Actinium Pharmaceuticals Advances ATNM-400 in Phase 1 Trial for Prostate Cancer

Early clinical data from a Phase 1 theranostic trial indicate progress for ATNM-400 as a non-PSMA targeted alpha therapy for metastatic castration-resistant prostate cancer (mCRPC). This study evaluates Zirconium-89-labeled ATNM-400 to determine safety, biodistribution, and dosimetry, informing the further development of Actinium-225-labeled ATNM-400 as a targeted radiotherapy.

ATNM-400 is a novel Actinium-225 (²²⁵Ac) antibody radioconjugate that targets a non-PSMA antigen involved in tumor survival and treatment resistance. It aims to serve a broad population of mCRPC patients, including those with PSMA-low or PSMA-negative disease and individuals who do not respond to or progress after PSMA-directed therapies.

Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) announced that initial results from this first-in-human Phase 1 study will be presented in an oral session at the 39th Annual Congress of the European Association of Nuclear Medicine (EANM), scheduled for October 17–21, 2026, in Vienna, Austria.

The presentation will include findings from the ongoing first-in-human Phase 1 dose-escalation study of ATNM-400 in mCRPC. The study's objectives include characterizing the safety, biodistribution, and dosimetry of Zirconium-89-labeled ATNM-400 using serial PET imaging to assess tumor uptake, distribution, and clearance, with dosimetry estimates guiding therapeutic dosing of ²²⁵Ac-ATNM-400.

"These first clinical data from ATNM-400 mark an important milestone for Actinium and for prostate cancer treatment beyond PSMA," stated Sandesh Seth, Actinium's Chairman and CEO. "ATNM-400 has the potential to serve a broad mCRPC population, including patients who do not respond to or progress after PSMA-directed therapies. These findings signify a crucial step for ATNM-400 and our Actinium-225 development program."

ATNM-400 EANM 2026 Presentation Details

• Abstract Title: First-In-Human Phase 1 Study of ATNM-400, Actinium-225 Antibody Radioconjugate, in Metastatic Castration-Resistant Prostate Cancer (mCRPC)
• Abstract Number: OP-525
• Presentation Type: Oral presentation
• Session: 1111 — Theranostics Track: Prostate Cancer Therapy II
• Session Date & Time: Monday, October 19, 2026, 4:45–6:15 p.m. CEST | Vienna, Austria
• Location: Hall G1

Actinium is committed to transforming cancer treatment through innovative radioconjugates that enhance therapeutic efficacy while protecting healthy tissue. Its extensive pipeline includes agents targeting solid tumors and hematologic malignancies, alongside a focus on developing innovative therapies.

For further details, visit Actinium Pharmaceuticals.