Prognostic significance of the therapeutic targets histone deacetylase 1, 2, 6 and acetylated histone H4 in cutaneous T-cell lymphoma

HDAC2 Is Involved in the Regulation of BRN3A in Melanocytes and Melanoma

The neural crest transcription factor BRN3A is essential for the proliferation and survival of melanoma cells. It is frequently expressed in melanoma but not in normal melanocytes or benign nevi. The mechanisms underlying the aberrant expression of BRN3A are unknown. Here, we investigated the epigenetic regulation of BRN3A in melanocytes and melanoma cell lines treated with DNA methyltransferase (DNMT), histone acetyltransferase (HAT), and histone deacetylase (HDAC) inhibitors. DNMT and HAT inhibition did not significantly alter BRN3A expression levels, whereas panHDAC inhibition by trichostatin A led to increased expression. Treatment with the isoform-specific HDAC inhibitor mocetinostat, but not with PCI-34051, also increased BRN3A expression levels, suggesting that class I HDACs HDAC1, HDAC2, and HDAC3, and class IV HDAC11, were involved in the regulation of BRN3A expression. Transient silencing of HDACs 1, 2, 3, and 11 by siRNAs revealed that, specifically, HDAC2 inhibition was able to increase BRN3A expression. ChIP-Seq analysis uncovered that HDAC2 inhibition specifically increased H3K27ac levels at a distal enhancer region of the BRN3A gene. Altogether, our data suggest that HDAC2 is a key epigenetic regulator of BRN3A in melanocytes and melanoma cells. These results highlight the importance of epigenetic mechanisms in regulating melanoma oncogenes.

Epigenetics in the Pathogenesis and Treatment of Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphomas (CTCLs) comprise a group of heterogeneous diseases involving malignant T cells. The pathogenesis and etiology of CTCL are still unclear, although a large number of genetic and epidemiological studies on CTCL have been conducted. Most CTCLs have an indolent course, making early diagnosis difficult. Once large-cell transformation occurs, CTCL progresses to more aggressive types, resulting in an overall survival of less than five years. Epigenetic drugs, which have shown certain curative effects, have been selected as third-line drugs in patients with relapsing and refractory CTCL. Many studies have also identified epigenetic biomarkers from tissues and peripheral blood of patients with CTCL and suggested that epigenetic changes play a role in malignant transformation and histone deacetylase inhibitor (HDACi) resistance in CTCL. Single-cell sequencing has been applied in CTCL studies, revealing heterogeneity in CTCL malignant T cells. The mechanisms of HDACi resistance have also been described, further facilitating the discovery of novel HDACi targets. Despite the heterogeneity of CTCL disease and its obscure pathogenesis, more epigenetic abnormalities have been gradually discovered recently, which not only enables us to understand CTCL disease further but also improves our understanding of the specific role of epigenetics in the pathogenesis and treatment. In this review, we discuss the recent discoveries concerning the pathological roles of epigenetics and epigenetic therapy in CTCL.

Citarinostat and Momelotinib co-target HDAC6 and JAK2/STAT3 in lymphoid malignant cell lines: a potential new therapeutic combination

Histone deacetylase (HDAC) inhibitors represent an encouraging class of antitumor drugs. HDAC inhibitors induce a series of molecular and biological responses and minimal toxicity to normal cells. Citarinostat (Acy-241) is a second generation, orally administered, HDAC6-selective inhibitor. Momelotinib (CYT387) is an orally administered inhibitor of Janus kinase/signal transducer of transcription-3 (JAK/STAT3) signaling. Momelotinib showed efficacy in patients with myelofibrosis. We hypothesized that both HDAC and JAK/STAT pathways were important in lymphoproliferative disorders, and that inhibiting JAK/STAT3 and HDAC simultaneously might enhance the efficacy of momelotinib and citarinostat without increasing toxicity. Accordingly, we tested the citarinostat + momelotinib combination in lymphoid cell lines. Citarinostat + momelotinib showed strong cytotoxicity; it significantly reduced mitochondrial membrane potential, down-regulated Bcl-2 and Bcl-xL, and activated caspases 9 and 3. Caspase-8 was upregulated in only two lymphoid cell lines, which indicated activation of the extrinsic apoptotic pathway. We identified a lymphoid cell line that was only slightly sensitive to the combination treatment. We knocked down thioredoxin expression by transfecting with small interfering RNA that targeted thioredoxin. This knockdown increased cell sensitivity to the combination-induced cell death. The combination treatment reduced Bcl-2 expression, activated caspase 3, and significantly inhibited cell viability and clonogenic survival.

Epigenetic alterations and advancement of treatment in peripheral T-cell lymphoma

Peripheral T-cell lymphoma (PTCL) is a rare and heterogeneous group of clinically aggressive diseases associated with poor prognosis. Except for ALK + anaplastic large-cell lymphoma (ALCL), most peripheral T-cell lymphomas are highly malignant and have an aggressive disease course and poor clinical outcomes, with a poor remission rate and frequent relapse after first-line treatment. Aberrant epigenetic alterations play an important role in the pathogenesis and development of specific types of peripheral T-cell lymphoma, including the regulation of the expression of genes and signal transduction. The most common epigenetic alterations are DNA methylation and histone modification. Histone modification alters the level of gene expression by regulating the acetylation status of lysine residues on the promoter surrounding histones, often leading to the silencing of tumour suppressor genes or the overexpression of proto-oncogenes in lymphoma. DNA methylation refers to CpG islands, generally leading to tumour suppressor gene transcriptional silencing. Genetic studies have also shown that some recurrent mutations in genes involved in the epigenetic machinery, including TET2, IDH2-R172, DNMT3A, RHOA, CD28, IDH2, TET2, MLL2, KMT2A, KDM6A, CREBBP, and EP300, have been observed in cases of PTCL. The aberrant expression of miRNAs has also gradually become a diagnostic biomarker. These provide a reasonable molecular mechanism for epigenetic modifying drugs in the treatment of PTCL. As epigenetic drugs implicated in lymphoma have been continually reported in recent years, many new ideas for the diagnosis, treatment, and prognosis of PTCL originate from epigenetics in recent years. Novel epigenetic-targeted drugs have shown good tolerance and therapeutic effects in the treatment of peripheral T-cell lymphoma as monotherapy or combination therapy. NCCN Clinical Practice Guidelines also recommended epigenetic drugs for PTCL subtypes as second-line therapy. Epigenetic mechanisms provide new directions and therapeutic strategies for the research and treatment of peripheral T-cell lymphoma. Therefore, this paper mainly reviews the epigenetic changes in the pathogenesis of peripheral T-cell lymphoma and the advancement of epigenetic-targeted drugs in the treatment of peripheral T-cell lymphoma (PTCL).

Epigenetic Aberrations in Multiple Myeloma

Simple Summary

Multiple Myeloma (MM) is a blood cancer characterized by an uncontrolled growth of cells named plasma cells, within the bone marrow. Patients with MM may present with anemia, bone lesions and kidney impairment. Several studies have been performed in order to provide an explanation to how this tumor may develop. Among them, the so called “epigenetic modifications” certainly represent important players that have been shown to support MM development and disease progression. The present article aims to summarize the current knowledge in the specific are of “epigenetics” in MM.

Abstract

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by proliferation of clonal plasma cells within the bone marrow. Several advances in defining key processes responsible for MM pathogenesis and disease progression have been made; and dysregulation of epigenetics, including DNA methylation and histone modification, has emerged as a crucial regulator of MM pathogenesis. In the present review article, we will focus on the role of epigenetic modifications within the specific context of MM.

