Nature of the Business	3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]
Nature of the Business	1. Nature of the Business On January 10, 2025, Aileron Therapeutics, Inc., or Aileron, amended its Restated Certificate of Incorporation, as amended, to effect a change of the Company’s name from “Aileron Therapeutics, Inc.” to “Rein Therapeutics, Inc.”, or Rein, or the Company. Prior to the Lung Acquisition (as defined below), the Company was a clinical stage chemoprotection oncology company. The Company’s product candidate, ALRN-6924, was a MDM2/MDMX dual inhibitor that leverages its proprietary peptide drug technology. In February 2023, the Company decided to terminate further development of ALRN-6924. On October 31, 2024, the Company entered into an exclusive option agreement with Advancium Health Network, or Advancium, for the sale of ALRN-6924. The Company is a clinical stage biopharmaceutical company focused on developing novel therapies for the treatment of fibrosis indications with no approved or limited effective treatments. The Company currently has two product candidates in clinical development, LTI-03 and LTI-01, and multiple candidates in preclinical development focused on fibrosis indications. On October 31, 2023, the Company acquired Lung Therapeutics, Inc., or Lung Therapeutics or Lung, pursuant to an Agreement and Plan of Merger, dated October 31, 2023, or the Lung Acquisition Agreement, by and among the Company, AT Merger Sub I, Inc., a Delaware corporation and its wholly owned subsidiary, or the First Merger Sub, AT Merger Sub II, LLC, a Delaware limited liability company and its wholly owned subsidiary, or the Second Merger Sub, and Lung. Its principal offices are in Austin, Texas. Following the Lung Acquisition, the Company shifted its operating disease focus to advancing a pipeline of first-in-class medicines to address significant unmet medical needs in orphan pulmonary and fibrosis indications with the potential to greatly improve patient outcomes over currently available treatments. Following expiration of the lease on March 31, 2024, Rein currently operates and expects to operate virtually for the foreseeable future. The Company is subject to risks and uncertainties common to clinical-stage companies in the biotechnology industry, including, but not limited to the risk that the Company never achieves profitability, the need for substantial additional financing, the risk of relying on third parties, risks of clinical trial failures, dependence on key personnel, protection of proprietary technology, and compliance with government regulations. The Company’s lead product candidate, LTI-03, is being developed for the treatment of Idiopathic Pulmonary Fibrosis, or IPF, and has been evaluated in a healthy volunteer Phase 1a clinical trial and in a Phase 1b clinical trial in IPF patients. A Phase 2 multi-center, randomized, double-blind, and placebo-controlled study evaluating the safety, tolerability, and efficacy of LTI-03 in patients with IPF will enroll up to 120 IPF patients with interim topline data expected in the first half of 2026. The Company’s second product candidate, LTI-01, is in development for loculated pleural effusion, or LPE. The Company has completed Phase 1b and Phase 2a clinical trials in LPE patients. In June 2024, the Company decided to temporarily delay clinical development of LTI-01 in an effort to focus its resources on clinical development of LTI-03 and until additional funds are raised. In the fourth quarter of 2024, the Company determined that the temporary delay of further clinical development of LTI-01 may not be a short-term measure. Liquidity and Going Concern In accordance with Accounting Standards Update, or ASU, No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the accompanying condensed consolidated financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the condensed consolidated financial statements are issued. When substantial doubt exists, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the condensed consolidated financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the condensed consolidated financial statements are issued. The Company’s condensed consolidated financial statements have been prepared assuming that the Company will continue to operate as a going concern, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through March 31, 2025, the Company has financed its operations primarily through $145,467 in net proceeds from sales of common stock and warrants, $712 in net proceeds from sales of common stock under our “at-the-market” offering program, $131,211 from sales of preferred stock prior to its initial public offering, or IPO, $34,910 from a collaboration agreement in 2010, $17,536 in net proceeds in connection with a private placement following the Lung Acquisition in 2023, and $17,675 in net proceeds in connection with an underwritten offering of the Company's common stock and accompanying warrants to purchase common stock in May 2024. As of March 31, 2025, the Company had $7,428 in cash and cash equivalents. In May 2024, the Company completed an underwritten follow-on public offering, or the Offering, pursuant to which the Company issued and sold 4,273,505 shares of the Company’s common stock, par value $0.001 per share, or the Offering Shares, and accompanying warrants, or the Offering Warrants, to purchase 4,273,505 shares of common stock, or the Offering Warrant Shares. All of the Offering Shares and Offering Warrants were sold by the Company. Each Offering Share was offered and sold together with an accompanying Offering