Superior efficacy of a combined epigenetic therapy against human mantle cell lymphoma cells

Cyclohexene oxide CA, a derivative of zeylenone, exhibits anti-cancer activity in glioblastoma by inducing G0/G1 phase arrest through interference with EZH2

Introduction: Due to its highly aggressiveness and malignancy, glioblastoma (GBM) urgently requires a safe and effective treatment strategy. Zeylenone, a natural polyoxygenated cyclohexenes compound isolated from Uvaria grandiflora, has exhibited potential biological activities in various human diseases, including tumors. Methods: We designed and synthesized a series of (+)-Zeylenone analogues and evaluated their anti-GBM roles through structural-activity analysis. Cell Counting Kit-8, TUNEL, transwell and flow cytometry were employed for investigating the anticancer effects of CA on GBM cells. Western blotting, molecular docking, qRT-PCR and ChIP assays were performed to reveal the underlying mechanisms by which CA regulates the GBM cell cycle. The nude mouse xenograft model, HE staining, immunohistochemistry and was used to evaluate the anticancer effect of CA in vivo. Results: We identified CA ((1R, 2R, 3S)-3-p-fluorobenzoyl-zeylenone) as having the lowest IC50 value in GBM cells. CA treatment significantly inhibited the malignant behaviors of GBM cells and induced G0/G1 phase arrest in vitro. Furthermore, we validated the molecular mechanism by which CA interferes with EZH2, attenuating the down-regulation of cyclin-dependent kinase inhibitors p27 and p16 by the PRC2 complex. By establishing orthotopic nude mice models, we further validated the inhibitory role of CA on tumorigenesis of GBM cells in vivo and its potential values to synergistically potentiate the anti-tumor effects of EZH2 inhibitors. Conclusion: Overall, this paper elucidated the anti-GBM effects and potential mechanisms of CA, and may provide a therapeutic drug candidate for GBM treatment.

Targeting epigenetic regulation for cancer therapy using small molecule inhibitors

Cancer cells display pervasive changes in DNA methylation, disrupted patterns of histone posttranslational modification, chromatin composition or organization and regulatory element activities that alter normal programs of gene expression. It is becoming increasingly clear that disturbances in the epigenome are hallmarks of cancer, which are targetable and represent attractive starting points for drug creation. Remarkable progress has been made in the past decades in discovering and developing epigenetic-based small molecule inhibitors. Recently, epigenetic-targeted agents in hematologic malignancies and solid tumors have been identified and these agents are either in current clinical trials or approved for treatment. However, epigenetic drug applications face many challenges, including low selectivity, poor bioavailability, instability and acquired drug resistance. New multidisciplinary approaches are being designed to overcome these limitations, e.g., applications of machine learning, drug repurposing, high throughput virtual screening technologies, to identify selective compounds with improved stability and better bioavailability. We provide an overview of the key proteins that mediate epigenetic regulation that encompass histone and DNA modifications and discuss effector proteins that affect the organization of chromatin structure and function as well as presently available inhibitors as potential drugs. Current anticancer small-molecule inhibitors targeting epigenetic modified enzymes that have been approved by therapeutic regulatory authorities across the world are highlighted. Many of these are in different stages of clinical evaluation. We also assess emerging strategies for combinatorial approaches of epigenetic drugs with immunotherapy, standard chemotherapy or other classes of agents and advances in the design of novel epigenetic therapies.

Identification of EZH2 as Cancer Stem Cell Marker in Clear Cell Renal Cell Carcinoma and the Anti-Tumor Effect of Epigallocatechin-3-Gallate (EGCG)

The aim of the study was to develop a new therapeutic strategy to target cancer stem cells (CSCs) in clear cell renal cell carcinoma (ccRCC) and to identify typical CSC markers to improve therapy effectiveness. It was found that the corrected-mRNA expression-based stemness index was upregulated in kidney renal clear cell carcinoma (KIRC) tissues compared to non-tumor tissue and increased with higher tumor stage and grade. EZH2 was identified as a CSC marker and prognosis factor for KIRC patients. The expression of EZH2 was associated with several activated tumor-infiltrating immune cells. High expression of EZH2 was enriched in immune-related pathways, low expression was related to several metabolic pathways. Epigallocatechin-3-gallate (EGCG) was identified as the most potent suppressor of EZH2, was able to inhibit viability, migration, and invasion, and to increase the apoptosis rate of ccRCC CSCs. KIF11, VEGF, and MMP2 were identified as predictive EGCG target genes, suggesting a potential mechanism of how EZH2 might regulate invasiveness and migration. The percentages of FoxP3+ Treg cells in the peripheral blood mononuclear cells of ccRCC patients decreased significantly when cultured with spheres pretreated with EGCG plus sunitinib compared to spheres without treatment. Our findings provide new insights into the treatment options of ccRCC based on targeting CSCs.

Acquired resistance to DZNep-mediated apoptosis is associated with copy number gains of AHCY in a B-cell lymphoma model

BACKGROUND

Enhancer of zeste homolog 2 (EZH2) is considered an important driver of tumor development and progression by its histone modifying capabilities. Inhibition of EZH2 activity is thought to be a potent treatment option for eligible cancer patients with an aberrant EZH2 expression profile, thus the indirect EZH2 inhibitor 3-Deazaneplanocin A (DZNep) is currently under evaluation for its clinical utility. Although DZNep blocks proliferation and induces apoptosis in different tumor types including lymphomas, acquired resistance to DZNep may limit its clinical application.

METHODS

To investigate possible mechanisms of acquired DZNep resistance in B-cell lymphomas, we generated a DZNep-resistant clone from a previously DZNep-sensitive B-cell lymphoma cell line by long-term treatment with increasing concentrations of DZNep (ranging from 200 to 2000 nM) and compared the molecular profiles of resistant and wild-type clones. This comparison was done using molecular techniques such as flow cytometry, copy number variation assay (OncoScan and TaqMan assays), fluorescence in situ hybridization, Western blot, immunohistochemistry and metabolomics analysis.

RESULTS

Whole exome sequencing did not indicate the acquisition of biologically meaningful single nucleotide variants. Analysis of copy number alterations, however, demonstrated among other acquired imbalances an amplification (about 30 times) of the S-adenosyl-L-homocysteine hydrolase (AHCY) gene in the resistant clone. AHCY is a direct target of DZNep and is critically involved in the biological methylation process, where it catalyzes the reversible hydrolysis of S-adenosyl-L-homocysteine to L-homocysteine and adenosine. The amplification of the AHCY gene is paralleled by strong overexpression of AHCY at both the transcriptional and protein level, and persists upon culturing the resistant clone in a DZNep-free medium.

CONCLUSIONS

This study reveals one possible molecular mechanism how B-cell lymphomas can acquire resistance to DZNep, and proposes AHCY as a potential biomarker for investigation during the administration of EZH2-targeted therapy with DZNep.

EZH2 abnormalities in lymphoid malignancies: underlying mechanisms and therapeutic implications

EZH2 is the catalytic subunit of the polycomb repressive complex 2 (PRC2), which along with other PRC2 components mediates gene expression suppression via the methylation of Histone H3 at lysine 27. Recent studies have revealed a dichotomous role of EZH2 in physiology and in the pathogenesis of cancer. While it plays an essential role in the development of the lymphoid system, its deregulation, whether due to genetic or non-genetic causes, promotes B cell- and T cell-related lymphoma or leukemia. These findings triggered a boom in the development of therapeutic EZH2 inhibitors in recent years. Here, we discuss physiologic and pathogenic function of EZH2 in lymphoid context, various internal causes of EZH2 aberrance and how EZH2 modulates lymphomagenesis through epigenetic silencing, post-translational modifications (PTMs), orchestrating with surrounding tumor micro-environment and associating with RNA or viral partners. We also summarize different strategies to directly inhibit PRC2-EZH2 or to intervene EZH2 upstream signaling.

