Targeting EZH2-mediated methylation of H3K27 inhibits proliferation and migration of Synovial Sarcoma in vitro

The SS18-SSX fusion oncoprotein: Friend and foe in targeted therapy for synovial sarcoma

Synovial sarcoma is a high-grade soft tissue malignancy characterized by a unique fusion gene known as SS18-SSX. The SS18-SSX fusion protein acts as an oncogenic driver of synovial sarcoma, and it has thus been commonly accepted that disruption of SS18-SSX function represents a therapeutic means of treating synovial sarcoma, but emerging evidence suggests that upon depletion of SS18-SSX, an anti-apoptotic signal surprisingly arises to protect synovial sarcoma cell survival. In this article, we discuss the controversial roles of SS18-SSX's transcriptional activity in synovial sarcoma biology and outline a synergistic strategy for overcoming the resistance of synovial sarcoma cells to SS18-SSX targeted therapeutics.

Genetic and Molecular Heterogeneity of Synovial Sarcoma and Associated Challenges in Therapy

Synovial sarcoma (SS) is one of the most common types of pediatric soft tissue sarcoma (STS) being far less frequent in adults. This STS type is characterized by one specific chromosomal translocation SS18-SSX and the associated changes in signaling. However, other genetic and epigenetic abnormalities in SS do not necessarily include SS18-SSX-related events, but abnormalities are more sporadic and do not correlate well with the prognosis and response to therapy. Currently, targeted therapy for synovial sarcoma includes a limited range of drugs, and surgical resection is the mainstay treatment for localized cancer with adjuvant or neoadjuvant chemotherapy and radiotherapy. Understanding the molecular characteristics of synovial sarcoma subtypes is becoming increasingly important for detecting new potential targets and developing innovative therapies. Novel approaches to treating synovial sarcoma include immune-based therapies (such as TCR-T cell therapy to NY-ESO-1, MAGE4, PRAME or using immune checkpoint inhibitors), epigenetic modifiers (HDAC inhibitors, EZH2 inhibitors, BRD disruptors), as well as novel or repurposed receptor tyrosine kinase inhibitors. In the presented review, we aimed to summarize the genetic and epigenetic landscape of SS as well as to find out the potential niches for the development of novel diagnostics and therapies.

Novel combination of imipridones and histone deacetylase inhibitors demonstrate cytotoxic effect through integrated stress response in pediatric solid tumors

There is a demonstrated need for new chemotherapy options in pediatric oncology, as pediatric solid tumors continue to plateau at 60% with event-free survival. Imipridones, a novel class of small molecules, represent a potential new therapeutic option, with promising pre-clinical data and emerging clinical trial data in adult malignancies. ONC201, ONC206, and ONC212 are imipridones showing pro-apoptotic anti-cancer response. Using cell viability assays, and protein immunoblotting, we were able to demonstrate single-agent efficacy of all 3 imipridones inducing cell death in pediatric solid tumor cell lines, including osteosarcoma, malignant peripheral nerve sheath tumors, Ewing sarcoma (EWS), and neuroblastoma. ONC201 displayed IC50 values for non-H3K27M-mutated EWS cell lines ranging from 0.86 µM (SK-N-MC) to 2.76 µM (RD-ES), which were comparable to the range of IC50 values for H3K27M-mutated DIPG cells lines (range 1.06 to 1.56 µM). ONC212 demonstrated the highest potency in single-agent cell killing, followed by ONC206, and ONC201. Additionally, pediatric solid tumor cells were treated with single-agent therapy with histone deacetylase inhibitors (HDACi) vorinostat, entinostat, and panobinostat, showing cell killing with all 3 HDACi drugs, with panobinostat showing the greatest potency. We demonstrate that dual-agent therapy with combinations of imipridones and HDACi lead to synergistic cell killing and apoptosis in all pediatric solid tumor cell lines tested, with ONC212 and panobinostat combinations demonstrating maximal potency. The imipridones induced the integrated stress response with ATF4 and TRAIL receptor upregulation, as well as reduced expression of ClpX. Hyperacetylation of H3K27 was associated with synergistic killing of tumor cells following exposure to imipridone plus HDAC inhibitor therapies. Our results introduce a novel class of small molecules to treat pediatric solid tumors in a precision medicine framework. Use of impridones in pediatric oncology is novel and shows promising pre-clinical efficacy in pediatric solid tumors, including in combination with HDAC inhibitors.

Comparative analysis of EZH2, p16 and p53 expression in uterine carcinosarcomas

Introduction: The role of p16 and p53 immunohistochemistry in the diagnosis of rare and aggressive uterine carcinosarcoma (UCS) has been well established. However, enhancer of zeste homolog 2 (EZH2), a histone methyltransferase and a member of the polycomb group family is a relatively new biomarker, with limited published data on its significance in this tumor type. The goal of this study was to examine EZH2 expression in UCS and its components, in correlation with morphological features, and p16 and p53 staining patterns. Methods: Twenty-eight UCSs were included in the study. EZH2, p16 and p53 immunoreactivity were assessed independently by two pathologists in both tumor components (epithelial and mesenchymal). EZH2 and p16 immunostains were scored semiquantitatively: based on the percentage and intensity of tumor cell staining a binary staining index ("high- or low-expressing") was calculated. The p53 staining pattern was evaluated as wild-type or aberrant (diffuse nuclear, null, or cytoplasmic expression). Statistical tests were used to evaluate the correlation between staining patterns for all three markers and the different tumor components and histotypes. Results: High EZH2 and p16 expression and aberrant p53 patterns were present in 89.3% 78.6% and 85.7% of the epithelial component and in 78.6%, 62.5% and 82.1% of the mesenchymal component, respectively. Differences among these expression rates were not found to be significant (p > 0.05). Regarding the epithelial component, aberrant p53 pattern was found to be significantly (p = 0.0474) more frequent in the serous (100%) than in endometrioid (66.6%) histotypes. Within the mesenchymal component, p53 null expression pattern occurred significantly (p = 0.0257) more frequently in heterologous sarcoma components (71.4%) compared to the homologous histotype (18.8%). Conclusion: In conclusion, EZH2, p16 and p53 seem to play a universal role in the pathogenesis of UCS; however, a distinctive pattern of p53 expression appears to exist between the serous and endometrioid carcinoma components and also between the homologous and heterologous sarcoma components.

