Actinium Pharmaceuticals to Highlight First-in-Human Phase 1 Study of ATNM-400 a HER3-Targeted Non-PSMA Radiotherapy in Prostate Cancer at ESMO 2026
Actinium Pharmaceuticals to Highlight First-in-Human Phase 1 Study of ATNM-400 a HER3-Targeted Non-PSMA Radiotherapy in Prostate Cancer at ESMO 2026 |
| [23-October-2026] |
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. In prostate cancer, HER3 targeting offers potential across a broad mCRPC population, including patients with PSMA‑positive, PSMA‑low or PSMA‑negative disease. This includes patients who have not received PSMA‑directed therapy and those who progress following it. The Phase 1 study pairs Zirconium‑89‑labeled ATNM‑400 imaging with the development of therapeutic Actinium‑225‑labeled ATNM‑400 to inform patient selection and dosing. "We are excited to take this first step in our pan‑cancer strategy for ATNM‑400 with its first‑in‑human Phase 1 study in prostate cancer," said Sandesh Seth, Actinium's Chairman and CEO. "The initial results shared at EANM, including tumor retention through Day 7 with HER3‑targeted imaging and encouraging tolerability, reinforce our enthusiasm for ATNM‑400. We believe ATNM‑400's differentiated HER3‑targeting approach could benefit patients across the full mCRPC spectrum, including those with PSMA‑positive, PSMA‑low or PSMA‑negative disease, as well as patients who have not received or have progressed following PSMA‑directed therapy. This study represents an important milestone toward realizing ATNM‑400's broad potential in prostate cancer and building the clinical foundation for expansion into additional solid tumors." First-in-human Phase 1 study in mCRPC. The multicenter, open-label dose-escalation and expansion study enrolls patients with progressive mCRPC previously treated with an androgen receptor pathway inhibitor (ARPI) and taxane‑based chemotherapy; prior lutetium is permitted but not required. Patients with positive Zirconium-89-ATNM-400 PET imaging proceed to Actinium-225-ATNM-400 treatment every six weeks for up to four cycles. The study evaluates safety and tolerability to establish a recommended Phase 2 dose, with additional assessments of dosimetry, pharmacokinetics and antitumor activity. "Our clinical strategy uses imaging to understand where ATNM-400 distributes, how much reaches tumors and how long it is retained," said Steffen Heeger, MD, MSc, Actinium's Chief Medical Officer. "HER3 signaling can support prostate cancer cell growth and survival and has been implicated in resistance to androgen receptor‑directed therapies. This connection to disease progression and treatment resistance provides a strong biological rationale for evaluating HER3‑targeted radiotherapy in mCRPC. ATNM‑400 is designed to deliver Actinium‑225 to HER3‑expressing tumor cells, an approach we are evaluating in this first‑in‑human study." ATNM‑400 ESMO 2026 Presentation Details About ATNM‑400 and HER3 ATNM‑400 is differentiated from PSMA‑targeted radiotherapies by its focus on HER3, an antigen implicated in tumor survival and treatment resistance. PSMA‑directed approaches include Novartis' Pluvicto and a broad pipeline of investigational therapies, including Telix Pharmaceuticals' TLX591‑Tx, Clarity Pharmaceuticals' ⁶⁷Cu‑SAR‑bisPSMA, Convergent Therapeutics' CONV01‑α, AstraZeneca's AZD2265 (formerly FPI‑2265), Curium's lutetium‑177 zadavotide guraxetan (¹⁷⁷Lu‑PSMA‑I&T), ARTBIO's AB001 and AdvanCell's ADVC001. These programs span small‑molecule and antibody‑based therapies using beta‑ or alpha‑emitting isotopes. ATNM‑400 combines HER3 targeting with an Actinium‑225 antibody radioconjugate, offering a distinct biological approach with the potential to expand radiotherapy across the broad mCRPC population, including patients with PSMA‑low or PSMA‑negative disease and those who do not respond to or progress following PSMA‑directed treatment. Its HER3‑directed mechanism also supports investigation beyond prostate cancer in other HER3‑expressing solid tumors. HER3, also known as ERBB3, is a member of the epidermal growth factor receptor family involved in signaling pathways that support tumor growth, survival and resistance to treatment. HER3‑directed antibody‑drug conjugates in clinical development include BioNTech and MediLink's BNT326/YL202, Bristol Myers Squibb and SystImmune's EGFR × HER3 bispecific ADC izalontamab brengitecan (iza‑bren), and Daiichi Sankyo and Merck's patritumab deruxtecan (HER3‑DXd). These programs underscore the clinical development interest in HER3 as an oncology target. ATNM‑400 applies a distinct payload strategy, using alpha radiation in place of a conventional cytotoxic drug. Its preclinical activity in prostate, non‑small cell lung and breast cancer models supports investigation as a potential pan‑cancer radiotherapy, as a monotherapy and in rational combinations. About Actinium Pharmaceuticals, Inc. Forward‑Looking Statements Investor Contact
SOURCE Actinium Pharmaceuticals, Inc. | ||
Company Codes: NYSE:ATNM,Amex:ATNM,NYSE-MKT:ATNM |
View original content to download multimedia:
