Multicenter phase II trial of the histone deacetylase inhibitor pyridylmethyl-N-{4-[(2-aminophenyl)-carbamoyl]-benzyl}-carbamate in pretreated metastatic melanoma. Melanoma Res. 2008;18:274-278. [PMID: 18626312 DOI: 10.1097/cmr.0b013e328307c248]

Lactate and lysine lactylation of histone regulate transcription in cancer

Histone lysine modifications were well-established epigenetic markers, with many types identified and extensively studied. The discovery of histone lysine lactylation had revealed a new form of epigenetic modification. The intensification of this modification was associated with glycolysis and elevated intracellular lactate levels, both of which were closely linked to cellular metabolism. Histone lactylation plays a crucial role in multiple cellular homeostasis, including immune regulation and cancer progression, thereby significantly influencing cell fate. Lactylation can modify both histone and non-histone proteins. This paper provided a comprehensive review of the typical epigenetic effects and lactylation on classical transcription-related lysine sites and summarized the known enzymes involved in histone lactylation and delactylation. Additionally, some discoveries of histone lactylation in tumor biology were also discussed, and some prospects for this field were put forward.

Entinostat Enhances the Efficacy of Chemotherapy in Small Cell Lung Cancer Through S-phase Arrest and Decreased Base Excision Repair

PURPOSE

Acquired chemoresistance is a frequent event in small cell lung cancer (SCLC), one of the deadliest human malignancies. Histone deacetylase inhibitors (HDACi) have been shown to synergize with different chemotherapeutic agents including cisplatin. Accordingly, we aimed to investigate the dual targeting of HDAC inhibition and chemotherapy in SCLC.

EXPERIMENTAL DESIGN

The efficacy of HDACi and chemotherapy in SCLC was investigated both in vitro and in vivo. Synergistic drug interactions were calculated based on the HSA model (Combenefit software). Results from the proteomic analysis were confirmed via ICP-MS, cell-cycle analysis, and comet assays.

RESULTS

Single entinostat- or chemotherapy significantly reduced cell viability in human neuroendocrine SCLC cells. The combination of entinostat with either cisplatin, carboplatin, irinotecan, epirubicin, or etoposide led to strong synergy in a subset of resistant SCLC cells. Combination treatment with entinostat and cisplatin significantly decreased tumor growth in vivo. Proteomic analysis comparing the groups of SCLC cell lines with synergistic and additive response patterns indicated alterations in cell-cycle regulation and DNA damage repair. Cell-cycle analysis revealed that cells exhibiting synergistic drug responses displayed a shift from G1 to S-phase compared with cells showing additive features upon dual treatment. Comet assays demonstrated more DNA damage and decreased base excision repair in SCLC cells more responsive to combination therapy.

CONCLUSIONS

In this study, we decipher the molecular processes behind synergistic interactions between chemotherapy and HDAC inhibition. Moreover, we report novel mechanisms to overcome drug resistance in SCLC, which may be relevant to increasing therapeutic success.

Targeting YB-1 via entinostat enhances cisplatin sensitivity of pleural mesothelioma in vitro and in vivo

Pleural mesothelioma (PM) is characterized by poor prognosis and limited therapeutic options. Y-box-binding protein 1 (YB-1) was shown to drive growth and migration of PM cells. Here, we evaluated the effect of genetic and pharmacological targeting of YB-1 on PM growth and response to cisplatin and radiation treatment. YB-1 knockdown via siRNA resulted in reduced PM cell growth, which significantly correlated with wt BAP1 and mutant NF2 and P53 status. Entinostat inhibited YB-1 deacetylation and its efficacy correlated with YB-1 knockdown-induced growth inhibition in 20 PM cell lines. Tumor growth inhibition by siRNA as well as entinostat was confirmed in mouse xenotransplant models. Furthermore, both YBX1-targeting siRNA and entinostat enhanced sensitivity to cisplatin and radiation. In particular, entinostat showed strong synergistic interactions with cisplatin which was linked to significantly increased cellular platinum uptake in all investigated cell models. Importantly, in a mouse model, the combination of cisplatin and entinostat also resulted in stronger growth inhibition than each treatment alone. Our study highlights YB-1 as an attractive target in PM and demonstrates that targeting YB-1 via entinostat is a promising approach to enhance cisplatin and radiation sensitivity.

Retinoblastoma: A review of the molecular basis of tumor development and its clinical correlation in shaping future targeted treatment strategies

Retinoblastoma is a retinal cancer that affects children and is the most prevalent intraocular tumor worldwide. Despite tremendous breakthroughs in our understanding of the fundamental mechanisms that regulate progression of retinoblastoma, the development of targeted therapeutics for retinoblastoma has lagged. Our review highlights the current developments in the genetic, epigenetic, transcriptomic, and proteomic landscapes of retinoblastoma. We also discuss their clinical relevance and potential implications for future therapeutic development, with the aim to create a frontline multimodal therapy for retinoblastoma.

HDAC Inhibitors Enhance Efficacy of the Oncolytic Adenoviruses Ad∆∆ and Ad-3∆-A20T in Pancreatic and Triple-Negative Breast Cancer Models

The prognosis for triple-negative breast cancer (TNBC) and pancreatic ductal adenocarcinoma (PDAC) is dismal. TNBC and PDAC are highly aggressive cancers with few treatment options and a potential for rapid resistance to standard-of-care chemotherapeutics. Oncolytic adenoviruses (OAds) represent a promising tumour-selective strategy that can overcome treatment resistance and eliminate cancer cells by lysis and host immune activation. We demonstrate that histone deacetylase inhibitors (HDACi) potently enhanced the cancer-cell killing of our OAds, Ad∆∆ and Ad-3∆-A20T in TNBC and PDAC preclinical models. In the TNBC cell lines MDA-MB-436, SUM159 and CAL51, cell killing, viral uptake and replication were increased when treated with sublethal doses of the Class-I-selective HDACis Scriptaid, Romidepsin and MS-275. The pan-HDACi, TSA efficiently improved OAd efficacy, both in vitro and in SUM159 xenograft models in vivo. Cell killing and Ad∆∆ replication was also significantly increased in five PDAC cell lines when pre-treated with TSA. Efficacy was dependent on treatment time and dose, and on the specific genetic alterations in each cell line. Expression of the cancer specific αvß6-integrin supported higher viral uptake of the integrin-retargeted Ad-3∆-A20T in combination with Scriptaid. In conclusion, we demonstrate that inhibition of specific HDACs is a potential means to enhance OAd activity, supporting clinical translation.

