Abstract LB166: Discovery of CT3021, a novel potent adenosine A2a/A2b/A1 receptor triple antagonist

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Abstract In a CD73-positive tumor microenvironment (TME), ATP released from apoptotic tumor cells converts to adenosine, generating an adenosine-rich immunosuppressive environment. Adenosine activates G-protein coupled receptors expressed on immune cells to achieve immune suppression, with a mechanism of action involving 1) dampening antitumor effector cells (T eff and NK cells) via adenosine engagement on A2a receptor, (2) reducing dendritic cell antigen presentation and promoting MDSC differentiation by activating A2b and A2a receptors, and (3) inducing chemotactic migration of immature plasmacytoid dendritic cells to infiltrate tumor tissue via A1 receptor. Furthermore, A1 receptor expression in certain tumors mediates an adenosine-driven tumor cell proliferation, likely through A1 receptor Gi coupling to the Hippo-YAP signal transduction pathway. Thus, pharmacologic inhibition of A2a, A2b, and A1 receptors by a triple antagonist in the context of adenosine-rich TME may represent an attractive strategy to achieve a better outcome in treating solid tumors. We discovered and characterized a novel adenosine receptor antagonist CT3021. CT3021 exhibits high binding affinity to A2a, A2b, and A1, with a Ki value of 0.37 nM, 1.76 nM, and 1.26 nM, respectively, and is selective against the A3 receptor and other 84 pharmacologically and/or toxicologically relevant targets. Schild analysis demonstrated that CT3021 is a competitive antagonist with a calculated KB value of 0.18 nM on A2a receptor in a whole cell cAMP assay in transfected HEK293 cells. In functional antagonist assays, CT3021 maintains its high potency full antagonism under an adenosine-rich TME-like condition (10-100 µM adenosine) both in transfected HEK293 cells and in isolated human T lymphocytes. CT3021 has a high oral bioavailability, a limited CNS exposure, and a favorable ADME profile. CT3021 is well tolerated in rats after repeat dosing. Further toxicology and efficacy studies are underway to explore the potential of CT3021 as a best-in-class adenosine receptor antagonist immunotherapy for the treatment of CD73 positive and A1 receptor positive solid tumors. Citation Format: Sandong Han, Nam Hee Kim, Hongmei He, Zhi Liang Chu. Discovery of CT3021, a novel potent adenosine A2a/A2b/A1 receptor triple antagonist [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB166.