Regulus Therapeutics (RGLS) 10-Q 9 May 24 2024 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2024	May 03, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		65,465,876
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001505512
Current Fiscal Year End Date	--12-31

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 29,586	$ 23,767
Short-term investments	67,968	0
Restricted cash	62	62
Prepaid materials, net	3,010	3,010
Prepaid expenses and other current assets	821	1,340
Total current assets	101,447	28,179
Long-term investments	10,171	0
Property and equipment, net	1,086	1,061
Intangibles, net	30	33
Right of use asset	1,330	1,477
Other assets	74	0
Total assets	114,138	30,750
Current liabilities:
Accounts payable	406	204
Accrued liabilities	604	691
Accrued research and development expenses	700	921
Accrued compensation	1,185	2,979
Term loan, less debt issuance costs	540	1,334
Other current liabilities	2,247	2,379
Total current liabilities	5,682	8,508
Lease liability, less current portion	868	1,055
Total liabilities	6,550	9,563
Commitments and Contingencies
Stockholders’ equity:
Common stock, $0.001 par value; 300,000,000 shares authorized at March 31, 2024 and December 31, 2023; 65,465,251 and 20,222,672 shares issued and outstanding at March 31, 2024 (unaudited) and December 31, 2023, respectively	65	20
Additional paid-in capital	629,245	534,375
Accumulated other comprehensive loss	(45)	0
Accumulated deficit	(521,682)	(513,213)
Total stockholders’ equity	107,588	21,187
Total liabilities and stockholders’ equity	114,138	30,750
Class A-1 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	0	0
Class A-2 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	1	1
Class A-3 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	0	0
Class A-4 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	4	4
Class A-5 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	0	0
Class A-6 Convertible Preferred Stock
Stockholders’ equity:
Convertible preferred stock	$ 0	$ 0

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Common stock par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	65,465,251	20,222,672
Common stock, shares outstanding (in shares)	65,465,251	20,222,672
Class A-1 Convertible Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	256,700	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 usd 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 usd 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 usd 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
Class A-5 Convertible Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	140,827	140,827
Preferred stock, shares issued (in shares)	140,827	140,827
Preferred stock, shares outstanding (in shares)	140,827	140,827
Class A-6 Convertible Preferred Stock
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	173,915	0
Preferred stock, shares issued (in shares)	173,915	0
Preferred stock, shares outstanding (in shares)	173,915	0

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 6,040	$ 4,925
General and administrative	2,786	2,444
Total operating expenses	8,826	7,369
Loss from operations	(8,826)	(7,369)
Other income (expense):
Interest and other income	438	415
Interest and other expense	(81)	(185)
Loss before income taxes	(8,469)	(7,139)
Net loss and comprehensive loss	(8,469)	(7,139)
Other comprehensive loss:
Unrealized (loss) gain on investments, net	(45)	12
Comprehensive loss	$ (8,514)	$ (7,127)
Net loss per share, basic (in usd per share)	$ (0.29)	$ (0.42)
Net loss per share, diluted (in usd per share)	$ (0.29)	$ (0.42)
Weighted average shares used to compute basic net loss per share (in shares)	28,746,802	16,844,243
Weighted average shares used to compute diluted net loss per share (in shares)	28,746,802	16,844,243