Histone Deacetylase (HDAC) Inhibitors: A Promising Weapon to Tackle Therapy Resistance in Melanoma

Melanoma is an aggressive malignant tumor, arising more commonly on the skin, while it can also occur on mucosal surfaces and the uveal tract of the eye. In the context of the unresectable and metastatic cases that account for the vast majority of melanoma-related deaths, the currently available therapeutic options are of limited value. The exponentially increasing knowledge in the field of molecular biology has identified epigenetic reprogramming and more specifically histone deacetylation (HDAC), as a crucial regulator of melanoma progression and as a key driver in the emergence of drug resistance. A variety of HDAC inhibitors (HDACi) have been developed and evaluated in multiple solid and hematologic malignancies, showing promising results. In melanoma, various experimental models have elucidated a critical role of histone deacetylases in disease pathogenesis. They could, therefore, represent a promising novel therapeutic approach for advanced disease. A number of clinical trials assessing the efficacy of HDACi have already been completed, while a few more are in progress. Despite some early promising signs, a lot of work is required in the field of clinical studies, and larger patient cohorts are needed in order for more valid conclusions to be extracted, regarding the potential of HDACi as mainstream treatment options for melanoma.

Dissecting Histone Deacetylase 3 in Multiple Disease Conditions: Selective Inhibition as a Promising Therapeutic Strategy

The acetylation of histone and non-histone proteins has been implicated in several disease states. Modulation of such epigenetic modifications has therefore made histone deacetylases (HDACs) important drug targets. HDAC3, among various class I HDACs, has been signified as a potentially validated target in multiple diseases, namely, cancer, neurodegenerative diseases, diabetes, obesity, cardiovascular disorders, autoimmune diseases, inflammatory diseases, parasitic infections, and HIV. However, only a handful of HDAC3-selective inhibitors have been reported in spite of continuous efforts in design and development of HDAC3-selective inhibitors. In this Perspective, the roles of HDAC3 in various diseases as well as numerous potent and HDAC3-selective inhibitors have been discussed in detail. It will surely open up a new vista in the discovery of newer, more effective, and more selective HDAC3 inhibitors.

Cancer stem cells, epigenetics, tumor microenvironment and future therapeutics in cutaneous malignant melanoma: a review

This review provides an overview of the current understanding of the ontogeny and biology of melanoma stem cells in cutaneous malignant melanoma. This article also summarizes and evaluates the current knowledge of the underlying epigenetic mechanisms, the regulation of melanoma progress by the tumor microenvironment as well as the therapeutic implications and applications of these novel insights, in the setting of personalized medicine. Unraveling the complex ecosystem of cutaneous malignant melanoma and the interplay between its components, aims to provide novel insights into the establishment of efficient therapeutic strategies.

The "ART" of Epigenetics in Melanoma: From histone "Alterations, to Resistance and Therapies"

Malignant melanoma is the most deadly form of skin cancer. It originates from melanocytic cells and can also arise at other body sites. Early diagnosis and appropriate medical care offer excellent prognosis with up to 5-year survival rate in more than 95% of all patients. However, long-term survival rate for metastatic melanoma patients remains at only 5%. Indeed, malignant melanoma is known for its notorious resistance to most current therapies and is characterized by both genetic and epigenetic alterations. In cutaneous melanoma (CM), genetic alterations have been implicated in drug resistance, yet the main cause of this resistance seems to be non-genetic in nature with a change in transcription programs within cell subpopulations. This change can adapt and escape targeted therapy and immunotherapy cytotoxic effects favoring relapse. Because they are reversible in nature, epigenetic changes are a growing focus in cancer research aiming to prevent or revert the drug resistance with current therapies. As such, the field of epigenetic therapeutics is among the most active area of preclinical and clinical research with effects of many classes of epigenetic drugs being investigated. Here, we review the multiplicity of epigenetic alterations, mainly histone alterations and chromatin remodeling in both cutaneous and uveal melanomas, opening opportunities for further research in the field and providing clues to specifically control these modifications. We also discuss how epigenetic dysregulations may be exploited to achieve clinical benefits for the patients, the limitations of these therapies, and recent data exploring this potential through combinatorial epigenetic and traditional therapeutic approaches.

Epigenetic mechanisms underlying the therapeutic effects of HDAC inhibitors in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a hematological disorder caused by the oncogenic BCR-ABL fusion protein in more than 90% of patients. Despite the striking improvements in the management of CML patients since the introduction of tyrosine kinase inhibitors (TKis), the appearance of TKi resistance and side effects lead to treatment failure, justifying the need of novel therapeutic approaches. Histone deacetylase inhibitors (HDACis), able to modulate gene expression patterns and important cellular signaling pathways through the regulation of the acetylation status of both histone and non-histone protein targets, have been reported to display promising anti-leukemic properties alone or in combination with TKis. This review summarizes pre-clinical and clinical studies that investigated the mechanisms underlying the anticancer potential of HDACis and discusses the rationale for a combination of HDACis with TKis as a therapeutic option in CML.

Combined pharmacophore modeling, 3D-QSAR and docking studies to identify novel HDAC inhibitors using drug repurposing

Histone deacetylases (HDACs), a critical family of epigenetic enzymes, has emerged as a promising target for antitumor drugs. Here, we describe our protocol of virtual screening in identification of novel potential HDAC inhibitors through pharmacophore modeling, 3D-QSAR, molecular docking and molecular dynamics (MD) simulation. Considering the limitation of current virtual screening works, drug repurposing strategy was applied to discover druggable HDAC inhibitor. The ligand-based pharmacophore and 3D-QSAR models were established, and their reliability was validated by different methods. Then, the DrugBank database was screened, followed by molecular docking. MD simulation (100 ns) was performed to further study the stability of ligand binding modes. Finally, results indicated the hit DB03889 with high in silico inhibitory potency was suitable for further experimental analysis.Communicated by Ramaswamy H. Sarma.

