Merger Deal: Galera Therapeutics (GRTX) to Merge with Obsidian; ASCO Phase 2 Data Ahead

Rhea-AI Filing Summary

Galera Therapeutics, Inc. disclosed a proposed merger agreement dated April 14, 2026 under which Galera and Obsidian Therapeutics will combine into a newly-formed parent, with Galera and Obsidian each becoming wholly owned subsidiaries of the parent following the Galera Merger. The companies said the combined entity will file a registration statement on Form S-4 containing a proxy statement/prospectus and that materials will be mailed to Galera stockholders.

The filing also includes an Obsidian press release announcing an oral presentation of Phase 2 OBX-115 data in advanced melanoma at the 2026 ASCO Annual Meeting (May 29–June 2, 2026). The release describes OBX-115 as an engineered TIL therapy armored with membrane-bound IL15 and references ongoing Phase 1/2 Agni-01 (NCT06060613) clinical development.

Insights

Corporate Transactions Attorney

Merger steps disclosed; proxy/prospectus filing planned.

The companies cite an Agreement and Plan of Merger dated April 14, 2026 and state they will file a Form S-4 with a proxy statement/prospectus. That filing is the central disclosure vehicle for shareholder votes and registration of securities to be issued.

Key contingencies and approvals are referenced implicitly; closing will depend on satisfaction or waiver of the Merger Agreement conditions. Subsequent SEC filings will provide the full transaction economics, vote requirements, and any financing terms.

Clinical Development Strategist

OBX-115 Phase 2 data to be presented at ASCO may affect program value.

Obsidian announced an oral Phase 2 presentation of OBX-115 in advanced melanoma at the 2026 ASCO Annual Meeting (May 29–June 2, 2026). The program is described as a cytoTIL15™ engineered TIL therapy with mbIL15 modulation, studied in Agni-01 (NCT06060613).

Data content and endpoints are not disclosed here; the clinical readout in the Form S-4/prospectus or subsequent SEC filings will clarify efficacy, safety, and any implications for combined-company valuation.

Key Figures

Merger agreement date: April 14, 2026 Press filing date: April 22, 2026 ASCO presentation dates: May 29–June 2, 2026 +2 more

5 metrics

Merger agreement date April 14, 2026 Agreement and Plan of Merger executed

Press filing date April 22, 2026 425 filing date noted at top of disclosure

ASCO presentation dates May 29–June 2, 2026 2026 ASCO Annual Meeting where Phase 2 data will be presented

Clinical trial identifier NCT06060613 Agni-01 Phase 1/2 multicenter trial for OBX-115

Planned SEC filing Form S-4 Registration statement to include proxy statement/prospectus

Key Terms

cytoTIL15™, mbIL15 (membrane-bound IL15), cytoDRiVE®, Form S-4

4 terms

cytoTIL15™ medical

"Obsidian’s lead investigational cytoTIL15™ program, OBX-115, is a novel engineered tumor-derived"

mbIL15 (membrane-bound IL15) medical

"armored with pharmacologically regulatable membrane-bound IL15 (mbIL15)"

cytoDRiVE® technical

"Obsidian’s proprietary cytoDRiVE® technology is designed to precisely regulate the timing"

Form S-4 regulatory

"the newly-formed company will file a registration statement on Form S-4 that will include a proxy statement"

A Form S-4 is a legal document that companies file with the government to announce and explain a major business move, such as a merger or acquisition. It provides detailed information to help investors understand how the deal might affect the company's value and future prospects, similar to a detailed blueprint that clarifies the impact of a significant change.

Filed by Galera Therapeutics, Inc.

pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Galera Therapeutics, Inc.

Filer’s SEC File No.: 001-39114

Date: April 22, 2026

This filing relates to the proposed transaction pursuant to the terms of that certain Agreement and Plan of Merger, dated as of April 14, 2026, by and among Galera Therapeutics, Inc., a Delaware corporation (“Galera”), Obsidian Therapeutics, Inc., a Delaware corporation (“Obsidian”), Gazelle Parent, Inc., a Delaware corporation (“Parent”), Onyx MergerSub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Parent (“Obsidian Merger Sub”), and Gazelle Merger Subsidiary, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Parent (“Galera Merger Sub”), pursuant to which, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Galera will be merged with and into Galera Merger Sub, with Galera surviving as a wholly owned subsidiary of Parent (the “Galera Merger”), and Obsidian will be merged with and into Obsidian Merger Sub, with Obsidian surviving as a wholly owned subsidiary of Parent.

