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Multiple myeloma (MM) is the second most common hematological malignancy with poor prognosis. Enhancer of zeste homolog 2 (EZH2) is the enzymatic subunit of polycomb repressive complex 2 (PRC2), which catalyzes trimethylation of histone H3 lysine 27 (H3K27me3) for transcriptional repression. EZH2 have been implicated in numerous hematological malignancies, including MM. However, noncanonical functions of EZH2 in MM tumorigenesis are not well understood. Here, we uncovered a noncanonical function of EZH2 in MM malignancy. In addition to the PRC2-mediated and H3K27me3-dependent canonical function, EZH2 interacts with cMyc and co-localizes with gene activation-related markers, promoting MM tumorigenesis in a PRC2- and H3K27me3-independent manner. Both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes can be effectively depleted in MM cells by MS177, an EZH2 degrader we reported previously, leading to profound activation of EZH2-PRC2-associated genes and simultaneous suppression of EZH2-cMyc oncogenic nodes. The MS177-induced degradation of both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes also reactivated immune response genes in MM cells. Phenotypically, targeting of EZH2's both canonical and noncanonical functions by MS177 effectively suppressed the proliferation of MM cells both in vitro and in vivo. Collectively, this study uncovers a new noncanonical function of EZH2 in MM tumorigenesis and provides a novel therapeutic strategy, pharmacological degradation of EZH2, for treating EZH2-dependent MM., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Canonically, EZH2 serves as the catalytic subunit of PRC2, which mediates H3K27me3 deposition and transcriptional repression. Here, we report that in acute leukaemias, EZH2 has additional noncanonical functions by binding cMyc at non-PRC2 targets and uses a hidden transactivation domain (TAD) for (co)activator recruitment and gene activation. Both canonical (EZH2-PRC2) and noncanonical (EZH2-TAD-cMyc-coactivators) activities of EZH2 promote oncogenesis, which explains the slow and ineffective antitumour effect of inhibitors of the catalytic function of EZH2. To suppress the multifaceted activities of EZH2, we used proteolysis-targeting chimera (PROTAC) to develop a degrader, MS177, which achieved effective, on-target depletion of EZH2 and interacting partners (that is, both canonical EZH2-PRC2 and noncanonical EZH2-cMyc complexes). Compared with inhibitors of the enzymatic function of EZH2, MS177 is fast-acting and more potent in suppressing cancer growth. This study reveals noncanonical oncogenic roles of EZH2, reports a PROTAC for targeting the multifaceted tumorigenic functions of EZH2 and presents an attractive strategy for treating EZH2-dependent cancers., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Both EZH2 and its homolog EZH1 function as histone H3 Lysine 27 (H3K27) methyltransferases and repress the transcription of target genes. Dysregulation of H3K27 trimethylation (H3K27me3) plays an important role in the development and progression of cancers such as hepatocellular carcinoma (HCC). This study investigated the relationship between the expression of EZH1/2 and the level of H3K27me3 in HCC. Additionally, the role of EZH1/2 in cell growth, tumorigenicity, and resistance to sorafenib were also analyzed. Both the lentiviral knockdown and the pharmacological inhibition of EZH1/2 (UNC1999) diminished the level of H3K27me3 and suppressed cell growth in liver cancer cells, compared with EZH1 or EZH2 single knockdown. Although a significant association was observed between EZH2 expression and H3K27me3 levels in HCC samples, overexpression of EZH1 appeared to contribute to enhanced H3K27me3 levels in some EZH2 low H3K27me3 high cases. Akt suppression following sorafenib treatment resulted in an increase of the H3K27me3 levels through a decrease in EZH2 phosphorylation at serine 21. The combined use of sorafenib and UNC1999 exhibited synergistic antitumor effects in vitro and in vivo. Combination treatment canceled the sorafenib-induced enhancement in H3K27me3 levels, indicating that activation of EZH2 function is one of the mechanisms of sorafenib-resistance in HCC. In conclusion, sorafenib plus EZH1/2 inhibitors may comprise a novel therapeutic approach in HCC., (© 2021. The Author(s).)

Multiple myeloma (MM) is a heterogeneous haematological disease that remains clinically challenging. Increased activity of the epigenetic silencer EZH2 is a common feature in patients with poor prognosis. Previous findings have demonstrated that metabolic profiles can be sensitive markers for response to treatment in cancer. While EZH2 inhibition (EZH2i) has proven efficient in inducing cell death in a number of human MM cell lines, we hereby identified a subset of cell lines that despite a global loss of H3K27me3, remains viable after EZH2i. By coupling liquid chromatography-mass spectrometry with gene and miRNA expression profiling, we found that sensitivity to EZH2i correlated with distinct metabolic signatures resulting from a dysregulation of genes involved in methionine cycling. Specifically, EZH2i resulted in a miRNA-mediated downregulation of methionine cycling-associated genes in responsive cells. This induced metabolite accumulation and DNA damage, leading to G2 arrest and apoptosis. Altogether, we unveiled that sensitivity to EZH2i in human MM cell lines is associated with a specific metabolic and gene expression profile post-treatment.