Impact of HDAC Inhibitors on Protein Quality Control Systems: Consequences for Precision Medicine in Malignant Disease

Lysine acetylation is one of the major posttranslational modifications (PTM) in human cells and thus needs to be tightly regulated by the writers of this process, the histone acetyl transferases (HAT), and the erasers, the histone deacetylases (HDAC). Acetylation plays a crucial role in cell signaling, cell cycle control and in epigenetic regulation of gene expression. Bromodomain (BRD)-containing proteins are readers of the acetylation mark, enabling them to transduce the modification signal. HDAC inhibitors (HDACi) have been proven to be efficient in hematologic malignancies with four of them being approved by the FDA. However, the mechanisms by which HDACi exert their cytotoxicity are only partly resolved. It is likely that HDACi alter the acetylation pattern of cytoplasmic proteins, contributing to their anti-cancer potential. Recently, it has been demonstrated that various protein quality control (PQC) systems are involved in recognizing the altered acetylation pattern upon HDACi treatment. In particular, molecular chaperones, the ubiquitin proteasome system (UPS) and autophagy are able to sense the structurally changed proteins, providing additional targets. Recent clinical studies of novel HDACi have proven that proteins of the UPS may serve as biomarkers for stratifying patient groups under HDACi regimes. In addition, members of the PQC systems have been shown to modify the epigenetic readout of HDACi treated cells and alter proteostasis in the nucleus, thus contributing to changing gene expression profiles. Bromodomain (BRD)-containing proteins seem to play a potent role in transducing the signaling process initiating apoptosis, and many clinical trials are under way to test BRD inhibitors. Finally, it has been demonstrated that HDACi treatment leads to protein misfolding and aggregation, which may explain the effect of panobinostat, the latest FDA approved HDACi, in combination with the proteasome inhibitor bortezomib in multiple myeloma. Therefore, proteins of these PQC systems provide valuable targets for precision medicine in cancer. In this review, we give an overview of the impact of HDACi treatment on PQC systems and their implications for malignant disease. We exemplify the development of novel HDACi and how affected proteins belonging to PQC can be used to determine molecular signatures and utilized in precision medicine.

Selective inhibition of HDAC6 sensitizes cutaneous T-cell lymphoma to PI3K inhibitors

Histone deacetylase (HDAC) inhibitors, approved for the treatment of cutaneous T-cell lymphoma (CTCL), are non-selective agents associated with an unsatisfactory response and considerable side-effects. Targeting single HDAC isoforms is considered to provide novel therapeutic options. HDAC6 is overexpressed in primary samples from patients with CTCL and preclinical studies using transgenic mice that spontaneously develop a CTCL-like disease, have suggested that combinations including HDAC6 inhibitors may be successful in the treatment of CTCL. PI3K inhibition is currently being tested in clinical trials for CTCL with promising results. Since HDAC6 is known to diminish the activity of Akt via its deacetylation, the aim of the present study was to evaluate the therapeutic potential of selective HDAC6 inhibitors in combination with PI3K inhibitors in CTCL. Through the genetic and pharmacological inhibition of HDAC6, it was demonstrated that combining HDAC6 with PI3K inhibition may be an attractive therapeutic option for patients with CTCL.

EGFR-vIII downregulated H2AZK4/7AC though the PI3K/AKT-HDAC2 axis to regulate cell cycle progression

BACKGROUND

The EGFR-vIII mutation is the most common malignant event in GBM. Epigenetic reprogramming in EGFR-activated GBM has recently been suggested to downregulate the expression of tumour suppressor genes. Histone acetylation is important for chromatin structure and function. However, the role and biological function of H2AZK4/7AC in tumours have not yet been clarified.

RESULTS

In our study, we found that EGFR-vIII negatively regulated H2AZK4/7AC expression though the PI3K/AKT-HDAC2 axis. Because HDAC1 and HDAC2 are highly homologous enzymes that usually form multi-protein complexes for transcriptional regulation and epigenetic landscaping, we simultaneously knocked out HDAC1 and HDAC2 and found that H2AZK4/7AC and H3K27AC were upregulated, which partially released EGFR-vIII-mediated inhibition of USP11, negative regulator of cell cycle. In addition, we demonstrated in vitro and in vivo that FK228 induced G1/S transition arrest in GBM with EGFR-vIII mutation. FK228 could enhance anti-tumour activity by upregulating expression of the tumour suppressor USP11 in GBM cells.

CONCLUSIONS

EGFR-vIII mutation downregulates H2AZK4/7AC and H3K27AC, inhibiting USP11 expression though the PI3K/AKT-HDAC1/2 axis. FK228 is an effective and promising treatment for GBM with EGFR-vIII mutation.

Clinical significance of enhancer of zeste homolog 2 and histone deacetylases 1 and 2 expression in peripheral T-cell lymphoma

Epigenetics serve a key role in peripheral T cell lymphoma (PTCL). The purpose of the present study was to investigate the clinical significance of enhancer of zeste homolog 2 (EZH2) and histone deacetylase 1 and 2 (HDAC1/2) expression in PTCL. A total of 82 patients were enrolled in the present study, including 43 with PTCL not otherwise specified (PTCL-NOS), 10 with angioimmunoblastic T-cell lymphoma (AITL), 14 with natural killer/T-cell lymphoma (NK/TCL) and 15 with anaplastic large cell lymphoma (ALCL). EZH2 and HDAC1/2 expression was detected by immunohistochemistry and any correlations between them were evaluated. Additionally, any correlations between EZH2 or HDAC1/2 expression and a number of clinicopathological characteristics were analyzed, and survival curves were created. Results revealed that 55.8% of patients with PTCL-NOS, 57.1% of patients with NK/TCL, 86.7% of patients ALCL and 50% of patients with AITL highly expressed HDAC1. Furthermore, 58.1% of patients with PTCL-NOS, 57.1% of patients with NK/TCL, 53.3% of patients with ALCL and 60% of patients with AITL highly expressed HDAC2. Additionally, 67.5% of patients with PTCL-NOS, 50% of patients with NK/TCL, 73.3% of patients with ALCL and 60% of patients with AITL highly expressed EZH2. EZH2 expression was significantly correlated with the presence of B symptoms, elevated LDH and elevated β2 microglobulin (B2M; P<0.05), and HDAC2 expression was significantly correlated with sex, advanced clinical stages, high international prognostic index scores and elevated B2M levels (P<0.05) in all the patients with PTCL. However, different subtypes of PTCL are correlated with different clinical characteristics. Patients with PTCL highly expressing EZH2 or HDAC2 exhibit a poorer overall survival rate. In conclusion, EZH2 and HDAC1/2 were frequently upregulated in patients with PTCL, and the patients with a higher EZH2 and HDAC2 expression usually exhibited a poorer survival rate. Therefore, EZH2 and HDAC2 may be prognostic markers in patients with PTCL, particularly in those with PTCL-NOS.

Elucidating the mechanism of action of domatinostat (4SC-202) in cutaneous T cell lymphoma cells

Background

Targeting epigenetic modifiers is effective in cutaneous T cell lymphoma (CTCL). However, there is a need for further improvement of this therapeutic approach. Here, we compared the mode of action of romidepsin (FK228), an established class I histone deacetylase inhibitor, and domatinostat (4SC-202), a novel inhibitor of class I HDACs, which has been reported to also target the lysine-specific histone demethylase 1A (LSD1).

Methods

We performed MTS assays and flow cytometric analyses of propidium iodide or annexin V-stained cells to assess drug impact on cellular proliferation, cell cycle distribution, and survival. Histone acetylation and methylation as well as caspase activation was analyzed by immunoblot. Gene expression analysis was performed using NanosString technology. Knockdown and knockout of LSD1 was achieved with shRNA and CRISPR/Cas9, respectively, while the CRISPR/Cas9 synergistic activation mediator system was used to induce expression of endogenous HDACs and LSD1. Furthermore, time-lapse fluorescence microscopy and an in vitro tubulin polymerization assay were applied.