Treatment at Relapse for Synovial Sarcoma of Children, Adolescents and Young Adults: From the State of Art to Future Clinical Perspectives

While the overall prognosis is generally quite satisfactory in children, adolescents and young adults with localised synovial sarcoma at first diagnosis, the outcome remains poor for patients after relapse. Conversely to the front-line standardised treatment options, patients with relapse generally have an individualised approach and to date, there is still a lack of consensus regarding standard treatment approaches. Studies on relapsed synovial sarcoma were able to identify some prognostic variables that influence post-relapse survival, in order to plan risk-adapted salvage protocols. Treatment proposals must consider previous first-line treatments, potential toxicities, and the possibility of achieving an adequate local treatment by new surgery and/or re-irradiation. Effective second-line drug therapies are urgently needed. Notably, experimental treatments such as adoptive engineered TCR-T cell immunotherapy seem promising in adults and are currently under validation also in paediatric patients.

Targeting EZH2 in SMARCB1-deficient sarcomas: Advances and opportunities to potentiate the efficacy of EZH2 inhibitors

Soft tissue sarcomas (STSs) are rare mesechymal malignancies characterized by distintive molecular, histological and clinical features. Many STSs are considered as predominatly epigenetic diseases due to underlying chromatin deregulation. Discovery of deregulated functional antagonism between the chromatin remodeling BRG1/BRM-associated (BAFs) and the histone modifying Polycomb repressor complexes (PRCs) has provided novel actionable targets. In epithelioid sarcoma (ES), extracranial, extrarenal malignant rhabdoid tumors (eMRTs) and synovial sarcoma (SS), the total or partial loss of the BAF core subunit SMARCB1, driven by different alterations, is associated with PRC2 deregulation and dependency on its enzymatic subunit, EZH2. In these SMARCB1-deficient STSs, aberrant EZH2 expression and/or activity emerged as a druggable vulnerability. Although preclinical investigation supported EZH2 targeting as a promising therapeutic option, clinical studies demonstrated a variable response to EZH2 inhibitors. Actually, whereas the clinical benefit recorded in ES patients prompted the FDA approval of the EZH2 inhibitor tazemetostat, the modest and sporadic responses observed in eMRT and SS patients highlighted the need to deepen mechanistic as well as pharmacological investigations to improve drug effectiveness. We summarize the current knowledge of different mechanisms driving SMARCB1 deficiency and EZH2 deregulation in ES, eMRT and SS along with preclinical and clinical studies of EZH2-targeting agents. Possible implication of the PRC2- and enzymatic-independent functions of EZH2 and of its homolog, EZH1, in the response to anti-EZH2 agents will be discussed together with combinatorial strategies under investigation to improve the efficacy of EZH2 targeting in these tumors.

Crosstalk between Noncoding RNAs and the Epigenetics Machinery in Pediatric Tumors and Their Microenvironment

According to the World Health Organization, every year, an estimated 400,000+ new cancer cases affect children under the age of 20 worldwide. Unlike adult cancers, pediatric cancers develop very early in life due to alterations in signaling pathways that regulate embryonic development, and environmental factors do not contribute much to cancer development. The highly organized complex microenvironment controlled by synchronized gene expression patterns plays an essential role in the embryonic stages of development. Dysregulated development can lead to tumor initiation and growth. The low mutational burden in pediatric tumors suggests the predominant role of epigenetic changes in driving the cancer phenotype. However, one more upstream layer of regulation driven by ncRNAs regulates gene expression and signaling pathways involved in the development. Deregulation of ncRNAs can alter the epigenetic machinery of a cell, affecting the transcription and translation profiles of gene regulatory networks required for cellular proliferation and differentiation during embryonic development. Therefore, it is essential to understand the role of ncRNAs in pediatric tumor development to accelerate translational research to discover new treatments for childhood cancers. This review focuses on the role of ncRNA in regulating the epigenetics of pediatric tumors and their tumor microenvironment, the impact of their deregulation on driving pediatric tumor progress, and their potential as effective therapeutic targets.

Evaluation of Tazemetostat as a Therapeutically Relevant Substance in Biliary Tract Cancer

Biliary tract cancer (BTC) is a gastrointestinal malignancy associated with a poor survival rate. Current therapies encompass palliative and chemotherapeutic treatment as well as radiation therapy, which results in a median survival of only one year due to standard therapeutic ineffectiveness or resistance. Tazemetostat is an FDA-approved inhibitor of enhancer of Zeste homolog 2 (EZH2), a methyltransferase involved in BTC tumorigenesis via trimethylation of histone 3 at lysine 27 (H3K27me3), an epigenetic mark associated with silencing of tumor suppressor genes. Up to now, there are no data available regarding tazemetostat as a possible treatment option against BTC. Therefore, the aim of our study is a first-time investigation of tazemetostat as a potential anti-BTC substance in vitro. In this study, we demonstrate that tazemetostat affects cell viability and the clonogenic growth of BTC cells in a cell line-dependent manner. Furthermore, we found a strong epigenetic effect at low concentrations of tazemetostat, which was independent of the cytotoxic effect. We also observed in one BTC cell line that tazemetostat increases the mRNA levels and protein expression of the tumor suppressor gene Fructose-1,6-bisphosphatase 1 (FBP1). Interestingly, the observed cytotoxic and epigenetic effects were independent of the mutation status of EZH2. To conclude, our study shows that tazemetostat is a potential anti-tumorigenic substance in BTC with a strong epigenetic effect.

Chemical biology and pharmacology of histone lysine methylation inhibitors

Histone lysine methylation is a post-translational modification that plays a key role in the epigenetic regulation of a broad spectrum of biological processes. Moreover, the dysregulation of histone lysine methyltransferases (KMTs) has been implicated in the pathogenesis of several diseases particularly cancer. Due to their pathobiological importance, KMTs have garnered immense attention over the last decade as attractive therapeutic targets. These endeavors have culminated in tens of chemical probes that have been used to interrogate many aspects of histone lysine methylation. Besides, over a dozen inhibitors have been advanced to clinical trials, including the EZH2 inhibitor tazemetostat approved for the treatment of follicular lymphoma and advanced epithelioid sarcoma. In this Review, we highlight the chemical biology and pharmacology of KMT inhibitors and targeted protein degraders focusing on the clinical development of EZH1/2, DOT1L, Menin-MLL, and WDR5-MLL inhibitors. We also briefly discuss the pharmacologic targeting of other KMTs.