The synergistic effect of DZ‑NEP, panobinostat and temozolomide reduces clonogenicity and induces apoptosis in glioblastoma cells

Current treatment against glioblastoma consists of surgical resection followed by temozolomide, with or without combined radiotherapy. Glioblastoma frequently acquires resistance to chemotherapy and/or radiotherapy. Novel therapeutic approaches are thus required. The inhibition of enhancer of zeste homolog 2 (EZH2; a histone methylase) and histone deacetylases (HDACs) are possible epigenetic treatments. Temozolomide, 3‑deazaneplanocin A (DZ‑Nep; an EZH2 inhibitor) and panobinostat (an HDAC inhibitor) were tested in regular and temozolomide‑resistant glioblastoma cells to confirm whether the compounds could behave in a synergistic, additive or antagonistic manner. A total of six commercial cell lines, two temozolomide‑induced resistant cell lines and two primary cultures derived from glioblastoma samples were used. Cell lines were exposed to single treatments of the drugs in addition to all possible two‑ and three‑drug combinations. Colony formation assays, synergistic assays and reverse transcription‑quantitative PCR analysis of apoptosis‑associated genes were performed. The highest synergistic combination was DZ‑Nep + panobinostat. Triple treatment was also synergistic. Reduced clonogenicity and increased apoptosis were both induced. It was concluded that the therapeutic potential of the combination of these three drugs in glioblastoma was evident and should be further explored.

Targeting EZH1/2 induces cell cycle arrest and inhibits cell proliferation through reactivation of p57CDKN1C and TP53INP1 in mantle cell lymphoma

Objective

To explore the effect of dysregulation of epigenetic regulator EZH1 and EZH2 on the proliferation in MCL and the underlying mechanisms.

Methods

In this study, we elucidated the role of EZH1 and EZH2 overexpression by immunohistochemistry and correlated them to clinical outcome in 41 MCL patients. Quantitative real-time PCR and Western blot were applied to confirm the level of EZH1 and EZH2 in well-characterized MCL cell lines which were compared to those of naïve B cells. Then we manipulated the expression of EZH1 and EZH2 in MCL cells using CRISPR/Cas9 system to directly investigate their functional roles in MCL. We also evaluated the effect of two small molecule selective inhibitors, EPZ005687 and UNC1999, on MCL cell proliferation, cell cycle distribution and apoptosis in vitro. Finally, we performed RNA-sequencing (RNA-Seq) and Chromatin immunoprecipitation (ChIP) assay to further gain insight into the underlying molecular mechanisms.

Results

We found that EZH2 protein is overexpressed in approximately half of this cohort of MCL cases. More importantly, the overexpression of EZH2 is associated with poor OS in the patients. Nevertheless, simple EZH2 depletion in vitro has little impact on the viability of MCL cells, predominantly because of the consequent up-regulation of EZH1. Consistently, UNC1999, a dual EZH1/2 inhibitor, unlike the EZH2 selective inhibitor EPZ005687, exerts a potent inhibitory effect on MCL cells. Furthermore, we discover CDKN1C and TP53INP1 as the two important cell cycle regulators, the expression of which are repressed by EZH1/2 mediated epigenetic regulation and are restored by EZH1/2 dual inhibition.

Conclusions

Our study suggests that EZH2 participates in the pathogenesis of MCL which may serve as a potential biomarker for prognosis prediction. The dual inhibition of EZH1/2 is a promising therapeutic strategy for MCL.

DZNep-mediated apoptosis in B-cell lymphoma is independent of the lymphoma type, EZH2 mutation status and MYC, BCL2 or BCL6 translocations

Enhancer of zeste homolog 2 (EZH2) tri-methylates histone 3 at position lysine 27 (H3K27me3). Overexpression and gain-of-function mutations in EZH2 are regarded as oncogenic drivers in lymphoma and other malignancies due to the silencing of tumor suppressors and differentiation genes. EZH2 inhibition is sought to represent a good strategy for tumor therapy. In this study, we treated Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) cell lines with 3-deazaneplanocin—A (DZNep), an indirect EZH2 inhibitor which possesses anticancer properties both in-vitro and in-vivo. We aimed to address the impact of the lymphoma type, EZH2 mutation status, as well as MYC, BCL2 and BCL6 translocations on the sensitivity of the lymphoma cell lines to DZNep-mediated apoptosis. We show that DZNep inhibits proliferation and induces apoptosis of these cell lines independent of the type of lymphoma, the EZH2 mutation status and the MYC, BCL2 and BCL6 rearrangement status. Furthermore, DZNep induced a much stronger apoptosis in majority of these cell lines at a lower concentration, and within a shorter period when compared with EPZ-6438, a direct EZH2 inhibitor currently in phase II clinical trials. Apoptosis induction by DZNep was both concentration-dependent and time-dependent, and was associated with the inhibition of EZH2 and subsequent downregulation of H3K27me3 in DZNep-sensitive cell lines. Although EZH2, MYC, BCL2 and BCL6 are important prognostic biomarkers for lymphomas, our study shows that they poorly influence the sensitivity of lymphoma cell lines to DZNep-mediated apoptosis.

SETDB-1: A Potential Epigenetic Regulator in Breast Cancer Metastasis

The full epigenetic repertoire governing breast cancer metastasis is not completely understood. Here, we discuss the histone methyltransferase SET Domain Bifurcated Histone Lysine Methyltransferase 1 (SETDB1) and its role in breast cancer metastasis. SETDB1 serves as an exemplar of the difficulties faced when developing therapies that not only specifically target cancer cells but also the more elusive and aggressive stem cells that contribute to metastasis via epithelial-to-mesenchymal transition and confer resistance to therapies.

EZH2 upregulates the PI3K/AKT pathway through IGF1R and MYC in clinically aggressive chronic lymphocytic leukaemia

EZH2 is overexpressed in poor-prognostic chronic lymphocytic leukaemia (CLL) cases, acting as an oncogene; however, thus far, the EZH2 target genes in CLL have not been disclosed. In this study, using ChIP-sequencing, we identified EZH2 and H3K27me3 target genes in two prognostic subgroups of CLL with distinct prognosis and outcome, i.e., cases with unmutated (U-CLL, n = 6) or mutated IGHV genes (M-CLL, n = 6). While the majority of oncogenic pathways were equally enriched for EZH2 target genes in both prognostic subgroups, PI3K pathway genes were differentially bound by EZH2 in U-CLL versus M-CLL. The occupancy of EZH2 for selected PI3K pathway target genes was validated in additional CLL samples (n = 16) and CLL cell lines using siRNA-mediated EZH2 downregulation and ChIP assays. Intriguingly, we found that EZH2 directly binds to the IGF1R promoter along with MYC and upregulates IGF1R expression in U-CLL, leading to downstream PI3K activation. By investigating an independent CLL cohort (n = 96), a positive correlation was observed between EZH2 and IGF1R expression with higher levels in U-CLL compared to M-CLL. Accordingly, siRNA-mediated downregulation of either EZH2, MYC or IGF1R and treatment with EZH2 and MYC pharmacological inhibitors in the HG3 CLL cell line induced a significant reduction in PI3K pathway activation. In conclusion, we characterize for the first time EZH2 target genes in CLL revealing a hitherto unknown implication of EZH2 in modulating the PI3K pathway in a non-canonical, PRC2-independent way, with potential therapeutic implications considering that PI3K inhibitors are effective therapeutic agents for CLL.

