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

Discovery of novel inhibitors of histone deacetylase 6: Structure-based virtual screening, molecular dynamics simulation, enzyme inhibition and cell viability assays

Histone deacetylase 6 (HDAC6) contributes to cancer metastasis in several cancers, including triple-negative breast cancer (TNBC)-the most lethal form that lacks effective therapy. Although several efforts have been invested to develop selective HDAC6 inhibitors, none have been approved by the FDA. Toward this goal, existing computational studies used smaller compound libraries and shorter MD simulations. Here, we conducted a structure-based virtual screening of ZINC "Druglike" library containing 17,900,742 compounds using a Glide virtual screening protocol comprising various filters with increasing accuracy. The top 20 hits were subjected to molecular dynamics simulation, MM-GBSA binding energy calculations, and further ADMET prediction. Furthermore, enzyme inhibition assay and cell viability assay were performed on six available compounds from the identified hits. C4 (ZINC000077541942) with a good profile of predicted drug properties was found to inhibit HDAC6 (IC50: 4.7 ± 11.6 μM) with comparative affinity to that of the known HDAC6 selective inhibitor Tubacin (TA) in our experiments. C4 also demonstrated cytotoxic effects against triple-negative breast cancer (TNBC) cell line MDA-MB-231 with EC50 of 40.6 ± 12.7 μM comparable to that of TA (2-20 μM). Therefore, this compound, with pharmacophore features comprising a non-hydroxamic acid zinc-binding group, heteroaromatic linker, and cap group, is proposed as a novel HDAC6 inhibitor.

HDAC inhibitors: Promising agents for leukemia treatment

The essential role of epigenetic modification in the pathogenesis of a series of cancers have gradually been recognized. Histone deacetylase (HDACs), as well-known epigenetic modulators, are responsible for DNA repair, cell proliferation, differentiation, apoptosis and angiogenesis. Studies have shown that aberrant expression of HDACs is found in many cancer types. Thus, inhibition of HDACs has provided a promising therapeutic approach alternative for these patients. Since HDAC inhibitor (HDACi) vorinostat was first approved by the Food and Drug Administration (FDA) for treating cutaneous T-cell lymphoma (CTCL) in 2006, the combination of HDAC inhibitors with other molecules such as chemotherapeutic drugs has drawn much attention in current cancer treatment, especially in hematological malignancies therapy. Up to now, there have been more than twenty HDAC inhibitors investigated in clinic trials with five approvals being achieved. Indeed, Histone deacetylase inhibitors promote or enhance several different anticancer mechanisms and therefore are in evidence as potential antileukemia agents. In this review, we will focus on possible mechanisms by how HDAC inhibitors exert therapeutic benefit and their clinical utility in leukemia.

Histone deacetylase 6: at the interface of cancer and neurodegeneration

With the recognition in the early 1960s that histones can be post-translationally modified, the list of different post-translational modifications of histones and their biological consequences has continued to expand. In addition, the idea of the 'histone code' hypothesis, later introduced by David Allis and colleagues, further broaden the horizon of chromatin biology. Currently, there is a wealth of knowledge about the transition between the active and the repressive state of chromatin, and modifications of histones remains at the center of chromatin biology. Histone deacetylases (HDACs) in particular are of great importance for the therapeutic success of cancer treatment. Focusing primarily on HDAC6, herein we have briefly highlighted its unique involvement in cancer and also apparently in neurodegeneration.

