A synthetic inhibitor of histone deacetylase, MS-27-275, with marked in vivo antitumor activity against human tumors

New therapeutic approaches to acute myeloid leukemia

BACKGROUND

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the pathogenesis and treatment of patients with AML. Understanding the basic cellular and molecular pathogenesis of leukemic cells is vital to the development of new treatment approaches.

OBJECTIVE/METHODS

To review progress until now with agents that are showing promise in the treatment of AML, we summarize the published preclinical and clinical trials that have been completed.

RESULTS

Based on recent progress of investigations, more specifically targeted agents have been developed for the treatment of AML such as tyrosine kinase inhibitors, monoclonal antibodies, epigenetic agents, antiangiogenic agents, and farnesyl transferase inhibitors.

CONCLUSION

In the future, in addition to performing therapeutic trials of these agents, it will be important to identify other highly specific therapeutic agents based on our evolving understanding of the biology of AML.

Current evidence for histone deacetylase inhibitors in pancreatic cancer

Pancreatic cancer is one of the most aggressive human cancers, with more than 200 000 deaths worldwide every year. Despite recent efforts, conventional treatment approaches, such as surgery and classic chemotherapy, have only slightly improved patient outcomes. More effective and well-tolerated therapies are required to reverse the current poor prognosis of this type of neoplasm. Among new agents, histone deacetylase inhibitors (HDACIs) are now being tested. HDACIs have multiple biological effects related to acetylation of histones and many non-histone proteins that are involved in regulation of gene expression, apoptosis, cell cycle progression and angiogenesis. HDACIs induce cell cycle arrest and can activate the extrinsic and intrinsic pathways of apoptosis in different cancer cell lines. In the present review, the main mechanisms by which HDACIs act in pancreatic cancer cells in vitro, as well as their antiproliferative effects in animal models are presented. HDACIs constitute a promising treatment for pancreatic cancer with encouraging anti-tumor effects, at well-tolerated doses.

Toxicological and metabolic considerations for histone deacetylase inhibitors

INTRODUCTION

Vorinostat and romidepsin were the first histone deacetylase (HDAC) inhibitors (HDi) that fulfilled the preclinical promise of anticancer potential in clinical trials. Nevertheless, they merely opened a new chapter in the history of cancer therapy. Demonstration of their antitumor activity was a straightforward task in in vitro setting. Proving their efficacy in vivo was much more difficult, since the effects of an administrated drug strongly depend on its absorption, distribution, metabolism and excretion.

AREAS COVERED

This article summarizes clinical data on the pharmacokinetic properties of HDi that are currently at more advanced stages of clinical development. Specific attention is paid to the metabolic pathways. Moreover, a comprehensive overview of HDi-related adverse effects is given.

EXPERT OPINION

At this moment, HDi form one of the most interesting classes of therapeutics, yet their efficacy and safety profiles could still be improved by i) designing better formulations, ii) more extensive characterization of their disposition at the preclinical stage, iii) targeting of individual disease-related deacetylase isoforms and/or their complexes, iv) selecting a target patient population with the highest probability of response based on molecular signatures.

Genetic and Epigenetic Regulation of CCR5 Transcription

The chemokine receptor CCR5 regulates trafficking of immune cells of the lymphoid and the myeloid lineage (such as monocytes, macrophages and immature dendritic cells) and microglia. Because of this, there is an increasing recognition of the important role of CCR5 in the pathology of (neuro-) inflammatory diseases such as atherosclerosis and multiple sclerosis. Expression of CCR5 is under the control of a complexly organized promoter region upstream of the gene. The transcription factor cAMP-responsive element binding protein 1 (CREB-1) transactivates the CCR5 P1 promoter. The cell-specific expression of CCR5 however is realized by using various epigenetic marks providing a multivalent chromatin state particularly in monocytes. Here we discuss the transcriptional regulation of CCR5 with a focus on the epigenetic peculiarities of CCR5 transcription.

Epigenetic contributions in the development of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease, characterized by chronic inflammation of the joints with severe pain and swelling, joint damage and disability, which leads to joint destruction and loss of function. Despite extensive research efforts, the underlying cause for RA is still unknown and current therapies are more or less effective in controlling symptoms but still fail to cure the disease. In recent years, epigenetic modifications were found to strongly contribute to the development of RA by affecting diverse aspects of the disease and modifying gene expression levels and behavior of several cell types, first and foremost joint resident synovial fibroblasts (SF). RASF are the most common cell type at the site of invasion. Owing to their aggressive, intrinsically activated phenotype, RASF are active contributors in joint damage. RASF are characterized by their ability to secrete cytokines, chemokines and joint-damaging enzymes. Furthermore, these cells are resistant to apoptosis, leading to hyperplasia of the synovium. In addition, RASF have invasive and migratory properties that could lead to spreading of the disease to unaffected joints. Epigenetic modifications, including DNA methylation and post-translational histone modifications, such as histone (de)acetylation, histone methylation and histone sumoylation were identified as regulatory mechanisms in controlling aggressive cell activation in vitro and in disease outcome in animal models in vivo. In the last 5 years, the field of epigenetics in RA has impressively increased. In this review we consider the role of diverse epigenetic modifications in the development of RA, with a special focus on epigenetic modifications in RASF.

Evaluating the effect of therapeutic stem cells on TRAIL resistant and sensitive medulloblastomas

Mesenchymal stem cells (MSC) are emerging as novel cell-based delivery agents; however, a thorough investigation addressing their therapeutic potential in medulloblastomas (MB) has not been explored to date. In this study, we engineered human MSC to express a potent and secretable variant of a tumor specific agent, tumor necrosis factor-apoptosis-inducing ligand (S-TRAIL) and assessed the ability of MSC-S-TRAIL mediated MB killing alone or in combination with a small molecule inhibitor of histone-deacetylase, MS-275, in TRAIL-sensitive and -resistant MB in vitro and in vivo. We show that TRAIL sensitivity/resistance correlates with the expression of its cognate death receptor (DR)5 and MSC-S-TRAIL induces caspase-3 mediated apoptosis in TRAIL-sensitive MB lines. In TRAIL-resistant MB, we show upregulation of DR4/5 levels when pre-treated with MS-275 and a subsequent sensitization to MSC-S-TRAIL mediated apoptosis. Using intracranially implanted MB and MSC lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that MSC-S-TRAIL has significant anti-tumor effects in mice bearing TRAIL-sensitive and MS-275 pre-treated TRAIL-resistant MBs. To our knowledge, this is the first study that explores the use of human MSC as MB-targeting therapeutic-vehicles in vivo in TRAIL-sensitive and resistant tumors, and has implications for developing effective therapies for patients with medulloblastomas.