Entinostat reverses P-glycoprotein activation in snail-overexpressing adenocarcinoma HCC827 cells

Epithelial-to-mesenchymal transition (EMT) in cancer cells facilitates tumor progression by promoting invasion and metastasis. Snail is a transcriptional factor that induces EMT, while P-glycoprotein (P-gp) is an efflux transporter involved in anticancer drug resistance, and P-gp efflux activity is stimulated in Snail-overexpressing lung cancer cells with EMT characteristics. Since the histone deacetylase (HDAC) inhibitor entinostat (Ent) reverses EMT features, our aim in this study was to determine whether Ent also suppresses P-gp activation in Snail-induced cells. First, we confirmed that Ent treatment reduced migration activity, downregulated E-cadherin and upregulated vimentin at the mRNA level in Snail-overexpressing cells, thus inhibiting EMT. Efflux and uptake assays using rhodamine123 (Rho123), a fluorescent P-gp substrate, showed that Ent also inhibited Snail-induced activation of P-gp. Moreover, P-gp activity was more strongly inhibited by Ent in Snail-overexpressing cells than in Mock cells. When we evaluated the uptakes of Rho123 by LLC-PK1 cells and P-gp-overexpressing LLC-GA5COL150 cells, Rho123 accumulation in LLC-GA5COL150 cells was significantly decreased compared with that in LLC-PK1 cells. Coincubation with Ent had no effect on Rho123 accumulation in either of the cell lines. Thus, Ent appears to be an inhibitor, but not a substrate, of P-gp at low concentration. Our results suggest that Ent treatment might suppress not only Snail-induced cancer malignant alteration, but also P-gp-mediated multidrug resistance.

Advances and Challenges of HDAC Inhibitors in Cancer Therapeutics

Since the identification and cloning of human histone deacetylases (HDACs) and the rapid approval of vorinostat (Zolinza®) for the treatment of cutaneous T-cell lymphoma, the field of HDAC biology has met many initial successes. However, many challenges remain due to the complexity involved in the lysine posttranslational modifications, epigenetic transcription regulation, and nonepigenetic cellular signaling cascades. In this chapter, we will: review the discovery of the first HDAC inhibitor and present discussion regarding the future of next-generation HDAC inhibitors, give an overview of different classes of HDACs and their differences in lysine deacylation activity, discuss different classes of HDAC inhibitors and their HDAC isozyme preferences, and review HDAC inhibitors' preclinical studies, their clinical trials, their pharmacokinetic challenges, and future direction. We will also discuss the likely reason for the failure of multiple HDAC inhibitor clinical trials in malignancies other than lymphoma and multiple myeloma. In addition, the potential molecular mechanism(s) that may play a key role in the efficacy and therapeutic response rate in the clinic and the likely patient population for HDAC therapy will be discussed.

In silico and in vitro drug screening identifies new therapeutic approaches for Ewing sarcoma

The long-term overall survival of Ewing sarcoma (EWS) patients remains poor; less than 30% of patients with metastatic or recurrent disease survive despite aggressive combinations of chemotherapy, radiation and surgery. To identify new therapeutic options, we employed a multi-pronged approach using in silico predictions of drug activity via an integrated bioinformatics approach in parallel with an in vitro screen of FDA-approved drugs. Twenty-seven drugs and forty-six drugs were identified, respectively, to have anti-proliferative effects for EWS, including several classes of drugs in both screening approaches. Among these drugs, 30 were extensively validated as mono-therapeutic agents and 9 in 14 various combinations in vitro. Two drugs, auranofin, a thioredoxin reductase inhibitor, and ganetespib, an HSP90 inhibitor, were predicted to have anti-cancer activities in silico and were confirmed active across a panel of genetically diverse EWS cells. When given in combination, the survival rate in vivo was superior compared to auranofin or ganetespib alone. Importantly, extensive formulations, dose tolerance, and pharmacokinetics studies demonstrated that auranofin requires alternative delivery routes to achieve therapeutically effective levels of the gold compound. These combined screening approaches provide a rapid means to identify new treatment options for patients with a rare and often-fatal disease.

Inhibition of histone deacetylases in melanoma-a perspective from bench to bedside

Histone deacetylases (HDACs) are critically involved in epigenetic gene regulation through alterations of the chromatin status of DNA. Aberrant expression, dysregulation of their enzymatic activity or imbalances between HDACs and histone acetyltransferases are likely involved in the development and progression of cancer. Pharmacologic inhibition of HDACs shows potent antitumor activity in a panel of malignancies such as colon or gastric cancer and multiple myeloma. In this review, we summarize the current knowledge of HDACs in melanoma and evaluate the application of HDAC inhibition from an experimental and clinical perspective. The molecular functions of HDACs can be classified into histone and non-histone effects with diverse implications in proliferation, cell cycle progression and apoptosis. HDAC inhibition results in G1 cell cycle arrest, induces apoptosis and increases the immunogenicity of melanoma cells. Some studies proposed that HDAC inhibition may overcome the resistance of melanoma cells to BRAF inhibition. Several inhibitors such as vorinostat, entinostat and valproic acid have recently been tested in phase I and early phase II trials, yet most agents show limited efficacy and tolerability as single agents. The most frequent adverse events of HDAC inhibition comprise haematological toxicity, fatigue, nausea and laboratory abnormalities. Existing evidence supports the hypothesis that HDAC inhibitors (HDACi) may sensitize melanoma cells to immunotherapy and targeted therapy and hence bear therapeutic potential concurrent with immune checkpoint blockade or BRAF and MEK inhibition.