Results

While FK228 as well as 4SC-202 potently induced cell death in six different CTCL cell lines, only in the case of 4SC-202 death was preceded by an accumulation of cells in the G2/M phase of the cell cycle. Surprisingly, apoptosis and accumulation of cells with double DNA content occurred already at 4SC-202 concentrations hardly affecting histone acetylation and methylation, and provoking significantly less changes in gene expression compared to biologically equivalent doses of FK228. Indeed, we provide evidence that the 4SC-202-induced G2/M arrest in CTCL cells is independent of de novo transcription. Furthermore, neither enforced expression of HDAC1 nor knockdown or knockout of LSD1 affected the 4SC-202-induced effects. Since time-lapse microscopy revealed that 4SC-202 could affect mitotic spindle formation, we performed an in vitro tubulin polymerization assay revealing that 4SC-202 can directly inhibit microtubule formation.

Conclusions

We demonstrate that 4SC-202, a drug currently tested in clinical trials, effectively inhibits growth of CTCL cells. The anti-cancer cell activity of 4SC-202 is however not limited to LSD1-inhibition, modulation of histone modifications, and consecutive alteration of gene expression. Indeed, the compound is also a potent microtubule-destabilizing agent.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0719-4) contains supplementary material, which is available to authorized users.

Role of Natural Products in Modulating Histone Deacetylases in Cancer

Histone deacetylases (HDACs) are enzymes that can control transcription by modifying chromatin conformation, molecular interactions between the DNA and the proteins as well as the histone tail, through the catalysis of the acetyl functional sites removal of proteins from the lysine residues. Also, HDACs have been implicated in the post transcriptional process through the regulation of the proteins acetylation, and it has been found that HDAC inhibitors (HDACi) constitute a promising class of pharmacological drugs to treat various chronic diseases, including cancer. Indeed, it has been demonstrated that in several cancers, elevated HDAC enzyme activities may be associated with aberrant proliferation, survival and metastasis. Hence, the discovery and development of novel HDACi from natural products, which are known to affect the activation of various oncogenic molecules, has attracted significant attention over the last decade. This review will briefly emphasize the potential of natural products in modifying HDAC activity and thereby attenuating initiation, progression and promotion of tumors.

The Therapeutic Strategy of HDAC6 Inhibitors in Lymphoproliferative Disease

Histone deacetylases (HDACs) are master regulators of chromatin remodeling, acting as epigenetic regulators of gene expression. In the last decade, inhibition of HDACs has become a target for specific epigenetic modifications related to cancer development. Overexpression of HDAC has been observed in several hematologic malignancies. Therefore, the observation that HDACs might play a role in various hematologic malignancies has brought to the development of HDAC inhibitors as potential antitumor agents. Recently, the class IIb, HDAC6, has emerged as one potential selective HDACi. This isoenzyme represents an important pharmacological target for selective inhibition. Its selectivity may reduce the toxicity related to the off-target effects of pan-HDAC inhibitors. HDAC6 has also been studied in cancer especially for its ability to coordinate a variety of cellular processes that are important for cancer pathogenesis. HDAC6 has been reported to be overexpressed in lymphoid cells and its inhibition has demonstrated activity in preclinical and clinical study of lymphoproliferative disease. Various studies of HDAC6 inhibitors alone and in combination with other agents provide strong scientific rationale for the evaluation of these new agents in the clinical setting of hematological malignancies. In this review, we describe the HDACs, their inhibitors, and the recent advances of HDAC6 inhibitors, their mechanisms of action and role in lymphoproliferative disorders.

Ricolinostat (ACY-1215) suppresses proliferation and promotes apoptosis in esophageal squamous cell carcinoma via miR-30d/PI3K/AKT/mTOR and ERK pathways

Ricolinostat (ACY-1215), a first-in-class selective HDAC6 inhibitor, exhibits antitumor effects alone or in combination with other drugs in various cancers. However, its efficacy in esophageal cancer remains unclear. In this study, we found that the high expression of HDAC6 was associated with poor prognosis in esophageal squamous cell carcinoma (ESCC) tissues. Then, we identified that ACY-1215 significantly inhibited cellular proliferation in ESCC, and caused G2/M phase arrest and apoptosis. We further demonstrated that ACY-1215 treatment reduced the expression of PI3K, P-AKT, P-mTOR, and P-ERK1/2 and increased that of Ac-H3K9 and Ac-H4K8. In addition, using miRNA microarray and bioinformatics analysis, we detected that ACY-1215 promoted miR-30d expression, and PI3K regulatory subunit 2 (PIK3R2) was a direct target of miR-30d. Anti-miR-30d partially rescued the G2/M phase arrest and apoptosis caused by ACY-1215 treatment. The reductions in PI3K, P-AKT, and P-mTOR expression were also partially reversed by miR-30d inhibitor. Furthermore, the effects of ACY-1215 inhibited ESCC proliferation were validated in a mouse xenograft model in vivo. In conclusion, our study showed that ACY-1215 suppressed proliferation and promoted apoptosis in ESCC via miR-30d/PI3K/AKT/mTOR and ERK pathways and that ACY-1215 may be a promising antitumor agent in ESCC.

Overexpressed HDAC4 is associated with poor survival and promotes tumor progression in esophageal carcinoma

Histone deacetylases (HDACs) mediate histone deacetylation, leading to transcriptional repression, which is involved in many diseases, including age-related tissue degeneration, heart failure and cancer. In this study, we were aimed to investigate the expression, clinical significance and biological function of HDAC4 in esophageal carcinoma (EC). We found that HDAC4 mRNA and protein are overexpressed in esophageal squamous cell carcinoma (ESCC) tissues and cell lines. HDAC4 overexpression is associated with higher tumor grade, advanced clinical stage and poor survival. Mechanistically, HDAC4 promotes proliferation and G1/S cell cycle progression in EC cells by inhibiting cyclin-dependent kinase (CDK) inhibitors p21 and p27 and up-regulating CDK2/4 and CDK-dependent Rb phosphorylation. HDAC4 also enhances ESCC cell migration. Furthermore, HDAC4 positively regulates epithelial-mesenchymal transition (EMT) by increasing the expression of Vimentin and decreasing the expression of E-Cadherin/α-Catenin. Together, our study shows that HDAC4 overexpression is important for the oncogenesis of EC, which may serve as a useful prognostic biomarker and therapeutic target for this malignancy.

Increased histone deacetylase 6 expression serves as a favorable prognostic factor for diffuse large B-cell lymphoma

Objective

This study aims to investigate ectopic expression of histone deacetylase 6 (HDAC6) in diffuse large B-cell lymphoma (DLBCL).

Methods

This study analyzed patients with DLBCL (n=132) and reactive lymph node hyperplasia (n=32) diagnosed in our hospital from December 2007 to May 2016. Correlation between HDAC6 expression and clinical pathologic features was analyzed by χ² test. The significant differences between the 5-year overall survival (OS) or progression-free survival (PFS) and high HDAC6 expression as well as DLBCL clinic-pathological features including age, International Prognostic Index (IPI) score, Eastern Cooperative Oncology Group score, lactate dehydrogenase (LDH), and germinal center B-cell-like were assessed by univariate and multivariate analyses.

