On December 14, 2021 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) ("Actinium" or the "Company"), a leader in the development of targeted radiotherapies for patients with unmet needs reported that updated data from the recently complete Actimab-A and CLAG-M Phase 1 combination trial being conducted at the Medical College of Wisconsin (MCW) was presented at the 63rd American Society of Hematology (ASH) (Free ASH Whitepaper) Annual Meeting and Exposition (ASH) (Free ASH Whitepaper) that is being held December 11 – 14, 2021 in Atlanta, Georgia and virtually (Press release, Actinium Pharmaceuticals, DEC 14, 2021, View Source [SID1234597107]). This Phase 1 trial was a dose escalation study that evaluated Actimab-A, a CD33 targeting antibody radiation conjugate (ARC) armed with the alpha-emitting radioisotope Actinum-225, combined with CLAG-M (Cladribine, Cytarabine, G-CSF and Mitoxantrone), a salvage chemotherapy regimen for patients fit for intensive therapy.

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Actimab-A + CLAG-M Phase 1 Results:

Complete remissions (CR/CRp) in all dose cohorts
80% overall response rate (CR/CRp/MLFS) in patients receiving less than 4 lines of prior therapy with a total of 10 complete remissions across all four dose cohorts
72% MRD negativity rate determined by flow cytometry compares favorably to 39% MRD negativity rate with CLAG-M alone in MCW’s institutional experience1
60% response rate in patients receiving prior venetoclax therapy including 4 patients that achieved a complete remission
75% of patients proceeded to a bone marrow transplant, excluding patients with prior transplant experience
Median time to best response was 40 days
No 30-day mortality
0.75uCi/kg of Actimab-A identified as recommended Phase 2 dose
Dr. Sameem Abedin, Assistant Professor of Medicine, Medical College of Wisconsin, Division of Hematology and Oncology and Principal Investigator of the study, commented, "We are excited to have completed dose escalation and to report the Phase 1 results of this novel combination of CLAG-M with Actimab-A. AML is known to be highly radio-sensitive, but we cannot treat AML effectively with external radiation sources. Actimab-A solves this issue by directing the potent alpha-emitting radioisotope Actinium-225 at the cellular level inside the body to CD33, which is expressed in virtually all AML patients. Based on our experience with Actimab-A as a single agent, we believed that in combination with CLAG-M it would improve remission rates and the depth of remissions while being safe, given the non-overlapping mechanisms of action. We are very encouraged by the high rates of remissions with MRD negativity, indicating deep responses, and the high number responses seen in patients that had previously failed venetoclax, which is becoming an increasingly larger portion of the AML patient population. Also of note is the high number of patients able to proceed to bone marrow transplant on the study. We look forward to continuing to study this novel combination."

Dr. Avinash Desai, Actinium’s Chief Medical Officer, said, "This study will prove invaluable to our future development of Actimab-A. There are several positive findings from this study including high rates of MRD negativity, strong responses in patients failing venetoclax therapy and high rates of transplant, which all represent future development opportunities. With these data and the recommended Phase 2 dose level determined, we look forward to finalizing our future development strategy for Actimab-A and CLAG-M for patients with relapsed or refractory AML. In addition, these results support our broader strategy of leveraging the differentiated mechanism of targeted radiotherapy utilizing Actimab-A as a backbone in combination with other therapeutic modalities to improve patient outcomes."

Sources:

1)Mushtaq et al. Leukemia & Lymphoma 2020