Regulus Therapeutics (RGLS) 10-K 23 Mar 23 2022 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Mar. 17, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-35670
Entity Registrant Name	Regulus Therapeutics Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-4738379
Entity Address, Address Line One	4224 Campus Point Court, Suite 210
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	202-6300
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RGLS
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 29
Entity Common Stock, Shares Outstanding		16,840,261
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission pursuant on Schedule 14A in connection with the registrant’s 2023 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K. Such proxy statement will be filed with the Securities and Exchange Commission no later than May 1, 2023.
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Central Index Key	0001505512
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2022
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	San Diego, California
Auditor Firm ID	42

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 24,228	$ 60,383
Short-term investments	14,932	0
Restricted cash	62	62
Prepaid materials, net	3,010	3,010
Prepaid expenses and other current assets	1,847	1,780
Total current assets	44,079	65,235
Property and equipment, net	536	281
Intangibles, net	62	83
Right of use asset	2,039	2,564
Other assets	0	291
Total assets	46,716	68,454
Current liabilities:
Accounts payable	175	285
Accrued liabilities	961	821
Accrued research and development expenses	1,252	810
Accrued compensation	2,205	2,016
Current portion of term loan, less debt issuance costs	4,511	0
Other current liabilities	2,553	1,295
Total current liabilities	11,657	5,227
Operating lease liability, less current portion	1,768	2,417
Term loan, less current portion and debt issuance costs	0	4,673
Other long-term liabilities	0	1,179
Total liabilities	13,425	13,496
Commitments and Contingencies
Stockholders’ equity (deficit):
Common stock, $0.001 par value; 300,000,000 and 400,000,000 shares authorized at December 31, 2022 and 2021, respectively; 16,840,261 and 14,597,118 shares issued and outstanding at December 31, 2022 and 2021, respectively	17	15
Additional paid-in capital	516,457	509,791
Accumulated other comprehensive loss	(12)	0
Accumulated deficit	(483,176)	(454,853)
Total stockholders’ equity	33,291	54,958
Total liabilities and stockholders’ equity	46,716	68,454
Class A-1 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	0	0
Class A-2 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	1	1
Class A-3 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	0	0
Class A-4 Convertible Preferred Stock
Stockholders’ equity (deficit):
Convertible preferred stock	$ 4	$ 4

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	400,000,000
Common stock, shares issued (shares)	16,840,261	14,597,118
Common stock, shares outstanding (in shares)	16,840,261	14,597,118
Class A-1 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	256,700
Preferred stock, shares issued (in shares)	256,700	256,700
Preferred stock, shares outstanding (in shares)	256,700	256,700
Class A-2 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,330,832	1,330,832
Preferred stock, shares issued (in shares)	1,330,832	1,330,832
Preferred stock, shares outstanding (in shares)	1,330,832	1,330,832
Class A-3 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	258,707	258,707
Preferred stock, shares issued (in shares)	258,707	258,707
Preferred stock, shares outstanding (in shares)	258,707	258,707
Class A-4 Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	3,725,720	3,725,720
Preferred stock, shares issued (in shares)	3,725,720	3,725,720
Preferred stock, shares outstanding (in shares)	3,725,720	3,725,720

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 18,410	$ 17,794
General and administrative	9,829	10,022
Total operating expenses	28,239	27,816
Loss from operations	(28,239)	(27,816)
Other income (expense):
Interest and other income	605	864
Interest and other expense	(688)	(855)
Loss before income taxes	(28,322)	(27,807)
Income tax expense	(1)	(1)
Net loss	(28,323)	(27,808)
Other comprehensive loss:
Unrealized loss on short-term investments, net	(12)	0
Comprehensive loss	$ (28,335)	$ (27,808)
Net loss per share, basic (in dollars per share)	$ 1.86	$ 3.24
Net loss per share, diluted (in dollars per share)	$ 1.86	$ 3.24
Weighted average shares used to compute basic net loss per share (in shares)	15,259,958	8,569,854
Weighted average shares used to compute diluted net loss per share (in shares)	15,259,958	8,569,854

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred stock Convertible Preferred Stock	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2020		1,931,860	6,743,271
Beginning balance at Dec. 31, 2020	$ 26,026	$ 2	$ 7	$ 453,062	$ 0	$ (427,045)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)			2,768
Issuance of common stock upon exercise of options	26			26
Issuance of common stock upon exercise of warrants (in shares)			266,866
Issuance of common stock upon exercise of warrants	832			832
Issuance of common stock upon vesting of restricted stock units (in shares)			3,363
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs (in shares)		3,725,720	5,892,335
Issuance of common stock, preferred stock and warrants from private placement, net of offering costs	32,359	$ 3	$ 6	32,350
Stock-based compensation expense	2,923			2,923
Issuance of common stock under Employee Stock Purchase Plan (in shares)			1,160
Issuance of common stock under Employee Stock Purchase Plan	7			7
Issuance of common stock through ATM (in shares)			1,601,734
Issuance of common stock through ATM	20,593		$ 2	20,591
Conversions of convertible preferred stock (in shares)		(85,621)	85,621
Conversions of convertible preferred stock	0
Unrealized loss on short-term investments, net	0
Net loss	(27,808)					(27,808)
Ending balance (in shares) at Dec. 31, 2021		5,571,959	14,597,118
Ending balance at Dec. 31, 2021	54,958	$ 5	$ 15	509,791	0	(454,853)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)			36,300
Stock-based compensation expense	2,177			2,177
Issuance of common stock under Employee Stock Purchase Plan (in shares)			1,743
Issuance of common stock under Employee Stock Purchase Plan	3			3
Issuance of common stock through ATM (in shares)			2,205,100
Issuance of common stock through ATM	4,488		$ 2	4,486
Unrealized loss on short-term investments, net	(12)				(12)
Net loss	(28,323)					(28,323)
Ending balance (in shares) at Dec. 31, 2022		5,571,959	16,840,261
Ending balance at Dec. 31, 2022	$ 33,291	$ 5	$ 17	$ 516,457	$ (12)	$ (483,176)

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net loss	$ (28,323)	$ (27,808)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	122	459
Gain on PPP Loan forgiveness	0	(662)
Stock-based compensation	2,177	2,923
Amortization of premiums and accretion of discounts on investments, net	(185)	0
Other	133	46
Change in operating assets and liabilities:
Contracts and other receivables	0	503
Prepaid materials	0	304
Prepaid expenses and other assets	(67)	(221)
Accounts payable	(110)	(250)
Accrued liabilities	140	240
Accrued research and development expenses	442	(287)
Accrued compensation	189	273
Operating lease right-of-use assets and liabilities, net	(64)	279
Other liabilities	20	73
Net cash used in operating activities	(25,526)	(24,128)
Investing activities
Payments to Acquire Short-Term Investments	(32,759)	0
Sales and maturities of short-term investments	18,000	0
Purchases of property and equipment	(361)	(251)
Net cash used in investing activities	(15,120)	(251)
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	0	32,360
Proceeds from issuance of common stock, net	4,491	21,431
Proceeds from exercise of common stock options	0	26
Payments on financing leases	0	(80)
Net cash provided by financing activities	4,491	53,737
Net (decrease) increase in cash, cash equivalents and restricted cash	(36,155)	29,358
Cash, cash equivalents and restricted cash at beginning of period	60,445	31,087
Cash, cash equivalents and restricted cash at end of period	24,290	60,445
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	24,228	60,383
Restricted cash	62	62
Total cash, cash equivalents and restricted cash	24,290	60,445
Supplemental disclosure of cash flow information
Interest paid	(491)	(729)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Paycheck Protection Program loan forgiveness	0	662
Purchases of property and equipment included in accrued liabilities	$ 6	$ 0

