-- 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:

Overall Survival in Patients with a TP53 Mutation:

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."