Toxicological and metabolic considerations for histone deacetylase inhibitors

Advances in dual-targeting inhibitors of HDAC6 for cancer treatment

Histone Deacetylase 6 (HDAC6) is an essential regulator of histone acetylation processes, exerting influence on a multitude of cellular functions such as cell motility, endocytosis, autophagy, apoptosis, and protein trafficking through its deacetylation activity. The significant implications of HDAC6 in diseases such as cancer, neurodegenerative disorders, and immune disorders have motivated extensive investigation into the development of specific inhibitors targeting this enzyme for therapeutic purposes. Single targeting drugs carry the risk of inducing drug resistance, thus prompting exploration of dual targeting therapy which offers the potential to impact multiple signaling pathways simultaneously, thereby lowering the likelihood of resistance development. While pharmacological studies have exhibited promise in combined therapy involving HDAC6, challenges related to potential drug interactions exist. In response to these challenges, researchers are investigating HDAC6 hybrid molecules which enable the concomitant targeting of HDAC6 and other key proteins, thus enhancing treatment efficacy while mitigating side effects and reducing the risk of resistance compared to traditional combination therapies. The published design strategies for dual targeting inhibitors of HDAC6 are summarized and discussed in this review. This will provide some valuable insights into more novel HDAC6 dual targeting inhibitors to meet the urgent need for innovative therapies in oncology and other related fields.

Discovery of chiral 1,4-diarylazetidin-2-one-based hydroxamic acid derivatives as novel tubulin polymerization inhibitors with histone deacetylase inhibitory activity

Tubulin and histone deacetylase have been clinically proven as promising targets for cancer therapy. Herein, we describe the design and synthesis of chiral 1,4-diarylazetidin-2-one-based hydroxamic acids as novel tubulin/HDAC dual inhibitors. Among them, compound 12a was validated to effectively disrupt tubulin polymerization, and exhibited potent HDAC1/8 inhibitory activities. Meanwhile, 12a showed good antiproliferative activities against four tumor cell lines. Further studies showed 12a works through blocking cellular cycle, inducing apoptosis and inhibiting colony formation. In addition, 12a has suitable physicochemical properties and high liver microsomal metabolic stability. Importantly, compound 12a was found to exhibit significant antitumor efficacy in vivo, thus warranting it as a promising tubulin/HDAC dual inhibitor for further development.

Reversibility and therapeutic development for neurodevelopmental disorders, insights from genetic animal models

Neurodevelopmental Disorders (NDDs) encompass a broad spectrum of conditions resulting from atypical brain development. Over the past decades, we have had the fortune to witness enormous progress in diagnosis, etiology discovery, modeling, and mechanistic understanding of NDDs from both fundamental and clinical research. Here, we review recent neurobiological advances from experimental models of NDDs. We introduce several examples and highlight breakthroughs in reversal studies of phenotypes using genetically engineered models of NDDs. The in-depth understanding of brain pathophysiology underlying NDDs and evaluations of reversibility in animal models paves the foundation for discovering novel treatment options. We discuss how the expanding property of cutting-edge technologies, such as gene editing and AAV-mediated gene delivery, are leveraged in animal models for the therapeutic development of NDDs. We envision opportunities and challenges toward faithful modeling and fruitful clinical translation.

The Class I HDAC Inhibitor, MS-275, Prevents Oxaliplatin-Induced Chronic Neuropathy and Potentiates Its Antiproliferative Activity in Mice

Oxaliplatin, the first-line chemotherapeutic agent against colorectal cancer (CRC), induces peripheral neuropathies, which can lead to dose limitation and treatment discontinuation. Downregulation of potassium channels, which involves histone deacetylase (HDAC) activity, has been identified as an important tuner of acute oxaliplatin-induced hypersensitivity. MS-275, a class I histone deacetylase inhibitor (HDACi), prevents acute oxaliplatin-induced peripheral neuropathy (OIPN). Moreover, MS-275 exerts anti-tumor activity in several types of cancers, including CRC. We thus hypothesized that MS-275 could exert both a preventive effect against OIPN and potentially a synergistic effect combined with oxaliplatin against CRC development. We first used RNAseq to assess transcriptional changes occurring in DRG neurons from mice treated by repeated injection of oxaliplatin. Moreover, we assessed the effects of MS-275 on chronic oxaliplatin-induced peripheral neuropathy development in vivo on APC^Min/+ mice and on cancer progression when combined with oxaliplatin, both in vivo on APC^Min/+ mice and in a mouse model of an orthotopic allograft of the CT26 cell line as well as in vitro in T84 and HT29 human CRC cell lines. We found 741 differentially expressed genes (DEGs) between oxaliplatin- and vehicle-treated animals. While acute OIPN is known as a channelopathy involving HDAC activity, chronic OIPN exerts weak ion channel transcriptional changes and no HDAC expression changes in peripheral neurons from OIPN mice. However, MS-275 prevents the development of sensory neuropathic symptoms induced by repeated oxaliplatin administration in APC^Min/+ mice. Moreover, combined with oxaliplatin, MS-275 also exerts synergistic antiproliferative and increased survival effects in CT26-bearing mice. Consistently, combined drug associations exert synergic apoptotic and cell death effects in both T84 and HT29 human CRC cell lines. Our results strongly suggest combining oxaliplatin and MS-275 administration in CRC patients in order to potentiate the antiproliferative action of chemotherapy, while preventing its neurotoxic effect.

Brief Report: Case Comparison of Therapy With the Histone Deacetylase Inhibitor Vorinostat in a Neonatal Calf Model of Pulmonary Hypertension

Pulmonary hypertension (PH) is an incurable condition in humans; driven by pulmonary vascular remodeling partially mediated by epigenetic mechanisms; and leading to right ventricular hypertrophy, failure, and death. We hypothesized that targeting chromatin-modifying histone deacetylases may provide benefit. In this Brief Report we describe case comparison studies using the histone deacetylase inhibitor vorinostat (suberanilohydroxamic acid, 5 mg/kg/day for the first 5 study days) in an established model of severe neonatal bovine PH induced by 14 days of environmental hypoxia. Echocardiographic, hemodynamic, and pharmacokinetic data were obtained in hypoxia-exposed (one each, vorinostat-treated vs. untreated) and normoxic vorinostat-treated control animals (n = 2). Echocardiography detected PH changes by day 4 and severe PH over 14 days of continued hypoxic exposure. RV dysfunction at day 4 was less severe in vorinostat-treated compared to untreated hypoxic calves. Cardioprotective effects were partially maintained following cessation of treatment through the duration of hypoxic exposure, accompanied by hemodynamic evidence suggestive of reduced pulmonary vascular stiffening, and modulated expression of HDAC1 protein and genes involved in RV and pulmonary vascular remodeling and pathological RV hypertrophy. Control calves did not develop PH, nor show adverse cardiac or clinical effects. These results provide novel translation of epigenetic-directed therapy to a large animal severe PH model that recapitulates important features of human disease.

Dual BET/HDAC inhibition to relieve neuropathic pain: Recent advances, perspectives, and future opportunities

Despite the intense research on developing new therapies for neuropathic pain states, available treatments have limited efficacy and unfavorable safety profiles. Epigenetic alterations have a great influence on the development of cancer and neurological diseases, as well as neuropathic pain. Histone acetylation has prevailed as one of the well investigated epigenetic modifications in these diseases. Altered spinal activity of histone deacetylase (HDAC) and Bromo and Extra terminal domain (BET) have been described in neuropathic pain models and restoration of these aberrant epigenetic modifications showed pain-relieving activity. Over the last decades HDACs and BETs have been the focus of drug discovery studies, leading to the development of numerous small-molecule inhibitors. Clinical trials to evaluate their anticancer activity showed good efficacy but raised toxicity concerns that limited translation to the clinic. To maximize activity and minimize toxicity, these compounds can be applied in combination of sub-maximal doses to produce additive or synergistic interactions (combination therapy). Recently, of particular interest, dual BET/HDAC inhibitors (multi-target drugs) have been developed to assure simultaneous modulation of BET and HDAC activity by a single molecule. This review will summarize the most recent advances with these strategies, describing advantages and limitations of single drug treatment vs combination regimens. This review will also provide a focus on dual BET/HDAC drug discovery investigations as future therapeutic opportunity for human therapy of neuropathic pain.

Non-Hydroxamate Zinc-Binding Groups as Warheads for Histone Deacetylases

Histone deacetylases (HDACs) remove acetyl groups from acetylated lysine residues and have a large variety of substrates and interaction partners. Therefore, it is not surprising that HDACs are involved in many diseases. Most inhibitors of zinc-dependent HDACs (HDACis) including approved drugs contain a hydroxamate as a zinc-binding group (ZBG), which is by far the biggest contributor to affinity, while chemical variation of the residual molecule is exploited to create more or less selectivity against HDAC isozymes or other metalloproteins. Hydroxamates have a propensity for nonspecificity and have recently come under considerable suspicion because of potential mutagenicity. Therefore, there are significant concerns when applying hydroxamate-containing compounds as therapeutics in chronic diseases beyond oncology due to unwanted toxic side effects. In the last years, several alternative ZBGs have been developed, which can replace the critical hydroxamate group in HDACis, while preserving high potency. Moreover, these compounds can be developed into highly selective inhibitors. This review aims at providing an overview of the progress in the field of non-hydroxamic HDACis in the time period from 2015 to present. Formally, ZBGs are clustered according to their binding mode and structural similarity to provide qualitative assessments and predictions based on available structural information.

Overexpression of Human ABCB1 and ABCG2 Reduces the Susceptibility of Cancer Cells to the Histone Deacetylase 6-Specific Inhibitor Citarinostat

Citarinostat (ACY-241) is a promising oral histone deacetylase 6 (HDAC6)-selective inhibitor currently in clinical trials for the treatment of multiple myeloma (MM) and non-small-cell lung cancer (NSCLC). However, the inevitable emergence of resistance to citarinostat may reduce its clinical effectiveness in cancer patients and limit its clinical usefulness in the future. In this study, we investigated the potential role of the multidrug efflux transporters ABCB1 and ABCG2, which are two of the most common mechanisms of acquired resistance to anticancer drugs, on the efficacy of citarinostat in human cancer cells. We discovered that the overexpression of ABCB1 or ABCG2 significantly reduced the sensitivity of human cancer cells to citarinostat. We demonstrated that the intracellular accumulation of citarinostat and its activity against HDAC6 were substantially reduced by the drug transport function of ABCB1 and ABCG2, which could be restored by treatment with an established inhibitor of ABCB1 or ABCG2, respectively. In conclusion, our results revealed a novel mechanism by which ABCB1 and ABCG2 actively transport citarinostat away from targeting HDAC6 in cancer cells. Our results suggest that the co-administration of citarinostat with a non-toxic modulator of ABCB1 and ABCG2 may optimize its therapeutic application in the clinic.

Design, synthesis, and biological evaluation of dual targeting inhibitors of histone deacetylase 6/8 and bromodomain BRPF1

Histone modifying proteins, specifically histone deacetylases (HDACs) and bromodomains, have emerged as novel promising targets for anticancer therapy. In the current work, based on available crystal structures and docking studies, we designed dual inhibitors of both HDAC6/8 and the bromodomain and PHD finger containing protein 1 (BRPF1). Biochemical and biophysical tests showed that compounds 23a,b and 37 are nanomolar inhibitors of both target proteins. Detailed structure-activity relationships were deduced for the synthesized inhibitors which were supported by extensive docking and molecular dynamics studies. Cellular testing in acute myeloid leukemia (AML) cells showed only a weak effect, most probably because of the poor permeability of the inhibitors. We also aimed to analyse the target engagement and the cellular activity of the novel inhibitors by determining the protein acetylation levels in cells by western blotting (tubulin vs histone acetylation), and by assessing their effects on various cancer cell lines.

Targeting the C-Terminal Domain Small Phosphatase 1

The human C-terminal domain small phosphatase 1 (CTDSP1/SCP1) is a protein phosphatase with a conserved catalytic site of DXDXT/V. CTDSP1’s major activity has been identified as dephosphorylation of the 5th Ser residue of the tandem heptad repeat of the RNA polymerase II C-terminal domain (RNAP II CTD). It is also implicated in various pivotal biological activities, such as acting as a driving factor in repressor element 1 (RE-1)-silencing transcription factor (REST) complex, which silences the neuronal genes in non-neuronal cells, G1/S phase transition, and osteoblast differentiation. Recent findings have denoted that negative regulation of CTDSP1 results in suppression of cancer invasion in neuroglioma cells. Several researchers have focused on the development of regulating materials of CTDSP1, due to the significant roles it has in various biological activities. In this review, we focused on this emerging target and explored the biological significance, challenges, and opportunities in targeting CTDSP1 from a drug designing perspective.

Novel 2, 5-diketopiperazine derivatives as potent selective histone deacetylase 6 inhibitors: Rational design, synthesis and antiproliferative activity

Histone deacetylase 6 (HDAC6) has gained popular attention for its wide participation in various pathological process recently. In this paper, a series of novel derivatives containing 2, 5-diketopiperazine (DKP) skeleton were developed as potent selective HDAC6 inhibitors (sHDAC6is). Most of these compounds exhibited low nanomolar IC₅₀ values toward HDAC6, and the best compound was 21b (IC₅₀ = 0.73 nM) which had 144-10941-fold selectivity over other HDAC isoforms. Western blot assay further validated these compounds to be sHDAC6is. Molecular simulation of 21b was conducted to rationalize the high binding affinity for HDAC6. In the cytotoxicity experiment, 18a, 18b and 18d gave superior or comparable influence on the growth of two multiple myeloma cells U266 and RPMI-8226 compared to ACY-1215. Moreover, the combination of 18a and adriamycin showed synergistic effect against non-small cell lung cancer cell A549. 18a and 18b also demonstrated appropriate drug metabolism in human liver microsome (HLM).

MPT0G612, a Novel HDAC6 Inhibitor, Induces Apoptosis and Suppresses IFN-γ-Induced Programmed Death-Ligand 1 in Human Colorectal Carcinoma Cells

Colorectal cancer (CRC) is the third most common cancer and the leading cause of cancer-associated death worldwide. Histone deacetylases (HDACs) have been implicated in regulating complex cellular mechanisms to influence tumor biology and immunogenicity in various types of cancer. The potential of selective inhibition of HDAC6 has been widely discussed for the treatment of hematologic malignancies. We previously identified that MPT0G612 is a novel HDAC6 inhibitor exhibiting a promising antitumor activity against several solid tumors. The purpose of the present study was to evaluate the feasibility and pharmacological mechanisms of MPT0G612 as a potential therapy for CRC patients. Results revealed that MPT0G612 significantly suppresses the proliferation and viability, as well as induces apoptosis in CRC cells. Autophagy activation with LC3B-II formation and p62 degradation was observed, and the inhibition of autophagy by pharmacological inhibitor or Atg5 knockdown enhances MPT0G612-induced cell death. In addition, HDAC6 knockdown reduces MPT0G612-mediated autophagy and further potentiates apoptotic cell death. Furthermore, MPT0G612 downregulates the expression of PD-L1 induced by IFN-γ in CRC cells. These results suggest that MPT0G612 is a potent cell death inducer through inhibiting HDAC6-associated pathway, and a potential agent for combination strategy with immune checkpoint inhibitors for the treatment of CRC.

Evaluation of the antioxidant effects of different histone deacetylase inhibitors (HDACis) on human lens epithelial cells (HLECs) after UVB exposure

BACKGROUND

To compare the protective effects of the histone deacetylase inhibitors (HDACis) β-hydroxybutyrate (βOHB), trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA) and valproic acid (VPA) on human lens epithelial cells(HLECs) following ultraviolet-B (UVB) exposure.

METHODS

HLECs were divided into subgroups: four HDACi groups, a control group, a UVB-treated group and a DMSO group (cells treated with DMSO and UVB irradiation). In the HDACi groups, HLECs were cultured with different concentrations of HDACis 12 h prior to UVB irradiation. The protective effects of the HDACis were evaluated by assessing apoptosis rates, cell activity and expression levels of genes associated with apotosis (caspase-3, Bcl-2, BAX, SOD1, FOXO3A and MT2). The levels of superoxide dismutase (SOD), reactive oxygen species (ROS), malondialdehyde (MDA) and total antioxidant capacity (T-AOC) were detected in order to evaluate oxidative stress.

RESULTS

The results showed that SAHA (1 μmol/L, 2 μmol/L) and TSA (0.2 μmol/L) had mild protective effects on cell viability. βOHB (4 mmol/L) and TSA (0.2 mol/L) demonstrated protective effects on BCL-2 expression. TSA (0.2 mol/L) showed protective effects on SOD1 expression. TSA (0.2 mol/L) and SAHA (1 μmol/L) suppressed BAX and caspase-3 expression. TSA (0.2 mol/L, 0.8 mol/L) and SAHA (1 μmol/L, 2 μmol/L) suppressed the expression of FOXO3A and MT2. SOD levels were increased after treatment with βOHB (4 mmol/L), SAHA (8 μmol/L) and TSA (0.1 mol/L, 0.2 mol/L). T-AOC levels were increased in UVB-treated HLECs after treatment with SAHA (2 μmol/L). MDA levels decreased in UVB-treated HLECs following treatment with TSA (0.2 mol/L, 0.8 mol/L). ROS levels decreased in UVB-treated HLECs following treatment with βOHB (4 mmol/L), SAHA (1 μmol/L, 2 μmol/L) and TSA (0.2 mol/L). Western blotting results demonstrated that SOD1 levels significantly increased in the βOHB (4 mmol/L), SAHA (1 μmol/L, 2 μmol/L), TSA (0.1 mol/L, 0.2 mol/L) and VPA (5 mmol/L) groups. Only SAHA (1 μmol/L) had an anti-apoptotic effect on UVB-treated HLECs.