CONDENSED STATEMENTS OF CHANGES

CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible preferred stock Convertible preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Beginning balance, preferred stock shares (in shares) at Dec. 31, 2022		5,571,959
Beginning balance, common stock shares (in shares) at Dec. 31, 2022			16,840,261
Beginning balance at Dec. 31, 2022	$ 33,291	$ 5	$ 17	$ 516,457	$ (12)	$ (483,176)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under Employee Stock Purchase Plan (in shares)			19,472
Issuance of common stock under Employee Stock Purchase Plan	21			21
Stock-based compensation expense	410			410
Unrealized (loss) gain on investments	12				12
Net loss	(7,139)					(7,139)
Ending balance, preferred stock shares (in shares) at Mar. 31, 2023		5,571,959
Ending balance, common stock shares (in shares) at Mar. 31, 2023			16,859,733
Ending balance at Mar. 31, 2023	$ 26,595	$ 5	$ 17	516,888	0	(490,315)
Beginning balance, preferred stock shares (in shares) at Dec. 31, 2023		5,712,786
Beginning balance, common stock shares (in shares) at Dec. 31, 2023	20,222,672		20,222,672
Beginning balance at Dec. 31, 2023	$ 21,187	$ 5	$ 20	534,375	0	(513,213)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and preferred stock from private placement, net of offering costs (in shares)		173,915	45,108,667
Issuance of common stock and preferred stock from private placement, net of offering costs	93,897		$ 45	93,852
Issuance of common stock through upon vesting of restricted stock units (in shares)			105,000
Issuance of common stock through upon vesting of restricted stock units	0
Issuance of common stock under Employee Stock Purchase Plan (in shares)			27,612
Issuance of common stock under Employee Stock Purchase Plan	31			31
Issuance of common stock upon exercise of common stock options (in shares)			1,300
Issuance of common stock upon exercise of common stock options	2			2
Stock-based compensation expense	985			985
Unrealized (loss) gain on investments	(45)				(45)
Net loss	$ (8,469)					(8,469)
Ending balance, preferred stock shares (in shares) at Mar. 31, 2024		5,886,701
Ending balance, common stock shares (in shares) at Mar. 31, 2024	65,465,251		65,465,251
Ending balance at Mar. 31, 2024	$ 107,588	$ 5	$ 65	$ 629,245	$ (45)	$ (521,682)

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities
Net loss	$ (8,469)	$ (7,139)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	81	48
Stock-based compensation	985	410
Amortization of premiums and accretion of discounts on investments, net	130	(56)
Other	32	31
Change in operating assets and liabilities:
Contracts and other receivables	0	(4)
Prepaid expenses and other assets	445	669
Accounts payable	202	406
Accrued liabilities	39	(290)
Accrued research and development expenses	(221)	(714)
Accrued compensation	(1,794)	(1,183)
Operating lease right-of-use assets and liabilities, net	(23)	(18)
Other liabilities	(149)	(274)
Net cash used in operating activities	(8,742)	(8,114)
Investing activities
Purchases of investments	(78,315)	0
Maturities of investments	0	15,000
Purchases of property and equipment	(229)	(1)
Net cash (used in) provided by investing activities	(78,544)	14,999
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	93,897	0
Proceeds from issuance of common stock, net	32	21
Proceeds from exercise of common stock options	2	0
Principal payments on term loan	(826)	(826)
Net cash provided by (used in) financing activities	93,105	(805)
Net increase in cash and cash equivalents	5,819	6,080
Cash and cash equivalents at beginning of period	23,829	24,290
Cash and cash equivalents at end of period	29,648	30,370
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	29,586	30,308
Restricted cash	62	62
Total cash, cash equivalents and restricted cash	29,648	30,370
Supplemental disclosure of cash flow information
Interest paid	$ (45)	$ (148)

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 8 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2023, from which the balance sheet information herein was derived. Liquidity Through March 31, 2024, we have principally been financed through net 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 $651.7 million. As of March 31, 2024, we had approximately $107.7 million of cash, cash equivalents and investments. Based on our operating plans, we believe our cash and cash equivalents will be sufficient to fund our planned operations for at least 12 months following the issuance of these financial statements. As of March 31, 2024, w e 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 raise additional capital when needed, 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 condensed 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 ("RSUs") by determining the fair value of each RSU 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, contract research organizations ("CROs") and contract manufacturing organizations ("CMOs") 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. Recent Accounting Pronouncements 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	3 Months Ended
	Mar. 31, 2024
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, RSUs, warrants and convertible preferred stock outstanding. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted net loss per share.