The Business, Basis of Presenta

The Business, Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
The Business, Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies We are a clinical-stage biopharmaceutical company focused on discovering and developing first-in-class drugs targeting micro RNAs to treat diseases with significant unmet medical need. We were formed in 2007 when Alnylam Pharmaceuticals, Inc. ("Alnylam") and Ionis Pharmaceuticals, Inc. ("Ionis") contributed significant intellectual property, know-how and financial and human capital to pursue the development of drugs targeting micro RNAs pursuant to a license and collaboration agreement. Basis of Presentation On June 24, 2022, we filed a Certificate of Amendment of Amended and Restated Certificate of Incorporation with the Secretary of State of the state of Delaware to effect a 1-for-10 reverse stock split of our issued and outstanding common stock. The primary purpose of the reverse stock split was to raise the per share trading price of our common stock to seek to maintain the listing of our common stock on The Nasdaq Capital Market. At the effective time of the reverse stock split, 5:00 p.m. on June 28, 2022, each 10 shares of our issued and outstanding common stock were automatically combined and converted into one issued and outstanding share of common stock. All of our stock options, RSUs and warrants outstanding immediately prior to the reverse stock split, as well as the conversion ratio of our outstanding convertible preferred stock, were proportionately adjusted. All issued and outstanding common stock, options exercisable for common stock, restricted stock units, common stock issuable upon conversion of outstanding convertible preferred stock, warrants a nd per share amounts contained in these financial statements have been retrospectively adjusted. Liquidity The accompanying financial statements have been prepared on a basis which assumes we are a going concern, and does not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from any uncertainty related to our ability to continue as a going concern. Through the date of the issuance of these financial statements, we have principally been financed through proceeds received from the sale of our common stock and other equity securities, debt financings, up-front payments and milestones received from collaboration agreements, totaling $542.5 million. As of December 31, 2022, we had approximately $39.2 million of cash, cash equivalents and short-term investments. Based on our operating plans, we believe our cash, cash equivalents and short-term investments will not be sufficient to fund our operations for the period one year following the issuance of these financial statements. Specifically, we believe these existing resources will only be sufficient to fund our planned operations and expenditures into the early part of the first quarter of 2024. Our current liquidity position, recurring losses from operations since inception and negative cash flows from operating activities raise substantial doubt about our ability to continue as a going concern. All amounts due under the Term Loan (see note 9) have been classified as a current liability as of December 31, 2022 due to the considerations discussed above and the assessment that the material adverse change clause under the Term Loan is not within our control. We are in compliance with all Loan Agreement covenants. We intend to seek additional capital through equity and/or debt financings, collaborative or other funding arrangements with partners or through other sources of financing. Should we seek additional financing from outside sources, we may not be able to raise such financing on terms acceptable to us or at all. If we are unable to raise additional capital when required or on acceptable terms, we may be required to scale back or discontinue the advancement of product candidates, reduce headcount, file for bankruptcy, reorganize, merge with another entity, or cease operations. If we are unable to continue as a going concern, we may have to liquidate our assets, and in doing so might realize significantly less for those assets than the values at which they are carried on our financial statements. Stockholders may lose all or part of their investment in our common stock. Use of Estimates Our financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions. Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for restricted stock units by determining the fair value of each restricted stock unit based on the closing market price of our common stock on the date of grant. We recognize stock-based compensation expense using the accelerated multiple-option approach over the requisite service periods of the awards. Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and progression through the various stages of our clinical trials. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals. Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our preclinical and clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which an impairment is identified. Research and Development Research and development costs are expensed as incurred and consist of costs associated with research activities supporting our drug discovery efforts, compensation and related benefits, non-cash stock-based compensation, license fees, laboratory supplies and associated overhead and facility costs. Income Taxes Income taxes are accounted for under the asset and liability method. This approach requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of the differences between the tax basis of assets or liabilities and their carrying amounts in the financial statements using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. We provide a valuation allowance against net deferred tax assets if it is more likely than not that these items will either expire before we are able to realize their benefit or if future deductibility is uncertain. In accordance with the accounting standards for uncertain tax positions, we evaluate the recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. Cash and Cash Equivalents We classify time deposits and other investments that are highly liquid and have maturities of 90 days or less at the date of purchase as cash equivalents. The carrying amounts approximate fair value due to the short maturities of these instruments. Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have not experienced any material losses in such accounts and believe we are not exposed to significant risk. We have invested our excess cash primarily in money market funds and U.S. Treasury securities. Additionally, we adhere to established guidelines regarding approved investments and maturities of investments, which are designed to preserve their principal value and maintain liquidity. Property and Equipment We carry our property and equipment at cost, which consists of lab equipment, computer equipment and software, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three Impairment of Long-Lived Assets We regularly review the carrying amount of our property, equipment and intangible assets to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. If indications of impairment exist, projected future undiscounted cash flows associated with the asset are compared to the carrying amount to determine whether the asset’s value is recoverable. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value. No impairment charges were recorded during the years ended December 31, 2022 or 2021. 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. To date, we have viewed our operations and managed our business as one segment operating primarily within the United States. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. Our only component of other comprehensive loss is unrealized gains (losses) on available-for-sale securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss and as a separate component in the statements of stockholders’ equity for all periods presented. Leases At the inception of a contractual arrangement, we determine whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. For operating leases with an initial term greater than 12 months, we recognize operating lease right of use assets ("ROU assets") and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when we are reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. Leases with a lease term of 12 months or less at inception are not recorded on the balance sheet. Instead, we recognize lease expense for these leases on a straight-line basis over the lease term. Our lease agreements do not contain any material variable lease payments, residual value guarantees or restrictive covenants. Certain leases require us to pay taxes, insurance, utilities, and maintenance costs for the building, which do not represent lease components. We elected to not separate lease and non-lease components. Fair Value of Financial Instruments We follow ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Our financial instruments consist of cash, cash equivalents and short-term investments, contract and other receivables, accounts payable, accrued liabilities, and our Term Loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash, cash equivalents, contract and other receivables, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. We believe that the fair value of the Term Loan approximates its carrying value. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit losses for most financial assets held at the reporting date based on an expected loss model which includes historical experience, current conditions, an d reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help financial statement users better understand significant estimates and judgments used in estimating credit losses. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2022, with early adoption permitted. We are assessing the impact this standard will have on our financial statements and disclosures. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides guidance around reference rate reform initiatives to identify alternative reference rates that are more observable or transaction-based and less susceptible to manipulation in response to concerns about structural risks of interbank offered rates and the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments in the ASU provide option expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform and apply only if such contracts, hedging relationships and other transactions that reference LIBOR or another reference rate are expected to be discontinued because of reference rate reform. On December 21, 2022, the FASB issued ASU No. 2022-06, Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848,

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of common share equiva lents outstanding for the period determined using the treasury-stock method or if-converted method. Dilutive common stock equivalents are comprised of stock options, restricted stock units,

Investments

Investments	12 Months Ended
	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Historically, we have invested our excess cash primarily in debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. We generally hold our investments to maturity and do not sell our investments before we have recovered our amortized cost basis. Unrealized Maturity (in years) Amortized cost Gains Losses Estimated fair value As of December 31, 2022 U.S. Treasury securities 1 or less $ 14,944 $ — $ (12) $ 14,932 $ 14,944 $ — $ (12) $ 14,932

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Financial Assets Measured at Fair Value The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2022 and 2021 (in thousands): Fair value as of December 31, 2022 Total Level 1 Level 2 Level 3 Cash equivalents and short-term investments: Money market funds $ 21,490 $ 21,490 $ — $ — U.S. Treasury securities 14,932 14,932 — — $ 36,422 $ 36,422 $ — $ — Fair value as of December 31, 2021 Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 57,905 $ 57,905 $ — $ — $ 57,905 $ 57,905 $ — $ — We obtain pricing information from quoted market prices or quotes from brokers/dealers. We have historically determined the fair value of our investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers.

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations	Collaborations Sanofi In February 2014, we and Sanofi entered into a second amended and restated collaboration and license agreement (the “Sanofi Agreement”) to discover, develop and commercialize micro RNA therapeutics to focus on specific orphan disease and oncology targets. Under the terms of the Sanofi Agreement, Sanofi had opt-in rights to our clinical fibrosis program targeting miR-21 for the treatment of Alport syndrome (which rights were relinquished by Sanofi in November 2018), our preclinical program targeting miR-21 for oncology indications, and our preclinical program targeting miR-221/222 for HCC. We were responsible for developing each of these programs to proof-of-concept, at which time Sanofi had an exclusive option on each program. We were eligible to receive royalties on micro RNA therapeutic products commercialized by Sanofi and would have had have the right to co-promote these products relating to our preclinical program targeting miR-221/222. As of December 31, 2022, we were eligible to receive milestone payments related to the development and commercialization of miR-221/222 for HCC of up to $38.8 million for proof-of-concept option exercise fees (net of a $1.25 million creditable option fee), $25.0 million for clinical milestones and up to $130.0 million for regulatory and commercial milestones. In addition, we were eligible to receive royalties based on a percentage of net sales of any products from the miR-221/222 program which, in the case of sales in the United States, were in the middle of the 10% to 20% range, and, in the case of sales outside of the United States, were in the low end to the middle of the 10% to 20% range, depending upon the volume of sales. On July 12, 2022, we received notification from Sanofi of its decision to terminate the Phase 2 clinical study of lademirsen (RG-012) for the treatment of Alport syndrome for failure to meet Sanofi’s pre-defined futility criteria. Sanofi also notified us that they were evaluating different opportunities with respect to RG-012. As of December 31, 2022, we remained eligible to receive the $25.0 million milestone in the event of successful completion of a Phase 2 fibrosis proof of concept study. As of December 31, 2022, the $25.0 million in development milestone payments (variable consideration) was fully constrained and, therefore, did not meet the criteria for revenue recognition.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net The following table summarizes our major classes of property and equipment (in thousands): December 31, 2022 2021 Laboratory equipment $ 4,359 $ 4,215 Computer equipment and software 470 265 Furniture and fixtures 12 — Leasehold improvements 115 115 4,956 4,595 Less accumulated depreciation and amortization (4,420) (4,314) Property and equipment, net $ 536 $ 281 Depreciation and amortization of property and equipment of $0.1 million and $0.4 million was recorded for the years ended December 31, 2022 and 2021, respectively.

Intangible Assets, net

Intangible Assets, net	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, net	Intangible Assets, net The following table summarizes our major classes of intangible assets (in thousands): December 31, 2022 2021 Patents $ 183 $ 189 Accumulated amortization - Patents (121) (106) Intangibles, net $ 62 $ 83 Intangible asset amortization of less than $0.1 million was recorded for the years ended December 31, 2022 and 2021. Amortization of intangible assets over the next five years is expected to be less than $0.1 million per year. The weighted-average period over which the amortization remaining at December 31, 2022 is expected to be recognized is approximately 11.7 years.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies License Agreements We have license agreements with third parties that require us to make annual license maintenance payments and future payments upon the success of licensed products that include milestones and/or royalties. Minimum future payments over the next five years are not material. Litigation From time to time, we may be involved in various lawsuits, legal proceedings, or claims that arise in the ordinary course of business. We believe there are no claims or actions pending against us at December 31, 2022 which will have, individually, or in the aggregate, a material adverse effect on our business, liquidity, financial position or results of operations. Litigation, however, is subject to inherent uncertainties, and an adverse result in such matters may arise from time to time that may harm our business.