Warrant at a combined offering price of $4.68, and the underwriter purchased each Offering Share with an accompanying Offering Warrant from the Company at a combined price of $4.35. Net proceeds from the Offering were $17,675, after deducting underwriting discounts and commissions and offering expenses, and excluding any proceeds that may be received from exercise of the Offering Warrants. As of March 31, 2025, none of the Offering Warrants had been exercised. On May 15, 2025, the Company entered into an “at the market offering” agreement, or the Wainwright Sales Agreement, with H.C. Wainwright & Co., LLC, or H.C. Wainwright, as agent and/or principal, pursuant to which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $13,702 from time to time through or to H.C. Wainwright by any method permitted that is deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended. Prior to entering into the Wainwright Sales Agreement, the Company terminated the equity distribution agreement, dated July 26, 2024, or the Equity Distribution Agreement, with Citizens JMP Securities, LLC, or Citizens JMP, as agent and/or principal, under which the Company could offer and sell up to $50,000 of shares of its common stock from time to time through or to Citizens JMP by any method that was deemed an “at the market” offering as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended. In January 2025, the Company issued and sold 317,772 shares of common stock pursuant to the Equity Distribution Agreement for total net proceeds of $712, after deducting transaction fees of $22 paid by the Company. In April 2025, the Company entered into privately negotiated letter agreements with certain holders of the PIPE Warrants, as described in Note 3, and certain holders of the Offering Warrants, who agreed to exercise for cash the PIPE Warrants and the Offering Warrants, or the Warrant Exercises. The total gross proceeds for the Warrant Exercises were $1,679. Also in April 2025, the Company entered into privately negotiated letter agreements with additional holders of the PIPE Warrants who, in exchange for pre-funded warrants, or the Exchange Pre-Funded Warrants, surrendered PIPE Warrants to the Company for cancellation and made an aggregate cash payment into which the Exchange Pre-Funded Warrants are exercisable, or the Warrant Exchanges. The total gross proceeds for the Warrant Exchanges were $3,101. In addition, an entity affiliated with Bios Partners, or the Bios Purchaser, purchased additional pre-funded warrants in a private placement, or the Placement Pre-Funded Warrants, pursuant to a subscription agreement underlying the Placement Pre-Funded Warrants, or the Private Placement. Total gross proceeds for the Private Placement were $500. The Warrant Exercises, Warrant Exchanges and Private Placement are collectively referred to as the April 2025 Transactions. Refer to Note 15 for more details. Management believes that, based on the Company’s current operating plan, the Company’s cash and cash equivalents of $7,428 as of March 31, 2025, together with the proceeds received by the Company in the April 2025 Transactions will not be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements for at least twelve months from the date of issuance of these consolidated financial statements, which raises substantial doubt about our ability to continue as a going concern. Since its inception, the Company has not generated any revenue from product sales and has never generated an operating profit. The Company has incurred significant losses on an aggregate basis. The Company’s net losses were $5,501 and $7,113 for the three months ended March 31, 2025 and 2024, respectively. As of March 31, 2025, the Company had an accumulated deficit of $356,901. These losses have resulted primarily from costs incurred in connection with research and development activities, licensing and patent investment and general and administrative costs associated with the Company’s operations. Management expects to continue to incur operating losses for the foreseeable future. The Company expects to finance its operations primarily through utilization of its current financial resources and through the sale of additional equity or debt financings, collaborations, licensing arrangements or other sources. The Company plans to address these conditions by, among other things, raising additional funds through equity or debt financings, strategic collaborations, licensing arrangements or other sources. However, there is no assurance that such funding will be available to the Company, will be obtained on terms favorable to the Company or will provide the Company with sufficient funds to meet its objectives. The Company’s funding estimates are based on assumptions that may prove to be wrong, and the Company could use its available capital resources sooner than it currently expects. If additional funds are not available, the Company could be forced to delay, reduce or eliminate its research and development programs or future commercialization efforts and its business could be materially harmed. The Company’s future viability is dependent on its ability to raise additional capital, enter into a financing, consummate a successful acquisition, merger, business combination, or sale of assets or other transaction. If the Company becomes unable to continue as a going concern, it may have to liquidate its assets and the values it receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in its consolidated financial statements. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Nature of the Business