Results

HDAC6 high-expression percentage in DLBCL was significantly higher than that in the control group. The proportion of IPI score of 0–2, 5-year OS, and PFS in the high-expression group, which had lower percentage of patients with increased LDH and β₂-microglobulin, were significantly higher than those in the low-expression group. Moreover, HDAC6 mRNA expression in HDAC6 protein low expression was markedly lower than that in protein high expression. The multivariate analysis demonstrated that HDAC6 high expression was an independent prognostic factor for patients with DLBCL.

Conclusion

HDAC6 high expression might be a prognostic factor for DLBCL.

Ricolinostat, a selective HDAC6 inhibitor, shows anti-lymphoma cell activity alone and in combination with bendamustine

Histone deacetylase inhibitors (HDACis) have emerged as a new class of anticancer agents, targeting the biological process including cell cycle and apoptosis. We investigated and explained the anticancer effects of an HDAC6 inhibitor, ricolinostat alone and in combination with bendamustine in lymphoma cell lines. Cell viability was measured by MTT assay. Apoptosis, reactive oxygen species (ROS) generation, Bcl-2 protein expression, cell cycle progression and tubuline expression were determined by flow cytometry. The effects of ricolinostat alone and in combination on the caspases, PI3K/Akt, Bcl-2 pathways, ER stress and UPR were assessed by immunoblotting. Ricolinostat shows anti lymphoma activity when used as single agent and its capability to induce apoptosis is synergistically potentiated by the bendamustine in lymphoma cell lines. Drug combination reduced the proportion of cells in the G0/G1 and S phases and caused an increase of "sub-G0/G1" peak. The synergistic effect accompanied with the increased ROS, activation of caspase-8, -9, and -3, the cleavage of PARP and modulated by Bcl-2 proteins family. In addition, the exposure of ricolinostat induced the acetylation level of α-tubulin, the extend of which was not further modified by bendamustine. Finally, the apoptosis effect of ricolinostat/bendamustine may be mediated by a corresponding effect on microtubule stabilization. Our data suggest that ricolinostat in combination with bendamustine may be a novel combination with potential for use as an antitumor agent in lymphoma.

HDACs and HDAC Inhibitors in Cancer Development and Therapy

Over the last several decades, it has become clear that epigenetic abnormalities may be one of the hallmarks of cancer. Posttranslational modifications of histones, for example, may play a crucial role in cancer development and progression by modulating gene transcription, chromatin remodeling, and nuclear architecture. Histone acetylation, a well-studied posttranslational histone modification, is controlled by the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). By removing acetyl groups, HDACs reverse chromatin acetylation and alter transcription of oncogenes and tumor suppressor genes. In addition, HDACs deacetylate numerous nonhistone cellular substrates that govern a wide array of biological processes including cancer initiation and progression. This review will discuss the role of HDACs in cancer and the therapeutic potential of HDAC inhibitors (HDACi) as emerging drugs in cancer treatment.

Mechanism, Consequences, and Therapeutic Targeting of Abnormal IL15 Signaling in Cutaneous T-cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is the most common type of primary cutaneous lymphoma. Here, we report that patients with CTCL show increased IL15 in a clinical stage-dependent manner. Mechanistically, we show that ZEB1 is a transcriptional repressor of IL15 in T cells and that hypermethylation of the ZEB1 binding region within the IL15 promoter, as seen in patients with CTCL, prevents ZEB1 binding and causes increased transcription of IL15 Using a transgenic mouse model of IL15, we provide evidence that overexpression of IL15 induces a spontaneous CTCL that mimics the human neoplasm. Excessive autocrine production of IL15 in T cells inhibits an HDAC1-mediated negative autoregulatory loop, resulting in the upregulation of HDAC1 and HDAC6 and transcriptional induction of the onco-miR-21. Interruption of IL15 downstream signaling with isotype-specific HDAC inhibitors halts (HDAC1) or significantly delays (HDAC6) the progression of CTCL in vivo and provides preclinical evidence supporting a hierarchical model of oncogenic signaling in CTCL.

SIGNIFICANCE

To date, CTCL pathogenesis remains unknown, and there are no curative therapies. Our findings not only demonstrate a critical role for IL15-mediated inflammation in cutaneous T-cell lymphomagenesis, but also uncover a new oncogenic regulatory loop in CTCL involving IL15, HDAC1, HDAC6, and miR-21 that shows differential sensitivity to isotype-specific HDAC inhibitors. Cancer Discov; 6(9); 986-1005. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 932.

H3K27 Methylation: A Focal Point of Epigenetic Deregulation in Cancer

Epigenetics, the modification of chromatin without changing the DNA sequence itself, determines whether a gene is expressed, and how much of a gene is expressed. Methylation of lysine 27 on histone 3 (H3K27me), a modification usually associated with gene repression, has established roles in regulating the expression of genes involved in lineage commitment and differentiation. Not surprisingly, alterations in the homeostasis of this critical mark have emerged as a recurrent theme in the pathogenesis of many cancers. Perturbations in the distribution or levels of H3K27me occur due to deregulation at all levels of the process, either by mutation in the histone itself, or changes in the activity of the writers, erasers, or readers of this mark. Additionally, as no single histone mark alone determines the overall transcriptional readiness of a chromatin region, deregulation of other chromatin marks can also have dramatic consequences. Finally, the significance of mutations altering H3K27me is highlighted by the poor clinical outcome of patients whose tumors harbor such lesions. Current therapeutic approaches targeting aberrant H3K27 methylation remain to be proven useful in the clinic. Understanding the biological consequences and gene expression pathways affected by aberrant H3K27 methylation may lead to identification of new therapeutic targets and strategies.

Clinical use and applications of histone deacetylase inhibitors in multiple myeloma

The incorporation of various novel therapies has resulted in a significant survival benefit in newly diagnosed and relapsed patients with multiple myeloma (MM) over the past decade. Despite these advances, resistance to therapy leads to eventual relapse and fatal outcomes in the vast majority of patients. Hence, there is an unmet need for new safe and efficacious therapies for continued improvement in outcomes. Given the role of epigenetic aberrations in the pathogenesis and progression of MM and the success of histone deacetylase inhibitors (HDACi) in other malignancies, many HDACi have been tried in MM. Various preclinical studies helped us to understand the antimyeloma activity of different HDACi in MM as a single agent or in combination with conventional, novel, and immune therapies. The early clinical trials of HDACi depicted only modest single-agent activity, but recent studies have revealed encouraging clinical response rates in combination with other antimyeloma agents, especially proteasome inhibitors. This led to the approval of the combination of panobinostat and bortezomib for the treatment of relapsed/refractory MM patients with two prior lines of treatment by the US Food and Drug Administration. However, it remains yet to be defined how we can incorporate HDACi in the current therapeutic paradigms for MM that will help to achieve longer disease control and significant survival benefits. In addition, isoform-selective and/or class-selective HDAC inhibition to reduce unfavorable side effects needs further evaluation.

Epigenomic regulation of oncogenesis by chromatin remodeling

Disruption of the intricate gene expression program represents one of major driving factors for the development, progression and maintenance of human cancer, and is often associated with acquired therapeutic resistance. At the molecular level, cancerous phenotypes are the outcome of cellular functions of critical genes, regulatory interactions of histones and chromatin remodeling complexes in response to dynamic and persistent upstream signals. A large body of genetic and biochemical evidence suggests that the chromatin remodelers integrate the extracellular and cytoplasmic signals to control gene activity. Consequently, widespread dysregulation of chromatin remodelers and the resulting inappropriate expression of regulatory genes, together, lead to oncogenesis. We summarize the recent developments and current state of the dysregulation of the chromatin remodeling components as the driving mechanism underlying the growth and progression of human tumors. Because chromatin remodelers, modifying enzymes and protein-protein interactions participate in interpreting the epigenetic code, selective chromatin remodelers and bromodomains have emerged as new frontiers for pharmacological intervention to develop future anti-cancer strategies to be used either as single-agent or in combination therapies with chemotherapeutics or radiotherapy.

