Small-molecule Inhibitors Of EZH2 Research Articles

Abstract 1944: Tazemetostat displays synergistic antiproliferative activity with backbone therapies in preclinical models of AT/RT and MRT

Abstract Malignant Rhabdoid Tumors (MRT) and Atypical Teratoid Rhabdoid Tumors (AT/RT) are typically pediatric cancers which are rare and aggressive with extremely high unmet medical need. At a molecular level MRT and AT/RT tumors are almost universally characterized by loss of the INI1 protein (also known as SNF5 or SMARCB1), a component of the Switch Sucrose Non-fermentable (SWI/SNF) multimeric chromatin modifying complex. In many cell types, the SWI/SNF complex and the PRC2 complex have an antagonistic relationship in the regulation of tumor suppressor genes, cell cycle checkpoints, hedgehog and myc pathway genes, among others [Wilson et al, Cancer Cell. 2010 Oct 19;18(4):316-28.]. This explicated the possibility of a novel treatment modality for these tumors, based on inhibition of EZH2 - the catalytic subunit of PRC2. Tazemetostat (EPZ-6438) is a potent and orally bioavailable small molecule inhibitor of EZH2 currently in phase 2 clinical trials in adult patients with non-Hodgkin lymphoma, INI1-negative tumors and mesothelioma. Dependency of INI1-negative tumors on EZH2 catalytic activity was demonstrated in preclinical models of MRT, where robust tumor regressions were induced with tazemetostat treatment [Knutson et al, Proc Natl Acad Sci USA. 2013 May 7;110(19):7922-7]. Consistent with this, tazemetostat demonstrated activity in relapsed or refractory patients with INI1-negative tumors enrolled in the adult phase 1 clinical trial. In addition, a phase 1 dose escalation study in pediatric patients with INI1-negative solid tumors is currently ongoing. Backbone therapies for MRT and AT/RT are comprised of cytotoxic chemotherapy which may or may not be administered in the context of stem cell transplant, in addition to surgical resection and radiation therapy. In support of combination clinical scenarios including EZH2 inhibition in this setting, we sought to explore the antiproliferative effects of combining tazemetostat with current small molecule treatment therapies in cell line models of AT/RT and MRT. Synergistic activity was observed when tazometostat was combined with individual components of chemotherapeutic regimens and targeted therapies such as vincristine, doxorubicin, alisertib and HDAC inhibitors.Further, we investigated the effects of ionizing radiation together with tazemetostat treatment. Application of X-ray irradiation concomitantly or after tazemetostat treatment, induced robust antiproliferative activity and reduction in clonogenic potential of both AT/RT cell lines tested.Taken together these results suggest that pharmacological inhibition of EZH2 enhances the activity of backbone therapy and may have an advantage over monotherapy in INI1-negative cancers supporting the therapeutic potential of combination regimens that include tazemetostat in these tumors. Citation Format: Christine R. Klaus, Jeffrey A. Keats, Jesse J. Smith, Richard Chesworth, Robert A. Copeland, Scott Ribich, Alejandra Raimondi. Tazemetostat displays synergistic antiproliferative activity with backbone therapies in preclinical models of AT/RT and MRT [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 1944. doi:10.1158/1538-7445.AM2017-1944

Abstract 5060: Activity of the EZH2 inhibitor tazemetostat as a monotherapy and in combination with multiple myeloma therapies in preclinical models