The enhancer of zeste homolog 2 (EZH2) is the main enzymatic subunit of the PRC2 complex, which catalyzes trimethylation of histone H3 lysine 27 (H3K27me3) to promote transcriptional silencing. EZH2 is overexpressed in multiple types of cancer including triple-negative breast cancer (TNBC), and high expression levels correlate with poor prognosis. Several EZH2 inhibitors, which inhibit the methyltransferase activity of EZH2, have shown promise in treating sarcoma and follicular lymphoma in clinics. However, EZH2 inhibitors are ineffective at blocking proliferation of TNBC cells, even though they effectively reduce the H3K27me3 mark. Using a hydrophobic tagging approach, we generated MS1943, a first-in-class EZH2 selective degrader that effectively reduces EZH2 levels in cells. Importantly, MS1943 has a profound cytotoxic effect in multiple TNBC cells, while sparing normal cells, and is efficacious in vivo, suggesting that pharmacologic degradation of EZH2 can be advantageous for treating the cancers that are dependent on EZH2.

ATRX alterations occur at high frequency in neuroblastoma of adolescents and young adults. Particularly intriguing are the large N-terminal deletions of ATRX (Alpha Thalassemia/Mental Retardation, X-linked) that generate in-frame fusion (IFF) proteins devoid of key chromatin interaction domains, while retaining the SWI/SNF-like helicase region. We demonstrate that ATRX IFF proteins are redistributed from H3K9me3-enriched chromatin to promoters of active genes and identify REST as an ATRX IFF target whose activation promotes silencing of neuronal differentiation genes. We further show that ATRX IFF cells display sensitivity to EZH2 inhibitors, due to derepression of neurogenesis genes, including a subset of REST targets. Taken together, we demonstrate that ATRX structural alterations are not loss-of-function and put forward EZH2 inhibitors as a potential therapy for ATRX IFF neuroblastoma., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Purpose: EZH2 and EZH1, the catalytic components of polycomb repressive complex 2 (PRC2), trigger trimethylation of H3K27 (H3K27me3) to repress the transcription of target genes and are implicated in the pathogenesis of various cancers including multiple myeloma and prostate cancer. Here, we investigated the preclinical effects of UNC1999, a dual inhibitor of EZH2 and EZH1, in combination with proteasome inhibitors on multiple myeloma and prostate cancer. Experimental Design: In vitro and in vivo efficacy of UNC1999 and the combination with proteasome inhibitors was evaluated in multiple myeloma cell lines, primary patient cells, and in a xenograft model. RNA-seq and ChIP-seq were performed to uncover the targets of UNC1999 in multiple myeloma. The efficacy of the combination therapy was validated in prostate cancer cell lines. Results: Proteasome inhibitors repressed EZH2 transcription via abrogation of the RB-E2F pathway, thereby sensitizing EZH2-dependent multiple myeloma cells to EZH1 inhibition by UNC1999. Correspondingly, combination of proteasome inhibitors with UNC1999, but not with an EZH2-specific inhibitor, induced synergistic antimyeloma activity in vitro Bortezomib combined with UNC1999 remarkably inhibited the growth of myeloma cells in vivo Comprehensive analyses revealed several direct targets of UNC1999 including the tumor suppressor gene NR4A1 Derepression of NR4A1 by UNC1999 resulted in suppression of MYC , which was enhanced by the combination with bortezomib, suggesting the cooperative blockade of PRC2 function. Notably, this combination also exhibited strong synergy in prostate cancer cells. Conclusions: Our results identify dual inhibition of EZH2 and EZH1 together with proteasome inhibition as a promising epigenetics-based therapy for PRC2-dependent cancers. Clin Cancer Res; 23(16); 4817-30. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Modulating T-cell alloreactivity has been a main strategy to reduce graft-versus-host disease (GVHD), a life-threatening complication after allogeneic hematopoietic stem-cell transplantation (HSCT). Genetic deletion of T-cell Ezh2, which catalyzes trimethylation of histone H3 at lysine 27 (H3K27me3), inhibits GVHD. Therefore, reducing Ezh2-mediated H3K27me3 is thought to be essential for inhibiting GVHD. We tested this hypothesis in mouse GVHD models. Unexpectedly, administration of the Ezh2 inhibitor GSK126, which specifically decreases H3K27me3 without affecting Ezh2 protein, failed to prevent the disease. In contrast, destabilizing T-cell Ezh2 protein by inhibiting Hsp90 using its specific inhibitor AUY922 reduced GVHD in mice undergoing allogeneic HSCT. In vivo administration of AUY922 selectively induced apoptosis of activated T cells and decreased the production of effector cells producing interferon γ and tumor necrosis factor α, similar to genetic deletion of Ezh2. Introduction of Ezh2 into alloreactive T cells restored their expansion and production of effector cytokines upon AUY922 treatment, suggesting that impaired T-cell alloreactivity by inhibiting Hsp90 is achieved mainly through depleting Ezh2. Mechanistic analysis revealed that the enzymatic SET domain of Ezh2 directly interacted with Hsp90 to prevent Ezh2 from rapid degradation in activated T cells. Importantly, pharmacological inhibition of Hsp90 preserved antileukemia activity of donor T cells, leading to improved overall survival of recipient mice after allogeneic HSCT. Our findings identify the Ezh2-Hsp90 interaction as a previously unrecognized mechanism essential for T-cell responses and an effective target for controlling GVHD., (© 2017 by The American Society of Hematology.)

