Moleculin Biotech (NASDAQ: MBRX) boosts at-the-market share sale capacity

Rhea-AI Filing Summary

Moleculin Biotech, Inc. (MBRX) is increasing the capacity of its existing at-the-market common stock program under its At The Market Offering Agreement with Roth Capital Partners to allow sales of up to $19,700,000 of common stock from and after August 21, 2026, not including shares previously sold. This supplements earlier ATM capacities of $6,500,000 set in July 2025 and $8,200,000 set in December 2025. As of this supplement, Moleculin has sold 486,775 shares for aggregate gross sales of $1,890,241 under the ATM program. The company’s common stock trades on the Nasdaq Capital Market under the symbol MBRX, with a last reported sale price of $0.5906 per share on August 20, 2026. Public float is approximately $64,852,256 based on 19,477,380 outstanding shares, of which 1,311,482 are held by affiliates, and Moleculin states it is subject to the one‑third public float limit for primary offerings under General Instruction I.B.6 of Form S‑3.

Filing Explained

The ATM expansion permits potential issuance, but dilution remains conditional on future sales rather than the full amount being sold now.

The company has expanded the existing ATM program to permit up to $19,700,000 of additional aggregate gross sales from August 21, 2026; if shares are sold, existing holders’ percentage ownership would decline as the total share count increases.

In practical terms, this supplement changes the program’s registered offering capacity, not its completion state: it does not show that the increased amount has been issued or that those potential sales proceeds have been received.

The filing says another prospectus supplement would precede any additional sales under the ATM agreement, providing the next filing-based checkpoint for actual use of the capacity.

Key Figures

ATM Offering Size Increase: $19,700,000 Initial ATM capacity (July 2025 prospectus): $6,500,000 Revised ATM capacity (December 2025 prospectus): $8,200,000 +5 more

8 metrics

ATM Offering Size Increase $19,700,000 Maximum aggregate gross sales price of common stock that may be offered under the ATM Agreement from and after August 21, 2026

Initial ATM capacity (July 2025 prospectus) $6,500,000 Common stock registered for offer and sale under the ATM Agreement in July 2025

Revised ATM capacity (December 2025 prospectus) $8,200,000 Increased common stock capacity under the ATM Agreement as of December 2025

Shares sold under ATM 486,775 shares Common stock sold under the July 2025 and December 2025 ATM prospectuses

Aggregate gross sales under ATM $1,890,241 Total gross sales price of shares sold under the ATM Agreement as of this supplement

Last reported sale price $0.5906 per share MBRX common stock on Nasdaq on August 20, 2026

Public float $64,852,256 Aggregate market value of non-affiliate common equity based on $3.57 per share as of June 29, 2026

Shares outstanding 19,477,380 shares Outstanding common stock as of the date of the prospectus supplement; 1,311,482 shares held by affiliates

Key Terms

At The Market Offering Agreement, public float, General Instruction I.B.6 of Form S-3, Nasdaq Capital Market

4 terms

At The Market Offering Agreement financial

"We have previously entered into an At The Market Offering Agreement (“ATM Agreement”) with Roth"

An at-the-market offering agreement is a contract that lets a company sell newly issued shares directly into the open market through a broker, at whatever price the stock is trading at that moment. For investors this matters because it can increase the number of shares available (which may dilute existing ownership) while providing a flexible, often faster way for the company to raise cash without fixing a price, similar to a vendor selling small batches at current market stalls rather than setting a single fixed price.

public float financial

"the aggregate market value of the voting and non-voting common equity held by non-affiliates, our public float, was approximately"

Public float is the total number of a company's shares that are available for trading by the general public. It excludes shares held by company insiders or large stakeholders who are unlikely to sell them easily. This figure helps investors understand how much of the company's stock is actively available, which can influence its liquidity and how easily its price might change.

General Instruction I.B.6 of Form S-3 regulatory

"Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities"

Nasdaq Capital Market market

"Our common stock is listed on The Nasdaq Capital Market (“Nasdaq”), under the symbol “MBRX.”"

The Nasdaq Capital Market is a platform where smaller, emerging companies can list their shares for trading by investors. It provides these companies with access to funding and visibility, helping them grow, much like a local marketplace where new vendors can introduce their products to potential customers. For investors, it offers opportunities to discover early-stage companies with growth potential.

Offering Details

ATM

Offering

Offering Type ATM

FAQ

What is Moleculin Biotech (MBRX) registering in this 424B5 supplement?

Moleculin Biotech is increasing the size of its at-the-market common stock offering program to permit sales of up to $19,700,000 of common stock under its At The Market Offering Agreement with Roth Capital Partners, excluding shares previously sold.

How much has Moleculin Biotech (MBRX) already sold under its ATM program?

Moleculin Biotech reports that it has sold 486,775 shares of common stock for an aggregate gross sales price of $1,890,241 under the July 2025 and December 2025 ATM prospectuses.