Histone deacetylase inhibitors: a patent review (2009 - 2011)

INTRODUCTION

Given the involvement of histone deacetylases (HDACs) in regulation of gene expression, they are believed to be 'master regulators' of many diseases. Thus, HDAC inhibitors (HDACis) are able to modulate transcriptional activity. These molecules can induce cell cycle arrest, differentiation and apoptosis of tumor cells in culture and in animal models and therefore are emerging as an exciting new class of potential anti-cancer agents for the treatment of solid and hematological malignancies.

AREAS COVERED

The aim of this review is to provide an overview of current knowledge and molecular mechanisms of HDACis, and the most recent patents existing in the field of HDACis from 2009 until 2011.

EXPERT OPINION

In recent years, an increasing number of structurally diverse HDACis have been identified. In addition, non-cancer diseases, including neurodegeneration, metabolic, inflammatory and autoimmune disorders, infectious and cardiovascular diseases have also been proposed for an HDACi treatment. The growing body of evidence of the potential benefits of disease treatment based on the use of HDACis has led to a large number of patent applications throughout the world.

Trials with 'epigenetic' drugs: an update

Epigenetic inactivation of pivotal genes involved in correct cell growth is a hallmark of human pathologies, in particular cancer. These epigenetic mechanisms, including crosstalk between DNA methylation, histone modifications and non-coding RNAs, affect gene expression and are associated with disease progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. Re-expression of genes epigenetically inactivated can result in the suppression of disease state or sensitization to specific therapies. Small molecules that reverse epigenetic inactivation, so-called epi-drugs, are now undergoing clinical trials. Accordingly, the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment have approved some of these drugs. Here, we focus on the biological features of epigenetic molecules, analyzing the mechanism(s) of action and their current use in clinical practice.

Current and Emerging Therapeutics for Cutaneous T-Cell Lymphoma: Histone Deacetylase Inhibitors

Cutaneous T-cell lymphoma is a term that encompasses a spectrum of non-Hodgkin’s T-cell lymphomas with primary manifestations in the skin. It describes a heterogeneous group of neoplasms that are characterised by an accumulation of malignant T cells of the CD4 phenotype that have the propensity to home and accumulate in the skin, lymph nodes, and peripheral blood. The two most common variants of cutaneous T-cell lymphoma include mycosis fungoides and the leukemic variant, the Sézary syndrome. While numerous treatments are available for cutaneous T-cell lymphoma and have shown to have success in those with patch and plaque lesions, for those patients with tumour stage or lymph node involvement there is a significant decline in response. The relatively new therapeutic option with the use of histone deacetylase inhibitors is being advanced in the hope of decreasing morbidity and mortality associated with the disease. Histone deacetylase inhibitors have been shown to induce changes in gene expression, affecting cell cycle regulation, differentiation, and apoptosis. The aim of this paper is to discuss CTCL in the context of advances in CTCL treatment, specifically with HDAC inhibitors.

P38 MAP kinase functions as a switch in MS-275-induced reactive oxygen species-dependent autophagy and apoptosis in human colon cancer cells

MS-275 is a synthetic benzamide derivative of the histone deacetylase inhibitor and is currently in phase I/II clinical trials. Many reports have shown that the anti-tumor activity of MS-275 in several types of cancer is mainly attributable to its capacity to induce the apoptotic death of tumor cells. It remains unclear if autophagy is involved in MS-275 treatment of cancer cells. Here, we first show that MS-275 induces human colon cancer cell HCT116 autophagy as well as apoptosis. Short-term treatment (24h) induced HCT116 cells to undergo autophagy with dependence on intracellular reactive oxygen species production and ERK activation. The activated reactive oxygen species/ERK signal promoted Atg7 protein expression, which triggered MS-275-induced cancer cell autophagy. However, after prolonged treatment with MS-275 (over 48h), autophagic cells turned apoptotic, which was also dependent on reactive oxygen species generation. Interestingly, we found that p38 MAP kinase played a vital role in the switch from autophagy to apoptosis in MS-275-induced human colon cancer cells. High expression of p38 induced cell autophagy, but low expression resulted in apoptosis. In addition, observations in vivo are strongly consistent with the in vitro results. Therefore, these findings extend our understanding of the action of MS-275 in inducing cancer cell death and suggest that it may be a promising clinical chemotherapeutic agent with multiple effects.

Overcoming nucleoside analog chemoresistance of pancreatic cancer: a therapeutic challenge

Clinical refractoriness to nucleoside analogs (e.g., gemcitabine, capecitabine) is a major scientific problem and is one of the main reasons underlying the extremely poor prognostic state of pancreatic cancer. The drugs' effects are suboptimal partly due to cellular mechanisms limiting their transport, activation, and overall efficacy. Nonetheless, novel therapeutic approaches are presently under study to circumvent nucleoside analog resistance in pancreatic cancer. With these new approaches come additional challenges to be addressed. This review describes the determinants of chemoresistance in the gemcitabine cytotoxicity pathways, provides an overview of investigational approaches for overcoming chemoresistance, and discusses new challenges presented. Understanding the future directions of the field may assist in the successful development of novel treatment strategies for enhancing chemotherapeutic efficacy in pancreatic cancer.

The relationship between cisplatin resistance and histone deacetylase isoform overexpression in epithelial ovarian cancer cell lines

Objective

To investigate the relationship between cisplatin resistance and histone deacetylase (HDAC) isoform overexpression in ovarian cancer cell lines.

