Abstract PR09: EZH2 inhibitors reveal broad EZH2 dependencies in multiple myeloma

Abstract

Abstract Histone methyl transferases (HMTs) and demethylases are chromatin modifying enzymes known to play a key role in establishing and maintaining chromatin structure and thereby contributing to the control of gene expression. The histone methyltransferase Enhancer of Zeste Homologue 2 (EZH2) is the catalytic component of the Polycomb Repressive Complex 2 and mediates trimethylation of lysine 27 on histone 3 (H3K27me3), which correlates with transcriptional repression. EZH2 has been widely implicated in cancer and inhibition of its catalytic activity recently emerged as a novel therapeutic approach to treat human cancers. Constellation has developed potent, selective and reversible EZH2 small molecule inhibitors that are currently being tested in clinical trials. We have previously reported EZH2 dependencies across non-Hodgkin Lymphoma subtypes, including models harboring both wild-type and mutant EZH2. To identify other cancer types that may rely on EZH2 for survival, we carried out long term growth assays across a 200+ cancer cell line panel. We observed that over 50% of multiple myeloma cell lines show -time and -dose dependent phenotypic response to EZH2 inhibition. Similar to lymphoma, EZH2 inhibitors induce apoptosis after continuous treatment over a longer time period. To understand the underlying molecular consequences of EZH2 inhibition in multiple myeloma, we performed RNA-sequencing and ChIP-sequencing in the absence and presence of the inhibitor. We identified an EZH2-controlled transcriptional signature across various multiple myeloma models and key downstream effectors including CDKN1A in individual models. EZH2 inhibitors such as CPI-169 achieve tumor growth inhibition in several multiple myeloma subcutaneous xenograft models at well tolerated doses, and this impact on tumor growth correlated well with target inhibition. To expand the scope of EZH2 inhibitor application in multiple myeloma, we systematically combined EZH2 inhibitors with standard of care agents, including, lenalidomide, prednisolone, bortezomib and HDAC inhibitors. We observed synergy of EZH2 inhibitors with several of these agents in vitro and in vivo and are currently exploring the molecular basis of these combinatorial effects. In conclusion, we provide ample evidence suggesting multiple myeloma as a disease indication in which EZH2 inhibitors may show clinical benefit as a single agent and in combination with approved therapeutics. Citation Format: Shilpi Arora, Kaylyn Williamson, Srividya Balasubramanian, Jennifer Busby, Shivani Garapaty-Rao, Charlie Hatton, Dhanalakshmi Sivanandhan, Barbara Bryant, Emmanuel Normant, Patrick Trojer. EZH2 inhibitors reveal broad EZH2 dependencies in multiple myeloma. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr PR09.