3-deazaneplanocin A protects against cisplatin-induced renal tubular cell apoptosis and acute kidney injury by restoration of E-cadherin expression

3-deazaneplanocin A (3-DZNeP) has been used as an inhibitor of enhancer of zeste homolog 2 (EZH2). Here, we explore the role and underlying mechanisms action of 3-DZNeP in abrogating cisplatin nephrotoxicity. Exposure of cultured mouse renal proximal tubular epithelial cells (mTECs) to cisplatin resulted in dose and time-dependent cleavage of caspase-3, decrease of cell viability, and increase of histone H3 lysine 27 trimethylation (H3K27me3), whereas expression levels of EZH2, a major methyltransferase of H3K27me3, were not affected. Treatment with 3-DZNeP significantly inhibited cisplatin-induced activation of caspase-3, apoptosis, loss of cell viability but did not alter levels of EZH2 and H3K27me3 in cultured mTECs. 3-DZNeP treatment did not affect activation of extracellular signal-regulated kinase (ERK) 1/2, p38 or c-Jun N-terminal kinases (JNK) 1/2, which contribute to renal epithelial cell death, but caused dose-dependent restoration of E-cadherin in mTECs exposed to cisplatin. Silencing of E-cadherin expression by siRNA abolished the cytoprotective effects of 3-DZNeP. In contrast, 3-DZNeP treatment potentiated the cytotoxic effect of cisplatin in H1299, a non-small cell lung cancer cell line that expresses lower E-cadherin levels. Finally, administration of 3-DZNeP attenuated renal dysfunction, morphological damage, and renal tubular cell death, which was accompanied by E-cadherin preservation, in a mouse model of cisplatin nephrotoxicity. Overall, these data indicate that 3-DZNeP suppresses cisplatin-induced tubular epithelial cell apoptosis and acute kidney injury via an E-cadherin-dependent mechanism, and suggest that combined application of 3-DZNeP with cisplatin would be a novel chemotherapeutic strategy that enhances the anti-tumor effect of cisplatin and reduces its nephrotoxicity.

Long Non-Coding RNAs Guide the Fine-Tuning of Gene Regulation in B-Cell Development and Malignancy

With the introduction of next generation sequencing methods, such as RNA sequencing, it has become apparent that alterations in the non-coding regions of our genome are important in the development of cancer. Particularly interesting is the class of long non-coding RNAs (lncRNAs), including the recently described subclass of circular RNAs (circRNAs), which display tissue- and cell-type specific expression patterns and exert diverse regulatory functions in the cells. B-cells undergo complex and tightly regulated processes in order to develop from antigen naïve cells residing in the bone marrow to the highly diverse and competent effector cells circulating in peripheral blood. These processes include V(D)J recombination, rapid proliferation, somatic hypermutation and clonal selection, posing a risk of malignant transformation at each step. The aim of this review is to provide insight into how lncRNAs including circRNAs, participate in normal B-cell differentiation, and how deregulation of these molecules is involved in the development of B-cell malignancies. We describe the prognostic value and functional significance of specific deregulated lncRNAs in diseases such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, mantle cell lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, Burkitt lymphoma and multiple myeloma, and we provide an overview of the current knowledge on the role of circRNAs in these diseases.

EZH2 enhances the differentiation of fibroblasts into myofibroblasts in idiopathic pulmonary fibrosis

The accumulation of fibroblasts/myofibroblasts in fibrotic foci is one of the characteristics of idiopathic pulmonary fibrosis (IPF). Enhancer of zeste homolog 2 (EZH2) is the catalytic component of a multiprotein complex, polycomb repressive complex 2, which is involved in the trimethylation of histone H3 at lysine 27. In this study, we investigated the role and mechanisms of EZH2 in the differentiation of fibroblasts into myofibroblasts. We found that EZH2 was upregulated in the lungs of patients with IPF and in mice with bleomycin-induced lung fibrosis. The upregulation of EZH2 occurred in myofibroblasts. The inhibition of EZH2 by its inhibitor 3-deazaneplanocin A (DZNep) or an shRNA reduced the TGF-β1-induced differentiation of human lung fibroblasts into myofibroblasts, as demonstrated by the expression of the myofibroblast markers α-smooth muscle actin and fibronectin, and contractility. DZNep inhibited Smad2/3 nuclear translocation without affecting Smad2/3 phosphorylation. DZNep treatment attenuated bleomycin-induced pulmonary fibrosis in mice. We conclude that EZH2 induces the differentiation of fibroblasts to myofibroblasts by enhancing Smad2/3 nuclear translocation.

Efficacy of EZH2 inhibitory drugs in human papillomavirus-positive and human papillomavirus-negative oropharyngeal squamous cell carcinomas

Background

Head and neck squamous cell carcinoma (HNSCC) is the sixth most prevalent cancer worldwide with rates of HPV-positive oropharyngeal squamous cell carcinoma (OPSCC) dramatically increasing. The overexpression of enhancer of zeste homolog 2 (EZH2), a histone methyltransferase responsible for the trimethylation at lysine 27 of histone 3 (H3K27me3), is associated with a poor clinical prognosis and aggressive HPV-positive phenotypes.

Methods

We utilized three EZH2 pathway inhibitors, GSK-343, DZNeP, and EPZ-5687, and tested their efficacy in two HPV-positive and two HPV-negative OPSCC cell lines.

Results

Treatment with GSK-343 decreased H3K27me3 in all cell lines and treatment with DZNeP decreased H3K27me3 in only HPV-negative cell lines as determined by Western blot. Cells treated with EPZ-5687 displayed no appreciable change in H3K27me3. Epigenetic effect on gene expression was measured via ddPCR utilizing 11 target probes. Cells treated with DZNeP showed the most dramatic expressional changes, with decreased EGFR in HPV-positive cell lines and an overall increase in proliferation markers in HPV-negative cell lines. GSK-343-treated cells displayed moderate expressional changes, with CCND1 increased in HPV-positive cell lines and decreased TP53 in HPV-negative SCC-1. EPZ-5687-treated cell lines displayed few expressional changes overall. Only DZNeP-treated cells displayed anti-proliferative characteristics shown in wound-healing assays.

Conclusions

Our findings suggest that EZH2 inhibitors are a viable therapeutic option for the role of epigenetic effect, potentially sensitizing tumors to current chemotherapies or limiting cell differentiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0390-y) contains supplementary material, which is available to authorized users.

LncRNA MALAT1 promotes development of mantle cell lymphoma by associating with EZH2

Background

Mantle cell lymphoma (MCL) is considered an aggressive subtype of non-Hodgkin’s lymphoma with variable treatment responses. There is an urgent need to identify novel markers with prognostic and therapeutic value for MCL. Long non-coding RNAs (lncRNAs) have emerged as key regulators in cancers, including MCL. Metastasis-associated lung adenocarcinoma transcript 1(MALAT1), a lncRNA located at pathognomonic translocation site of t (11; 14) of MCL. MALAT1 is known to be overexpressed in solid tumors and hematologic malignancies. However, the pathological role and clinical relevance of MALAT1 in MCL are not completely understood.

