Plus Therapeutics (PSTV) 10-Q 31 Oct 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Oct. 25, 2023
Cover [Abstract]
Entity Registrant Name	PLUS THERAPEUTICS, INC.
Entity Central Index Key	0001095981
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		4,522,656
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Trading Symbol	PSTV
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Entity File Number	001-34375
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0827593
Entity Address, Address Line One	4200 MARATHON BLVD
Entity Address, Address Line Two	SUITE 200
Entity Address, City or Town	AUSTIN
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78756
City Area Code	737
Local Phone Number	255-7194

CONDENSED BALANCE SHEETS (UNAUD

CONDENSED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 11,006	$ 18,120
Grant receivable	91
Other current assets	487	3,697
Total current assets	11,584	21,817
Property and equipment, net	1,009	1,324
Operating lease right-of-use assets	232	248
Goodwill	372	372
Intangible assets, net	49	94
Other assets	32	12
Total assets	13,278	23,867
Current liabilities:
Accounts payable and accrued expenses	6,073	10,134
Operating lease liability	117	110
Term loan obligation	4,348	1,608
Total current liabilities	10,538	11,852
Term loan obligation		3,786
Noncurrent operating lease liability	118	141
Deferred grant liability		1,643
Total liabilities	10,656	17,422
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,952 shares issued and outstanding at June 30, 2023 and December 31, 2022, respectively
Common stock, $0.001 par value; 100,000,000 shares authorized; 4,522,656 and 2,240,092 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	5	2
Additional paid-in capital	479,308	473,628
Accumulated deficit	(476,691)	(467,185)
Total stockholders’ equity	2,622	6,445
Total liabilities and stockholders’ equity	$ 13,278	$ 23,867

CONDENSED BALANCE SHEETS (UNA_2

CONDENSED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Stockholders’ equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	1,952	1,952
Preferred stock, shares outstanding (in shares)	1,952	1,952
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	4,522,656	2,240,092
Common stock, shares outstanding (in shares)	4,522,656	2,240,092

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 2,493	$ 2,945	$ 6,896	$ 7,560
General and administrative	1,998	2,222	6,165	6,653
Total operating expenses	4,491	5,167	13,061	14,213
Loss from operations	(3,251)	(5,094)	(9,461)	(14,140)
Other income (expense):
Interest income	119	48	290	74
Interest expense	(87)	(173)	(333)	(552)
Loss on disposal of property and equipment			(2)
Change in fair value of liability instruments				1
Total other income (expense)	32	(125)	(45)	(477)
Net loss	$ (3,219)	$ (5,219)	$ (9,506)	$ (14,617)
Net loss per share, basic	$ (1)	$ (2.85)	$ (3.54)	$ (9.22)
Net loss per share, diluted	$ (1)	$ (2.85)	$ (3.54)	$ (9.22)
Basic weighted average shares used in calculating net loss per share attributable to common stockholders	3,225,351	1,829,444	2,688,232	1,585,946
Diluted weighted average shares used in calculating net loss per share attributable to common stockholders	3,225,351	1,829,444	2,688,232	1,585,946
Grant [Member]
Revenue	$ 1,240	$ 73	$ 3,600	$ 73

CONDENSED STATEMENTS OF STOCKHO

CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Series F Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series F Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series F Preferred Stock [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2021	$ 10,836					$ 1	$ 457,745		$ (446,910)
Balance (in shares) at Dec. 31, 2021		1,952				1,034,002
Stock-based compensation	180						180
Issue and sale of stock, net	7,742						7,742
Issue and sale of share						445,840
Net loss	(4,116)								(4,116)
Balance at Mar. 31, 2022	14,642					$ 1	465,667		(451,026)
Balance (in shares) at Mar. 31, 2022		1,952				1,479,842
Balance at Dec. 31, 2021	10,836					$ 1	457,745		(446,910)
Balance (in shares) at Dec. 31, 2021		1,952				1,034,002
Net loss	(14,617)
Balance at Sep. 30, 2022	11,404					$ 2	472,929		(461,527)
Balance (in shares) at Sep. 30, 2022		1,952				2,171,333
Balance at Dec. 31, 2021	10,836					$ 1	457,745		(446,910)
Balance (in shares) at Dec. 31, 2021		1,952				1,034,002
Balance at Dec. 31, 2022	6,445					$ 2	473,628		(467,185)
Balance (in shares) at Dec. 31, 2022		1,952				2,240,092
Balance at Mar. 31, 2022	14,642					$ 1	465,667		(451,026)
Balance (in shares) at Mar. 31, 2022		1,952				1,479,842
Stock-based compensation	167						167
Issue and sale of stock, net	152						152
Issue and sale of share						18,070
Net loss	(5,282)								(5,282)
Balance at Jun. 30, 2022	9,679					$ 1	465,986		(456,308)
Balance (in shares) at Jun. 30, 2022		1,952				1,497,912
Stock-based compensation	129						129
Issue and sale of stock, net	6,815					$ 1	6,814
Issue and sale of share						673,421
Net loss	(5,219)								(5,219)
Balance at Sep. 30, 2022	11,404					$ 2	472,929		(461,527)
Balance (in shares) at Sep. 30, 2022		1,952				2,171,333
Balance at Dec. 31, 2022	6,445					$ 2	473,628		(467,185)
Balance (in shares) at Dec. 31, 2022		1,952				2,240,092
Stock-based compensation	140						140
Issue and sale of stock, net	895		$ 1				895	$ 1
Issue and sale of share					1	168,164
Net loss	(4,805)								(4,805)
Balance at Mar. 31, 2023	2,676					$ 2	474,664		(471,990)
Balance (in shares) at Mar. 31, 2023		1,952		1		2,408,256
Balance at Dec. 31, 2022	6,445					$ 2	473,628		(467,185)
Balance (in shares) at Dec. 31, 2022		1,952				2,240,092
Net loss	(9,506)
Balance at Sep. 30, 2023	2,622					$ 5	479,308		(476,691)
Balance (in shares) at Sep. 30, 2023		1,952				4,522,656
Balance at Mar. 31, 2023	2,676					$ 2	474,664		(471,990)
Balance (in shares) at Mar. 31, 2023		1,952		1		2,408,256
Redemption of Series F preferred stock (in shares)				(1)
Fractional adjustment						(1,310)
Stock-based compensation	140						140
Issue and sale of stock, net	1,328					$ 1	1,327
Issue and sale of share						472,674
Net loss	(1,482)								(1,482)
Balance at Jun. 30, 2023	2,662					$ 3	476,131		(473,472)
Balance (in shares) at Jun. 30, 2023		1,952				2,879,620
Stock-based compensation	148						148
Issue and sale of stock, net	2,956					$ 2	2,954
Issue and sale of share						1,589,655
Issuance of common stock for in process research and development	75						75
Issuance of common stock for in process research and development (in shares)						53,381
Net loss	(3,219)								(3,219)
Balance at Sep. 30, 2023	$ 2,622					$ 5	$ 479,308		$ (476,691)
Balance (in shares) at Sep. 30, 2023		1,952				4,522,656

