• New data demonstrated ATNM-400 remains potently active in prostate cancer cells and tumors resistant to all three approved androgen receptor inhibitors (ARPIs) -enzalutamide (Xtandi®), apalutamide (Erleada®), and darolutamide (Nubeqa®)- directly targeting the point of failure for a high proportion of mCRPC patients
     
  • ATNM-400 substantially outperformed apalutamide and darolutamide in an ARPI-resistant tumor model, and in combination with either ARPI it showed durable complete responses, supporting both monotherapy and combination strategies in refractory disease similar to prior data with enzalutamide
     
  • ATNM-400 delivered superior tumor control as a single bolus or repeat dose with a consistent safety profile and minimal off-target toxicity across treatment regimens, indicating dosing flexibility and a wide therapeutic window that could de-risk clinical translation.
     
  • In high PSMA expressing disease, ATNM-400 outperformed 177Lu-PSMA-617 in terms of activity and was similar to 225Ac-PSMA-617. However, as its target is not expressed in the salivary glands, ATNM-400 is not expected to cause xerostomia which is a key limitation of PSMA directed therapies

NEW YORK, June 3, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE:ATNM) (Actinium or the Company), a pioneer in the development of targeted radiotherapies, on June 2, 2026, presented new data on ATNM-400 in prostate cancer at the Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2026 Annual Meeting taking place in Los Angeles, California.

Androgen receptor pathway inhibitors (ARPIs) such as enzalutamide (Xtandi®, Astellas/Pfizer), apalutamide (Erleada®, Johnson & Johnson), and darolutamide (Nubeqa®, Bayer) are foundational to advanced prostate cancer care, but virtually all patients eventually develop resistance and progress -with up to 50,0001 patients per year exhausting ARPI therapy- creating a large and recurring unmet need. ATNM-400, Actinium's first-in-class Actinium-225 antibody radioconjugate, targets a non-PSMA antigen linked to aggressive prostate cancer biology and delivers a high-energy alpha-particle payload that kills tumor cells through a mechanism independent of PSMA expression and androgen receptor signaling. In preclinical head-to-head studies, this PSMA-independent mechanism allowed ATNM-400 to match or exceed PSMA-targeted radioligand therapies, including 177Lu-PSMA-617 (active ingredient of Pluvicto®, Novartis) and 225Ac-PSMA-617, across PSMA-high, PSMA-low, and PSMA-negative models.