Actinium Pharmaceuticals Presents EANM 2026 Results Reinforcing ATNM-400's Pan-Tumor Potential Across Lung, Colorectal and Ovarian Cancer Models

• 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.

ATNM-400 is the Company's first-in-class Actinium-225 (²²⁵Ac) antibody radioconjugate targeting HER3, a tumor-associated antigen implicated in cancer-cell survival and treatment resistance. By delivering high-energy alpha-particle radiation to HER3-expressing tumor cells, ATNM-400 is designed to induce DNA double-strand breaks through a mechanism distinct from conventional pathway inhibition. The EANM results demonstrate activity across molecularly diverse tumors and treatment-resistant disease, supporting development as both a standalone therapy and a combination partner for established treatments.

The studies broaden ATNM-400's preclinical evidence beyond previously reported prostate and breast cancer findings and extend its lung cancer program across multiple oncogenic drivers. Together with the Company's ongoing clinical development in metastatic castration-resistant prostate cancer (mCRPC), these results support a strategy to advance ATNM-400 across multiple large solid tumor indications.

Sandesh Seth, Actinium's Chairman and CEO, said, "These results strengthen our conviction in ATNM-400's pan-tumor potential and our opportunity to expand targeted radiotherapy across major solid tumor indications. In lung cancer, activity across EGFR-, KRAS- and ALK-driven models supports an approach that could reach patients beyond a single mutation-defined population. In colorectal cancer, ATNM-400 substantially improved tumor control when added to a standard regimen with limited activity, while in ovarian cancer it demonstrated strong single-agent activity, including after bevacizumab failure. This breadth of activity supports our vision for ATNM-400 as a potential treatment backbone, both on its own and alongside established therapies, for patients whose cancers are inadequately served by current options."

Adeela Kamal, Ph.D., Actinium's Chief Scientific Officer, added, "HER3 provides a compelling biological link across these cancers through its role in tumor-cell survival and treatment resistance. ATNM-400 uses this target to deliver the potent DNA-damaging effects of Actinium-225, with activity that is not dependent on inhibiting a specific oncogenic driver. The activity across distinct lung cancer subtypes, improved responses to standard therapy in colorectal cancer, and retained activity after bevacizumab failure in ovarian cancer strengthen the scientific rationale for this approach. These findings support further development of ATNM-400 across HER3-expressing solid tumors, with combinations selected to build on its single-agent activity."

Highlights from the EANM 2026 Presentations

Non-Small Cell Lung Cancer | Oral Presentation EPS-149

ATNM-400 demonstrated antitumor activity across EGFR-mutant, KRAS G12C-mutant and ALK-rearranged NSCLC models, supporting a HER3-directed approach with potential beyond any single oncogenic driver.

• In the KRAS G12C-mutant NCI-H358 model, ATNM-400 monotherapy achieved 81% tumor growth inhibition (TGI), compared with 38% for adagrasib and 29% for the HER3-directed antibody-drug conjugate patritumab deruxtecan. Combining ATNM-400 with adagrasib increased TGI to 105%, consistent with tumor regression. These findings support both single-agent activity and the potential to deepen responses to KRAS-targeted therapy.
  
  
• In the ALK-rearranged NCI-H3122 model, ATNM-400 plus crizotinib achieved 97% TGI, compared with 50% for ATNM-400, 55% for crizotinib and 26% for patritumab deruxtecan alone. ATNM-400-containing regimens were well tolerated and extended survival relative to controls and the HER3-directed antibody-drug conjugate.
  
  
• In the EGFR-mutant NCI-H1975 model, ATNM-400 plus pemetrexed and cisplatin achieved 86% TGI, compared with 52% for amivantamab plus chemotherapy and 48% for amivantamab plus lazertinib. ATNM-400 monotherapy achieved 63% TGI. The ATNM-400 and chemotherapy combination also prolonged survival during the study period.

