Actinium trial testing Iomab-B in AML patients still highly encouraging

Actinium Pharmaceuticals on Monday announced key interim findings from the pivotal Phase 3 SIERRA trial of Iomab-B at 50% of total of 150-patient, compared to physician’s choice of salvage chemotherapy in patients age 55 and above with active, relapsed or refractory AML (Acute Myeloid Leukemia).

These interim data provide information on safety and feasibility of using Iomab-B to enable a BMT (Bone Marrow Transplant), the only curative treatment option in this patient population that is not typically considered eligible for BMT.

Key findings from the first 75 patients enrolled (50% of total enrollment) in the trial include:

– Patients enrolled in the SIERRA trial were a median age of 64 (55-76) and had active disease with a median bone marrow blast percentage at randomization of 28 percent (5-97%). All patients were intermediate or poor, adverse risk groups.  Two-thirds (68%) of the patients enrolled were in the poor prognostic, adverse cytogenetic and molecular risk group.

– All patients receiving a therapeutic dose of Iomab-B (31/31) in the study arm received a bone marrow transplant and engrafted rapidly without delay in blood count recovery.

– Only 7/38 patients (18%) randomized to the control arm achieved an initial complete response (CR) and were able to proceed to a conventional bone marrow transplant.

– Of the 31 patients who failed the primary endpoint in the control arm (82% failure), 20 (64%) were considered eligible for potential rescue by treatment with Iomab-B followed by a BMT.  All 20 patients (100%) who crossed over and received a therapeutic dose of Iomab-B followed by a BMT achieved engraftment without delay in blood count recovery despite high blast count burden prior to transplant (median 35%).

– 12/38 patients (32%) randomized to the control arm received targeted agents all of which were recently approved.  11/12 patients (92%) received the Bcl-2 inhibitor venetoclax with either an hypomethylating agent or low dose cytarabine.  Of these, only 3/11 patients (27%) achieved a CR.

– 100-day Non-Relapse Transplant Related Mortality remains lower in the Iomab-B arm (1/31 patients or 3%) compared to patients in the control arm who received conventional transplants (2/7 or 29%).  Of the 31 patients who received Iomab-B in the study arm, 30 are potentially evaluable for the primary endpoint compared to 5 in the control arm.  This difference between study arm and control arm remains consistent with that reported at the interim update at 25% of enrollment.

– The SIERRA trial remains the only randomized Phase 3 clinical trial to offer BMT as an option for patients age 55 and above with active, relapsed or refractory AML.

Sergio Giralt, M.D., Chief of Adult BMT, Memorial Sloan Kettering Cancer Center; Chair, Myeloma Service, said that the results from the first 50% of patients to be enrolled in the SIERRA trial continue to be highly encouraging, particularly Iomab-B’s ability to enable a transplant in this patient population that would otherwise be ineligible. He said that, despite eight new therapies having been approved for patients with AML, better outcomes for patients with AML are needed, in particular for the large number of relapsed and refractory patients. Giralt said that newly approved targeted agents are not curative and as seen in the SIERRA trial do not enable a high rate of potentially curative BMT.