Multiple Myeloma (MM) is a plasma cell tumor localized to the bone marrow (BM). Despite the fact that current treatment strategies have improved patients' median survival time, MM remains incurable. Epigenetic aberrations are emerging as important players in tumorigenesis making them attractive targets for therapy in cancer including MM. Recently, we suggested the polycomb repressive complex 2 (PRC2) as a common denominator of gene silencing in MM and presented the PRC2 enzymatic subunit enhancer of zeste homolog 2 (EZH2) as a potential therapeutic target in MM. Here we further dissect the anti-myeloma mechanisms mediated by EZH2 inhibition and show that pharmacological inhibition of EZH2 reduces the expression of MM-associated oncogenes; IRF-4, XBP-1, PRDM1/BLIMP-1 and c-MYC. We show that EZH2 inhibition reactivates the expression of microRNAs with tumor suppressor functions predicted to target MM-associated oncogenes; primarily miR-125a-3p and miR-320c. ChIP analysis reveals that miR-125a-3p and miR-320c are targets of EZH2 and H3K27me3 in MM cell lines and primary cells. Our results further highlight that polycomb-mediated silencing in MM includes microRNAs with tumor suppressor activity. This novel role strengthens the oncogenic features of EZH2 and its potential as a therapeutic target in MM.

EZH2 or EZH1 (enhancer of zeste homologue 2 or 1) is the catalytic subunit of polycomb repressive complex 2 (PRC2) that catalyzes methylation of histone H3 lysine 27 (H3K27). PRC2 hyperactivity and/or hypertrimethylation of H3K27 are associated with numerous human cancers, therefore inhibition of PRC2 complex has emerged as a promising therapeutic approach. Recent studies have shown that EZH2 and EZH1 are not functionally redundant and inhibition of both EZH2 and EZH1 is necessary to block the progression of certain cancers such as mixed-lineage leukemia (MLL)-rearranged leukemias. Despite the significant advances in discovery of EZH2 inhibitors, there has not been a systematic structure-activity relationship (SAR) study to investigate the selectivity between EZH2 and EZH1 inhibition. Here, we report our SAR studies that focus on modifications to various regions of the EZH2/1 inhibitor UNC1999 (5) to investigate the impact of the structural changes on EZH2 and EZH1 inhibition and selectivity., Competing Interests: Notes The authors declare no competing financial interest.

Multiple myeloma (MM) is a malignancy of the antibody-producing plasma cells. MM is a highly heterogeneous disease, which has hampered the identification of a common underlying mechanism for disease establishment as well as the development of targeted therapy. Here we present the first genome-wide profiling of histone H3 lysine 27 and lysine 4 trimethylation in MM patient samples, defining a common set of active H3K4me3-enriched genes and silent genes marked by H3K27me3 (H3K27me3 alone or bivalent) unique to primary MM cells, when compared to normal bone marrow plasma cells. Using this epigenome profile, we found increased silencing of H3K27me3 targets in MM patients at advanced stages of the disease, and the expression pattern of H3K27me3-marked genes correlated with poor patient survival. We also demonstrated that pharmacological inhibition of EZH2 had anti-myeloma effects in both MM cell lines and CD138+ MM patient cells. In addition, EZH2 inhibition decreased the global H3K27 methylation and induced apoptosis. Taken together, these data suggest an important role for the Polycomb repressive complex 2 (PRC2) in MM, and highlights the PRC2 component EZH2 as a potential therapeutic target in MM.