Abstract 5526: Inhibition of the histone methyl transferase EZH2 causes viability defects in multiple myeloma

Abstract

Histone lysine methylation, which is dynamically regulated by methyltransferases and demethylases, plays an important role in the establishment and maintenance of chromatin structure and thereby contributes to the control of gene expression. The development of small molecule methyltransferase and demethylase inhibitors provides an approach to manipulate transcriptional programs, and thus potentially allow interference with aberrant cellular states as observed in cancer. The histone methyltransferase Enhancer of Zeste Homologue 2 (EZH2) is a component of the Polycomb Repressive Complex 2. It mediates trimethylation of lysine 27 on histone 3 (H3K27me3), which leads to transcriptional repression. EZH2 has been widely implicated in cancer and inhibition of its catalytic activity provides a novel therapeutic approach to treat human cancers. Constellation has identified, characterized and optimized potent, selective and reversible EZH2 small molecule inhibitors as well as studied the biological impact of such inhibition. We have previously shown that pharmacological inhibition of EZH2 causes selective lymphoma cell viability defects with cell lines harboring EZH2 mutations being the most sensitive. The discovery of small molecules that specifically inhibit EZH2 has enabled us to look for other disease indications that might be dependent on EZH2 for survival. We carried out a long term cell viability screen in ∼75 cell lines across several different hematological malignancies using an EZH2 inhibitor. About 30% of all tested Mutliple Myeloma and Plasmacytoma cell lines showed a time-dependent phenotypic response. In these cell lines H3K27me3 levels were effectively reduced in a dose dependent manner within 4 days of compound treatment which was followed by the induction of apoptotsis at later time points. EZH2 inhibitors also achieved tumor growth inhibition in a Multiple Myeloma subcutaneous xenograft model. To understand the underlying molecular mechanism of EZH2 inhibitor sensitivity in Multiple Myeloma, genome-wide mapping of EZH2 and H3K27me3 sites in the absence and presence of the compound have been performed in conjunction with gene expression profiling and the results will be discussed. In conclusion, we identified Multiple Myeloma as a disease modality where EZH2 inhibition leads to cell viability defects both in vitro and in vivo. Citation Format: Shilpi Arora, Vidya Balasubramanian, Kaylyn Williamson, Victor Gehling, Chris Nasveschuk, Rishi Vaswani, Jennifer Busby, Shivani Garapaty, Priya Iyer, Feng Zhao, Robert Campbell, Richard Cummings, Jim Audia, JC Harmange, Brian Albrecht, Andrew Cook, Les Dakin, Emmanuel Normant, Patrick Trojer. Inhibition of the histone methyl transferase EZH2 causes viability defects in multiple myeloma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5526. doi:10.1158/1538-7445.AM2014-5526