Methods

We quantified MALAT1 in MCL samples (40) and CD19+ B cells by quantitative real time polymerase chain reaction (qRT-PCR) and correlated levels with clinical outcome. We silenced MALAT1 in MCL cell lines and analyzed cells in tumorigenic assays and formation of transcription complexes.

Results

We found that the expression of MALAT1 was elevated in human MCL tumors and cell lines as compared to normal controls, and the elevated levels of MALAT1 correlated with higher MCL international prognostic index (MIPI) and reduced overall survival. MCL with knockdown of MALAT1 showed impaired cell proliferation, facilitated apoptosis and produced fewer clonogenic foci. The increased expression of p21 and p27 upon MALAT1 knockdown was regulated by enhancer of zeste homolog 2 (EZH2). Moreover, decreased phosphorylation of EZH2 at T350 attenuated the binding to MALAT1.

Conclusions

Our findings illuminate the oncogenic role of MALAT1, which may serve as a novel biomarker and as a therapeutic target in MCL.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1100-9) contains supplementary material, which is available to authorized users.

Decoding the DNA Methylome of Mantle Cell Lymphoma in the Light of the Entire B Cell Lineage

We analyzed the in silico purified DNA methylation signatures of 82 mantle cell lymphomas (MCL) in comparison with cell subpopulations spanning the entire B cell lineage. We identified two MCL subgroups, respectively carrying epigenetic imprints of germinal-center-inexperienced and germinal-center-experienced B cells, and we found that DNA methylation profiles during lymphomagenesis are largely influenced by the methylation dynamics in normal B cells. An integrative epigenomic approach revealed 10,504 differentially methylated regions in regulatory elements marked by H3K27ac in MCL primary cases, including a distant enhancer showing de novo looping to the MCL oncogene SOX11. Finally, we observed that the magnitude of DNA methylation changes per case is highly variable and serves as an independent prognostic factor for MCL outcome.

Acquired platinum resistance involves epithelial to mesenchymal transition through ubiquitin ligase FBXO32 dysregulation

To identify the molecules involved in epithelial to mesenchymal transition (EMT) in urothelial carcinoma (UC) after acquisition of platinum resistance, here we examined the changes in global gene expression before and after platinum treatment. Four invasive UC cell lines, T24, 5637, and their corresponding sublines T24PR and 5637PR with acquired platinum resistance, were assessed by microarray, and the ubiquitin E3 ligase FBXO32 was newly identified as a negative regulator of EMT in UC tumors after acquisition of platinum resistance. In vitro and in vivo studies showed an intimate relationship between FBXO32 expression and EMT, demonstrating that FBXO32 dysregulation in T24PR cells results in elevated expression of the mesenchymal molecules SNAIL and vimentin and decreased expression of the epithelial molecule E-cadherin. The association between FBXO32 expression and EMT was further validated using clinical samples. Knockdown of MyoD expression, a specific target of FBXO32 polyubiquitination, revealed upregulation of E-cadherin expression and downregulation of SNAIL and vimentin expression in T24PR cells. Comparative genomic hybridization array analysis demonstrated loss of heterozygosity at 8q24.13 in T24PR cells, which harbors FBXO32. Our findings suggest the importance of the association between EMT and ubiquitin-proteasome regulation when tumors develop acquired platinum resistance.

Aberrant differential expression of EZH1 and EZH2 in Polycomb repressive complex 2 among B- and T/NK-cell neoplasms

The Polycomb repressive complex-2 members (EZH2, EED, SUZ12 and EZH1) are important regulators of haematopoiesis, cell cycle and differentiation. Over-expression of EZH2 has been linked to cancer metastases and poor prognosis. Detailed information on the expression of other members in normal and neoplastic lymphoid tissue remains to be elucidated. Immunohistochemical and immunofluorescent analyses of 156 samples from haematopoietic neoplasms patients and 27 haematopoietic cell lines were used. B-cell neoplasms showed a significant over-expression of EZH2, EED and SUZ12 in the aggressive subtypes compared to the indolent subtypes and normal tissue (p = 0.000-0.046) while expression of EZH1 was decreased in mantle cell lymphoma compared to normal tissue (p = 0.011). T/NK-cell neoplasms also showed significant over-expression of EZH2, EED and SUZ12 (p = 0.000-0.002) and decreased expression of EZH1 (p = 0.001) compared to normal cells. EZH2 and EZH1 have opposite expression patterns both in normal and neoplastic lymphoid tissues as well as an opposite relation to Ki-67. These results were supported by western blotting analyses. Immunofluorescent staining revealed a difference in the intracellular localisation of EZH1 compared to other members. These evidences suggest that EZH2 and EZH1 are important in the counter-balancing mechanisms controlling proliferation/resting of lymphoid cells. The disruption of the balanced EZH2/EZH1 ratio may play important roles in the pathogenesis of lymphomas.

Combined inhibition of EZH2 and histone deacetylases as a potential epigenetic therapy for non-small-cell lung cancer cells

Recent discoveries have revealed that human cancer involves aberrant epigenetic alterations. We and others have previously shown that the histone methyltransferase EZH2, the catalytic subunit of polycomb repressive complex 2 (PRC2), is frequently overexpressed in non‐small‐cell lung cancer (NSCLC) and that an EZH2 inhibitor, 3‐deazaneplanocin A, inhibits the proliferation of NSCLC cells. Transcriptional silencing by EZH2 was recently shown to be required for the activity of histone deacetylases (HDACs) that interact with another PRC2 protein, EED. To develop a more effective epigenetic therapy for NSCLC, we determined the effects of co‐treatment with 3‐deazaneplanocin A and the HDAC inhibitor vorinostat (SAHA) in NSCLC cells. The co‐treatment synergistically suppressed the proliferation of all tested NSCLC cell lines, regardless of their epidermal growth factor receptor (EGFR) status. The synergistic effect was associated with slightly decreased histone H3 lysine 27 trimethylation, modestly increased histone acetylation, and the depletion of EZH2 and other PRC2 proteins. The co‐treatment resulted in an accumulation of p27Kip1, decrease in cyclin A, and increased apoptotic fraction in an additive/synergistic manner. Interestingly, the co‐treatment strongly suppressed EGFR signaling, not only in EGFR‐wild‐type NSCLC cells, but also in EGFR‐mutant cells, mainly through dephosphorylation of EGFR. Furthermore, the co‐treatment suppressed the in vivo tumor growth of EGFR‐mutant, EGFR–tyrosine kinase‐resistant H1975 cells more effectively than did each agent alone, without visible toxicity. These results suggest that the combined pharmacological targeting of EZH2 and HDACs may provide more effective epigenetic therapeutics for NSCLC.

Recent advances in SCF ubiquitin ligase complex: Clinical implications

F-box proteins, which are subunit recruiting modules of SCF (SKP1-Cullin 1-F-box protein) E3 ligase complexes, play critical roles in the development and progression of human malignancies through governing multiple cellular processes including cell proliferation, apoptosis, invasion and metastasis. Moreover, there are emerging studies that lead to the development of F-box proteins inhibitors with promising therapeutic potential. In this article, we describe how F-box proteins including but not restricted to well-established Fbw7, Skp2 and β-TRCP, are involved in tumorigenesis. However, in-depth investigation is required to further explore the mechanism and the physiological contribution of undetermined F-box proteins in carcinogenesis. Lastly, we suggest that targeting F-box proteins could possibly open new avenues for the treatment and prevention of human cancers.