Recent advancement of HDAC inhibitors against breast cancer

Recent studies highlight the great potential impact of HDAC inhibitors (HDACis) in suppressing TNBC, even though clinical trials including a single HDACis demonstrated unsatisfactory outcomes against TNBC. New compounds created to achieve isoform selectivity and/or a polypharmacological HDAC strategy have also produced interesting results. The current study discusses the HDACis pharmacophoric models and the structural alterations that produced drugs with strong inhibitory effects on TNBC progression. With more than 2 million new cases reported in 2018, breast cancer-the most common cancer among women worldwide-poses a significant financial burden on an already deteriorating public health system. Due to a lack of therapies being developed for triple-negative breast cancers and the development of resistance to the current treatment options, it is imperative to plan novel therapeutics in order to bring new medications to the pipeline. Additionally, HDACs deacetylate a large number of nonhistone cellular substrates that control a variety of biological processes, such as the beginning and development of cancer. The significance of HDACs in cancer and the therapeutic potential of HDAC inhibitor. Furthermore, we also reported molecular docking study with four HDAC inhibitors and performed molecular dynamic stimulation of the best dock score compound. Among the four ligands belinostat compound showed best binding affinity with histone deacetylase protein which was -8.7 kJ/mol. It also formed five conventional hydrogen bond with Gly 841, His 669, His 670, pro 809, and His 709 amino acid residues.

Oral HDAC inhibitor tucidinostat in patients with relapsed or refractory peripheral T-cell lymphoma: phase IIb results

Tucidinostat (formerly known as chidamide) is an orally available, novel benzamide class of histone deacetylase (HDAC) inhibitor that selectively blocks class I and class IIb HDAC. This multicenter phase IIb study aimed to investigate the efficacy and safety of tucidinostat, 40 mg twice per week (BIW), in patients with relapsed/refractory (R/R) peripheral T-cell lymphoma (PTCL). The primary endpoint was overall response rate (ORR) assessed by an independent overall efficacy review committee. Between March 2017 and March 2019, 55 patients were treated, and 46 and 55 were evaluated for efficacy and safety, respectively. Twenty-one of 46 patients achieved objective responses with an ORR of 46% (95% confidence interval : 30.9-61.0), including five patients with complete response (CR). Responses were observed across various PTCL subtypes. In angioimmunoblastic T-cell lymphoma, there were two CR and five partial responses (PR) among eight patients, achieving an ORR of 88%. The disease control rate (CR + PR + stable disease) was 72% (33/46). The median progression-free survival, duration of response, and overall survival were 5.6 months, 11.5 months, 22.8 months, respectively. The most common adverse events (AE) (all grades) were thrombocytopenia, neutropenia, leukopenia, anemia, and diarrhea. The grade ≥3 AE emerging in ≥20% of patients included thrombocytopenia (51%), neutropenia (36%), lymphopenia (22%), and leukopenia (20%). Importantly, most of the AE were manageable by supportive care and dose modification. In conclusion, the favorable efficacy and safety profiles indicate that tucidinostat could be a new therapeutic option in patients with R/R PTCL (clinicaltrials gov. Identifier: NCT02953652).

Clinical Significance of the Histone Deacetylase 2 (HDAC-2) Expression in Human Breast Cancer

BACKGROUND/AIM

There is a strong association between malignancy and histone deacetylases (HDACs). Histone deacetylase inhibitors (HDACIs) are now being tested as antitumor agents in various clinical trials. We aimed to assess the clinical importance of HDAC-2 in breast cancer (BC).

MATERIALS AND METHODS

A total of 118 BC specimens were examined immunohistochemically. A statistical analysis was conducted in order to examine the relation between HDAC-2 and the clinicopathological features and survival of the patients.

RESULTS

Higher HDAC-2 expression was related to lobular histological type of cancer, grade III, and stage III BC. In addition, the disease-free period and overall survival were curtailed and negatively related to the over-expression of HDAC-2. Other factors correlating with worse survival were histological types other than ductal or lobular, and the stage of the disease.

CONCLUSIONS

This study showed a relationship between HDAC-2 and BC. Further studies are required in order to eventually potentiate the role of HDACIs as anticancer agents in BC.

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.