What was the previous ATM capacity before this Moleculin (MBRX) increase?

The company initially registered up to $6,500,000 of common stock for the ATM in July 2025, which was later increased to $8,200,000 in December 2025 before this new $19,700,000 capacity.

What is Moleculin Biotech’s (MBRX) public float and share count?

Public float is approximately $64,852,256, based on 19,477,380 outstanding common shares, of which 1,311,482 are held by affiliates, using a price of $3.57 per share as of June 29, 2026.

What trading price for MBRX is referenced in this prospectus supplement?

The supplement cites a last reported sale price of Moleculin Biotech common stock on Nasdaq of $0.5906 per share on August 20, 2026.

What limitation under Form S-3 applies to Moleculin Biotech (MBRX) ATM sales?

Moleculin states that under General Instruction I.B.6 of Form S‑3, it will not sell primary offering securities exceeding more than one-third of its public float in any 12‑month period while its public float remains below $75.0 million.

How much has Moleculin Biotech (MBRX) sold under the I.B.6 limit in the last 12 months?

The company discloses that it has sold approximately $1,890,241 of securities during the 12 calendar months prior to and including the date of this prospectus supplement pursuant to General Instruction I.B.6 of Form S‑3.

AI-generated analysis. How Rhea-AI works. Not financial advice.

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google

Add on Google Not now

Available on EDGAR 08/21/2026 - 05:16 PM Accepted by SEC EDGAR 08/21/2026 - 05:16 PM Learn about SEC filing dates

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-280064

Prospectus Supplement No. 2

(to Prospectus dated July 1, 2024)

Moleculin Biotech, Inc.

Up to $19,700,000

Common Stock

We have previously entered into an At The Market Offering Agreement (“ATM Agreement”) with Roth Capital Partners, LLC (“Roth”) relating to shares of our common stock offered by this second prospectus supplement (this "prospectus supplement"), the first prospectus supplement dated December 31, 2025 (the “December 2025 prospectus”), and the initial prospectus dated July 11, 2025 (the “July 2025 prospectus”) and the base prospectus dated July 1, 2024 (the “base prospectus”). In accordance with the terms of the ATM Agreement, we may offer and sell shares of our common stock, $0.001 par value per share, from time to time through Roth acting as our agent (the “ATM Offering”).

We are filing this prospectus supplement to supplement and amend, as of August 21, 2026, the December 2025 prospectus, and the July 2025 prospectus to increase the maximum aggregate gross sales price of our common stock that may be offered, issued and sold under the ATM Agreement from and after the date hereof to $19,700,000 (the “ATM Offering Size Increase”), not including the shares of common stock previously sold. Under the July 2025 prospectus, we initially registered up to $6,500,000 of our common stock for offer and sale pursuant to the ATM Agreement, which was increased to $8,200,000 pursuant to the December 2025 prospectus. As of the date of the filing of this prospectus supplement, we have sold 486,775 shares of our common stock that are covered by the December 2025 prospectus and the July 2025 prospectus pursuant to the ATM Agreement for an aggregate gross sales price of $1,890,241.

The purpose of this prospectus supplement is to update the December 2025 prospectus and the July 2025 prospectus to reflect the ATM Offering Size Increase. Except as modified by this prospectus supplement, the terms of the ATM Offering remain unchanged, and the ATM Agreement remains in full force and effect.

Our common stock is listed on The Nasdaq Capital Market (“Nasdaq”), under the symbol “MBRX.” On August 20, 2026, the last reported sale price of our common stock on Nasdaq was $0.5906 per share.

As of the date of this prospectus supplement, the aggregate market value of the voting and non-voting common equity held by non-affiliates, our public float, was approximately $64,852,256, based on 19,477,380 shares of outstanding common stock as of the date of this prospectus supplement, of which 1,311,482 shares were held by affiliates, and at a price of $3.57 per share, the closing sale price of our common stock on June 29, 2026, which is the highest closing sale price of our common stock on Nasdaq within the prior 60 days of this prospectus supplement. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities in a public primary offering with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75.0 million. During the 12 calendar months prior to and including the date of this prospectus supplement, we have sold approximately $1,890,241 of securities pursuant to General Instruction I.B.6 of Form S-3. In the event that we may sell additional amounts under the ATM Agreement, we will file another prospectus supplement prior to making such additional sales.

Investing in our securities involves a high degree of risk. These risks are described under the caption “Risk Factors” beginning on page S-9 of the July 2025 prospectus and the base prospectus, respectively, and in the documents incorporated by reference into the July 2025 prospectus and base prospectus, as well as the risks and uncertainties described in other documents we file with the Securities and Exchange Commission.

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 this prospectus supplement or the accompanying base prospectus. Any representation to the contrary is a criminal offense.

Roth Capital Partners

The date of this prospectus supplement is August 21, 2026