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Cash flows used in operating activities:
Net loss	$ (3,219)	$ (4,805)	$ (5,219)	$ (4,116)	$ (9,506)	$ (14,617)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization					477	460
Amortization of deferred financing costs and debt discount					160	309
Stock issued for research and development					75
Loss on disposal of property and equipment					2
Stock-based compensation expense					428	476
Change in fair value of derivative instruments						(1)
Amortization of operating lease right-of-use assets					86	66
Increases (decreases) in cash caused by changes in operating assets and liabilities:
Grant Receivable					(91)	73
Other assets					3,190	642
Accounts payable and accrued expenses					(4,061)	1,955
Change in operating lease liabilities					(87)	(101)
Deferred grant liability					(1,643)
Net cash used in operating activities					(10,970)	(10,738)
Cash flows used in investing activities:
Purchases of property and equipment					(118)	(381)
Purchase of intangible assets						(117)
In process research and development acquired						(250)
Net cash used in investing activities					(118)	(748)
Cash flows from financing activities:
Principal payments of term loan obligation					(1,206)	(1,206)
Proceeds from sale of common stock, net of offering cost of $0.2 million and $0.7 million, respectively					5,180	14,558
Net cash provided by financing activities					3,974	13,352
Net increase (decrease) in cash and cash equivalents					(7,114)	1,866
Cash and cash equivalents at beginning of period		$ 18,120		$ 18,400	18,120	18,400	$ 18,400
Cash and cash equivalents at end of period	$ 11,006		$ 20,266		11,006	20,266	$ 18,120
Cash paid during period for:
Interest					186	248
Supplemental schedule of non-cash investing and financing activities:
Unpaid offering cost					1	$ 68
Right-of-use assets acquired by assuming operating lease liabilities					71
Common stock issued in payment for in process research and development					$ 75

CONDENSED STATEMENTS OF CASH _2

CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Statement of Cash Flows [Abstract]
Offering cost	$ 0.2	$ 0.7

Basis of Presentation and New A

Basis of Presentation and New Accounting Standards	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and New Accounting Standards	1. Basis of Presentation and New Accounting Standards The accompanying unaudited condensed financial statements for the nine months ended September 30, 2023 and 2022 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2022 has been derived from the audited financial statements at December 31, 2022, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc. (the “Company”) have been included. Operating results for the nine months ended September 30, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the Securities and Exchange Commission on February 23, 2023. Amendments to Certificate of Incorporation and Reverse Stock Split At the Annual Meeting of Stockholders of the Company held on April 20, 2023 (the “Annual Meeting”), the stockholders of the Company approved an amendment to the Company’s Amended and Restated Certificate of Incorporation (the “Charter”) to implement a reverse stock split of the Company’s common stock, par value $ 0.001 per share, with the ratio to be determined by the Board of Directors (the “Board”) of the Company, within a range of not less than 1-for-3 and not greater than 1-for-15 . Subsequently, on April 21, 2023, the Board determined to fix the ratio for the reverse stock split at 1-for-15 , without any change to its par value (the "Reverse Stock Split"). On April 27, 2023, following stockholder and Board approval, the Company filed a Certificate of Amendment to its Charter (the “Amendment”), with the Secretary of State of the State of Delaware to effectuate the Reverse Stock Split. The Amendment became effective on May 1, 2023 . Upon effectiveness of the Reverse Stock Split, the number of shares of the Company’s common stock (x) issued and outstanding decreased from approximately 37.4 million shares to approximately 2.5 million shares; (y) reserved for issuance upon exercise of outstanding warrants and options decreased from approximately 2.0 million shares to app roximately 0.1 million shares, and (z) reserved but unallocated under the Company ’ s current equity incentive plans decreased from approximately 3.0 million common shares to approximately 0.2 million common shares. The Company's common stock began trading on the NASDAQ Capital Market on a post-split basis on May 1, 2023. The Company’s 5,000,000 shares of authorized Preferred Stock were not affected by the Reverse Stock Split. No fractional shares were issued in connection with the Reverse Stock Split, and accordingly, the outstanding number of shares post Reverse Stock Split was adjusted down by approximately 1,310 (post-effect of Reverse Stock Split) shares. Proportional adjustments for the reverse stock split were made to the Company’s outstanding stock options, warrants and equity incentive plans for all periods presented in the condensed financial statements in this Form 10-Q. The Company’s financial statements, and all references thereto have been retroactively adjusted to reflect the reverse split unless specifically stated otherwise. Grant Receivable and Revenue Recognition In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as the Company does not consider there to be a transfer of control of goods or services. With respect to the grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies International Accounting Standards No. 20 ("IAS 20"), Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract. The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of the grant, of whether the agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred. Grant receivable represents qualified expenses incurred to date in excess of the amounts submitted for reimbursement. Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. This new guidance is effective in the first quarter of 2023 for calendar-year SEC filers that are smaller reporting companies as of the one-time determination date. Early adoption was permitted beginning in 2019. The Company adopted the new guidance as of January 1, 2023 , which did no t have a material impact on its financial statements and related disclosures.

Use of Estimates

Use of Estimates	9 Months Ended
	Sep. 30, 2023
Use Of Estimates [Abstract]
Use of Estimates	2. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve reviewing assets for impairment and determining the assumptions used in measuring stock-based compensation expense.

Liquidity and Going Concern

Liquidity and Going Concern	9 Months Ended
	Sep. 30, 2023
Liquidity [Abstract]
Liquidity and Going Concern	3. Liquidity and Going Concern The Company incurred a net loss of $ 9.5 million for the nine months ended September 30, 2023 . The Company had an accumulated deficit of $ 476.7 million as of September 30, 2023. Additionally, the Company used net cash of $ 11.0 million to fund its operating activities for the nine months ended September 30, 2023 . The Company's term loan (Note 5) matures on June 1, 2024 with total principal and final payment of $ 4.4 million due upon maturity. These factors raise substantial doubt about the Company’s ability to continue as a going concern. To date, the Company’s operating losses have been funded primarily from outside sources of invested capital from issuance of its common and preferred stocks, proceeds from its term loan and grant funding. However, the Company has had, and will continue to have, an ongoing need to raise additional cash from outside sources to fund its future clinical development programs and other operations. There can be no assurance that the Company will be able to continue to raise additional capital in the future. The Company’s inability to raise additional cash would have a material and adverse impact on its operations and could cause the Company to default on its term loan. On May 24, 2022, the Company received notice from The Nasdaq Stock Market LLC (“Nasdaq”) that, because the closing bid price for the Company’s common stock had fallen below $ 1.00 per share for 30 consecutive business days, the Company no longer complied with the minimum bid price requirement pursuant to Nasdaq Listing Rule 5550(a)(2) (the “Minimum Bid Requirement”). Nasdaq’s notice had no immediate effect on the listing or trading of the Company’s common stock. On November 22, 2022, the Company received a second letter from Nasdaq advising that the Company had been granted an additional 180 calendar days, or to May 22, 2023 , to regain compliance with the Minimum Bid Requirement, in accordance with Nasdaq Listing Rule 5810(c)(3)(A). On April 20, 2023, the Company held its annual meeting of stockholders and its stockholders approved an amendment to the Company’s Charter, to effect a reverse stock split of its issued and outstanding shares of common stock, at a specific ratio, ranging from one-for-three ( 1:3 ) to one-for-fifteen ( 1:15 ). After receiving approval from the Board, on April 27, 2023, the Company filed the Amendment with the Secretary of State of the State of Delaware, to implement the Reverse Stock Split at the one-for-fifteen ratio ( 1:15 ). The Reverse Stock Split was effective on May 1, 2023 , and the Company’s common stock began trading on The Nasdaq Capital Market on a post-split basis on May 1, 2023. On May 15, 2023, the Company received written notice from Nasdaq notifying the Company that it had regained compliance with the Minimum Bid Requirement. The Company continues to seek additional capital from other financing alternatives and other sources. Without additional capital, current working capital will not provide adequate funding for research and product development activities at their current levels. If sufficient capital is not raised, the Company will at a minimum need to significantly reduce or curtail its research and development and other operations, and this would negatively affect its ability to achieve corporate growth goals. Should the Company fail to raise additional cash from outside sources, this would have a material adverse impact on its operations. The accompanying condensed financial statements have been prepared assuming the Company will continue to operate as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business, and do 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 uncertainty related to its ability to continue as a going concern.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements Fair value measurements are market-based measurements, not entity-specific measurements. Therefore, fair value measurements are determined based on the assumptions that market participants would use in pricing the asset or liability. The Company follows a three-level hierarchy to prioritize the inputs used in the valuation techniques to derive fair values. The basis for fair value measurements for each level within the hierarchy is described below: • Level 1: Quoted prices in active markets for identical assets or liabilities. • Level 2: Quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs are observable in active markets. • Level 3: Valuations derived from valuation techniques in which one or more significant inputs are unobservable in active markets. The Company has investments in money market accounts, which are included in cash and cash equivalents on the balance sheets. Fair value inputs for these investments are considered Level 1 measurements within the fair value hierarchy since money market account fair values are known and observable through daily published floating net asset values. The following table summarizes the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022, respectively. Fair Value Measurements Using As of September 30, 2023 Fair Value Level 1 Level 2 Level 3 Money market $ 10,688,964 $ 10,688,964 $ — $ — Fair Value Measurements Using As of December 31, 2022 Fair Value Level 1 Level 2 Level 3 Money market $ 17,573,584 $ 17,573,584 $ — $ — Certain warrants issued in an underwritten public offering in September 2019 (the “Series U Warrants”) are classified as liability instruments. The Company estimated the fair value of the Series U Warrants with the Black Scholes model. Because some of the inputs to the Company’s valuation model are either not observable or are not derived principally from or corroborated by observable market data by correlation or other means, the warrant liability is classified as Level 3 in the fair value hierarchy. Liability-classified Series U Warrants are marked to market as of each balance sheet date until they are exercised or upon expiration, with the changes in fair value recorded as non-operating income or loss in the statements of operations. As of September 30, 2023, the fair value of the Series U Warrants was immaterial, and the change in the fair value of liability classified Series U Warrants during the three and nine months ended September 30, 2023 and 2022 was immaterial.

