Actinium Pharmaceuticals announced 100% of evaluable patients in the third and planned final dose cohort of the Actimab-A CLAG-M Phase 1 trial being conducted at the Medical College of Wisconsin (MCW) achieved remission. Across all three cohorts, 67% or 10/15 patients treated with 0.25, 0.50 and 0.75 uCi/kg of Actimab-A and the standard regimen of CLAG-M achieved a Complete Remission (CR) or Complete Remission with inadequate hematopoietic recovery (CRi). Further, 83% of patients (10/12) who received 3 or fewer prior lines of treatment achieved CR or CRi. Notably, 70% of CR/CRi patients were MRD negative indicating a deep remission with no detectable disease. These results which include subtherapeutic doses of Actimab-A in the first two dose cohorts and represent a marked improvement over CLAG-M treatment alone (ORR: 55%, MRD negativity: 39%) implying potential mechanistic synergy. This novel Phase 1 combination trial is for patients with relapsed or refractory acute myeloid leukemia (R/R AML) age 18 and above deemed medically fit for cytotoxic chemotherapy.

"We are thrilled with the high rates of remission, MRD negativity and transplant in this trial, which highlights the potential this combination may have for patients with R/R AML. Actimab-A targets CD33, which is expressed in virtually all patients with AML, and delivers potent radiation via the alpha-emitting radioisotope Actinium-225. Actimab-A has produced single-agent response rates as high as 69% in a Phase 2 trial, demonstrating its potential in radiation sensitive blood cancers like AML,” Dr. Mark Berger, Actinium's Chief Medical Officer, said. “While the synergies of radiation with chemotherapy and other modalities is well known, we are highly encouraged that Actimab-A at low doses with CLAG-M produced higher rates of remission and MRD negativity than either agent alone, supporting the synergy of this combination and potential of other Actimab-A combinations. It's still the case that there is no standard of care for R/R AML despite it being a large segment of the AML patient population. Our efforts with our CD33 program are intended to show that Actimab-A, when used together with other synergistic therapeutic modalities, can serve as the backbone of combinations that we hope will be new standards of care for both fit and unfit patients with R/R AML. With supporting data also being reported from our Actimab-A venetoclax combination trial we have great enthusiasm of the potential of additional Actimab-A combination with other therapeutic agents, that can treat patients with significant unmet need."

Patients enrolled on this study to date had intermediate (5/15, 33%) or adverse (10/15, 67%) cytogenetics. Patients received a median of 2 lines of prior therapies (range 1-5) with 47% of patients (7/15) previously receiving venetoclax with a hypomethylating agent and 53% of patients (8/15) having undergone an allogeneic BMT and then relapsed prior to Actimab-A CLAG-M. In the third dose cohort of 0.75 uCi/kg, 100% of evaluable patients (3/3) achieved complete remission [1 CR, 2 Complete Remission with inadequate platelet recovery (CRp)] with 2 patients being MRD negative and the other patient having only 0.2% AML cells detected.