Abstract 2247: Platinoid-induced MHCI antigen presentation enables checkpoint inhibitor responsiveness

Abstract Many cancers are refractory to immune checkpoint therapy (ICT), but the causes of ICT resistance remain unknown. Despite low mutational burden, hepatocellular carcinoma (HCC) responds to PD-1 blockade, but prostate cancer (PCa) does not. RNA-seq analysis revealed that, unlike HCC, PCa cells poorly express MHC-I molecules and components of the MHC-I antigen processing and presentation machinery. We found that treatment of PCa cells and other tumor types with platin-based drugs, especially low dose Oxaliplatin, led to a pronounced upregulation of MHC-I molecules and their antigen generating and loading machinery. Most importantly, Oxaliplatin synergistically potentiated the effect of exogenous IFNγ; a conclusion based on two cumulative observations. First, ATAC-seq analyses revealed that Oxaliplatin activates MHC machinery through different pathways compared to well-known IFNγ signaling. Second, Oxaliplatin upregulates IFNγR2 expression in cancer cells. Induction of IFNγR2, which was needed for Oxaliplatin-potentiation of ICT-induced tumor rejection in vivo, depended on NF-κB signaling. Induction of IFNγR2, which was needed for Oxaliplatin-potentiation of ICT-induced tumor rejection in vivo, depended on NF-κB signaling. Moreover, we found that Oxaliplatin activates histone acetyltransferases (HATs) which alter chromatin structure of genes encoding MHC-I complex components, thereby enabling recruitment of a diverse array of activating transcription factors. Our data indicates that combining ICT with an appropriate low dose platinoid chemotherapeutic agent is useful in reinvigorating the immune response to tumors that have escaped immune destruction due to MHC-I downregulation and do not respond to single agent therapy. Citation Format: Ingmar Niels Bastian, Weihua Li, Qui Phung, Kathleen Fisch, Jennie Lill, Michael Karin, Shabnam Shalapour. Platinoid-induced MHCI antigen presentation enables checkpoint inhibitor responsiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2247.