Debt

Debt	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Debt	Debt Term Loan On June 17, 2016, we entered into a loan and security agreement (“Loan Agreement”) with Oxford Finance, LLC, (the “ Lender ” ), pursuant to which we received $20.0 million in proceeds, net of debt issuance costs, on June 22, 2016 (the “Term Loan”). The outstanding Term Loan will mature on May 1, 2024 (the “Maturity Date”) and bears interest at a floating per annum rate equal to (i) 8.51% plus (ii) the greater of (a) the 30 day U.S. Dollar LIBOR rate reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue and (b) 0.44%. Under the original Loan Agreement, we were required to make interest-only payments through June 1, 2018, followed by 24 equal monthly payments of principal and unpaid accrued interest. The Loan Agreement was amended ten times between October 2017 through August 2020. On December 31, 2021, we entered into an eleventh amendment to the Loan Agreement (the “Eleventh Amendment ” ). Under the terms of the Eleventh Amendment, the maturity date for the Term Loan was extended to May 1, 2024. In addition, under the Eleventh Amendment, our required monthly payments to the Lender were comprised of interest only through and including (i) December 1, 2022, if the 2022 Equity Event (as defined below) did not occur or (ii) December 1, 2023 if the 2022 Equity Event did occur. The “2022 Equity Event” meant the receipt by us, during the calendar year 2022, of unrestricted net cash proceeds of at least $20.0 million from the sale and issuance of our equity securities. The 2022 Equity Event did not occur. The Eleventh Amendment also provides that we are required to maintain a minimum cash balance of $5.0 million. As consideration for the Lender’s entry into the Eleventh Amendment, we made a payment of $0.3 million to the Lender. We used the proceeds from the Term Loan solely for working capital and to fund our general business requirements. Our obligations under the Loan Agreement are secured by a first priority security interest in substantially all of our current and future assets, other than our intellectual property, for which the Lender currently has a positive lien. We have also agreed not to encumber our intellectual property assets, except as permitted by the Loan Agreement. The Loan Agreement includes customary events of default, including instances of a material adverse change in our operations, that may require prepayment of the outstanding Term Loan. We are in compliance with all Loan Agreement covenants as of the date of the filing of this Form 10-K. As of December 31, 2022, $4.7 million of principal was outstanding under the Term Loan. An additional $1.3 million is also payable at the conclusion of the Term Loan (the related $1.2 million accrued liability balance is presented in other current liabilities on our balance sheet at December 31, 2022) . We had less than $0.1 million of debt issuance costs outstanding as of December 31, 2022, which are being accreted to interest expense over the life of the T erm Loan using an effective interest rate of 8.98%. The exit fees are being accrued over the life of the Term Loan through interest expense. As of December 31, 2022, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2023 $ 3,304 2024 1,377 $ 4,681 Paycheck Protection Program Loan On April 23, 2020, we received proceeds in the amount of approximately $0.7 million (the “ PPP Loan”) from Silicon Valley Bank, as lender, pursuant to the Paycheck Protection Program of the Coronavirus Aid, Relief, and Economic Security Act. The PPP Loan was set to mature on April 23, 2022, and bore interest at a rate of 1.0% per annum. The PPP Loan was evidenced by a promissory note dated April 23, 2020, which contained customary events of default relating to, among other things, payment defaults and breaches of representations and warranties. The PPP Loan was prepayable by us at any time prior to maturity with no prepayment penalties. We used all proceeds from the PPP Loan to retain employees, maintain payroll and make lease and utility payments, and we sought forgiveness in accordance with the program. We received full forgiveness of our PPP Loan in the second quarter of 2021. We accounted for the full forgiveness of our PPP Loan by recording a gain in interest and other income for the year ended December 31, 2021.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock As of December 31, 2022, there were 16,840,261 shares of common stock outstanding. Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by our Board of Directors. 2019 Equity Incentive Plan On June 15, 2019 the Company’s board of directors approved, and on August 1, 2019 the Company's stockholders approved, the Company’s 2019 Equity Incentive Plan (the “2019 Plan”). The 2019 Plan is the successor to and continuation of the Company’s 2012 Equity Incentive Plan. The number of shares authorized for issuance under the 2019 Plan may be increased by (a) the shares subject to outstanding stock awards granted under the Company’s 2009 Equity Incentive Plan (the “2009 Plan”) and the Company’s 2012 Equity Incentive Plan (together with the 2009 Plan, the “Prior Plans”) that on or after the effective date of the 2019 Plan (i) expire or terminate for any reason prior to exercise or settlement; (ii) are forfeited because of the failure to meet a contingency or condition required to vest such shares or otherwise return to the Company, or (iii) are reacquired, withheld (or not issued) to satisfy a tax withholding obligation in connection with an award or to satisfy the purchase price or exercise price of a stock award. No further grants will be made under the Prior Plans. In addition, on January 22, 2020, an additional 416,686 shares of common stock became available for issuance under the 2019 Plan pursuant to the second closing under our May 2019 securities purchase agreement. Further, on January 1 st of each year, for a period of not more than ten years, beginning on January 1, 2021 and continuing through January 1, 2029, the number of shares authorized for issuance under the 2019 Plan will increase by 5.0% of the total number of shares of our capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by our Board of Directors. As of December 31, 2022, 394,261 shares of common stock were available for new equity award grants under the 2019 Plan and 1,442,135 shares of common stock were reserved for issuance pursuant to equity awards outstanding under the 2019 Plan as of December 31, 2022. 2021 Inducement Plan On November 23, 2021, our Board of Directors adopted the 2021 Inducement Plan (the “Inducement Plan”), which became effective immediately. Stockholder approval of the Inducement Plan was not required pursuant to Rule 5635I(4) of the Nasdaq Listing Rules. The Inducement Plan initially reserved 200,000 shares of common stock and provides for the grant of non-qualified stock options that was used exclusively for grants to individuals that were not previously employees or directors of the Company, as an inducement material to the individual’s entry into employment with the Company. The authorized number of shares available for grant under the Inducement Plan was subsequently increased in October 2022 to 540,000 shares in the aggregate. Under the Inducement Plan, options are granted with varying vesting terms, but typically vested over four years, with 25% of the total grant vesting on the first anniversary of the effective date of the option grant and the remaining grant vesting monthly thereafter over the following 36 months. As of December 31, 2022, 500,000 shares of common stock were reserved for future issuance under the Inducement Plan and 40,000 shares of common stock were reserved for future issuance pursuant to equity awards outstanding under the Inducement Plan. 2022 Employee Stock Purchase Plan In June 2022, our stockholders approved and we adopted the 2022 Employee Stock Purchase Plan (the “2022 Purchase Plan”), which enables participants to contribute up to 15% of such participant’s eligible compensation during defined rolling six-month periods to purchase our common stock. The purchase price of common stock under the 2022 Purchase Plan will be the lesser of: (i) 85% of the fair market value of our common stock at the inception of the enrollment period or (ii) 85% of the fair market value of our common stock at the applicable purchase date. The 2022 Purchase Plan supersedes the 2012 Employee Stock Purchase Plan, and no further offerings will be made under the 2012 Employee Stock Purchase Plan. As of December 31, 2022, a maximum of 129,107 shares of our common stock were reserved for future issuance and have been authorized for purchase under the 2022 Purchase Plan. 2021 Private Placement of Common Stock and Non-Voting Preferred Stock On November 24, 2021, we entered into a Securities Purchase Agreement (the “November 2021 SPA”) with certain institutional and other accredited investors, including one of the Company's directors (the “2021 Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock and shares of newly designated non-voting convertible preferred stock (the “2021 PIPE”). At the closing under the November 2021 SPA that occurred on November 30, 2021 (the “2021 Closing”), we sold and issued to the 2021 Purchasers (i) 5,892,335 shares of common stock at a purchase price of $3.60 per share, and (ii) 3,725,720 shares of non-voting Class A-4 convertible preferred stock, in lieu of shares of common stock, at a price of $3.60 per share. Total gross proceeds from the 2021 Closing were approximately $34.6 million. Each share of non-voting Class A-4 convertible preferred stock is convertible into one share of common stock, subject to certain beneficial ownership conversion limitations. An aggregate of 222,222 shares of common stock were purchased for $0.8 million by a director of the Company at the 2021 Closing. We evaluated the non-voting Class A-4 convertible preferred stock sold in the 2021 PIPE under ASC 480, Distinguishing Liabilities from Equity, and ASC 815, Derivatives and Hedging, and determined permanent equity treatment was appropriate for these freestanding financial instruments and there were no embedded features that required bifurcation. Additional Outstanding Non-Voting Preferred Stock and Warrants In May 2019, we sold and issued (i) 973,045 shares of common stock (ii) 415,898 shares of non-voting Class A-1 convertible preferred stock and (iii) accompanying warrants to purchase an aggregate of 1,388,943 shares of common stock. Each share of non-voting Class A-1 convertible preferred stock is convertible into one share of common stock, subject to certain beneficial ownership conversion limitations. The warrants are exercisable for a period of five years following the date of issuance and have an exercise price of $10.80 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise "cashless" basis. In December 2019, we sold and issued 3,288,390 shares of non-voting Class A-2 convertible preferred stock and accompanying warrants to purchase an aggregate of 3,288,390 shares of common stock. Each share of non-voting Class A-2 convertible preferred stock is convertible into one share of common stock, subject to certain beneficial ownership conversion limitations. The warrants will be exercisable for a period of five years following the date of issuance and have an exercise price of $6.66 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise “cashless” basis. In December 2020, we sold and issued (i) 2,434,152 shares of common stock (ii) 272,970 shares of non-voting Class A-3 convertible preferred stock and (iii) accompanying warrants to purchase an aggregate of 2,030,341 shares of common stock. Each share of non-voting Class A-3 convertible preferred stock is convertible into one share of common stock, subject to certain beneficial ownership conversion limitations. The warrants are exercisable for a period of five years following the date of issuance and have an exercise price of $7.46 per share, subject to proportional adjustments in the event of stock splits or combinations or similar events. The warrants are exercisable on a net exercise "cashless" basis. The following table summarizes preferred stock conversions and warrant exercises (and the related impact on common stock) for the years ended December 31, 2022 and 2021 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Class A-4 Convertible Preferred Stock May 2019 Warrants December 2019 Warrants December 2020 Warrants Common Stock Balance at December 31, 2020 257 1,416 259 — 1,389 3,185 2,030 2021 Closing — — — 3,726 — — — 5,892 Conversions/Exercises — (85) — — (111) (125) (181) 352 Balance at December 31, 2021 257 1,331 259 3,726 1,278 3,060 1,849 Conversions/Exercises — — — — — — — — Balance at December 31, 2022 257 1,331 259 3,726 1,278 3,060 1,849 ATM Offering On December 12, 2018, we entered into a Common Stock Sales Agreement (the “Stock Sales Agreement”) with H.C. Wainwright & Co., LLC (“HCW”), pursuant to which we may sell and issue shares of our common stock from time to time through HCW, as our sales agent (the “ATM Offering”). We have no obligation to sell any shares of common stock in the ATM Offering, and may at any time suspend offers under the Stock Sales Agreement or terminate the Stock Sales Agreement. Subject to the terms and conditions of the Stock Sales Agreement, HCW will use its commercially reasonable efforts to sell shares of our common stock from time to time based upon our instructions (including any price, time or size limits or other parameters or conditions that we may impose, subject to certain restrictions). We pay HCW a commission of 3.0% of the gross sales price of any shares sold under the Stock Sales Agreement. On August 10, 2021, we increased the amount of common stock available for sale in the ATM Offering under the Stock Sales Agreement to $50.0 million. A total of 2,205,100 shares were sold and settled for proceeds of $4.5 million (net of $0.1 million in offering costs) under the ATM Offering during the year ended December 31, 2022. A total of 1,601,734 shares were sold and settled for proceeds of $20.5 million (net of $0.8 million in offering costs) under the ATM Offering during the year ended December 31, 2021. At December 31, 2022, approximately $45.4 million remained eligible to be sold in the ATM Offering, subject to compliance with the rules applicable to sales on Form S-3. Shares Reserved for Future Issuance The following shares of commo n stock were reserved for future is suance as of December 31, 2022 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 257 Class A-2 convertible preferred stock outstanding (as-converted) 1,331 Class A-3 convertible preferred stock outstanding (as-converted) 259 Class A-4 convertible preferred stock outstanding (as-converted) 3,726 Warrants to purchase Common Stock 6,186 Common stock options outstanding 1,372 RSUs outstanding 70 Common stock available for future grant under the 2019 Equity Incentive Plan 394 Common stock available for future grant under the 2021 Inducement Plan 160 2022 Employee Stock Purchase Plan 129 Total common shares reserved for future issuance 13,884 The following table summarizes our stock option and RSU (together "Stock Awards") activity under all equity incentive plans for the year ended December 31, 2022 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Stock Awards outstanding at December 31, 2021 866 $ 11.72 Granted 570 $ 2.59 Exercised (options) or Vested (RSUs) — $ — Canceled/forfeited/expired (64) $ 20.42 Stock Awards outstanding at December 31, 2022 1,372 $ 7.53 7.1 $ — Vested and exercisable at December 31, 2022 742 $ 8.69 6.3 $ — The weighted average grant date fair value per share of employee stock options granted during the years ended December 31, 2022 and 2021 was $2.00 and $10.26, respectively. There were no stock option exercises in 2022. The total intrinsic value of stock options exercised was less than $0.1 million for the year ended December 31, 2021. Cash received from the exercise of stock options was less than $0.1 million for the year ended December 31, 2021. The total compensation cost related to stock options not yet recognized was $0.9 million as of December 31, 2022. The weighted-average period over which this expense is expected to be recognized is approximately 1.3 years. The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2022 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2021 40 $ 9.50 Granted 85 $ 2.57 Vested (36) $ 9.50 Canceled/forfeited/expired (19) $ 3.97 RSUs outstanding at December 31, 2022 70 $ 2.57 0.8 $ 96 The total compensation cost related to non-vested RSUs not yet recognized was $0.2 million as of December 31, 2022. The weighted-average period over which this expense is expected to be recognized is approximately 1.3 years. Stock-Based Compensation The following table su mmarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2019 Equity Incentive Plan, 2021 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plans during the periods presented: Year ended December 31, 2022 2021 Stock options Risk-free interest rate 2.0 % 1.0 % Volatility 96.1 % 95.8 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate — 1.0 % Volatility — 95.7 % Dividend yield — — Expected term (years) 0 6.1 Employee stock purchase plan shares Risk-free interest rate 1.6 % 0.1 % Volatility 104.7 % 101.2 % Dividend yield — — Expected term (years) 0.5 0.5 Risk-free interest rate - The risk-free interest rate assumption was based on observed interest rates appropriate for the expected term of the stock option grants. Expected dividend yield - The expected dividend yield assumption was based on the fact that we have never paid cash dividends and have no present intention to pay cash dividends. Expected volatility - The expected volatility assumption was based on the historical volatility of the trading price of our common stock. Expected term - The expected term represents the period of time that options are expected to be outstanding. Because we do not have sufficient historical exercise behavior data, we determine the expected life using the simplified method, which was an average of the contractual term of the option and its ordinary vesting period. Forfeitures - We account for forfeitures as they occur. The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands): Year ended December 31, 2022 2021 Research and development $ 594 $ 821 General and administrative 1,583 2,102 Total $ 2,177 $ 2,923

