On April 19, 2023 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of targeted radiotherapies, reported the first ever data demonstrating the utility of Actimab-A to depleted myeloid derived suppressor cells (MDSCs), which are ubiquitously present within the solid tumor microenvironment as well as blood cancers (Press release, Actinium Pharmaceuticals, APR 19, 2023, View Source [SID1234630323]). The new data were showcased in a poster presentation at the American Association for Cancer Research (AACR) (Free AACR Whitepaper) 2023 Annual Meeting, which is being held April 14 – 19, 2023 in Orlando, Florida.
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Sandesh Seth, Actinium’s Chairman and CEO, said, "Significant research and development activities are being applied to understanding the complex biological activities within the tumor microenvironment in order to generate better treatment responses and patient outcomes. MDSCs are recruited to sites of chronic inflammation, such as the tumor microenvironment, where they exert immunosuppressive effects including inhibition of immune responses mediated by T cells, B cells, and NK cells. At Actinium, we believe Actimab-A can play an important role in the tumor microenvironment by depleting MDSCs, which express CD33, in a targeted manner. In doing so, Actimab-A can mitigate a major immunosuppressive contributor and potentially improve response rates as well as the duration of responses for a wide array of immunotherapies. With the substantial number of immunotherapies in development or currently in clinical use, we see multiple opportunities to synergize with immunotherapies such as checkpoint inhibitors and T and NK cell therapies. These data are an important step forward and we are excited to continue development of Actimab-A for MDSC depletion and beyond."
Highlights from the AACR (Free AACR Whitepaper) poster titled, "Targeting myeloid-derived suppressor cells with actinium-225 lintuzumab, a CD33 antibody radioconjugate to enhance antitumor immunity", include:
Actimab-A demonstrated efficient depletion of ex vivo human MDSCs derived from colorectal and lung cancer patient samples in vitro in addition to an in vivo humanized mouse model of Non-Small Cell Lung Cancer
Colorectal cancer blood MDSCs treated with Actimab-A were more effectively cleared (p<0.01) compared to depletion by Mylotarg, a CD33-targeted antibody-drug conjugate, highlighting the powerful cytotoxicity and potential therapeutic benefit of radiotherapy compared to naked antibodies or ADCs
Flow cytometry data confirmed an upregulation of CD33+ MDSCs in both lung and colorectal cancer patient samples compared to healthy donor controls. Following Actimab-A treatment in mice, a specific and robust depletion of ex vivo CD33+ MDSCs was observed
These results suggest that targeted blockade of MDSC activity via treatment with Actimab-A can alleviate their pro-tumorigenic and immunosuppressive activities to bolster the efficacy of immunotherapy such as checkpoint inhibitors.
The poster will be available on the presentations page of Actinium’s investor relations page of its website: View Source