Abstract 2576: ATG-037, a highly potent small molecule CD73 inhibitor has superior activity of reversing immunosuppression in higher-AMP environments compared with anti-CD73 antibodies
Authors: Bian Gang , Hua Jiahui , Tian Linjie , Lynch Kevin , Mei Jay , Shan Bo , Hou Bing 
Published: June 2022

Abstract
Background: CD73 is a cell surface enzyme which is highly expressed in the tumor microenvironment (TME). Degradation of adenosine monophosphate (AMP) into adenosine by CD73 results in the generation of an immunosuppressed and pro-angiogenic niche within the TME that promotes the onset and progression of cancer. Targeting CD73 has resulted in favourable anti-tumor effects in preclinical models and in clinic. One of the key mechanisms of therapeutic activity by CD73 inhibition is restoring the normal function of effector T cells from adenosine inhibition. ATG-037 is a highly potent and selective oral small molecule inhibitor of CD73. This study compared the ability of ATG-037 and clinical CD73 antibodies in reverting immunosuppression in higher-AMP environments in vitro.
Methods: The activity of ATG-037 and CD73 antibodies (Hu101-28, MEDI9447) in inhibiting enzyme function of cell surface CD73 was evaluated by measuring the ATP-dependent oxidation of luciferin, which is inhibited by AMP, using Cell Titer Glo assay. Reversal of AMP/adenosine-mediated immune suppression of human T cells by CD73 inhibitors was determined by measuring T cell function in the presence of different concentrations of exogenous AMP. Markers for T cell proliferation, activation and cytotoxicity were assessed by flow cytometry, and the cytokine levels were measured by ELISA.
Results: ATG-037, Hu101-28 and MEDI9447 inhibited the enzyme activity of cell surface-expressed CD73 on human A375 cells under 100 µM AMP with a half-maximal inhibitory concentration (IC50) of 0.36 nM,20.94 nM and 3.46 nM, respectively. ATG-037 demonstrated complete inhibition of CD73 activity, whereas MEDI9447 did not reach complete CD73 inhibition. T cell proliferation and activation induced by CD3/CD28 dynabeads were suppressed by 100 µM of extracellular AMP and the suppression was relieved by the addition of ATG-037 with half-maximal effective concentration (EC50) of 21.6 nM for CD8+ T cell proliferation, 27 nM for T cell activation, 2 nM for granzyme B expression, and 6.5 nM for T cell IFN-γ production. While Hu101-28 and MEDI9447 fail to restore the T cell function. In a mixed lymphocyte reaction assay, ATG-037, but not Hu101-28 or MEDI9447 reversed AMP-dependent T cell suppression. In addition, ATG-037 rescued immune cell activation in high AMP (500 µM, 1000 µM) environments.
Conclusion: ATG-037 demonstrated potent and complete CD73 enzyme inhibition and stronger ability in restoring T cell function from high-level AMP mediated suppression, compared with clinical anti-CD73 antibodies. These data implicate the potential therapeutic advantages of small molecule CD73 inhibitors over blocking antibodies.
Citation Format: Gang Bian, Jiahui Hua, Linjie Tian, Kevin Lynch, Jay Mei, Bo Shan, Bing Hou. ATG-037, a highly potent small molecule CD73 inhibitor has superior activity of reversing immunosuppression in higher-AMP environments compared with anti-CD73 antibodies [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 2576.