Investments

Investments	3 Months Ended
	Mar. 31, 2024
Debt Securities, Available-for-Sale [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 Amortized cost Gains Losses Estimated fair value As of March 31, 2024 Short-Term U.S. Treasury securities Less than 1 year $ 68,005 $ — $ (37) $ 67,968 Long-Term U.S. Treasury securities 1 to 2 years 10,179 — (8) 10,171 $ 78,184 $ — $ (45) $ 78,139 As of December 31, 2023, our cash balance was comprised entirely of cash and cash equivalents (money market funds) and there was no unrealized gain or loss.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 and December 31, 2023 (in thousands): Fair value as of March 31, 2024 Total Level 1 Level 2 Level 3 Cash equivalents and investments: Money market funds $ 27,542 $ 27,542 $ — $ — U.S. Treasury securities 78,139 78,139 — — $ 105,681 $ 105,681 $ — $ — Fair value as of December 31, 2023 Total Level 1 Level 2 Level 3 Cash equivalents and investments: Money market funds $ 23,084 $ 23,084 $ — $ — $ 23,084 $ 23,084 $ — $ —

Debt

Debt	3 Months Ended
	Mar. 31, 2024
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 bore 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%. In June 2023, we entered into an amendment to the Loan Agreement (the “Rate Amendment”) pursuant to which, effective July 1, 2023, the Term Loan bore interest at a floating per annum rate equal to the greater of (a) 8.95% and (b) the sum of (i) the 1-month CME Term Secured Overnight Financing Rate ("SOFR") reference rate on the last business day of the month that immediately preceded the month in which the interest accrued, (ii) 0.10% and (iii) 8.51%. 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 December 31, 2022. The Eleventh Amendment also provided that we were 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. As of March 31, 2024 , $0.6 million o f principal was outstanding under the Term Loan. An additional $1.3 million was also payable at the conclusion of the Term Loan (the related $1.3 million accrued l iability balance is presented in other current liabilities on our balance sheet at March 31, 2024). We had less than $0.1 million of debt issuance costs outstanding as of March 31, 2024, which are being accreted to interest expense over the life of the Term 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. All amounts that remained payable under the Term Loan as of March 31, 2024 were paid as of May 1, 2024.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock As of March 31, 2024, the re were 65,465,251 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 the Company's 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 Plan s. 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 1st 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 the Company's board of directors. In addition, on June 13, 2023, our stockholders approved an amendment to the 2019 Plan, which authorized an additional 5,000,000 shares of common stock available for issuance thereunder. As of March 31, 2024, 471,540 shares of common stock were available for new equity award grants under the 2019 Plan and 8,073,002 shares of common stock were reserved for issuance pursuant to equity awards outstanding under the 2019 Plan as of March 31, 2024. 2021 Inducement Plan On November 23, 2021, the Company's 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 5635(c)(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, and subsequently increased again in December 2023 to 1,030,000 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 March 31, 2024, 500,000 shares of common stock were reserved for future issuance under the Inducement Plan and 530,000 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 a 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 March 31 2024, a maximu m of 159,812 shares of our common stock were reserved for future issuance and have been authorized for purchase under the 2022 Purchase Plan . 2024 Private Placement of Common Stock and Non-Voting Preferred Stock On March 11, 2024, we entered into a Securities Purchase Agreement (the “March 2024 SPA”) with certain institutional and other accredited investors (the “2024 Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock and shares of our newly designated non-voting Class A-6 convertible preferred stock in a private placement transaction (the "2024 PIPE"). At the closing under the March 2024 SPA that occurred on March 14, 2024 (the “2024 Closing”), we sold and issued to the 2024 Purchasers (i) 45,108,667 shares of common stock at a purchase price of $1.60 per share, and (ii) 173,915 shares of non-voting Class A-6 convertible preferred stock, in lieu of shares of common stock, at a price of $160.00 per share. The Company received net proceeds of approximately $93.9 million in the 2024 PIPE after deducting placement agent and financial advisor fees and other expenses. Each share of non-voting Class A-6 convertible preferred stock is convertible into 100 shares of common stock, subject to certain beneficial ownership conversion limitations. Stelios Papadopoulos, Ph.D., Chairman of the Company's board of directors, was a 2024 Purchaser under the March 2024 SPA and purchased 250,000 shares of common stock for $0.4 million. We evaluated the non-voting Class A-6 convertible preferred stock sold in the 2024 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. 