BIK is involved in BRAF/MEK inhibitor induced apoptosis in melanoma cell lines

In patients with BRAF-mutated melanoma specific inhibitors of BRAF^V600E and MEK1/2 frequently induce initial tumor reduction, frequently followed by relapse. As demonstrated previously, BRAF^V600E-inhibition induces apoptosis only in a fraction of treated cells, while the remaining arrest and survive providing a source or a niche for relapse. To identify factors contributing to the differential initial response towards BRAF/MEK inhibition, we established M14 melanoma cell line-derived single cell clones responding to treatment with BRAF inhibitor vemurafenib and MEK inhibitor trametinib predominantly with either cell cycle arrest (CCA-cells) or apoptosis (A-cells). Screening for differentially expressed apoptosis-related genes revealed loss of BCL2-Interacting Killer (BIK) mRNA in CCA-cells. Importantly, ectopic expression of BIK in CCA-cells resulted in increased apoptosis rates following vemurafenib/trametinib treatment, while knockdown/knockout of BIK in A-cells attenuated the apoptotic response. Furthermore, we demonstrate reversible epigenetic silencing of BIK mRNA expression in CCA-cells. Importantly, HDAC inhibitor treatment associated with re-expression of BIK augmented sensitivity of CCA-cells towards vemurafenib/trametinib treatment both in vitro and in vivo. In conclusion, our results suggest that BIK can be a critical mediator of melanoma cell fate determination in response to MAPK pathway inhibition.

miR-92a-3p and MYCBP2 are involved in MS-275-induced and c-myc-mediated TRAIL-sensitivity in melanoma cells

Increasing evidence has demonstrated that in several tumors c-myc acts either as an oncogène or as a proapoptotic agent, depending on binding partner interactions. Recently, we showed that up-regulation of this gene by the histone deacetylase inhibitor MS-275 was responsible for sensitization to TRAIL-induced apoptosis through c-FLIP repression in melanoma. The present study aimed at investigating whether, in addition to inducing H3 hyperacetylation at the c-myc promoter, MS-275 could enhance cell death through the regulation of miRNAs involved in apoptosis, such as the miR-17-92 cluster. Following MS-275 treatment, a decrease in miR-92a-3p was observed either in TRAIL-resistant or TRAIL-sensitive cutaneous and uveal melanoma cells. Prediction tools revealed that miR-92a-3p targeted MYCBP2. Gain- and loss-of-function experiments showed that the 3'-UTR of MYCBP2 mRNA was the target of miR-92a-3p, as ectopic expression of miR-92a-3p resulted in MYCBP2 downregulation whereas miR-92a-3p knockdown markedly increased the expression of MYCBP2. Silencing of MYCBP2 counteracted the pro-apoptotic effects exerted by the down-regulation of miR-92a-3p and prevented c-myc-induced repression of c-FLIP, indicating a pivotal role of MYCBP2 as a mediator of miR-92a-3p and c-myc function. Together, our findings indicate that the MS-275-triggered downregulation of the oncogenic miR-92a-3p- which leads to the overexpression of its target gene MYCBP2 - is an event required for the enhanced susceptibility of melanoma cells to TRAIL-mediated apoptosis. Our data illustrate another epigenetic mechanism activated by MS-275 at the post-transcriptional level in melanoma, in addition to its best-known effects at the transcriptional level.

Epigenetic Therapy for Solid Tumors: Highlighting the Impact of Tumor Hypoxia

In the last few decades, epigenetics has emerged as an exciting new field in development and disease, with a more recent focus towards cancer. Epigenetics has classically referred to heritable patterns of gene expression, primarily mediated through DNA methylation patterns. More recently, it has come to include the reversible chemical modification of histones and DNA that dictate gene expression patterns. Both the epigenetic up-regulation of oncogenes and downregulation of tumor suppressors have been shown to drive tumor development. Current clinical trials for cancer therapy include pharmacological inhibition of DNA methylation and histone deacetylation, with the aim of reversing these cancer-promoting epigenetic changes. However, the DNA methyltransferase and histone deacetylase inhibitors have met with less than promising results in the treatment of solid tumors. Regions of hypoxia are a common occurrence in solid tumors. Tumor hypoxia is associated with increased aggressiveness and therapy resistance, and importantly, hypoxic tumor cells have a distinct epigenetic profile. In this review, we provide a summary of the recent clinical trials using epigenetic drugs in solid tumors, discuss the hypoxia-induced epigenetic changes and highlight the importance of testing the epigenetic drugs for efficacy against the most aggressive hypoxic fraction of the tumor in future preclinical testing.

Evaluation of azacitidine and entinostat as sensitization agents to cytotoxic chemotherapy in preclinical models of non-small cell lung cancer

Recent clinical data in lung cancer suggests that epigenetically targeted therapy may selectively enhance chemotherapeutic sensitivity. There have been few if any studies rigorously evaluating this hypothesized priming effect. Here we describe a series of investigations testing whether epigenetic priming with azacitidine and entinostat increases sensitivity of NSCLC to cytotoxic agents.

We noted no differences in chemosensitivity following treatment with epigenetic therapy in in vitro assays of viability and colony growth. Using cell line and patient-derived xenograft (PDX) models, we also observed no change in responsiveness to cisplatin in vivo. In select models, we noted differential responses to irinotecan treatment in vivo. In vitro epigenetic therapy prior to tumor implantation abrogated response of H460 xenografts to irinotecan. Conversely, in vitro epigenetic therapy appeared to sensitize A549 xenografts (tumor growth inhibition 51%, vs. 22% in mock-pretreated control). In vivo epigenetic therapy enhanced the response of adenocarcinoma PDX to irinotecan.

Taken together, these data do not support broadly applicable epigenetic priming in NSCLC. Priming effects may be context-specific, dependent on both tumor and host factors. Further preclinical study is necessary to determine whether, and in which contexts, priming with epigenetic therapy has potential to enhance chemotherapeutic efficacy in NSCLC patients.

A phase I study of the histone deacetylase (HDAC) inhibitor entinostat, in combination with sorafenib in patients with advanced solid tumors

Based on preclinical data demonstrating cytotoxic synergy between sorafenib and entinostat, a phase I study of this combination was conducted in patients with advanced solid tumors. Enrollment followed the traditional "3 + 3" dose escalation scheme. Entinostat was given orally once every 2 weeks, starting at a dose of 4 mg and escalating to 6 and 10 mg every 2 weeks. Sorafenib was administered as a continuous oral dose, escalating from 200 to 400 mg twice daily. A treatment cycle was 28 days. A total of 31 patients with advanced solid tumors were enrolled on the study. The three dose-limiting toxicities (DLTs) observed were grade 3 hand-foot syndrome, nausea/vomiting, and fatigue. MTD was not reached. The recommended phase II dose was defined as the full dose of the respective drugs administered individually. The most common grade 3-4 toxicities were muscle weakness (13 %), skin rash (10 %), fatigue (6 %), diarrhea (6 %), and hand-foot syndrome (3 %). One NSCLC patient achieved a partial response. Two patients (adenocarcinoma of GE junction and Hurthle cell carcinoma of the thyroid) were on the study for more than 9 months with stable disease. The combination of entinostat and sorafenib was well tolerated. Entinostat 10 mg orally once every 2 weeks in combination with sorafenib 400 mg orally twice daily, representing full single agent doses of each drug was identified as the recommended phase 2 dose (RP2D). These data support future clinical development of the combination of entinostat and sorafenib.