CONCLUSIONS

Our findings indicate that low concentrations of HDACis (1 μmol/L of SAHA) mildly inhibit oxidative stress, thus protecting HLECs from oxidation. These results may suggest that there is a possibility to explore the clinical applications of HDACis for treatment and prevention of cataracts.

Histone Deacetylases (HDACs) Guided Novel Therapies for T-cell lymphomas

T-cell lymphomas are a heterogeneous group of cancers with different pathogenesis and poor prognosis. Histone deacetylases (HDACs) are epigenetic modifiers that modulate many key biological processes. In recent years, HDACs have been fully investigated for their roles and potential as drug targets in T-cell lymphomas. In this review, we have deciphered the modes of action of HDACs, HDAC inhibitors as single agents, and HDACs guided combination therapies in T-cell lymphomas. The overview of HDACs on the stage of T-cell lymphomas, and HDACs guided therapies both as single agents and combination regimens endow great opportunities for the cure of T-cell lymphomas.

Histone deacetylase 6 selective inhibitor ACY1215 inhibits cell proliferation and enhances the chemotherapeutic effect of 5-fluorouracil in HCT116 cells

Background

ACY1215 is a selective histone deacetylase 6 (HDAC6) inhibitor, and can suppress tumor growth for many human cancers. However, its role in colon cancer and its impact on the chemotherapeutic effect of 5-fluorouracil (5-Fu) are largely unknown. The aim of the present study is to explore the effect of ACY1215 on cell growth, migration, invasion and apoptosis, along with its impact on the chemotherapeutic effect of 5-Fu in HCT116 cells.

Methods

HCT116 cells were treated with ACY1215 with or without 5-Fu, and cell viability, proliferation, migration, invasion and apoptosis were explored.

Results

The cell viability, colony formation number, wound closure rate, and migrated cell numbers of HCT116 cells significantly decreased, while the apoptotic cells significantly increased with the increased concentration of ACY1215 (P<0.05). The combination of ACY1215 and 5-Fu was more potent than either drug alone, as indicated by an increase of apoptotic cells, and by a decrease of cell viability, colony formation number, wound closure rate and migrated cell numbers. The expression of phosphorylated mitogen-activated protein kinases (pMEK) and phosphorylated extracellular-signal regulated protein kinase (pERK) were decreased when HCT116 cells were cultured with ACY1215.

Conclusions

Selective HDAC6 inhibitor, ACY1215, could inhibit the cell proliferation, migration and invasion, and induce apoptosis of HCT116 colon cancer cells. Furthermore, ACY1215 may enhance the chemotherapeutic effect of 5-Fu in HCT116 cells.

A selenium-containing selective histone deacetylase 6 inhibitor for targeted in vivo breast tumor imaging and therapy

We have developed a HDAC6-selective inhibitor, SelSA, which can be utilized as a target for the detection and treatment of ERα(+) breast cancer and TNBC. The biodistribution study showed that SelSA can specifically target the breast tumor and display potent antitumor effects in vivo. This result will help to better improve the treatment efficacy against breast cancer.

Evaluation of WO2017018805: 1,3,4-oxadiazole sulfamide derivatives as selective HDAC6 inhibitors

INTRODUCTION

There are great potential in the development of selective HDAC6 inhibitors for the treatment of infectious diseases, neoplasms, endocrine diseases, and other diseases associated with HDAC6 activity. Areas covered: The application claims 1,3,4-oxadiazole sulfamide derivatives as selective HDAC6 inhibitors for the treatment of infectious diseases, neoplasms, endocrine, nutritional, and metabolic diseases; mental and behavioral disorders; neurological diseases; diseases of the eye and adnexa; cardiovascular diseases; respiratory diseases; digestive diseases; diseases of the skin and subcutaneous tissue; disease of the musculoskeletal system and connective tissue; or congenital malformations, deformations and chromosomal abnormalities. Many of the exemplified compounds showed nanomole potency against HDAC6 and were more than 5000-fold selectivity for HDAC6 over HDAC1. Expert opinion: These 1,3,4-oxadiazole sulfamide derivatives have a unique zinc-binding group (ZBG) that provide good leads for the discovery of potent selective HDAC6 inhibitors for the treatment of a variety of diseases associated with HDAC6 activity.

Human ATP-binding cassette transporters ABCB1 and ABCG2 confer resistance to histone deacetylase 6 inhibitor ricolinostat (ACY-1215) in cancer cell lines

Ricolinostat is the first orally available, selective inhibitor of histone deacetylase 6 (HDAC6), currently under evaluation in clinical trials in patients with various malignancies. It is likely that the inevitable emergence of resistance to ricolinostat is likely to reduce its clinical effectiveness in cancer patients. In this study, we investigated the potential impact of multidrug resistance-linked ATP-binding cassette (ABC) transporters ABCB1 and ABCG2 on the efficacy of ricolinostat, which may present a major hurdle to its development as an anticancer drug in the future. We demonstrated that the overexpression of ABCB1 or ABCG2 reduces the intracellular accumulation of ricolinostat, resulting in reduced efficacy of ricolinostat to inhibit the activity of HDAC6 in cancer cells. Moreover, the efficacy of ricolinostat can be fully restored by inhibiting the drug efflux function of ABCB1 and ABCG2 in drug-resistant cancer cells. In conclusion, our results provide some insights into the basis for the development of resistance to ricolinostat and suggest that co-administration of ricolinostat with a modulator of ABCB1 or ABCG2 could overcome ricolinostat resistance in human cancer cells, which may be relevant to its use in the clinic.