2023 Private Placement of Common Stock and Non-Voting Preferred Stock On April 13, 2023, we entered into a Securities Purchase Agreement (the “April 2023 SPA”) with certain institutional and other accredited investors (the “2023 Purchasers”), pursuant to which we agreed to sell and issue shares of our common stock and shares of our newly designated non-voting Class A-5 convertible preferred stock in a private placement transaction (the "2023 PIPE"). At the closing under the April 2023 SPA that occurred on April 13, 2023 (the “2023 Closing”), we sold and issued to the 2023 Purchasers (i) 2,615,536 shares of common stock at a purchase price of $0.9001 per share, and (ii) 140,827 shares of non-voting Class A-5 convertible preferred stock, in lieu of shares of common stock, at a price of $90.01 per share. Total gross proceeds from the 2023 Closing were approximately $15.0 million. Each share of non-voting Class A-5 convertible preferred stock is convertible into 100 shares of common stock, subject to certain beneficial ownership conversion limitations. Stelios Papadopoulos, Ph.D., Chairman of the Company's board of directors, was a 2023 Purchaser under the April 2023 SPA and purchased 222,198 shares of common stock for $0.2 million. We evaluated the non-voting Class A-5 convertible preferred stock sold in the 2023 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 On May 7, 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 were exercisable for a period of five years following the date of issuance and had 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 were also exercisable on a net exercise "cashless" basis. On December 24, 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 are 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 also exercisable on a net exercise “cashless” basis. On December 4, 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 also exercisable on a net exercise "cashless" basis. On November 30, 2021, we sold and issued (i) 5,892,335 shares of common stock and (ii) 3,725,720 shares of non-voting Class A-4 convertible preferred stock. 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. 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. No shares were sold under the ATM Offering during the three months ended March 31, 2024 or 2023. Shares Reserved for Future Issuance The following shares of common stock were reserved for future issuance as of March 31, 2024 (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 Class A-5 convertible preferred stock outstanding (as-converted) 14,083 Class A-6 convertible preferred stock outstanding (as-converted) 17,392 Warrants to purchase Common Stock 6,186 Common stock options outstanding 7,175 RSUs outstanding 1,428 Common stock available for future grant under the 2019 Equity Incentive Plan 472 Common stock available for future grant under the 2021 Inducement Plan 500 2022 Employee Stock Purchase Plan 160 Total common shares reserved for future issuance 52,969 The following table summarizes our stock option, performance stock awards and RSU (together, "Stock Awards") activity under all equity incentive plans for the three months ended March 31, 2024 (shares in thousands): Number of Weighted Number of Weighted average grant date fair value Stock Awards outstanding at December 31, 2023 6,188 $ 2.58 1,161 $ 1.38 Granted 1,002 $ 1.30 372 $ 1.30 Exercised (options) or Vested (RSUs) (1) $ 1.36 (105) $ 1.48 Canceled/forfeited/expired (14) $ 1.48 — $ — Stock Awards outstanding at March 31, 2024 7,175 $ 2.41 1,428 $ 1.35 Stock-Based Compensation 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: Three months ended 2024 2023 Stock options Risk-free interest rate 3.9 % 3.6 % Volatility 95.5 % 96.5 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 5.5 % 4.0 % Volatility 98.4 % 104.4 % Dividend yield — — Expected term (years) 0.5 0.5 The following table summarizes the allocation of our stock-based compensation expense for all Stock Awards during the periods presented (in thousands): Three months ended 2024 2023 Research and development $ 410 $ 173 General and administrative 575 237 Total $ 985 $ 410

Collaborations

Collaborations	3 Months Ended
	Mar. 31, 2024
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.

