Role of EZH2 in cancer stem cells: from biological insight to a therapeutic target

[EZH2 is therapeutic target for personalized treatment in multiple myeloma]

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that functions as the catalytic subunit of the polycomb repressive complex 2 (PRC2). PRC2 represses gene transcription through tri-methylation of lysine 27 of histone 3 (H3K27me3) by its catalytic subunit EZH2. EZH2 is also involved in normal B cell differentiation. EZH2 deregulation has been described in many cancer types including hematological malignancies. The oncogenic addiction of tumor cells to EZH2 represents a therapeutic target in several hematological malignancies and solid cancers. Specific small molecules have been recently developed to target cancer cells with EZH2 overexpression or activating mutation. Their therapeutic potential is currently under evaluation. In particular, EZH2 is overexpressed in multiple myeloma (MM), a neoplasia characterized by the accumulation of clonal plasma cells within the bone marrow, with biological functions in the pathophysiology. This review summarizes the roles of EZH2 in B cell differentiation and pathologic hematological processes with a particular focus in multiple myeloma. We also discuss recent advances in the development of EZH2 inhibitors for the personalized treatment of patients with hematological malignancies.

Sodium Valproate Inhibits Small Cell Lung Cancer Tumor Growth on the Chicken Embryo Chorioallantoic Membrane and Reduces the p53 and EZH2 Expression

The study aims to test the effect of different sodium valproate (NaVP) doses on small cell lung cancer NCI-H146 cells tumor in chicken embryo chorioallantoic membrane (CAM) model. Xenografts were investigated in the following groups: nontreated control and 5 groups treated with different NaVP doses (2, 3, 4, 6, and 8 mmol/L). Invasion of tumors into CAM in the nontreated group reached 76%. Tumors treated with 8 mmol/L NaVP doses significantly differed in tumor invasion frequency from the control and those treated with 2 mmol/L (P < .01). The calculated probability of 50% tumor noninvasion into CAM was when tumors were treated with 4 mmol/L of NaVP. Number of p53-positive cells in tumors was significantly reduced when treated with NaVP doses from 3 to 8 mmol/L as compared with control; number of EZH2-positive cells in control significantly differed from all NaVP-treated groups. No differences in p53- and EZH2-positive cell numbers were found among 4, 6, and 8 mmol/L NaVP-treated groups. Invaded tumors had an increased N-cadherin and reduced E-cadherin expression. The results indicate the increasing NaVP dose to be able to inhibit tumors progression. Expression of p53 and EZH2 may be promising target markers of therapeutic efficacy evaluation.

EZH2 inhibitors sensitize myeloma cell lines to panobinostat resulting in unique combinatorial transcriptomic changes

Multiple myeloma (MM) remains a largely incurable hematologic cancer due to an inability to broadly target inevitable drug-resistant relapse. Epigenetic abnormalities are abundantly present in multiple myeloma and have increasingly demonstrated critical roles for tumor development and relapse to standard therapies. Accumulating evidence suggests that the histone methyltransferase EZH2 is aberrantly active in MM. We tested the efficacy of EZH2 specific inhibitors in a large panel of human MM cell lines (HMCLs) and found that only a subset of HMCLs demonstrate single agent sensitivity despite ubiquitous global H3K27 demethylation. Pre-treatment with EZH2 inhibitors greatly enhanced the sensitivity of HMCLs to the pan-HDAC inhibitor panobinostat in nearly all cases regardless of single agent EZH2 inhibitor sensitivity. Transcriptomic profiling revealed large-scale transcriptomic alteration by EZH2 inhibition highly enriched for cancer-related pathways. Combination treatment greatly increased the scale of gene expression change with a large portion of differentially expressed genes being unique to the combination. Transcriptomic analysis demonstrated that combination treatment further perturbed oncogenic pathways and signaling nodes consistent with an antiproliferative/pro-apoptotic state. We conclude that combined inhibition of HDAC and EZH2 inhibitors is a promising therapeutic strategy to broadly target the epigenetic landscape of aggressive MM.

MUC1-C activates polycomb repressive complexes and downregulates tumor suppressor genes in human cancer cells

The PRC2 and PRC1 complexes are aberrantly expressed in human cancers and have been linked to decreases in patient survival. MUC1-C is an oncoprotein that is also overexpressed in diverse human cancers and is associated with a poor prognosis. Recent studies have supported a previously unreported function for MUC1-C in activating PRC2 and PRC1 in cancer cells. In the regulation of PRC2, MUC1-C (i) drives transcription of the EZH2 gene, (ii) binds directly to EZH2, and (iii) enhances occupancy of EZH2 on target gene promoters with an increase in H3K27 trimethylation. Regarding PRC1, which is recruited to PRC2 sites in the hierarchical model, MUC1-C induces BMI1 transcription, forms a complex with BMI1, and promotes H2A ubiquitylation. MUC1-C thereby contributes to the integration of PRC2 and PRC1-mediated repression of tumor suppressor genes, such as CDH1, CDKN2A, PTEN and BRCA1. Like PRC2 and PRC1, MUC1-C is associated with the epithelial-mesenchymal transition (EMT) program, cancer stem cell (CSC) state, and acquisition of anticancer drug resistance. In concert with these observations, targeting MUC1-C downregulates EZH2 and BMI1, inhibits EMT and the CSC state, and reverses drug resistance. These findings emphasize the significance of MUC1-C as a therapeutic target for inhibiting aberrant PRC function and reprogramming the epigenome in human cancers.