Targeting EZH2 for cancer therapy: progress and perspective

Enhancer of Zeste Homolog 2 (EZH2) is the core component of the polycomb repressive complex 2 (PRC2), possessing the enzymatic activity in generating di/tri-methylated lysine 27 in histone H3. EZH2 has important roles during early development, and its dysregulation is heavily linked to oncogenesis in various tissue types. Accumulating evidences suggest a remarkable therapeutic potential by targeting EZH2 in cancer cells. The first part reviews current strategies to target EZH2 in cancers, and evaluates the available compounds and agents used to disrupt EZH2 functions. Then we provide insight to the future direction of the research on targeting EZH2 in different cancer types. We comprehensively discuss the current understandings of the 1) structure and biological activity of EZH2, 2) its role during the assembling of PRC2 and recruitment of other protein components, 3) the molecular events directing EZH2 to target genomic regions, and 4) post-translational modification at EZH2 protein. The discussion provides the basis to inspire the development of novel strategies to abolish EZH2-related effects in cancer cells.

Epigenetic silencing of tumor suppressor genes: Paradigms, puzzles, and potential

Cancer constitutes a set of diseases with heterogeneous molecular pathologies. However, there are a number of universal aberrations common to all cancers, one of these being the epigenetic silencing of tumor suppressor genes (TSGs). The silencing of TSGs is thought to be an early, driving event in the oncogenic process. With this in consideration, great efforts have been made to develop small molecules aimed at the restoration of TSGs in order to limit tumor cell proliferation and survival. However, the molecular forces that drive the broad epigenetic reprogramming and transcriptional repression of these genes remain ill-defined. Undoubtedly, understanding the molecular underpinnings of transcriptionally silenced TSGs will aid us in our ability to reactivate these key anti-cancer targets. Here, we describe what we consider to be the five most logical molecular mechanisms that may account for this widely observed phenomenon: 1) ablation of transcription factor binding, 2) overexpression of DNA methyltransferases, 3) disruption of CTCF binding, 4) elevation of EZH2 activity, 5) aberrant expression of long non-coding RNAs. The strengths and weaknesses of each proposed mechanism is highlighted, followed by an overview of clinical efforts to target these processes.

Histone methylases as novel drug targets: developing inhibitors of EZH2

Post-translational modifications of histones (so-called epigenetic modifications) play a major role in transcriptional control and normal development, and are tightly regulated. Disruption of their control is a frequent event in disease. In particular, the methylation of lysine 27 on histone H3 (H3K27), induced by the methylase EZH2, emerges as a key control of gene expression and a major regulator of cell physiology. The identification of driver mutations in EZH2 has already led to new prognostic and therapeutic advances, and new classes of potent and specific inhibitors for EZH2 show promising results in preclinical trials. This review examines the roles of histone lysine methylases and demethylases in cells and focuses on the recent knowledge and developments about EZH2.

EZH2 is increased in paediatric T-cell acute lymphoblastic leukemia and is a suitable molecular target in combination treatment approaches

Background

T-cell Acute Lymphoblastic Leukemia (ALL) represents about 10–15 % of pediatric ALL cases. EZH2, one of the components of Polycomb group proteins (PRC2) complex, catalyzes the trimethylation of histone H3 lysine 27 that is associated with transcriptional repression and tumor development.

Methods

We examined the expression levels of PRC2 complex in primary samples of T cells ALL at diagnosis by western blotting and real time PCR. We evaluated the effect of 3-deazaneplanocin-A (DZNep), an EZH2 inhibitor, alone and in combination with Daunoblastine on cell viability, apoptotic death and cell cycle distribution of T cell established Jurkat cell line.

Results

EZH2 was expressed in 75 % samples at different extents mainly with high expression level. SUZ12 was expressed in 60 % samples and EED in all samples, respectively. The Kaplan-Meier analysis shows that T-ALL expressing EZH2 had a lower probability of disease-free survival (DFS) compared to T-ALL negative for EZH2 (23 % vs 100 %) (p = 0.01). The EZH2 inhibitor DZNep used in combination with Daunoblastine was synergistic in inducing growth inhibition and increasing the apoptosis in T-ALL Jurkat cells at 48 and 72 h paralleled by EZH2 decreased expression. Moreover, the combination decreased the activity of Erk-1/2 proliferation enzymes with no effects on Akt survival pathway.

Conclusions

The evaluation of EZH2 expression in pediatric T-ALL can be useful in predict the clinical outcome of the patients and EZH2 can be a useful target to improve the efficacy of conventional chemotherapy in this subset of patients with bad prognosis.

Synergistic activity of BET protein antagonist-based combinations in mantle cell lymphoma cells sensitive or resistant to ibrutinib

Mantle cell lymphoma (MCL) cells exhibit increased B-cell receptor and nuclear factor (NF)-κB activities. The bromodomain and extra-terminal (BET) protein bromodomain 4 is essential for the transcriptional activity of NF-κB. Here, we demonstrate that treatment with the BET protein bromodomain antagonist (BA) JQ1 attenuates MYC and cyclin-dependent kinase (CDK)4/6, inhibits the nuclear RelA levels and the expression of NF-κB target genes, including Bruton tyrosine kinase (BTK) in MCL cells. Although lowering the levels of the antiapoptotic B-cell lymphoma (BCL)2 family proteins, BA treatment induces the proapoptotic protein BIM and exerts dose-dependent lethality against cultured and primary MCL cells. Cotreatment with BA and the BTK inhibitor ibrutinib synergistically induces apoptosis of MCL cells. Compared with each agent alone, cotreatment with BA and ibrutinib markedly improved the median survival of mice engrafted with the MCL cells. BA treatment also induced apoptosis of the in vitro isolated, ibrutinib-resistant MCL cells, which overexpress CDK6, BCL2, Bcl-xL, XIAP, and AKT, but lack ibrutinib resistance-conferring BTK mutation. Cotreatment with BA and panobinostat (pan-histone deacetylase inhibitor) or palbociclib (CDK4/6 inhibitor) or ABT-199 (BCL2 antagonist) synergistically induced apoptosis of the ibrutinib-resistant MCL cells. These findings highlight and support further in vivo evaluation of the efficacy of the BA-based combinations with these agents against MCL, including ibrutinib-resistant MCL.

Targeting of cancer stem cells by inhibitors of DNA and histone methylation

INTRODUCTION

Curative chemotherapy should target cancer stem cells (CSCs). The key characteristics of CSCs are a block in differentiation and an epigenetic signature similar to embryonic stem cells (ESCs). Differentiation by ESCs and CSCs is suppressed by gene silencing through the polycomb repressive complex 2 (PRC2) and/or DNA methylation. PRC2 contains the EZH2 subunit, which catalyzes the trimethylation of histone 3 lysine 27, a gene silencing marker. It is possible to reverse this 'double lock' mechanism using a combination of inhibitors of EZH2 and DNA methylation (5-aza-2'-deoxycytidine), which exhibits remarkable synergistic antineoplastic activity in preclinical studies.

AREAS COVERED

The authors discuss several specific EZH2 inhibitors that have been synthesized with antineoplastic activity. One such inhibitor, EPZ-6438 (E7438), has been shown to be effective against lymphoma in a Phase I study. The indirect EZH2 inhibitor, 3-deazaneplanocin-A (DZNep), also exhibits remarkable anticancer activity due to its inhibition of methionine metabolism.