Leases

Leases	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Leases	Leases 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 $61,591 in a specially designated bank account, which we recorded as restricted cash on our balance sheet at March 31, 2024 and December 31, 2023. Our future lease payments under operating leases at March 31, 2024 are as follows (in thousands): Operating Leases Remaining 2024 604 2025 824 2026 277 Total operating lease payments $ 1,705 Less: amount representing interest (107) Present value of obligations under operating leases 1,598 Less: current portion (730) Long-term operating lease obligations $ 868

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and the instructions to Form 10-Q and Article 8 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed financial statements should be read in conjunction with the audited financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2023, from which the balance sheet information herein was derived.
Use of Estimates	Use of Estimates
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 ("RSUs") by determining the fair value of each RSU 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, contract research organizations ("CROs") and contract manufacturing organizations ("CMOs") 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements 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 Measurement	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)	3 Months Ended
	Mar. 31, 2024
Debt Securities, Available-for-Sale [Abstract]
Schedule of Debt Securities	Unrealized Maturity Amortized cost Gains Losses Estimated fair value As of March 31, 2024 Short-Term U.S. Treasury securities Less than 1 year $ 68,005 $ — $ (37) $ 67,968 Long-Term U.S. Treasury securities 1 to 2 years 10,179 — (8) 10,171 $ 78,184 $ — $ (45) $ 78,139

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023 (in thousands): Fair value as of March 31, 2024 Total Level 1 Level 2 Level 3 Cash equivalents and investments: Money market funds $ 27,542 $ 27,542 $ — $ — U.S. Treasury securities 78,139 78,139 — — $ 105,681 $ 105,681 $ — $ — Fair value as of December 31, 2023 Total Level 1 Level 2 Level 3 Cash equivalents and investments: Money market funds $ 23,084 $ 23,084 $ — $ — $ 23,084 $ 23,084 $ — $ —

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of March 31, 2024 (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 Class A-5 convertible preferred stock outstanding (as-converted) 14,083 Class A-6 convertible preferred stock outstanding (as-converted) 17,392 Warrants to purchase Common Stock 6,186 Common stock options outstanding 7,175 RSUs outstanding 1,428 Common stock available for future grant under the 2019 Equity Incentive Plan 472 Common stock available for future grant under the 2021 Inducement Plan 500 2022 Employee Stock Purchase Plan 160 Total common shares reserved for future issuance 52,969
Schedule of Stock Option Activity RSU	The following table summarizes our stock option, performance stock awards and RSU (together, "Stock Awards") activity under all equity incentive plans for the three months ended March 31, 2024 (shares in thousands): Number of Weighted Number of Weighted average grant date fair value Stock Awards outstanding at December 31, 2023 6,188 $ 2.58 1,161 $ 1.38 Granted 1,002 $ 1.30 372 $ 1.30 Exercised (options) or Vested (RSUs) (1) $ 1.36 (105) $ 1.48 Canceled/forfeited/expired (14) $ 1.48 — $ — Stock Awards outstanding at March 31, 2024 7,175 $ 2.41 1,428 $ 1.35
Schedule of 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: Three months ended 2024 2023 Stock options Risk-free interest rate 3.9 % 3.6 % Volatility 95.5 % 96.5 % Dividend yield — — Expected term (years) 6.1 6.1 Employee stock purchase plan shares Risk-free interest rate 5.5 % 4.0 % Volatility 98.4 % 104.4 % Dividend yield — — Expected term (years) 0.5 0.5
Schedule of 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): Three months ended 2024 2023 Research and development $ 410 $ 173 General and administrative 575 237 Total $ 985 $ 410

