Actinium Pharmaceuticals' Iomab-B (Iodine-131-apamistamab) has shown promising results in the Phase 3 SIERRA trial for patients with relapsed or refractory acute myeloid leukemia (r/r AML). The study, published in the Journal of Clinical Oncology, highlights Iomab-B's potential as a conditioning agent prior to bone marrow transplant (BMT).
The SIERRA trial was a randomized, multi-center, controlled study involving 153 patients aged 55 and above with active r/r AML. The trial included heavily pre-treated patients and those with high-risk characteristics, such as a TP53 mutation. Patients were randomized to receive either Iomab-B followed by BMT or physician's choice of salvage chemotherapy followed by standard allogeneic BMT.
Primary Endpoint Achieved
The SIERRA trial met its primary endpoint of durable Complete Remission (dCR) at 6 months post-BMT with high statistical significance (p < 0.0001). Specifically, 22% of patients (13/76) in the Iomab-B arm achieved dCR compared to 0% of patients (0/77) in the control arm.
Significant Improvement in Event-Free Survival
A secondary endpoint, Event-Free Survival (EFS), also showed significant improvement in the Iomab-B arm, with a Hazard Ratio of 0.22 (p < 0.0001). This indicates a substantial reduction in the risk of events such as relapse or death.
Overall Survival and Crossover Rate
While the trial did not meet the secondary endpoint of overall survival (OS) on an intent-to-treat basis, this was largely attributed to a high crossover rate. Nearly 60% of patients in the control arm ultimately received Iomab-B followed by BMT.
Subgroup Analyses Show Promise
Supplemental analyses of the SIERRA results revealed improved survival outcomes in specific patient subgroups. Patients with a TP53 mutation, which is typically associated with poor outcomes, showed improved survival. Additionally, patients aged 65 and above demonstrated increased 1- and 2-year overall survival rates.
Expert Commentary
Dr. Sergio Giralt, a leading SIERRA Trial investigator from Memorial Sloan Kettering Cancer Center, noted that the trial demonstrated Iomab-B's ability to improve access to potentially curative hematopoietic stem cell transplant and improve outcomes compared to chemotherapy-based regimens. He expressed disappointment that the trial results may not support immediate approval despite the positive outcomes and significant unmet medical need.
Future Plans for Iomab-B
Actinium Pharmaceuticals is currently seeking a strategic partner to further develop Iomab-B in the U.S. The FDA has indicated that demonstrating an overall survival benefit in a randomized head-to-head trial will be required for a Biologics License Application (BLA) filing. Actinium plans to conduct an additional Phase 3 randomized trial to meet this requirement.
Sandesh Seth, Actinium's Chairman and CEO, stated that the company believes the SIERRA trial was a major advancement for the field of BMT and targeted radiotherapeutics. He expressed hope that securing a U.S. partner will accelerate Iomab-B's availability to patients with high unmet needs who can benefit from bone marrow transplants.