EXPERT OPINION

Agents that target EZH2 warrant Phase I trials. Due to its positive pharmacodynamics, DZNep merits a high priority for clinical investigation. Agents that show positive results in Phase I studies should be advanced to clinical trials for use in combination with 5-aza-2'-deoxycytidine due to the interesting potential of this epigenetic therapy to target CSCs.

Inhibition of methyltransferases accelerates degradation of cFLIP and sensitizes B-cell lymphoma cells to TRAIL-induced apoptosis

Non-Hodgkin lymphomas (NHLs) are characterized by specific abnormalities that alter cell cycle regulation, DNA damage response, and apoptotic signaling. It is believed that cancer cells are particularly sensitive to cell death induced by tumor necrosis factor α–related apoptosis-inducing ligand (TRAIL). However, many cancer cells show blocked TRAIL signaling due to up-regulated expression of anti-apoptotic factors, such as cFLIP. This hurdle to TRAIL’s tumor cytotoxicity might be overcome by combining TRAIL-based therapy with drugs that reverse blockages of its apoptotic signaling. In this study, we investigated the impact of a pan-methyltransferase inhibitor (3-deazaneplanocin A, or DZNep) on TRAIL-induced apoptosis in aggressive B-cell NHLs: mantle cell, Burkitt, and diffuse large B-cell lymphomas. We characterized TRAIL apoptosis regulation and caspase activation in several NHL-derived cell lines pre-treated with DZNep. We found that DZNep increased cancer cell sensitivity to TRAIL signaling by promoting caspase-8 processing through accelerated cFLIP degradation. No change in cFLIP mRNA level indicated independence of promoter methylation alterations in methyltransferase activity induced by DZNep profoundly affected cFLIP mRNA stability and protein stability. This appears to be in part through increased levels of cFLIP-targeting microRNAs (miR-512-3p and miR-346). However, additional microRNAs and cFLIP-regulating mechanisms appear to be involved in DZNep-mediated enhanced response to extrinsic apoptotic stimuli. The capacity of DZNep to target cFLIP expression on multiple levels underscores DZNep’s potential in TRAIL-based therapies for B-cell NHLs.

Panobinostat reduces hypoxia-induced cisplatin resistance of non-small cell lung carcinoma cells via HIF-1α destabilization

BACKGROUND

Lung cancer is one of the most frequent cancer types and the leading cause of cancer death worldwide. Cisplatin is a widely used chemotherapeutic for non-small cell lung carcinoma (NSCLC), however, its positive effects are diminished under hypoxia. We wanted to determine if co-treatment with cisplatin and histone deacetalyse (HDAC) inhibitor panobinostat can reduce hypoxia-induced cisplatin resistance in NSCLC cells, and to elucidate mechanism involved.

METHODS

Expression status of different HDACS was determined in two cell lines and in tumor tissue from 20 patients. Cells were treated with cisplatin, panobinostat, or with combination of both under normoxic and hypoxic (1% O(2)) conditions. Cell cycle, viability, acetylation of histones, and activation of apoptosis were determined. HIF-1α stability and its interaction with HDAC4 were analyzed.

RESULTS

Most class I and II HDACs were expressed in NSCLC cells and tumor samples. Co-treatment of tumor cells with cisplatin and panobinostat decreased cell viability and increased apoptosis more efficiently than in primary, non-malignant bronchial epithelial cells. Co-treatment induced apoptosis by causing chromatin fragmentation, activation of caspases-3 and 7 and PARP cleavage. Toxic effects were more pronounced under hypoxic conditions. Co-treatment resulted in destabilization and degradation of HIF-1α and HDAC4, a protein responsible for acetylation and de/stabilization of HIF-1α. Direct interaction between HDAC4 and HIF-1α proteins in H23 cells was detected.

CONCLUSIONS

Here we show that hypoxia-induced cisplatin resistance can be overcome by combining cisplatin with panobinostat, a potent HDAC inhibitor. These findings may contribute to the development of a new therapeutic strategy for NSCLC.

The polycomb group protein EZH2 is a novel therapeutic target in tongue cancer

EZH2, a core member of the Polycomb Repressor Complex 2 (PRC2), mediates transcriptional silencing by catalyzing the trimethylation of histone 3 lysine 27 (H3K27), which plays key roles in cancer initiation and progression. Here, we investigated the expression pattern and biological roles of EZH2 in tongue tumorigenesis by loss-of-function assays using small interference RNA and EZH2 inhibitor DZNep. Also we determined the therapeutic efficiency of DZNep against tongue cancer in vivo. We found that aberrantly overexpressed EZH2 was associated with pathological grade, cervical nodes metastasis and Ki-67 expression in tongue cancers. Elevated EZH2 correlated with shorter overall survival and showed significant and independent prognostic importance in patients with tongue cancer. Both genetic and pharmacological depletion of EZH2 inhibited cell proliferation, migration, invasion and colony formation and decreased CD44+ subpopulation probably in part through modulating p16, p21 and E-caherin. Moreover, DZNep enhanced the anticancer effects of 5-Fluorouracil. Furthermore, intratumoral EZH2 inhibition induced by DZNep intraperitoneal administration significantly attenuated tumor growth in a tongue cancer xenograft model. Taken together, our results indicate that EZH2 serves as a key driver with multiple oncogenic functions during tongue tumorigenesis and a new biomarker for tongue cancer diagnosis and prognostic prediction. These findings open up possibilities for therapeutic intervention against EZH2 in tongue cancer.

The specific alteration of histone methylation profiles by DZNep during early zebrafish development

Early embryo development constitutes a unique opportunity to study acquisition of epigenetic marks, including histone methylation. This study investigates the in vivo function and specificity of 3-deazaneplanocin A (DZNep), a promising anti-cancer drug that targets polycomb complex genes. One- to two-cell stage embryos were cultured with DZNep, and subsequently evaluated at the post-mid blastula transition stage for H3K27me3, H3K4me3 and H3K9me3 occupancy and enrichment at promoters using ChIP-chip microarrays. DZNep affected promoter enrichment of H3K27me3 and H3K9me3, whereas H3K4me3 remained stable. Interestingly, DZNep induced a loss of H3K27me3 and H3K9me3 from a substantial number of promoters but did not prevent de novo acquisition of these marks on others, indicating gene-specific targeting of its action. Loss/gain of H3K27me3 on promoters did not result in changes in gene expression levels until 24h post-fertilization. In contrast, genes gaining H3K9me3 displayed strong and constant down-regulation upon DZNep treatment. H3K9me3 enrichment on these gene promoters was observed not only in the proximal area as expected, but also over the transcription start site. Altered H3K9me3 profiles were associated with severe neuronal and cranial phenotypes at day 4-5 post-fertilization. Thus, DZNep was shown to affect enrichment patterns of H3K27me3 and H3K9me3 at promoters in a gene-specific manner.