Molecular Targets for Novel Therapeutics in Pediatric Fusion-Positive Non-CNS Solid Tumors

Chromosomal fusions encoding novel molecular drivers have been identified in several solid tumors, and in recent years the identification of such pathogenetic events in tumor specimens has become clinically actionable. Pediatric sarcomas and other rare tumors that occur in children as well as adults are a group of heterogeneous tumors often with driver gene fusions for which some therapeutics have already been developed and approved, and others where there is opportunity for progress and innovation to impact on patient outcomes. We review the chromosomal rearrangements that represent oncogenic events in pediatric solid tumors outside of the central nervous system (CNS), such as Ewing Sarcoma, Rhabdomyosarcoma, Fibrolamellar Hepatocellular Carcinoma, and Renal Cell Carcinoma, among others. Various therapeutics such as CDK4/6, FGFR, ALK, VEGF, EGFR, PDGFR, NTRK, PARP, mTOR, BRAF, IGF1R, HDAC inhibitors are being explored among other novel therapeutic strategies such as ONC201/TIC10.

Molecular targeted therapy for advanced or metastatic soft tissue sarcoma

Soft tissue sarcomas are a form of rare and heterogeneous neoplasms with high recurrence rate and mortality. Over the past decades, less progress has been achieved. Surgical management with or without adjuvant/neoadjuvant radiotherapy is still the first-line treatment for localized soft tissue sarcomas, and chemotherapy is the additional option for those with high-risk. However, not all patients with advanced or metastatic soft tissue sarcomas benefit from conventional chemotherapy, targeted therapy takes the most relevant role in the management of those resistant to or failed to conventional chemotherapy. Heterogeneous soft tissue sarcomas vary from biological behavior, genetic mutations, and clinical presentation with a low incidence, indicating the future direction of histotype-based even molecule-based personalized therapy. Furthermore, increasing preclinical studies were carried out to investigate the pathogenesis and potential therapeutic targets of soft tissue sarcomas and increasing new drugs have been developed in recent years, which had started opening new doors for clinical treatment for patients with advanced/metastatic soft tissue sarcomas. Here we sought to summarize the concise characteristics and advance in the targeted therapy for the most common subtypes of soft tissue sarcomas.

The Biology of Synovial Sarcoma: State-of-the-Art and Future Perspectives

New molecular insights are being achieved in synovial sarcoma (SS) that can provide new potential diagnostic and prognostic markers as well as therapeutic targets. In particular, the advancement of research on epigenomics and gene regulation is promising. The concrete hypothesis that the pathogenesis of SS might mainly depend on the disruption of the balance of the complex interaction between epigenomic regulatory complexes and the consequences on gene expression opens interesting new perspectives. The standard of care for primary SS is wide surgical resection combined with radiation in selected cases. The role of chemotherapy is still under refinement and can be considered in patients at high risk of metastasis or in those with advanced disease. Cytotoxic chemotherapy (anthracyclines, ifosfamide, trabectedin, and pazopanib) is the treatment of choice, despite several possible side effects. Many possible drug-able targets have been identified. However, the impact of these strategies in improving SS outcome is still limited, thus making current and future research strongly needed to improve the survival of patients with SS.

Polycomb group proteins in cancer: multifaceted functions and strategies for modulation

Polycomb repressive complexes (PRCs) are a heterogenous collection of dozens, if not hundreds, of protein complexes composed of various combinations of subunits. PRCs are transcriptional repressors important for cell-type specificity during development, and as such, are commonly mis-regulated in cancer. PRCs are broadly characterized as PRC1 with histone ubiquitin ligase activity, or PRC2 with histone methyltransferase activity; however, the mechanism by which individual PRCs, particularly the highly diverse set of PRC1s, alter gene expression has not always been clear. Here we review the current understanding of how PRCs act, both individually and together, to establish and maintain gene repression, the biochemical contribution of individual PRC subunits, the mis-regulation of PRC function in different cancers, and the current strategies for modulating PRC activity. Increased mechanistic understanding of PRC function, as well as cancer-specific roles for individual PRC subunits, will uncover better targets and strategies for cancer therapies.

The BAF chromatin remodeling complexes: structure, function, and synthetic lethalities

BAF complexes are multi-subunit chromatin remodelers, which have a fundamental role in genomic regulation. Large-scale sequencing efforts have revealed frequent BAF complex mutations in many human diseases, particularly in cancer and neurological disorders. These findings not only underscore the importance of the BAF chromatin remodelers in cellular physiological processes, but urge a more detailed understanding of their structure and molecular action to enable the development of targeted therapeutic approaches for diseases with BAF complex alterations. Here, we review recent progress in understanding the composition, assembly, structure, and function of BAF complexes, and the consequences of their disease-associated mutations. Furthermore, we highlight intra-complex subunit dependencies and synthetic lethal interactions, which have emerged as promising treatment modalities for BAF-related diseases.

Unmasking BCL-2 Addiction in Synovial Sarcoma by Overcoming Low NOXA

Simple Summary

Synovial sarcoma is a soft-tissue sarcoma that lacks effective systemic therapy and carries poor prognosis due to frequent late local recurrence and metastases. The cancer is known to be driven in part by increased expression of the pro-survival protein BCL-2. Surprisingly, synovial sarcoma proved resistant to BCL-2 inhibitors in pre-clinical trials. We identified increased activity of a second pro-survival protein, MCL-1, as responsible for this resistance. We showed that co-targeting both BCL-2 and MCL-1 proves to be an effective therapeutic approach both in cell culture and animal models of synovial sarcoma, supporting translation into clinical trials.

