Abstract 1384: The epigenetic modifier EZH2 represses antitumor immunity in melanoma

Despite major advances in immuno- and targeted therapies for metastatic melanoma, not all patients respond to such treatments and the development of therapy resistance remains a key obstacle. Novel targets are required and the epigenetic modifier EZH2 may represent such a solution. EZH2 methylates histones causing chromatin compaction and silencing of gene expression. Aberrant EZH2 in cancer results in the silencing of hundreds of tumor-suppressor genes that would normally constrain cancer growth, and 26% of patients in the Australian Melanoma Genome Project (AMGP) display such abnormal EZH2. Using ChIP-seq and microarrays to reveal downstream EZH2 target genes, we identified many tumor-suppressor genes including some that play a role in the antitumor immune response. Interestingly, xenografts in immune-deficient NOD SCID mice showed no significant inhibition in tumor growth when treated with an EZH2 inhibitor. However, growth inhibition was achieved when the same experiment was performed in nude mice, which retain some mediators of innate immunity. The effect of EZH2 overexpression in melanoma on immune-mediated rejection was studied in an inducible in vivo model. Subcutaneous B16 tumors expressing model antigen were initially rejected but relapsed in the majority of immunodeficient mice transferred with CD4 T cells. Long-term (120-day) survival was reduced from 40% to 22% if the tumors also overexpressed EZH2. Our studies suggest that aberrant EZH2 in melanoma drives aggressive disease via suppression of genes that would normally trigger the antitumor immune response. The progression of several preclinical, small-molecule inhibitors of EZH2 remains promising. Citation Format: Jessamy Tiffen, Elena Shklovskaya, Stuart Gallagher, Dilini Gunatilake, Peter Hersey. The epigenetic modifier EZH2 represses antitumor immunity in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1384.