3 Months Ended

Mar. 31, 2025

1. Nature of the Business

On January 10, 2025, Aileron Therapeutics, Inc., or Aileron, amended its Restated Certificate of Incorporation, as amended, to effect a change of the Company’s name from “Aileron Therapeutics, Inc.” to “Rein Therapeutics, Inc.”, or Rein, or the Company.

Prior to the Lung Acquisition (as defined below), the Company was a clinical stage chemoprotection oncology company. The Company’s product candidate, ALRN-6924, was a MDM2/MDMX dual inhibitor that leverages its proprietary peptide drug technology. In February 2023, the Company decided to terminate further development of ALRN-6924. On October 31, 2024, the Company entered into an exclusive option agreement with Advancium Health Network, or Advancium, for the sale of ALRN-6924.

The Company is a clinical stage biopharmaceutical company focused on developing novel therapies for the treatment of fibrosis indications with no approved or limited effective treatments. The Company currently has two product candidates in clinical development, LTI-03 and LTI-01, and multiple candidates in preclinical development focused on fibrosis indications.

On October 31, 2023, the Company acquired Lung Therapeutics, Inc., or Lung Therapeutics or Lung, pursuant to an Agreement and Plan of Merger, dated October 31, 2023, or the Lung Acquisition Agreement, by and among the Company, AT Merger Sub I, Inc., a Delaware corporation and its wholly owned subsidiary, or the First Merger Sub, AT Merger Sub II, LLC, a Delaware limited liability company and its wholly owned subsidiary, or the Second Merger Sub, and Lung. Its principal offices are in Austin, Texas. Following the Lung Acquisition, the Company shifted its operating disease focus to advancing a pipeline of first-in-class medicines to address significant unmet medical needs in orphan pulmonary and fibrosis indications with the potential to greatly improve patient outcomes over currently available treatments. Following expiration of the lease on March 31, 2024, Rein currently operates and expects to operate virtually for the foreseeable future.

The Company is subject to risks and uncertainties common to clinical-stage companies in the biotechnology industry, including, but not limited to the risk that the Company never achieves profitability, the need for substantial additional financing, the risk of relying on third parties, risks of clinical trial failures, dependence on key personnel, protection of proprietary technology, and compliance with government regulations. The Company’s lead product candidate, LTI-03, is being developed for the treatment of Idiopathic Pulmonary Fibrosis, or IPF, and has been evaluated in a healthy volunteer Phase 1a clinical trial and in a Phase 1b clinical trial in IPF patients. A Phase 2 multi-center, randomized, double-blind, and placebo-controlled study evaluating the safety, tolerability, and efficacy of LTI-03 in patients with IPF will enroll up to 120 IPF patients with interim topline data expected in the first half of 2026. The Company’s second product candidate, LTI-01, is in development for loculated pleural effusion, or LPE. The Company has completed Phase 1b and Phase 2a clinical trials in LPE patients. In June 2024, the Company decided to temporarily delay clinical development of LTI-01 in an effort to focus its resources on clinical development of LTI-03 and until additional funds are raised. In the fourth quarter of 2024, the Company determined that the temporary delay of further clinical development of LTI-01 may not be a short-term measure.

Liquidity and Going Concern

In accordance with Accounting Standards Update, or ASU, No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the accompanying condensed consolidated financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the condensed consolidated financial statements are issued. When substantial doubt exists, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the condensed consolidated financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the condensed consolidated financial statements are issued.

The Company’s condensed consolidated financial statements have been prepared assuming that the Company will continue to operate as a going concern, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through March 31, 2025, the Company has financed its operations primarily through $145,467 in net proceeds from sales of common stock and warrants, $712 in net proceeds from sales of common stock under our “at-the-market” offering program, $131,211 from sales of preferred stock prior to its initial public offering, or IPO, $34,910 from a collaboration agreement in 2010, $17,536 in net proceeds in connection with a private placement following the Lung Acquisition in 2023, and $17,675 in net proceeds in connection with an underwritten offering of the Company's common stock and accompanying warrants to purchase common stock in May 2024. As of March 31, 2025, the Company had $7,428 in cash and cash equivalents.