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Schedule of Operating Lease, Liability, Maturity	Our future lease payments under operating leases at March 31, 2024 are as follows (in thousands): Operating Leases Remaining 2024 604 2025 824 2026 277 Total operating lease payments $ 1,705 Less: amount representing interest (107) Present value of obligations under operating leases 1,598 Less: current portion (730) Long-term operating lease obligations $ 868

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Accounting Policies [Abstract]
Financing from sale proceeds, debt, and agreement revenues	$ 651.7
Cash, cash equivalents and short-term investments	$ 107.7

Net Loss Per Share (Details)

Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	29,509,969	14,020,658

Investments (Details)

Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Mar. 31, 2024
Long-Term Investments [Abstract]
Amortized cost		$ 78,184,000
Unrealized gains		0
Unrealized losses		(45,000)
Estimated fair value		78,139,000
Unrealized gain (loss)	$ 0
U.S. Treasury securities
Short-Term Investments [Abstract]
Amortized cost		68,005,000
Unrealized gains		0
Unrealized losses		(37,000)
Estimated fair value		67,968,000
Long-Term Investments [Abstract]
Amortized cost		10,179,000
Unrealized gains		0
Unrealized losses		(8,000)
Estimated fair value		$ 10,171,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 105,681	$ 23,084
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	105,681	23,084
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	27,542	23,084
Money market funds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	27,542	23,084
Money market funds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Money market funds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	$ 0
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	78,139
U.S. Treasury securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	78,139
U.S. Treasury securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0
U.S. Treasury securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 0

Debt (Details)

Debt (Details) $ in Millions			3 Months Ended	32 Months Ended
	Jun. 22, 2016 USD ($)	Jun. 17, 2016 payment	Mar. 31, 2024 USD ($)	May 31, 2020 amendment
Debt Instrument [Line Items]
Number of times agreement was amended | amendment				10
Term Loan
Debt Instrument [Line Items]
Proceeds from borrowing under term loan	$ 20
Stated interest rate, percentage		8.51%
Number of monthly payments | payment		24
Debt fee			$ 1.3
Long-term debt			0.6
Other long-term liabilities			1.3
Debt issuance costs			$ 0.1
Debt instrument effective rate (as a percent)			8.98%
Term Loan | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, percentage		0.44%
Term Loan | Secured Overnight Financing Rate Sofr Over night Index Swap Rate | Option One
Debt Instrument [Line Items]
Basis spread on variable rate, percentage			8.95%
Term Loan | Secured Overnight Financing Rate Sofr Over night Index Swap Rate | Option Two, First Contributor
Debt Instrument [Line Items]
Basis spread on variable rate, percentage			0.10%
Term Loan | Secured Overnight Financing Rate Sofr Over night Index Swap Rate | Option Two, Second Contributor
Debt Instrument [Line Items]
Basis spread on variable rate, percentage			8.51%
Eleventh Amendment
Debt Instrument [Line Items]
Cash collateral for borrowed securities			$ 5
Debt fee			$ 0.3

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) $ / shares in Units, $ in Millions

1 Months Ended

3 Months Ended

Mar. 11, 2024 USD ($) $ / shares shares

Jun. 13, 2023 shares

Apr. 13, 2023 USD ($) $ / shares shares

Jun. 24, 2022

Nov. 23, 2021 shares

Dec. 04, 2020 $ / shares shares

Jan. 22, 2020 shares

Dec. 24, 2019 $ / shares shares

May 07, 2019 $ / shares shares

Jun. 30, 2022

Nov. 30, 2021 shares

Mar. 31, 2024 vote shares

Mar. 31, 2023 shares

Dec. 31, 2023 shares

Dec. 31, 2022 shares

Oct. 31, 2022 shares

Subsidiary, Sale of Stock [Line Items]

Common stock, shares outstanding (in shares)