Abstract

Synovial sarcoma (SS) is frequently diagnosed in teenagers and young adults and continues to be treated with polychemotherapy with variable success. The SS18-SSX gene fusion is pathognomonic for the disease, and high expression of the anti-apoptotic BCL-2 pathologically supports the diagnosis. As the oncogenic SS18-SSX fusion gene itself is not druggable, BCL-2 inhibitor-based therapies are an appealing therapeutic opportunity. Venetoclax, an FDA-approved BCL-2 inhibitor that is revolutionizing care in some BCL-2-expressing hematological cancers, affords an intriguing therapeutic possibility to treat SS. In addition, there are now dozens of venetoclax-based combination therapies in clinical trials in hematological cancers, attributing to the limited toxicity of venetoclax. However, preclinical studies of venetoclax in SS have demonstrated an unexpected ineffectiveness. In this study, we analyzed the response of SS to venetoclax and the underlying BCL-2 family biology in an effort to understand venetoclax treatment failure and find a therapeutic strategy to sensitize SS to venetoclax. We found remarkably depressed levels of the endogenous MCL-1 inhibitor, NOXA, in SS compared to other sarcomas. Expressing NOXA led to sensitization to venetoclax, as did the addition of the MCL-1 BH3 mimetic, S63845. Importantly, the venetoclax/S63845 combination induced tumor regressions in SS patient-derived xenograft (PDX) models. As a very close analog of S63845 (S64315) is now in clinical trials with venetoclax in AML (NCT03672695), the combination of MCL-1 BH3 mimetics and venetoclax should be considered for SS patients as a new therapy.

RePhine: An Integrative Method for Identification of Drug Response-related Transcriptional Regulators

Transcriptional regulators (TRs) participate in essential processes in cancer pathogenesis and are critical therapeutic targets. Identification of drug response-related TRs from cell line-based compound screening data is often challenging due to low mRNA abundance of TRs, protein modifications, and other confounders (CFs). In this study, we developed a regression-based pharmacogenomic and ChIP-seq data integration method (RePhine) to infer the impact of TRs on drug response through integrative analyses of pharmacogenomic and ChIP-seq data. RePhine was evaluated in simulation and pharmacogenomic data and was applied to pan-cancer datasets with the goal of biological discovery. In simulation data with added noises or CFs and in pharmacogenomic data, RePhine demonstrated an improved performance in comparison with three commonly used methods (including Pearson correlation analysis, logistic regression model, and gene set enrichment analysis). Utilizing RePhine and Cancer Cell Line Encyclopedia data, we observed that RePhine-derived TR signatures could effectively cluster drugs with different mechanisms of action. RePhine predicted that loss-of-function of EZH2/PRC2 reduces cancer cell sensitivity toward the BRAF inhibitor PLX4720. Experimental validation confirmed that pharmacological EZH2 inhibition increases the resistance of cancer cells to PLX4720 treatment. Our results support that RePhine is a useful tool for inferring drug response-related TRs and for potential therapeutic applications. The source code for RePhine is freely available at https://github.com/coexps/RePhine.

Antihistamine Drug Ebastine Inhibits Cancer Growth by Targeting Polycomb Group Protein EZH2

Enhancer of zester homolog 2 (EZH2), a histone lysine methyltransferase and the catalytic component of polycomb repressive complex 2, has been extensively investigated as a chromatin regulator and a transcriptional suppressor by methylating H3 at lysine 27 (H3K27). EZH2 is upregulated or mutated in most cancers, and its expression levels are negatively associated with clinical outcomes. However, the current developed small-molecule inhibitors targeting EZH2 enzymatic activities could not inhibit the growth and progression of solid tumors. Here, we discovered an antihistamine drug, ebastine, as a novel EZH2 inhibitor by targeting EZH2 transcription and subsequently downregulating EZH2 protein level and H3K27 trimethylation in multiple cancer cell lines at concentrations below 10 μmol/L. The inhibition of EZH2 by ebastine further impaired the progression, migration, and invasiveness of these cancer cells. Overexpression of Ezh2 wild-type and its mutant, H689A (lacking methyltransferase activity), rescued the neoplastic properties of these cancer cells after ebastine treatment, suggesting that EZH2 targeted by ebastine is independent of its enzymatic function. Next-generation RNA-sequencing analysis also revealed that C4-2 cells treated with 8 μmol/L ebastine showed a gene profiling pattern similar to EZH2-knockdown C4-2 cells, which was distinctively different from cells treated with GSK126, an EZH2 enzyme inhibitor. In addition, ebastine treatment effectively reduced tumor growth and progression, and enhanced progression-free survival in triple-negative breast cancer and drug-resistant castration-resistant prostate cancer patient-derived xenograft mice. Our data demonstrated that ebastine is a novel, safe, and potent anticancer agent for patients with advanced cancer by targeting the oncoprotein EZH2.

Cancer Stem Cells in Soft-Tissue Sarcomas

Soft tissue sarcomas (STS) are a rare group of mesenchymal solid tumors with heterogeneous genetic profiles and clinical features. Systemic chemotherapy is the backbone treatment for advanced STS; however, STS frequently acquire resistance to standard therapies, which highlights the need to improve treatments and identify novel therapeutic targets. Increases in the knowledge of the molecular pathways that drive sarcomas have brought to light different molecular alterations that cause tumor initiation and progression. These findings have triggered a breakthrough of targeted therapies that are being assessed in clinical trials. Cancer stem cells (CSCs) exhibit mesenchymal stem cell (MSC) features and represent a subpopulation of tumor cells that play an important role in tumor progression, chemotherapy resistance, recurrence and metastasis. In fact, CSCs phenotypes have been identified in sarcomas, allied to drug resistance and tumorigenesis. Herein, we will review the published evidence of CSCs in STS, discussing the molecular characteristic of CSCs, the commonly used isolation techniques and the new possibilities of targeting CSCs as a way to improve STS treatment and consequently patient outcome.

Epigenetic Modulators as Potential Multi-targeted Drugs Against Hedgehog Pathway for Treatment of Cancer

The Sonic hedgehog signalling is known to play a crucial role in regulating embryonic development, cancer stem cell maintenance and tissue patterning. Dysregulated hedgehog signalling has been reported to affect tumorigenesis and drug response in various human malignancies. Epigenetic therapy relying on DNA methyltransferase and Histone deacetylase inhibitors are being proposed as potential drug candidates considering their efficiency in preventing development of cancer progenitor cells, killing drug resistant cells and also dictating "on/off" switch of tumor suppressor genes and oncogenes. In this docking approach, epigenetic modulators were virtually screened for their efficiency in inhibiting key regulators of SHH pathway viz., sonic hedgehog, Smoothened and Gli using polypharmacological approach. The control drugs and epigenetic modulators were docked with PDB protein structures using AutoDock vina and further checked for their drug-likeness properties. Further molecular dynamics simulation using VMD and NAMD, and MMP/GBSA energy calculation were employed for verifying the stability and entropy of the ligand-receptor complex. EPZ-6438 and GSK 343 (EZH2 inhibitors), CHR 3996 and Mocetinostat (HDAC inhibitors), GSK 126 (HKMT inhibitor) and UNC 1215 (L3MBTL3 antagonist) exhibited multiple-targeted approach in modulating HH signalling. This is the first study to report these epigenetic drugs as potential multi-targeted hedgehog pathway inhibitors. Thus, epigenetic polypharmacology approach can be explored as a better alternative to challenges of acute long term toxicity and drug resistance occurring due to traditional single targeted chemotherapy in the future.