Abstract The EZH2 inhibitor tazemetostat (EPZ-6438) is currently being evaluated in phase 2 clinical trials for the treatment of non-Hodgkin’s Lymphoma (NHL). EZH2 inhibitors have shown anti-proliferative effects in multiple preclinical models of NHL and objective clinical responses have been reported in patients with B-cell lymphomas in phase 1 and phase 2 studies of tazemetostat. Mounting evidence suggests that EZH2 is an important regulator of B cell differentiation, both in normal B-cells and in B-cell lymphoma, and may be an important mediator of cell fate in B-cell malignancies in the clinic. Consistent with its essential role in regulating B cell differentiation, recent studies have also shown a dependence on EZH2 activity in multiple myeloma (MM), a disease arising from terminally-differentiated B-cell lymphocyte plasmablasts. Frequent genetic alterations of epigenetic modulators are observed in MM, pointing towards an important role in the initiation and maintenance of this disease. Dysregulation of the H3K27 methyltransferase EZH2, its corresponding histone demethylase UTX and the H3K36 methyltransferase WHSC1 in MM suggest that disruption of the balance of histone methylation may be fundamental to MM pathogenesis in a subset of cases. Indeed, inhibition of EZH2 alone has shown potent anti-proliferative effects both in in vitro and in vivo preclinical models of MM. Here, we describe the effects of small molecule EZH2 inhibitors as monotherapy and in combination with standard of care agents in preclinical models of MM. Tazemetostat selectively inhibits intracellular H3K27 methylation in MM cell lines and elicits a robust anti-proliferative effect in 14-day assays. Following demonstration of single agent activity, we then investigated potential for combinatorial activity of tazemetostat with first and second line therapies for multiple myeloma as well as other non-approved but emerging therapies. Synergistic anti-proliferative activity was observed when tazemetostat was combined with glucocorticoid receptor agonists (dexamethasone, prednisolone), small molecule immune system modulators (lenalidomide, pomalidomide) and proteasome inhibitors (bortezomib, ixazomib) when cells were primed with tazemetostat for seven days prior to the addition of the standard of care drugs. Combination activity was also observed with an alternate treatment schedule where cells were co-treated with tazemetostat along with the combination partner for seven days. Studies with selected therapeutic modalities were expanded into in vivo xenograft models to further evaluate monotherapy and combination activity of EZH2 inhibitors in MM. Citation Format: Allison E. Drew, Vinny Motwani, John E. Campbell, Cuyue Tang, Jesse J. Smith, Richard Chesworth, Robert A. Copeland, Alejandra Raimondi, Scott Ribich. Activity of the EZH2 inhibitor tazemetostat as a monotherapy and in combination with multiple myeloma therapies in preclinical models [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 5060. doi:10.1158/1538-7445.AM2017-5060

EZH2 is a potential therapeutic target for H3K27M-mutant pediatric gliomas.

Diffuse intrinsic pontine glioma (DIPG) is an aggressive brain tumor that is located in the pons and primarily affects children. Nearly 80% of DIPGs harbor mutations in histone H3 genes, wherein lysine 27 is substituted with methionine (H3K27M). H3K27M has been shown to inhibit polycomb repressive complex 2 (PRC2), a multiprotein complex responsible for the methylation of H3 at lysine 27 (H3K27me), by binding to its catalytic subunit EZH2. Although DIPGs with the H3K27M mutation show global loss of H3K27me3, several genes retain H3K27me3. Here we describe a mouse model of DIPG in which H3K27M potentiates tumorigenesis. Using this model and primary patient-derived DIPG cell lines, we show that H3K27M-expressing tumors require PRC2 for proliferation. Furthermore, we demonstrate that small-molecule EZH2 inhibitors abolish tumor cell growth through a mechanism that is dependent on the induction of the tumor-suppressor protein p16INK4A. Genome-wide enrichment analyses show that the genes that retain H3K27me3 in H3K27M cells are strong polycomb targets. Furthermore, we find a highly significant overlap between genes that retain H3K27me3 in the DIPG mouse model and in human primary DIPGs expressing H3K27M. Taken together, these results show that residual PRC2 activity is required for the proliferation of H3K27M-expressing DIPGs, and that inhibition of EZH2 is a potential therapeutic strategy for the treatment of these tumors.

EZH2 phosphorylation by JAK3 mediates a switch to noncanonical function in natural killer/T-cell lymphoma

AbstractThe best-understood mechanism by which EZH2 exerts its oncogenic function is through polycomb repressive complex 2 (PRC2)-mediated gene repression, which requires its histone methyltransferase activity. However, small-molecule inhibitors of EZH2 that selectively target its enzymatic activity turn out to be potent only for lymphoma cells with EZH2-activating mutation. Intriguingly, recent discoveries, including ours, have placed EZH2 into the category of transcriptional coactivators and thus raised the possibility of noncanonical signaling pathways. However, it remains unclear how EZH2 switches to this catalytic independent function. In the current study, using natural killer/T-cell lymphoma (NKTL) as a disease model, we found that phosphorylation of EZH2 by JAK3 promotes the dissociation of the PRC2 complex leading to decreased global H3K27me3 levels, while it switches EZH2 to a transcriptional activator, conferring higher proliferative capacity of the affected cells. Gene expression data analysis also suggests that the noncanonical function of EZH2 as a transcriptional activator upregulates a set of genes involved in DNA replication, cell cycle, biosynthesis, stemness, and invasiveness. Consistently, JAK3 inhibitor was able to significantly reduce the growth of NKTL cells, in an EZH2 phosphorylation-dependent manner, whereas various compounds recently developed to inhibit EZH2 methyltransferase activity have no such effect. Thus, pharmacological inhibition of JAK3 activity may provide a promising treatment option for NKTL through the novel mechanism of suppressing noncanonical EZH2 activity.