KDM2B overexpression correlates with poor prognosis and regulates glioma cell growth

Background

Gliomas are one of the most lethal cancers in the human central nervous system. Despite clinical treatment advancements, the prognosis of patients with glioma remains poor. KDM2B is a histone lysine demethylase, which has been observed in multiple tumors. But the concrete role of KDM2B in gliomas remains to be further illustrated.

Methods

The KDM2B expression in gliomas was detected with immunohistochemistry and Western blot assay. Furthermore, knockdown of KDM2B in U87 and U251 glioma cell lines, the proliferation capacity was evaluated by cell viability assay, colon formation assay and flow cytometry in vitro. Western blot assay was used to analyze the p21, EZH2 and cyclinD1 changes followed by knockdown of KDM2B.

Results

KDM2B was upregulated in tissues of glioma patients, and the expression was correlated to cancer progression. Downregulation of KDM2B in U87 and U251 glioma cell lines inhibited cell proliferation and arrested cell cycle in G0/G1 phase. In addition, silencing KDM2B promoted the upregulation of p21 while reduced the expression of EZH2 and cyclinD1.

Conclusion

Taken together, our results revealed that KDM2B might influence gliomas growth and act as a novel therapeutic target for glioma patients.

Small-cell lung cancer: what we know, what we need to know and the path forward

Small-cell lung cancer (SCLC) is a deadly tumour accounting for approximately 15% of lung cancers and is pathologically, molecularly, biologically and clinically very different from other lung cancers. While the majority of tumours express a neuroendocrine programme (integrating neural and endocrine properties), an important subset of tumours have low or absent expression of this programme. The probable initiating molecular events are inactivation of TP53 and RB1, as well as frequent disruption of several signalling networks, including Notch signalling. SCLC, when diagnosed, is usually widely metastatic and initially responds to cytotoxic therapy but nearly always rapidly relapses with resistance to further therapies. There were no important therapeutic clinical advances for 30 years, leading SCLC to be designated a 'recalcitrant cancer'. Scientific studies are hampered by a lack of tissue availability. However, over the past 5 years, there has been a worldwide resurgence of studies on SCLC, including comprehensive molecular analyses, the development of relevant genetically engineered mouse models and the establishment of patient-derived xenografts. These studies have led to the discovery of new potential therapeutic vulnerabilities for SCLC and therefore to new clinical trials. Thus, while the past has been bleak, the future offers greater promise.

The role of EZH2 in overall survival of colorectal cancer: a meta-analysis

Enhancer of zeste homolog 2 (EZH2) is the catalitic subunit of polycomb repressive complex 2 and mediates gene silencing. EZH2 is overexpressed in many cancers and correlates with poor prognosis. The role of the gene EZH2 in colorectal cancer survival is uncertainly, the aim of this study is clear this relationship. Relevant literaure was searched from electronic databases. A meta-analysis was performed with elegible studies which quantitatively evaluated the relationship between EZH2 overexpression and survival of patients with colorectal cancer. Survival data were aggregated and quantitatively analyzed. We performed a meta-analysis of 8 studies (n = 1059 patients) that evaluated the correlation between EZH2 overexpression and survival in patients with colorectal cancer. Combined hazard ratios suggested that EZH2 overexpression was associated with better prognosis of overall survival (OS) HR(hazard ratio) = 0.61 95% CI (0.38-0.84) We performed bias analysis according Egger and Begg,s test and we did not find publication bias. EZH2 overexpression indicates a better prognosis for colorectal cancer.

Statin and Bisphosphonate Induce Starvation in Fast-Growing Cancer Cell Lines

Statins and bisphosphonates are increasingly recognized as anti-cancer drugs, especially because of their cholesterol-lowering properties. However, these drugs act differently on various types of cancers. Thus, the aim of this study was to compare the effects of statins and bisphosphonates on the metabolism (NADP⁺/NADPH-relation) of highly proliferative tumor cell lines from different origins (PC-3 prostate carcinoma, MDA-MB-231 breast cancer, U-2 OS osteosarcoma) versus cells with a slower proliferation rate like MG-63 osteosarcoma cells. Global gene expression analysis revealed that after 6 days of treatment with pharmacologic doses of the statin simvastatin and of the bisphosphonate ibandronate, simvastatin regulated more than twice as many genes as ibandronate, including many genes associated with cell cycle progression. Upregulation of starvation-markers and a reduction of metabolism and associated NADPH production, an increase in autophagy, and a concomitant downregulation of H3K27 methylation was most significant in the fast-growing cancer cell lines. This study provides possible explanations for clinical observations indicating a higher sensitivity of rapidly proliferating tumors to statins and bisphosphonates.

Structure, mechanism, and regulation of polycomb-repressive complex 2

Polycomb repressive complex 2 (PRC2) methylates lysine 27 in histone H3, a modification associated with epigenetic gene silencing. This complex plays a fundamental role in regulating cellular differentiation and development, and PRC2 overexpression and mutations have been implicated in numerous cancers. In this Minireview, we examine recent studies elucidating the first crystal structures of the PRC2 core complex, yielding seminal insights into its catalytic mechanism, substrate specificity, allosteric regulation, and inhibition by a class of small molecules that are currently undergoing cancer clinical trials. We conclude by exploring unresolved questions and future directions for inquiry regarding PRC2 structure and function.