The contributory roles of histone deacetylases (HDACs) in hematopoiesis regulation and possibilities for pharmacologic interventions in hematologic malignancies

Although the definitive role of epigenetic modulations in a wide range of hematologic malignancies, spanning from leukemia to lymphoma and multiple myeloma, has been evidenced, few articles reviewed the task. Given the high accessibility of histone deacetylase (HDACs) to necessary transcription factors involved in hematopoiesis, this review aims to outline physiologic impacts of these enzymes in normal hematopoiesis, and also to outline the original data obtained from international research laboratories on their regulatory role in the differentiation and maturation of different hematopoietic lineages. Questions on how aberrant expression of HDACs contributes to the formation of hematologic malignancies are also responded, because these classes of enzymes have a respectable share in the development, progression, and recurrence of leukemia, lymphoma, and multiple myeloma. The last section provides a special focus on the therapeutic perspectiveof HDACs inhibitors, either as single agents or in a combined-modal strategy, in these neoplasms. In conclusion, optimizing the dose and the design of more patient-tailored inhibitors, while maintaining low toxicity against normal cells, will help improve clinical outcomes of HDAC inhibitors in hematologic malignancies.

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.

Current status of histone deacetylase inhibitors in cutaneous T-cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a non-Hodgkin's lymphoma with a heterogenous presentation and highly variable disease course. The most common subtypes of CTCL are mycosis fungoides (MF) and Sézary Syndrome (SS). Treatment varies based on the stage of the disease with skin directed therapies typically utilized for early stage disease, and systemic therapies employed for more advanced disease. There are few highly effective treatments available, and systemic therapies have limited response rates. Histone deacetylase inhibitors have emerged as mainstream treatments for MF/SS over the past several years. Here, we discuss the mechanism of action of histone deacetylase inhibitors in relation to the pathogenesis of MF/SS, evaluate the clinical trials that led to Food and Drug Administration approval of two of the histone deacetylase inhibitors for MF/SS and describe the results for those still under investigation. Additionally, we discuss the potential for combination therapies in order to optimize outcomes of treatment with histone deacetylase inhibitors.

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.

Emerging role of histone deacetylase inhibitors in the treatment of diffuse large B-cell lymphoma

Although current immunochemotherapy has increased the therapeutic efficacy in diffuse large B-cell lymphoma (DLBCL), there are still some patients who present unfavorable outcomes. Novel effective treatment strategies are needed to improve the prognosis of DLBCL. In this review, we discussed the functional mechanisms and therapeutic applications of histone deacetylases inhibitors (HDIs) in DLBCL from preclinical and clinical studies. The mechanistic rationale of HDIs involved a wide range of effects including the regulation of transcription factors, tumor suppressors, and cell surface molecules. Histone deacetylases inhibitors as monotherapy performed limited activity in the treatment of DLBCL in present clinical trials, but its combination with other regimens has emerged as potential treatment candidates with generally acceptable and manageable adverse effects. Further investigation on the anti-tumor mechanisms of HDIs and ongoing clinical trials will hopefully facilitate the application of HDIs in patients with DLBCL.

Targeting epigenetic machinery: Emerging novel allosteric inhibitors

Epigenetics has emerged as an extremely exciting fast-growing area of biomedical research in post genome era. Epigenetic dysfunction is tightly related with various diseases such as cancer and aging related degeneration, potentiating epigenetics modulators as important therapeutics targets. Indeed, inhibitors of histone deacetylase and DNA methyltransferase have been approved for treating blood tumor malignancies, whereas inhibitors of histone methyltransferase and histone acetyl-lysine recognizer bromodomain are in clinical stage. However, it remains a great challenge to discover potent and selective inhibitors by targeting catalytic site, as the same subfamily of epigenetic enzymes often share high sequence identity and very conserved catalytic core pocket. It is well known that epigenetic modifications are usually carried out by multi-protein complexes, and activation of catalytic subunit is often tightly regulated by other interactive protein component, especially in disease conditions. Therefore, it is not unusual that epigenetic complex machinery may exhibit allosteric regulation site induced by protein-protein interactions. Targeting allosteric site emerges as a compelling alternative strategy to develop epigenetic drugs with enhanced druggability and pharmacological profiles. In this review, we highlight recent progress in the development of allosteric inhibitors for epigenetic complexes through targeting protein-protein interactions. We also summarized the status of clinical applications of those inhibitors. Finally, we provide perspectives of future novel allosteric epigenetic machinery modulators emerging from otherwise undruggable single protein target.