Term Loan Obligations

Term Loan Obligations	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Term Loan Obligations	5. Term Loan Obligations On May 29, 2015 , the Company entered into the Loan and Security Agreement (the “Loan and Security Agreement”), pursuant to which Oxford Finance, LLC (“Oxford”) funded an aggregate principal amount of $ 17.7 million (the “Term Loan”), subject to the terms and conditions set forth in the Loan and Security Agreement. The Term Loan accrues interest at a floating rate of at least 8.95 % per annum, comprised of a three-month LIBOR rate with a floor of 1.00 % plus 7.95 %. Pursuant to the Loan and Security Agreement, as amended, the Company made interest only payments through May 1, 2021 , and thereafter is required to make payments of principal and accrued interest in equal monthly installments sufficient to amortize the Term Loan through June 1, 2024, the maturity date. At maturity of the Term Loan, or earlier repayment in full following voluntary prepayment or upon acceleration, the Company is required to make a final payment in an aggregate amount equal to approximately $ 3.2 million. From September 2017 to March 2020, the Company entered into a total of nine amendments to the Term Loan that, among other things, extended the interest only period, required repayment of $ 3.1 million using the proceeds received from sale of the Company’s former UK and Japan subsidiaries in April 2019, increased the final payment, increased the final payment fee upon maturity or early repayment of the Term Loan, increased the minimum liquidity covenant level to $ 2.0 million and deferred the start date of principal repayment from May 1, 2020 to May 1, 2021 and extended the term of the Term Loan from September 1, 2021 to June 1, 2024 . On June 28, 2023, the Company and Oxford entered into a tenth amendment to the Loan and Security Agreement (the “Tenth Amendment”), and revised the interest rate of the Loan to the greater of: (1) 8.95 %, or (2) the sum of 1-month Secured Overnight Financing Rate and 8.05 %, effective July 1, 2023. The Term Loan, as amended, is collateralized by a security interest in substantially all of the Company’s existing and subsequently acquired assets, including its intellectual property assets, subject to certain exceptions set forth in the Loan and Security Agreement, as amended. The intellectual property asset collateral will be released upon the Company achieving a certain liquidity level when the total principal outstanding under the Loan and Security Agreement is less than $ 3.0 million. As of September 30, 2023 , there was $ 1.2 million principal amount outstanding under the Term Loan, excluding the $ 3.2 million final payment fee, and the Company was in compliance with all of the debt covenants under the Loan and Security Agreement. The Company’s interest expense for the three and nine months ended September 30, 2023 and 2022 was $ 0.1 million and $ 0.2 million, and $ 0.3 million and $ 0.6 million, respectively. Interest expense is calculated using the effective interest method; therefore it is inclusive of non-cash amortization in the amount of $ 41,000 and $ 0.2 million for the three and nine months ended September 30, 2023 , and $ 0.1 and $ 0.3 million for the three and nine months ended September 30, 2022, respectively, related to the amortization of the debt discount, capitalized loan costs, and accretion of final payment. The Loan and Security Agreement, as amended, contains customary indemnification obligations and customary events of default, including, among other things, the Company’s failure to fulfill certain obligations under the Term Loan, as amended, and the occurrence of a material adverse change, which is defined as a material adverse change in the Company’s business, operations, or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the loan. In the event of default by the Company or a declaration of material adverse change by its lender, under the Term Loan, the lender would be entitled to exercise its remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Term Loan, which could materially harm the Company’s financial condition. As of September 30, 2023, the Company has not received any notification or indication from Oxford that it intends to invoke the material adverse change clause.

Loss per Share

Loss per Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Loss per Share	6 . Loss per Share Basic per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding as calculated using the treasury stock method. Potential dilutive common shares were related to outstanding but unexercised options, multiple series of convertible preferred stock, and warrants for all periods presented. The following were excluded from the diluted loss per share calculation for the three and nine month periods presented because their effect would be anti-dilutive: September 30, 2023 September 30, 2022 Outstanding stock options 141,077 78,334 Outstanding warrants 142,733 142,747 Preferred stock 28,190 28,190 Total 312,000 249,271