Histone deacetylase (HDAC)-1, -2, -4 and -6 expression in human pancreatic adenocarcinoma: associations with clinicopathological parameters, tumor proliferative capacity and patients' survival

Background

Histone deacetylases (HDACs) have been associated with malignant tumor development and progression in humans. HDAC inhibitors (HDACIs) are currently being explored as anti-cancer agents in clinical trials. The present study aimed to evaluate the clinical significance of HDAC-1, −2, −4 and −6 protein expression in pancreatic adenocarcinoma.

Methods

HDAC-1, −2, −4 and −6 protein expression was assessed immunohistochemically on 70 pancreatic adenocarcinoma tissue specimens and was statistically analyzed with clinicopathological characteristics and patients’ survival.

Results

Enhanced HDAC-1 expression was significantly associated with increased tumor proliferative capacity (p = 0.0238) and borderline with the absence of lymph node metastases (p = 0.0632). Elevated HDAC-4 expression was significantly associated with the absence of organ metastases (p = 0.0453) and borderline with the absence of lymph node metastases (p = 0.0571) and tumor proliferative capacity (p = 0.0576). Enhanced HDAC-6 expression was significantly associated with earlier histopathological stage (p = 0.0115) and borderline with smaller tumor size (p = 0.0864). Pancreatic adenocarcinoma patients with enhanced HDAC-1 and −6 expression showed significantly longer survival times compared to those with low expression (p = 0.0022 and p = 0.0113, respectively), while a borderline association concerning HDAC-2 expression was noted (p = 0.0634).

Conclusions

The present study suggested that HDACs may be implicated in pancreatic malignant disease progression, being considered of clinical utility with potential use as therapeutic targets.

Dysregulated Class I histone deacetylases are indicators of poor prognosis in multiple myeloma

Histone deacetylases (HDAC) control gene expression through their ability to acetylate proteins, thereby influencing a diverse range of cellular functions. Class I HDAC (HDAC1-3 and 8) and HDAC6 are predominantly upregulated in malignancies and their altered expression in some cancers has a significant prognostic implication. The expression and prognostic consequence of dysregulated Class I HDAC and HDAC6, key players in multiple myeloma (MM), are unknown. This study hypothesized that HDAC are dysregulated in MM and patients with high expression have significantly poorer prognostic outcomes. Quantitative PCR for 11 HDAC (Class I, II, and IV) was performed in genetically heterogeneous human myeloma cell lines (HMCL) and primary MM and compared to normal plasma cells (PC). In HMCL, HDAC1-3 and 8 (Class I), and HDAC5 and HDAC10 (Class II) were significantly upregulated compared to normal PC. In primary MM, the median expression level of all of the HDAC, except HDAC1 and HDAC11, were elevated when compared to normal PC. Patients with higher levels of HDAC1-3, HDAC4, HDAC6, and HDAC11 transcripts demonstrated a significantly shorter progression-free survival (PFS). Immunohistochemical staining for HDAC1 and HDAC6 on bone marrow trephines from a uniformly treated cohort of transplant eligible MM patients revealed that HDAC1 protein was detectable in most patients and that higher levels of MM cell HDAC1 protein expression (≥90 % versus ≤20 % MM cell positivity) correlated with both shorter PFS (P = 0 .07) and shorter overall survival (P = 0 .003). Conversely, while the majority of patients expressed HDAC6, there was no correlation between HDAC6 levels and patient outcome. Together, these results indicate that overexpression of Class I HDAC, particularly HDAC1, is associated with poor prognosis in MM.

Profile of belinostat for the treatment of relapsed or refractory peripheral T-cell lymphoma

The peripheral T-cell lymphomas are a rare and heterogeneous group of mature T-cell lymphomas with limited available therapies. The outcome of frontline chemotherapy regimens has been disappointing, with a long-term survival of only 20%–30%. There is an urgent need to optimize induction therapy by incorporating novel agents that target the dysregulated pathways. Histone deacetylase inhibitors that induce acetylation of histones and enhance apoptosis have shown promising activity. In this article, we summarize the role of histone deacetylase inhibitors and specifically discuss pharmacokinetics, efficacy, and toxicity of the recently US Food and Drug Administration-approved agent belinostat for its use in patients with relapsed/refractory peripheral T-cell lymphoma.

Dido3-dependent HDAC6 targeting controls cilium size

Primary cilia are involved in a variety of physiological processes such as sensing of the environment, cell growth and development. Numerous developmental disorders and pathologies arise from defects in these organelles. Multiple proteins that promote formation and disassembly of the primary cilium have been identified, but little is known about the mechanisms that control steady-state cilium size. Here, we show that death inducer obliterator (Dido3)-dependent targeting of histone deacetylase 6 (HDAC6) is a key determinant of cilium size in growth-arrested cells. The amount of either protein negatively correlates with cilium size. Dido3 availability at the centrosome governs ciliary HDAC6 levels, and redistribution of the two proteins controls tubulin acetylation. In turn, basal body localization of Dido3 and HDAC6 depends on the actin network, previously shown to limit cilium size independent of the cell cycle. These results show that not only kinase-dependent activation of a deacetylase but also its subcellular distribution controls substrate selection.

Predicting response to epigenetic therapy

Drugs targeting the epigenome are new promising cancer treatment modalities; however, not all patients receive the same benefit from these drugs. In contrast to conventional chemotherapy, responses may take several months after the initiation of treatment to occur. Accordingly, identification of good pretreatment predictors of response is of great value. Many clinical parameters and molecular targets have been tested in preclinical and clinical studies with varying results, leaving room for optimization. Here we provide an overview of markers that may predict the efficacy of FDA- and EMA-approved epigenetic drugs.

New and emerging HDAC inhibitors for cancer treatment

Epigenetic enzymes are often dysregulated in human tumors through mutation, altered expression, or inappropriate recruitment to certain loci. The identification of these enzymes and their partner proteins has driven the rapid development of small-molecule inhibitors that target the cancer epigenome. Herein, we discuss the influence of aberrantly regulated histone deacetylases (HDACs) in tumorigenesis. We examine HDAC inhibitors (HDACis) targeting class I, II, and IV HDACs that are currently under development for use as anticancer agents following the FDA approval of two HDACis, vorinostat and romidepsin.

Expression of histone deacetylases in diffuse large B-cell lymphoma and its clinical significance

BACKGROUND

Histone deacetylase inhibitors are a new class of drugs used in treatment of malignant tumors. Diffuse large B-cell lymphoma (DLBCL) is the most common type of B-cell lymphoma, and it accounts for more than 40% of all B-cell lymphomas. In this study, we aimed to determine the expression patterns of histone deacetylases (HDACs) in DLBCL, to examine whether HDAC expression patterns differ among cases, and to assess whether these findings have clinical significance.

MATERIALS AND METHODS

We selected 91 cases of DLBCL diagnosed at St. Vincent Hospital, The Catholic University of Korea, from 2001-2012. We performed a pathology slide review and collected clinical data including age, sex, tumor site, survival time, and mortality. Immunohistochemical analysis was performed using primary antibodies for HDACs, including HDAC1 and 2 of class I, HDAC4 and 5 of class IIa, and HDAC6 of class IIb. Expression site was determined to be nuclear, cytoplasmic, or both. Staining intensities were graded as low and high. We assessed correlations between HDAC expression levels and clinical data and survival analysis.

