On June 14, 2024 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of Antibody Radiation Conjugates (ARCs) and other targeted radiotherapies, reported that results from the Phase 3 SIERRA trial of Iomab-B were presented at the 2024 European Hematology Association (EHA) (Free EHA Whitepaper) Hybrid Congress being held June 13 – 16, 2024, in Madrid, Spain (Press release, Actinium Pharmaceuticals, JUN 14, 2024, View Source [SID1234644327]). The two presentations at EHA (Free EHA Whitepaper) highlighted outcomes in patients with active relapsed or refractory acute myeloid leukemia (r/r AML) enrolled in the SIERRA trial who had a TP53 mutation and long-term efficacy results in this older patient population.

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The Phase 3 SIERRA trial enrolled 153 patients ages 55 and above with active r/r AML and compared outcomes of patients receiving an Iomab-B led bone marrow transplant (BMT) to those of patients receiving physician’s choice of care in the control arm. Across all patients in SIERRA study, only patients receiving an Iomab-B led BMT achieved the trial’s primary endpoint of durable complete remission with these patients having 92% 1-year survival and 69% 2-year survival with statistically significant higher event free survival. The SIERRA trial enrolled high-risk patients including those with one or more of the following: a TP53 mutation, advanced age up to 77 years old, complex cytogenetics and prior therapy including venetoclax and other targeted agents.

Highlights from Oral Presentation of Outcomes in Patients with a TP53 Mutation

– In total, 24% (37/153) of the patients enrolled on SIERRA had a TP53 mutation, which is usually associated with limited treatment options and poor outcomes
– For patients with TP53 mutation only those receiving Iomab-B (either at randomization or via cross-over) achieved complete remission or achieve a durable complete remission (dCR), the primary endpoint of the SIERRA trial
– Median Overall Survival (OS) 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)
– 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

Presentation Title: 131I-APAMISTAMAB-LED ALLOGENEIC HEMATOPOIETIC CELL TRANSPLANT RESULTS IN IMPROVED SURVIVAL OUTCOMES IN R/R AML PATIENTS WITH HIGH-RISK TP53 MUTATIONS IN THE RANDOMIZED PHASE III SIERRA TRIAL

Presenter: Dr. Hannah Choe, Assistant Professor of Medicine at Ohio State University and SIERRA trial investigator

Highlights from Presentation of Long-Term Efficacy Results

– All patients receiving Iomab-B underwent a BMT compared to 18% on the control arm
– 75% of patients on the Iomab-B arm achieved a complete remission (CR) compared to 6.3% on the control arm
– The durable complete remission (dCR) was 22% on the Iomab-B arm compared to 0% on the control arm. dCR is the primary endpoint of the SIERRA study and was met with high statistical significance with a p-value<0.0001
– Of the patients achieving dCR after an Iomab-B led BMT, there was 92% 1-year survival and 69% 2-year survival with median overall survival not reached
– Iomab-B was well tolerated with a favorable safety profile including lower rates of sepsis and mucositis in patients receiving an Iomab-B led BMT

Presentation Title: LONG TERM EFFICACY RESULTS OF THE SIERRA TRIAL: A PHASE 3 STUDY OF 131I-APAMISTAMAB-LED ALLOGENEIC HEMATOPOIETIC CELL TRANSPLANTATION VERSUS CONVENTIONAL CARE IN OLDER PATIENTS WITH ACTIVE, R/R AML