Grant Revenue

Grant Revenue	9 Months Ended
	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Grant Revenue	7. Grant Revenue On September 19, 2022, the Company entered into the CPRIT Contract, effective as of August 31, 2022 , with CPRIT, pursuant to which CPRIT will provide the Company with the CPRIT Grant over a three-year period to fund the continued development of rhenium ( 186 Re) obisbemeda (previously known as 186 RNL) for the treatment of patients with leptomeningeal metastases (“LM”). The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium ( 186 Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400 % of the proceeds awarded under the CPRIT Grant, and certain reporting requirements. The CPRIT Contract will terminate on August 30, 2025 , unless terminated earlier by (a) the mutual written consent of all parties to the CPRIT Contract, (b) CPRIT for an event of default by the Company, (c) CPRIT, if the funds allocated to the CPRIT Grant become legally unavailable during the term of the CPRIT Contract and CPRIT is unable to obtain additional funds for such purposes, and (d) the Company for convenience. CPRIT may require the Company to repay some or all of the disbursed CPRIT Grant proceeds (with interest not to exceed 5 % annually) in the event of the early termination of the CPRIT Contract by CPRIT for an event of default by the Company or by the Company for convenience, or if the Company relocates its principal place of business outside of the state of Texas during the CPRIT Contract term or within three years after the final payment of the grant funds. The Company retains ownership over any intellectual property developed under the contract (each, a “Project Result”). With respect to non-commercial use of any Project Result, the Company granted to CPRIT a nonexclusive, irrevocable, royalty-free, perpetual, worldwide license with right to sublicense any necessary additional intellectual property rights to exploit all Project Results by CPRIT, other governmental entities and agencies of the State of Texas, and private or independent institutions of higher education located in Texas, for education, research and other non-commercial purposes. The Company determined that the CPRIT Contract is not in the scope of ASC 808, ASC 958-605, or ASC 606. Applying IAS 20 by analogy, the Company recognizes proceeds received under the CPRIT Contract as grant revenue on the statement of operations when related costs are incurred. During the three months ended June 30, 2023, the Company identified eligible costs of approximately $ 637,000 and $ 168,000 that were incurred in the fourth quarter of 2022 and the three months ended March 31, 2023, respectively, that were reimbursable under the CPRIT arrangement. The Company determined that these costs should have been recorded in these respective periods as grant revenue. The Company assessed the impact of this error on the Company’s previously issued financial statements and determined that it was immaterial. As a result, an out-of-period adjustment of approximately $ 805,000 has been recorded as an increase in grant revenue in the nine months ended September 30, 2023. The Company recognized $ 1.2 million and $ 3.6 million in grant revenue from the CPRIT Contract during the three and nine months ended September 30, 2023 , respectively. The Company recognized $ 73,000 of CPRIT revenue in the three and nine months ended September 30, 2022.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Leases The Company leases laboratory, office and storage facilities in San Antonio, Texas, under operating lease agreements that expire in 2025 . The Company also leases certain office space in Austin, Texas under a month-to-month operating lease agreement and certain office space in Charlottesville, Virginia (the “Charlottesville Lease”). The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods. The Charlottesville Lease is currently set to expire on March 31, 2024 , and is renewable twice for twelve months each time. On March 31, 2023, Company believed that it was reasonably certain that the Charlottesville Lease will be renewed through March 31, 2026, and as a result, it remeasured the related lease liability as of March 31, 2023 to be $ 80,000 using the then-in-effect discount rate of 12.76 %. Effective July 1, 2023, the Company added additional office lease premises in Charlottesville, which was accounted for as a separate operating lease contract with a lease liability and corresponding right-of-use asset of $ 19,000 , as a discount rate of 13.47 %. Services Agreement and Sales Order with Medidata On March 31, 2022, the Company and Medidata Solutions, Inc. (“Medidata”) entered into a Sales Order (the “Sales Order”), pursuant to which Medidata will build a Synthetic Control Arm ® (“SCA”) platform that facilitates the use of historical clinical data to incorporate into the Company’s Phase 2 clinical trial of rhenium ( 186 Re) obisbemeda in recurrent glioblastoma (“GBM”). The Sales Order is governed under the terms of a services agreement, dated November 5, 2021. The Sales Order had a term of six months , and work under the Sales Order has been completed. Piramal Master Services Agreement On January 8, 2021 , the Company entered into a Master Services Agreement (the “MSA”) with Piramal Pharma Solutions, Inc. (“Piramal”), for Piramal to perform certain services related to the development, manufacture, and supply of the Company’s rhenium ( 186 Re) obisbemeda Intermediate Drug Product. The MSA includes the transfer of analytical methods, development of microbiological methods, process transfer and optimization, intermediate drug product manufacturing, and stability studies for the Company, which has been initiated at Piramal’s facility located in Lexington, Kentucky. The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice. Either party may terminate the MSA upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party. Other commitments and contingencies The Company has entered into agreements with various research organizations for pre-clinical and clinical development studies, which have provisions for cancellation. Under the terms of these agreements, the vendors provide a variety of services including conducting research, recruiting and enrolling patients, monitoring studies and data analysis. Payments under these agreements typically include fees for services and reimbursement of expenses. The timing of payments due under these agreements is estimated based on current study progress. As of September 30, 2023 , the Company did no t have any clinical research study obligations. Legal proceedings On December 9, 2022, the Company entered into a settlement agreement (the “Settlement Agreement”) with Lorem Vascular, Pte. Ltd. (“Lorem”) to settle a prior litigation matter. Under the terms of the Settlement Agreement, the Company made a payment to Lorem, and Lorem moved to dismiss the lawsuit with prejudice. The Settlement Agreement released the Company from all claims made by Lorem. The parties to the Settlement Agreement recognized that it did not constitute an admission of liability, wrongdoing, or any matter of fact or law. The Settlement was conditioned on the customary terms contained in the Settlement Agreement and was approved by the Court and the case was dismissed on January 17, 2023. As of December 31, 2022, the Company accrued the settlement amount, as well as the accounts that the Company has confirmed to be recoverable under its insurance claims on the matter. The net amount of $ 1.4 million that was not recoverable under the Company’s insurance has been reflected as an expense in the condensed statement of operations for the year ended December 31, 2022. The full settlement amount was paid in January 2023. All legal costs related to the Lorem Claim were expensed as incurred. The Company is subject to various claims and contingencies related to legal proceedings. Due to their nature, such legal proceedings involve inherent uncertainties including, but not limited to, court rulings, negotiations between affected parties and governmental actions. Management assesses the probability of loss for such contingencies and accrues a liability and/or discloses the relevant circumstances, as appropriate.

License Agreements

License Agreements	9 Months Ended
	Sep. 30, 2023
License Agreement [Abstract]
License Agreements	9. License Agreements Biocept License Agreement On September 7, 2023, the Company entered into a Non-Exclusive License and Services Agreement (the “Biocept Agreement”) with Biocept, Inc (“Biocept”), pursuant to which Biocept granted the Company a non-exclusive license to use the Biocept proprietary cell enumeration test, CNsideTM. In exchange for the license, the Company issued to Biocept 53,381 unregistered shares, the fair value of which was $ 75,000 . The Biocept Agreement also provides that if Biocept fully transfers the technology to the Company, a tech transfer and validation fee of $ 300,000 will be payable. In addition, the Company was granted an option for an exclusive worldwide license for $ 1,000,000 on or before December 31, 2024, to process and perform cell enumeration testing for treatments for other patients including those on the Company’s radiotherapeutic drugs. On October 16, 2023, Biocept filed a voluntary petition for relief under the provisions of Chapter 7 of Title 11 of the United States Bankruptcy Code, making the full transfer of the Biocept technology to the Company unlikely. In addition, the Biocept Agreement is subject to provisions under the Bankruptcy Code. UT Health Science Center at San Antonio (“UTHSCSA”) License Agreement On December 31, 2021, the Company entered into a Patent and Know-How License Agreement (the “UTHSCSA License Agreement”) with The University of Texas Health Science Center at San Antonio (“UTHSCSA”), pursuant to which UTHSCSA granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of biodegradable alginate microspheres (“BAM”) containing nanoliposomes loaded with imaging and/or therapeutic payloads. Pursuant to the UTHSCSA License Agreement, the Company was required to make an upfront payment, which was recorded as in process research and development acquired in the condensed statement of operations for the year ended December 31, 2021. The upfront payment of $ 0.3 million was paid in cash in January 2022. NanoTx License Agreement On March 29, 2020, the Company and NanoTx, Corp. (“NanoTx”) entered into a Patent and Know-How License Agreement (the “NanoTx License Agreement”), pursuant to which NanoTx granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of radiolabeled nanoliposomes. The transaction terms included an upfront payment of $ 0.4 million in cash and $ 0.3 million in the Company's voting stock. The transaction terms also included success-based milestone and royalty payments contingent on key clinical, regulatory and sales milestones, as well as the requirement to pay 15 % of any non-dilutive monetary awards or grants received from external agencies to support product development of the nanoliposome encapsulated BMEDA-chelated radioisotope, which includes grants from CPRIT. As of September 30, 2023, the Company accru ed $ 1.3 million o f payments due to NanoTx as a result of the CPRIT grant received (Note 7).