RESULTS

Of the 91 cases examined, 46 (50.5%) were men and 45 (49.5%) were women. Most of the patients were elderly, and 74 (81.3%) cases were older than 46 y. Forty-six (50.5%) cases showed lymph node involvement, and 45 (49.5%) cases showed lymphoma at extranodal sites. In nodal lymphoma, staining was strongly positive for HDAC2, whereas staining was weak or negative for HDAC4; however, there was no significant correlation with survival. But nodal lymphoma cases with high nuclear expression of HDAC2 and nodal lymphoma cases with high nuclear expression of HDAC2 and low nuclear expression of HDAC4 showed significantly shorter survival times compared with other cases.

CONCLUSIONS

High nuclear expression of HDAC2 may play an important role in survival of DLBCL patients, especially in those with nodal lymphoma, which is associated with a shorter survival time. Our results may have important implications for treatment of DLBCL by epigenetic regulation.

The antiparasitic clioquinol induces apoptosis in leukemia and myeloma cells by inhibiting histone deacetylase activity

The antiparasitic clioquinol (CQ) represents a class of novel anticancer drugs by interfering with proteasome activity. In the present study, we found that CQ induced blood cancer cell apoptosis by inhibiting histone deacetylases (HDACs). CQ accumulated the acetylation levels of several key proteins including histone H3 (H3), p53, HSP90, and α-tubulin. In the mechanistic study, CQ was found to down-regulate HDAC1, -3, -4, and -5 in both myeloma and leukemia cells. Computer modeling analysis revealed that CQ was well docked into the active pocket of the enzyme, where the oxygen and nitrogen atoms in CQ formed stable coordinate bonds with the zinc ion, and the hydroxyl group from CQ formed an effective hydrogen bond with Asp-267. Moreover, co-treatment with CQ and zinc/copper chloride led to decreased Ac-H3. Furthermore, CQ inhibited the activity of Class I and IIa HDACs in the cell-free assays, demonstrating that CQ interfered with HDAC activity. By inhibiting HDAC activity, CQ induced expression of p21, p27, and p53, cell cycle arrest at G1 phase, and cell apoptosis. This study suggested that the HDAC enzymes are targets of CQ, which provided a novel insight into the molecular mechanism of CQ in the treatment of hematological malignancies.

Tropolones as lead-like natural products: the development of potent and selective histone deacetylase inhibitors

Natural products have long been recognized as a rich source of potent therapeutics but further development is often limited by high structural complexity and high molecular weight. In contrast, at the core of the thujaplicins is a lead-like tropolone scaffold characterized by relatively low molecular weight, ample sites for diversification, and metal-binding functionality poised for targeting a range of metalloenzyme drug targets. Here, we describe the development of this underutilized scaffold for the discovery of tropolone derivatives that function as isozyme-selective inhibitors of the validated anticancer drug target, histone deacetylase (HDAC). Several monosubstituted tropolones display remarkable levels of selectivity for HDAC2 and potently inhibit the growth of T-cell lymphocyte cell lines. The tropolones represent a new chemotype of isozyme-selective HDAC inhibitors.

Clinical significance of histone deacetylase (HDAC)-1, HDAC-2, HDAC-4, and HDAC-6 expression in human malignant and benign thyroid lesions

Histone deacetylases (HDACs) have been associated with human malignant tumor development and progression, and HDAC inhibitors are currently being explored as anticancer agents in clinical trials. The present study aimed to evaluate the clinical significance of HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression in human malignant and benign thyroid lesions. HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression was assessed immunohistochemically on paraffin-embedded thyroid tissues obtained from 74 patients with benign and malignant thyroid lesions. Enhanced HDAC-2 and HDAC-6 expression was significantly more frequently observed in malignant, compared to benign, thyroid lesions (p = 0.0042 and p = 0.0069, respectively). Enhanced HDAC-2, HDAC-4, and HDAC-6 expression was significantly more frequently observed in cases with papillary carcinoma compared to hyperplastic nodules (p = 0.0065, p = 0.0394, and p = 0.0061, respectively). In malignant thyroid lesions, HDAC-1, HDAC-4, and HDAC-6 expression was significantly associated with tumor size (p = 0.0169, p = 0.0056, and p = 0.0234, respectively); HDAC-2 expression with lymphatic and vascular invasion (p = 0.0299 and p = 0.0391, respectively); and HDAC-4 expression with capsular invasion (p = 0.0464). The cellular pattern of HDAC-1 and HDAC-2 distribution (nuclear vs. nuclear and cytoplasmic) presented a distinct discrimination between malignant and benign thyroid lesions (p = 0.0030 and p = 0.0028, respectively) as well as between papillary carcinoma and hyperplastic nodules (p = 0.0036 and p = 0.0028, respectively). HDAC-1, HDAC-2, HDAC-4, and HDAC-6 may be associated with the malignant thyroid transformation and could be considered as useful biomarkers and possible therapeutic targets in this neoplasia.

The effects of a histone deacetylase inhibitor on biological behavior of diffuse large B-cell lymphoma cell lines and insights into the underlying mechanisms

Background

Epigenetic control using histone deacetylase (HDAC) inhibitors is a promising therapy for lymphomas. Insights into the anti-proliferative effects of HDAC inhibitors on diffuse large B-cell lymphoma (DLBCL) and further understanding of the underlying mechanisms, which remain unclear to date, are of great importance.

Methods

Three DLBCL cell lines (DoHH2, LY1 and LY8) were used to define the potential epigenetic targets for Trichostatin A (TSA)-mediated anti-proliferative effects via CCK-8 assay. Cell cycle distribution and apoptosis were detected by flow cytometry. We further investigated the underlying molecular mechanisms by examining expression levels of relevant proteins using western blot analysis.

Results

TSA treatment inhibited the growth of all three DLBCL cell lines and enhanced cell cycle arrest and apoptosis. Molecular analysis revealed upregulated acetylation of histone H3, α-tubulin and p53, and dephosphorylation of pAkt with altered expression of its main downstream effectors (p21, p27, cyclin D1 and Bcl-2). HDAC profiling revealed that all three cell lines had varying HDAC1–6 expression levels, with the highest expression of all six isoforms, in DoHH2 cells, which displayed the highest sensitivity to TSA.

Conclusion

Our results demonstrated that the HDAC inhibitor TSA inhibited DLBCL cell growth, and that cell lines with higher expression of HDACs tended to be more sensitive to TSA. Our data also suggested that inhibition of pAkt and activation of p53 pathway are the main molecular events involved in inhibitory effects of TSA.

Sustained inhibition of deacetylases is required for the antitumor activity of the histone deactylase inhibitors panobinostat and vorinostat in models of colorectal cancer

Despite compelling preclinical data in colorectal cancer (CRC), the efficacy of HDACIs has been disappointing in the clinic. The goal of this study was to evaluate the effectiveness of vorinostat and panobinostat in a dose- and exposure-dependent manner in order to better understand the dynamics of drug action and antitumor efficacy. In a standard 72 h drug exposure MTS assay, notable concentration-dependent antiproliferative effects were observed in the IC50 range of 1.2-2.8 μmol/L for vorinostat and 5.1-17.5 nmol/L for panobinostat. However, shorter clinically relevant exposures of 3 or 6 h failed to elicit any significant growth inhibition and in most cases a >24 h exposure to vorinostat or panobinostat was required to induce a sigmoidal dose-response. Similar results were observed in colony formation assays where ≥ 24 h of exposure was required to effectively reduce colony formation. Induction of acetyl-H3, acetyl-H4 and p21 by vorinostat were transient and rapidly reversed within 12 h of drug removal. In contrast, panobinostat-induced acetyl-H3, acetyl-H4, and p21 persisted for 48 h after an initial 3 h exposure. Treatment of HCT116 xenografts with panobinostat induced significant increases in acetyl-H3 and downregulation of thymidylate synthase after treatment. Although HDACIs exert both potent growth inhibition and cytotoxic effects when CRC cells were exposed to drug for ≥ 24 h, these cells demonstrate an inherent ability to survive HDACI concentrations and exposure times that exceed those clinically achievable. Continued efforts to develop novel HDACIs with improved pharmacokinetics/phamacodynamics, enhanced intratumoral delivery and class/isoform-specificity are needed to improve the therapeutic potential of HDACIs and HDACI-based combination regimens in solid tumors.

