Actinium-225 (Ac-225) - (ATNM-400)

October 15, 2026: Actinium Pharmaceuticals, Inc. (NYSE: ATNM) announced that early results from the first-in-human Phase 1 trial of ATNM-400 in metastatic castration-resistant prostate cancer (mCRPC) will be presented orally at the 39th Annual Congress of the European Association of Nuclear Medicine (EANM) in Vienna.

ATNM-400 is described as a first-in-class, non-PSMA-targeted Actinium-225 antibody radioconjugate for mCRPC, including patients with PSMA-low/negative disease or those who progressed after PSMA-directed therapy. The ongoing Phase 1 dose-escalation study is evaluating Zirconium-89-labeled ATNM-400 to characterize safety, biodistribution, and dosimetry. Serial PET imaging is being used to assess tumor uptake, distribution, and clearance, with dosimetry estimates intended to inform dosing of therapeutic 225Ac-ATNM-400.

The company said the early clinical data support advancement of ATNM-400, but no numerical efficacy or safety results were disclosed in the release.

Upcoming catalyst: EANM 2026 oral presentation, abstract OP-525, “First-In-Human Phase 1 Study of ATNM-400… in mCRPC,” in Session 1111 (Theranostics Track: Prostate Cancer Therapy II) on October 19, 2026, 4:45–6:15 p.m. CEST, Hall G1.