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Defined Contribution Plan	Defined Contribution Plan In 2009, we established an employee 401(k) salary deferral plan (“401(k) Plan”) covering all eligible employees. Active employees who are at least 18 years old and are not otherwise disqualified under the terms of the 401(k) Plan are eligible to participate. Employees may contribute up to 50% of their compensation per year (subject to a maximum limit prescribed by federal tax law). Under the 401(k) Plan, we may elect to match a discretionary percentage of employee contributions. We elected to match 50% of employees’ contributions up to 6% of the employees’ eligible salary for the per iods presented. We made matching contributions of $0.1 million for the years ended December 31, 2022 and 2021.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table summarizes the components of our income ta x expense (i n thousands): Year ended December 31, 2022 2021 Current: Federal $ — $ — State 1 1 1 1 Deferred: Federal — — State — — — — Income tax expense $ 1 $ 1 The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands): Year ended December 31, 2022 2021 Expected income tax benefit at federal statutory tax rate $ (5,948) $ (5,840) State income taxes, net of federal benefit 1 1 Tax credits (1,850) (1,180) Change in valuation allowance 7,327 6,659 Return to provision adjustments (18) 80 Stock compensation 236 243 Reserve for uncertain tax positions 253 176 Other — (138) Income tax expense $ 1 $ 1 The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands): December 31, 2022 2021 Deferred tax assets: Net operating loss carryovers $ 90,085 $ 87,877 Research and development and other tax credits 36,963 35,344 Intangibles and property and equipment basis difference 496 607 Section 174 research and development 3,302 — Stock compensation expense 818 587 Lease liability 508 631 Other 597 564 Total deferred tax assets 132,769 125,610 Total deferred tax liabilities (611) (782) Gross deferred tax asset 132,158 124,828 Valuation allowance (132,158) (124,828) Net deferred tax asset $ — $ — For all periods presented, we have determined that it is more likely than not that our deferred tax asset will not be realized. Accordingly, we have recorded a valuation allowance to offset the net deferred tax asset of $132.2 million. As of December 31, 2022, we had NOL carryforwards for U.S. federal and California state tax purposes of $377.4 million and $146.3 million, respectively, portions of which begin to expire in 2030 and 2033, respectively. Our federal NOL carryforwards generated in tax years beginning after December 31, 2017 of $114.1 million will carry forward indefinitely. As of December 31, 2022, we also had federal research and development tax credits, orphan drug credits and California research and development tax credit carryforwards of $12.6 million, $21.9 million and $10.1 million, respectively. The federal research and development tax credit carryforwards will begin to expire in 2029 and the federal orphan drug credits will begin to expire in 2034. The California research and development tax credit carryforwards are available indefinitely. Pursuant to Sections 382 and 383, use of the Company’s net operating loss and credit carryforwards may be limited if a cumulative change in ownership of more than 50% (by value) occurs within a three-year period. The Company has not performed an analysis through December 31, 2022 to determine whether its net operating loss and research and development credit carryforwards are subject to annual limitation under Sections 382 or 383 of the Code, and these financial statements do not contain any adjustment relating to such potential limitations. However, if the Company experienced an ownership change that resulted in an annual limitation on the Company’s net operating loss carryforwards under Section 382 of the Code there would be no material impact to the Company’s financial statements. The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands): Year Ended December 31, 2022 2021 Beginning balance of unrecognized tax benefits $ 16,953 $ 17,939 Decrease for prior year tax positions (11,463) (1,174) Increase for current year tax positions 295 188 Total $ 5,785 $ 16,953 Included in unrecognized tax benefits of $5.8 million at December 31, 2022 was $5.0 million of tax benefits that, if recognized, would reduce our annual effective tax rate, subject to valuation allowance. We do not expect that there will be a significant change in the unrecognized tax benefits over the next 12 months. We are subject to taxation in the United States and state jurisdictions where applicable. Our tax years for 2010 and forward are subject to examination by the U.S. and California tax authorities due to carryforward of unutilized net operating losses and research and development credits. It is our practice to recognize interest and/or penalties related to income tax matters in income tax expense. For the years ended December 31, 2022 and 2021, we have not recognized any interest or penalties related to income taxes.