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2023
Stockholders' Equity Note [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Preferred Stock The Company has authorized 5,000,000 shares of preferred stock, par value $ 0.001 per share. The Company’s Board of Directors is authorized to designate the terms and conditions of any preferred stock the Company issues without further action by the common stockholders. Series F Preferred Stock On March 3, 2023, the Company filed a certificate of designation (the “Certificate of Designation”) with the Secretary of State of the State of Delaware, effective as of the time of filing, designating the rights, preferences, privileges and restrictions of the Series F Preferred Stock, with the total authorization of one ( 1 ) share of Series F Preferred Stock. The Certificate of Designation provided that the share of Series F Preferred Stock will have 50,000,000 votes per share of Series F Preferred Stock and will vote together with the Company’s common stock, $ 0.001 par value (the “Common Stock”) as a single class exclusively with respect to any proposal to amend the Company’s Charter to effect a reverse stock split of the Common Stock (the “Reverse Stock Split”). On March 3, 2023, the Company entered into a Subscription and Investment Representation Agreement (the “Subscription Agreement”) with Richard J. Hawkins, Chairman of the board of directors of the Company, who is an accredited investor (the “Purchaser”), pursuant to which the Company agreed to issue and sell one ( 1 ) share of the Company’s Series F Preferred Stock, par value $ 0.001 per share (the “Preferred Stock”), to the Purchaser for $ 1,000 in cash. The sale closed on March 3, 2023 . At the Company’s annual meeting of stockholders held on April 20, 2023, the Series F Preferred Stock was voted, without action by the holder, on the proposal to approve the Reverse Stock Split in the same proportion as shares of Common Stock voted to approve the Reverse Stock Split. The Series F Preferred Stock otherwise had no voting rights except as otherwise required by the General Corporation Law of the State of Delaware. The Series F Preferred Stock was not convertible into, or exchangeable for, shares of any other class or series of stock or other securities of the Company. The Series F Preferred Stock had no rights with respect to any distribution of assets of the Company, including upon a liquidation, bankruptcy, reorganization, merger, acquisition, sale, dissolution or winding up of the Company, whether voluntarily or involuntarily. The holder of the Series F Preferred Stock was not entitled to receive dividends of any kind. The outstanding share of Series F Preferred Stock was redeemed in whole, automatically effective upon the approval by the Company’s stockholders of a Reverse Stock Split. Upon such redemption, the holder of the Series F Preferred Stock received consideration of $ 1,000 in cash. Series B and C Preferred Stock As of September 30, 2023 , there were 938 outstanding shares of Series C Preferred Stock that can be converted into an aggregate of 27,792 shares of common stock, and 1,014 shares of Series B Convertible Preferred Stock that can be converted into an aggregate of 398 shares of common stock. Warrants On September 25, 2019, the Company completed an underwritten public offering. The Company issued 19,266 shares of its common stock, along with pre-funded warrants to purchase 180,733 shares of its common stock and Series U Warrants to purchase 230,000 shares of its common stock at $ 75.00 per share. The Series U Warrants have a term of five years from the issuance date. In addition, the Company issued warrants to H.C. Wainwright & Co., LLC, as representatives of the underwriters, to purchase 5,000 shares of its common stock at $ 93.75 per share with a term of 5 years from the issuance date, in the form of Series U Warrants (the “Representative Warrants”). As of September 30, 2023 , there were 142,733 outstanding Series U Warrants which can be exercised into an aggregate of 142,733 shares of common stock at a weighted average exercise price of $ 34.10 per share. Common Stock Lincoln Park Purchase Agreements On August 2, 2022, the Company entered into a purchase agreement (the “2022 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park committed to purchase up to $ 50.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2022 Purchase Agreement, the Company has the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park is obligated to purchase up to $ 50.0 million of the Company’s common stock. Such sales of common stock by the Company are subject to certain limitations, and can occur from time to time, at the Company’s sole discretion, over the 36-month period commencing on August 17, 2022, subject to the satisfaction of certain conditions. Lincoln Park has no right to require the Company to sell any shares of common stock to Lincoln Park, but Lincoln Park is obligated to make purchases as the Company directs, subject to certain conditions. On May 16, 2022, the Company received stockholder approval for purposes of the Nasdaq listing rules to permit issuances of up to 57.5 million shares of the Company’s common stock (including the issuance of more than 19.99 % of the Company’s common stock) to Lincoln Park, and it was pursuant to that approval that the Company entered into the 2022 Purchase Agreement. Upon execution of the 2022 Purchase Agreement, the Company paid $ 125,000 in cash as the initial commitment fee, and issued 32,846 shares as the initial commitment shares, to Lincoln Park as consideration for its irrevocable commitment to purchase shares of the Company ’s common stock at its direction under the Purchase Agreement. The Company has agreed to pay an additional commitment fee, which it may elect to pay in cash and/or shares of its common stock, upon receipt of $ 25.0 million aggregate gross proceeds from sales of common stock to Lincoln Park under the 2022 Purchase Agreement. On August 17, 2022, a registration statement (the “First Registration Statement”) was declared effective to cover the resale of up to 633,333 shares of the Company’s common stock comprised of (i) the 32,846 initial commitment shares, and (ii) up to 600,486 that the Company has reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time from and after the date of the prospectus . The Company sold approximately 527,166 shares under the First Registration Statement. On August 18, 2023, a second registration statement (the “Second Registration Statement”) was declared effective to cover the resale of up to an additional 1,500,000 shares of the Company’s common stock that the Company reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time. The Company cannot sell more shares than registered under the Second Registration Statement under the 2022 Purchase Agreement without registering additional shares. Actual sales of shares of common stock to Lincoln Park under the 2022 Purchase Agreement depend on a variety of factors to be determined by the Company from time to time, including, among others, market conditions, the trading price of the common stock and determinations by the Company as to the appropriate sources of funding for the Company and its operations. The net proceeds under the 2022 Purchase Agreement to the Company depend on the frequency and prices at which the Company sells shares of its stock to Lincoln Park. During the period from August 17, 2022 to December 31, 2022, the Company issued 266,666 shares under the 2022 Purchase Agreement for net proceeds of approximately $ 3.2 million. The Company issued 410,500 shares under the 2022 Purchase Agreement for net proceeds of approximately $ 1.0 million from January 1, 2023 to September 30, 2023. On September 30, 2020, the Company entered into a purchase agreement (the “2020 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park committed to purchase up to $ 25.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2020 Purchase Agreement, the Company had the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park was obligated to purchase up to $ 25.0 million of the Company’s common stock. Such sales of common stock by the Company were subject to certain limitations, and could occur from time to time, at the Company’s sole discretion, over the 36 -month period commencing on November 6, 2020, subject to the satisfaction of certain conditions. During the year ended December 31, 2021, the Company issued 379,012 shares of its common stock under the 2020 Purchase Agreement for net proceeds of approximately $ 12.5 million. During the year ended December 31, 2022, the Company issued 377,666 shares of its common stock under the 2020 Purchase Agreement for net proceeds of approximately $ 7.0 million. The Company no longer has any additional shares of common stock registered to sell under the 2020 Purchase Agreement and has terminated the 2020 Purchase Agreement. At-the-market Issuances On September 9, 2022, the Company entered into an Equity Distribution Agreement (the “September 2022 Distribution Agreement”) with Canaccord Genuity LLC (“Canaccord”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $ 5,000,000 , depending on market demand, with Canaccord acting as an agent for sales. Sales of the Company’s common stock may be made by any method permitted by law deemed to be an “at-the-market offering” as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended (the “Securities Act”), including, without limitation, sales made directly on or through the NASDAQ Capital Market. Canaccord will use its commercially reasonable efforts to sell common stock requested by the Company to be sold on its behalf, consistent with Canaccord’s normal trading and sales practices, under the terms and subject to the conditions set forth in the September 2022 Distribution Agreement. The Company has no obligation to sell any of its common stock. The Company may instruct Canaccord not to sell any common stock if the sales cannot be effected at or above the price designated by the Company from time to time and the Company may at any time suspend sales pursuant to the September 2022 Distribution Agreement. During the period from September 9, 2022 to December 31, 2022, the Company issued 68,758 shares of its common stock under the September 2022 Distribution Agreement for net proceeds of approximately $ 0.6 million. From January 1, 2023 through September 30, 2023, the Company issued 1,819,993 shares under the September 2022 Distribution Agreement for net proceeds of approximately $ 4.3 million. The Company has reached the capacity for sales of shares under the September 2022 Distribution Agreement. The Company is obligated to pay Canaccord a commission of up to 3.0 % of the gross proceeds from the sale of its common stock under the September 2022 Distribution Agreement. The Company has also agreed to reimburse Canaccord for its reasonable documented out-of-pocket expenses, including fees and disbursements of its counsel, in the amount of $ 50,000 . In addition, the Company has agreed to provide customary indemnification rights to Canaccord. The offering pursuant to the September 2022 Distribution Agreement will terminate upon the earlier of (1) the issuance and sale of all shares of the Company’s common stock subject to the September 2022 Distribution Agreement, or (2) the termination of the September 2022 Distribution Agreement as permitted therein, including by either party at any time without liability of any party. On January 14, 2022, the Company entered into an Equity Distribution Agreement (the “January 2022 Distribution Agreement”) with Canaccord, pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $ 5,000,000 , with Canaccord acting as an agent for sales. The Company had no obligation to sell any of the Company’s shares and it could instruct Canaccord not to sell any shares if the sales could not be effected at or above the price designated by the Company from time to time and the Company could at any time suspend sales pursuant to the January 2022 Distribution Agreement. During the year ended December 31, 2022, the Company issued 460,151 shares under the January 2022 Distribution Agreement for net proceeds of approximately $ 4.8 million. The January 2022 Distribution Agreement has been terminated after all available registered shares were fully utilized.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-based Compensation	11. Stock-based Compensation Under the Company’s 2015 New Employee Incentive Plan (the “2015 Plan”), awards may only be granted to employees who were not previously an employee or director of the Company, or following a bona fide period of non-employment, as a material inducement to entering into employment with the Company. As of September 30, 2023 , there were 6,023 shares of common stock remaining and available for future issuances under the 2015 Plan. The Company’s 2020 Stock Incentive Plan (the “2020 Plan”), which replaced the Company’s 2014 Equity Incentive Plan, provides for the award or sale of shares of common stock (including restricted stock), the award of stock units and stock appreciation rights, and the grant of both incentive stock options to purchase common stock to directors, officers, employees and consultants of the Company. The 2020 Plan, as amended, provides for the issuance of up to 236,666 shares of common stock, plus the number of shares available for issuance is increased to the extent that awards granted under the 2020 Plan and the Company’s 2014 Equity Incentive Plan are forfeited or expire (except as otherwise provided in the 2020 Plan). As of September 30, 2023 , there were 179,640 shares remaining and available for future issuances under the 2020 Plan. Generally, options issued under the 2020 Plan are subject to a two-year or four-year vesting schedule with 25 % of the options vesting on the one year anniversary of the grant date followed by equal monthly installment vesting, and have a contractual term of 10 years. A summary of activity for the nine months ended September 30, 2023 is as follows: Options Weighted Weighted Average Remaining Contractual Life Aggregate Outstanding as of December 31, 2022 78,334 $ 68.10 9.00 Granted 68,422 $ 5.00 Cancelled/forfeited ( 5,679 ) $ 325.82 Outstanding as of September 30, 2023 141,077 $ 37.47 8.32 $ 2 Vested and exercisable as of September 30, 2023 65,008 $ 65.51 7.53 $ — Vested and expected to be vested as of September 30, 2023 133,570 $ 38.83 8.26 $ 2 As of September 30, 2023 , the total compensation cost related to non-vested stock options not yet recognized for all the Company’s plans is approximately $ 0.8 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 1.95 years.