Methods

Expression of four HDAC isoforms (HDAC 1, 2, 3, and 4) in two ovarian cancer cell lines, SKOV3 and OVCAR3, exposed to various concentrations of cisplatin was examined by western blot analyses. Cells were transfected with plasmid DNA of each HDAC. The overexpression of protein and mRNA of each HDAC was confirmed by western blot and reverse transcriptase-polymerase chain reaction analyses, respectively. The cell viability of the SKOV3 and OVCAR3 cells transfected with HDAC plasmid DNA was measured using the cell counting kit-8 assay after treatment with cisplatin.

Results

The 50% inhibitory concentration of the SKOV3 and OVCAR3 cells can be determined 15-24 hours after treatment with 15 µg/mL cisplatin. The expression level of acetylated histone 3 protein in SKOV3 cells increased after exposure to cisplatin. Compared with control cells at 24 hours after cisplatin exposure, the viability of SKOV3 cells overexpressing HDAC 1 and 3 increased by 15% and 13% (p<0.05), respectively. On the other hand, OVCAR3 cells that overexpressed HDAC 2 and 4 exhibited increased cell viability by 23% and 20% (p<0.05), respectively, compared with control cells 24 hours after exposure to cisplatin.

Conclusion

In SKOV3 and OVCAR3 epithelial ovarian cancer cell lines, the correlation between HDAC overexpression and cisplatin resistance was confirmed. However, the specific HDAC isoform associated with resistance to cisplatin varied depending on the ovarian cancer cell line. These results may suggest that each HDAC isoform conveys cisplatin resistance via different mechanisms.

Regulation of ROCK1 via Notch1 during breast cancer cell migration into dense matrices

Background

The behaviour of tumour cells depends on factors such as genetics and the tumour microenvironment. The latter plays a crucial role in normal mammary gland development and also in breast cancer initiation and progression. Breast cancer tissues tend to be highly desmoplastic and dense matrix as a pre-existing condition poses one of the highest risk factors for cancer development. However, matrix influence on tumour cell gene expression and behaviour such as cell migration is not fully elucidated.

Results

We generated high-density (HD) matrices that mimicked tumour collagen content of 20 mg/cm³ that were ~14-fold stiffer than low-density (LD) matrix of 1 mg/cm³. Live-cell imaging showed breast cancer cells utilizing cytoplasmic streaming and cell body contractility for migration within HD matrix. Cell migration was blocked in the presence of both the ROCK inhibitor, Y-27632, and the MMP inhibitor, GM6001, but not by the drugs individually. This suggests roles for ROCK1 and MMP in cell migration are complicated by compensatory mechanisms. ROCK1 expression and protein activity, were significantly upregulated in HD matrix but these were blocked by treatment with a histone deacetylase (HDAC) inhibitor, MS-275. In HD matrix, the inhibition of ROCK1 by MS-275 was indirect and relied upon protein synthesis and Notch1. Inhibition of Notch1 using pooled siRNA or DAPT abrogated the inhibition of ROCK1 by MS-275.

Conclusion

Increased matrix density elevates ROCK1 activity, which aids in cell migration via cell contractility. The upregulation of ROCK1 is epigenetically regulated in an indirect manner involving the repression of Notch1. This is demonstrated from inhibition of HDACs by MS-275, which caused an upregulation of Notch1 levels leading to blockade of ROCK1 expression.

Emerging promise of epigenetics and DNA methylation for the diagnosis and management of women's cancers

Over the last two decades, survival rates from women's cancers (breast, ovarian, endometrial and cervical cancer) have all but modestly improved despite huge efforts from both research and clinical communities. In parallel with this, the field of epigenetics has grown from its infancy into a promising scientific discipline. In particular, DNA methylation analysis has been adopted by oncologists in an attempt to better understand and manage cancer. Now that the epigenetic technological base has caught up, the potential of methylation markers in cancer research is finally being realized. In this review, we present the current status of epigenetic research into women's cancers with a main focus on DNA methylation analysis. We provide an overview of technological development, current markers of risk prediction, early detection, diagnosis, prognosis and response to treatment, and highlight the progression of epigenetic therapies. Finally, we comment on the potential impact of epigenetic analyses on the future of women's health.

Elucidating the mechanism of regulation of transforming growth factor β Type II receptor expression in human lung cancer cell lines

Lung carcinogenesis in humans involves an accumulation of genetic and epigenetic changes that lead to alterations in normal lung epithelium, to in situ carcinoma, and finally to invasive and metastatic cancers. The loss of transforming growth factor β (TGF-β)-induced tumor suppressor function in tumors plays a pivotal role in this process, and our previous studies have shown that resistance to TGF-β in lung cancers occurs mostly through the loss of TGF-β type II receptor expression (TβRII). However, little is known about the mechanism of down-regulation of TβRII and how histone deacetylase (HDAC) inhibitors (HDIs) can restore TGF-β-induced tumor suppressor function. Here we show that HDIs restore TβRII expression and that DNA hypermethylation has no effect on TβRII promoter activity in lung cancer cell lines. TGF-β-induced tumor suppressor function is restored by HDIs in lung cancer cell lines that lack TβRII expression. Activation of mitogen-activated protein kinase/extracellular signal-regulated kinase pathway by either activated Ras or epidermal growth factor signaling is involved in the down-regulation of TβRII through histone deacetylation. We have immunoprecipitated the protein complexes by biotinylated oligonucleotides corresponding to the HDI-responsive element in the TβRII promoter (-127/-75) and identified the proteins/factors using proteomics studies. The transcriptional repressor Meis1/2 is involved in repressing the TβRII promoter activity, possibly through its recruitment by Sp1 and NF-YA to the promoter. These results suggest a mechanism for the downregulation of TβRII in lung cancer and that TGF-β tumor suppressor functions may be restored by HDIs in lung cancer patients with the loss of TβRII expression.