Histone deacetylase inhibitors and cell death

Histone deacetylases (HDACs) are a vast family of enzymes involved in chromatin remodeling and have crucial roles in numerous biological processes, largely through their repressive influence on transcription. In addition to modifying histones, HDACs also target many other non-histone protein substrates to regulate gene expression. Recently, HDACs have gained growing attention as HDAC-inhibiting compounds are being developed as promising cancer therapeutics. Histone deacetylase inhibitors (HDACi) have been shown to induce differentiation, cell cycle arrest, apoptosis, autophagy and necrosis in a variety of transformed cell lines. In this review, we mainly discuss how HDACi may elicit a therapeutic response to human cancers through different cell death pathways, in particular, apoptosis and autophagy.

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.

Epigenetics of melanoma: implications for immune-based therapies

Malignant melanoma is a complex disease that arises and evolves due to a myriad of genetic and epigenetic events. Among these, the interaction between epigenetic alterations (i.e., histone modifications, DNA methylation, mRNA silencing by miRNAs and nucleosome repositioning) has been recently identified as playing an important role in melanoma development and progression by affecting key cellular pathways such as cell cycle regulation, DNA repair, apoptosis, invasion and immune recognition. Differently to genetic lesions, epigenetic changes are potentially pharmacologically reversible by using epigenetic drugs. Along this line, preclinical and clinical findings indicate that these drugs, given alone or in combination therapies, can efficiently modulate the immunophenotype of melanoma cells. The aim of this review is to provide a comprehensive summary of melanoma epigenetics and the current use of epigenetic drugs in the clinical setting.

BRD4 sustains melanoma proliferation and represents a new target for epigenetic therapy

Metastatic melanoma remains a mostly incurable disease. Although newly approved targeted therapies are efficacious in a subset of patients, resistance and relapse rapidly ensue. Alternative therapeutic strategies to manipulate epigenetic regulators and disrupt the transcriptional program that maintains tumor cell identity are emerging. Bromodomain and extraterminal domain (BET) proteins are epigenome readers known to exert key roles at the interface between chromatin remodeling and transcriptional regulation. Here, we report that BRD4, a BET family member, is significantly upregulated in primary and metastatic melanoma tissues compared with melanocytes and nevi. Treatment with BET inhibitors impaired melanoma cell proliferation in vitro and tumor growth and metastatic behavior in vivo, effects that were mostly recapitulated by individual silencing of BRD4. RNA sequencing of BET inhibitor-treated cells followed by Gene Ontology analysis showed a striking impact on transcriptional programs controlling cell growth, proliferation, cell-cycle regulation, and differentiation. In particular, we found that, rapidly after BET displacement, key cell-cycle genes (SKP2, ERK1, and c-MYC) were downregulated concomitantly with the accumulation of cyclin-dependent kinase (CDK) inhibitors (p21 and p27), followed by cell-cycle arrest. Importantly, BET inhibitor efficacy was not influenced by BRAF or NRAS mutational status, opening the possibility of using these small-molecule compounds to treat patients for whom no effective targeted therapy exists. Collectively, our study reveals a critical role for BRD4 in melanoma tumor maintenance and renders it a legitimate and novel target for epigenetic therapy directed against the core transcriptional program of melanoma.

Effects of treatment with histone deacetylase inhibitors in solid tumors: a review based on 30 clinical trials

It has been found that the epigenetic silence of tumor suppressor genes induced by overexpression of histone deacetylases (HDACs) plays an important role in carcinogenesis. HDAC inhibitors (HDACi) that block the activity of specific HDACs have emerged as the accessory therapeutic agents for multiple human cancers. To better understand the effects of HDACi in cancer treatment, we carried out a review based on 30 published clinical trials to determine whether HDACi will benefit patients with solid tumors. Information of complete response, partial response, stable disease, objective responses and objective response rate was collected to assess clinical outcomes. A lack of therapeutic effects was observed when HDACi was used as a single agent. However, when HDACi treatment was combined with other agents, it appeared to increase the anti-tumor activity. High-quality studies are required to better understand the clinical effects of HDACi.

Cotargeting histone deacetylases and oncogenic BRAF synergistically kills human melanoma cells by necrosis independently of RIPK1 and RIPK3

Past studies have shown that histone deacetylase (HDAC) and mutant BRAF (v-Raf murine sarcoma viral oncogene homolog B1) inhibitors synergistically kill melanoma cells with activating mutations in BRAF. However, the mechanism(s) involved remains less understood. Here, we report that combinations of HDAC and BRAF inhibitors kill BRAF^V600E melanoma cells by induction of necrosis. Cotreatment with the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) or panobinostat (LBH589) and the BRAF inhibitor PLX4720 activated the caspase cascade, but caspases appeared dispensable for killing, in that inhibition of caspases did not invariably block induction of cell death. The majority of dying cells acquired propidium iodide positivity instantly when they became positive for Annexin V, suggesting induction of necrosis. This was supported by caspase-independent release of high-mobility group protein B1, and further consolidated by rupture of the plasma membrane and loss of nuclear and cytoplasmic contents, as manifested by transmission electron microscopic analysis. Of note, neither the necrosis inhibitor necrostatin-1 nor the small interference RNA (siRNA) knockdown of receptor-interacting protein kinase 3 (RIPK3) inhibited cell death, suggesting that RIPK1 and RIPK3 do not contribute to induction of necrosis by combinations of HDAC and BRAF inhibitors in BRAF^V600E melanoma cells. Significantly, SAHA and the clinically available BRAF inhibitor vemurafenib cooperatively inhibited BRAF^V600E melanoma xenograft growth in a mouse model even when caspase-3 was inhibited. Taken together, these results indicate that cotreatment with HDAC and BRAF inhibitors can bypass canonical cell death pathways to kill melanoma cells, which may be of therapeutic advantage in the treatment of melanoma.

