)	Dec. 31, 2023 $ / shares shares
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	1,533,293
January 25, 2024
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	4,669
Exercise price (per share) | $ / shares	$ 51.4
March 27, 2024
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	1,369,602
Exercise price (per share) | $ / shares	$ 27
June 4, 2024
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	2,906
Exercise price (per share) | $ / shares	$ 77.4
May 3, 2025
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	5,363
Exercise price (per share) | $ / shares	$ 26.1
September 2, 2032
Class Of Stock [Line Items]
Conversion of warrants to purchase shares	150,753
Exercise price (per share) | $ / shares	$ 1.99

Stockholders' Equity - (SBC) -

Stockholders' Equity - (SBC) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jan. 02, 2015	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2015
Stock Plans
Shares of common stock reserved for future issuance		5,515,700	9,406,708
Stock Option
Stock options, additional disclosures
Weighted-average grant date fair value (in dollars per share)		$ 1.31	$ 1.65	$ 6.05
Share price (in dollar per share)		$ 0.1751
Shares Options, Exercises in Period		0	0
Total fair value of options vested during the year		$ 1.9	$ 2.6	$ 0.8
Share-based compensation
Unrecognized compensation cost		$ 2.8	$ 3.6
Unrecognized compensation cost, period of recognition		2 years 4 months 24 days	2 years 6 months
Stock Option | Year One
Stock Plans
Grants vesting period		1 year
Grants vesting (as a percent)		25%
Stock Option | Thereafter
Stock Plans
Grants vesting period		36 months
ESPP
Stock Plans
Shares of common stock reserved for future issuance	18,346
Percentage of total number of shares of common stock outstanding	1%
Stock options, additional disclosures
Number of shares that could potentially be issued	250,000
Share-based compensation
Percentage of eligible compensation					15%
2015 Equity Incentive Plan
Stock Plans
Maximum term of options granted		10 years
Shares of common stock reserved for future issuance	80,103	431,755	150,335
Percentage of total number of shares of common stock outstanding	5%
Additional shares to be used exclusively for grant for Inducement awards	200,000

Stockholders' Equity- Summary o

Stockholders' Equity- Summary of Stock Option Activity (Details) - Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Balance (in shares)	2,246,310
Granted (in shares)	1,089,400
Exercised (in shares)	0	0
Forfeited (in shares)	(214,558)
Balance (in shares)	3,121,152	2,246,310
Weighted-Average Exercise Price
Balance (in dollars per share)	$ 9.07
Granted (in dollars per share)	1.71
Forfeited (in dollars per share)	8.59
Balance (in dollars per share)	$ 6.53	$ 9.07

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Company's Outstanding Stock Option (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Number of shares, options vested and expected to vest	3,121,152	2,246,310
Stock Option
Number of Options
Number of shares, options outstanding	3,121,152	2,246,310
Number of shares, options vested and expected to vest	3,121,152
Number of shares, options exercisable	1,446,873
Weighted-Average Exercise Price
Weighted-average exercise price, options outstanding (in dollars per share)	$ 6.53	$ 9.07
Weighted-average exercise price, options vested and expected to vest (in dollars per share)	6.53
Weighted-average exercise price, options exercisable (in dollars per share)	$ 11.11
Weighted-average remaining contractual term, options outstanding (in years)	7 years 4 months 9 days
Weighted-average remaining contractual term, options vested and expected to vest (in years)	7 years 4 months 9 days
Weighted-average remaining contractual term, options exercisable (in years)	6 years 5 months 19 days

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Weighted-Average Assumptions Fair Value of the Employee Stock Option Grants (Details) - Stock Option	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Class Of Stock [Line Items]
Risk-free interest rate	3.50%	1.90%	0.80%
Expected volatility	90.10%	89.80%	90.30%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days	6 years 2 months 12 days
Expected dividend yield	0%	0%	0%

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Allocation of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Class Of Stock [Line Items]
Stock based compensation expense	$ 1,969	$ 2,041	$ 1,775
Research and development
Class Of Stock [Line Items]
Stock based compensation expense	935	830	628
General and administrative
Class Of Stock [Line Items]
Stock based compensation expense	$ 1,034	$ 1,211	$ 1,147

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Common Stock Reserved For Future Issuance (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Jan. 02, 2015
Stock Plans
Shares of common stock reserved for future issuance	5,515,700	9,406,708
Number of shares, options vested and expected to vest	3,121,152	2,246,310
2015 Equity Incentive Plan
Stock Plans
Shares of common stock reserved for future issuance	431,755	150,335	80,103
Common Stock. | Warrants
Stock Plans
Shares of common stock reserved for future issuance	1,533,293	6,766,246
ESPP
Stock Plans
Shares of common stock reserved for future issuance			18,346
Shares of common stock reserved for future issuance	429,500	243,817