Leases

Leases	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Leases	Leases On June 19, 2019, we entered into a lease agreement (the “Prior Lease”) with ARE SD Region No. 44 LLC ("Landlord") for the lease of approximately 8,727 square feet of rentable area of the building located at 10628 Science Center Drive, Suite 225, San Diego, California 92121 (the “Prior Premises”). The commencement date of the Prior Lease was July 1, 2019 (the “Prior Commencement Date”). We used the Prior Premises as our principal executive offices and as a laboratory for research and development and other related uses. The term of the Prior Lease (the “Prior Initial Term”) was two years, six months, ending December 31, 2021. The base rent payments due for the Prior Premises were $0.4 million in 2020 and $0.4 million in 2021, net of certain rent abatement terms. We were also responsible for the payment of additional rent to cover our share of the annual operating expenses of the building, the annual tax expenses of the building and the annual utilities cost of the building. On July 1, 2019, we recorded a $0.8 million lease liability for the Prior Lease, which was calculated as the present value of future lease payments to be made under the Prior Lease. A $0.6 million ROU asset was also recorded on July 1, 2019, which represents the difference between the lease liability and the remaining $0.2 million deferred credit for the reduction of the lease liability under the operating lease agreement with Landlord dated February 25, 2019. On February 11, 2021, we entered into a lease agreement (the "Campus Point Lease") with ARE-SD Region No. 61, LLC (as successor in interest to ARE-SD Region No. 58, LLC) ("Campus Point Landlord"), for the lease of approximately 13,438 square feet of rentable area located at 4224 Campus Point Court, Suite 210, San Diego, California, 92121 (the "Campus Point Premises"). The commencement date of the Campus Point Lease was April 15, 2021. However, for accounting purposes the lease commencement date was February 11, 2021. We are using the Campus Point Premises as our principal executive offices and as a laboratory for research and development. The term of the Campus Point Lease (“Campus Point Initial Term”) is 60 months, ending April 30, 2026. The aggregate base rent due over the initial term of the Campus Point Lease is approximately $3.8 million. We are also responsible for the payment of additional amounts to cover our share of the annual operating expenses of the building, the annual tax expenses of the building and the utilities costs for the building. Under the Campus Point Lease, we were required to maintain a deposit of $62,000 in a specially designated bank account, which we recorded as restricted cash on our balance sheet at December 31, 2022 and 2021. On February 11, 2021, concurrently with entry into the Campus Point Lease, we entered into an Assignment and Assumption of Lease (the “Assignment Agreement”) with Turning Point Therapeutics, Inc. (“Assignee”) and a Consent to Assignment (the "Consent") with Landlord. Pursuant to the Assignment Agreement, we assigned all rights, title, and interest under the Prior Lease to Assignee and delivered the Prior Premises to Assignee on April 22, 202 1. Pursuant to the Assignment Agreement, Assignee paid us $60,000 in non-refundable assignment consideration. Additionally, the Consent stipulates that we were not required to pay a fee pursuant to the Prior Lease in connection with the assignment. The execution of the Campus Point Lease, Consent, and Assignment Agreement resulted in a modification which was not accounted for as a separate contract. Rather, we accounted for the three contracts with Campus Point Landlord in combination, as they were entered into at the same time and negotiated as a package to achieve the same commercial objective. We accounted for a $0.2 million reduction in the lease liability for the Prior Lease as a deferred credit that is amortized as a reduction to rent expense over the term of the Campus Point Lease. A lease liability of less than $0.1 million and ROU asset of less than $0.1 million remained with respect to the Prior Lease and was fully amortized as of April 30, 2021. On February 11, 2021, we recorded a $3.2 million lease liability for the Campus Point Lease, which was calculated as the present value of future lease payments to be made under the Campus Point Lease. A $3.0 million ROU asset was also recorded on February 11, 2021, which represents the difference between the lease liability and the $0.2 million deferred credit for the reduction of the lease liability under the Prior Lease. The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2022 and 2021 (in thousands): Year Ended December 31, 2022 2021 Assets Operating $ 2,039 $ 2,564 Total ROU assets $ 2,039 $ 2,564 Liabilities Current: Operating $ 649 $ 589 Long-term: Operating 1,768 2,417 Total lease liabilities $ 2,417 $ 3,006 The table below summarizes our lease costs from our statement of operations and cash payments from our statement of cash flows during the years ended December 31, 2022 and 2021 (in thousands): Year Ended December 31, 2022 2021 Lease cost: Operating lease cost $ 690 $ 746 Finance lease cost: Amortization of right-of-use assets — 29 Interest expense on finance lease liabilities — 1 Total finance lease cost $ — $ 30 Cash payment information: Operating cash used for operating leases $ 754 $ 468 Operating cash used for finance leases — 1 Financing cash used for finance leases — 80 Total cash paid for amounts included in the measurement of lease liabilities $ 754 $ 549 The table below summarizes other non-cash information under our operating lease obligations as of December 31, 2022 and 2021 (in thousands, except years and rates): Year Ended December 31, 2022 2021 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ — $ 3,006 Weighted-average remaining lease term (years) - operating leases 3.3 4.3 Weighted-average discount rate - operating leases 6.0 % 6.0 % We did not have any finance lease obligations as of December 31, 2022 or 2021. Our future lease payments under our operating lease at December 31, 2022 are as follows (in thousands): Operating Leases 2023 $ 776 2024 800 2025 824 2026 277 2027 — Total operating lease payments $ 2,677 Less: amount representing interest (260) Present value of obligations under operating lease 2,417 Less: current portion (649) Long-term operating lease obligations $ 1,768

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	Subsequent Event Termination of Collaboration and License Agreement with Sanofi On January 6, 2023, Sanofi delivered to us a written notice of Sanofi's election to terminate, in its entirety, the Sanofi Agreement. Previously, on July 12, 2022, we received notification from Sanofi of its decision to terminate the Phase 2 clinical study of lademirsen for the treatment of Alport syndrome for failure to meet Sanofi’s pre-defined futility criteria. We were notified at that time that Sanofi was evaluating other opportunities for the program in other indications and, according to Sanofi, the decision to terminate the study did not stem from any safety issues. In accordance with the Sanofi Agreement, the termination became effective on February 5, 2023, which was 30 days following the date of delivery of the notice by Sanofi. As of the effective date of the termination of the Sanofi Agreement, we were no longer eligible to receive any option exercise fees, royalties, or development, clinical, regulatory or commercial milestones from Sanofi.

The Business, Basis of Presen_2

The Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Use of Estimates	Use of EstimatesOur financial statements are prepared in accordance with GAAP, which requires us to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in our financial statements and accompanying notes. An estimated loss contingency is accrued in our financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Although these estimates are based on our knowledge of current events and actions we may undertake in the future, actual results may ultimately differ from these estimates and assumptions.
Stock-Based Compensation	Stock-Based Compensation We account for stock-based compensation expense related to stock options granted to employees and members of our board of directors by estimating the fair value of each stock option on the date of grant using the Black-Scholes option pricing model. We recognize stock-based compensation expense using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award was in substance multiple awards, resulting in accelerated expense recognition over the vesting period. For performance-based awards granted to employees (i) the fair value of the award is determined on the grant date, (ii) we assess the probability of the individual milestones under the award being achieved and (iii) the fair value of the shares subject to the milestone is expensed over the implicit service period commencing once management believes the performance criteria is probable of being met. We account for restricted stock units by determining the fair value of each restricted stock unit based on the closing market price of our common stock on the date of grant. We recognize stock-based compensation expense using the accelerated multiple-option approach over the requisite service periods of the awards.
Clinical Trial and Preclinical Study Accruals	Clinical Trial and Preclinical Study Accruals We make estimates of our accrued expenses for clinical trial and preclinical study activities as of each balance sheet date in our financial statements based on the facts and circumstances known to us at that time. These accruals are based upon estimates of costs incurred and fees that may be associated with services provided by clinical trial investigational sites and CROs and for other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and progression through the various stages of our clinical trials. In accruing for these services, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If possible, we obtain information regarding unbilled services directly from these service providers. However, we may be required to estimate these services based on other information available to us. If we underestimate or overestimate the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, our estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in our accruals.
Prepaid Materials	Prepaid Materials We capitalize the purchase of certain raw materials and related supplies for use in the manufacturing of drug product in our preclinical and clinical development programs, as we have determined that these materials have alternative future use. We can use these raw materials and related supplies in multiple clinical drug products, and therefore have future use independent of the development status of any particular program until it is utilized in the manufacturing process. We expense the cost of materials when used. We periodically review these capitalized materials for continued alternative future use and write down the asset to its net realizable value in the period in which an impairment is identified.
Research and Development	Research and Development Research and development costs are expensed as incurred and consist of costs associated with research activities supporting our drug discovery efforts, compensation and related benefits, non-cash stock-based compensation, license fees, laboratory supplies and associated overhead and facility costs.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. This approach requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of the differences between the tax basis of assets or liabilities and their carrying amounts in the financial statements using the enacted tax rates and laws that are anticipated to be in effect when the differences are expected to reverse. We provide a valuation allowance against net deferred tax assets if it is more likely than not that these items will either expire before we are able to realize their benefit or if future deductibility is uncertain.
Cash and Cash Equivalents	Cash and Cash Equivalents We classify time deposits and other investments that are highly liquid and have maturities of 90 days or less at the date of purchase as cash equivalents. The carrying amounts approximate fair value due to the short maturities of these instruments.
Concentration of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have not experienced any material losses in such accounts and believe we are not exposed to significant risk. We have invested our excess cash primarily in money market funds and U.S. Treasury securities. Additionally, we adhere to established guidelines regarding approved investments and maturities of investments, which are designed to preserve their principal value and maintain liquidity.
Property and Equipment	Property and Equipment three
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We regularly review the carrying amount of our property, equipment and intangible assets to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. If indications of impairment exist, projected future undiscounted cash flows associated with the asset are compared to the carrying amount to determine whether the asset’s value is recoverable. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value.
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. To date, we have viewed our operations and managed our business as one segment operating primarily within the United States.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. Our only component of other comprehensive loss is unrealized gains (losses) on available-for-sale securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss and as a separate component in the statements of stockholders’ equity for all periods presented.
Leases	Leases At the inception of a contractual arrangement, we determine whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. For operating leases with an initial term greater than 12 months, we recognize operating lease right of use assets ("ROU assets") and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when we are reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. Leases with a lease term of 12 months or less at inception are not recorded on the balance sheet. Instead, we recognize lease expense for these leases on a straight-line basis over the lease term. Our lease agreements do not contain any material variable lease payments, residual value guarantees or restrictive covenants. Certain leases require us to pay taxes, insurance, utilities, and maintenance costs for the building, which do not represent lease components. We elected to not separate lease and non-lease components.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We follow ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Our financial instruments consist of cash, cash equivalents and short-term investments, contract and other receivables, accounts payable, accrued liabilities, and our Term Loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash, cash equivalents, contract and other receivables, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. We believe that the fair value of the Term Loan approximates its carrying value.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses . ASU 2016-13 requires entities to measure all expected credit losses for most financial assets held at the reporting date based on an expected loss model which includes historical experience, current conditions, an d reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help financial statement users better understand significant estimates and judgments used in estimating credit losses. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2022, with early adoption permitted. We are assessing the impact this standard will have on our financial statements and disclosures. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848), which provides guidance around reference rate reform initiatives to identify alternative reference rates that are more observable or transaction-based and less susceptible to manipulation in response to concerns about structural risks of interbank offered rates and the risk of cessation of the London Interbank Offered Rate ("LIBOR"). The amendments in the ASU provide option expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform and apply only if such contracts, hedging relationships and other transactions that reference LIBOR or another reference rate are expected to be discontinued because of reference rate reform. On December 21, 2022, the FASB issued ASU No. 2022-06, Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848,
Fair Value Measurements	Fair Value Measurements We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy: • Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets. • Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. • Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Schedule of Debt Securities	Unrealized Maturity (in years) Amortized cost Gains Losses Estimated fair value As of December 31, 2022 U.S. Treasury securities 1 or less $ 14,944 $ — $ (12) $ 14,932 $ 14,944 $ — $ (12) $ 14,932

