Abstract 5632: Combinatorial epigenetic targeting of PRC2 complexes upregulates MHC antigen presentation components in melanoma and gastrointestinal cancer cells
Authors: Perez Jorge E. Tovar , Dashwood Roderick H. 
Published: June 2022

Low tumor immunogenicity is associated with immune escape, immunotherapy resistance, and poor patient survival [1-3]. Major histocompatibility complex (MHC) antigen presentation pathways (APPs) play a crucial role in promoting tumor T-cell recognition and initiating antitumoral immune responses. However, epigenetic silencing of APPs is a common mechanism in various cancers, including melanoma and gastrointestinal malignancies [3,4]. In the current investigation, mouse melanoma (B16/OVA) and human colon cancer (LOVO and HCT116), small intestine cancer (HUTU80), and normal colonic epithelial (CCD841) cell lines were treated with epigenetic drug candidates. As reported [5], a decrease in histone H3K27 methylation marks via polycomb repressive complex 2 (PRC2) inhibitors, as well as altered histone acetylation status from histone deacetylase 3 (HDAC3)-specific inhibition, increased the expression of APP components, based on immunoblotting and RT-qPCR experiments. Normal colonic epithelial cells showed resistance to the treatments, indicating cancer cell-specific effects of the test agents. In B16/OVA cells, flow cytometry and enzyme linked immunosorbent assays corroborated that HDAC3 and/or PRC2 inhibitor combinations increased cell surface occupancy of MHC-I complexes and increased CD8+ T-cell activation. These findings have implications for the clinical application of next-generation combinatorial epigenetic agents [6,7], targeted towards increased tumor immunogenicity and enhanced efficacy of new immunoepigenetic strategies. Supported in part by NCI grant CA122959, by the John S. Dunn Foundation, and by a Chancellor’s Research Initiative.

References1. J Galon, D Bruni. Approaches to treat immune hot, altered, and cold tumours with combination immunotherapies. Nat Rev Drug Discov 2019;18:197-218.2. S Yoshihama et al. NLRC5/CITA expression correlates with efficient response to checkpoint blockade immunotherapy. Sci Rep 2021;11:3258.3. S Yoshihama et al. NLRC5/MHC class I transactivator is a target for immune evasion in cancer. Proc Natl Acad Sci USA 2016;113:5999-6004.4. K Suzuki, Y Luo. Histone acetylation and the regulation of major histocompatibility class II gene expression. Adv Protein Chem Struct Biol 2017;106:71-111.5. ML Burr et al. An evolutionarily conserved function of polycomb silences the MHC class I antigen presentation pathway and enables immune evasion in cancer. Cancer Cell 2019;36:385-401.6. P Rajendran et al. Acetylation of CCAR2 establishes a BET/BRD9 acetyl switch in response to combined deacetylase and bromodomain inhibition. Cancer Res 2019;79:918-927.7. S Kapoor et al. Deacetylase plus bromodomain inhibition downregulates ERCC2 and suppresses the growth of metastatic colon cancer cells. Cancers (Basel) 2021;13:1438.

Citation Format: Jorge E. Tovar Perez, Roderick H. Dashwood. Combinatorial epigenetic targeting of PRC2 complexes upregulates MHC antigen presentation components in melanoma and gastrointestinal cancer cells [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 5632.