65,465,251

20,222,672

Common stock voting rights votes | vote

1

Reverse stock split ratio

0.1

Total common shares reserved for future issuance (in shares)

52,969,000

Common stock

Subsidiary, Sale of Stock [Line Items]

Common stock, shares outstanding (in shares)

65,465,251

16,859,733

20,222,672

16,840,261

2024Closing

Subsidiary, Sale of Stock [Line Items]

Consideration received | $

$ 93.9

2024Closing | Common stock

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

45,108,667

Sale of stock price (in usd per share) | $ / shares

$ 1.60

Shares issued upon conversion (in shares)

100

2023 Closing

Subsidiary, Sale of Stock [Line Items]

Consideration received | $

$ 15

2023 Closing | Common stock

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

2,615,536

Sale of stock price (in usd per share) | $ / shares

$ 0.9001

Shares issued upon conversion (in shares)

100

Private Placement

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

2,434,152

973,045

5,892,335

Nonvoting convertible preferred stock issued (in shares)

415,898

Warrants callable (in shares)

2,030,341

Class of warrant

5 years

ATM Offering

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

0

0

Class A-5 Convertible Preferred Stock | 2024Closing

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

173,915

Sale of stock price (in usd per share) | $ / shares

$ 160

Class A-5 Convertible Preferred Stock | 2023 Closing

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

140,827

Sale of stock price (in usd per share) | $ / shares

$ 90.01

Class A-1 Convertible Preferred Stock | Private Placement

Subsidiary, Sale of Stock [Line Items]

Warrants callable (in shares)

1,388,943

Preferred Class A | Private Placement

Subsidiary, Sale of Stock [Line Items]

Sale of stock price (in usd per share) | $ / shares

$ 10.80

Shares issued upon conversion (in shares)

1

Class A-2 Convertible Preferred Stock | 2019 PIPE Milestone Closing warrants

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

3,288,390

Shares issued upon conversion (in shares)

1

Warrants callable (in shares)

3,288,390

Class of warrant

5 years

Warrant exercise price (in usd per share) | $ / shares

$ 6.66

Class A-3 Convertible Preferred Stock | Private Placement

Subsidiary, Sale of Stock [Line Items]

Shares issued upon conversion (in shares)

1

1

Nonvoting convertible preferred stock issued (in shares)

272,970

3,725,720

Class of warrant

5 years

Warrant exercise price (in usd per share) | $ / shares

$ 7.46

Director | 2024Closing

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

250,000

Director | 2023 Closing

Subsidiary, Sale of Stock [Line Items]

Share sold (in shares)

222,198

Director | Class A-4 Convertible Preferred Stock | 2024Closing

Subsidiary, Sale of Stock [Line Items]

Consideration received | $

$ 0.4

Director | Class A-4 Convertible Preferred Stock | 2023 Closing

Subsidiary, Sale of Stock [Line Items]

Consideration received | $

$ 0.2

2019 Plan

Subsidiary, Sale of Stock [Line Items]

Number of additional shares authorized (in shares)

5,000,000

416,686

Number of years for increase of authorized shares

10 years

Number of additional shares authorized yearly increase (as a percent)

5%

Common stock available for future grant (in shares)

471,540

Total common shares reserved for future issuance (in shares)

8,073,002

Inducement Plan

Subsidiary, Sale of Stock [Line Items]

Common stock available for future grant (in shares)

500,000

Total common shares reserved for future issuance (in shares)

200,000

530,000

1,030,000

540,000

Vesting period

4 years

Inducement Plan | Share-based Payment Arrangement, Tranche One

Subsidiary, Sale of Stock [Line Items]

Award vesting percentage

25%

Inducement Plan | Share-based Payment Arrangement, Tranche Two

Subsidiary, Sale of Stock [Line Items]

Vesting period for remaining vesting rights

36 months

2022 ESPP | 2022 Employee Stock Purchase Plan

Subsidiary, Sale of Stock [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)