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Hierarchy for Assets	The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of December 31, 2022 and 2021 (in thousands): Fair value as of December 31, 2022 Total Level 1 Level 2 Level 3 Cash equivalents and short-term investments: Money market funds $ 21,490 $ 21,490 $ — $ — U.S. Treasury securities 14,932 14,932 — — $ 36,422 $ 36,422 $ — $ — Fair value as of December 31, 2021 Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 57,905 $ 57,905 $ — $ — $ 57,905 $ 57,905 $ — $ —

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table summarizes our major classes of property and equipment (in thousands): December 31, 2022 2021 Laboratory equipment $ 4,359 $ 4,215 Computer equipment and software 470 265 Furniture and fixtures 12 — Leasehold improvements 115 115 4,956 4,595 Less accumulated depreciation and amortization (4,420) (4,314) Property and equipment, net $ 536 $ 281

Intangible Assets, net (Tables)

Intangible Assets, net (Tables)	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	The following table summarizes our major classes of intangible assets (in thousands): December 31, 2022 2021 Patents $ 183 $ 189 Accumulated amortization - Patents (121) (106) Intangibles, net $ 62 $ 83

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	As of December 31, 2022, future principal payments for the Term Loan due under the Loan Agreement are as follows (in thousands): 2023 $ 3,304 2024 1,377 $ 4,681

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Activity of Shares Issued, Converted or Exercised	The following table summarizes preferred stock conversions and warrant exercises (and the related impact on common stock) for the years ended December 31, 2022 and 2021 (in thousands): Class A-1 Convertible Preferred Stock Class A-2 Convertible Preferred Stock Class A-3 Convertible Preferred Stock Class A-4 Convertible Preferred Stock May 2019 Warrants December 2019 Warrants December 2020 Warrants Common Stock Balance at December 31, 2020 257 1,416 259 — 1,389 3,185 2,030 2021 Closing — — — 3,726 — — — 5,892 Conversions/Exercises — (85) — — (111) (125) (181) 352 Balance at December 31, 2021 257 1,331 259 3,726 1,278 3,060 1,849 Conversions/Exercises — — — — — — — — Balance at December 31, 2022 257 1,331 259 3,726 1,278 3,060 1,849
Common Stock Reserved for Future Issuance	The following shares of commo n stock were reserved for future is suance as of December 31, 2022 (in thousands): Class A-1 convertible preferred stock outstanding (as-converted) 257 Class A-2 convertible preferred stock outstanding (as-converted) 1,331 Class A-3 convertible preferred stock outstanding (as-converted) 259 Class A-4 convertible preferred stock outstanding (as-converted) 3,726 Warrants to purchase Common Stock 6,186 Common stock options outstanding 1,372 RSUs outstanding 70 Common stock available for future grant under the 2019 Equity Incentive Plan 394 Common stock available for future grant under the 2021 Inducement Plan 160 2022 Employee Stock Purchase Plan 129 Total common shares reserved for future issuance 13,884
Stock Option Activity	The following table summarizes our stock option and RSU (together "Stock Awards") activity under all equity incentive plans for the year ended December 31, 2022 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value Stock Awards outstanding at December 31, 2021 866 $ 11.72 Granted 570 $ 2.59 Exercised (options) or Vested (RSUs) — $ — Canceled/forfeited/expired (64) $ 20.42 Stock Awards outstanding at December 31, 2022 1,372 $ 7.53 7.1 $ — Vested and exercisable at December 31, 2022 742 $ 8.69 6.3 $ —
Schedule of Restricted Stock Units Activity	The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2022 (shares and aggregate intrinsic value in thousands): Number of Weighted Weighted average remaining contractual term Aggregate intrinsic value RSUs outstanding at December 31, 2021 40 $ 9.50 Granted 85 $ 2.57 Vested (36) $ 9.50 Canceled/forfeited/expired (19) $ 3.97 RSUs outstanding at December 31, 2022 70 $ 2.57 0.8 $ 96
Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan	The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2019 Equity Incentive Plan, 2021 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plans during the periods presented: Year ended December 31, 2022 2021 Stock options Risk-free interest rate 2.0 % 1.0 % Volatility 96.1 % 95.8 % Dividend yield — — Expected term (years) 6.1 6.1 Performance stock options Risk-free interest rate — 1.0 % Volatility — 95.7 % Dividend yield — — Expected term (years) 0 6.1 Employee stock purchase plan shares Risk-free interest rate 1.6 % 0.1 % Volatility 104.7 % 101.2 % Dividend yield — — Expected term (years) 0.5 0.5
Stock-Based Compensation	The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands): Year ended December 31, 2022 2021 Research and development $ 594 $ 821 General and administrative 1,583 2,102 Total $ 2,177 $ 2,923

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense	The following table summarizes the components of our income ta x expense (i n thousands): Year ended December 31, 2022 2021 Current: Federal $ — $ — State 1 1 1 1 Deferred: Federal — — State — — — — Income tax expense $ 1 $ 1
Schedule of Effective Income Tax Rate Reconciliation	The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands): Year ended December 31, 2022 2021 Expected income tax benefit at federal statutory tax rate $ (5,948) $ (5,840) State income taxes, net of federal benefit 1 1 Tax credits (1,850) (1,180) Change in valuation allowance 7,327 6,659 Return to provision adjustments (18) 80 Stock compensation 236 243 Reserve for uncertain tax positions 253 176 Other — (138) Income tax expense $ 1 $ 1
Schedule of Deferred Tax Assets and Liabilities	The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands): December 31, 2022 2021 Deferred tax assets: Net operating loss carryovers $ 90,085 $ 87,877 Research and development and other tax credits 36,963 35,344 Intangibles and property and equipment basis difference 496 607 Section 174 research and development 3,302 — Stock compensation expense 818 587 Lease liability 508 631 Other 597 564 Total deferred tax assets 132,769 125,610 Total deferred tax liabilities (611) (782) Gross deferred tax asset 132,158 124,828 Valuation allowance (132,158) (124,828) Net deferred tax asset $ — $ —
Summary of Income Tax Contingencies	The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands): Year Ended December 31, 2022 2021 Beginning balance of unrecognized tax benefits $ 16,953 $ 17,939 Decrease for prior year tax positions (11,463) (1,174) Increase for current year tax positions 295 188 Total $ 5,785 $ 16,953

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Schedule of Lease Liabilities and ROU Assets	The table below summarizes our lease liabilities and corresponding ROU assets as of December 31, 2022 and 2021 (in thousands): Year Ended December 31, 2022 2021 Assets Operating $ 2,039 $ 2,564 Total ROU assets $ 2,039 $ 2,564 Liabilities Current: Operating $ 649 $ 589 Long-term: Operating 1,768 2,417 Total lease liabilities $ 2,417 $ 3,006
Schedule of Lease Cost	The table below summarizes our lease costs from our statement of operations and cash payments from our statement of cash flows during the years ended December 31, 2022 and 2021 (in thousands): Year Ended December 31, 2022 2021 Lease cost: Operating lease cost $ 690 $ 746 Finance lease cost: Amortization of right-of-use assets — 29 Interest expense on finance lease liabilities — 1 Total finance lease cost $ — $ 30 Cash payment information: Operating cash used for operating leases $ 754 $ 468 Operating cash used for finance leases — 1 Financing cash used for finance leases — 80 Total cash paid for amounts included in the measurement of lease liabilities $ 754 $ 549 The table below summarizes other non-cash information under our operating lease obligations as of December 31, 2022 and 2021 (in thousands, except years and rates): Year Ended December 31, 2022 2021 Supplemental non-cash information: Operating lease liabilities arising from obtaining right-of-use assets $ — $ 3,006 Weighted-average remaining lease term (years) - operating leases 3.3 4.3 Weighted-average discount rate - operating leases 6.0 % 6.0 %
Schedule of Operating Lease, Liability, Maturity	Our future lease payments under our operating lease at December 31, 2022 are as follows (in thousands): Operating Leases 2023 $ 776 2024 800 2025 824 2026 277 2027 — Total operating lease payments $ 2,677 Less: amount representing interest (260) Present value of obligations under operating lease 2,417 Less: current portion (649) Long-term operating lease obligations $ 1,768