Histone deacetylase inhibitor MS-275 restores social and synaptic function in a Shank3-deficient mouse model of autism

Autism is a neurodevelopmental disorder characterized by social deficits and repetitive behaviors. Genetic screening has identified synaptic, transcriptional, and chromatin genes disrupted in autistic patients. Haploinsufficiency of Shank3, which encodes a scaffold protein at glutamatergic synapses, is causally linked to autism. Using a Shank3-deficient mouse model that exhibits prominent autism-like phenotypes, we have found that histone acetylation in the prefrontal cortex (PFC) is abnormally low, which can be reversed by MS-275 (also known as Entinostat, SNDX-275), a class I histone deacetylase (HDAC) inhibitor that is selectively potent in PFC. A brief (3-day) treatment with MS-275 (i.p.) led to the sustained (11 days) rescue of autistic social preference deficits in Shank3-deficient mice, without altering locomotion, motor coordination, anxiety, or the increased grooming. MS-275 treatment also rescued the diminished NMDAR surface expression and NMDAR function induced by Shank3 deficiency. Moreover, F-actin at synapses was restored and the transcription of actin regulators was elevated by MS-275 treatment of Shank3-deficient mice, which may contribute to the recovery of actin-based NMDAR synaptic delivery. Taken together, these results suggest that MS-275 treatment could normalize the aberrant epigenetic regulation of genes, leading to the amelioration of synaptic and social deficits associated with autism.

Synthesis and biological evaluation of novel quinolone derivatives dual targeting histone deacetylase and tubulin polymerization as antiproliferative agents

A strategy to develop chemotherapy agents by combining two complimentary chemo-active groups into a single molecule may have higher efficacy and fewer side effects than that of single-target drugs. In this article, we describe the synthesis and evaluation of a series of novel dual-acting levofloxacin-HDACi conjugates to target both histone deacetylase (HDAC) and tubulin polymerization. These bifunctional conjugates exhibited potent inhibitory activities against HDACs and tubulin polymerization. In docking analysis provides a structural basis for HDACs inhibition activities. Moreover, these conjugates showed selective anticancer activity that is more potent against MCF-7 compared to other four cancer cells A549, HepG2, PC-3, HeLa, but they had no toxicity toward normal cells.

Megakaryocyte lineage development is controlled by modulation of protein acetylation

Treatment with lysine deacetylase inhibitors (KDACi) for haematological malignancies, is accompanied by haematological side effects including thrombocytopenia, suggesting that modulation of protein acetylation affects normal myeloid development, and specifically megakaryocyte development. In the current study, utilising ex-vivo differentiation of human CD34+ haematopoietic progenitor cells, we investigated the effects of two functionally distinct KDACi, valproic acid (VPA), and nicotinamide (NAM), on megakaryocyte differentiation, and lineage choice decisions. Treatment with VPA increased the number of megakaryocyte/erythroid progenitors (MEP), accompanied by inhibition of megakaryocyte differentiation, whereas treatment with NAM accelerated megakaryocyte development, and stimulated polyploidisation. Treatment with both KDACi resulted in no significant effects on erythrocyte differentiation, suggesting that the effects of KDACi primarily affect megakaryocyte lineage development. H3K27Ac ChIP-sequencing analysis revealed that genes involved in myeloid development, as well as megakaryocyte/erythroid (ME)-lineage differentiation are uniquely modulated by specific KDACi treatment. Taken together, our data reveal distinct effects of specific KDACi on megakaryocyte development, and ME-lineage decisions, which can be partially explained by direct effects on promoter acetylation of genes involved in myeloid differentiation.

Anticancer drug-induced cardiac rhythm disorders: Current knowledge and basic underlying mechanisms

Significant advances in cancer treatment have resulted in decreased cancer related mortality for many malignancies with some cancer types now considered chronic diseases. Despite these improvements, there is increasing recognition that many cancer patients or cancer survivors can develop cardiovascular diseases, either due to the cancer itself or as a result of anticancer therapy. Much attention has focused on heart failure; however, other cardiotoxicities, notably cardiac rhythm disorders, can occur without underlying cardiomyopathy. Supraventricular tachycardias occur in cancer patients treated with cytotoxic chemotherapy (anthracyclines, gemcitabine, cisplatin and alkylating-agents) or kinase-inhibitors (KIs) such as ibrutinib. Ventricular arrhythmias, with a subset of them being torsades-de-pointes (TdP) favored by QTc prolongation have been reported: this may be the result of direct hERG-channel inhibition or a more recently-described mechanism of phosphoinositide-3-kinase inhibition. The major anticancer drugs responsible for QTc prolongation in this context are KIs, arsenic trioxide, anthracyclines, histone deacetylase inhibitors, and selective estrogen receptor modulators. Anticancer drug-induced cardiac rhythm disorders remain an underappreciated complication even by experienced clinicians. Moreover, the causal relationship of a particular anticancer drug with cardiac arrhythmia occurrence remains challenging due in part to patient comorbidities and complex treatment regimens. For example, any cancer patient may also be diagnosed with common diseases such as hypertension, diabetes or heart failure which increase an individual's arrhythmia susceptibility. Further, anticancer drugs are generally usually used in combination, increasing the challenge around establishing causation. Thus, arrhythmias appear to be an underappreciated adverse effect of anticancer agents and the incidence, significance and underlying mechanisms are now being investigated.