Colorectal Cancer | e-Poster EP-0163

ATNM-400 demonstrated combination activity in colorectal cancer models spanning moderate-to-high HER3 expression, including tumors with limited sensitivity to standard therapy.

• In the HCT15 model with moderate HER3 expression, ATNM-400 plus oxaliplatin and bevacizumab achieved 72% TGI, compared with 25% for oxaliplatin and bevacizumab and 27% for ATNM-400 alone at the corresponding dose. The combination extended survival, supporting its potential to improve tumor control where standard therapy has limited activity.
  
  
• In the SW620 model with high HER3 expression, ATNM-400 plus bevacizumab achieved 88% TGI, comparable to 85% for oxaliplatin plus bevacizumab, while ATNM-400 monotherapy achieved 57% TGI. Survival with ATNM-400 plus bevacizumab was also comparable to the chemotherapy-containing regimen, supporting further evaluation of a combination that omits oxaliplatin.

Ovarian Cancer | e-Poster EP-0176

ATNM-400 demonstrated strong single-agent activity in ovarian cancer, including after bevacizumab failure, with additional survival findings in an immunocompetent model of disseminated disease.

• In the OVCAR-5 model, ATNM-400 monotherapy achieved 93% TGI, compared with 54% for bevacizumab. The combination achieved 85% TGI without additional benefit over ATNM-400 alone, highlighting the strength of its standalone activity in this model. ATNM-400-containing regimens were favorably tolerated and prolonged survival relative to control groups.
  
  
• Following bevacizumab failure, ATNM-400 monotherapy retained activity, achieving 50% TGI with prolonged survival and favorable tolerability. These findings support development in treatment-resistant ovarian cancer.
  
  
• In the disseminated ID8-fLuc ovarian cancer model in immunocompetent mice, ATNM-400-containing regimens prolonged survival relative to their respective controls. Combinations with carboplatin and paclitaxel also prolonged survival compared with chemotherapy alone. Survival follow-up remained ongoing at the time of the presentation, with some animals in ATNM-400 treatment groups still alive.

Preclinical Tolerability and Translational Development

The studies generally showed favorable tolerability at the evaluated doses. In ovarian cancer studies, single-bolus and fractionated dosing produced minimal changes in assessed blood, liver and kidney markers. No treatment-related abnormalities were observed in the assessed markers in the HCT15 colorectal model; a slight ALT elevation was observed with ATNM-400 plus bevacizumab in the SW620 model. These findings support continued translational evaluation of ATNM-400 as monotherapy and in selected combinations.

About ATNM‑400 and HER3
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.

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.
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 mission is to transform cancer treatment through innovative radioconjugates that maximize therapeutic efficacy while minimizing toxicity to healthy tissue by combining expertise in tumor biology, translational medicine, and radiochemistry. Since inception, Actinium has focused on developing innovative radiotherapies. Its pipeline reflects this strategy across 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. ATNM‑400 targets HER3, an antigen distinct from PSMA, and is in a first‑in‑human Phase 1 study in mCRPC, with preclinical activity across metastatic castration‑resistant prostate cancer (mCRPC), non‑small cell lung cancer (NSCLC), and breast cancer. Actimab‑A has shown improved survival in relapsed/refractory AML with CLAG‑M and is advancing toward a Phase 2/3 trial, with additional development ongoing through a CRADA with the NCI. Actinium is also advancing preclinical solid tumor programs and holds ~250 patents and patent applications, including intellectual property related to cyclotron‑based production of Ac‑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 the 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 the anticipated or estimated future results, including the risks and uncertainties associated with preliminary study results varying from final results, estimates of potential markets for drugs under development, clinical trials, actions by the FDA and other governmental agencies, regulatory clearances, responses to regulatory matters, the market demand for and acceptance of Actinium'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 (the "SEC"), including without limitation its most recent annual report on form 10‑K, subsequent quarterly reports on Forms 10‑Q and Forms 8‑K, each as amended and supplemented from time to time.

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