The Business, Basis of Presen_3

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Liquidity (Details) $ in Millions		12 Months Ended
	Jun. 24, 2022	Dec. 31, 2022 USD ($)
Accounting Policies [Abstract]
Reverse stock split ratio	0.1
Financing from sale proceeds, debt, and agreement revenues		$ 542.5
Cash, cash equivalents and short-term investments		$ 39.2

The Business, Basis of Presen_4

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2022
Minimum
Property, Plant and Equipment [Line Items]
Useful life, in years	3 years
Maximum
Property, Plant and Equipment [Line Items]
Useful life, in years	5 years

The Business, Basis of Presen_5

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Impairment of Long-Lived Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Asset impairment charges	$ 0	$ 0

The Business, Basis of Presen_6

The Business, Basis of Presentation and Summary of Significant Accounting Policies - Segment Reporting (Details)	12 Months Ended
	Dec. 31, 2022 segment
Accounting Policies [Abstract]
Number of operating segments	1

Net Loss Per Share (Details)

Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	13,200,906	9,255,645

Investments (Details)

Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized cost		$ 14,944,000
Unrealized gains		0
Unrealized losses		(12,000)
Estimated fair value		14,932,000
Unrealized gain (loss)	$ 0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost		14,944,000
Unrealized gains		0
Unrealized losses		(12,000)
Estimated fair value		$ 14,932,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	$ 36,422	$ 57,905
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	21,490	57,905
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	14,932
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	36,422	57,905
Fair Value, Inputs, Level 1 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	21,490	57,905
Fair Value, Inputs, Level 1 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	14,932
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 2 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 2 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Fair Value, Inputs, Level 3 | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	$ 0
Fair Value, Inputs, Level 3 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	$ 0

Collaborations (Details)

Collaborations (Details) - Sanofi - USD ($)	12 Months Ended
	Dec. 31, 2022	Jul. 12, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Development milestone not achievable	$ 25,000,000
United States | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales	10%
United States | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales	20%
Outside of the US | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales	10%
Outside of the US | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales	20%
Development Commercialization And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue creditable against future milestones	$ 1,250,000
Proof-of-Concept Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments	38,800,000
Clinical
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments	25,000,000
Regulatory and Commercialization Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments	$ 130,000,000
Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments		$ 25,000,000

Property and Equipment, net - M

Property and Equipment, net - Major Classes of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 4,956	$ 4,595
Less accumulated depreciation and amortization	(4,420)	(4,314)
Property and equipment, net	536	281
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,359	4,215
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	470	265
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12	0
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 115	$ 115

Property and Equipment, net - N

Property and Equipment, net - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 0.1	$ 0.4

Intangible Assets, net - Major

Intangible Assets, net - Major Classes of Intangible Assets (Details) - Patents - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 183	$ 189
Accumulated amortization - Patents	(121)	(106)
Intangibles, net	$ 62	$ 83

Intangible Assets, net - Narrat

Intangible Assets, net - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible asset amortization (less than)	$ 0.1	$ 0.1
Finite-lived intangible assets, amortization expense, next 12 months (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year two (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year three (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year four (less than $0.1 million)	0.1
Finite-lived intangible assets, amortization expense, year five (less than $0.1 million)	$ 0.1
Remaining amortization period	11 years 8 months 12 days

Debt - Narrative (Details)

Debt - Narrative (Details)			12 Months Ended	32 Months Ended
	Jun. 22, 2016 USD ($)	Jun. 17, 2016 payment	Dec. 31, 2023 USD ($)	May 31, 2020 amendment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Apr. 23, 2020 USD ($)
Debt Instrument [Line Items]
Number of times agreement was amended | amendment				10
Other long-term liabilities					$ 0	$ 1,179,000
Term Loan
Debt Instrument [Line Items]
Proceeds from borrowing under term loan	$ 20,000,000
Stated interest rate, percentage		8.51%
Number of monthly payments | payment		24
Long-term debt					4,681,000
Other long-term liabilities					1,200,000
Deferred finance costs					$ 100,000
Debt instrument effective rate					8.98%
Term Loan | Other Current Liabilities
Debt Instrument [Line Items]
Fee amount					$ 1,300,000
Term Loan | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, percentage		0.44%
Eleventh Amendment
Debt Instrument [Line Items]
Cash collateral for borrowed securities					5,000,000
Fee amount					$ 300,000
Eleventh Amendment | Forecast
Debt Instrument [Line Items]
Unrestricted net cash proceeds amount			$ 20,000,000
PPP Loan
Debt Instrument [Line Items]
Debt instrument, face amount							$ 700,000

Debt - Future Principal Payment

Debt - Future Principal Payments (Details) - Term Loan $ in Thousands	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
2023	$ 3,304
2024	1,377
Long-term debt	$ 4,681

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock and Private Placements (Details) $ / shares in Units, $ in Millions				1 Months Ended
	Nov. 23, 2021 shares	Jan. 22, 2020 shares	Jun. 15, 2019 shares	Jun. 30, 2022	Nov. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	May 31, 2019 $ / shares shares	Dec. 31, 2022 vote shares	Oct. 31, 2022 shares	Dec. 31, 2021 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares outstanding (in shares)									16,840,261		14,597,118
Common stock voting rights per share | vote									1
Number of years for increase of authorized shares		10 years
Common shares reserved for future issuance (in shares)									13,884,000
2021 Closing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)					5,892,335
Sale of stock (usd per share) | $ / shares					$ 3.60
Consideration received on transaction | $					$ 34.6
Convertible preferred stock, shares issued upon conversion (in shares)					1
2021 Closing | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)					222,222
2021 Closing | Class A-4 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares					$ 3.60
Nonvoting convertible preferred stock issued (in shares)					3,725,720
2021 Closing | Class A-4 Convertible Preferred Stock | Directors, Executive Officers and Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of preferred warrants | $					$ 0.8
Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)						2,434,152		973,045
Nonvoting convertible preferred stock issued (in shares)								415,898
Number of securities called by warrants (in shares)						2,030,341
Warrant exercise period								5 years
Private Placement | Preferred Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock (usd per share) | $ / shares								$ 10.80
Convertible preferred stock, shares issued upon conversion (in shares)								1
Private Placement | Class A-1 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities called by warrants (in shares)								1,388,943
Private Placement | Class A-3 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvoting convertible preferred stock issued (in shares)						272,970
Convertible preferred stock, shares issued upon conversion (in shares)						1
Warrant exercise period						5 years
Warrant exercise price (usd per share) | $ / shares						$ 7.46
Milestone Closing | Class A-2 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)							3,288,390
Convertible preferred stock, shares issued upon conversion (in shares)							1
Number of securities called by warrants (in shares)							3,288,390
Warrant exercise period							5 years
Warrant exercise price (usd per share) | $ / shares							$ 6.66
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares available (in shares)		416,686
Yearly authorized increase		5%
Shares available for future grant (in shares)									394,261
Common shares reserved for future issuance (in shares)									1,442,135
Prior Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			0
Common stock available for future grant under the 2021 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)									500,000
Common shares reserved for future issuance (in shares)	200,000								40,000	540,000
Vesting period	4 years
Common stock available for future grant under the 2021 Inducement Plan | First anniversary of the effective date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	25%
Common stock available for future grant under the 2021 Inducement Plan | Remaining 75%, vesting monthly
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for remaining vesting rights	36 months
Employee Stock Purchase Plan Two Thousand Twenty Two | 2022 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price, purchase date				15%
Share-based compensation arrangement by share-based payment award, purchase price of common stock, percent				85%
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)									129,107

Stockholders' Equity - Share Ac

Stockholders' Equity - Share Activity (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)	14,597,118
Common stock, shares outstanding (in shares)	16,840,261	14,597,118
Class A-1 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	256,700	257,000
Conversions of convertible preferred stock (in shares)	0	0
Preferred stock, shares outstanding (in shares)	256,700	256,700
Class A-1 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-2 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	1,330,832	1,416,000
Conversions of convertible preferred stock (in shares)	0	(85,000)
Preferred stock, shares outstanding (in shares)	1,330,832	1,330,832
Class A-2 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-3 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	258,707	259,000
Conversions of convertible preferred stock (in shares)	0	0
Preferred stock, shares outstanding (in shares)	258,707	258,707
Class A-3 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		0
Class A-4 Convertible Preferred Stock
Activity of Shares [Roll Forward]
Preferred stock, shares outstanding (in shares)	3,725,720	0
Conversions of convertible preferred stock (in shares)	0	0
Preferred stock, shares outstanding (in shares)	3,725,720	3,725,720
Class A-4 Convertible Preferred Stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		3,726,000
May 2019 Warrants | May 2019 Warrants
Activity of Shares [Roll Forward]
Warrants outstanding (in shares)	1,278,000	1,389,000
Conversions of convertible preferred stock (in shares)	0	(111,000)
Warrants outstanding (in shares)	1,278,000	1,278,000
May 2019 Warrants | December 2019 Warrants
Activity of Shares [Roll Forward]
Warrants outstanding (in shares)	3,060,000	3,185,000
Conversions of convertible preferred stock (in shares)	0	(125,000)
Warrants outstanding (in shares)	3,060,000	3,060,000
May 2019 Warrants | December 2020 Warrants
Activity of Shares [Roll Forward]
Warrants outstanding (in shares)	1,849,000	2,030,000
Conversions of convertible preferred stock (in shares)	0	(181,000)
Warrants outstanding (in shares)	1,849,000	1,849,000
May 2019 Warrants | 2021 Closing | May 2019 Warrants
Activity of Shares [Roll Forward]
Warrants issued (in shares)		0
May 2019 Warrants | 2021 Closing | December 2019 Warrants
Activity of Shares [Roll Forward]
Warrants issued (in shares)		0
May 2019 Warrants | 2021 Closing | December 2020 Warrants
Activity of Shares [Roll Forward]
Warrants issued (in shares)		0
Common stock
Activity of Shares [Roll Forward]
Common stock, shares outstanding (in shares)
Conversions of convertible preferred stock (in shares)	0	(352,000)
Common stock, shares outstanding (in shares)
Common stock | 2021 Closing
Activity of Shares [Roll Forward]
Shares issued (in shares)		5,892,000

