[424B5] Rein Therapeutics, Inc. Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

Rein Therapeutics (Nasdaq: RNTX) filed a Rule 424(b)(5) prospectus supplement that amends its May 22 2025 at-the-market (ATM) shelf with H.C. Wainwright.

The filing reduces the remaining issuance capacity under the Form S-3 from $15.77 million to $8.07 million. The cut aligns with General Instruction I.B.6, which limits sales to one-third of the company’s $42.3 million public float (calculated on July 24 2025) during any 12-month period while the float remains below $75 million.

To date the company has raised only $35,460 (16,127 shares) through the ATM. Following the adjustment, up to approximately $8.03 million of common stock can still be issued from time to time. Additional supplements will be required if a larger float later permits greater issuance capacity.

RNTX shares last closed at $1.41 on July 28 2025. Investors should evaluate the dilution risk associated with future ATM sales versus the financing flexibility this mechanism provides.

Positive

• Maintains ~$8.07 m ATM capacity, providing flexible, quick-access financing without underwriting fees.
• Filing keeps the shelf fully compliant with SEC Form S-3 limits, avoiding potential registration issues.

Negative

• Potential dilution of up to 19% of current market cap if full $8 m is issued at recent prices.
• Reduced capacity from $15.77 m highlights limited public float and micro-cap status, potentially restricting longer-term funding options.

Insights

Securities Analyst

TL;DR: Neutral—capacity cut reflects regulatory cap, modest dilution risk, improves compliance.

The supplement simply aligns the ATM program with the one-third public-float restriction applicable to micro-caps. Only $35k has been raised so far, so near-term dilution is minimal. However, authorizing up to $8 m (≈19% of market cap) leaves open incremental dilution at market prices that have drifted to $1.41. The action signals continued reliance on equity financing, but also shows management is maintaining registration-statement compliance. Overall financial impact is limited today; future effect depends on usage pace and pricing.

Corporate Finance Specialist

TL;DR: Procedural adjustment; keeps ATM valid, liquidity optionality intact.

The downsizing is mechanical under Form S-3 rules, not a strategic reversal. By preserving ~$8 m of shelf room, the company secures flexible, low-cost capital for working capital or R&D without renegotiating new agreements. Yet, given sub-$75 m float, any sizable draw will meaningfully dilute holders. Investors should watch trading volumes and subsequent 424(b)(5) filings for execution pace; heavy usage during price weakness could pressure shares.

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-287342

PROSPECTUS SUPPLEMENT

(To Prospectus dated May 22, 2025)

$8,066,607

Common Stock

This prospectus supplement amends and supplements certain information in the prospectus, dated May 22, 2025, filed with the Securities and Exchange Commission as a part of our registration statement on Form S-3 (File No. 333-287342), which we refer to as the Prior Prospectus, relating to the offer and sale of shares of our common stock, $0.001 par value per share, having an aggregate offering price of up to $15,773,673 pursuant to the At the Market Offering Agreement, dated May 15, 2025, or the sales agreement, that we previously entered into with H.C. Wainwright & Co., LLC. As of the date of this prospectus supplement, we had sold an aggregate of 16,127 shares of our common stock in accordance with the sales agreement under the Prior Prospectus for aggregate gross proceeds of $35,460. This prospectus supplement should be read in conjunction with the Prior Prospectus, and is qualified by reference thereto, except to the extent that the information herein amends or supersedes the information contained in the Prior Prospectus. This prospectus supplement is not complete without, and may only be delivered or utilized in connection with, the Prior Prospectus and any future amendments or supplements thereto.

We are filing this prospectus supplement to amend the Prior Prospectus to reduce the amount of common stock we may offer and sell under the sales agreement. As of the date of this prospectus supplement, we are subject to General Instruction I.B.6 of Form S-3, which limits the amounts that we may sell under the registration statement of which this prospectus supplement and the Prior Prospectus are a part. After giving effect to these limits and other amounts we may sell under the registration statement of which this prospectus supplement and the Prior Prospectus are a part, we may offer and sell from and after the date hereof shares of our common stock having an aggregate offering price of up to $8,066,607 from time to time in accordance with the terms of the sales agreement pursuant to this prospectus supplement and the Prior Prospectus, inclusive of the shares sold prior to the date hereof. If our public float increases such that we may sell additional amounts under the sales agreement and the registration statement of which this prospectus supplement and the Prior Prospectus are a part, we will file a prospectus supplement prior to selling such additional amounts.

As of July 24, 2025, the aggregate market value of our outstanding common stock held by non-affiliates was approximately $42,306,201, which we calculated based on 23,046,121 shares of outstanding common stock as of July 24, 2025, of which 20,943,664 shares were held by non-affiliates, and a price per share of $2.02, which was the closing price of our common stock on June 3, 2025. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell, pursuant to the registration statement of which this prospectus supplement and the Prior Prospectus form a part, securities with a value exceeding one-third of the aggregate market value of our outstanding common stock held by non-affiliates in any 12-month period, so long as the aggregate market value of our outstanding common stock held by non-affiliates remains below $75.0 million. During the 12 calendar months prior to and including the date of this prospectus supplement, we have offered or sold shares of our common stock having an aggregate purchase price of $35,460 pursuant to General Instruction I.B.6 of Form S-3.

Our common stock is listed on The Nasdaq Capital Market under the trading symbol “RNTX.” On July 28, 2025, the last sale price of our common stock as reported on The Nasdaq Capital Market was $1.41 per share.

Investing in our common stock involves certain risks. See “Risk Factors” beginning on page SA-6 of the Prior Prospectus and in the documents incorporated by reference in the Prior Prospectus for a discussion of the factors you should carefully consider before deciding to invest in our common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Prior Prospectus or this prospectus supplement. Any representation to the contrary is a criminal offense.

H.C. Wainwright & Co.

July 30, 2025

FAQ

How much common stock can Rein Therapeutics (RNTX) now sell under its ATM program?

Up to $8,066,607 in aggregate, inclusive of $35,460 already sold.

Why was the ATM capacity reduced?

Form S-3 Instruction I.B.6 caps issuance to one-third of the $42.3 m public float; the prior $15.77 m exceeded that limit.

How many shares has RNTX sold so far through the ATM?

Only 16,127 shares generating gross proceeds of $35,460.

What is RNTX’s current share price and market cap?

The stock last closed at $1.41 (July 28 2025) with a public float value of $42.3 m.

Will future ATM sales dilute existing shareholders?

Yes; issuing the remaining $8 m at current prices could increase the share count materially, pressuring EPS and ownership percentages.