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 HDAC6-selective inhibitor is effective against non-Hodgkin lymphoma and synergizes with ibrutinib in follicular lymphoma

Follicular lymphoma (FL) is the most common indolent B-cell non-Hodgkin lymphoma (NHL) with genetic alterations of BCL-2, KMT2B, and KMT6. FL is refractory to conventional chemotherapy and is still incurable in most patients. Thus, new drugs and/or novel combination treatment strategies are needed to further improve FL patient outcome. We investigated the efficacy of the histone deacetylase 6 (HDAC6) inhibitor A452 combined with a Bruton's tyrosine kinase (BTK) inhibitor ibrutinib on NHL and the underlying mechanisms compared with the current clinically tested HDAC6 inhibitor ACY-1215. We first showed that FL is the most sensitive to HDAC6 inhibitor. We showed that combining A452 with ibrutinib led to the synergistic inhibition of cell growth and decreased viability of FL cells, as well as increased levels of apoptosis. Similar synergistic interactions occur in chronic lymphocytic leukemia (CLL) and germinal center diffuse large B-cell lymphoma cells (DLBCL). Enhanced cell death is associated with AKT and ERK1/2 inactivation and increased DNA damage (induction of γH2A.X and reduction of pChk1/2). In addition, A452 downregulates c-Myc, an effect significantly enhanced by ibruninib. Although ACY-1215 is less potent than A452, it displays synergism with ibrutinib. Overall, our results suggest that A452 is more effective as an anticancer agent than ACY-1215 in FL. These findings suggest that a combination of HDAC6-selective inhibitor and ibrutinib is a potent therapeutic strategy for NHL including FL.

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.

Comparison of DNA demethylating and histone deacetylase inhibitors hydralazine-valproate versus vorinostat-decitabine incutaneous t-cell lymphoma in HUT78 cells

PURPOSE

Cutaneous T-cell lymphoma (CTCL) is an uncommon extranodal non-Hodgkin T-cell lymphoma that originates from mature T lymphocytes homed at the skin. Epigenetic alterations observed in CTCL are not limited to overexpression of Histone Deacetylases but also to DNA hypermethylation. The known synergy between Histone deacetylase inhibitors (HDACi) and DNA methyltransferases inhibitors (DNMTi) suggests that combining these agent classes could be effective for CTCL.

METHODS

In this study, the combinations of the HDACi and DNMTi hydralazine/valproate (HV) and vorinostat/decitabine (VD) were compared in regard to viability inhibition, clonogenicity, pharmacological interaction and cell cycle effects in the CTCL cell line Hut78. In addition, the effect of these combinations was evaluated in normal peripheral blood mononuclear cells.

RESULTS

The results show that each of the DNMTi and HDACi exerts growth inhibition, mostly by inducing apoptosis as shown in the cell cycle distribution. However, in the combination of HV the interaction is more synergic and also it inhibits the clonogenic capacity of cells over time. Additionally, the HV combination seems to affect in a minor degree the viability of peripheral blood mononuclear cells.

CONCLUSIONS

The results of this study and the preclinical and clinical evidence on the efficacy of combining HDACi with DNMTi strongly suggest that more studies are needed with this drug class combination in CTCL, particularly with the hydralazine-valproate scheme, which is safe, and these drugs are widely available and administered by oral route.