Targeting the undruggable: exploiting neomorphic features of fusion oncoproteins in childhood sarcomas for innovative therapies

While sarcomas account for approximately 1% of malignant tumors of adults, they are particularly more common in children and adolescents affected by cancer. In contrast to malignancies that occur in later stages of life, childhood tumors, including sarcoma, are characterized by a striking paucity of somatic mutations. However, entity-defining fusion oncogenes acting as the main oncogenic driver mutations are frequently found in pediatric bone and soft-tissue sarcomas such as Ewing sarcoma (EWSR1-FLI1), alveolar rhabdomyosarcoma (PAX3/7-FOXO1), and synovial sarcoma (SS18-SSX1/2/4). Since strong oncogene-dependency has been demonstrated in these entities, direct pharmacological targeting of these fusion oncogenes has been excessively attempted, thus far, with limited success. Despite apparent challenges, our increasing understanding of the neomorphic features of these fusion oncogenes in conjunction with rapid technological advances will likely enable the development of new strategies to therapeutically exploit these neomorphic features and to ultimately turn the "undruggable" into first-line target structures. In this review, we provide a broad overview of the current literature on targeting neomorphic features of fusion oncogenes found in Ewing sarcoma, alveolar rhabdomyosarcoma, and synovial sarcoma, and give a perspective for future developments. Graphical abstract Scheme depicting the different targeting strategies of fusion oncogenes in pediatric fusion-driven sarcomas. Fusion oncogenes can be targeted on their DNA level (1), RNA level (2), protein level (3), and by targeting downstream functions and interaction partners (4).

Epigenetic Targets in Synovial Sarcoma: A Mini-Review

Synovial Sarcomas (SS) are a type of Soft Tissue Sarcoma (STS) and represent 8-10% of all STS cases. Although SS can arise at any age, it typically affects younger individuals aged 15-35 and is therefore part of both pediatric and adult clinical practices. SS occurs primarily in the limbs, often near joints, but can present anywhere. It is characterized by the recurrent pathognomonic chromosomal translocation t(X;18)(p11.2;q11.2) that most frequently fuses SSX1 or SSX2 genes with SS18. This leads to the expression of the SS18-SSX fusion protein, which causes disturbances in several interacting multiprotein complexes such as the SWItch/Sucrose Non-Fermentable (SWI/SNF) complex, also known as the BAF complex and the Polycomb Repressive Complex 1 and 2 (PRC1 and PRC2). Furthermore, this promotes widespread epigenetic rewiring, leading to aberrant gene expression that drives the pathogenesis of SS. Good prognoses are characterized predominantly by small tumor size and young patient age. Whereas, high tumor grade and an increased genomic complexity of the tumor constitute poor prognostic factors. The current therapeutic strategy relies on chemotherapy and radiotherapy, the latter of which can lead to chronic side effects for pediatric patients. We will focus on the known roles of SWI/SNF, PRC1, and PRC2 as the main effectors of the SS18-SSX-mediated genome modifications and we present existing biological rationale for potential therapeutic targets and treatment strategies.

Long noncoding RNA MALAT1 potentiates growth and inhibits senescence by antagonizing ABI3BP in gallbladder cancer cells

Background

Gallbladder cancer (GBC) is the most malignant cancer occurring in the biliary tract cancer featured with undesirable prognosis, in which most patients die within a year of cholecystectomy. Long noncoding RNAs (lncRNAs) function as critical regulators of multiple stages of cancers. Herein, the mechanism of lncRNA metastasis associated lung adenocarcinoma transcript 1 (MALAT1) in GBC is investigated.

Methods

Microarray-based analysis initially provided data suggesting that the expression of MALAT1 was up-regulated while that of the ABI family member 3 binding protein (ABI3BP) was down-regulated in GBC tissues and cell lines. Kaplan-Meier method was then adopted to analyze the relationship between the MALAT1 expression and overall survival and disease-free survival of patients with GBC. A set of in vitro and in vivo experiments were conducted by transducing ABI3BP-vector or sh-MALAT1 into GBC cells.

Results

The results confirmed that the cancer prevention effects triggered by restored ABI3BP and depleted MALAT1 as evidenced by suppressed cell growth and enhanced cell senescence. MALAT1 was observed to down-regulate ABI3BP expression through recruitment of the enhancer of zeste homolog 2 (EZH2) to the ABI3BP promoter region while the silencing of MALAT1 or suppression of H3K27 methylation was observed to promote the expression of ABI3BP. Furthermore, GBC patients with high expression of MALAT1 indicated poor prognosis.

Conclusion

The current study clarifies that MALAT1 silencing and ABI3BP elevation impede the GBC development through the H3K27 methylation suppression induced by EZH2, highlighting a promising competitive paradigm for therapeutic approaches of GBC.

Precision Oncology in Sarcomas: Divide and Conquer

Sarcomas are a heterogeneous group of rare malignancies that exhibit remarkable heterogeneity, with more than 50 subtypes recognized. Advances in next-generation sequencing technology have resulted in the discovery of genetic events in these mesenchymal tumors, which in addition to enhancing understanding of the biology, have opened up avenues for molecularly targeted therapy and immunotherapy. This review focuses on how incorporation of next-generation sequencing has affected drug development in sarcomas and strategies for optimizing precision oncology for these rare cancers. In a significant percentage of soft tissue sarcomas, which represent up to 40% of all sarcomas, specific driver molecular abnormalities have been identified. The challenge to evaluate these mutations across rare cancer subtypes requires the careful characterization of these genetic alterations to further define compelling drivers with therapeutic implications. Novel models of clinical trial design also are needed. This shift would entail sustained efforts by the sarcoma community to move from one-size-fits-all trials, in which all sarcomas are treated similarly, to divide-and-conquer subtype-specific strategies.

