gsk-2816126 and Ovarian-Neoplasms

Topics: Aminoquinolines; Animals; Cell Line, Tumor; Down-Regulation; Enhancer of Zeste Homolog 2 Protein; Epigenesis, Genetic; Female; Gene Expression Regulation, Neoplastic; Genes, Tumor Suppressor; Humans; Indoles; Mice, SCID; Neoplastic Stem Cells; Ovarian Neoplasms; Pyridones; Pyrimidines; rac1 GTP-Binding Protein; ras GTPase-Activating Proteins; Spheroids, Cellular; Wnt Proteins; Xenograft Model Antitumor Assays

Inactivation of the subunits of SWI/SNF complex such as ARID1A is synthetically lethal with inhibition of EZH2 activity. However, mechanisms of de novo resistance to EZH2 inhibitors in cancers with inactivating SWI/SNF mutations are unknown. Here we show that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 drives resistance to EZH2 inhibitors in ARID1A-mutated cells. SMARCA4 loss upregulates anti-apoptotic genes in the EZH2 inhibitor-resistant cells. EZH2 inhibitor-resistant ARID1A-mutated cells are hypersensitive to BCL2 inhibitors such as ABT263. ABT263 is sufficient to overcome resistance to an EZH2 inhibitor. In addition, ABT263 synergizes with an EZH2 inhibitor in vivo in ARID1A-inactivated ovarian tumor mouse models. Together, these data establish that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 underlies the acquired resistance to EZH2 inhibitors. They suggest BCL2 inhibition alone or in combination with EZH2 inhibition represents urgently needed therapeutic strategy for ARID1A-mutated cancers.

Topics: Aniline Compounds; Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Chromosomal Proteins, Non-Histone; DNA Helicases; DNA-Binding Proteins; Drug Resistance, Neoplasm; Enhancer of Zeste Homolog 2 Protein; Female; Gene Expression Regulation, Neoplastic; Humans; Indoles; Mice, Inbred NOD; Mice, Knockout; Mice, SCID; Mutation; Nuclear Proteins; Ovarian Neoplasms; Pyridones; Sulfonamides; Transcription Factors; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

Subunits of the SWI/SNF chromatin remodeling complex are frequently mutated in human cancers leading to epigenetic dependencies that are therapeutically targetable. The dependency on the polycomb repressive complex (PRC2) and EZH2 represents one such vulnerability in tumors with mutations in the SWI/SNF complex subunit, SNF5; however, whether this vulnerability extends to other SWI/SNF subunit mutations is not well understood. Here we show that a subset of cancers harboring mutations in the SWI/SNF ATPase, SMARCA4, is sensitive to EZH2 inhibition. EZH2 inhibition results in a heterogenous phenotypic response characterized by senescence and/or apoptosis in different models, and also leads to tumor growth inhibition in vivo. Lower expression of the SMARCA2 paralog was associated with cellular sensitivity to EZH2 inhibition in SMARCA4 mutant cancer models, independent of tissue derivation. SMARCA2 is suppressed by PRC2 in sensitive models, and induced SMARCA2 expression can compensate for SMARCA4 and antagonize PRC2 targets. The induction of SMARCA2 in response to EZH2 inhibition is required for apoptosis, but not for growth arrest, through a mechanism involving the derepression of the lysomal protease cathepsin B. Expression of SMARCA2 also delineates EZH2 inhibitor sensitivity for other SWI/SNF complex subunit mutant tumors, including SNF5 and ARID1A mutant cancers. Our data support monitoring SMARCA2 expression as a predictive biomarker for EZH2-targeted therapies in the context of SWI/SNF mutant cancers.

Topics: Animals; Antineoplastic Agents; Apoptosis; Benzamides; Biphenyl Compounds; Cathepsin B; DNA-Binding Proteins; Enhancer of Zeste Homolog 2 Protein; Enzyme Inhibitors; Female; Gene Expression Regulation, Neoplastic; Humans; Indoles; Mice; Morpholines; Mutation; Nuclear Proteins; Ovarian Neoplasms; Polycomb Repressive Complex 2; Prognosis; Pyridones; Signal Transduction; SMARCB1 Protein; Transcription Factors; Tumor Burden; Xenograft Model Antitumor Assays

Cancer cells acquire essential characteristics for metastatic dissemination through the process of epithelial-to-mesenchymal transition (EMT), which is regulated by gene expression and chromatin remodeling changes. The enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the polycomb repressive complex 2 (PRC2), catalyzes trimethylation of lysine 27 of histone H3 (H3K27me3) to repress gene transcription. Here we report the functional roles of EZH2-catalyzed H3K27me3 during EMT in ovarian cancer (OC) cells. TGF-β-induced EMT in SKOV3 OC cells was associated with decreased levels of EZH2 and H3K27me3 (P<0.05). These effects were delayed (~72 h relative to EMT initiation) and coincided with increased (>15-fold) expression of EMT-associated transcription factors ZEB2 and SNAI2. EZH2 knockdown (using siRNA) or enzymatic inhibition (by GSK126) induced EMT-like changes in OC cells. The EMT regulator ZEB2 was upregulated in cells treated with either approach. Furthermore, TGF-β enhanced expression of ZEB2 in EZH2 siRNA- or GSK126-treated cells (P<0.01), suggesting that H3K27me3 plays a role in TGF-β-stimulated ZEB2 induction. Chromatin immunoprecipitation assays confirmed that TGF-β treatment decreased binding of EZH2 and H3K27me3 to the ZEB2 promoter (P<0.05). In all, these results demonstrate that EZH2, by repressing ZEB2, is required for the maintenance of an epithelial phenotype in OC cells.

Topics: Cell Line, Tumor; Enhancer of Zeste Homolog 2 Protein; Epithelial-Mesenchymal Transition; Female; Gene Expression Regulation, Neoplastic; Histones; Humans; Indoles; Methylation; Ovarian Neoplasms; Promoter Regions, Genetic; Protein Binding; Pyridones; RNA Interference; Transforming Growth Factor beta; Zinc Finger E-box Binding Homeobox 2

The gene encoding ARID1A, a chromatin remodeler, shows one of the highest mutation rates across many cancer types. Notably, ARID1A is mutated in over 50% of ovarian clear cell carcinomas, which currently have no effective therapy. To date, clinically applicable targeted cancer therapy based on ARID1A mutational status has not been described. Here we show that inhibition of the EZH2 methyltransferase acts in a synthetic lethal manner in ARID1A-mutated ovarian cancer cells and that ARID1A mutational status correlated with response to the EZH2 inhibitor. We identified PIK3IP1 as a direct target of ARID1A and EZH2 that is upregulated by EZH2 inhibition and contributed to the observed synthetic lethality by inhibiting PI3K-AKT signaling. Importantly, EZH2 inhibition caused regression of ARID1A-mutated ovarian tumors in vivo. To our knowledge, this is the first data set to demonstrate a synthetic lethality between ARID1A mutation and EZH2 inhibition. Our data indicate that pharmacological inhibition of EZH2 represents a novel treatment strategy for cancers involving ARID1A mutations.

Topics: Animals; Cell Line, Tumor; DNA-Binding Proteins; Enhancer of Zeste Homolog 2 Protein; Female; Humans; Indoles; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Methyltransferases; Mice; Mice, Nude; Mutation; Nuclear Proteins; Ovarian Neoplasms; Polycomb Repressive Complex 2; Proto-Oncogene Proteins c-akt; Pyridones; Signal Transduction; Transcription Factors; Up-Regulation; Xenograft Model Antitumor Assays