Abstract 4236: Temporal inhibition of BCAT1 alters metal homeostasis leading to reversal of terminal exhaustion of CD8 T cells, increased cytotoxicity, and increased efficacy of checkpoint inhibition in cancer

Abstract

Abstract We have previously demonstrated that BCAT1, the enzyme responsible for the reversible transamination of leucine in the cytosol, is a druggable target in immune-oncology: the small molecule inhibitor ERG245 dramatically increases the efficacy of anti-PD-1 treatment in the moderately immunogenic CT26 colon cancer model. We have also shown that Bcat1 gene expression is enriched in exhausted CD4+ and CD8+ intratumoral cells in cancer patients from diverse cancers. Here, we illustrate that the adoptive cell transfer (ACT) of murine CD8+ T cells treated with ERG245 increased the median survival of CT26 tumor-bearing mice from 25 days, observed with the ACT of untreated CD8+ T cells, to 32 days. This suggested that inhibition of BCAT1 prevented the known exhaustion of adoptively transferred CD8+ T cells, induced by the tumor microenvironment of CT26 tumors. To confirm this hypothesis, we developed an in vitro model of generating terminally exhausted (PD-1+TIM-3+GZMB+CXCL13+) CD8+ T cells by subjecting the cells to consecutive cycles of αCD3/αCD28 activation in the presence of TGF-β. Addition of ERG245 in the last activation cycle decreased terminal exhaustion of the cells. Mechanistically, bulk RNAseq experiments indicated and ICP analysis confirmed that inhibition of BCAT1 interfered with metal homeostasis leading to increased concentrations of Fe in the mitochondria and decreased concentrations of Zn in the nucleus of newly activated CD8+ T cells. The immediate impact of ERG245 treatment on the cells included a general decrease in the genes of processes depending on proper metal equilibrium such as cholesterol biosynthesis and ribosome biogenesis. Withdrawal of BCAT1 restored or reversed the cell phenotype leading to epigenetically altered CD8+ T cells with decreased histone acetyltransferase and histone demethylase presence, increased cytotoxicity, and increased ribosome biogenesis. Collectively, the data suggest that temporal inhibition of BCAT1 inhibition induces profound effects on CD8+ T cells including increased cytotoxicity and suppression of terminal exhaustion, thus rendering the cells rescuable by anti-PD-1 therapy. Citation Format: Adonia E. Papathanassiu, Weixing Li, Hong A. Vu. Temporal inhibition of BCAT1 alters metal homeostasis leading to reversal of terminal exhaustion of CD8 T cells, increased cytotoxicity, and increased efficacy of checkpoint inhibition in 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 4236.