Moleculin Biotech increases ATM stock offering size to $19.7 million

Moleculin Biotech, Inc. filed a Form 424B5 prospectus supplement dated August 21, 2026, to supplement and amend the December 2025 prospectus and the July 2025 prospectus to increase the maximum aggregate gross sales price of common stock that may be offered under the ATM Agreement to $19,700,000, not including shares previously sold.¹

The offering is conducted under an At The Market Offering Agreement with Roth Capital Partners, LLC, covering shares offered through this prospectus supplement, the December 2025 prospectus supplement, and the initial July 2025 prospectus.¹ The size of the program has grown over time: the company initially registered up to $6,500,000 of common stock under the July 2025 prospectus, which was increased to $8,200,000 under the December 2025 prospectus.¹

As of the filing date, Moleculin had sold 486,775 shares under the December 2025 and July 2025 prospectuses for an aggregate gross sales price of $1,890,241.¹

Moleculin's common stock trades on Nasdaq under the ticker "MBRX," and the last reported sale price on August 20, 2026 was $0.5906 per share.¹ The company's public float calculation used a price of $3.57 per share, the closing sale price on June 29, 2026, described as the highest closing price within the prior 60 days, with a public float of approximately $64,852,256 based on 19,477,380 shares outstanding, of which 1,311,482 shares were held by affiliates.¹

Under SEC rules, the company is limited to selling no more than one-third of its public float in any 12-month period under General Instruction I.B.6 of Form S-3 while its public float remains below $75.0 million.¹ Sales under that instruction over the trailing 12 months totaled approximately $1,890,241.¹ The filing states that further sales beyond the amounts covered here would require an additional prospectus supplement before proceeding.¹