In May 2024, the Company completed an underwritten follow-on public offering, or the Offering, pursuant to which the Company issued and sold 4,273,505 shares of the Company’s common stock, par value $0.001 per share, or the Offering Shares, and accompanying

warrants, or the Offering Warrants, to purchase 4,273,505 shares of common stock, or the Offering Warrant Shares. All of the Offering Shares and Offering Warrants were sold by the Company. Each Offering Share was offered and sold together with an accompanying Offering Warrant at a combined offering price of $4.68, and the underwriter purchased each Offering Share with an accompanying Offering Warrant from the Company at a combined price of $4.35. Net proceeds from the Offering were $17,675, after deducting underwriting discounts and commissions and offering expenses, and excluding any proceeds that may be received from exercise of the Offering Warrants. As of March 31, 2025, none of the Offering Warrants had been exercised.

On May 15, 2025, the Company entered into an “at the market offering” agreement, or the Wainwright Sales Agreement, with H.C. Wainwright & Co., LLC, or H.C. Wainwright, as agent and/or principal, pursuant to which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $13,702 from time to time through or to H.C. Wainwright by any method permitted that is deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended. Prior to entering into the Wainwright Sales Agreement, the Company terminated the equity distribution agreement, dated July 26, 2024, or the Equity Distribution Agreement, with Citizens JMP Securities, LLC, or Citizens JMP, as agent and/or principal, under which the Company could offer and sell up to $50,000 of shares of its common stock from time to time through or to Citizens JMP by any method that was deemed an “at the market” offering as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended. In January 2025, the Company issued and sold 317,772 shares of common stock pursuant to the Equity Distribution Agreement for total net proceeds of $712, after deducting transaction fees of $22 paid by the Company.

In April 2025, the Company entered into privately negotiated letter agreements with certain holders of the PIPE Warrants, as described in Note 3, and certain holders of the Offering Warrants, who agreed to exercise for cash the PIPE Warrants and the Offering Warrants, or the Warrant Exercises. The total gross proceeds for the Warrant Exercises were $1,679. Also in April 2025, the Company entered into privately negotiated letter agreements with additional holders of the PIPE Warrants who, in exchange for pre-funded warrants, or the Exchange Pre-Funded Warrants, surrendered PIPE Warrants to the Company for cancellation and made an aggregate cash payment into which the Exchange Pre-Funded Warrants are exercisable, or the Warrant Exchanges. The total gross proceeds for the Warrant Exchanges were $3,101. In addition, an entity affiliated with Bios Partners, or the Bios Purchaser, purchased additional pre-funded warrants in a private placement, or the Placement Pre-Funded Warrants, pursuant to a subscription agreement underlying the Placement Pre-Funded Warrants, or the Private Placement. Total gross proceeds for the Private Placement were $500. The Warrant Exercises, Warrant Exchanges and Private Placement are collectively referred to as the April 2025 Transactions. Refer to Note 15 for more details.

Management believes that, based on the Company’s current operating plan, the Company’s cash and cash equivalents of $7,428 as of March 31, 2025, together with the proceeds received by the Company in the April 2025 Transactions will not be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements for at least twelve months from the date of issuance of these consolidated financial statements, which raises substantial doubt about our ability to continue as a going concern.

Since its inception, the Company has not generated any revenue from product sales and has never generated an operating profit. The Company has incurred significant losses on an aggregate basis. The Company’s net losses were $5,501 and $7,113 for the three months ended March 31, 2025 and 2024, respectively. As of March 31, 2025, the Company had an accumulated deficit of $356,901. These losses have resulted primarily from costs incurred in connection with research and development activities, licensing and patent investment and general and administrative costs associated with the Company’s operations. Management expects to continue to incur operating losses for the foreseeable future. The Company expects to finance its operations primarily through utilization of its current financial resources and through the sale of additional equity or debt financings, collaborations, licensing arrangements or other sources.

The Company plans to address these conditions by, among other things, raising additional funds through equity or debt financings, strategic collaborations, licensing arrangements or other sources. However, there is no assurance that such funding will be available to the Company, will be obtained on terms favorable to the Company or will provide the Company with sufficient funds to meet its objectives. The Company’s funding estimates are based on assumptions that may prove to be wrong, and the Company could use its available capital resources sooner than it currently expects. If additional funds are not available, the Company could be forced to delay, reduce or eliminate its research and development programs or future commercialization efforts and its business could be materially harmed. The Company’s future viability is dependent on its ability to raise additional capital, enter into a financing, consummate a successful acquisition, merger, business combination, or sale of assets or other transaction. If the Company becomes unable to continue as a going concern, it may have to liquidate its assets and the values it receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in its consolidated financial statements. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.