HDAC isoenzyme expression is deregulated in chronic lymphocytic leukemia B-cells and has a complex prognostic significance

Histone deacetylases (HDACs) play a crucial role in chromatin structure and, consequently, gene expression. Their deregulation has been reported in various cancers. We performed a complete and comprehensive study of the expression of 18 HDACs (including Sirtuin; SIRT) by real-time PCR in a cohort of 200 chronic lymphocytic leukemia (CLL) patients with a median follow-up of 77 mo, and compared it with the results obtained from normal B cells. We also compared HDAC expression at diagnosis and after relapse. We observed significant deregulation (mostly upregulation) of HDACs in CLL. In terms of clinical significance, only HDAC6 was significantly correlated with treatment-free survival (TFS), whereas HDAC3 and SIRT2, 3 and 6 were correlated with overall survival (OS). A multivariate Cox regression stepwise analysis indicated that HDAC6, 7 and 10 and SIRT3 were TFS independent predictors. Interestingly, poor prognosis was associated with an overexpression of HDAC7 and 10 but an underexpression of HDAC6 and SIRT3. Therefore, these factors were combined in a TFS score: patients with a score of 0-1-2, 3 and 4 had a median TFS of 107, 57 and 26 mo, respectively (HR = 4.03, p < 0.0001). For OS, SIRT5 and 6 allowed stratification into 3 groups, with a median OS of > 360, 237 and 94 mo (HR = 6.38, p < 0.0001). However, we could not find statistical differences in HDAC expression after relapse. These results, validated by a 5-fold cross-validation, highlight the complex impact of HDAC expression in CLL clinical course.

HDAC inhibitor-based therapies: can we interpret the code?

Abnormal epigenetic control is a common early event in tumour progression, and aberrant acetylation in particular has been implicated in tumourigenesis. One of the most promising approaches towards drugs that modulate epigenetic processes has been seen in the development of inhibitors of histone deacetylases (HDACs). HDACs regulate the acetylation of histones in nucleosomes, which mediates changes in chromatin conformation, leading to regulation of gene expression. HDACs also regulate the acetylation status of a variety of other non-histone substrates, including key tumour suppressor proteins and oncogenes. Histone deacetylase inhibitors (HDIs) are potent anti-proliferative agents which modulate acetylation by targeting histone deacetylases. Interest is increasing in HDI-based therapies and so far, two HDIs, vorinostat (SAHA) and romidepsin (FK228), have been approved for treating cutaneous T-cell lymphoma (CTCL). Others are undergoing clinical trials. Treatment with HDIs prompts tumour cells to undergo apoptosis, and cell-based studies have shown a number of other outcomes to result from HDI treatment, including cell-cycle arrest, cell differentiation, anti-angiogenesis and autophagy. However, our understanding of the key pathways through which HDAC inhibitors affect tumour cell growth remains incomplete, which has hampered progress in identifying malignancies other than CTCL which are likely to respond to HDI treatment.

Novel therapeutic agents for cutaneous T-Cell lymphoma

Mycosis fungoides (MF) and Sezary Syndrome (SS) represent the most common subtypes of primary Cutaneous T-cell lymphoma (CTCL). Patients with advanced MF and SS have a poor prognosis leading to an interest in the development of new therapies with targeted mechanisms of action and acceptable safety profiles. In this review we focus on such novel strategies that have changed the treatment paradigm of this rare malignancy.

Expression of HAT1 and HDAC1, 2, 3 in Diffuse Large B-Cell Lymphomas, Peripheral T-Cell Lymphomas, and NK/T-Cell Lymphomas

Background

It has generally been proven that histone acetylation and deacetylation are involved in the malignant transformation. To date, however, this has rarely been studied in cases of malignant lymphoma.

Methods

We studied nine cases of reactive lymphoid hyperplasia, 78 cases of diffuse large B-cell lymphoma (DLBCL), 13 cases of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), and 13 cases of extranodal NK/T-cell lymphoma, nasal type (NKTCL). Thus, we attempted to elucidate the associations of the degree of the expression of histone acetyltransferase 1 (HAT1), histone deacetylase (HDAC) 1, HDAC2, and HDAC3 with the clinical behaviors of above malignant lymphomas using the immunohistochemistry and a western blot analysis.

Results

The degree of the expression of HAT1 was higher in cases of DLBCL, PTCL-NOS or NKTCL as compared with reactive lymphoid hyperplasia (p<0.05). The degree of the expression of HAT1 was correlated with that of HDAC1 in cases of DLBCL or NKTCL (p<0.05). The degree of the expression of HAT1 and HDAC1 was correlated with a poor survival in cases of DLBCL or PTCL-NOS (p>0.05).

Conclusions

HAT1, HDAC1, and HDAC2 play a critical role in the development of malignant lymphomas. Both HAT1 and HDAC1 might be indicators for a poor prognosis in cases of DLBCL as cooperating factors.

Myelodysplastic syndrome and histone deacetylase inhibitors: "to be or not to be acetylated"?

Myelodysplastic syndrome (MDS) represents a heterogeneous group of diseases with clonal proliferation, bone marrow failure and increasing risk of transformation into an acute myeloid leukaemia. Structured guidelines are developed for selective therapy based on prognostic subgroups, age, and performance status. Although many driving forces of disease phenotype and biology are described, the complete and possibly interacting pathogenetic pathways still remain unclear. Epigenetic investigations of cancer and haematologic diseases like MDS give new insights into the pathogenesis of this complex disease. Modifications of DNA or histones via methylation or acetylation lead to gene silencing and altered physiology relevant for MDS. First clinical trials give evidence that patients with MDS could benefit from epigenetic treatment with, for example, DNA methyl transferase inhibitors (DNMTi) or histone deacetylase inhibitors (HDACi). Nevertheless, many issues of HDACi remain incompletely understood and pose clinical and translational challenges. In this paper, major aspects of MDS, MDS-associated epigenetics and the potential use of HDACi are discussed.

Targeting histone deacetyalses in the treatment of B- and T-cell malignancies

HDAC inhibitors (HDACI) are now emerging as one of the most promising new classes of drugs for the treatment of select forms of non-Hodgkin’s lymphoma (NHL). They are particularly active in T-cell lymphomas, possibly hodgkin’s lymphoma and indolent B cell lymphomas. Presently, two of these agents, vorinostat and romidepsin, have been approved in the US for the treatment of relapsed and refractory cutaneous T cell lymphomas (CTCL). Initially, these agents were developed with the idea that they affected transcriptional activation and thus gene expression, by modulating chromatin condensation and decondensation. It is now clear that their effects go beyond chromatin and by affecting the acetylation status of histones and other intra-cellular proteins, they modify gene expression and cellular function via multiple pathways. Gene expression profiles and functional genetic analysis has led to further understanding of the various molecular pathways that are affected by these agents including cell cycle regulation, pathways of cellular proliferation, apoptosis and angiogenesis all important in lymphomagenesis. There is also increasing data to support the effects of these agents on T cell receptor and immune function which may explain the high level of activity of these agents in T cell lymphomas and hodgkin’s lymphoma. There is ample evidence of epigenetic dysregulation in lymphomas which may underlie the mechanisms of action of these agents but how these agents work is still not clear. Current HDAC inhibitors can be divided into at least four classes based on their chemical structure. At present several of these HDAC inhibitors are in clinical trials both as single agents and in combination with chemotherapy or other biological agents. They are easy to administer and are generally well tolerated with minimal side effects. Different dosing levels and schedules and the use of isospecific HDAC inhibitors are some of the strategies that are being employed to increase the therapeutic effect of these agents in the treatment of lymphomas. There may also be class differences that translate into specific activity against different lymphoma. HDAC inhibitors will likely be incorporated into combinations of targeted therapies both in the upfront and relapsed setting for lymphomas.