On April 21, 2026, Obsidian published the following communication:

Obsidian Therapeutics to Present OBX-115 Phase 2 Clinical Data in Advanced

Melanoma in Oral Presentation at 2026 ASCO Annual Meeting

• Oral presentation of Phase 2 results of OBX-115 in patients with advanced melanoma that has progressed following immune checkpoint inhibitor therapy from the Phase 1/2 Agni-01 multicenter study.

• OBX-115 is a novel, engineered, autologous TIL cell therapy currently in a Phase 2 clinical trial for the treatment of advanced melanoma and a Phase 1 clinical trial for the treatment of non-small cell lung cancer (NSCLC).

Cambridge, MA, April 21, 2026 – Obsidian Therapeutics, Inc., a clinical-stage biopharmaceutical company harnessing novel protein-regulation technology to develop engineered tumor-infiltrating lymphocyte (TIL) cell therapies, today announced an oral presentation of Phase 2 results in patients with advanced melanoma from the Phase 1/2 Agni-01 multicenter study of OBX-115, at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, taking place in Chicago, IL, May 29–June 2, 2026.

Oral Presentation Details:

• Title: OBX-115 engineered tumor-infiltrating lymphocyte (TIL) cell therapy with regulatable membrane-bound IL15 (mbIL15) in patients with advanced melanoma that has progressed on/after immune checkpoint inhibitors (ICI): Phase 2 results

• Session Type/Title: Oral Abstract Session – Melanoma/Skin Cancers

• Date: Monday, June 1

• Abstract Number: 9507

• Speaker/Lead Author: Allison S Betof, Division of Oncology, Stanford University School of Medicine, Stanford, CA

• Clinical Trial Identifier: NCT06060613

About OBX-115

Obsidian’s lead investigational cytoTIL15^™ program, OBX-115, is a novel engineered tumor-derived autologous T cell immunotherapy (tumor-infiltrating lymphocyte [TIL] cell therapy) armored with pharmacologically regulatable membrane-bound IL15 (mbIL15). OBX-115 has the potential to become a meaningful therapeutic option for patients with advanced or metastatic melanoma and other solid tumors by leveraging the expected benefits of mbIL15 and Obsidian’s proprietary, differentiated manufacturing process to enhance persistence, antitumor activity, and clinical safety of TIL cell therapy. Obsidian is investigating OBX-115 in the phase 1/2 Agni-01 multicenter trial in patients with advanced solid tumors (NCT06060613).

About Obsidian Therapeutics

Obsidian Therapeutics, Inc. is a clinical-stage biopharmaceutical company harnessing novel protein-regulation technology to develop engineered TIL cell therapies for the treatment of patients with solid tumors. Obsidian’s proprietary cytoDRiVE^® technology is designed to precisely regulate the timing and level of protein function by using FDA-approved small-molecule drugs. Obsidian is headquartered in Cambridge, MA. For more information, please visit www.obsidiantx.com.

Additional Information and Where to Find It

In connection with the proposed transactions between Obsidian and Galera, Galera and the newly-formed company will file relevant materials with the SEC. The newly-formed company will file a registration statement on Form S-4 that will include a proxy statement or information statement and prospectus relating to the proposed transaction, which will constitute a proxy statement or information statement of Galera and a prospectus of the newly-formed company (the “Prospectus”). Galera and the newly-formed company may also file other documents with the SEC regarding the proposed transaction. This press release is not a substitute for the Prospectus or any other document which Galera or the newly-formed company may file with the SEC or send to stockholders of Galera or Obsidian in connection with the proposed transaction. The Prospectus will be mailed to stockholders of Galera. INVESTORS AND SECURITYHOLDERS OF GALERA ARE URGED TO READ THE REGISTRATION STATEMENT AND THE PROSPECTUS AND ALL OTHER DOCUMENTS FILED OR THAT WILL BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT GALERA, OBSIDIAN AND THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain free copies of the registration statement and the Prospectus (when available) and other documents filed with the SEC by Galera or the newly-formed company through the website maintained by the SEC at www.sec.gov. Copies of the documents filed with the SEC by Galera will be available free of charge on Galera’s website at www.Galeratx.com.