Deazaneplanocin a is a promising drug to kill multiple myeloma cells in their niche

Tumoral plasma cells has retained stemness features and in particular, a polycomb-silenced gene expression signature. Therefore, epigenetic therapy could be a mean to fight for multiple myeloma (MM), still an incurable pathology. Deazaneplanocin A (DZNep), a S-adenosyl-L-homocysteine hydrolase inhibitor, targets enhancer of zest homolog 2 (EZH2), a component of polycomb repressive complex 2 (PRC2) and is capable to induce the death of cancer cells. We show here that, in some MM cell lines, DZNep induced both caspase-dependent and -independent apoptosis. However, the induction of cell death was not mediated through its effect on EZH2 and the trimethylation on lysine 27 of histone H3 (H3K27me3). DZNep likely acted through non-epigenetic mechanisms in myeloma cells. In vivo, in xenograft models, and in vitro DZNep showed potent antimyeloma activity alone or in combination with bortezomib. These preclinical data let us to envisage new therapeutic strategies for myeloma.

The KDM2B- let-7b -EZH2 axis in myelodysplastic syndromes as a target for combined epigenetic therapy

Both DNA and histone methylation are dysregulated in the myelodysplastic syndromes (MDS). Based on preliminary data we hypothesized that dysregulated interactions of KDM2B, let-7b and EZH2 signals lead to an aberrant epigenetic landscape. Gene expression in CD34+ cells from MDS marrows was analyzed by NanoString miR array and validated by real-time polymerase chain reaction (PCR). The functions of KDM2B, let-7b and EZH2 were characterized in myeloid cell lines and in primary MDS cells. Let-7b levels were significantly higher, and KDM2B and EZH2 expression was lower in primary CD34+ MDS marrow cells (n = 44) than in healthy controls (n = 21; p<0.013, and p<0.0001, respectively). Overexpression of let-7b reduced EZH2 and KDM2B protein levels, and decreased cells in S-phase while increasing G0/G1 cells (p = 0.0005), accompanied by decreased H3K27me3 and cyclin D1. Silencing of KDM2B increased let-7b expression. Treatment with the cyclopentanyl analog of 3-deazaadenosine, DZNep, combined with the DNA hypomethylating agent 5-azacitidine, decreased levels of EZH2, suppressed methylation of di- and tri-methylated H3K27, and increased p16 expression, associated with cell proliferation. Thus, KDM2B, via let-7b/EZH2, promotes transcriptional repression. DZNep bypassed the inhibitory KDM2B/let-7b/EZH2 axis by preventing H3K27 methylation and reducing cell proliferation. DZNep might be able to enhance the therapeutic effects of DNA hypomethylating agents such as 5-azacitidine, currently considered standard therapy for patients with MDS.

The Polycomb group (PcG) protein EZH2 supports the survival of PAX3-FOXO1 alveolar rhabdomyosarcoma by repressing FBXO32 (Atrogin1/MAFbx)

The Polycomb group (PcG) proteins regulate stem cell differentiation via the repression of gene transcription, and their deregulation has been widely implicated in cancer development. The PcG protein Enhancer of Zeste Homolog 2 (EZH2) works as a catalytic subunit of the Polycomb Repressive Complex 2 (PRC2) by methylating lysine 27 on histone H3 (H3K27me3), a hallmark of PRC2-mediated gene repression. In skeletal muscle progenitors, EZH2 prevents an unscheduled differentiation by repressing muscle-specific gene expression and is downregulated during the course of differentiation. In rhabdomyosarcoma (RMS), a pediatric soft-tissue sarcoma thought to arise from myogenic precursors, EZH2 is abnormally expressed and its downregulation in vitro leads to muscle-like differentiation of RMS cells of the embryonal variant. However, the role of EZH2 in the clinically aggressive subgroup of alveolar RMS, characterized by the expression of PAX3-FOXO1 oncoprotein, remains unknown. We show here that EZH2 depletion in these cells leads to programmed cell death. Transcriptional derepression of F-box protein 32 (FBXO32) (Atrogin1/MAFbx), a gene associated with muscle homeostasis, was evidenced in PAX3-FOXO1 RMS cells silenced for EZH2. This phenomenon was associated with reduced EZH2 occupancy and H3K27me3 levels at the FBXO32 promoter. Simultaneous knockdown of FBXO32 and EZH2 in PAX3-FOXO1 RMS cells impaired the pro-apoptotic response, whereas the overexpression of FBXO32 facilitated programmed cell death in EZH2-depleted cells. Pharmacological inhibition of EZH2 by either 3-Deazaneplanocin A or a catalytic EZH2 inhibitor mirrored the phenotypic and molecular effects of EZH2 knockdown in vitro and prevented tumor growth in vivo. Collectively, these results indicate that EZH2 is a key factor in the proliferation and survival of PAX3-FOXO1 alveolar RMS cells working, at least in part, by repressing FBXO32. They also suggest that the reducing activity of EZH2 could represent a novel adjuvant strategy to eradicate high-risk PAX3-FOXO1 alveolar RMS.

Regulation and Role of EZH2 in Cancer

Polycomb repressive complex 2 (PRC2) is the epigenetic regulator that induces histone H3 lysine 27 methylation (H3K27me3) and silences specific gene transcription. Enhancer of zeste homolog 2 (EZH2) is an enzymatic subunit of PRC2, and evidence shows that EZH2 plays an essential role in cancer initiation, development, progression, metastasis, and drug resistance. EZH2 expression is indeed regulated by various oncogenic transcription factors, tumor suppressor miRNAs, and cancer-associated non-coding RNA. EZH2 activity is also controlled by post-translational modifications, which are deregulated in cancer. The canonical role of EZH2 is gene silencing through H3K27me3, but accumulating evidence shows that EZH2 methlyates substrates other than histone and has methylase-independent functions. These non-canonical functions of EZH2 are shown to play a role in cancer progression. In this review, we summarize current information on the regulation and roles of EZH2 in cancer. We also discuss various therapeutic approaches to targeting EZH2.

Highly effective combination of LSD1 (KDM1A) antagonist and pan-histone deacetylase inhibitor against human AML cells

The histone demethylase LSD1 (KDM1A) demethylates mono- and di-methylated (Me2) lysine (K) 4 on histone H3. High LSD1 expression blocks differentiation and confers a poor prognosis in AML. Here, treatment with the novel LSD1 antagonist SP2509 attenuated the binding of LSD1 with the co-repressor CoREST, increased the permissive H3K4Me3 mark on the target gene promoters, and increased the levels of p21, p27 and C/EBPα in cultured AML cells. Additionally, SP2509 treatment or LSD1 shRNA inhibited the colony growth of AML cells. SP2509 also induced morphologic features of differentiation in the cultured and primary AML blasts. SP2509 induced more apoptosis of AML cells expressing mutant NPM1 than MLL fusion oncoproteins. Treatment with SP2509 alone significantly improved the survival of immune-depleted mice following tail-vein infusion and engraftment of cultured or primary human AML cells. Co-treatment with pan-HDAC inhibitor (HDI) panobinostat (PS) and SP2509 was synergistically lethal against cultured and primary AML blasts. Compared to each agent alone, co-treatment with SP2509 and PS significantly improved the survival of the mice engrafted with the human AML cells, without exhibiting any toxicity. Collectively, these findings show that the combination of LSD1 antagonist and pan-HDI is a promising therapy warranting further testing against AML.