A novel series of l-2-benzyloxycarbonylamino-8-(2-pyridyl)-disulfidyloctanoic acid derivatives as histone deacetylase inhibitors: design, synthesis and molecular modeling study

Histone deacetylases inhibitors (HDACIs) have become an attractive class of anticancer agents. In order to find some novel potent HDACIs, we designed and synthesized a series of l-2-benzyloxycarbonylamino-8-(2-pyridyl)-disulfidyloctanoic acid derivatives. All compounds exhibited potent HDAC-inhibitory activity, and two of them had similar potency to TSA. The introduction of 2-amino-4-phenylthiazole or 9-methyleneoxy-fluorenyl group at the surface recognize domain of these HDACIs could greatly increase their HDAC-inhibitory activity. Molecular modeling studies indicated that coordination of the zinc ion by these inhibitors, and formation of hydrogen bond and hydrophobic interaction between inhibitors and HDACs were essential for the HDAC-inhibitory activities of these inhibitors. Asp181, Asp269, Leu276 and Tyr308 in the active site of HDAC2 gave favorable contributions for binding with all compounds.

Dual targeting of histone deacetylase and topoisomerase II with novel bifunctional inhibitors

Strategies to ameliorate the flaws of current chemotherapeutic agents, while maintaining potent anticancer activity, are of particular interest. Agents which can modulate multiple targets may have superior utility and fewer side effects than current single-target drugs. To explore the prospect in cancer therapy of a bivalent agent that combines two complementary chemo-active groups within a single molecular architecture, we have synthesized dual-acting histone deacetylase and topoisomerase II inhibitors. These dual-acting agents are derived from suberoylanilide hydroxamic acid (SAHA) and anthracycline daunorubicin, prototypical histone deacetylase (HDAC) and topoisomerase II (Topo II) inhibitors, respectively. We report herein that these agents present the signatures of inhibition of HDAC and Topo II in both cell-free and whole-cell assays. Moreover, these agents potently inhibit the proliferation of representative cancer cell lines.

Class I histone deacetylase inhibitor entinostat suppresses regulatory T cells and enhances immunotherapies in renal and prostate cancer models

Background

Immunosuppressive factors such as regulatory T cells (Tregs) limit the efficacy of immunotherapies. Histone deacetylase (HDAC) inhibitors have been reported to have antitumor activity in different malignancies and immunomodulatory effects. Herein, we report the Tregs-targeting and immune-promoting effect of a class I specific HDAC inhibitor, entinostat, in combination with either IL-2 in a murine renal cell carcinoma (RENCA) model or a survivin-based vaccine therapy (SurVaxM) in a castration resistant prostate cancer (CR Myc-CaP) model.

Methods and Results

RENCA or CR Myc-CaP tumors were implanted orthotopically or subcutaneously, respectively. Inoculated mice were randomized into four treatment groups: vehicle, entinostat, cytokine or vaccine, and combination. Tregs in the blood were assessed by FACS analysis. Real time quantitative PCR and Western blot analysis of isolated T cell subpopulations from spleen were performed to determine Foxp3 gene and protein expression. The suppressive function of Tregs was tested by T cell proliferation assay. Low dose (5 mg/kg) entinostat reduced Foxp3 levels in Tregs and this was associated with enhanced tumor growth inhibition in combination with either IL-2 or a SurVaxM vaccine. Entinostat down-regulated Foxp3 expression transcriptionally and blocked Tregs suppressive function without affecting T effector cells (Teffs). In vitro low dose entinostat (0.5 µM) induced STAT3 acetylation and a specific inhibitor of STAT3 partially rescued entinostat-induced down-regulation of Foxp3, suggesting that STAT3 signaling is involved in Foxp3 down-regulation by entinostat.

Conclusions

These results demonstrate a novel immunomodulatory effect of class I HDAC inhibition and provide a rationale for the clinical testing of entinostat to enhance cancer immunotherapy.

P53-dependent antiproliferative and pro-apoptotic effects of trichostatin A (TSA) in glioblastoma cells

Glioblastomas are known to be highly chemoresistant, but HDAC inhibitors (HDACi) have been shown to be of therapeutic relevance for this aggressive tumor type. We treated U87 glioblastoma cells with trichostatin A (TSA) to define potential epigenetic targets for HDACi-mediated antitumor effects. Using a cDNA array analysis covering 96 cell cycle genes, cyclin-dependent kinase inhibitor p21(WAF1) was identified as the major player in TSA-induced cell cycle arrest. TSA slightly inhibited proliferation and viability of U87 cells, cumulating in a G1/S cell cycle arrest. This effect was accompanied by a significant up-regulation of p53 and its transcriptional target p21(WAF1) and by down-regulation of key G1/S regulators, such as cdk4, cdk6, and cyclin D1. Nevertheless, TSA did not induce apoptosis in U87 cells. As expected, TSA promoted the accumulation of total acetylated histones H3 and H4 and a decrease in endogenous HDAC activity. Characterizing the chromatin modulation around the p21(WAF1) promoter after TSA treatment using chromatin immunoprecipitation, we found (1) a release of HDAC1, (2) an increase of acetylated H4 binding, and (3) enhanced recruitment of p53. p53-depleted U87 cells showed an abrogation of the G1/S arrest and re-entered the cell cycle. Immunofluorescence staining revealed that TSA induced the nuclear translocation of p21(WAF1) verifying a cell cycle arrest. On the other hand, a significant portion of p21(WAF1) was present in the cytoplasmic compartment causing apoptosis resistance. Furthermore, TSA-treated p53-mutant cell line U138 failed to show an induction in p21(WAF1), showed a deficient G2/M checkpoint, and underwent mitotic catastrophe. We suggest that HDAC inhibition in combination with other clinically used drugs may be considered an effective strategy to overcome chemoresistance in glioblastoma cells.

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.