Inhibition of Ezh2 In Vitro and the Decline of Ezh2 in Developing Midbrain Promote Dopaminergic Neurons Differentiation Through Modifying H3K27me3

Epigenetic modifications play an important role in neural development. Trimethylated histone H3 at lysine 27 (H3K27me3) is a repressive epigenetic marker that mediates tissue development. In this study, we demonstrate that H3K27me3 and histone methyl transferase Ezh2 regulated the development of dopaminergic (DA) neurons in vitro and in vivo. We found that H3K27me3 increased during differentiation of ventral midbrain-derived neural stem cells (VM-NSCs). However, histone demethylase selective inhibitor GSK-J1 increased H3K27me3 level and decreased the expression of tyrosine hydroxylase. Treated with Ezh2-selective inhibitor EPZ005687 repressed the trimethylation of H3K27 and enhanced differentiation of DA neurons in VM-NSCs cultures. Furthermore, Ezh2 inhibition promoted the expression of DA neurons developmental-related factors by modifying H3K27 trimethylation on the relevant promoter regions. Moreover, the effect of Ezh2 inhibition-mediated DA neurons differentiation was blocked by the expression of shRNA specific for Nurr1. In vivo, Ezh2 decreased and resulted in a reduction of H3K27me3 in developing midbrain. Deletion of Ezh2 by RNA interference approach promoted differentiation of DA neurons during midbrain development. Overexpression of Ezh2 enhanced cell self-renewal and did not affect differentiation of DA neurons.

Standard treatment and emerging drugs for managing synovial sarcoma: adult's and pediatric oncologist perspective

INTRODUCTION

in this review we discuss the standard of care for both pediatric and adult synovial sarcoma (SS), the prognostic differences between them, and the treatments available for localized and advanced diseases. We also overview the biology and the recent drugs under consideration in clinical trials on SS. Areas covered: we focus on new targeted therapies being investigated for advanced SS, especially anti-angiogenic drugs, and immunotherapy. We review all the published data and ongoing trials dedicated to SS or to soft tissue sarcoma in general, paying particular attention to the results obtained in SS patients. Expert opinion: we expect new treatment strategies to become available for SS in the near future. The ongoing and published trials on targeted therapies and immunotherapy mainly concern adult patients, but the somatic biology of pediatric SS has some similarities as in adult disease. A stronger cooperation between adult and pediatric oncologists in recent years has led to a more shared effort to find new treatment strategies for advanced SS patients, regardless of their age.

Clinical Benefit to an Aurora A Kinase Inhibitor in a Patient with Metastatic Integrase Interactor 1-Deficient Carcinoma

Integrase interactor 1 (INI-1)-deficient carcinoma is a rare cancer characterized by the loss of the SWItch/Sucrose Non-Fermentable-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 gene (SMARCB1) and tends to follow an aggressive clinical course. There is no currently available standard therapy option, although a few promising treatment strategies, including enhancer of zeste homolog 2 (EZH2) inhibition, are under active investigation. This report describes a 30-year-old woman with INI-1-deficient carcinoma who progressed on combination chemotherapy and an EZH2 inhibitor. Next-generation-sequencing-based targeted cancer-related gene assay confirmed SMARCB1 loss and revealed other mutations in breast cancer 1 gene and checkpoint kinase 2 gene, which may have impacted her clinical course. After discussion at the molecular tumor board, she was offered alisertib, an aurora A kinase inhibitor, on a single-patient expanded-use program and achieved prolonged disease stabilization. Aurora A kinase inhibition may have an important role in the management of patients with INI-1-deficient tumors, warranting further evaluation in clinical studies. KEY POINTS: Loss of the SWItch/Sucrose Non-Fermentable-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 gene (SMARCB1), which encodes integrase interactor 1 (INI-1), is associated with various mesenchymal malignancies, but a few carcinomas with rhabdoid features have been recently described as a distinct entity.INI-1-deficient carcinoma can be very aggressive, and there is no known treatment option available.There are encouraging preliminary data with an enhancer of zeste homolog 2 inhibitor, tazematostat, in INI-1-deficient malignancies, including INI-1-deficient carcinomas.Loss of INI-1 can activate aurora A kinase (AurkA), and inhibition of AurkA by alisertib could be a viable option and warrants further investigation in this cancer.Clinical genomic profiling can confirm diagnosis of molecularly defined malignancy and provide insights on therapeutic options.

High expression of EZH2 as a marker for the differential diagnosis of malignant and benign myogenic tumors

Overlap in morphologic features between malignant and benign myogenic tumors, such as leiomyosarcoma (LMS) vs. leiomyoma as well as rhabdomyosarcoma (RMS) vs. rhabdomyoma, often makes differential diagnosis difficult and challenging. Here the expressions of Enhancer of Zeste Homolog 2 (EZH2), Suppressor of Zeste 12 (SUZ12), retinoblastoma protein associated protein 46 (RbAp46), Embryonic Ectoderm Development (EED) and ki-67 protein were detected by immunohistochemistry to evaluate their values in differential diagnosis. The expression of EZH2 mRNA was investigated by analyzing the Gene Expression Omnibus Datasets. The results demonstrated that EZH2 protein was detected in 81.25% (26/32) of LMS and 70.58% (36/51) of RMS, whereas none of leiomyoma (n = 16), rhabdomyoma (n = 15) and normal tissues (n = 31) showed positive immunostaining (p < 0.05). EZH2 protein was found to have a sensitivity of 91.30% and specificity of 100% in distinguishing well-differentiated LMS from cellular leiomyoma, and a sensitivity of 92.86% and specificity of 100% in distinguishing well-differentiated embryonal rhabdomyosarcoma (ERMS) from fetal rhabdomyoma. Besides, the expression of EZH2 mRNA was higher in LMS and RMS than in benign tumors (p < 0.05). The expressions of SUZ12 and RbAp46 protein were higher in RMS than in rhabdomyoma (p < 0.05). Conclusively, the high expression of EZH2 is a promising marker in distinguishing well–differentiated LMS from cellular leiomyoma, or well–differentiated ERMS from fetal rhabdomyoma, and the upregulation of EZH2 protein expression may occur at transcriptional level.

Oncogenic roles of enhancer of zeste homolog 1/2 in hematological malignancies

Polycomb group (PcG) proteins regulate the expression of target genes by modulating histone modifications and are representative epigenetic regulators that maintain the stemness of embryonic and hematopoietic stem cells. Histone methyltransferases enhancer of zeste homolog 1 and 2 (EZH1/2), which are subunits of polycomb repressive complexes (PRC), are recurrently mutated or highly expressed in many hematological malignancies. EZH2 has a dual function in tumorigenesis as an oncogene and tumor suppressor gene, and targeting PRC2, in particular EZH1/2, for anticancer therapy has been extensively developed in the clinical setting. Here, we review the oncogenic function of EZH1/2 and introduce new therapeutic drugs targeting these enzymes.

