Rein Therapeutics, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31,2025

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM TO

Commission File Number 001-38130

Rein Therapeutics, Inc.

(Exact name of Registrant as specified in its Charter)

Registrant’s telephone number, including area code: (737)802-1989

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YES ☐No ☒

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. YES ☐No ☒

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ NO ☐

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yes ☒ NO ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Ifan emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C.7262(b)) by the registered public accounting firm that prepared or issued its audit report.☐

Indicate by check mark whether the Registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). YES ☐ NO☒

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to § 240.10D-1(b). ☐

As of June 30, 2025, the last business day of the Registrant’s most recently completed second fiscal quarter, the aggregate market value of the voting and non-voting common equity held by non-affiliates of the Registrant, based on the last reported sale price of the shares of common stock on The Nasdaq Capital Market was$32,264,569.

As of March 24, 2026 the Registrant has 28,039,032 shares of Common Stock, $0.001 par value per share, outstanding.

Portions of the Registrant’s definitive proxy statement for its 2025 Annual Meeting of Stockholders, which the Registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the end of the Registrant’s fiscal year ended December 31, 2025, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Table of Contents

Rein and the other trademarks or service marks of Rein appearing in this Annual Report on Form 10-K are the property of Rein. All other trademarks, service marks or other trade names appearing in this Annual Report on Form 10-K are the property of their respective owners.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS AND INDUSTRY DATA

This Annual Report on Form 10-K of Rein Therapeutics, Inc. (“Rein,” “we,” “us,” “our,” or the “Company”) contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this Annual Report on Form 10-K, including statements regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management and expected market growth are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “would,” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

These forward-looking statements include, among other things, statements about:

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our plans to develop and commercialize LTI-03, including the potential benefits thereof;

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our ability to secure sufficient additional capital in the near term or implement other strategies needed to alleviate our current substantial doubt about our ability to continue as a going concern;

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our expectations regarding our ability to fund our operating expenses, our planned activities, and capital expenditure requirements with our cash, cash equivalents and investments

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our Phase 2 clinical trial of LTI-03 and our ability to re-start and complete such clinical trial, subject to obtaining additional funding;

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our decision to further delay clinical development of LTI-01 for an undetermined period of time until additional funds are raised;

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our unproven approach to drug research and development in the area of fibrotic diseases, with a focus on Caveolin-1, or Cav1, related peptides, and our ability to develop marketable products;

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our future clinical trials for LTI-03, whether conducted by us or by any future collaborators, including our ability to enroll patients in our clinical trials, the timing of initiation of these trials and of the anticipated results;

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the success of our remediation efforts related to the material weaknesses identified in our internal controls over financial reporting;

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the timing of and our ability to obtain and maintain marketing approvals for LTI-03;

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the rate and degree of market acceptance and clinical utility of any products for which we receive marketing approval;

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our commercialization, marketing and manufacturing capabilities and strategy;

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our intellectual property position and strategy, and our ability to obtain, maintain and enforce intellectual property rights for our platform and development candidates;

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our ability to identify additional product candidates with significant commercial potential;

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our plans to enter into collaborations for the development and commercialization of LTI-03, LTI-01 and any additional future product candidates;

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our reliance on third-party manufacturing and supply vendors and contract research organizations, or CROs;

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potential benefits of any future collaboration;

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developments relating to our competitors and our industry;

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the impact of general economic conditions, including inflation and the imposition of new or revised tariffs or other trade restrictions; and

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the impact of government laws and regulations.

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. We have included important factors in the cautionary statements included in our Annual Report on Form 10-K, or the Annual Report, and subsequently filed reports, particularly in the “Risk Factors” section, which could cause actual results or events to differ materially from the forward-looking statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, collaborations, joint ventures or investments that we may make or enter into.

You should read this Annual Report and the documents that we reference herein and have filed or incorporated by reference hereto completely and with the understanding that our actual future results may be materially different from what we expect. We do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

This Annual Report includes or incorporates by reference statistical and other industry and market data that we obtained from industry publications and research, surveys and studies conducted by third parties. Industry publications and third-party research, surveys and studies generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information.