Social deficits in Shank3-deficient mouse models of autism are rescued by histone deacetylase (HDAC) inhibition

Haploinsufficiency of the SHANK3 gene is causally linked to autism spectrum disorder (ASD), and ASD-associated genes are also enriched for chromatin remodelers. Here we found that brief treatment with romidepsin, a highly potent class I histone deacetylase (HDAC) inhibitor, alleviated social deficits in Shank3-deficient mice, which persisted for ~3 weeks. HDAC2 transcription was upregulated in these mice, and knockdown of HDAC2 in prefrontal cortex also rescued their social deficits. Nuclear localization of β-catenin, a Shank3-binding protein that regulates cell adhesion and transcription, was increased in Shank3-deficient mice, which induced HDAC2 upregulation and social deficits. At the downstream molecular level, romidepsin treatment elevated the expression and histone acetylation of Grin2a and actin-regulatory genes and restored NMDA-receptor function and actin filaments in Shank3-deficient mice. Taken together, these findings highlight an epigenetic mechanism underlying social deficits linked to Shank3 deficiency, which may suggest potential therapeutic strategies for ASD patients bearing SHANK3 mutations.

Repression of Fyn-related kinase in breast cancer cells is associated with promoter site-specific CpG methylation

The triple-negative breast cancer subtype is highly aggressive and has no defined therapeutic target. Fyn-related kinase (FRK) is a non-receptor tyrosine kinase, reported to be downregulated in breast cancer and gliomas, where it is suggested to have tumor suppressor activity. We examined the expression profile of FRK in a panel of 40 breast cancer cells representing all the major subtypes, as well as in 4 non-malignant mammary epithelial cell lines. We found that FRK expression was significantly repressed in a proportion of basal B breast cancer cell lines. We then determined the mechanism of suppression of FRK in FRK-low or negative cell lines. In silico analyses of the FRK promoter region led to the identification of at least 17 CpG sites. Bisulphite sequencing of the promoter region revealed that two of these sites were consistently methylated in FRK-low/negative cell lines and especially in the basal B breast cancer subtype. We further show that treatment of these cells with histone deacetylase inhibitors, Entinostat and Mocetinostat' promoted re-expression of FRK mRNA and protein. Further, using luciferase reporter assays, we show that both GATA3-binding protein FOG1 and constitutively active STAT5A increased the activity of FRK promoter. Together, our results present the first evidence that site-specific promoter methylation contributes to the repression of FRK more so in basal B breast cancers. Our study also highlights the potential clinical significance of targeting FRK using epigenetic drugs specifically in basal B breast cancers which are usually triple negative and very aggressive.

Targeted Cancer Therapies and QT Interval Prolongation: Unveiling the Mechanisms Underlying Arrhythmic Complications and the Need for Risk Stratification Strategies

The care and treatment of cancer patients has significantly changed in the last decade with a remarkable shift towards novel targeted therapies. These promising new drugs may represent effective and potentially life-saving therapeutic options in cancer patients, but are also emerging in the cardiotoxicity scenario for their arrhythmogenic potential due to their QT-prolonging activity. In this article we review the mechanisms underlying drug-induced QT interval prolongation and the classes of anticancer-targeted therapies most frequently responsible for this adverse event, with a particular focus on tyrosine kinase-targeting molecules. Since up to 49 % of serious adverse drug reactions (ADRs) and 58 % of potentially fatal ADRs may not appear on initial drug safety labels, we also review and discuss data from the post-marketing VigiBase^® safety reporting system, the World Health Organization's global database of ADRs. Finally, we discuss arrhythmic risk stratification and prevention strategies in the complex multiple-risk setting of cancer patients, paying particular attention to drug-drug interactions with common antimicrobial, psychotropic and antiemetic supportive care, and we also provide an electrocardiographic QT monitoring algorithm for patients who are candidates for targeted cancer therapies.

Discovery of Therapeutic Approaches for Polyglutamine Diseases: A Summary of Recent Efforts

Polyglutamine (PolyQ) diseases are a group of neurodegenerative disorders caused by the expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats in the coding region of specific genes. This leads to the production of pathogenic proteins containing critically expanded tracts of glutamines. Although polyQ diseases are individually rare, the fact that these nine diseases are irreversibly progressive over 10 to 30 years, severely impairing and ultimately fatal, usually implicating the full-time patient support by a caregiver for long time periods, makes their economic and social impact quite significant. This has led several researchers worldwide to investigate the pathogenic mechanism(s) and therapeutic strategies for polyQ diseases. Although research in the field has grown notably in the last decades, we are still far from having an effective treatment to offer patients, and the decision of which compounds should be translated to the clinics may be very challenging. In this review, we provide a comprehensive and critical overview of the most recent drug discovery efforts in the field of polyQ diseases, including the most relevant findings emerging from two different types of approaches-hypothesis-based candidate molecule testing and hypothesis-free unbiased drug screenings. We hereby summarize and reflect on the preclinical studies as well as all the clinical trials performed to date, aiming to provide a useful framework for increasingly successful future drug discovery and development efforts.

Histone deacetylase 3 (HDAC 3) as emerging drug target in NF-κB-mediated inflammation

Activation of inflammatory gene expression is regulated, among other factors, by post-translational modifications of histone proteins. The most investigated type of histone modifications is lysine acetylations. Histone deacetylases (HDACs) remove acetylations from lysines, thereby influencing (inflammatory) gene expression. Intriguingly, apart from histones, HDACs also target non-histone proteins. The nuclear factor κB (NF-κB) pathway is an important regulator in the expression of numerous inflammatory genes, and acetylation plays a crucial role in regulating its responses. Several studies have shed more light on the role of HDAC 1-3 in inflammation with a particular pro-inflammatory role for HDAC 3. Nevertheless, the HDAC-NF-κB interactions in inflammatory signalling have not been fully understood. An important challenge in targeting the regulatory role of HDACs in the NF-κB pathway is the development of highly potent small molecules that selectively target HDAC iso-enzymes. This review focuses on the role of HDAC 3 in (NF-κB-mediated) inflammation and NF-κB lysine acetylation. In addition, we address the application of frequently used small molecule HDAC inhibitors as an approach to attenuate inflammatory responses, and their potential as novel therapeutics. Finally, recent progress and future directions in medicinal chemistry efforts aimed at HDAC 3-selective inhibitors are discussed.

