Radiopharm Theranostics updates $9.3M ATM share program

Radiopharm Theranostics Limited is amending its existing prospectus supplement to update the terms of an at-the-market equity program for its American Depositary Shares, or ADSs.

Rhea-AI Filing Summary

Radiopharm Theranostics Limited is amending its existing prospectus supplement to update the terms of an at-the-market equity program for its American Depositary Shares, or ADSs. Under this updated prospectus supplement, the company may sell ADSs having an aggregate offering price of up to $9,300,000 from time to time through or to Leerink Partners LLC, acting as sales agent or principal, under a December 16, 2025 sales agreement. Each ADS represents 300 ordinary shares. Leerink Partners will use commercially reasonable efforts to place the ADSs in transactions deemed an “at the market” offering and will receive a 3.0% commission on the gross sales price per ADS. As of July 7, 2026, the company’s public float was approximately US$40,165,592, and sales are subject to the one-third public float limitation under General Instruction I.B.5 of Form F-3. The ADSs trade on Nasdaq under the symbol RADX, where the last reported sale price on July 21, 2026 was $4.29 per ADS.

Filing Explained

The amendment creates up to $9.3 million of potential ATM capacity; it does not establish that any ADSs have been sold.

Radiopharm Theranostics filed this amendment to update its at-the-market prospectus supplement, creating authority to offer up to $9,300,000 of ADSs, but the filing reports no sale or proceeds; its present effect is potential financing capacity rather than a completed financing.

The sales agent is not required to sell any amount, there are no minimum sale requirements, and no funds are arranged for escrow, trust, or similar holding.

Accordingly, the $9,300,000 figure is a maximum program amount, not a committed funding amount; any primary sales remain subject to the Form F-3 one-third-of-public-float ceiling while the public float is below $75.0 million.

The company reports no securities offered under that Form F-3 limitation in the prior 12 calendar months, and a later takedown disclosure would be needed to establish actual sales, price, and fees.

Key Figures

ATM Offering Capacity: Up to $9,300,000 ADS-to-Ordinary Share Ratio: 1 ADS = 300 ordinary shares Public Float: US$40,165,592 +5 more

8 metrics

ATM Offering Capacity Up to $9,300,000 Aggregate offering price of ADSs that may be sold under the updated prospectus supplement

ADS-to-Ordinary Share Ratio 1 ADS = 300 ordinary shares Each American Depositary Share represents 300 ordinary shares

Public Float US$40,165,592 Worldwide aggregate market value of common equity held by non-affiliates as of July 7, 2026

Non-affiliate Ordinary Shares 2,825,200,337 shares Ordinary shares held by non-affiliates used to calculate public float

ASX Ordinary Share Price A$0.0205 per share Average of bid and asked prices on ASX within 60 days of the filing date

Recent ADS Price $4.29 per ADS Last reported sale price of ADSs on Nasdaq on July 21, 2026

Sales Agent Commission 3.0% of gross sales price per ADS Commission payable to Leerink Partners on ADSs sold under the Sales Agreement

Public Float Threshold $75.0 million Level below which one-third public float limit under Form F-3 Instruction I.B.5 applies

Key Terms

at the market offering, General Instruction I.B.5 of Form F-3, public float, underwriter, +1 more

5 terms

at the market offering financial

"made by any method permitted that is deemed an “at the market” offering"

An at-the-market offering is a way a company raises cash by selling newly issued shares directly into the open market at prevailing prices, rather than all at once in a single deal. Think of it like turning a faucet on to drip shares into trading at current prices when needed; it gives the company flexibility to raise funds over time but can dilute existing shareholders and potentially affect the stock price, which investors should monitor.

General Instruction I.B.5 of Form F-3 regulatory

"Pursuant to General Instruction I.B.5 of Form F-3, in no event will we sell"

public float financial

"aggregate market value of our common equity held by non-affiliates, or 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.

underwriter regulatory

"Leerink Partners will be deemed to be an “underwriter” within the meaning of the Securities Act"

An underwriter is a financial firm that evaluates, guarantees and helps sell a new security offering—such as a stock or bond—by buying the issue from the issuer and reselling it to investors or organizing the sale. Think of them as a bridge or safety net: they take on the risk, set the price, handle marketing and paperwork, and their work determines how much money a company can raise and how smoothly the offering reaches the market.

indemnification and contribution regulatory

"We have also agreed in the Sales Agreement to provide indemnification and contribution to Leerink Partners"

Offering Details

ATM

Offering

Offering Type ATM

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What is Radiopharm Theranostics (RADX) registering in this amendment?

Radiopharm Theranostics is updating an at-the-market program to sell up to $9,300,000 in American Depositary Shares through or to Leerink Partners, under an existing Form S-3 shelf registration and sales agreement.

How many ordinary shares does each RADX American Depositary Share represent?

Each American Depositary Share of Radiopharm Theranostics represents 300 ordinary shares. This structure allows U.S. investors to trade ADSs on Nasdaq while the underlying ordinary shares trade on the Australian Securities Exchange.

What commission will Leerink Partners receive under the RADX at-the-market program?