Basis of Presentation and New_2

Basis of Presentation and New Accounting Standards (Policies)	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and New Accounting Standards	The accompanying unaudited condensed financial statements for the nine months ended September 30, 2023 and 2022 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2022 has been derived from the audited financial statements at December 31, 2022, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc. (the “Company”) have been included. Operating results for the nine months ended September 30, 2023 are not necessarily indicative of the results that may be expected for the year ending December 31, 2023. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the Securities and Exchange Commission on February 23, 2023.
Grant Receivable and Revenue Recognition	Grant Receivable and Revenue Recognition In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as the Company does not consider there to be a transfer of control of goods or services. With respect to the grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies International Accounting Standards No. 20 ("IAS 20"), Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract. The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of the grant, of whether the agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred. Grant receivable represents qualified expenses incurred to date in excess of the amounts submitted for reimbursement. Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. This new guidance is effective in the first quarter of 2023 for calendar-year SEC filers that are smaller reporting companies as of the one-time determination date. Early adoption was permitted beginning in 2019. The Company adopted the new guidance as of January 1, 2023 , which did no t have a material impact on its financial statements and related disclosures.
Use of Estimates	The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve reviewing assets for impairment and determining the assumptions used in measuring stock-based compensation expense.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022, respectively. Fair Value Measurements Using As of September 30, 2023 Fair Value Level 1 Level 2 Level 3 Money market $ 10,688,964 $ 10,688,964 $ — $ — Fair Value Measurements Using As of December 31, 2022 Fair Value Level 1 Level 2 Level 3 Money market $ 17,573,584 $ 17,573,584 $ — $ —

Loss per Share (Tables)

Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share	The following were excluded from the diluted loss per share calculation for the three and nine month periods presented because their effect would be anti-dilutive: September 30, 2023 September 30, 2022 Outstanding stock options 141,077 78,334 Outstanding warrants 142,733 142,747 Preferred stock 28,190 28,190 Total 312,000 249,271

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock Option Activity	A summary of activity for the nine months ended September 30, 2023 is as follows: Options Weighted Weighted Average Remaining Contractual Life Aggregate Outstanding as of December 31, 2022 78,334 $ 68.10 9.00 Granted 68,422 $ 5.00 Cancelled/forfeited ( 5,679 ) $ 325.82 Outstanding as of September 30, 2023 141,077 $ 37.47 8.32 $ 2 Vested and exercisable as of September 30, 2023 65,008 $ 65.51 7.53 $ — Vested and expected to be vested as of September 30, 2023 133,570 $ 38.83 8.26 $ 2