Could interleukin-15 potentiate histone deacetylase inhibitor effects in haematological malignancy?

Despite significant progress in cancer therapy, prognosis in acute leukaemia remains dismal, and the development of new therapies is urgently warranted: in acute myeloid leukaemia, the current cure rate is of 30-40% in younger and much less in older patients. Chromatin remodeling through histone acetylation is one of the major mechanisms of transcriptional control of genes, and is involved in 'gene silencing' of antioncogenes in various tumour cells. Chromatin remodeling is also involved in transcriptional control of other genes, such as NKG2D ligand genes. Histone deacetylases and acetyltransferases are involved in the epigenetic regulation of gene expression, and increased/decreased activity of histone deacetylases has been reported in several cancer types. Histone deacetylase inhibitors were reportedly active in many cancers including hematological malignancies, and have been shown in numerous experiments to reduce cancer cell growth and enhance cell differentiation, growth arrest and apoptosis. In acute myeloid leukaemia, histone deacetylase inhibitors alone had limited efficacy, but their combination with other anticancer agents yielded promising results. Interleukin (IL)-15 is regarded with great hope in the immunotherapy of cancer, and IL-15-activated cytokine-induced killer cells showed potent antileukemic activity both in vitro and in vivo. IL-15 increases expression of NKG2D and its ligands and can increase natural killer cell mediated cytotoxicity against tumour cells. The administration of IL-15 was recently shown to be safe in preclinical models, and there are ongoing clinical trials of IL-15 in patients with cancer and HIV infection. We hypothesise that IL-15 will synergise with histone deacetylase inhibitors in increasing the levels of activatory NKG2D receptors on natural killer and CD8(+) T cells and of their ligands, the MHC class I related molecule A and B, on tumor cells, and will enhance innate immune antitumour responses in acute myeloid leukaemia and other haematological malignancies. Up-regulation of NKG2D-NKG2D-ligand antitumour immune response by combining histone deacetylase inhibitors with IL-15 has the potential to improve the efficacy of acute myeloid leukaemia treatment.

Targeted cancer therapy: giving histone deacetylase inhibitors all they need to succeed

Histone deacetylase inhibitors (HDACis) have now emerged as a powerful new class of small-molecule therapeutics acting through the regulation of the acetylation states of histone proteins (a form of epigenetic modulation) and other non-histone protein targets. Over 490 clinical trials have been initiated in the last 10 years, culminating in the approval of two structurally distinct HDACis - SAHA (vorinostat, Zolinza™) and FK228 (romidepsin, Istodax™). However, the current HDACis have serious limitations, including ineffectively low concentrations in solid tumors and cardiac toxicity, which is hindering their progress in the clinic. Herein, we review the primary paradigms being pursued to overcome these hindrances, including HDAC isoform selectivity, localized administration, and targeting cap groups to achieve selective tissue and cell type distribution.

Vorinostat approved in Japan for treatment of cutaneous T-cell lymphomas: status and prospects

Histone acetylation and deacetylation play important roles in the regulation of gene transcription and in the modulation of chromatin structure. The levels of histone acetylation are determined by the activities of histone acetyltransferases and histone deacetylases (HDACs). HDACs are associated with a number of oncogenes and tumor suppressor genes and can be aberrantly expressed and/or inappropriately activated in cancer cells. HDAC inhibitors have therefore recently emerged as a novel treatment modality against malignancies. They regulate gene expression by enhancing the acetylation of not only histones but also nonhistone proteins, including transcription factors, transcription regulators, signal transduction mediators, and DNA repair enzymes, and they inhibit cancer growth. Vorinostat (suberoylanilide hydroxamic acid) is one of the most potent HDAC inhibitors, and was approved in Japan in 2011 for the treatment of cutaneous T-cell lymphoma. Numerous clinical trials have shown it to be effective against cutaneous T-cell lymphoma but less so against other types of cancer. Because vorinostat can overcome resistance to or enhance the efficacy of other anticancer agents, such as 5-fluorouracil, carboplatin, paclitaxel, bortezomib, and tamoxifen, combination therapies using vorinostat and these agents have been investigated. This review introduces the background and mechanism of action of vorinostat and describes the results of clinical trials using vorinostat, both as a single agent and in combination with other anticancer agents, against cutaneous T-cell lymphoma and other malignancies.

Promises and challenges of anticancer drugs that target the epigenome

The occurrence of epigenetic aberrations in cancer and their role in promoting tumorigenesis has led to the development of various small molecule inhibitors that target epigenetic enzymes. In preclinical settings, many epigenetic inhibitors demonstrate promising activity against a variety of both hematological and solid tumors. The therapeutic efficacy of those inhibitors that have entered the clinic however, is restricted predominantly to hematological malignancies. Here we outline the observed epigenetic aberrations in various types of cancer and the clinical responses to epigenetic drugs. We furthermore discuss strategies to improve the responsiveness of both hematological and solid malignancies to epigenetic drugs.

From genes to drugs: targeted strategies for melanoma

The past decade has revealed that melanoma is comprised of multiple subclasses that can be categorized on the basis of key features, including the clinical stage of disease, the oncogenic molecular 'drivers', the anatomical location or the behaviour of the primary lesion and the expression of specific biomarkers. Although exercises in subclassification are not new in oncology, progress in this area has produced both conceptual and clinical breakthroughs, which, for melanoma, are unprecedented in the modern history of the disease. This Review focuses on these recent striking advances in the strategy of molecularly targeted approaches to the therapy of melanoma in humans.