The SS18-SSX Fusion Oncoprotein Hijacks BAF Complex Targeting and Function to Drive Synovial Sarcoma

Synovial sarcoma (SS) is defined by the hallmark SS18-SSX fusion oncoprotein, which renders BAF complexes aberrant in two manners: gain of SSX to the SS18 subunit and concomitant loss of BAF47 subunit assembly. Here we demonstrate that SS18-SSX globally hijacks BAF complexes on chromatin to activate an SS transcriptional signature that we define using primary tumors and cell lines. Specifically, SS18-SSX retargets BAF complexes from enhancers to broad polycomb domains to oppose PRC2-mediated repression and activate bivalent genes. Upon suppression of SS18-SSX, reassembly of BAF47 restores enhancer activation, but is not required for proliferative arrest. These results establish a global hijacking mechanism for SS18-SSX on chromatin, and define the distinct contributions of two concurrent BAF complex perturbations.

Advances in sarcoma diagnostics and treatment

The heterogeneity of sarcomas with regard to molecular genesis, histology, clinical characteristics, and response to treatment makes management of these rare yet diverse neoplasms particularly challenging. This review encompasses recent developments in sarcoma diagnostics and treatment, including cytotoxic, targeted, epigenetic, and immune therapy agents. In the past year, groups internationally explored the impact of adding mandatory molecular testing to histological diagnosis, reporting some changes in diagnosis and/or management; however, the impact on outcomes could not be adequately assessed. Transcriptome sequencing techniques have brought forward new diagnostic tools for identifying fusions and/or characterizing unclassified entities. Next-generation sequencing and advanced molecular techniques were also applied to identify potential targets for directed and epigenetic therapy, where preclinical studies reported results for agents active within the receptor tyrosine kinase, mTOR, Notch, Wnt, Hedgehog, Hsp90, and MDM2 signaling networks. At the level of clinical practice, modest developments were seen for some sarcoma subtypes in conventional chemotherapy and in therapies targeting the pathways activated by various receptor tyrosine kinases. In the burgeoning field of immune therapy, sarcoma work is in its infancy; however, elaborate protocols for immune stimulation are being explored, and checkpoint blockade agents advance from preclinical models to clinical studies.

Chromatin organization regulated by EZH2-mediated H3K27me3 is required for OPN-induced migration of bone marrow-derived mesenchymal stem cells

Osteopontin (OPN) is a chemokine-like extracellular matrix-associated protein involved in the migration of bone marrow-derived mesenchymal stem cells (BMSCs). An increasing number of studies have found that chromatin organization may affect cellular migration. However, whether OPN regulates chromatin organization is not understood, nor are the underlying molecular mechanisms. In this study, we investigated the link between chromatin organization and BMSC migration and demonstrated that OPN-mediated BMSC migration leads to elevated levels of heterochromatin marker histone H3 lysine 27 trimethylation (H3K27me3) through the methyltransferase EZH2. The expression of EZH2 reorganizes the chromatin structure of BMSCs. Pharmacological inhibition or depletion of EZH2 blocks BMSC migration. Moreover, using an atomic force microscope (AFM), we found that chromatin decondensation alters the mechanical properties of the nucleus. In addition, inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) signals represses OPN-promoted chromatin condensation and cell migration. Thus, our results identify a mechanism by which ERK1/2 signalling drives specific chromatin modifications in BMSCs, which alters chromatin organization and thereby enables OPN-mediated BMSC migration.

Advances in chromosomal translocations and fusion genes in sarcomas and potential therapeutic applications

Chromosomal translocations and fusion genes are very common in human cancer especially in subtypes of sarcomas, such as rhabdomyosarcoma, Ewing's sarcoma, synovial sarcoma and liposarcoma. The discovery of novel chromosomal translocations and fusion genes in different tumors are due to the advancement of next-generation sequencing (NGS) technologies such as whole genome sequencing. Recently, many novel chromosomal translocations and gene fusions have been identified in different types of sarcoma through NGS approaches. In addition to previously known sarcoma fusion genes, these novel specific fusion genes and associated molecular events represent important targets for novel therapeutic approaches in the treatment of sarcomas. This review focuses on recent advances in chromosomal translocations and fusion genes in sarcomas and their potential therapeutic applications in the treatment of sarcomas.

Enhancer of zeste homologue 2 (EZH2) expression in synovial sarcomas as a promising indicator of prognosis

Synovial sarcoma (SS) is a type of soft-tissue sarcoma, often linked to poor survival. Although overexpression of enhancer of zeste homologue 2 (EZH2) has been associated with poor prognosis in different tumors, a few studies investigated this link in SS. Here, we analyzed the relationship between EZH2 expression and prognostic factors in SS. We included 29 patients with SS. Immunostaining of EZH2 was performed with (D2C9) XPTM Rabbit mAb antibody, and the results were classified as low EZH2 expression (negative or weak expression) and high EZH2 expression category (moderate or strong expression). Analysis of survival in relation to prognostic factors was performed with Kaplan-Meier survival curves and Cox proportional hazard regression analysis. Our sample included 19/29 female and 10/29 male patients, with age range 16-63 years. The tumor diameter ranged from 2 to 15 cm. Necrosis was observed in 15/29 cases. Sixteen cases had >10 mitoses per 50 high-power fields (HPFs). Out of 29 cases, 14 showed low and 15 had high EZH2 expression. Statistically significant results were obtained for the association between the presence of metastasis and necrosis (p = 0.042), high EZH2 expression and distant metastasis (p = 0.018), high EZH2 expression and necrosis (p = 0.016), and high EZH2 expression and the tumor size >5 cm versus tumor size ≤5 cm (p = 0.014). Patients with all of the following: the tumor size ≤5 cm, low EZH2 expression, and without necrosis and distant metastasis had significantly longer survival time. Our results are consistent with previous studies, suggesting that EZH2 overexpression is an indicator of poor prognosis in SS.