Basis of Presentation and New_3

Basis of Presentation and New Accounting Standards - Additional Information (Details)				9 Months Ended
	Apr. 27, 2023	Apr. 21, 2023	Apr. 20, 2023 $ / shares	Sep. 30, 2023 $ / shares shares	May 01, 2023 shares	Apr. 30, 2023 shares	Dec. 31, 2022 $ / shares shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001			$ 0.001
Stock split conversion ratio	0.06	0.06
Reverse stock split effective date	May 01, 2023
Common stock, shares issued (in shares)				4,522,656	2,500,000	37,400,000	2,240,092
Common stock, shares outstanding (in shares)				4,522,656	2,500,000	37,400,000	2,240,092
Preferred stock, shares authorized (in shares)				5,000,000			5,000,000
Common stock, reverse stock split, fractional shares issued | shares				0
Stock issued during period reverse stock splits, shares				1,310
Equity Incentive Plans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock capital shares reserved for future issuance					200,000	3,000,000
Outstanding Warrants and Options [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock capital shares reserved for future issuance					100,000	2,000,000
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.06
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.33
ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2023
Change in accounting principle, accounting standards update, immaterial effect				true

Liquidity and Going Concern - A

Liquidity and Going Concern - Additional Information (Details)

3 Months Ended

9 Months Ended

Apr. 27, 2023

Apr. 21, 2023

Apr. 20, 2023

Nov. 22, 2022

May 24, 2022 $ / shares

Mar. 29, 2020

Mar. 28, 2020

May 29, 2015 USD ($)

Sep. 30, 2023 USD ($)

Jun. 30, 2023 USD ($)

Mar. 31, 2023 USD ($)

Sep. 30, 2022 USD ($)

Jun. 30, 2022 USD ($)

Mar. 31, 2022 USD ($)

Sep. 30, 2023 USD ($)

Sep. 30, 2022 USD ($)

Dec. 31, 2022 USD ($)

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Net loss

$ (3,219,000)

$ (1,482,000)

$ (4,805,000)

$ (5,219,000)

$ (5,282,000)

$ (4,116,000)

$ (9,506,000)

$ (14,617,000)

Accumulated deficit

(476,691,000)

(476,691,000)

$ (467,185,000)

Net cash used in operating activities

(10,970,000)

$ (10,738,000)

Closing bid price for common stock had fallen below | $ / shares

$ 1

Consecutive business days

30 days

Period for regain compliance

180 days

Regain compliance expiry date

May 22, 2023

Stock split conversion ratio

0.06

0.06

Reverse stock split effective date

May 01, 2023

Reverse stock split

one-for-fifteen

Term Loan [Member]

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Principal and final payment loan amount

$ 17,700,000

4,400,000

$ 4,400,000

Maturity date

Jun. 01, 2024

Sep. 01, 2021

May 01, 2021

Jun. 01, 2024

Maximum [Member]

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Stock split conversion ratio

0.06

Reverse stock split

one-for-fifteen

Maximum [Member] | Term Loan [Member]

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Principal and final payment loan amount

$ 3,000,000

$ 3,000,000

Minimum [Member]

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Stock split conversion ratio

0.33

Reverse stock split

one-for-three

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - Money Market [Member] - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 10,688,964	$ 17,573,584
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 10,688,964	$ 17,573,584

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	9 Months Ended
	Sep. 30, 2023
Series U Warrants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issued, underwritten public offering, period	2019-09

Term Loan Obligations - Additio

Term Loan Obligations - Additional Information (Details) - USD ($)					3 Months Ended		9 Months Ended
	Jun. 28, 2023	Mar. 29, 2020	Mar. 28, 2020	May 29, 2015	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Interest expense					$ 87,000	$ 173,000	$ 333,000	$ 552,000
Non-cash amortization					41,000	$ 100,000	$ 200,000	$ 300,000
LIBOR [Member] | Interest Rate Floor [Member]
Debt Instrument [Line Items]
Basis variable rate				1%
Term Loan [Member]
Debt Instrument [Line Items]
Origination date							May 29, 2015
Original loan amount				$ 17,700,000	4,400,000		$ 4,400,000
Basis variable rate				7.95%
Maturity date		Jun. 01, 2024	Sep. 01, 2021	May 01, 2021			Jun. 01, 2024
Fees amount associated with loan				$ 3,200,000	3,200,000		$ 3,200,000
Interest rate	8.95%
Minimum liquidity covenant					2,000,000		$ 2,000,000
Debt principal repayment start date		May 01, 2021	May 01, 2020
Debt instrument, covenant compliance							the Company was in compliance with all of the debt covenants under the Loan and Security Agreement.
Term Loan [Member] | Loan and Security Agreement [Member] | Sale of the Japanese Subsidiary and Certain Assets [Member]
Debt Instrument [Line Items]
Payments for principal, interest and fees				$ 3,100,000
Term Loan [Member] | SOFR [Member]
Debt Instrument [Line Items]
Basis variable rate	8.05%
Term Loan [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate				8.95%
Term Loan [Member] | Maximum [Member]
Debt Instrument [Line Items]
Original loan amount					$ 3,000,000		$ 3,000,000
Long term debt outstanding threshold amount							$ 1,200,000

Loss per Share - Schedule of An

Loss per Share - Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	312,000	249,271	312,000	249,271
Outstanding Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	141,077	78,334	141,077	78,334
Outstanding Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	142,733	142,747	142,733	142,747
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	28,190	28,190	28,190	28,190

Grant Revenue - Additional Info

Grant Revenue - Additional Information (Details) - USD ($)		3 Months Ended				9 Months Ended
	Sep. 19, 2022	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 1,240,000			$ 73,000	$ 3,600,000	$ 73,000
CPRIT Contract [Member]
Disaggregation of Revenue [Line Items]
Grant funding term	3 years
CPRIT grant funding term, description						The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements.
Contract effective date	Aug. 31, 2022
Contract termination date	Aug. 30, 2025
Percentage of aggregate amount of proceeds awarded under CPRIT grant	400%
Percentage of grant proceeds with interest not exceed annually	5%
Identified eligible reimbursable costs			$ 168,000	$ 637,000
Increase in grant revenue						$ 805,000
CPRIT Contract [Member] | Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 1,200,000			$ 73,000	$ 3,600,000	$ 73,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)			9 Months Ended	12 Months Ended
	Mar. 31, 2022	Jan. 08, 2021	Sep. 30, 2023	Dec. 31, 2022	Jul. 01, 2023	Mar. 31, 2023
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases expiry year			2025
Operating lease right-of-use assets			$ 232,000	$ 248,000
Lorem Vascular Pte Ltd [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Litigation settlement, expense				$ 1,400,000
Pre-clinical Research Study Obligations [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Contractual obligation			$ 0
Charlottesville [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, operating lease, term of contract			12 months
Lessee, operating lease, existence of option to extend [true false]			true
Lessee, operating lease, option to extend			The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods.
Lessee, operating lease, renewal term			1 year
Operating leases, expiration date			Mar. 31, 2024
Lease liability						$ 80,000
Operating lease discount rate					13.47%	12.76%
Operating lease right-of-use assets					$ 19,000
Medidata Solutions, Inc. [Member] | Services Agreement [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Sales order term	6 months
Piramal Pharma Solutions, Inc. [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Master service agreement date		Jan. 08, 2021
Master services agreement initial term		5 years
Master services agreement terms, Description			The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice.