Epigenetic biomarkers in skin cancer

Epigenetic aberrations have been associated with cutaneous melanoma tumorigenesis and progression including dysregulated DNA gene promoter region methylation, histone modification, and microRNA. Several of these major epigenetic aberrations have been developed into biomarkers. Epigenetic biomarkers can be detected in tissue and in blood as circulating DNA in melanoma patients. There is strong evidence that biomarkers in cutaneous melanoma will have an important role as companions to therapeutics and overall patient management. Important progress has been made in epigenetic melanoma biomarker development and verification of clinical utility, and this review discusses some of the key current developments and existing challenges.

New therapeutic targets in melanoma

Research into molecular targets for drug development in melanoma is starting to bear fruit. Of the drugs tested to date in patients with metastatic melanoma, those that have yielded the best results are V600E BRAF inhibitors in melanomas carrying the V600E mutation; c-kit tyrosine kinase activity inhibitors in melanomas carrying c-kit mutations; and anti-cytotoxic T lymphocyte antigen 4 (CTLA-4) antibodies, which block the mechanisms involved in immune tolerance. Many problems have yet to be resolved in these areas, however, such as the rapid development of resistance to BRAF and c-kit inhibitors and the lack of biomarkers to predict treatment response in the case of CTLA-4 blockers. We review the results of targeted therapy with these and other drugs in metastatic melanoma and discuss what the future holds for this field.

Histone acetyltransferases and deacetylases: molecular and clinical implications to gastrointestinal carcinogenesis

Histone acetyltransferases and deacetylases are two groups of enzymes whose opposing activities govern the dynamic levels of reversible acetylation on specific lysine residues of histones and many other proteins. Gastrointestinal (GI) carcinogenesis is a major cause of morbidity and mortality worldwide. In addition to genetic and environmental factors, the role of epigenetic abnormalities such as aberrant histone acetylation has been recognized to be pivotal in regulating benign tumorigenesis and eventual malignant transformation. Here we provide an overview of histone acetylation, list the major groups of histone acetyltransferases and deacetylases, and cover in relatively more details the recent studies that suggest the links of these enzymes to GI carcinogenesis. As potential novel therapeutics for GI and other cancers, histone deacetylase inhibitors are also discussed.

Mechanisms of resistance to histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are a new class of anticancer agents. HDAC inhibitors induce acetylation of histones and nonhistone proteins which are involved in regulation of gene expression and in various cellular pathways including cell growth arrest, differentiation, DNA damage and repair, redox signaling, and apoptosis (Marks, 2010). The U.S. Food and Drug Administration has approved two HDAC inhibitors, vorinostat and romidepsin, for the treatment of cutaneous T-cell lymphoma (Duvic & Vu, 2007; Grant et al., 2010; Marks & Breslow, 2007). Over 20 chemically different HDAC inhibitors are in clinical trials for hematological malignancies and solid tumors. This review considers the mechanisms of resistance to HDAC inhibitors that have been identified which account for the selective effects of these agents in inducing cancer but not normal cell death. These mechanisms, such as functioning Chk1, high levels of thioredoxin, or the prosurvival BCL-2, may also contribute to resistance of cancer cells to HDAC inhibitors.

Targeting the epigenome for treatment of cancer

Cancer genome analyses have revealed that the enzymes involved in epigenetic gene regulation are frequently deregulated in cancer. Here we describe the enzymes that control the epigenetic state of the cell, how they are affected in cancer and how this knowledge can be exploited to treat cancer with a new arsenal of selective therapies.

HDAC inhibitors in cancer biology: emerging mechanisms and clinical applications

Reversible acetylation mediated by histone deacetylases (HDACs) influences a broad repertoire of physiological processes, many of which are aberrantly controlled in tumor cells. As HDAC inhibition prompts tumor cells to enter apoptosis, small-molecule HDAC inhibitors have been developed as a new class of mechanism-based anti-cancer agent, many of which have entered clinical trials. Although the clinical picture is evolving and the precise utility of HDAC inhibitors remains to be determined, it is noteworthy that certain tumor types undergo a favorable response, in particular hematological malignancies. Vorinostat and romidepsin have been approved for treating cutaneous T-cell lymphoma in patients with progressive, persistent or recurrent disease. Here, we discuss developments in our understanding of molecular events that underlie the anti-cancer effects of HDAC inhibitors and relate this information to the emerging clinical picture for the application of these inhibitors in the treatment of cancer.

The biology and therapeutic implications of HDACs in the heart

The heart responds to stresses such as chronic hypertension and myocardial infarction by undergoing a remodeling process that is associated with myocyte hypertrophy, myocyte death, inflammation and fibrosis, often resulting in impaired cardiac function and heart failure. Recent studies have revealed key roles for histone deacetylases (HDACs) as both positive and negative regulators of pathological cardiac remodeling, and small molecule HDAC inhibitors have demonstrated efficacy in animal models of heart failure. This chapter reviews the functions of individual HDAC isoforms in the heart and highlights issues that need to be addressed to enable development of novel HDAC-directed therapies for cardiovascular indications.

Histone deacetylase inhibitors: emerging mechanisms of resistance

The histone deacetylase inhibitors (HDIs) have shown promise in the treatment of a number of hematologic malignancies, leading to the approval of vorinostat and romidepsin for the treatment of cutaneous T-cell lymphoma and romidepsin for the treatment of peripheral T-cell lymphoma by the U.S. Food and Drug Administration. Despite these promising results, clinical trials with the HDIs in solid tumors have not met with success. Examining mechanisms of resistance to HDIs may lead to strategies that increase their therapeutic potential in solid tumors. However, relatively few examples of drug-selected cell lines exist, and mechanisms of resistance have not been studied in depth. Very few clinical translational studies have evaluated resistance mechanisms. In the current review, we summarize many of the purported mechanisms of action of the HDIs in clinical trials and examine some of the emerging resistance mechanisms.

Special diaphragm-like strictures of small bowel unrelated to non-steroidal anti-inflammatory drugs

AIM: To summarize clinical, endoscopic, radiologic and pathologic features of special diaphragm-like strictures found in small bowel, with no patient use of non-steroidal anti-inflammatory drugs (NSAIDs).