159,812

Stockholders' Equity (ATM Offer

Stockholders' Equity (ATM Offering) (Details) - ATM Offering - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 12, 2018
Class of Stock [Line Items]
Commission fee rate (as a percent)			3%
Share sold (in shares)	0	0

Stockholders' Equity (Common St

Stockholders' Equity (Common Stock Reserved for Future Issuance) (Details) shares in Thousands	Mar. 31, 2024 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options outstanding (in shares)	7,175
Total common shares reserved for future issuance (in shares)	52,969
Common stock available for future grant under the 2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant (in shares)	472
Common stock available for future grant under the 2021 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant (in shares)	500
2022 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for future grant (in shares)	160
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	1,428
Warrants to purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants to purchase common stock (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 outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	3,726
Class A-5 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	14,083
Class A-6 convertible preferred stock outstanding (as-converted)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (in shares)	17,392

Stockholders' Equity (Stock Opt

Stockholders' Equity (Stock Option and RSU Activity) (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Number of options
Ending balance (in shares)	7,175
Stock options
Number of options
Beginning balance (in shares)	6,188
Granted (in shares)	1,002
Exercised (options) or Vested (RSUs) (in shares)	(1)
Canceled/forfeited/expired (in shares)	(14)
Ending balance (in shares)	7,175
Weighted average exercise price
Beginning balance (in usd per share) | $ / shares	$ 2.58
Granted (in usd per share) | $ / shares	1.30
Exercised (options) or Vested (RSUs) (in usd per share) | $ / shares	1.36
Canceled/forfeited/expired (in usd per share) | $ / shares	1.48
Ending balance (in usd per share) | $ / shares	$ 2.41
Restricted Stock Units (RSUs)
Number of RSUs
Beginning balance (in shares)	1,161
Shares granted (in shares)	372
Exercised (options) or Vested (RSUs) (in shares)	(105)
Canceled/forfeited/expired (in shares)	0
Ending balance (in shares)	1,428
Weighted average grant date fair value
Beginning balance (in usd per share) | $ / shares	$ 1.38
Granted (in usd per share) | $ / shares	1.30
Exercised (options) or Vested (RSUs) (in usd per share) | $ / shares	1.48
Canceled/forfeited/expired (in usd per share) | $ / shares	0
Ending balance (in usd per share) | $ / shares	$ 1.35

Stockholders' Equity (Assumptio

Stockholders' Equity (Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan) (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Stock options
Weighted average assumptions
Risk-free interest rate	3.90%	3.60%
Volatility	95.50%	96.50%
Dividend yield	0%	0%
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 days
Employee stock purchase plan shares
Weighted average assumptions
Risk-free interest rate	5.50%	4%
Volatility	98.40%	104.40%
Dividend yield	0%	0%
Expected term (years)	6 months	6 months

Stockholders' Equity (Stock-Bas

Stockholders' Equity (Stock-Based Compensation Expense Allocation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 985	$ 410
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	410	173
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expenses	$ 575	$ 237

Collaborations (Details)

Collaborations (Details)	Jan. 06, 2023
Sanofi
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Period for termination	30 days

Leases (Narrative) (Details)

Leases (Narrative) (Details)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Feb. 11, 2021 USD ($) ft²
Lessee, Lease, Description [Line Items]
Total operating lease payments	$ 1,705,000
Restricted cash	62,000	$ 62,000	$ 62,000
Campus Point Lease
Lessee, Lease, Description [Line Items]
Rented area | ft²				13,438
Term of contract				60 months
Total operating lease payments				$ 3,800,000
Restricted cash	$ 61,591	$ 61,591

Leases (Operating and Finance M

Leases (Operating and Finance Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Remaining 2024	$ 604
2025	824
2026	277
Total operating lease payments	1,705
Less: amount representing interest	(107)
Present value of obligations under operating leases	1,598
Less: current portion	(730)
Long-term operating lease obligations	$ 868	$ 1,055