License Agreements - Additional

License Agreements - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 07, 2023	Mar. 29, 2020	Jan. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Research and development expense				$ 2,493,000	$ 2,945,000	$ 6,896,000	$ 7,560,000
Voting stock, value				5,000		5,000		$ 2,000
Biocept Agreement [Member]
Shares issued	53,381
Research and development expense				75,000
Payment for tech transfer and validation fee	$ 300,000
Option for exclusive worldwide license	$ 1,000,000
UTHSCSA License Agreement [Member]
License fee payment in cash			$ 300,000
Nano Tx Licenses Agreement [Member]
License fee payment in cash		$ 400,000
Voting stock, value		$ 300,000
Percentage of non-dilutive monetary awards required to pay		15%
Accrued payments due to NanoTx				$ 1,300,000		$ 1,300,000

Stockholders' Equity - Preferre

Stockholders' Equity - Preferred Stock (Details)		9 Months Ended
	Mar. 03, 2023 USD ($) Votes $ / shares shares	Sep. 30, 2023 $ / shares shares	Apr. 20, 2023 $ / shares	Dec. 31, 2022 $ / shares shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		5,000,000		5,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.001		$ 0.001
Preferred stock, shares outstanding (in shares)		1,952		1,952
Common stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001	$ 0.001
Series B Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,014
Number of preferred stock, shares converted		398
Series C Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		938
Number of preferred stock, shares converted		27,792
Series F Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1
Number Of Votes Per Share | Votes	50,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Preferred stock, voting rights	no
Rights related to distribution of assets	no
Consideration paid to preferred stock holders | $	$ 1,000
Series F Convertible Preferred Stock [Member] | Subscription Agreement [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Consideration to purchaser in cash | $	$ 1,000
Issue and sale of share	1
Sale closed date	Mar. 03, 2023

Stockholders' Equity - Warrants

Stockholders' Equity - Warrants (Details) - $ / shares	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023
Series U Warrants [Member]
Class of Stock [Line Items]
Common stock issued (in shares)							230,000
Sale of Stock, Price Per Share	$ 75						$ 75
Warrants expected term	5 years						5 years
Representative Warrants [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	5,000						5,000
Warrant exercise price (in dollars per share)	$ 93.75						$ 93.75
Common Stock [Member]
Class of Stock [Line Items]
Common stock issued (in shares)	1,589,655	472,674	168,164	673,421	18,070	445,840
Warrants expected term	5 years						5 years
Outstanding Warrants [Member] | Series U Warrants [Member]
Class of Stock [Line Items]
Warrant exercise price (in dollars per share)	$ 34.1						$ 34.1
Class of warrant outstanding	142,733						142,733
Number of warrants exercised							142,733
Common Class A [Member]
Class of Stock [Line Items]
Common stock issued (in shares)							19,266
Common Class B [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	180,733						180,733

Stockholders' Equity - Common s

Stockholders' Equity - Common stock (Details) - USD ($)

3 Months Ended

4 Months Ended

9 Months Ended

12 Months Ended

13 Months Ended

Sep. 09, 2022

Aug. 02, 2022

May 16, 2022

Jan. 14, 2022

Sep. 30, 2023

Jun. 30, 2023

Mar. 31, 2023

Sep. 30, 2022

Jun. 30, 2022

Mar. 31, 2022

Dec. 31, 2022

Dec. 31, 2022

Sep. 30, 2023

Sep. 30, 2022

Sep. 30, 2020

Dec. 31, 2022

Dec. 31, 2021

Sep. 30, 2023

Aug. 18, 2023

Aug. 17, 2022

Jul. 14, 2022

Class of Stock [Line Items]

Sale of common stock, net

$ 2,956,000

$ 1,328,000

$ 895,000

$ 6,815,000

$ 152,000

$ 7,742,000

Common stock, shares authorized (in shares)

100,000,000

100,000,000

100,000,000

100,000,000

100,000,000

100,000,000

Proceeds from sale of common stock, net

$ 5,180,000

$ 14,558,000

Common Stock [Member]

Class of Stock [Line Items]

Sale of common stock, net

$ 2,000

$ 1,000

$ 1,000

Common stock issued (in shares)

1,589,655

472,674

168,164

673,421

18,070

445,840

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member]

Class of Stock [Line Items]

Common stock, shares authorized (in shares)

57,500,000

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Maximum value of shares to be issued under agreement

$ 50,000,000

Common stock issued (in shares)

266,666

410,500

Period exercisable from the date of issuance

36 months

Number of maximum common shares can be resale

633,333

Initial commitment shares

32,846

32,846

Initial commitment fee paid in cash

$ 125,000

Aggregate gross proceeds from sales of common stock

$ 25,000,000

Proceeds from sale of common stock, net

$ 3,200,000

$ 1,000,000

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Minimum [Member]

Class of Stock [Line Items]

Percentage issuance of common stock

19.99%

2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Maximum [Member]

Class of Stock [Line Items]

Number of maximum common shares can be resale

1,500,000

Number of shares reserved for issuance and sale

600,486

2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Sale of common stock, net

$ 377,666

$ 379,012

Maximum value of shares to be issued under agreement

$ 25,000,000

Common stock issued (in shares)

527,166

Period exercisable from the date of issuance

36 months

Proceeds from sale of common stock, net

$ 7,000,000

$ 12,500,000

Remaining common stock issued and sold (in shares)

0

0

0

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Reimburse of fee and disbursements expenses

$ 50,000

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Common stock issued (in shares)

68,758

1,819,993

Proceeds from sale of common stock, net

$ 600,000

$ 4,300,000

September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Proceeds from sale of common stock, net

$ 5,000,000

Percentage of commission on gross proceeds from sale of common stock

3%

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member]

Class of Stock [Line Items]

Common stock issued (in shares)

460,151

Proceeds from sale of common stock, net

$ 4,800,000

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Remaining availability under financing facility

$ 0

January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]

Class of Stock [Line Items]

Proceeds from sale of common stock, net

$ 5,000,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares to be issued (in shares)	68,422
Stock option contractual term	10 years
Stock option vesting percentage	25%
Total unamortized compensation cost related to outstanding unvested stock options and restricted stock awards | $	$ 0.8
Weighted average period for recognition of cost	1 year 11 months 12 days
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	2 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	4 years
2015 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	6,023
2020 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	179,640
Common stock shares to be issued (in shares)	236,666

Stock-based Compensation - Stoc

Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Options [Roll Forward]
Outstanding as of December 31, 2022 (in shares)	78,334
Granted (in shares)	68,422
Cancelled/forfeited (in shares)	(5,679)
Outstanding as of September 30, 2023 (in shares)	141,077	78,334
Vested and exercisable as of September 30, 2023	65,008
Vested and expected to be vested as of September 30, 2023 (in shares)	133,570
Weighted Average Exercise Price [Roll Forward]
Outstanding as of December 31, 2022 (in dollars per share)	$ 68.10
Granted (in dollars per share)	5
Cancelled/forfeited (in dollars per share)	325.82
Outstanding as of September 30, 2023 (in dollars per share)	37.47	$ 68.10
Vested and exercisable as of September 30, 2023	65.51
Vested and expected to be vested as of September 30, 2023 (in dollars per share)	$ 38.83
Weighted Average Remaining Contractual Life (years) [Roll Forward]
Outstanding as of December 31, 2022	8 years 3 months 25 days	9 years
Vested and exercisable as of September 30, 2023	7 years 6 months 10 days
Vested and expected to be vested as of September 30, 2023	8 years 3 months 3 days
Aggregate Intrinsic Value [Roll Forward]
Outstanding as of September 30, 2023	$ 2
Vested and exercisable as of September 30, 2023	0
Vested and expected to be vested as of September 30, 2023	$ 2