[Romidepsin (Istodax® for intravenous injection 10 mg): pharmacokinetics, pharmacodynamics and clinical study outcome]

Romidepsin (Brand name: ISTODAX_® for Injection 10 mg) is a novel antitumor drug that inhibits histone deacetylase (HDAC). Romidepsin strongly inhibited class I HDAC activity in vitro and demonstrated a strong antitumor activity against human tumor cell line xenograft in vivo. Based on its demonstrated efficacy against T-cell lymphoma in early clinical studies, multicenter phase II clinical studies in overseas with romidepsin were conducted in patients with cutaneous T-cell lymphoma (CTCL) and peripheral T-cell lymphoma (PTCL), followed by approval for the treatment of CTCL and PTCL in the U.S. and other countries. Thereafter, domestic phase I/II studies were planned. The phase I study was designed to evaluate the tolerability of romidepsin in Japanese patients with relapsed or refractory PTCL/CTCL and thereby determine the recommended dose, as patients were administered romidepsin by intravenous infusion at a dose of 9 or 14 mg/m² over 4 hours on days 1, 8 and 15 of each 28-day cycle, and 14 mg/m² was determined as the recommended dose for phase II. While the phase II study was designed to include 40 Japanese patients with relapsed or refractory PTCL to evaluate the efficacy and safety of romidepsin. Treatment response was 42.5% and the most common AEs of Grade ≥ 3 were lymphopenia (74.0%), neutropenia (54.0%), leukocytopenia (46.0%) and thrombocytopenia (38.0%). The overall safety profile was considered to be within the acceptable range. On the basis of these result, romidepsin was approved in July 2017 for the treatment of relapsed or refractory PTCL in Japan.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.

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.

Efficacy of hydralazine and valproate in cutaneous T-cell lymphoma, a phase II study

OBJECTIVES

To evaluate the activity and safety of hydralazine and valproate (Transkrip) in cutaneous T-cell lymphoma (CTCL).

METHODS

Previously untreated and progressive/refractory CTCL patients received hydralazine at 83 mg or 182 mg/day for slow and rapid acetylators respectively plus magnesium valproate at a total dose of 30 mg/Kg t.i.d daily in continuous 28-day cycles in this phase II study. The primary objective was overall response rate (ORR) measured by the modified severity weighted assessment tool (m-SWAT), secondary end-points were time to response (TTR), time to progression (TTP), duration of response (DOR), progression-free survival (PFS), overall survival (OS) and safety.

RESULTS

Fourteen patients were enrolled (7 untreated and 7 pretreated). ORR was 71% with 50% complete and 21% partial. Two had stable disease and two progressed. At a median follow-up of 36 months (5-52), median TTR was 2 months (1-4); median DOR was 28 months (5-45); median PFS 36 and not reached for OS. There were no differences in median TTR, DOR, and PFS between treated and pretreated patients. Pruritus relieve was complete in 13 out of 14 patients. No grade 3 or 4 toxicities were observed.

CONCLUSION

The combination of hydralazine and valproate is safe, very well tolerated and effective in CTCL.

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.

Phenylpyrrole-based HDAC inhibitors: synthesis, molecular modeling and biological studies

AIM

Histone deacetylases (HDACs) regulate the expression and activity of numerous proteins involved in the initiation and progression of cancer. Currently, three hydroxamate-containing HDAC pan-inhibitors have been approved as antitumor agents.

RESULTS

We herein present the development of a series of novel phenylpyrrole-based derivatives stemmed from combined computational and medicinal chemistry efforts to rationally modulate HDAC1/6 isoform selectivity. In vitro activity on HDAC1 and HDAC6 isoforms and the effects of selected analogs on histone H3 and α-tubulin acetylation levels were determined. Cell-based data evidenced, for selected compounds, a promising antitumor potential and low toxicity on normal cells.

CONCLUSION

The newly developed compounds represent a valuable starting point for the development of novel anticancer agents.