Collaboration and License Agr_2

Collaboration and License Agreements - Additional Information (Details) $ in Thousands	1 Months Ended				12 Months Ended
	Nov. 30, 2023 USD ($)	Jul. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)	Nov. 30, 2018 USD ($) Antibody	Dec. 31, 2023 USD ($)	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue					$ 9,000
Collaborative Arrangement, Revenue Not from Contract with Customer, Statement of Income or Comprehensive Income [Extensible Enumeration]					Revenue from Contract with Customer, Excluding Assessed Tax
Revenue, Product and Service [Extensible Enumeration]					us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember
Settlement received, net of termination fee		$ 13,000
Settlement received		22,000
Arbitration success fees					$ 2,375
Loss contingency payment write-off amount					$ 300
Bispecific Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalty on net sales					50%
Bispecific Agreement | I-Mab
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum number of proprietary bispecific antibodies under development | Antibody				5
TJ4309 Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of cost bearing				40%
TJ4309 Agreement | I-Mab
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of cost bearing				60%
Termination of agreement upon completion of clinical trial				90 days
TJ4309 Agreement | I-Mab | First Phase Clinical Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Termination fee				$ 9,000	$ 9,000
Termination fee payable			$ 9,000
Termination fee awarded		$ 9,000
TJ4309 Agreement | I-Mab | First Phase Two Clinical Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Termination fee				$ 15,000
Inhibrx, Inc.(Inhibrx) License Agreement | Inhibrx
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Nonrefundable upfront fee	$ 3,000
Additional payment on performance obligation	200
Transaction price	$ 3,200
Training period duration	6 months
License agreement term					The Company assessed this agreement and identified multiple promised goods and services, which included at contract inception: (1) the PDP license and (2) up to 500 hours of training over a six-month period. Management evaluated these promised goods and services and determined each was a separate performance obligation. The transaction price at contract inception included fixed consideration of the $3.0 million upfront payment and $0.2 million payment due upon the earlier of the completion of 500 hours of training or six months. The total $3.2 million transaction price was allocated to each performance obligation based on relative standalone selling price.
North America | Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Commercial sale						10 years

Leases - Additional Information

Leases - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Non-cancelable operating lease expiration term	2021-08
Non Cancelable Operating Lease Term To Be Extended	2027-04
Operating lease expense	$ 400,000	$ 400,000	$ 400,000
Irrevocable letter of credit provided to lessor	$ 73,000

Leases - Supplemental cash flow

Leases - Supplemental cash flow information related to operating leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Cash paid within operating cash flows	$ 320	$ 285	$ 461
ROU assets recognized in exchange for new lease obligations			$ 1,117

Leases - Supplemental balance s

Leases - Supplemental balance sheet information related to operating leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Reported as:
Other assets (ROU asset)	$ 905	$ 1,123
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Current portion of operating lease liability	$ 968	$ 1,167
Weighted average remaining lease term	3 years 3 months 18 days	4 years 3 months 18 days
Weighted average discount rate	11.30%	11.30%
Accounts payable and accrued expenses (lease liability)
Reported as:
Current portion of operating lease liability	$ 236	$ 198
Other long-term liabilities (lease liability)
Reported as:
Current portion of operating lease liability	$ 732	$ 969

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 334
2025	349
2026	365
2027	123
Total lease payments	1,171
Less imputed interest	(203)
Current portion of operating lease liability	$ 968	$ 1,167

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Effective Tax Rate and Federal Statutory Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of effective tax rate and federal statutory tax rate
Federal income taxes	$ (754)	$ (6,118)	$ (6,020)
State income taxes, net of federal benefit	(182)	(1,962)	(1,889)
Permanent items	56	81	93
Uncertain tax positions	344	2,477	494
Research and development credits	(1,569)	(2,119)	(1,661)
Other, net	(40)	125	28
Stock compensation	246	78	203
Change in valuation allowance	1,899	7,438	8,752
Provision for income taxes	$ 0	$ 0	$ 0

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of deferred tax assets and deferred tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 50,103	$ 50,779
Research and development and Orphan Drug credits	12,960	11,928
Depreciation and amortization	210	236
Right-of-use liability	204	245
Section 174 capitalized research expense	4,253	2,503
Other, net	1,720	1,906
Total deferred tax assets	69,450	67,597
Right-of-use asset	(190)	(236)
Total deferred tax liabilities	(190)	(236)
Total net deferred	69,260	67,361
Valuation allowance	(69,260)	(67,361)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Carryforwards
Net change in the total valuation allowance	$ 1,900,000	$ 7,400,000	$ 8,800,000
NOL carryforward	$ 106,900,000
NOL carryforward available to offset future taxable income, percentage	80%
Accrual for interest or penalties for unrecognized tax benefits	$ 0	$ 0
Income tax interest or penalties expense for unrecognized tax benefits	$ 0
Orphan Drug tax credit
Carryforwards
Credit carryforward begin to expire	2036
Minimum
Carryforwards
Percent of ownership	50%			50%
Federal
Carryforwards
NOL carryforward	$ 190,200,000
NOL carryforward begin to expire	2030
Federal | Research and Development and Orphan Drug Tax Credit Carryforwards
Carryforwards
Credit carryforward	$ 15,100,000
Federal | Research and Development Tax Credit
Carryforwards
Credit carryforward begin to expire	2031
Federal | Minimum
Carryforwards
Research and development expenditure amortization period	5 years
Foreign
Carryforwards
Research and development expenditure amortization period	15 years
California
Carryforwards
NOL carryforward	$ 146,900,000
NOL carryforward begin to expire	2033
California | Research and Development Tax Credit
Carryforwards
Credit carryforward	$ 3,300,000

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Unrecognized tax benefits
Balance, beginning of period	$ 10,096	$ 7,117	$ 6,610
Change related to prior year positions		(5)	1
Increase related to current year positions	532	2,984	506
Balance, end of period	$ 10,628	$ 10,096	$ 7,117

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined contribution, plan name	us-gaap:RetirementPlanNameOtherMember	us-gaap:RetirementPlanNameOtherMember	us-gaap:RetirementPlanNameOtherMember
Defined contribution amount	$ 0.2	$ 0.2	$ 0.1