Epigenetic Alterations in Bone and Soft Tissue Tumors

Human malignancies are driven by heritable alterations that lead to unchecked cellular proliferation, invasive growth and distant spread. Heritable changes can arise from changes in DNA sequence, or, alternatively, through altered gene expression rooted in epigenetic mechanisms. In recent years, high-throughput sequencing of tumor genomes has revealed a central role for mutations in epigenetic regulatory complexes in oncogenic processes. Through interactions with or direct modifications of chromatin, these proteins help control the accessibility of genes, and thus the transcriptional profile of a cell. Dysfunction in these proteins can lead to activation of oncogenic pathways or silencing of tumor suppressors. Although epigenetic regulators are altered across a broad spectrum of human malignancies, they play a particularly central role in tumors of mesenchymal and neuroectodermal origin. This review will focus on recent advances in the understanding of the molecular pathogenesis of a subset of tumors in which alterations in the polycomb family of chromatin modifying complexes, the SWI/SNF family of nucleosome remodelers, and histones play a central role in disease pathogenesis. Although this review will focus predominantly on the molecular mechanisms underlying these tumors, each section will also highlight areas in which an understanding of the molecular pathogenesis of these diseases has led to the adoption of novel immunohistochemical and molecular markers.

Downregulation of miR-130a promotes cell growth and epithelial to mesenchymal transition by activating HMGB2 in glioma

Aberrant expression of miR-130a is usually found in cancer studies; however, the role of miR-130a has seldom been reported in glioma. We explored miR-130a's function and the underlying mechanism in glioma. It was found that miR-130a expression was significantly down-regulated in glioma tissues and cell lines. Overexpression of miR-130a decreased glioma cell growth and invasion both in vitro and in vivo. We identified the oncogene HMGB2 as a downstream target of miR-130a by using luciferase and western blot assays. Knockdown of HMGB2 mimicked the effect of miR-130a in glioma cells. Taken together, our study demonstrate that miR-130a may function as a tumor suppressor in glioma and suggest that miR-130a is a potential therapeutic target for glioma patients.

Genetic Mutations and Epigenetic Modifications: Driving Cancer and Informing Precision Medicine

Cancer treatment is undergoing a significant revolution from "one-size-fits-all" cytotoxic therapies to tailored approaches that precisely target molecular alterations. Precision strategies for drug development and patient stratification, based on the molecular features of tumors, are the next logical step in a long history of approaches to cancer therapy. In this review, we discuss the history of cancer treatment from generic natural extracts and radical surgical procedures to site-specific and combinatorial treatment regimens, which have incrementally improved patient outcomes. We discuss the related contributions of genetics and epigenetics to cancer progression and the response to targeted therapies and identify challenges and opportunities for the success of precision medicine. The identification of patients who will benefit from targeted therapies is more complex than simply identifying patients whose tumors harbour the targeted aberration, and intratumoral heterogeneity makes it difficult to determine if a precision therapy is successful during treatment. This heterogeneity enables tumors to develop resistance to targeted approaches; therefore, the rational combination of therapeutic agents will limit the threat of acquired resistance to therapeutic success. By incorporating the view of malignant transformation modulated by networks of genetic and epigenetic interactions, molecular strategies will enable precision medicine for effective treatment across cancer subtypes.

Selective Killing of SMARCA2- and SMARCA4-deficient Small Cell Carcinoma of the Ovary, Hypercalcemic Type Cells by Inhibition of EZH2: In Vitro and In Vivo Preclinical Models

The SWI/SNF complex is a major regulator of gene expression and is increasingly thought to play an important role in human cancer, as evidenced by the high frequency of subunit mutations across virtually all cancer types. We previously reported that in preclinical models, malignant rhabdoid tumors, which are deficient in the SWI/SNF core component INI1 (SMARCB1), are selectively killed by inhibitors of the H3K27 histone methyltransferase EZH2. Given the demonstrated antagonistic activities of the SWI/SNF complex and the EZH2-containing PRC2 complex, we investigated whether additional cancers with SWI/SNF mutations are sensitive to selective EZH2 inhibition. It has been recently reported that ovarian cancers with dual loss of the redundant SWI/SNF components SMARCA4 and SMARCA2 are characteristic of a rare rhabdoid-like subtype known as small-cell carcinoma of the ovary hypercalcemic type (SCCOHT). Here, we provide evidence that a subset of commonly used ovarian carcinoma cell lines were misdiagnosed and instead were derived from a SCCOHT tumor. We also demonstrate that tazemetostat, a potent and selective EZH2 inhibitor currently in phase II clinical trials, induces potent antiproliferative and antitumor effects in SCCOHT cell lines and xenografts deficient in both SMARCA2 and SMARCA4. These results exemplify an additional class of rhabdoid-like tumors that are dependent on EZH2 activity for survival. Mol Cancer Ther; 16(5); 850-60. ©2017 AACR.

Preclinical Evidence of Anti-Tumor Activity Induced by EZH2 Inhibition in Human Models of Synovial Sarcoma

The catalytic activities of covalent and ATP-dependent chromatin remodeling are central to regulating the conformational state of chromatin and the resultant transcriptional output. The enzymes that catalyze these activities are often contained within multiprotein complexes in nature. Two such multiprotein complexes, the polycomb repressive complex 2 (PRC2) methyltransferase and the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeler have been reported to act in opposition to each other during development and homeostasis. An imbalance in their activities induced by mutations/deletions in complex members (e.g. SMARCB1) has been suggested to be a pathogenic mechanism in certain human cancers. Here we show that preclinical models of synovial sarcoma—a cancer characterized by functional SMARCB1 loss via its displacement from the SWI/SNF complex through the pathognomonic SS18-SSX fusion protein—display sensitivity to pharmacologic inhibition of EZH2, the catalytic subunit of PRC2. Treatment with tazemetostat, a clinical-stage, selective and orally bioavailable small-molecule inhibitor of EZH2 enzymatic activity reverses a subset of synovial sarcoma gene expression and results in concentration-dependent cell growth inhibition and cell death specifically in SS18-SSX fusion-positive cells in vitro. Treatment of mice bearing either a cell line or two patient-derived xenograft models of synovial sarcoma leads to dose-dependent tumor growth inhibition with correlative inhibition of trimethylation levels of the EZH2-specific substrate, lysine 27 on histone H3. These data demonstrate a dependency of SS18-SSX-positive, SMARCB1-deficient synovial sarcomas on EZH2 enzymatic activity and suggests the potential utility of EZH2-targeted drugs in these genetically defined cancers.