No Offer or Solicitation

This press release is for informational purposes only and not intended to and does not constitute an offer to subscribe for, buy or sell, or the solicitation of an offer to subscribe for, buy or sell, or an invitation to subscribe for, buy or sell, any securities of Galera, Obsidian or the newly-formed company, or the solicitation of any vote or approval in any jurisdiction pursuant to or in connection with the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended, and otherwise in accordance with applicable law.

Participants in the Solicitation

This press release is not a solicitation of a proxy from any security holder of Galera or Obsidian. However, Galera and Obsidian and each of their respective directors and executive officers may be considered participants in the solicitation of proxies in connection with the proposed transaction. Information about the directors and executive officers of Galera may be found in its Annual Report on Form 10-K for the year ended December 31, 2025, which was filed with the SEC on March 19, 2026 and its proxy statement for its 2026 annual meeting of stockholders, which was filed with the SEC on April 10, 2026. Other information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in Prospectus and other relevant materials to be filed with the SEC when they become available.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, statements concerning future clinical development activities, potential milestone payments, the merger transaction and completion of the concurrent private placement financing, the expected effects, perceived benefits or opportunities and related timing with respect thereto; expectations regarding or plans for the combined company’s pipeline, and the expectations regarding the use of proceeds from the concurrent private placement financing and cash runway expectations therefrom.

These forward-looking statements relate to Galera, Obsidian and the newly-formed company (together, “us” or “we”), our business prospects and our results of operations and are subject to certain risks and uncertainties posed by many factors and events that could cause our actual business, prospects and results of operations to differ materially from those anticipated by such forward-looking statements. Factors that could cause or contribute to such differences include, but are not limited to, those described under the heading “Risk Factors” included in Galera’s Annual Report on Form 10-K for the year ended December 31, 2025. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this release. In some cases, you can identify forward-looking statements by the following words: “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “aim,” “may,” “ongoing,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” or the negative of these terms or other comparable terminology, although not all forward-looking statements contain these words. We undertake no obligation to revise any forward-looking statements in order to reflect events or circumstances that might subsequently arise, except as required by applicable law.

These forward-looking statements are based upon our current expectations and involve assumptions that may never materialize or may prove to be incorrect. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of various risks and uncertainties, including, without limitation: statements about the synergies or benefits of the proposed transaction, including future financial and operating results, plans, objectives, expectations and intentions; the anticipated timing of closing of the proposed transaction and the private placement financing; risks related to the combined company’s ability to correctly estimate its operating and other expenses and its cash runway; the ability to retain key personnel; negative effects of the announcement or consummation of the proposed transaction on the market price of our capital stock and our operating results; risks relating to the value of shares of the newly-formed company to be issued in the proposed transaction; risks related to the newly-formed company’s ability to be listed on Nasdaq; risks related to the ability to obtain approval of the Galera stockholders; changes in capital resource requirements; risks related to our inability to obtain sufficient additional capital to continue to advance our product candidates; our and our collaborators’ ability to execute clinical programs for our product candidates; results of clinical trials with our product candidates; and our ability to obtain and maintain intellectual property rights and regulatory exclusivities.

Inquiries:

Caroline Code

VP Corporate Development and Investor Relations

ccode@obsidiantx.com

FAQ

What transaction did Galera Therapeutics (GRTX) disclose?

Galera disclosed a merger agreement dated April 14, 2026 to combine with Obsidian into a new parent company. The agreement contemplates Galera and Obsidian becoming wholly owned subsidiaries of the combined parent following the Galera Merger.

Will Galera file materials with the SEC for the merger?

Yes. Galera and the newly-formed company will file a registration statement on Form S-4 that will include a proxy statement/prospectus, and those materials will be mailed to Galera stockholders when available.

What clinical data did Obsidian announce in the filing?

Obsidian announced an oral presentation of Phase 2 results for OBX-115 in advanced melanoma at the 2026 ASCO Annual Meeting (May 29–June 2, 2026) from the Agni-01 Phase 1/2 study (NCT06060613).

What is OBX-115 and which trial is referenced?

OBX-115 is described as an engineered tumor-derived autologous TIL therapy (cytoTIL15™) armored with membrane-bound IL15 (mbIL15), being investigated in the Phase 1/2 Agni-01 multicenter trial (NCT06060613).

Where can investors get the proxy/prospectus and other filings?

Investors can obtain free copies of the registration statement and prospectus via the SEC website at www.sec.gov and from Galera’s website at www.Galeratx.com when those materials are filed and available.