Histone Deacetylase Inhibitors: Advancing Therapeutic Strategies in Hematological and Solid Malignancies

Advancement in the understanding of cancer development in recent years has identified epigenetic abnormalities as a common factor in both tumorigenesis and refractory disease. One such event is the dysregulation of histone deacetylases (HDACs) in both hematological and solid tumors, and has consequently resulted in the development of HDAC inhibitors (HDACI) to overcome this. HDACI exhibit pleiotropic biological effects including inhibition of angiogenesis and the induction of autophagy and apoptosis. Although HDACI exhibit modest results as single agents in preclinical and clinical data, they often fall short, and therefore HDACI are most promising in combinational strategies with either standard treatments or with other experimental chemotherapies and targeted therapies. This review will discuss the induction of autophagy and apoptosis and the inhibition of angiogenesis by HDACI, and also pre-clinical and clinical combination strategies using these agents.

Enhanced radiosensitivity of EC109 cells by inhibition of HDAC1 expression

Histone deacetylase (HDAC) activity plays the role of deacetylation of histone and non-histone proteins, which can alter gene expression patterns and cell behavior potentially associated with malignant transformation. Aberrant expression of HDAC1 has been found in various types of cancers, which indicated that it might be a target for cancer therapy. In this study, overexpression of HDAC1 was found in esophageal cancer samples by real-time RT-PCR, compared with adjacent non-cancerous tissues. To further verify the possibility of anticancer treatment by silencing the increased HDAC1 in esophageal carcinoma cells, HDAC1 expression was knockdown using plasmid-based RNA interference (RNAi). Results showed the HDAC1 expression was efficiently inhibited and the acetylation of histone H3 was significantly increased by RNAi in EC109 cells. Increased apoptotic cell death was observed when HDAC1 expression was knockdown, which indicated that cells were more sensitive to radiation. Moreover, the results also showed DNA was more easily broken by radiation in EC109 cells when HDAC1 expression was knockdown, as measured by γH2AX foci and single-cell electrophoresis. Our data suggested that targeting the increased HDAC1 expression might be feasible for esophageal cancer therapy.

Epigenetic Signatures in Breast Cancer: Clinical Perspective

There is now a compelling body of evidences sustaining the importance of epigenetic mechanisms in the development and progression of cancer. DNA methylation, post-translational histone and other protein modifications, microRNA expression, and nucleosome positioning, all act together to exert their cellular effects. The epigenome is responsible for controlling gene expression thus defining cell differentiation and tissue specificity. This review will focus on DNA methylation and histone modification because these epigenetic events are widely implicated in cancer development and progression. We will in particular address the translational aspects of breast cancer epigenomics including the development of biomarkers and the prospects for epigenetic based pharmacologic treatments. The analysis of DNA methylation has the advantage over other molecular methods (e.g. single gene mutation, microsatellite analysis) that it can be detected with a very high degree of specificity even in the presence of excess unmethylated DNA. Furthermore, the presence of specific CpG methylation signatures makes methylation-based markers attractive diagnostic, prognostic, and predictive tools for better management of breast cancer patients.

Response to hydralazine-valproate in a patient with mycosis fungoides

Histone deacetylase (HDAC) inhibitors have shown significant activity in the treatment of cutaneous T-cell lymphomas (CTCL). The epigenetic alterations of CTCL not only are limited to altered histone acetylation but also include aberrant DNA gene methylation hence, the combination of an HDAC inhibitor with a DNA demethylating agent is a promising therapy to be tested. Here we report a mycosis fungoides patient having a dramatic response to hydralazine and valproate, two repositioned drugs as HDAC and DNA methylation inhibitors, respectively.

DNA microarray profiling of genes differentially regulated by the histone deacetylase inhibitors vorinostat and LBH589 in colon cancer cell lines

BACKGROUND

Despite the significant progress made in colon cancer chemotherapy, advanced disease remains largely incurable and novel efficacious chemotherapies are urgently needed. Histone deacetylase inhibitors (HDACi) represent a novel class of agents which have demonstrated promising preclinical activity and are undergoing clinical evaluation in colon cancer. The goal of this study was to identify genes in colon cancer cells that are differentially regulated by two clinically advanced hydroxamic acid HDACi, vorinostat and LBH589 to provide rationale for novel drug combination partners and identify a core set of HDACi-regulated genes.

METHODS

HCT116 and HT29 colon cancer cells were treated with LBH589 or vorinostat and growth inhibition, acetylation status and apoptosis were analyzed in response to treatment using MTS, Western blotting and flow cytometric analyses. In addition, gene expression was analyzed using the Illumina Human-6 V2 BeadChip array and Ingenuity Pathway Analysis.

RESULTS

Treatment with either vorinostat or LBH589 rapidly induced histone acetylation, cell cycle arrest and inhibited the growth of both HCT116 and HT29 cells. Bioinformatic analysis of the microarray profiling revealed significant similarity in the genes altered in expression following treatment with the two HDACi tested within each cell line. However, analysis of genes that were altered in expression in the HCT116 and HT29 cells revealed cell-line-specific responses to HDACi treatment. In addition a core cassette of 11 genes modulated by both vorinostat and LBH589 were identified in both colon cancer cell lines analyzed.

CONCLUSION

This study identified HDACi-induced alterations in critical genes involved in nucleotide metabolism, angiogenesis, mitosis and cell survival which may represent potential intervention points for novel therapeutic combinations in colon cancer. This information will assist in the identification of novel pathways and targets that are modulated by HDACi, providing much-needed information on HDACi mechanism of action and providing rationale for novel drug combination partners. We identified a core signature of 11 genes which were modulated by both vorinostat and LBH589 in a similar manner in both cell lines. These core genes will assist in the development and validation of a common gene set which may represent a molecular signature of HDAC inhibition in colon cancer.

Expression of histone deacetylases in lymphoma: implication for the development of selective inhibitors

Unselective histone deacetylase (HDAC) inhibitors are a promising novel therapy for lymphoid malignancies. However, these treatments remain empiric as the pattern of HDAC enzymes in different types of cancer, including lymphoid malignancies, remains unknown. We examined the expression of class I and class II HDACs in a panel of cell lines and tissue sections from primary lymphoid tumours. Class I enzymes were highly expressed in all cell lines and primary tumours studied, including the non-malignant reactive cells in the Hodgkin lymphoma (HL) microenvironment. The most frequently altered HDAC expression was HDAC6, as it was either weakly expressed or undetected in 9/14 (64%) of lymphoid cell lines and in 83/89 (93%) of primary lymphoma tissue specimens, including 50/52 (96%) cases of diffuse large B-cell lymphoma, and 18/22 (82%) cases of classical HL. Cell lines that had low expression level of HDAC6 demonstrated aberrant expression of hyper-acetylated tubulin, and were found to be more sensitive to the growth inhibitory effects of the class I HDAC inhibitor MGCD0103. Collectively, our data demonstrate that HDAC6 is rarely expressed in primary lymphoma cases, suggesting that it may not be an important therapeutic target in these lymphoid malignancies.