Abstract IA27: Tazemetostat, an EZH2 inhibitor and potential therapeutic for non-Hodgkin lymphoma

Abstract Cell fate decisions, such as whether to self-renew or to differentiate, are regulated in large part by epigenetic mechanisms. Dysregulation of epigenetic machinery, such as histone methyltransferases, in certain progenitor cell contexts can promote increased self-renewal, decreased differentiation and ultimately oncogenesis. For example, EZH2, the histone H3K27 methyltransferase, has been implicated in a diverse set of cancer indications. As the catalytic subunit of the polycomb repressive complex 2 (PRC2), EZH2 is responsible for the initiation of gene silencing during embryonic development and in maintenance of pluripotency in certain adult stem cell settings. On the other hand, EZH2 activity is downregulated in the majority of adult somatic cells to facilitate the expression of lineage-specific gene programs, leading to differentiation. Thus, inappropriate activation of EZH2 can contribute to oncogenic signaling by potentiating “stem-like” programs in certain contexts. For example, during B cell maturation, EZH2 activity is critical for formation of the germinal center (GC) reaction. PRC2-mediated repression of certain target sets, such as cell cycle checkpoint genes and DNA damage response genes, allows germinal center B (GCB) cells to undergo clonal expansion and somatic hypermutation. In order for GCB cells to exit the germinal center reaction, EZH2 expression and activity must be attenuated – the failure to do so may contribute to oncogenic signaling in certain B cell lymphomas. We and others have previously reported on gain-of-function mutations in EZH2, involving residues such as Y646, A682 and A692. These lesions result in increased trimethylation of H3K27 on polycomb target genes, including those required for B cell maturation and exit from the germinal center reaction. Importantly, lymphoma cell lines bearing these mutations demonstrate robust antiproliferative phenotypes, both in culture and in subcutaneous xenograft models, in response to small molecule inhibitors of EZH2. Beyond these mutant EZH2 cell lines, there is evidence that small molecule inhibitors of EZH2 also have antiproliferative activity in GCB cell and non-GCB lymphomas with wild type (wt) EZH2. These data are consistent with the idea that EZH2 is a “lineage factor” for B cell maturation, and that certain B cell lymphomas may possibly become “addicted” to EZH2 through mechanisms other than gain-of-function mutations in said gene. In addition to these preclinical findings, a recent update from ongoing clinical trials reported objective responses to single-agent tazemetostat (an EZH2 inhibitor in clinical development) in both wild-type and mutant EZH2 non-Hodgkin lymphoma (NHL) patients. The focus of this presentation will be the emerging translational landscape for tazemetostat (EPZ-6438), a small molecule inhibitor of EZH2, currently in phase II clinical trials for multiple oncology indications, including subsets of NHL. Data to be discussed will include preclinical efforts to understand the molecular mechanisms that determine GCB and non-GCB lymphoma response to EZH2 inhibition. Additionally, preclinical investigations evaluating the combination of tazemetostat with multiple therapeutic modalities will be presented. Finally, a brief overview of the early clinical observations of tazemetostat will be discussed. Citation Format: Jesse J. Smith. Tazemetostat, an EZH2 inhibitor and potential therapeutic for non-Hodgkin lymphoma. [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 IA27.

ZLD1122, a novel EZH2 and EZH1 small molecular inhibitor, blocks H3K27 methylation and diffuse large B cell lymphoma cell growth

Here, we reported a novel, selective, small-molecule inhibitor of EZH2 and EZH1 synthesized by us, ZLD1122, which inhibited both EZH1 and wild type and mutant EZH2 activities with nanomolar potency.

The Ezh2 polycomb group protein drives an aggressive phenotype in melanoma cancer stem cells and is a target of diet derived sulforaphane.