Epigenetic-based therapies in cancer: progress to date

Epigenetic gene silencing is a hallmark of cancer cells. Two important types of epigenetic changes are DNA methylation and histone modification. These modifications are catalysed by DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), resulting in chromatin structure changes and gene inactivation. Interestingly, inhibition of these enzymes is known to induce differentiation or apoptosis of cancer cells. Therefore, DNMTs and HDACs have become attractive therapeutic targets. In recent years, many different DNMT and HDAC inhibitors have been developed, and multiple molecular mechanisms through which these agents exert anti-cancer effects have been identified. While a large number of clinical trials are ongoing, hypomethylating agents and HDAC inhibitors seem to be promising for treating several types of cancer. Moreover, developing effective strategies of combining epigenetic therapy with conventional chemotherapy will be one of the major challenges in the future. We briefly review current advances in epigenetic therapies with a focus on recently reported clinical trials.

Phase I study of the histone deacetylase inhibitor entinostat in combination with 13-cis retinoic acid in patients with solid tumours

BACKGROUND

Preclinical studies suggest that histone deacetylase (HDAC) inhibitors may restore tumour sensitivity to retinoids. The objective of this study was to determine the safety, tolerability, and the pharmacokinetic (PK)/pharmacodynamic (PD) profiles of the HDAC inhibitor entinostat in combination with 13-cis retinoic acid (CRA) in patients with solid tumours.

METHODS

Patients with advanced solid tumours were treated with entinostat orally once weekly and with CRA orally twice daily × 3 weeks every 4 weeks. The starting dose for entinostat was 4 mg m(-2) with a fixed dose of CRA at 1 mg kg(-1) per day. Entinostat dose was escalated by 1 mg m(-2) increments. Pharmacokinetic concentrations of entinostat and CRA were determined by LC/MS/MS. Western blot analysis of peripheral blood mononuclear cells and tumour samples were performed to evaluate target inhibition.

RESULTS

A total of 19 patients were enroled. The maximum tolerated dose (MTD) was exceeded at the entinostat 5 mg m(-2) dose level (G3 hyponatremia, neutropenia, and anaemia). Fatigue (G1 or G2) was a common side effect. Entinostat exhibited substantial variability in clearance (147%) and exposure. CRA trough concentrations were consistent with prior reports. No objective responses were observed, however, prolonged stable disease occurred in patients with prostate, pancreatic, and kidney cancer. Data further showed increased tumour histone acetylation and decreased phosphorylated ERK protein expression.

CONCLUSION

The combination of entinostat with CRA was reasonably well tolerated. The recommended phase II doses are entinostat 4 mg m(-2) once weekly and CRA 1 mg kg(-1) per day. Although no tumour responses were seen, further evaluation of this combination is warranted.

Chidamide (CS055/HBI-8000): a new histone deacetylase inhibitor of the benzamide class with antitumor activity and the ability to enhance immune cell-mediated tumor cell cytotoxicity

PURPOSE

Chidamide (CS055/HBI-8000) is a new histone deacetylase (HDAC) inhibitor of the benzamide class currently under clinical development in cancer indications. This study reports the in vitro and in vivo antitumor characteristics of the compound.

METHODS

Selectivity and potency of chidamide in inhibition of HDAC isotypes were analyzed by using a panel of human recombinant HDAC proteins. Tumor cell lines either in culture or inoculated in nude mice were used for the evaluation of the compound's antitumor activity. To investigate the immune cell-mediated antitumor effect, isolated peripheral blood mononuclear cells from healthy donors were treated with chidamide, and cytotoxicity and expression of relevant surface proteins were analyzed. Microarray gene expression studies were performed on peripheral white blood cells from two T-cell lymphoma patients treated with chidamide.

RESULTS

Chidamide was found to be a low nanomolar inhibitor of HDAC1, 2, 3, and 10, the HDAC isotypes well documented to be associated with the malignant phenotype. Significant and broad spectrum in vitro and in vivo antitumor activity, including a wide therapeutic index, was observed. Chidamide was also shown to enhance the cytotoxic effect of human peripheral mononuclear cells ex vivo on K562 target cells, accompanied by the upregulation of proteins involved in NK cell functions. Furthermore, the expression of a number of genes involved in immune cell-mediated antitumor activity was observed to be upregulated in peripheral white blood cells from two T-cell lymphoma patients who responded to chidamide administration.

CONCLUSIONS

The results presented in this study provide evidence that chidamide has potential applicability for the treatment of a variety of tumor types, either as a single agent or in combination therapies.

Sensitization of human colon cancer cells to sodium butyrate-induced apoptosis by modulation of sphingosine kinase 2 and protein kinase D

Sphingosine kinases (SphKs) have been recognized as important proteins regulating cell proliferation and apoptosis. Of the two isoforms of SphK (SphK1 and SphK2), little is known about the functions of SphK2. Sodium butyrate (NaBT) has been established as a promising chemotherapeutic agent, but the precise mechanism for its effects is unknown. In this study, we investigated the role of SphK2 in NaBT-induced apoptosis of HCT116 colon cancer cells. The results indicated that following NaBT treatment SphK2 was translocated from the nucleus to the cytoplasm, leading to its accumulation in the cytoplasm; in the meantime, only mild apoptosis occurred. However, downregulation of SphK2 resulted in sensitized apoptosis, and overexpression of SphK2 led to even lighter apoptosis; these strongly indicate an inhibitory role of SphK2 in cell apoptosis induced by NaBT. After knocking down protein kinase D (PKD), another protein reported to be critical in cell proliferation/apoptosis process, by using siRNA, blockage of cytoplasmic accumulation of SphK2 and sensitized apoptosis following NaBT treatment were observed. The present study suggests that PKD and SphK2 may form a mechanism for the resistance of cancer cells to tumor chemotherapies, such as HCT116 colon cancer cells to NaBT, and these two proteins may become molecular targets for designation of new tumor-therapeutic drugs.

