Actinium Pharmaceuticals Initiates RADIANZ Imaging Study to Expand ATNM-400 Development

Actinium Pharmaceuticals, Inc. has announced the initiation of the RADIANZ clinical trial, an imaging study that will assess ⁸⁹Zr-Barecetamab-DFO using PET imaging to guide the further development of ²²⁵Ac-Barecetamab-DOTA (ATNM-400) in patients with advanced HER3-expressing solid tumors beyond prostate cancer.

RADIANZ builds on the initial results from ATNM-400’s first-in-human Phase 1 study in metastatic castration-resistant prostate cancer (mCRPC). This investigational radioconjugate targets HER3, an antigen associated with tumor survival and treatment resistance. Initial findings were presented at the 39th Annual Congress of the European Association of Nuclear Medicine (EANM) in October 2026, where three patients received ATNM-400 at a dose of 1.0 µCi/kg with no dose-limiting toxicities observed. PET imaging indicated tumor uptake through Day 7, leading to further dose escalation to 1.5 µCi/kg. The mCRPC study was also featured at the European Society for Medical Oncology (ESMO) Congress 2026.

The company has reported preclinical findings at EANM 2026, which support the potential use of ATNM-400 in treatment combinations across various cancer settings, including non-small cell lung cancer (NSCLC), colorectal, and ovarian cancers. Additional data on breast cancer will be presented at the San Antonio Breast Cancer Symposium (SABCS) in December 2026.

Sandesh Seth, Actinium's Chairman and CEO, emphasized the importance of RADIANZ in pursuing a pan-cancer strategy for ATNM-400, underscoring the drug's potential applicability in multiple tumor types beyond prostate cancer.

The RADIANZ study aims to include patients with a variety of advanced solid tumors who have progressed after standard-of-care therapies. Participants will undergo Zirconium-89-barecetamab PET imaging to assess biodistribution, tumor uptake, pharmacokinetics, and dosimetry.

Dr. Steffen Heeger, Actinium's Chief Medical Officer, highlighted the necessity for new treatment options for patients whose cancers no longer respond to existing therapies, stating the insights gained from RADIANZ will inform the future development of ATNM-400 in different cancer types.

ATNM-400 represents a novel approach to targeting HER3, which has a distinct mechanism of action compared to current PSMA-targeted therapies, and presents a potential opportunity for treating difficult-to-manage cancers.

This initiative reflects Actinium's commitment to innovative radiotherapy development, aiming to improve treatment outcomes for patients with cancer through targeted therapies.