An Isochemogenic Set of Inhibitors To Define the Therapeutic Potential of Histone Deacetylases in β-Cell Protection

Modulation of histone deacetylase (HDAC) activity has been implicated as a potential therapeutic strategy for multiple diseases. However, it has been difficult to dissect the role of individual HDACs due to a lack of selective small-molecule inhibitors. Here, we report the synthesis of a series of highly potent and isoform-selective class I HDAC inhibitors, rationally designed by exploiting minimal structural changes to the clinically experienced HDAC inhibitor CI-994. We used this toolkit of isochemogenic or chemically matched inhibitors to probe the role of class I HDACs in β-cell pathobiology and demonstrate for the first time that selective inhibition of an individual HDAC isoform retains beneficial biological activity and mitigates mechanism-based toxicities. The highly selective HDAC3 inhibitor BRD3308 suppressed pancreatic β-cell apoptosis induced by inflammatory cytokines, as expected, or now glucolipotoxic stress, and increased functional insulin release. In addition, BRD3308 had no effect on human megakaryocyte differentiation, while inhibitors of HDAC1 and 2 were toxic. Our findings demonstrate that the selective inhibition of HDAC3 represents a potential path forward as a therapy to protect pancreatic β-cells from inflammatory cytokines and nutrient overload in diabetes.

Discovery of Selective Histone Deacetylase 6 Inhibitors Using the Quinazoline as the Cap for the Treatment of Cancer

Novel selective histone deacetylase 6 (HDAC6) inhibitors using the quinazoline as the cap were designed, synthesized, and evaluated for HDAC enzymatic assays. N-Hydroxy-4-(2-methoxy-5-(methyl(2-methylquinazolin-4-yl)amino)phenoxy)butanamide, 23bb, was the most potent selective inhibitor for HDAC6 with an IC50 of 17 nM and showed 25-fold and 200-fold selectivity relative to HDAC1 and HDAC8, respectively. In vitro, 23bb presented low nanomolar antiproliferative effects against panel of cancer cell lines. Western blot analysis further confirmed that 23bb increased acetylation level of α-tubulin in vitro. 23bb has a good pharmacokinetic profile with oral bioavailability of 47.0% in rats. In in vivo efficacy evaluations of colorectal HCT116, acute myelocytic leukemia MV4-11, and B cell lymphoma Romas xenografts, 23bb more effectively inhibited the tumor growth than SAHA even at a 4-fold reduced dose or ACY-1215 at the same dose. Our results indicated that 23bb is a potent oral anticancer candidate for selective HDAC6 inhibitor and deserves further investigation.

Histone Modifications, Modifiers and Readers in Melanoma Resistance to Targeted and Immune Therapy

The treatment of melanoma has been revolutionized by new therapies targeting MAPK signaling or the immune system. Unfortunately these therapies are hindered by either primary resistance or the development of acquired resistance. Resistance mechanisms involving somatic mutations in genes associated with resistance have been identified in some cases of melanoma, however, the cause of resistance remains largely unexplained in other cases. The importance of epigenetic factors targeting histones and histone modifiers in driving the behavior of melanoma is only starting to be unraveled and provides significant opportunity to combat the problems of therapy resistance. There is also an increasing ability to target these epigenetic changes with new drugs that inhibit these modifications to either prevent or overcome resistance to both MAPK inhibitors and immunotherapy. This review focuses on changes in histones, histone reader proteins and histone positioning, which can mediate resistance to new therapeutics and that can be targeted for future therapies.

Importance of investigating epigenetic alterations for industry and regulators: An appraisal of current efforts by the Health and Environmental Sciences Institute

Recent technological advances have led to rapid progress in the characterization of epigenetic modifications that control gene expression in a generally heritable way, and are likely involved in defining cellular phenotypes, developmental stages and disease status from one generation to the next. On November 18, 2013, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) held a symposium entitled "Advances in Assessing Adverse Epigenetic Effects of Drugs and Chemicals" in Washington, D.C. The goal of the symposium was to identify gaps in knowledge and highlight promising areas of progress that represent opportunities to utilize epigenomic profiling for risk assessment of drugs and chemicals. Epigenomic profiling has the potential to provide mechanistic information in toxicological safety assessments; this is especially relevant for the evaluation of carcinogenic or teratogenic potential and also for drugs that directly target epigenetic modifiers, like DNA methyltransferases or histone modifying enzymes. Furthermore, it can serve as an endpoint or marker for hazard characterization in chemical safety assessment. The assessment of epigenetic effects may also be approached with new model systems that could directly assess transgenerational effects or potentially sensitive stem cell populations. These would enhance the range of safety assessment tools for evaluating xenobiotics that perturb the epigenome. Here we provide a brief synopsis of the symposium, update findings since that time and then highlight potential directions for future collaborative efforts to incorporate epigenetic profiling into risk assessment.

Non-sirtuin histone deacetylases in the control of cardiac aging

Histone deacetylases (HDACs) catalyze the removal of acetyl-groups from lysine residues within nucelosomal histone tails and thousands of non-histone proteins. The 18 mammalian HDACs are grouped into four classes. Classes I, II and IV HDACs employ zinc as a co-factor for catalytic activity, while class III HDACs (also known as sirtuins) require NAD+ for enzymatic function. Small molecule inhibitors of zinc-dependent HDACs are efficacious in multiple pre-clinical models of pressure overload and ischemic cardiomyopathy, reducing pathological hypertrophy and fibrosis, and improving contractile function. Emerging data have revealed numerous mechanisms by which HDAC inhibitors benefit the heart, including suppression of oxidative stress and inflammation, inhibition of MAP kinase signaling, and enhancement of cardiac protein aggregate clearance and autophagic flux. Here, we summarize recent findings with zinc-dependent HDACs and HDAC inhibitors in the heart, focusing on newly described functions for distinct HDAC isoforms (e.g. HDAC2, HDAC3 and HDAC6). Potential for pharmacological HDAC inhibition as a means of treating age-related cardiac dysfunction is also discussed. This article is part of a Special Issue entitled: CV Aging.