Gene expression profiling of KBH-A42, a novel histone deacetylase inhibitor, in human leukemia and bladder cancer cell lines

The aim of this study was to investigate the anti-tumor activity of KBH-A42, a novel synthetic histone deacetylase (HDAC) inhibitor. KBH-A42 was shown to significantly suppress the proliferation of all 14 human cancer cell lines tested. Among these cell lines, the human leukemia cell line K562 was the most sensitive, whereas the UM-UC-3 bladder cancer cells were the least sensitive. Additionally, in a human tumor xenograft model using Balb/c nude mice, KBH-A42 was shown to significantly inhibit the growth of K562 tumors, although it only slightly inhibited the growth of UM-UC-3 tumors. The results of flow cytometry analysis and caspase 3/7 activation assays showed that the growth inhibition of K562 cells by KBH-A42 was mediated, at least in part, by the induction of apoptosis, but its growth inhibitory effects on UM-UC-3 cells were not mediated by apoptotic induction. In an effort to gain insight into the mechanism by which KBH-A42 inhibits the growth of cancer cells, a microarray analysis was conducted. Four genes were selected from the genes that were down-regulated or up-regulated by KBH-A42 and confirmed via reverse transcription-polymerase chain reaction as follows: Harakiri (HRK), tumor necrosis factor receptor superfamily, member 10b (TNFRSF10B), PYD and CARD domain containing protein gene (PYCARD) and tumor necrosis factor receptor superfamily, member 8 (TNFRSF8). Collectively, the in vitro and in vivo results suggested that KBH-A42 exhibits anti-cancer activity, but various types of cells may be regulated differentially by KBH-A42.

Real-time imaging of histone H4K12-specific acetylation determines the modes of action of histone deacetylase and bromodomain inhibitors

Histone acetylation constitutes an epigenetic mark for transcriptional regulation. Here we developed a fluorescent probe to visualize acetylation of histone H4 Lys12 (H4K12) in living cells using fluorescence resonance energy transfer (FRET) and the binding of the BRD2 bromodomain to acetylated H4K12. Using this probe designated as Histac-K12, we demonstrated that histone H4K12 acetylation is retained in mitosis and that some histone deacetylase (HDAC) inhibitors continue to inhibit cellular HDAC activity even after their removal from the culture. In addition, a small molecule that interferes with ability of the bromodomain to bind to acetylated H4K12 could be assessed using Histac-K12 in cells. Thus, Histac-K12 will serve as a powerful tool not only to understand the dynamics of H4K12-specific acetylation but also to characterize small molecules that modulate the acetylation or interaction status of histones.

The histone deacetylase inhibitor entinostat (SNDX-275) induces apoptosis in Hodgkin lymphoma cells and synergizes with Bcl-2 family inhibitors

OBJECTIVE

Based on promising in vitro and in vivo activity of several histone deacetylase inhibitors in Hodgkin lymphoma (HL), we investigated SNDX-275, an oral class 1 isoform-selective histone deacetylase inhibitors in HL-derived cell lines.

MATERIALS AND METHODS

Proliferation and cell death were examined by MTS assay, Annexin V/propidium iodide, and fluorescence-activated cell sorting analysis. Gene and protein expression were measured by reverse transcriptase polymerase chain reaction, Western blotting, and immunohistochemical analysis. A multiplex assay was used to determine cytokines and chemokines.

RESULTS

SNDX-275 induced cell death in a dose- and time-dependent manner with an IC(50) at the sub- and lower micromolar range at 72 hours. At the molecular level, SNDX-275 increased histone H3 acetylation, upregulated p21 expression, and activated the intrinsic apoptosis pathway by downregulating the X-linked inhibitor of apoptosis protein. SNDX-275 downregulated expression of antiapoptotic Bcl-2 and Bcl-xL proteins without altering Mcl-1 or Bax levels. Combination studies demonstrated that two Bcl-2 inhibitors (ABT-737 and obatoclax) significantly enhanced the effect of SNDX-275. SNDX-275 modulated the level of several cytokines and chemokines, including interleukin-12 p40-70, interferon-inducible protein-10, RANTES (regulated on activation, normal T expressed and secreted), interleukin-13, interleukin-4, and thymus and activation-regulated chemokine and variably induced the cancer/testis antigen expression of MAGE-A4 and survivin in HL cell lines.

CONCLUSIONS

SNDX-275 has antiproliferative activity in HL cell lines, involving several mechanisms: induction of apoptosis, regulation of cytokines and chemokines, and alteration of cancer/testis antigens. Clinical investigation of SNDX-275 alone or in combination with Bcl-2 inhibitors is warranted in patients with HL. Phase 2 studies with SNDX-275 in HL are ongoing, and future clinical studies should investigate combinations with SNDX-275.

Epigenetic therapy for breast cancer

Both genetic and epigenetic alterations can control the progression of cancer. Genetic alterations are impossible to reverse, while epigenetic alterations are reversible. This advantage suggests that epigenetic modifications should be preferred in therapy applications. DNA methyltransferases and histone deacetylases have become the primary targets for studies in epigenetic therapy. Some DNA methylation inhibitors and histone deacetylation inhibitors are approved by the US Food and Drug Administration as anti-cancer drugs. Therefore, the uses of epigenetic targets are believed to have great potential as a lasting favorable approach in treating breast cancer.

Involvement of insulin-like growth factor-binding protein-3 in the effects of histone deacetylase inhibitor MS-275 in hepatoma cells