METHODS: From January 2000 to December 2009, 5 cases (2 men and 3 women, with a mean age of 41.6 years) were diagnosed as having diaphragm-like strictures of small bowel on imaging, operation and pathology. All the patients denied the use of NSAIDs. The clinical, endoscopic, radiologic and pathologic findings in these 5 patients were retrospectively reviewed from the hospital database. Images of capsule endoscopy (CE) and small bowel follow-through (SBFT) obtained in 3 and 3 patients, respectively, and images of double-balloon enteroscopy and computed tomography enterography (CTE) obtained in all 5 patients were available for review.

RESULTS: All patients presented with long-term (2-16 years) symptoms of gastrointestinal bleeding and varying degrees of anemia. There was only one stricture in four cases and three lesions in one case, and all the lesions were located in the middle or distal segment of ileum. Circumferential stricture was shown in the small bowel in three cases in the CE image, but the capsule was retained in the small bowel of 2 patients. Routine abdomen computed tomography scan showed no other abnormal results except gallstones in one patient. The lesions were shown as circumferential strictures accompanied by dilated small bowel loops in the small bowel on the images of CTE (in all 5 cases), SBFT (in 2 cases) and double-balloon enteroscopy (in all cases). On microscopy, a chronic inflammatory infiltrate and circumferential diaphragm were found in all lesions.

CONCLUSION: Diaphragm-like strictures of small bowel might be a special consequence of unclear damaging insults to the intestine, having similar clinical, endoscopic, radiologic and pathologic features.

Combined inhibitors of angiogenesis and histone deacetylase: efficacy in rat hepatoma

AIM

To evaluate the antitumoral effect of combined inhibitors of angiogenesis and histone deacetylases in an experimental rat hepatoma model.

METHODS

MH7777A hepatoma cells were injected into the liver of male Buffalo rats. After 7 d treatment with the vascular endothelial growth factor receptor antagonist PTK787/ZK222584 (PTK/ZK), the histone deacetylase inhibitor MS-275, tamoxifen (TAM) and/or retinoic acid was initiated (n ≥ 8 animals/group). Natural tumor development was shown in untreated control groups (control 1 with n = 12, control 2 with n = 8). The control groups were initiated at different time points to demonstrate the stability of the hepatoma model. For documentation of possible side effects, we documented any change in body weight, loss of fur and diarrhea. After 21 d treatment, the rats were euthanized. Main target parameters were tumor size and metastasis rate. Additionally, immunohistochemistry for the proliferating cell nuclear antigen (PCNA) and TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay were performed.

RESULTS

The control groups developed large tumor nodules with extrahepatic tumor burden in the lung and abdominal organs (control 1: 6.18 cm(3) ± 4.14 cm(3) and control 2: 8.0 cm(3) ± 4.44 cm(3) 28 d after tumor cell injection). The tumor volume did not differ significantly in the control groups (P = 0.13). As single agents MS-275 and PTK/ZK reduced tumor volume by 58.6% ± 2.6% and 48.7% ± 3.2% vs control group 1, which was significant only for MS-275 (P = 0.025). The combination of MS-275 and PTK/ZK induced a nearly complete and highly significant tumor shrinkage by 90.3% ± 1% (P = 0.005). Addition of TAM showed no further efficacy, while quadruple therapy with retinoic acid increased antitumoral efficacy (tumor reduction by 93 ± 1%) and side effects. PCNA positive cells were not significantly reduced by the single agents, while dual therapy (MS-275 and PTK/ZK) and quadruple therapy reduced the PCNA-positive cell fraction significantly by 9.1 and 20.6% vs control 1 (P < 0.05). The number of TUNEL-positive cells, markers for ongoing apoptosis, was increased significantly by the single agents (control 1: 6.9%, PTK/ZK: 11.4%, MS-275: 12.2% with P < 0.05 vs control 1). The fraction of TUNEL-positive cells was upregulated highly significantly by dual therapy (18.4%) and quadruple therapy (24.8%, P < 0.01 vs control 1). For the proliferating (PCNA positive) and apoptotic cell fraction, quadruple therapy was significantly superior to dual therapy (P = 0.01).

CONCLUSION

Combined PTK/ZK and MS-275 were highly effective in this hepatoma model. Quadruple therapy enhanced the effects microscopically, but not macroscopically. These results should be investigated further.

Autophagic and apoptotic effects of HDAC inhibitors on cancer cells

Because epigenetic alterations are believed to be involved in the repression of tumor suppressor genes and the promotion of tumorigenesis in cancers, novel compounds endowed with histone deacetylase (HDAC) inhibitory activity are an attractive therapeutic approach. Indeed, the potential of HDAC inhibitors for cancer therapy has been explored in preclinical models, and some agents approved for hematologic malignancies have reached the clinical setting. HDAC inhibitors are able to mediate the induction of both apoptosis and autophagy, which are related to anticancer activity in a variety of cancer cell lines. Given the inherent resistance to apoptosis that characterizes cancer, the targeting of alternative pathways is an attractive strategy to improve anti-tumor therapy. The activation of autophagy represents novel cancer treatment targets. This paper aims to critically discuss how the anticancer potential of HDAC inhibitors may elicit a response to human cancers through different cell pathways leading to cell death.

Interpreting clinical assays for histone deacetylase inhibitors

As opposed to genetics, dealing with gene expressions by direct DNA sequence modifications, the term epigenetics applies to all the external influences that target the chromatin structure of cells with impact on gene expression unrelated to the sequence coding of DNA itself. In normal cells, epigenetics modulates gene expression through all development steps. When "imprinted" early by the environment, epigenetic changes influence the organism at an early stage and can be transmitted to the progeny. Together with DNA sequence alterations, DNA aberrant cytosine methylation and microRNA deregulation, epigenetic modifications participate in the malignant transformation of cells. Their reversible nature has led to the emergence of the promising field of epigenetic therapy. The efforts made to inhibit in particular the epigenetic enzyme family called histone deacetylases (HDACs) are described. HDAC inhibitors (HDACi) have been proposed as a viable clinical therapeutic approach for the treatment of leukemia and solid tumors, but also to a lesser degree for noncancerous diseases. Three epigenetic drugs are already arriving at the patient's bedside, and more than 100 clinical assays for HDACi are registered on the National Cancer Institute website. They explore the eventual additive benefits of combined therapies. In the context of the pleiotropic effects of HDAC isoforms, more specific HDACi and more informative screening tests are being developed for the benefit of the patients.