Melanoma is a metastatic cancer associated with poor survival. Here, we study a subpopulation of melanoma cancer cells displaying melanoma cancer stem cell (MCS cells) properties including elevated expression of stem cell markers, increased ability to survive as spheroids, and enhanced cell migration and invasion. We show that the Ezh2 stem cell survival protein is enriched in MCS cells and that Ezh2 knockdown or treatment with small molecule Ezh2 inhibitors, GSK126 or EPZ-6438, reduces Ezh2 activity. This reduction is associated with a reduced MCS cell spheroid formation, migration, and invasion. Moreover, the diet-derived cancer prevention agent, sulforaphane (SFN), suppresses MCS cell survival and this is associated with loss of Ezh2. Forced expression of Ezh2 partially reverses SFN suppression of MCS cell spheroid formation, migration, and invasion. A375 melanoma cell-derived MCS cells form rapidly growing tumors in immune-compromised mice and SFN treatment of these tumors reduces tumor growth and this is associated with reduced Ezh2 level and H3K27me3 formation, reduced matrix metalloproteinase expression, increased TIMP3 expression and increased apoptosis. These studies identify Ezh2 as a MCS cell marker and cancer stem cell prevention target, and suggest that SFN acts to reduce melanoma tumor formation via a mechanism that includes suppression of Ezh2 function. © 2015 Wiley Periodicals, Inc.

Discovery, design, and synthesis of indole-based EZH2 inhibitors.

The discovery and optimization of a series of small molecule EZH2 inhibitors is described. Starting from dimethylpyridone HTS hit (2), a series of indole-based EZH2 inhibitors were identified. Biochemical potency and microsomal stability were optimized during these studies and afforded compound 22. This compound demonstrates nanomolar levels of biochemical potency (IC50=0.002 μM), cellular potency (EC50=0.080 μM), and afforded tumor regression when dosed (200 mpk SC BID) in an EZH2 dependent tumor xenograft model.

Small molecule inhibitors of EZH2: the emerging translational landscape.

Small molecule inhibitors of EZH2: the emerging translational landscape.

Quantification of Histone H3 Lys27 Trimethylation (H3K27me3) by High-Throughput Microscopy Enables Cellular Large-Scale Screening for Small-Molecule EZH2 Inhibitors

EZH2 inhibition can decrease global histone H3 lysine 27 trimethylation (H3K27me3) and thereby reactivates silenced tumor suppressor genes. Inhibition of EZH2 is regarded as an option for therapeutic cancer intervention. To identify novel small-molecule (SMOL) inhibitors of EZH2 in drug discovery, trustworthy cellular assays amenable for phenotypic high-throughput screening (HTS) are crucial. We describe a reliable approach that quantifies changes in global levels of histone modification marks using high-content analysis (HCA). The approach was validated in different cell lines by using small interfering RNA and SMOL inhibitors. By automation and miniaturization from a 384-well to 1536-well plate, we demonstrated its utility in conducting phenotypic HTS campaigns and assessing structure-activity relationships (SAR). This assay enables screening of SMOL EZH2 inhibitors and can advance the mechanistic understanding of H3K27me3 suppression, which is crucial with regard to epigenetic therapy. We observed that a decrease in global H3K27me3, induced by EZH2 inhibition, comprises two distinct mechanisms: (1) inhibition of de novo DNA methylation and (II) inhibition of dynamic, replication-independent H3K27me3 turnover. This report describes an HCA assay for primary HTS to identify, profile, and optimize cellular active SMOL inhibitors targeting histone methyltransferases, which could benefit epigenetic drug discovery.

Abstract 1697: CPI-169, a novel and potent EZH2 inhibitor, synergizes with CHOP in vivo and achieves complete regression in lymphoma xenograft models