Leerink Partners will be entitled to a 3.0% commission on the gross sales price per ADS sold. This commission is treated as underwriting compensation, and Leerink Partners is deemed an underwriter under the Securities Act.

What is Radiopharm Theranostics’ public float referenced in this filing?

As of July 7, 2026, Radiopharm Theranostics’ public float was approximately US$40,165,592, based on 2,825,200,337 ordinary shares held by non-affiliates and an A$0.0205 per-share price on the Australian Securities Exchange.

How does Form F-3 General Instruction I.B.5 limit RADX’s primary offerings?

Under General Instruction I.B.5 of Form F-3, Radiopharm Theranostics states it will not sell in public primary offerings more than one-third of its public float in any 12‑month period while its public float remains below $75.0 million.

Where are Radiopharm Theranostics securities traded and what was the recent ADS price?

Radiopharm Theranostics’ ADSs trade on Nasdaq under RADX, and its ordinary shares trade on the ASX under RAD. On July 21, 2026, the last reported Nasdaq sale price was $4.29 per ADS.

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

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Accepted by SEC EDGAR 07/23/2026 - 09:09 AM Learn about SEC filing dates

Filed pursuant to Rule 424(b)(5)

Registration No. 333-292178

AMENDMENT NO. 1, dated July 23, 2026

to PROSPECTUS SUPPLEMENT dated December 23, 2025

Radiopharm Theranostics Limited

Up to $9,300,000

American Depositary Shares

This Amendment No. 1 to Prospectus Supplement (this “Amendment”) amends and updates our prospectus supplement, dated December 23, 2025, filed with the Securities and Exchange Commission, or SEC, as part of our registration statement on Form S-3, as amended, File No. 333-292178 (the “Prospectus Supplement”). This Amendment should be read in conjunction with the Prospectus Supplement and the accompanying prospectus dated December 23, 2025(the “Prospectus”), each of which are to be delivered with this Amendment, as well as any of our filings made with the SEC which amend, supplement and update the Prospectus Supplement. This Amendment amends and/or updates only those sections of the Prospectus Supplement set forth in this Amendment (other than as automatically updated and amended by the Company’s SEC filings available on Edgar, which are incorporated by reference herein). This Amendment is not complete without, and may only be delivered or utilized in connection with, the Prospectus Supplement, and any future amendments or supplements hereto or thereto.

We have entered into a sales agreement, or the Sales Agreement, dated December 16, 2025, with Leerink Partners LLC (“Leerink Partners”) relating to the American Depositary Shares, or ADSs, offered by the Prospectus Supplement. Each ADS represents 300 of our ordinary shares. Under the Prospectus Supplement, as updated by this Amendment, we may offer and sell ADSs having an aggregate offering price of up to $9,300,000 from time to time through or to Leerink Partners, acting as sales agent or principal, in accordance with the Sales Agreement.

Sales of the ADSs, if any, under the Prospectus Supplement, as amended, and the accompanying base prospectus may be made by any method permitted that is deemed an “at the market” offering as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act. Leerink Partners is not required to sell any specific number or dollar amount of securities but will act as our sales agent using commercially reasonable efforts consistent with its normal trading and sales practices and applicable state and federal laws, rules and regulations and the rules of the Nasdaq Capital Market (“Nasdaq”), on mutually agreed terms between Leerink Partners and us. There are no minimum sale requirements, and there is no arrangement for funds to be received in any escrow, trust or similar arrangement.

As of July 7, 2026, the worldwide aggregate market value of our common equity held by non-affiliates, or public float, was approximately US$40,165,592 based on 2,825,200,337 ordinary shares held by non-affiliates and a closing price of A$0.0205 per ordinary share, which was the average of the bid and asked prices of our ordinary shares on the Australian Securities Exchange, or the ASX, the principal market for our common equity, within 60 days of the filing date of this registration statement. We have not offered any securities pursuant to General Instruction I.B.5 of Form F-3 during the prior 12 calendar month period that ends on and includes the date of this Amendment. Pursuant to General Instruction I.B.5 of Form F-3, in no event will we sell securities registered on this registration statement 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.

Leerink Partners will be entitled to a commission of 3.0% of the gross sales price per ADS sold under the Sales Agreement. See “Plan of Distribution” beginning on page S-14 of the Prospectus Supplement for additional information regarding the compensation to be paid to Leerink Partners. In connection with the sale of the ADSs on our behalf, Leerink Partners will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to Leerink Partners will be deemed to be underwriting compensation. We have also agreed in the Sales Agreement to provide indemnification and contribution to Leerink Partners with respect to certain liabilities, including liabilities under the Securities Act.

The ADSs are listed on the Nasdaq under the symbol “RADX.” Our ordinary shares are listed on the ASX under the symbol “RAD.” On July 21, 2026, the last reported sale price of the ADSs on the Nasdaq was $4.29 per ADS.

Investing in our ADSs involves a high degree of risk. Before making an investment decision, please read the information under the heading “Risk Factors” beginning on page S-4 of the Prospectus Supplement and in the documents incorporated by reference into the Prospectus Supplement.

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

Leerink Partners

The date of this Amendment No. 1 to Prospectus Supplement is July 23, 2026.