Abstract 3437: Characterization of a potent and selective A2aR monoclonal antibody antagonist for the treatment of cancer

Abstract

Abstract Introduction: Adenosine-mediated suppression of anti-tumor immunity has been shown to be one of the mechanisms for immunosuppression and resistance to immune checkpoint blockade (ICB) therapies such as anti-PD-1 or anti-PD-L1 monoclonal antibodies (mAbs). Therapeutic candidates (biologics and small molecule inhibitors(SMIs)) targeting ectonucleotidases CD39 and CD73, enzymes responsible for hydrolyzing ATP to adenosine, and SMIs targeting adenosine receptors are currently under active preclinical and early clinical development. Here we present the characterization of a novel, selective anti-human A2aR antagonist mAb that showed high potency in inhibiting adenosine mediated immunosuppressive functions to enhance anti-tumor immunity. Methods: A panel of mAbs binding to human adenosine receptor A2aR (hA2aR) were generated via hybridoma technology. The specificity and cross-reactivity were measured by FACS using human A1R, A2aR, A2bR, A3R or mouse A2aR over-expressing cells, as well as human and cynomolgus monkey PBMC. The cellular potency of these mAbs was assessed by measuring decreased cAMP levels in engineered HEK293 cells stably over-expressing hA2aR, a Gs protein coupled receptor (GPCR), upon stimulation with agonist NECA. The ability of lead candidate AT-004 to reverse adenosine-mediated immune suppression of human CD8 T-cells was determined using standard CD3/CD28 activation conditions. The in vivo efficacy of humanized AT-004 is being evaluated using ICB treatment resistant solid tumor mouse models. Results: AT-004 represents a panel of novel, selective mAbs. These mAbs specifically bind to human A2aR, but not to family members including A1R, A2bR and A3R. Cross-reactivity to cynomolgus monkey PBMCs was also observed. AT-004 inhibited NECA-mediated A2aR activation with a potency over 100-fold higher than SMIs e.g. AZD4635. AT-004 significantly reversed the ability of adenosine to suppress CD8 T cell activation as indicated by restoration of cell surface marker expression and increased levels of cytokines such as IFN-γ in the supernatants. Conclusions: AT-004 is a potent, selective and highly potent antagonist of A2aR receptor. Considering its potential safety advantage as an mAb comparing to most known A2aR SMI antagonists in that it does not cross the blood brain barrier, AT-004 maybe a promising novel therapeutic candidate for immunotherapy, vital for enhancing anti-tumor responses in solid tumors that show an incomplete response or resistance to anti-PD-1 or anti-PD-L1 mAb treatment due to elevated adenosine level in tumor microenvironment (TME). Citation Format: Changyun Hu, Jiandong Zhang, Shuying Liu, Xinyan Zhao. Characterization of a potent and selective A2aR monoclonal antibody antagonist for the treatment of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3437.