Abstract Enhancer of Zeste Homolog 2 (EZH2) is the histone lysine methyltransferase (HKMT) component of the Polycomb Repressive Complex 2 (PRC2). In conjunction with other members of the complex, EZH2 represses gene expression through methylation of histone H3 on lysine 27 (H3K27). EZH2 overexpression is implicated in tumor progression and correlates with poor prognosis in several tumor types and enzymatic hyperactivity of EZH2 has been linked to aberrant repression of tumor suppressor genes in diverse cancers. Recently, direct inhibition of EZH2 HKMT activity by small molecules has been shown to be effective in inhibiting the proliferation of EZH2 mutant diffuse large B-cell lymphoma (DLBCL) cell lines and the growth of tumors in EZH2 mutant DLBCL xenografts. We have identified and optimized a series of small molecule EZH2 inhibitors that is structurally distinct from previously published chemotypes. CPI-169, a representative compound from that effort, inhibits the catalytic activity of PRC2 with an IC50 of < 1nM, decreases cellular levels of H3K27me3 with an EC50 of 70 nM, and triggers cell cycle arrest and apoptosis in a variety of cell lines. Importantly, compound treatment triggers a sequence of downstream functional consequences of EZH2 inhibition whereby apoptosis is not induced before ten days of continuous target engagement. Administered subcutaneously at 200 mpk twice daily (BID), CPI-169 is well tolerated in mice with no observed toxic effect or body weight loss. In the present study we show that CPI-169 treatment led to tumor growth inhibition (TGI) of an EZH2 mutant KARPAS-422 DLBCL xenograft. The TGI is proportional to the dose administered and to the reduction of the pharmacodynamic marker H3K27me3. The highest dose, 200 mpk, BID led to complete tumor regression. Since CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone) is the standard treatment of advanced DLBCL, we were interested in combining a suboptimal dose of CPI-169 (100 mpk, BID) with a single dose of CHOP in the KARPAS-422 model. After a week of combinatorial treatment the tumors rapidly regressed and became unpalpable. Four weeks after the last dose only a single mouse presented a palpable tumor. The immunohistochemical analysis of tumor samples revealed a strong correlation between the global decrease of H3K27me3, the decrease in the proliferation marker Ki-67 and the increase in cleaved-caspase 3 positive cells. In conclusion, we identified a strong synergistic anti-tumor activity between the standard of care CHOP and CPI-169, a distinct EZH2 inhibitor in an in vivo model of DLBCL. Citation Format: Vidya Balasubramanian, Priya Iyer, Shilpi Arora, Patrick Troyer, Emmanuel Normant. CPI-169, a novel and potent EZH2 inhibitor, synergizes with CHOP in vivo and achieves complete regression in lymphoma xenograft models. [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 1697. doi:10.1158/1538-7445.AM2014-1697

EZH2 as a potential target in cancer therapy.

Over the last several years, dysregulation of epigenetic mechanisms including DNA and histone methylation has been recognized as a hallmark of cancer. Alterations of epigenetic regulators themselves, including the histone lysine methyltransferase EZH2, have been reported in numerous cancer types. With the discovery of small molecule inhibitors of EZH2, we can now begin to evaluate EZH2 as a therapeutic target in cancer. This article will provide an overview of the dysregulation of EZH2 in cancer, possible mechanisms for inhibition of EZH2 activity, and the preclinical activity of currently available EZH2 inhibitors.

Selective Inhibition of EZH2 by EPZ-6438 Leads to Potent Antitumor Activity in EZH2-Mutant Non-Hodgkin Lymphoma

Mutations within the catalytic domain of the histone methyltransferase EZH2 have been identified in subsets of patients with non-Hodgkin lymphoma (NHL). These genetic alterations are hypothesized to confer an oncogenic dependency on EZH2 enzymatic activity in these cancers. We have previously reported the discovery of EPZ005678 and EPZ-6438, potent and selective S-adenosyl-methionine-competitive small molecule inhibitors of EZH2. Although both compounds are similar with respect to their mechanism of action and selectivity, EPZ-6438 possesses superior potency and drug-like properties, including good oral bioavailability in animals. Here, we characterize the activity of EPZ-6438 in preclinical models of NHL. 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) leads to selective cell killing of human lymphoma cell lines bearing EZH2 catalytic domain point mutations. Treatment of EZH2-mutant NHL xenograft-bearing mice with EPZ-6438 causes dose-dependent tumor growth inhibition, including complete and sustained tumor regressions 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 days after stopping compound treatment in two EZH2-mutant xenograft models. These data confirm the dependency of EZH2-mutant NHL on EZH2 activity and portend the utility of EPZ-6438 as a potential treatment for these genetically defined cancers.

Abstract B254: Targeted disruption of the EZH2-EED complex inhibits EZH2-dependent cancer.