Stockholders' Equity - ATM Offe

Stockholders' Equity - ATM Offerring (Details) - At The Moment - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Aug. 10, 2021	Dec. 12, 2018
Class of Stock [Line Items]
Commission fee rate				3%
Amount eligible to be drawn down under the ATM	$ 45.4		$ 50
Number of shares issued (in shares)	2,205,100	1,601,734
Consideration received on transaction	$ 4.5	$ 20.5
Payments for commissions	$ 0.1	$ 0.8

Stockholders' Equity - Shares R

Stockholders' Equity - Shares Reserved for Future Issuance (Details) shares in Thousands	Dec. 31, 2022 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding (in shares)	1,372
Total common shares reserved for future issuance (in shares)	13,884
Common stock available for future grant under the 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	394
Common stock available for future grant under the 2021 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	160
2022 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant (in shares)	129
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	70
Warrants to purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	6,186
Class A-1 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	257
Class A-2 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	1,331
Class A-3 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	259
Class A-4 Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	3,726

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Number of options
Options outstanding, ending period (in shares)	1,372,000
Stock options
Number of options
Options outstanding, beginning period (in shares)	866,000
Granted (in shares)	570,000
Exercised (options) or Vested (RSUs) (in shares)	0
Canceled/forfeited/expired (in shares)	(64,000)
Options outstanding, ending period (in shares)	1,372,000
Vested and Exercisable (in shares)	742,000
Weighted average exercise price
Options outstanding, beginning period (in dollars per share) | $ / shares	$ 11.72
Granted (in dollars per share) | $ / shares	2.59
Exercised (options) or Vested (RSUs) (in dollars per share) | $ / shares	0
Canceled/forfeited/expired (in dollars per share) | $ / shares	20.42
Options outstanding, ending period (in dollars per share) | $ / shares	7.53
Exercisable (in dollars per share) | $ / shares	$ 8.69
Weighted average remaining contractual term
Options outstanding	7 years 1 month 6 days
Exercisable	6 years 3 months 18 days
Aggregate intrinsic value
Options outstanding | $	$ 0
Exercisable | $	$ 0

Stockholders' Equity - Share _2

Stockholders' Equity - Share Activity and Employee Stock Purchase Plan Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Proceeds from stock options exercised	$ 0	$ 26
Stock options
Class of Stock [Line Items]
Weighted average grant date fair value of employee stock options (in dollars per share)	$ 2	$ 10.26
Issuance of common stock upon exercise of options (in shares)	0
Total intrinsic value of stock options exercised		$ 100
Proceeds from stock options exercised		$ 100
Compensation cost related to non-vested awards not yet recognized	$ 900
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized	1 year 3 months 18 days
RSUs outstanding
Class of Stock [Line Items]
Compensation cost related to non-vested awards not yet recognized	$ 200
Weighted-average recognition period of compensation cost related to non-vested awards not yet recognized	1 year 3 months 18 days

Stockholders' Equity - RSU Acti

Stockholders' Equity - RSU Activity (Details) - RSUs outstanding $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Number of options
RSUs outstanding, beginning balance (in shares) | shares	40
Granted (in shares) | shares	85
Vested (in shares) | shares	(36)
Canceled/forfeited/expired (in shares) | shares	(19)
RSUs outstanding, ending balance (in shares) | shares	70
Weighted average grant date fair value
RSUs outstanding, beginning balance (usd per share) | $ / shares	$ 9.50
Granted (usd per share) | $ / shares	2.57
Vested (usd per share) | $ / shares	9.50
Forfeited (usd per share) | $ / shares	3.97
RSUs outstanding, ending balance (usd per share) | $ / shares	$ 2.57
Weighted average remaining contractual term	9 months 18 days
Aggregate intrinsic value | $	$ 96

Stockholders' Equity - Assumpti

Stockholders' Equity - Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Stock options
Weighted average assumptions
Risk-free interest rate	2%	1%
Volatility	96.10%	95.80%
Dividend yield	0%	0%
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 days
Performance stock options
Weighted average assumptions
Risk-free interest rate	0%	1%
Volatility	0%	95.70%
Dividend yield	0%	0%
Expected term (years)	0 years	6 years 1 month 6 days
2022 Employee Stock Purchase Plan
Weighted average assumptions
Risk-free interest rate	1.60%	0.10%
Volatility	104.70%	101.20%
Dividend yield	0%	0%
Expected term (years)	6 months	6 months

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 2,177	$ 2,923
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	594	821
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 1,583	$ 2,102

Defined Contribution Plan (Deta

Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Defined contribution minimum age requirement of eligible employees	18 years
Maximum 401 (K) plan contribution rates as percentage of employees compensation	50%
Rate of contribution to 401(K) plan as a percentage of employees contribution	50%
Percentage of employee's earnings the company may contribute to the 401(k) plan	6%
Employer contribution to 401(k) plan	$ 0.1	$ 0.1

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Current:
Federal	$ 0	$ 0
State	1	1
Current income tax expense (benefit), total	1	1
Deferred:
Federal	0	0
State	0	0
Deferred income tax expense (benefit), total	0	0
Income tax expense	$ 1	$ 1

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax benefit at federal statutory tax rate	$ (5,948)	$ (5,840)
State income taxes, net of federal benefit	1	1
Tax credits	(1,850)	(1,180)
Change in valuation allowance	7,327	6,659
Return to provision adjustments	(18)	80
Stock compensation	236	243
Reserve for uncertain tax positions	253	176
Other	0	(138)
Income tax expense	$ 1	$ 1

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss carryovers	$ 90,085	$ 87,877
Research and development and other tax credits	36,963	35,344
Intangibles and property and equipment basis difference	496	607
Section 174 research and development	3,302	0
Stock compensation expense	818	587
Lease liability	508	631
Other	597	564
Total deferred tax assets	132,769	125,610
Total deferred tax liabilities	(611)	(782)
Gross deferred tax asset	132,158	124,828
Valuation allowance	(132,158)	(124,828)
Net deferred tax asset	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 132,158,000	$ 124,828,000
Net operating loss carryovers	90,085,000	87,877,000
Unrecognized tax benefits	5,785,000	16,953,000	$ 17,939,000
Unrecognized tax benefits that would impact effective tax rate	5,000,000
Income tax penalties and interest accrued	0	$ 0
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	377,400,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	12,600,000
Internal Revenue Service (IRS) | Orphan Drug Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	21,900,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	146,300,000
California | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	10,100,000
After 2017, No Expiration | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	$ 114,100,000

Income Taxes - Changes in Amoun

Income Taxes - Changes in Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance of unrecognized tax benefits	$ 16,953	$ 17,939
Decrease for prior year tax positions	(11,463)	(1,174)
Increase for current year tax positions	295	188
Total	$ 5,785	$ 16,953

Leases - Narrative (Details)

Leases - Narrative (Details)	Feb. 11, 2021 USD ($) ft² contract	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Apr. 30, 2021 USD ($)	Jul. 01, 2019 USD ($)	Jun. 19, 2019 USD ($) ft²
Lessee, Lease, Description [Line Items]
Liability to be paid		$ 776,000
Operating lease, liability, payments, due year two		800,000
Operating lease, right-of-use asset		2,039,000	$ 2,564,000
Operating lease payments due		2,677,000
Restricted cash		62,000	62,000
Finance lease liability		0	0
Prior Premises
Lessee, Lease, Description [Line Items]
Net rentable area | ft²						8,727
Term of lease						2 years 6 months
Liability to be paid						$ 400,000
Operating lease, liability, payments, due year two						$ 400,000
Initial direct cost liability					$ 800,000
Operating lease, right-of-use asset					600,000
Deferred credit, operating lease liability					$ 200,000
Campus Point Lease
Lessee, Lease, Description [Line Items]
Term of lease	60 months
Initial direct cost liability	$ 3,200,000			$ 100,000
Operating lease, right-of-use asset	3,000,000			100,000
Deferred credit, operating lease liability	$ 200,000
Rented area | ft²	13,438
Operating lease payments due	$ 3,800,000
Restricted cash		$ 62,000	$ 62,000
Nonrefundable lease cost for assignment of lease	$ 60,000
Number of operating lease contracts | contract	3
Deferred cost of liability				$ 200,000

Leases - Lease Asset and Liabil

Leases - Lease Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets
Operating	$ 2,039	$ 2,564
Current:
Operating	649	589
Long-term:
Operating	1,768	2,417
Total lease liabilities	$ 2,417	$ 3,006
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating	Operating

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease cost	$ 690	$ 746
Finance lease cost:
Amortization of right-of-use assets	0	29
Interest expense on finance lease liabilities	0	1
Total finance lease cost	0	30
Cash payment information:
Cash payment information:	754	468
Operating cash used for finance leases	0	1
Financing cash used for finance leases	0	80
Total cash paid for amounts included in the measurement of lease liabilities	754	549
Operating lease liabilities arising from obtaining right-of-use assets	$ 0	$ 3,006
Weighted-average remaining lease term (years) - operating leases	3 years 3 months 18 days	4 years 3 months 18 days
Weighted-average discount rate - operating leases	6%	6%

Leases - Future Lease Payments

Leases - Future Lease Payments Under Operating and Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Operating Leases
2023	$ 776
2024	800
2025	824
2026	277
2027	0
Total operating lease payments	2,677
Less: amount representing interest	(260)
Total lease liabilities	2,417	$ 3,006
Less: current portion	(649)	(589)
Long-term operating lease obligations	$ 1,768	$ 2,417