On December 11, 2017 Actinium Pharmaceuticals, Inc. (NYSE American:ATNM) ("Actinium" or "the Company") reported results from an analysis performed on a large U.S. library of samples from 865 multiple myeloma patients which showed that twenty-five percent of patients had CD33 expression on their multiple myeloma cells (Press release, Actinium Pharmaceuticals, DEC 11, 2017, View Source [SID1234522539]). Actinium is currently conducting a Phase 1 clinical trial for its Actimab-M drug candidate in patients with refractory multiple myeloma. Actinium is the first and only company thus far to have a CD33 targeted therapy for multiple myeloma and the results from this analysis provide further rationale for the Company’s myeloma initiative.
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This analysis was the first of its kind to analyze such a large, U.S. based patient sample library as previous studies exploring CD33 expression in multiple myeloma looked at significantly smaller sample sizes from established multiple myeloma cell lines. Patient samples at initial diagnosis were assessed for CD33 expression and CD33 expression was stratified with CD33 expression greater than 40% considered high and greater than 60% very high. The analysis showed that 61.6% of patients in the dataset had high CD33 expression and 41% of patients had very high CD33 expression which translates to approximately fifteen percent of the overall multiple myeloma sample population.
The online abstract can accessed through the following link:
View Source
Dr. Mark Berger, Actinium’s Chief Medical Officer said, "It is generally believed that expression of CD33 on multiple myeloma plasmocytes is in line with the low levels of expression in cells of the lymphoid lineage. The results from this study confirm that CD33 is expressed in a significant sub-set of multiple myeloma patients. Given that CD33 expression levels have been found to be high or very high in a large percentage of patients that do express the antigen, we have great confidence that our Actimab-M drug candidate, which uses an anti-CD33 antibody, can have a beneficial impact on these patients. In a disease like multiple myeloma, which remains incurable, we believe it is important to explore new therapeutic modalities and use of our CD33 targeting ARC or Antibody Radio-Conjugate is supported by these results. Additionally, myeloma cells are sensitive to radiation and targeting them using an ARC like Actimab-M may provide further advantages."
Patients that relapsed were also assessed for CD33 expression and 27.1% of relapsed patients were found to have CD33 expression with 58.3% of these patients having very high expression at initial diagnosis and relapse.
About Actimab-M
Actimab-M is being investigated in patients with refractory multiple myeloma. Multiple myeloma is a currently incurable cancer of plasma cells, which are white blood cells that produce antibodies. Actimab-M is currently being studied in a Phase 1 dose escalation study in up to 12 patients that is designed to establish safety, maximum tolerable dose and proof of concept. Actimab-M is an ARC or Antibody Radio-Conjugate that consists of Actinium-225, an alpha-emitting radioisotope coupled to the anti-CD33 monoclonal antibody, lintuzumab. CD33 has been shown to be expressed on myeloma plasmocytes in 25% of multiple myeloma patients and up to 35% of multiple myeloma patients and has also shown to be correlated with poorer outcomes.