Antidepressant action of HDAC inhibition in the prefrontal cortex

Previous research has demonstrated antidepressant-like effects in rodents upon intracerebral inhibition of histone deacetylases (HDACs). Such effects have been reported for local HDAC inhibition in the nucleus accumbens, hippocampus, and amygdala. However, the effect of HDAC inhibition within the medial prefrontal cortex, which is integral to depression-related symptoms and their treatment, remains unknown. Here we show that local infusion of the highly selective HDAC inhibitor, MS-275, into the medial prefrontal cortex exerts robust antidepressant-like effects in the chronic social defeat stress paradigm in mice. These findings provide further impetus for the assessment of HDAC inhibitors for the treatment of depression.

Epigenetic regulation of microRNAs controlling CLDN14 expression as a mechanism for renal calcium handling

The kidney has a major role in extracellular calcium homeostasis. Multiple genetic linkage and association studies identified three tight junction genes from the kidney--claudin-14, -16, and -19--as critical for calcium imbalance diseases. Despite the compelling biologic evidence that the claudin-14/16/19 proteins form a regulated paracellular pathway for calcium reabsorption, approaches to regulate this transport pathway are largely unavailable, hindering the development of therapies to correct calcium transport abnormalities. Here, we report that treatment with histone deacetylase (HDAC) inhibitors downregulates renal CLDN14 mRNA and dramatically reduces urinary calcium excretion in mice. Furthermore, treatment of mice with HDAC inhibitors stimulated the transcription of renal microRNA-9 (miR-9) and miR-374 genes, which have been shown to repress the expression of claudin-14, the negative regulator of the paracellular pathway. With renal clearance and tubule perfusion techniques, we showed that HDAC inhibitors transiently increase the paracellular cation conductance in the thick ascending limb. Genetic ablation of claudin-14 or the use of a loop diuretic in mice abrogated HDAC inhibitor-induced hypocalciuria. The genetic mutations in the calcium-sensing receptor from patients with autosomal dominant hypocalcemia (ADH) repressed the transcription of miR-9 and miR-374 genes, and treatment with an HDAC inhibitor rescued the phenotypes of cell and animal models of ADH. Furthermore, systemic treatment of mice with antagomiRs against these miRs relieved claudin-14 gene silencing and caused an ADH-like phenotype. Together, our findings provide proof of concept for a novel therapeutic principle on the basis of epigenetic regulation of renal miRs to treat hypercalciuric diseases.

Development and classes of epigenetic drugs for cancer

Emerging evidence supports an important, etiologic role for epigenetic modifications in cancer. Various post translational modifications of histone proteins together with DNA methylation constitute an 'epigenetic code' regulating the transcriptional status of the cell and aberrant writing and/or interpretation of the code can contribute to a dysregulated, hyperproliferative state. In some cases, epigenetic deregulation has also been reported to result in tumor initiation. The discovery of somatic mutations in some chromatin binding proteins associated with subtypes of lymphomas and the ability to regulate expression of proto oncogenes such as Myc has spurred the development of specific small molecule modulators of histone binding proteins. Several of these compounds have entered clinical development for the treatment of heme malignancies. This review summarizes progress in the discovery and advancement of epigenetic therapeutics for cancer and provides a perspective for future development.

Small molecule inhibitors of zinc-dependent histone deacetylases

Lysine acetylation is an ancient, evolutionarily conserved, reversible post-translational modification. A multitude of diverse cellular functions are regulated by this dynamic modification, including energy and metabolism, protein folding, transcription, and translation. Gene expression can be manipulated through changes in histone acetylation status, and this process is controlled by the function of 2 opposing enzymes: histone acetyl transferases and histone deacetylases (HDACs). The zinc-dependent HDACs are a family of hydrolases that remove acetyl groups from lysines, and their function can be modulated by the action of small molecule ligands. Inhibition through competitive binding of the catalytic domain of these enzymes has been achieved by a diverse array of small molecule chemotypes. Structural biology has aided the development of potent, and in some cases highly isoform-selective, inhibitors that have demonstrated utility in a number of neurological disease models. Continued development and characterization of highly optimized small molecule inhibitors of HDAC enzymes will help refine our understanding of their function and, optimistically, lead to novel therapeutic treatment alternatives for a host of neurological disorders.

Epigenetic mechanisms in cerebral ischemia

Treatment efficacy for ischemic stroke represents a major challenge. Despite fundamental advances in the understanding of stroke etiology, therapeutic options to improve functional recovery remain limited. However, growing knowledge in the field of epigenetics has dramatically changed our understanding of gene regulation in the last few decades. According to the knowledge gained from animal models, the manipulation of epigenetic players emerges as a highly promising possibility to target diverse neurologic pathologies, including ischemia. By altering transcriptional regulation, epigenetic modifiers can exert influence on all known pathways involved in the complex course of ischemic disease development. Beneficial transcriptional effects range from attenuation of cell death, suppression of inflammatory processes, and enhanced blood flow, to the stimulation of repair mechanisms and increased plasticity. Most striking are the results obtained from pharmacological inhibition of histone deacetylation in animal models of stroke. Multiple studies suggest high remedial qualities even upon late administration of histone deacetylase inhibitors (HDACi). In this review, the role of epigenetic mechanisms, including histone modifications as well as DNA methylation, is discussed in the context of known ischemic pathways of damage, protection, and regeneration.

Discovery of the first histone deacetylase 6/8 dual inhibitors

We disclose the first small molecule histone deacetylase (HDAC) inhibitor (3, BRD73954) capable of potently and selectively inhibiting both HDAC6 and HDAC8 despite the fact that these isoforms belong to distinct phylogenetic classes within the HDAC family of enzymes. Our data demonstrate that meta substituents of phenyl hydroxamic acids are readily accommodated upon binding to HDAC6 and, furthermore, are necessary for the potent inhibition of HDAC8.