Abstract 6360: In vivo antitumor efficacy evaluation of ASC63, an oral small molecule PD-L1 inhibitor, in a humanized mouse tumor model

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Abstract Background: ASC63 is an oral small molecule programmed cell death-ligand 1 (PD-L1) inhibitor. After oral dosing, ASC63 is rapidly absorbed and converted to its pharmacologically active metabolite ASC63-A in vivo. In vitro studies showed that ASC63-A could activate PD-L1 dimerization and internalization from cell membrane, thus interfere PD-1/PD-L1 interaction and enhance T-cell activation. Here we report the in vivo antitumor efficacy of ASC63 in a humanized mouse tumor model. Methods: 0.5×106 human PD-L1 knock in CT26 cells (CT26-hPD−L1) were implanted subcutaneously into BALB/c mice for tumor development. When the average tumor volume reached approximately 100 mm3, mice were randomly assigned (post-grouping, PG) and treated with vehicle, reference drug (10 mg/kg Atezolizumab intravenous injection twice a week [BIW]), 50 or 100 mg/kg ASC63 oral dosing twice a day (BID) for 18 days. Body weights and tumor volumes were measured regularly, and tumor growth inhibitions (TGI) of different groups were compared. TGI was calculated using the formula: TGI (%) =[1-(TRTV-1)/(CRTV-1)] ×100, where TRTV= mean relative tumor volume (RTV) of treatment group; CRTV= mean of control group. Results: At PG-D18, the tumor volume of vehicle group reached 1548 mm3, and Atezolizumab, 50 and 100 mg/kg AS63 groups showed TGI values of 35.17, 17.12 and 36.87%, respectively. Atezolizumab 10 mg/kg BIW and ASC63 100 mg/kg BID produced similar antitumor activities. One mouse in 100 mg/kg ASC63 group had body weight loss more than 10% at PG-D6, and was back to normal at PG-D9 after extra nutrition was provided, while the rest of mice showed a gradually increase in body weight during the study. No significant difference of body weight or body weight change was found among different groups of mice. Conclusion: Results of this study show that ASC63 is in general well tolerated in CT26-hPD−L1 humanized mouse tumor model, and ASC63 has comparable antitumor efficacy as the FDA-approved PD-L1 antibody, Atezolizumab. ASC63 is an oral small molecule PD-L1 inhibitor, and thus will have better patient compliance than injective PD-1/PD-L1 antibody. Results of this study support the continued investigation of ASC63. Citation Format: Jinzi J. Wu, Handan He. In vivo antitumor efficacy evaluation of ASC63, an oral small molecule PD-L1 inhibitor, in a humanized mouse tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6360.

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