Project description:Mutations within the catalytic domain of the histone methyltransferase (HMT) EZH2 have been identified in subsets of Non-Hodgkin Lymphoma (NHL) patients. These genetic alterations are hypothesized to confer an oncogenic dependency on EZH2 enzymatic activity in these cancers. We previously reported the discovery of a potent, selective, S-adenosyl-methionine-competitive and orally bioavailable small molecule inhibitor of EZH2, EPZ-6438. EPZ-6438 selectively inhibits intracellular lysine 27 of histone H3 (H3K27) methylation in a concentration- and time-dependent manner in both EZH2 wild type and mutant lymphoma cells. Inhibition of H3K27 trimethylation (H3K27Me3) led to selective cell killing of human lymphoma cell lines bearing EZH2 catalytic domain point mutations. Treatment of xenograft-bearing mice with EPZ-6438 leads to dose-dependent tumor growth inhibition and eradication of genetically altered NHL with correlative diminution of H3K27Me3 levels in tumors and selected normal tissues. Mice dosed orally with EPZ-6438 for 28 days remained tumor free for up to 63 day after stopping compound treatment in two EZH2 mutant xenograft models. These data confirm the dependency of mutant NHL on EZH2 activity and portend the utility of EZH2-targeted drugs for the treatment of these genetically defined cancers. To identify potential biomarker and gain mechanistic insights in EPZ6438 treated lymphoma, lymphoma cell lines with or without EZH2 Y641 mutation were treated with EPZ6438 at Lowest Cytotoxic Concentration (LCC) and 10xLCC. Transcriptomes were profiled on Affemetrix U133 Plus2 chips. Differentially expressed genes and pathways upon compound treatment were anayzed. Lymphoma cell lines WSU-DLCL2, SU-DHL6, Pfeiffer, and Karpas422 were treated by EPZ6438 for 2 days, 4 days and 6 days. Treatment doses are LCC and 10xLCC of each cell lines. KARPAS_422, SUDHL6, and WSU_DLCL2 have the EZH2 Y641 mutation. PFEIFFER does not have the EZH2 Y641 mutation.

Project description:Breast cancer (BCa) remains the second leading cause of cancer-related mortalities in women, and acquired resistance to hormone therapies, such as tamoxifen, an estrogen receptor inhibitor, is a major hurdle in the treatment of luminal BCa. Another subtype, triple negative BCa (TNBC), is associated with aggressive disease and poor prognosis. The enhancer of zeste homolog 2 (EZH2), the methyltransferase component of the polycomb repressive complex 2 (PRC2), is overexpressed in BCa and has been implicated in tamoxifen resistance. In addition to its PRC2-dependent canonical transcription repressive role through catalyzing histone 3 lysine 27 trimethylation (H3K27me3), evidence suggests that EZH2 can function noncanonically, in a methyltransferase-independent manner, as a transcription activator through interacting with hormone receptors and oncogenic transcription factors. Unlike methyltransferase inhibitors, proteolysis targeting chimeras (PROTAC), which target EZH2 and interacting proteins for degradation, can suppress both activating and repressive functions of EZH2. Previous studies have suggested that PROTACs can be leveraged to inhibit TNBC cell growth. In this study, we expand our scope to test whether EZH2 targeted PROTACs can effectively inhibit luminal BCa cell growth. We find that EZH2-targeted PROTACs, MS177 and MS8815, effectively inhibited the growth luminal BCa cells, including those with acquired tamoxifen resistance, to a much greater degree when compared to methyltransferase inhibitors. Similarly, PROTACs uniquely reduced the expression of genes involved in cell cycle progression, including forkhead box M1 (FOXM1) target genes, in BCa cell lines. Likewise, promoter regions with EZH2 binding in the absence of H3K27me3 were enriched with FOXM1 target genes in both luminal BCa and TNBC cell lines, suggesting a regulatory mechanism independent of hormone receptor status. EZH2 PROTAC treatment reduced FOXM1 protein expression and increased its degradation. In clinical samples, EZH2 mRNA expression tightly correlated with FOXM1 and FOXM1 target genes. Together, this study suggests that EZH2 targeted PROTACs represent a promising avenue of research for the future treatment of BCa, including in the setting of tamoxifen resistance.

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EZH2 PROTACs are unable to abolish EZH2 activator function but inhibit certain prostate cancer by rapid senescence induction

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