Actinium Highlights Ability of Iomab-B to Overcome High-Risk TP53 Mutation Resulting in Significant Improvement in Overall Survival in Patients with Active Relapsed Refractory AML at the European Bone Marrow Transplant Annual Meeting

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Apr 18, 2024, 08:00 ET

-- Iomab-B led bone marrow transplant produced high rates of complete remission and durable complete remission regardless of TP53 mutation status in patients age 55 and above with high-risk active relapsed or refractory acute myeloid leukemia

-- Median Overall Survival of 5.49 months observed in patients with a TP53 mutation receiving an Iomab-B led allogeneic bone marrow transplant compared to 1.66 months in patients that did not receive Iomab-B (hazard ratio=0.23, p=0.0002)

NEW YORK, April 18, 2024 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of Antibody Radiation Conjugates (ARCs) and other targeted radiotherapies, today announced that results from the Phase 3 SIERRA trial of Iomab-B were presented in an oral presentation at the 50^th Annual European Bone Marrow Transplant Society Meeting (EBMT) held in Glasgow, Scotland on April 14-17. The results showed that an Iomab-B led bone marrow transplant (BMT) results in higher rates of remissions and durable Complete Remission (dCR), which is the primary endpoint of the SIERRA trial, as well as significant improvement in overall survival in TP53 positive patients. Iomab-B is a targeted radiotherapeutic comprised of an anti-CD45 monoclonal antibody with the Iodine-131 radioisotope payload. The Phase 3 SIERRA trial enrolled 153 patients age 55 and above with active relapsed or refractory acute myeloid leukemia (AML) and compared outcomes of patients receiving Iomab-B BMT to those of patients receiving physician's choice of care in the control arm. In total, 24% (37/153) of the patients enrolled on SIERRA had a TP53 mutation, which is associated with limited treatment options and poor outcomes.

Data highlighted in the ASH oral presentation, which can be accessed on the investor relations page of Actinium's website, included:

Response rates by TP53 Mutation Status:

	Iomab-B & Crossover	Control Arm
TP53 Positive	N=27	N=10
CR	55.56% (15/27)	0 %
dCR	14.81% (4/27)	0 %
TP53 Wildtype	N=93	N=23
CR	58.06% (54/93)	17.39% (4/23)
dCR	16.13% (15/93)	0 %

Overall Survival in Patients with a TP53 Mutation:

	Iomab-B & Crossover	Control Arm
Median OS	5.49 months	1.66 months
Number of Patients	27	10
Hazard Ratio	0.23
p-value	0.0002

Median OS was 6.37 months in TP53 negative patients receiving Iomab-B and 5.72 months for TP53 positive patients demonstrating Iomab-B's ability to overcome TP53 gene mutations.

Dr. Hannah Choe, Assistant Professor of Medicine at Ohio State University and SIERRA trial investigator, commented, "TP53 mutations are associated with very poor outcomes due to resistance to anti-leukemic therapies with patients rarely offered access to potentially curative transplantation. The SIERRA trial showed that Iomab-B was well tolerated and can enable unprecedented access to transplant in this patient population and induce high complete remission rates despite active, relapsed/refractory disease and a TP53 mutation. These results were very well received at EBMT and demonstrate the novelty and safety of a CD45-directed antibody radiation conjugate. More importantly, we see that these response rates translated into improved overall survival, overcoming the increased risk associated with TP53 mutation while no other viable treatment options exist. We are excited for Iomab-B's potential use and safety for disease control in patients with a TP53 mutation."

About the EBMT Annual Meeting

The Annual Meeting of the EBMT is attended by more than 5,500 participants, including physicians, nurses, data managers, statisticians, quality managers, cell therapists, paediatricians, pharmacists, psychologists, psychiatrists and psychoanalysts, transplant coordinators, lab scientists, trainees, and patients. This important congress ensures and encourages dialogues and information exchange, education and scientific productivity.

The full annual meeting program is available online at:

https://ebmt2024.abstractserver.com/program/#/program/2/horizontal.

About Actinium Pharmaceuticals, Inc.

Actinium develops targeted radiotherapies to meaningfully improve survival for people who have failed existing oncology therapies. Advanced pipeline candidates Iomab-B (pre-BLA & MAA (EU)), an induction and conditioning agent prior to bone marrow transplant, and Actimab-A (National Cancer Institute CRADA pivotal development path), a therapeutic agent, have demonstrated potential to extend survival outcomes for people with relapsed and refractory acute myeloid leukemia. Actinium plans to advance Iomab-B for other blood cancers and next generation conditioning candidate Iomab-ACT to improve cell and gene therapy outcomes. Actinium holds more than 230 patents and patent applications including several patents related to the manufacture of the isotope Ac-225 in a cyclotron.

For more information, please visit: https://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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