Abstract 2790: PRC2 mediated repression of SMARCA2 predicts for EZH2 inhibitor activity in tumors with SWI/SNF mutations

A synthetic lethality caused by EZH2 inhibition in the context of SNF5 mutations is supported by both preclinical and recent clinical data, however the extent of the synthetic lethal relationship in the context of other SWI/SNF subunit mutations is not well understood. We determined that a subset of SMARCA4 mutant cancer models are sensitive to EZH2 inhibition. EZH2 inhibition resulted in a heterogenous phenotypic response characterized by senescence and/or apoptosis amongst models, and further lead to tumor growth inhibition in vivo. The differential sensitivity to EZH2 inhibition was not caused by a differential pharmacodynamic effect of the drug, nor differences in basal histone methylation or PRC2 subunit levels. However, expression of the SWI/SNF subunit, SMARCA2, delineated sensitivity amongst SMARCA4 mutant models tested. Expression of SMARCA2 further delineated sensitivity amongst other SWI/SNF mutant models tested, including SNF5 and ARID1A mutants. We determined that SMARCA2 is under PRC2 mediated suppression and the derepression of SMARCA2 was necessary for apoptosis, but not senescence, in response to EZH2 inhibition. SMARCA2 has been shown to be concurrently lost in a high percentage of SNF5 mutant malignant rhabdoid tumors and SMARCA4 mutant SCCOHT tumors, however we determined that ≈15% of SMARCA4 mutant NSCLCs concurrently lose SMARCA2. Our data supports monitoring SMARCA2 expression as a predictive biomarker for EZH2-targeted therapies that are currently being developed in the context of SWI/SNF mutant cancers. Citation Format: Thomas Januario, Xiaofen Ye, Russell Bainer, Bruno Alicke, Margaret Solon, Benjamin Haley, Zora Modrusan, Stephen Gould, Hartmut Koeppen, Robert L. Yauch. PRC2 mediated repression of SMARCA2 predicts for EZH2 inhibitor activity in tumors with SWI/SNF mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2790. doi:10.1158/1538-7445.AM2017-2790