Insulin-like growth factor-binding protein-3 (IGFBP-3) expression is frequently suppressed in liver cancers and can be reactivated by histone deacetylase (HDAC) inhibition. This study examined the role of IGFBP-3 in mediating the effects of the HDAC inhibitor MS-275 in liver cancer cells and identified IGFBP-3-dependent proteins that regulate proliferation and migration. In HepG2 cells, MS-275 inhibited DNA synthesis, cell cycle activity, and cell viability concomitantly with increased binding of acetylated histone H3 to IGFBP-3 promoter sequences and induction of IGFBP-3 expression. IGFBP-3 down-regulation by siRNA significantly reversed the inhibition of cell viability and DNA synthesis by MS-275, indicating an intermediary role for IGFBP-3. Induction of the cyclin-dependent kinase inhibitor p21 by MS-275 was attenuated by IGFBP-3 down-regulation, providing an explanation for IGFBP-3-dependent effects of MS-275 on cell cycle activity. In contrast, MS-275 stimulated HepG2 cell migration, an effect also inhibited by IGFBP-3 down-regulation. Among genes whose induction by MS-275 was attenuated by IGFBP-3 down-regulation, LYVE1 and THBS2 (thrombospondin-2) were identified as mediators of IGFBP-3-dependent effects of MS-275. Silencing of either protein had no effect on the inhibition of HepG2 viability by MS-275 but reversed its stimulatory effect on cell migration. We conclude that among genes up-regulated by MS-275, IGFBP-3 is a key mediator of effects on hepatoma cell growth and migration, involving IGFBP-3-dependent proteins p21 (proliferation) and LYVE1 and THBS2 (migration). The enhanced cell motility that accompanies reactivation of IGFBP-3 expression in liver cancer by HDAC inhibition suggests the possibility of increased metastatic spread despite inhibited cell proliferation.

Next generation histone deacetylase inhibitors: the answer to the search for optimized epigenetic therapies?

INTRODUCTION

HDAC inhibitors have demonstrated potent anticancer activities in preclinical and clinical studies. Currently, two drugs (SAHA and romidepsin) have gained the FDA approval for the treatment of cutaneous T-cell lymphoma. Clinical efficacy of HDAC inhibitors has been observed in advanced hematological malignancies, while response in other cancers has been in most cases unpredictable and often rather limited. The search for new molecules with the potential to overcome the limitations of the first HDAC inhibitors has become a primary goal in the field of epigenetic drug discovery as well as drugs acting on other chromatin modifying enzymes.

AREAS COVERED

The article shortlists seven new HDAC inhibitors that have recently entered clinical studies as representative examples of next generation drugs. The most recently published preclinical profile is reviewed, together with the first clinical data for these compounds. The article then focuses on challenges faced during the progress of first generation HDAC inhibitors and analyzes whether these new compounds are likely to provide a solution to the existing issues and needs.

EXPERT OPINION

Next generation HDAC inhibitors have the 'best-in-class' potential, particularly regarding potency and in vivo exposure. However, several issues remain unresolved. For example, none of the presented compounds appears to have a significantly different selectivity profile towards various HDAC isoforms and, thus, none of them may provide a further elucidation between the toxicity seen in more advanced HDAC inhibitors and isoform selectivity. Additionally, a need for a continuous effort on target validation is seen as a necessary requirement for further progress in the field.

Effect of the histone deacetylase inhibitor SNDX-275 on Fas signaling in osteosarcoma cells and the feasibility of its topical application for the treatment of osteosarcoma lung metastases

BACKGROUND

Patients with lung metastases from osteosarcoma (OS) have poor response to salvage therapy. Understanding the mechanisms involved in the metastatic process of OS may lead to new effective therapeutic approaches. The authors reported previously that up-regulation of the Fas receptor by transfecting OS cells with Fas plasmid inhibited the in vivo growth of metastases in the lungs.

METHODS

In the current study, the authors treated OS cells with the histone deacetylase inhibitor SNDX-275 and studied its cytotoxicity and its effect on Fas signaling in vitro and in vivo.

RESULTS

Subtoxic doses of SNDX-275 were able to activate the Fas pathway in OS cells by increasing the expression of Fas messenger RNA; however, the increased expression was not always followed by increased levels of Fas receptor expression on the cell surface. The treatment of cells with a combination of SNDX-275 and Fas ligand (FasL) had a stronger cytotoxic effect on tested OS cells than either agent alone. Inhibition of the Fas pathway in cells by inhibition of the Fas-associated death domain (FADD) molecule eliminated this combination effect, indicating that activity of FADD is important for the efficacy of this agent in the FasL-expressing environment of the lungs. Intranasal administration of SNDX-275 in mice with OS lung metastases revealed that SNDX-275 may inhibit metastatic growth at a dose of 0.13 mg/kg, which is approximately 200-fold lower than the therapeutically effective oral dose reported previously.

CONCLUSIONS

The current findings indicated that SNDX-275 can activate Fas signaling in OS cells in vitro and in vivo and that the administration of SDNX-275 by inhalation is feasible as a treatment for OS metastases and warrants its further investigation.

T-oligos inhibit growth and induce apoptosis in human ovarian cancer cells

Ovarian cancer remains a leading cause of death among women worldwide, and current treatment regimens for advanced disease are inadequate. Oligonucleotides with sequence homology to telomeres (called T-oligos) have been shown to mimic DNA damage responses in cells and induce cytotoxic effects in certain tumor cell lines. We studied the effects of 2 distinct 16 mer T-oligos in 4 human ovarian epithelial carcinoma cell lines. A T-oligo with perfect homology to the telomere overhang region demonstrated some cytotoxic activity in half of the cell lines. A G-rich T-oligo derivative showed more potency and broader cytotoxic activity in these lines than the parental T-oligo. Activation of apoptotic pathways in ovarian cancer cells by exposure to the T-oligo was demonstrated by multiple independent assays. T-oligo was shown to have additive, or more than additive, activity in combination with 2 different histone deacetylase drugs currently in clinical testing. T-oligos may therefore provide a new and tumor-targeted approach to ovarian cancers.

Total syntheses of the histone deacetylase inhibitors largazole and 2-epi-largazole: application of N-heterocyclic carbene mediated acylations in complex molecule synthesis

Details of the evolution of strategies toward convergent assembly of the histone deacetylase inhibiting natural product largazole exploiting γ,δ-unsaturated-α,β-epoxy-aldehydes and a thiazole-thiazoline containing ω-amino-acid are described. The initial N-heterocyclic carbene mediated redox amidation exploying these two types of building blocks representing largazole's structural domains of distinct biosynthetic origin directly afforded the seco-acid of largazole. This was accomplished without any protecting groups resident upon either thioester bearing epoxy-aldehyde or the tetrapeptide. However, the ineffective production of largazole via the final macrolactonization led to an alternative intramolecular esterification/macrolactamization strategy employing the established two building blocks. This provided largazole along with its C2-epimer via an unexpected inversion of the α-stereocenter at the valine residue. The biological evaluation demonstrated that both largazole and 2-epi-largazole led to dose-dependent increases of acetylation of histone H3, indicating their potencies as class I histone deacetylase selective inhibitiors. Enhanced p21 expression was also induced by largazole and its C2 epimer. In addition, 2-epi-largazole displayed more potent activity than largazole in cell viability assays against PC-3 and LNCaP prostate cancer cell lines.

