Abstract 5189: Activity of polycomb repressive complex 2 determines sensitivity to epigenetic therapy

Abstract

Abstract EZH2 is a histone methyltransferase that tri-methylates histone H3 at lysine 27 (H3K27me) in the context of the Polycomb Repressive Complex 2, and is highly correlated with poor prognosis of many cancers. However, recent data suggest a de-coupling of EZH2 expression from its enzymatic activity, and many poor prognosis tumors also have low H3K27me3. Therefore, we hypothesize that deletion of Ezh2 would drive more aggressive tumors which may have distinct epigenetic vulnerabilities. To test this hypothesis, we generated the LSL:KrasG12D/+; p53 flox/flox (LSL: lox-stop-lox) mice (Kras/p53 mice) with either zero, one or two floxed alleles of Ezh2 and induced lung tumors with intranasal adeno-Cre virus administration. Supporting our hypothesis, we observed mice with two floxed alleles of Ezh2 (Ezh2 null) had higher tumor burden, higher tumor grade and lower survival than Ezh2 wild-type or heterozygous Kras/p53 mice. Ezh2 null tumors also had a higher propensity to metastasize than Ezh2 wild-type tumors. Consistent with these results, Ezh2 null Kras/p53 tumors and cell lines had increased expression of genes involved in epithelial-mesenchymal transition (EMT), KRAS-driven tumorigenesis, metastasis, and cell cycle regulation. In order to examine the therapeutic vulnerabilities of Ezh2 depleted lung cancers, we built a panel of 2-dimensional cell lines and 3-dimensional organoid cultures of the Kras/p53 tumors that were Ezh2 null, heterozygous and wild-type. We reasoned that using the H3K27me3 demethylase inhibitor might be able to stabilize the residual H3K27me3 in Ezh2 null cells and decrease their aggressive properties. Intriguingly, while we observed no difference in sensitivity to H3K27me3 demethylase inhibitor in the various Ezh2 genotypes of 2-dimensional cultures, both 3-dimensional cultures and in vivo allografts demonstrated Ezh2 null tumors but not Ezh2 WT or heterozygous are sensitive to the H3K27me3 demethylase inhibitor. These data are interesting because they suggest that assays of 3-dimensional organoids may more faithfully recapitulate responses to epigenetic drugs than standard cell lines, and that aggressive tumors with low H3K27me3 might be selectively killed by demethylase inhibitor. We are now expanding our studies to include other targeting agents, including inhibitors of the kinase WEE1 and inhibitor of the chromatin reader BRD4. Citation Format: Fan Chen, Christine F. Brainson. Activity of polycomb repressive complex 2 determines sensitivity to epigenetic therapy [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 5189.