Abstract Enhancer of zeste homolog 2 (EZH2) is the histone lysine N-methyltransferase component of the Polycomb repressive complex 2 (PRC2), which, in conjunction with embryonic ectoderm development (EED) and suppressor of zeste 12 homolog(SUZ12), regulates cell lineage determination and homeostasis. Enzymatic hyperactivity of EZH2 has been linked to aberrant repression of tumor suppressor genes in diverse cancers. Here, we report the development of stabilized a-helix of EZH2 (SAH-EZH2) peptides that selectively inhibit H3 Lys27 trimethylation by dose-responsively disrupting the EZH2-EED complex and reducing EZH2 protein levels, a mechanism distinct from that reported for small-molecule EZH2 inhibitors targeting the enzyme catalytic domain. The essential α-helical domain of EZH2 (residues 40-68) that engages EED established the basis for designing hydrocarbon-stapled derivatives to disrupt the specific protein interaction. Non-natural amino acids with olefinic side chains were substituted at (i, i + 4) positions within the EZH2 α-helical sequence, followed by ruthenium-catalyzed olefin metathesis, to yield SAH-EZH2 peptides. Our lead, cell-permeable analog effectively targeted EED in situ, dissociated the EZH2-EED complex and impaired the function of PRC2, as reflected by reduction of the H3K27me3 and EZH2 protein levels, and increased expression of PRC2-regulated cell differentiation marker genes. In response to SAH-EZH2 treatment, murine MLL-AF9 leukemia cells, which are PRC2-dependent, manifested growth arrest and monocyte-macrophage differentiation, in accordance with the phenotypic consequences of shRNA-mediated reduction of EZH2 (or EED) or genetic ablation of Ezh2 (or Eed). In evaluating SAH-EZH2 activity alongside the small-molecule EZH2 inhibitor GSK126 in a series of B-cell lymphoma lines, we observed sequence-specific antiproliferative responses, transcriptional modulation, cellular specificity and a distinct mechanism of action for SAH-EZH2. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B254. Citation Format: Woojin Kim, Gregory H. Bird, Tobias Neff, Guoji Guo, Marc A. Kerenyi, Loren D. Walensky, Stuart H. Orkin. Targeted disruption of the EZH2-EED complex inhibits EZH2-dependent cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B254.

Recent Progress in the Discovery of Small-Molecule Inhibitors of the Hmt Ezh2 for the Treatment of Cancer

The histone lysine methyltransferase EZH2 is the catalytic component of the multi-protein PRC2 complex and methylates lysine 27 on histone H3. EZH2 overexpression is implicated in tumorigenesis and correlates with poor prognosis in several tumor types. Inhibition of aberrant EZH2 activity might attenuate tumorigenesis resulting from misregulated gene transcription derived from aberrant EZH2 activity. In the last year, the first reports of small molecules demonstrating potent and selective inhibition of EZH2 have been published by multiple groups. Herein, we review recent progress reported in the discovery of small molecule inhibitors of EZH2.

Epigenetic therapy gains momentum

Two groups have reported the discovery of small-molecule inhibitors of EZH2 that have the ability to selectively kill lymphoma cells with EZH2-activating mutations.

Abstract SY02-02: Inhibition of methyltransferase EZH2

Abstract Enhance of Zeste Homolog 2 (EZH2) is the biochemical activity of the Polycomb Repressive Complex 2 (PRC2) that transfers a methyl group from the cofactor S-adenosyl methionine (SAM) to histone H3 on lysine 27 (H3K27), resulting in epigenetic silencing of target gene expression. Activity of the multi-component PRC2 complex is crucial for normal development and differentiation. However, dysregulation of H3K27 methylation is implicated in tumorigenesis and occurs through multiple mechanisms. Elevated levels of EZH2 correlate with poor prognosis in a number of solid tumors including prostate, breast, kidney and lung. The increased EZH2 expression observed in many solid tumors has been linked to loss of one or more miRNAs including mir-101, mir-26A, and mir-214; aberrant E2F activity and chromosomal amplification. Inactivating mutations in UTX, an H3K27 demethylase which acts in opposition to EZH2, have been described in several tumor types including transitional cell bladder carcinoma, esophageal squamous cell carcinoma, renal cell carcinoma and multiple myeloma. Recently, somatic activating mutations in EZH2 have been identified in follicular lymphoma (FL) and GCB diffuse large B cell lymphoma (DLBCL). The frequency of the most prevalent mutation, Y641, is reported to be 7-12% in FL and as high as 22% in DLBCL. In view of the above, biochemical inhibitors of EZH2 may have therapeutic utility and herein we report on the identification and characterization of potent and selective small molecule EZH2 inhibitors with in vitro and in vivo antiproliferative activity in cancer cell lines and mouse xenografts. The studies provide a compelling rationale for the clinical evaluation of EZH2 inhibitors in EZH2 driven human cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY02-02. doi:1538-7445.AM2012-SY02-02