HDAC inhibitors and cancer therapy

Maintenance of normal cell growth and differentiation is highly dependent on coordinated and tight transcriptional regulation of genes. In cancer, genes encoding growth regulators are abnormally expressed. Particularly, silencing of tumor suppressor genes under the control of chromatin modifications is a major underlying cause of unregulated cellular proliferation and transformation. Thus mechanisms, which regulate chromatin structure and gene expression, have become attractive targets for anticancer therapy. Histone deacetylases are enzymes that modify chromatin structure and contribute to aberrant gene expression in cancer. Research over the past decade has led to the development of histone deacetylase inhibitors as anticancer agents. In addition to their effect on chromatin and epigenetic mechanisms, HDAC inhibitors also modify the acetylation state of a large number of cellular proteins involved in oncogenic processes, resulting in antitumor effects. The current monograph will review the role of histone deacetylases in protumorigenic mechanisms and the current developmental status and prospects for their inhibitors in cancer therapy.

Control of autophagy with small molecules

Autophagy is the mass degradation system that removes long-lived proteins and malfunctioning organelles within the cell. Dysfunctional autophagic processes can cause various diseases such as cancer and neurodegenerative disorders, but the underlying mechanisms responsible for such events remain undefined. Small molecules that control autophagy could be powerful tools to reveal autophagy mechanisms, and to develop treatments for autophagy-related diseases including Alzheimer's disease, Parkinson's disease and various cancer types. This review discusses the small molecules that have been identified to control autophagy and how they can be used to understand signaling pathways important for autophagy in the context of chemical genomics.

Potential anti-cancer activity of N-hydroxy-7-(2-naphthylthio) heptanomide (HNHA), a histone deacetylase inhibitor, against breast cancer both in vitro and in vivo

Histone deacetylase (HDAC) is an attractive target for cancer therapy because it plays a key role in gene expression and carcinogenesis. N-hydroxy-7-(2-naphthylthio) heptanomide (HNHA) is a novel synthetic HDAC inhibitor (HDACI) that shows better pharmacological properties than a known HDACI present in the human fibrosarcoma cell: suberoylanilide hydroxamic acid (SAHA). Here, we investigate the anti-cancer activity of HNHA against breast cancer both in vitro and in vivo. HNHA arrested the cell cycle at the G(1) /S phase via p21 induction, which led to profound inhibition of cancer cell growth in vitro. In addition, HNHA-treated cells showed markedly decreased levels of VEGF and HIF-1α than SAHA and fumagillin (FUMA) when accompanied by increased histone acetylation. HNHA significantly inhibited tumor growth in an in vivo mouse xenograft model. HNHA-treated mice survived significantly longer than SAHA- and FUMA-treated mice. Dynamic MRI showed significantly decreased blood flow in the HNHA-treated mice, implying that HNHA inhibits tumor neovascularization. This finding was accompanied by marked reductions of proangiogenic factors and significant induction of angiogenesis inhibitors in tumor tissues. We have shown that HNHA is an effective anti-tumor agent in breast cancer cells in vitro and in breast cancer xenografts in vivo. Collectively, these findings indicate that HNHA may be a potent anti-cancer agent against breast cancer due to its multi-faceted inhibition of HDAC activity, as well as anti-angiogenesis activity.

Histone deacetylase inhibitors: potential targets responsible for their anti-cancer effect

The histone deacetylase inhibitors (HDACi) have demonstrated anticancer efficacy across a range of malignancies, most impressively in the hematological cancers. It is uncertain whether this clinical efficacy is attributable predominantly to their ability to induce apoptosis and differentiation in the cancer cell, or to their ability to prime the cell to other pro-death stimuli such as those from the immune system. HDACi-induced apoptosis occurs through altered expression of genes encoding proteins in both intrinsic and extrinsic apoptotic pathways; through effects on the proteasome/aggresome systems; through the production of reactive oxygen species, possibly by directly inducing DNA damage; and through alterations in the tumor microenvironment. In addition HDACi increase the immunogenicity of tumor cells and modulate cytokine signaling and potentially T-cell polarization in ways that may contribute the anti-cancer effect in vivo. Here, we provide an overview of current thinking on the mechanisms of HDACi activity, with attention given to the hematological malignancies as well as scientific observations arising from the clinical trials. We also focus on the immune effects of these agents.

Histone deacetylase (HDAC) inhibitors in recent clinical trials for cancer therapy

Heritable changes in gene expression that are not based upon alterations in the DNA sequence are defined as epigenetics. The most common mechanisms of epigenetic regulation are the methylation of CpG islands within the DNA and the modification of amino acids in the N-terminal histone tails. In the last years, it became evident that the onset of cancer and its progression may not occur only due to genetic mutations but also because of changes in the patterns of epigenetic modifications. In contrast to genetic mutations, which are almost impossible to reverse, epigenetic changes are potentially reversible. This implies that they are amenable to pharmacological interventions. Therefore, a lot of work in recent years has focussed on the development of small molecule enzyme inhibitors like DNA-methyltransferase inhibitors or inhibitors of histone-modifying enzymes. These may reverse misregulated epigenetic states and be implemented in the treatment of cancer or other diseases, e.g., neurological disorders. Today, several epigenetic drugs are already approved by the FDA and the EMEA for cancer treatment and around ten histone deacetylase (HDAC) inhibitors are in clinical development. This review will give an update on recent clinical trials of the HDAC inhibitors used systemically that were reported in 2009 and 2010 and will present an overview of different biomarkers to monitor the biological effects.