Actinium Pharmaceuticals to Host KOL Webinar on ATNM-400, a First-in-Class HER3-Targeted Alpha Radiotherapy

• Leading prostate cancer expert Michael J. Morris, MD, of Memorial Sloan Kettering Cancer Center, to discuss unmet needs in metastatic castration-resistant prostate cancer (mCRPC) and the potential for therapies beyond PSMA
  
  
  
  
• Webinar on December 1, 2026, at 8:00 a.m. ET to review recently reported first-in-human Phase 1 findings for ATNM-400 in the HERACT-PRO-1 prostate cancer clinical trial and management will discuss further detail on the RADIANZ imaging study to validate its pan-tumor potential

NEW YORK, Nov. 12, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) ("Actinium" or the "Company"), a pioneer in the development of targeted radiotherapies, today announced that it will host a key opinion leader (KOL) webinar on Tuesday, December 1, 2026, at 8:00 a.m. ET to discuss the evolving treatment landscape in metastatic castration-resistant prostate cancer (mCRPC) and the potential of ATNM-400, its investigational, first-in-class, HER3-targeted Actinium-225 antibody radioconjugate.

The event will feature Michael J. Morris, MD, Prostate Cancer Section Head at Memorial Sloan Kettering Cancer Center, who will join members of Actinium's management team for the discussion. Participants can register for the webinar here.

The webinar will explore the applicability of a HER3-targeted radiotherapeutic across the broad mCRPC population, including those patients with low or negative PSMA expression and those who do not respond to or progress following PSMA-directed treatments. The discussion will also examine the role of HER3 in tumor progression and treatment resistance, the rationale for targeting HER3 with alpha radiotherapy, and the potential role of non-PSMA approaches in the evolving prostate cancer treatment paradigm.

Actinium management will review previously reported findings from ATNM-400's ongoing first-in-human Phase 1 study, HERACT-PRO-1, including initial data presented at the 2026 European Association of Nuclear Medicine (EANM) Congress. HER3-targeted PET imaging demonstrated tumor uptake and retention through Day 7, with no dose-limiting toxicities, xerostomia or Grade 3/4 hematologic adverse events observed in the initial three-patient cohort at the 1.0 µCi/kg dose level. Dose escalation has advanced to the second dose level of 1.5 µCi/kg and is ongoing. Additionally, further detail on the RADIANZ (Radiolabeled Antibody Distribution In Advanced Neoplasms with Zirconium-89) imaging study to validate ATNM-400's pan-tumor potential will be discussed. Management will also highlight preclinical findings demonstrating ATNM-400's activity across prostate cancer models with varying PSMA expression and will review clinical plans for ATNM-400 in prostate cancer and additional solid tumors, including lung, breast, colorectal and ovarian cancers.

A live question-and-answer session will follow the presentations.

Webinar Details

Date: Tuesday, December 1, 2026

Time: 8:00 a.m. Eastern Time

Registration: Here

The live webcast will be accessible through the registration link above. A replay will be available following the event through the Events and Presentations section of Actinium's website at www.actiniumpharma.com.

About Michael J. Morris, MD

Michael J. Morris, MD, is Prostate Cancer Section Head at Memorial Sloan Kettering Cancer Center and a leading investigator in the development of targeted radiopharmaceuticals for prostate cancer. He helped lead the pivotal Phase 3 VISION trial of lutetium-177–PSMA-617, which supported the initial FDA approval of Pluvicto®, and is the lead author of the Phase 3 PSMAfore publication. His expertise spans clinical trial development, molecular imaging and the integration of radiopharmaceuticals into prostate cancer care.

About ATNM-400

ATNM-400 is an investigational antibody radioconjugate that pairs the HER3-targeting monoclonal antibody barecetamab with the alpha-emitting isotope Actinium-225. Its antibody-based design combines antigen-specific targeting with the potential for sustained tumor localization, supporting prolonged delivery of high-energy alpha radiation. Tumor uptake and retention observed through Day 7 with the ⁸⁹Zr-labeled imaging counterpart support this development rationale alongside the approximately 10-day half-life of ²²⁵Ac. The theranostic approach enables noninvasive visualization of antibody distribution to inform therapeutic development.  The program is being evaluated in a first-in-human dose-escalation Phase 1 study of ATNM-400 in mCRPC, HERACT-PRO-1, which utlizes Zirconium-89-labeled barecetamab PET imaging to assess tumor targeting, biodistribution and dosimetry. Actinium is also conducting an imaging study, RADIANZ (Radiolabeled Antibody Distribution In Advanced Neoplasms with Zirconium-89) using PET to guide the pan-tumor development of ATNM-400 in various solid tumors outside of prostate cancer.

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.

About HER3

HER3, also known as ERBB3, belongs to the epidermal growth factor receptor family and participates in signaling pathways that promote tumor growth, survival and treatment resistance. HER3-directed antibody-drug conjugates (ADCs) 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 highlight clinical development interest in HER3 as an oncology target. ATNM-400 takes a different payload approach, delivering alpha radiation rather than a conventional cytotoxic drug. Preclinical activity in prostate, non-small cell lung, breast, colorectal and ovarian cancer models supports investigating ATNM-400 as a potential pan-cancer radiotherapy, both as monotherapy and in rational combinations.

About Actinium Pharmaceuticals, Inc.

Actinium is a pioneer in targeted radiotherapies designed to improve outcomes for patients with cancer. The Company employs a biology-driven approach to develop differentiated radiopharmaceuticals for solid tumors and hematologic malignancies. Its pipeline spans three areas: (1) solid tumor therapeutics including ATNM-400 and Actimab-A with pan-tumor potential; (2) Actimab-A as a therapeutic backbone for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) in collaboration with the National Cancer Institute (NCI); and (3) targeted conditioning agents including Iomab-B for bone marrow transplant and Iomab-ACT for cell and gene therapy conditioning. Actinium also holds approximately 250 patents and patent applications, including intellectual property related to cyclotron-based production of Actinium-225. For more information, please visit www.actiniumpharma.com.

Forward-Looking Statements

This press release may contain projections or other "forward-looking statements" within the meaning of the "safe-harbor" provisions of the Private Securities Litigation Reform Act of 1995 regarding future events or future financial performance of the Company, which the Company undertakes no obligation to update. These statements are based on management's current expectations and are subject to risks and uncertainties that may cause actual results to differ materially from anticipated or estimated future results, including risks and uncertainties associated with the conduct, timing and results of the ongoing first-in-human Phase 1 study of ATNM-400, including the possibility that preliminary results may differ from final results and that preclinical results may not be predictive of clinical outcomes; the potential of product candidates; clinical trials; actions by the FDA and other governmental agencies; regulatory clearances; market demand for and acceptance of the Company's products and services; performance of clinical research organizations; and other risks detailed from time to time in Actinium's filings with the Securities and Exchange Commission, including its most recent Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, each as amended and supplemented from time to time.

Investors Contact:

Peter (PJ) Kelleher

LifeSci Advisors

pkelleher@lifesciadvisors.com

(617) 430-7579

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