Actinium Pharmaceuticals, Inc.

First‑in‑human Phase 1 study evaluates HER3‑targeted ATNM‑400 in metastatic castration‑resistant prostate cancer population, including patients with and without prior PSMA‑directed therapy HER3‑targeted alpha radiotherapy offers a differentiated approach through a target distinct from PSMA and the potential to address treatment resistance across multiple solid tumors NEW YORK, Oct. 23, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) (Actinium or the Company), a pioneer in differentiated targeted radiotherapies with the potential to transform cancer treatment, today announced that the first‑in‑human Phase 1 study of ATNM‑400, a HER3-targeted, non-PSMA radiotherapy, in metastatic castration‑resistant prostate cancer (mCRPC) will be featured at the European Society for Medical Oncology (ESMO) Congress 2026, taking place October 23⁠–⁠27, 2026, in Madrid, Spain. ATNM‑400 is an investigational, first‑in‑class Actinium-225 antibody radioconjugate targeting HER3, an antigen distinct from PSMA that is implicated in tumor survival and treatment resistance.

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HER3‑targeted PET imaging demonstrated tumor uptake and retention, supporting ATNM‑400's potential to deliver sustained alpha radiation to tumors over a timeframe consistent with Actinium‑225's 10-day half‑life Initial three‑patient cohort completed the first dose level of 1.0 µCi/kg with no dose‑limiting toxicities, xerostomia or Grade 3/4 hematologic adverse events observed ATNM‑400 advanced to the second dose level of 1.5 µCi/kg, marking continued clinical progress for a first‑in‑class Actinium‑225 antibody radiotherapy with potential across the broad mCRPC population NEW YORK, Oct. 20, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) (Actinium or the Company), a pioneer in differentiated targeted radiotherapies with the potential to transform cancer treatment, today announced encouraging initial clinical results from the first‑in‑human Phase 1 study of ATNM‑400 in metastatic castration‑resistant prostate cancer (mCRPC). The findings, presented in an oral presentation on October 19 at the 39th Annual Congress of the European Association of Nuclear Medicine (EANM) in Vienna, Austria, showed a favorable initial safety profile at the first dose level and tumor uptake and retention with the HER3‑targeted imaging agent.

ATNM-400 demonstrated activity across EGFR-, KRAS- and ALK-driven lung cancer models, supporting mutation-agnostic development as monotherapy and in combination with established treatments In colorectal cancer, adding ATNM-400 to standard therapy increased tumor growth inhibition to 72% from 25% for oxaliplatin and bevacizumab in a poorly responsive model with moderate target expression In ovarian cancer, ATNM-400 achieved 93% tumor growth inhibition as monotherapy and retained activity following bevacizumab failure Three presentations expand the preclinical foundation for ATNM-400 as a potential pan-tumor treatment, complementing ongoing clinical development in prostate cancer NEW YORK, Oct. 20, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) (Actinium or the Company), a pioneer in differentiated targeted radiotherapies with the potential to transform cancer treatment, today announced new preclinical results demonstrating the broad antitumor potential of ATNM-400 across non-small cell lung cancer (NSCLC), colorectal cancer and ovarian cancer models. The findings were presented in an oral presentation and two e-posters at the 39th Annual Congress of the European Association of Nuclear Medicine (EANM), October 17–21, 2026, in Vienna, Austria.