FAS-antisense 1 lncRNA and production of soluble versus membrane Fas in B-cell lymphoma

Impaired Fas-mediated apoptosis is associated with poor clinical outcomes and cancer chemoresistance. Soluble Fas receptor (sFas), produced by skipping of exon 6, inhibits apoptosis by sequestering Fas ligand. Serum sFas is associated with poor prognosis of non-Hodgkin's lymphomas. We found that the alternative splicing of Fas in lymphomas is tightly regulated by a long-noncoding RNA corresponding to an antisense transcript of Fas (FAS-AS1). Levels of FAS-AS1 correlate inversely with production of sFas, and FAS-AS1 binding to the RBM5 inhibits RBM5-mediated exon 6 skipping. EZH2, often mutated or overexpressed in lymphomas, hyper-methylates the FAS-AS1 promoter and represses the FAS-AS1 expression. EZH2-mediated repression of FAS-AS1 promoter can be released by DZNeP (3-Deazaneplanocin A) or overcome by ectopic expression of FAS-AS1, both of which increase levels of FAS-AS1 and correspondingly decrease expression of sFas. Treatment with Bruton's tyrosine kinase inhibitor or EZH2 knockdown decreases the levels of EZH2, RBM5 and sFas, thereby enhancing Fas-mediated apoptosis. This is the first report showing functional regulation of Fas repression by its antisense RNA. Our results reveal new therapeutic targets in lymphomas and provide a rationale for the use of EZH2 inhibitors or ibrutinib in combination with chemotherapeutic agents that recruit Fas for effective cell killing.

3-Deazaneplanocin A (DZNep), an inhibitor of S-adenosylmethionine-dependent methyltransferase, promotes erythroid differentiation

EZH2, a core component of polycomb repressive complex 2 (PRC2), plays a role in transcriptional repression through histone H3 Lys-27 trimethylation and is involved in various biological processes, including hematopoiesis. It is well known that 3-deazaneplanocin A (DZNep), an inhibitor of S-adenosylmethionine-dependent methyltransferase that targets the degradation of EZH2, preferentially induces apoptosis in various hematological malignancies, suggesting that EZH2 may be a new target for epigenetic treatment. Because PRC2 participates in epigenetic silencing of a subset of GATA-1 target genes during erythroid differentiation, inhibition of EZH2 may influence erythropoiesis. To explore this possibility, we evaluated the impact of DZNep on erythropoiesis. DZNep treatment significantly induced erythroid differentiation of K562 cells, as assessed by benzidine staining and quantitative RT-PCR analysis for representative erythroid-related genes, including globins. When we evaluated the effects of DZNep in human primary erythroblasts derived from cord blood CD34-positive cells, the treatment significantly induced erythroid-related genes, as observed in K562 cells, suggesting that DZNep induces erythroid differentiation. Unexpectedly, siRNA-mediated EZH2 knockdown had no significant effect on the expression of erythroid-related genes. Transcriptional profiling of DZNep-treated K562 cells revealed marked up-regulation of SLC4A1 and EPB42, previously reported as representative targets of the transcriptional corepressor ETO2. In addition, DZNep treatment reduced the protein level of ETO2. These data suggest that erythroid differentiation by DZNep may not be directly related to EZH2 inhibition but may be partly associated with reduced protein level of hematopoietic corepressor ETO2. These data provide a better understanding of the mechanism of action of DZNep, which may be exploited for therapeutic applications for hematological diseases, including anemia.

Combating the epigenome: epigenetic drugs against non-Hodgkin's lymphoma

Non-Hodgkin's lymphomas (NHLs) comprise a large and diverse group of neoplasms of lymphocyte origin with heterogeneous molecular features and clinical manifestations. Current therapies are based on standard chemotherapy, immunotherapy, radiation or stem cell transplantation. The discovery of recurrent mutations in epigenetic enzymes, such as chromatin modifiers and DNA methyltransferases, has provided researchers with a rationale to develop novel inhibitors targeting these enzymes. Several clinical and preclinical studies have demonstrated the efficacy of epigenetic drugs in NHL therapy and a few specific inhibitors have already been approved for clinical use. Here, we provide an overview of current NHL classification and a review of the present literature describing epigenetic alterations in NHL, including a summary of different epigenetic drugs, and their use in preclinical and clinical studies.

A key role for EZH2 in epigenetic silencing of HOX genes in mantle cell lymphoma

The chromatin modifier EZH2 is overexpressed and associated with inferior outcome in mantle cell lymphoma (MCL). Recently, we demonstrated preferential DNA methylation of HOX genes in MCL compared with chronic lymphocytic leukemia (CLL), despite these genes not being expressed in either entity. Since EZH2 has been shown to regulate HOX gene expression, to gain further insight into its possible role in differential silencing of HOX genes in MCL vs. CLL, we performed detailed epigenetic characterization using representative cell lines and primary samples. We observed significant overexpression of EZH2 in MCL vs. CLL. Chromatin immune precipitation (ChIP) assays revealed that EZH2 catalyzed repressive H3 lysine 27 trimethylation (H3K27me3), which was sufficient to silence HOX genes in CLL, whereas in MCL H3K27me3 is accompanied by DNA methylation for a more stable repression. More importantly, hypermethylation of the HOX genes in MCL resulted from EZH2 overexpression and subsequent recruitment of the DNA methylation machinery onto HOX gene promoters. The importance of EZH2 upregulation in this process was further underscored by siRNA transfection and EZH2 inhibitor experiments. Altogether, these observations implicate EZH2 in the long-term silencing of HOX genes in MCL, and allude to its potential as a therapeutic target with clinical impact.

Rhabdoid tumors: clinical approaches and molecular targets for innovative therapy

Rhabdoid tumors are rare but highly aggressive tumors with a predilection for infants and young children. The majority of these tumors harbor biallelic mutations in SMARCB1/INI1/hSNF5. Rather rare cases with mutations in other SWI/SNF core members such as BRG1 are on record. Rhabdoid tumors have only recently been registered and treated according to specifically designed treatment recommendations and in the framework of clinical trials. Within the last decade, prognosis has improved significantly but at least 50% of patients still relapse and subsequently almost inevitably succumb to their disease. This review summarizes past and current clinical approaches and presents an overview of the rationales for targeted therapy with potential for future clinical treatment trials for rhabdoid tumors.

DZNep, inhibitor of S-adenosylhomocysteine hydrolase, down-regulates expression of SETDB1 H3K9me3 HMTase in human lung cancer cells

3-Deazaneplanocin A (DZNep), an epigenetic anticancer drug, leads to the indirect suppression of S-adenosyl methionine-dependent cellular methylations by inhibiting S-adenosyl homocystein (AdoHcy) hydrolase. Although it is well known that DZNep targets the degradation of EZH2 protein, H3K27me3 HMTase, there are still uncertainties about the regulation of other types of HMTases during cell death. In this study, we describe that SETDB1 gene expression was regulated by DZNep treatment in human lung cancer cells. We confirm that DZNep induced growth inhibition and increased the dead cell population of lung cancer cells. DZNep treatment affected histone methylations, including H3K27me3 and H3K9me3, but not H3K4me3. Reduced levels of H3K27me3 and H3K9me3 were related with the decreased EZH2 and SETDB1 proteins. Real time PCR analysis showed that SETDB1 gene expression was decreased by DZNep treatment, but no effect was observed for EZH2 gene expression. We cloned the promoter region of SETDB1 and SUV39H1 genes, and performed luciferase assays. The promoter activity of SETDB1 gene was down regulated by DZNep treatment, whereas no effect on SUV39H1 promoter activity was observed. In conclusion, we suggest that DZNep regulates not only on H3K27me3 HMTase EZH2, but also H3K9 HMTase SETDB1 gene expression at the transcription level, implicating that the mechanism of action of DZNep targets multiple HMTases during the death of lung cancer cells.