Actinium Appoints Accomplished Oncology Expert Steffen Heeger MD, MSc as Chief Medical Officer to Drive Rejuvenated Pipeline Development

• Proven Chief Medical Officer at several publicly listed and clinical-stage oncology companies with successful track record developing multiple modalities including radiotherapies from preclinical through global approvals across hematologic malignancies and solid tumors
• Played a leading role in clinical development and worldwide approvals of Erbitux® at Merck KGaA leading to its blockbuster status
• Led clinical development as CMO of NBE Therapeutics which was acquired by Boehringer Ingelheim for $1.4 billion, and most recently CMO of radiotherapy company Full-Life Technologies
• Timely key hire with Dr. Heeger's operational rigor and clinical expertise expected to elevate development of Actimab-A, ATNM-400, and Iomab-ACT as Actinium advances toward key data readouts and expanded clinical trials in 2H:2026

NEW YORK, June 1, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a pioneer in the development of targeted radiotherapies, today announced the appointment of Steffen Heeger, MD, MSc, as Chief Medical Officer. Dr. Heeger brings a rare combination of radiotherapy expertise, global oncology drug development leadership, and public-company experience.  Over his career, he has translated multiple programs from IND submission through global clinical approval in the US, EU, and Japan including the blockbuster Erbitux® and led as CMO an oncology company acquired for $1.4 billion.  Most recently Dr. Heeger served as CMO of a clinical-stage radiotherapy company where he advanced into global development, a PSMA program directly relevant to Actinium's ATNM-400 asset. His appointment comes at a pivotal moment as Actinium prepares to advance Actimab-A, ATNM-400, and Iomab-ACT toward key data readouts and expanded clinical trials in the second half of 2026.

"Steffen's background is uniquely suited to unlock the value in Actinium's pipeline" said Sandesh Seth, Chairman and Chief Executive Officer of Actinium Pharmaceuticals. "He has successfully taken multiple targeted oncology and radiotherapy programs from the lab into patients, including anti-PSMA programs directly relevant to our ATNM-400 asset, and has deep experience navigating global regulatory pathways with the FDA and international agencies. Steffen brings precisely the combination of deep radiotherapy expertise, global oncology clinical development leadership, regulatory experience, and executional intensity that we need as we advance and expand our pipeline of targeted radiotherapies."

"Importantly, Steffen's experience spans both hematologic malignancies and solid tumors, aligning exceptionally well with our strategic focus of building Actinium into a leading targeted radiotherapy company." Mr. Seth added. "His direct experience with alpha-emitting radiotherapies, translational medicine, and global clinical execution will be highly valuable as we progress our clinical programs and pursue new opportunities to unlock the full potential of our platform. Few clinical leaders know radiotherapy development as deeply as Steffen does, and fewer still pair that with the public-company experience and translational oncology track record he brings. We are thrilled to welcome him to Actinium."

Prior to Actinium, Dr. Heeger served as Chief Medical Officer of Full-Life Technologies, where he led global development, regulatory affairs, clinical operations, translational research, CMC, quality assurance, and program management for the company's radiotherapy pipeline. There he led the translation of three targeted radioconjugate compounds — including an anti-PSMA program in metastatic castration-resistant prostate cancer — from preclinical to clinical stage within two years, securing IND clearance and fast track designation. Prior to Full-Life, he was CMO of Pega-One, a clinical-stage oncology company that became part of Centessa Pharmaceuticals (Nasdaq: CNTA) ahead of its $380 million initial public offering. Earlier, he served as CMO of NBE-Therapeutics, where he led the IND submission and initial clinical trial of NBE-002, a first-in-class immune-stimulatory antibody-drug conjugate targeting ROR1 in triple-negative breast cancer, non-small cell lung cancer, and sarcoma. NBE-Therapeutics was subsequently acquired by Boehringer Ingelheim for $1.4 billion. Before NBE, Dr. Heeger was CMO of Selvita S.A. (WSE: SLV), where he advanced the company's lead anti-cancer compound through IND and into its first clinical trial.

Earlier in his career, Dr. Heeger served as Vice President, Head of Clinical Development at MorphoSys AG, where he led the clinical strategy and execution of the company's lead hematology and oncology programs, including monoclonal antibody therapeutics targeting CD19, CD38, and PSMA. He began his pharmaceutical career at Merck KGaA, where over nearly a decade, he led global clinical development and life cycle management for Erbitux® (cetuximab) across colorectal, head and neck, gastric, and lung cancers in major markets including the US, Europe, Japan, and China enabling its blockbuster status.

"Actinium is developing what I believe is one of the most compelling radiotherapy pipelines today." said Dr. Heeger. "Their biology-driven R&D has yielded several highly differentiated, even unique, assets that  offer real opportunity to bring transformative therapies to patients with limited options. Their assets have nothing comparable being developed and each has blockbuster potential; ATNM-400 with its novel target and compelling data across the largest solid tumor indications, Actimab-A's promise to resensitize immune checkpoint inhibitors in solid tumors and backbone potential in hematological malignancies, as well as their cell and gene therapy conditioning agent Iomab-ACT.  These are exactly the kinds of assets I have spent my career developing. I am honored to join Actinium at this pivotal stage and look forward to working closely with Sandesh and our team to unlock the value in our clinical programs."

Dr. Heeger holds an MD and a Master of Healthcare Management (MSc) from the University of Heidelberg, Germany, a world-leading institution for research in nuclear medicine and targeted radionuclide therapies. He trained as a clinical oncologist at the University Hospital Heidelberg, Department of Haematology and Oncology, and at the German Cancer Research Center. He has authored and co-authored more than 20 peer-reviewed publications across oncology and radiopharmaceutical research. Notably, Dr. Heeger's scientific roots include early work in alpha-radiotherapy, including published research involving alpha-radioimmunotherapy using antibody conjugates in hematologic malignancies which bring him to a full cycle at Actinium.

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 a novel antigen distinct from PSMA and has demonstrated 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, including statements as related to regaining compliance with the rules of the NYSE American and submission of a compliance plan, 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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