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 pharmacokinetics of panobinostat, a novel histone deacetylase (HDAC) inhibitor: review and perspectives

1. Panobinostat is a recently approved histone deacetylase (HDAC) inhibitor. 2. The pharmacokinetic data of panobinostat in patients with hematologic malignancies and advanced solid tumors have been collated and reviewed from the various published clinical studies for over a decade. Further perspectives and anticipated challenges in the clinical therapy with panobinostat are discussed in the review. 3. Regardless of intravenous or oral dosing, panobinostat showed a high degree of inter-patient variability in the pharmacokinetics. After oral administration, most of the administered dose is extensively metabolized and the metabolites are either fecally or renally excreted with trace amount of intact panobinostat. Both cytochrome p450 (CYP) 3A4 and non-CYP mechanisms govern the clearance of panobinostat. CYP3A4-related drug-drug interactions with panobinostat have been documented with ketoconazole (inhibitor) and dexamethasone (inducer). 4. In summary, the clinical pharmacokinetic data of panobinostat, a promising HDAC inhibitor, obtained from various clinical studies do not appear to limit the utility of panobinostat in the clinic.

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.

Histone deacetylase 6 in health and disease

Histone deacetylase (HDAC)6 is a member of the class IIb HDAC family. This enzyme is zinc-dependent and mainly localized in the cytoplasm. HDAC6 is a unique isoenzyme with two functional catalytic domains and specific physiological roles. Indeed, HDAC6 deacetylates various substrates including α-tubulin and HSP90α, and is involved in protein trafficking and degradation, cell shape and migration. Consequently, deregulation of HDAC6 activity was associated to a variety of diseases including cancer, neurodegenerative diseases and pathological autoimmune response. Therefore, HDAC6 represents an interesting potential therapeutic target. In this review, we discuss structural features of this histone deacetylase, regulation of its expression and activity, biological functions, implication in human disease initiation and progression. Finally will describe novel and selective HDAC6 inhibitors.

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.

Histone deacetylase inhibitors in hematological malignancies and solid tumors

Histone deacetylase (HDAC) inhibitors are emerging as promising anticancer drugs. Because aberrant activity and expression of HDACs have been implicated in various cancer types, a wide range of HDAC inhibitors are being investigated as anticancer agents. Furthermore, due to the demonstrable anticancer activity in both in vitro and in vivo studies, numerous HDAC inhibitors have undergone a rapid phase of clinical development in various cancer types, either as a monotherapy or in combination with other anticancer agents. Although preclinical trials show that HDAC inhibitors have a variety of biological effects across multiple pathways, including regulation of gene expression, inducing apoptosis and cell cycle arrest, inhibiting angiogenesis, and regulation of DNA damage and repair, the mechanism by which the clinical activity is mediated remains unclear. Understanding the mechanisms of anticancer activity of HDAC inhibitors is essential not only for rational drug design for targeted therapies, but for the design of optimized clinical protocols. This paper describes the links between HDACs and cancer, and the underlying mechanisms of action of HDAC inhibitors against hematological malignancies and solid tumors. Further, this review presents the clinical outcomes of vorinostat, romidepsin, and belinostat, which are approved by the United States Food and Drug Administration for the treatment of lymphomas.

Histone deacetylase 2 controls p53 and is a critical factor in tumorigenesis

Histone deacetylase 2 (HDAC2) regulates biological processes by deacetylation of histones and non-histone proteins. HDAC2 is overexpressed in numerous cancer types, suggesting general cancer-relevant functions of HDAC2. In human tumors the TP53 gene encoding p53 is frequently mutated and wild-type p53 is often disarmed. Molecular pathways inactivating wild-type p53 often remain to be defined and understood. Remarkably, current data link HDAC2 to the regulation of the tumor suppressor p53 by deacetylation and to the maintenance of genomic stability. Here, we summarize recent findings on HDAC2 overexpression in solid and hematopoietic cancers with a focus on mechanisms connecting HDAC2 and p53 in vitro and in vivo. In addition, we present an evidence-based model that integrates molecular pathways and feedback loops by which p53 and further transcription factors govern the expression and the ubiquitin-dependent proteasomal degradation of HDAC2 and of p53 itself. Understanding the interactions between p53 and HDAC2 might aid in the development of new therapeutic approaches against cancer.

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.

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.

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.