Effective on January 10, 2025, we amended our Restated Certificate of Incorporation, as amended, to effect a change in our name from “Aileron Therapeutics, Inc.” to “Rein Therapeutics, Inc.” Unless the context otherwise requires, references in this Annual Report to “we,” “us,” “our” and the “Company” refer to Rein Therapeutics, Inc. and its wholly owned subsidiaries.

Summary Risk Factors

Our business is subject to a number of risks of which you should be aware in evaluating our company and our business. These risks are discussed more fully in the “Risk Factors” section of this Annual Report. These risks include the following:

Risks Related to Our Financial Condition

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We believe that our existing cash and cash equivalents as of December 31, 2025, together with the proceeds received by us pursuant to the securities purchase agreements we entered into in January 2026 and February 2026, will be sufficient to enable us to fund our planned operating expense and capital expenditure requirements into the second quarter of 2026, as a result we will need to obtain sufficient additional funding in order to sustain our current level of operations and complete our Phase 2 RENEW clinical trial of LTI-03.

•

We will require substantial additional capital to finance our operations beyond the second quarter of 2026 and to complete the development and commercialization of our product candidates. Due to our current liquidity constraints, we have paused development of LTI‑01 and other preclinical programs for an undetermined period and are prioritizing LTI‑03. If we are unable to raise such capital when needed, or on acceptable terms, we may be forced to delay our clinical and research and development program, future commercialization efforts or other operations.

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We have identified material weaknesses in our internal control over financial reporting and may identify additional material weaknesses in the future or fail to maintain an effective system of internal control over financial reporting, which may result in material misstatements of our financial statements or cause us to fail to meet our periodic reporting obligations.

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We have incurred significant net losses since inception and we expect to continue to incur significant net losses for the foreseeable future.

Risks Related to the Discovery, Development and Commercialization of Product Candidates

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Our business is highly dependent on the success of our product candidate, LTI-03, which is now screening and recruiting patients in a Phase 2 clinical trial that initiated in May 2025.

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Our approach to drug research and development in the area of fibrotic diseases, with a focus on Cav1-related peptides, is unproven and may not result in marketable products.

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The outcome of preclinical testing and early clinical trials may not be predictive of the success of later clinical trials, interim results of a clinical trial, do not necessarily predict final results and the results of our clinical trials may not satisfy the requirements of the U.S. Food and Drug Administration, or the FDA, or comparable foreign regulatory authorities.

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We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of LTI-03.

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Our future clinical trials may reveal significant adverse events or unexpected drug-drug interactions not seen in our preclinical studies or earlier clinical studies and may result in a safety profile that could delay or prevent regulatory approval or market acceptance of any of our product candidates.

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Clinical development involves a lengthy, complex and expensive process, with an uncertain outcome.

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We have never obtained marketing approval for a product candidate and we may be unable to obtain, or may be delayed in obtaining, marketing approval for any product candidate. If we are unable to establish marketing and sales capabilities or enter into agreements with third parties to market and sell our products, we may not be able to generate product revenue.

Risks Related to Our Dependence on Third Parties

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We rely on third parties to conduct certain aspects of our clinical trials and preclinical studies. If these third parties do not successfully carry out their contractual duties, meet expected deadlines or comply with regulatory requirements, we may not be able to obtain regulatory approval of or commercialize any potential product candidates.

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Because we rely on third-party manufacturing and supply vendors, our supply of research and development, preclinical and clinical development materials may become limited or interrupted or may not be of satisfactory quantity or quality.

Risks Related to Our Intellectual Property

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Our success depends in part on our ability to protect our intellectual property. It is difficult and costly to protect our proprietary rights and technology, and we may not be able to ensure their protection.

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We are currently party to license or other collaboration agreements that impose certain obligations on us, and we may enter into additional license or collaboration agreements in the future. If we fail to comply with our obligations under such present or future agreements with third parties, we could lose license rights that may be important to our business.

Risks Related to Our Common Stock

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Assuming the conversion of all outstanding Series X Non-Voting Convertible Preferred Stock, or the Series X Preferred Stock, and the exercise of outstanding warrants to purchase shares of our common stock, or the Warrants, there is a concentration of ownership of our outstanding common stock by entities and individuals affiliated with Bios Partners. If this group chooses to act together, it could exert substantial influence over our business, and the interests of this group may conflict with those of other stockholders.