HDAC inhibitors: clinical update and mechanism-based potential

Exploring histone deacetylases in type 2 diabetes mellitus: pathophysiological insights and therapeutic avenues

Diabetes mellitus is a chronic disease that impairs metabolism, and its prevalence has reached an epidemic proportion globally. Most people affected are with type 2 diabetes mellitus (T2DM), which is caused by a decline in the numbers or functioning of pancreatic endocrine islet cells, specifically the β-cells that release insulin in sufficient quantity to overcome any insulin resistance of the metabolic tissues. Genetic and epigenetic factors have been implicated as the main contributors to the T2DM. Epigenetic modifiers, histone deacetylases (HDACs), are enzymes that remove acetyl groups from histones and play an important role in a variety of molecular processes, including pancreatic cell destiny, insulin release, insulin production, insulin signalling, and glucose metabolism. HDACs also govern other regulatory processes related to diabetes, such as oxidative stress, inflammation, apoptosis, and fibrosis, revealed by network and functional analysis. This review explains the current understanding of the function of HDACs in diabetic pathophysiology, the inhibitory role of various HDAC inhibitors (HDACi), and their functional importance as biomarkers and possible therapeutic targets for T2DM. While their role in T2DM is still emerging, a better understanding of the role of HDACi may be relevant in improving insulin sensitivity, protecting β-cells and reducing T2DM-associated complications, among others.

LINC00115 promotes chemoresistant breast cancer stem-like cell stemness and metastasis through SETDB1/PLK3/HIF1α signaling

BACKGROUND

Cancer stem-like cell is a key barrier for therapeutic resistance and metastasis in various cancers, including breast cancer, yet the underlying mechanisms are still elusive. Through a genome-wide lncRNA expression profiling, we identified that LINC00115 is robustly upregulated in chemoresistant breast cancer stem-like cells (BCSCs).

METHODS

LncRNA microarray assay was performed to document abundance changes of lncRNAs in paclitaxel (PTX)-resistant MDA-MB-231 BCSC (ALDH+) and non-BCSC (ALDH-). RNA pull-down and RNA immunoprecipitation (RIP) assays were performed to determine the binding proteins of LINC00115. The clinical significance of the LINC00115 pathway was examined in TNBC metastatic lymph node tissues. The biological function of LINC00115 was investigated through gain- and loss-of-function studies. The molecular mechanism was explored through RNA sequencing, mass spectrometry, and the CRISPR/Cas9-knockout system. The therapeutic potential of LINC00115 was examined through xenograft animal models.

RESULTS

LINC00115 functions as a scaffold lncRNA to link SETDB1 and PLK3, leading to enhanced SETDB1 methylation of PLK3 at both K106 and K200 in drug-resistant BCSC. PLK3 methylation decreases PLK3 phosphorylation of HIF1α and thereby increases HIF1α stability. HIF1α, in turn, upregulates ALKBH5 to reduce m6A modification of LINC00115, resulting in attenuated degradation of YTHDF2-dependent m6A-modified RNA and enhanced LINC00115 stability. Thus, this positive feedback loop provokes BCSC phenotypes and enhances chemoresistance and metastasis in triple-negative breast cancer. SETDB1 inhibitor TTD-IN with LINC00115 ASO sensitizes PTX-resistant cell response to chemotherapy in a xenograft animal model. Correlative expression of LINC00115, methylation PLK3, SETDB1, and HIF1α are prognostic for clinical triple-negative breast cancers.

CONCLUSIONS

Our findings uncover LINC00115 as a critical regulator of BCSC and highlight targeting LINC00115 and SETDB1 as a potential therapeutic strategy for chemotherapeutic resistant breast cancer.

A GSH-resistant FK228 analogue containing a stable disulfide bond

FK228 is a potent natural pan HDAC inhibitor approved by the FDA for the treatment of cutaneous T-cell lymphoma as well as peripheral T-cell lymphoma. It is generally believed that the mechanism of FK228 acting on HDACs is by reducing its disulfide bond after entering the cell, and the dithiol group may chelate with Zn2+ and form a weak reversible covalent bond with cysteine in the catalytic pocket of HDACs, therefore inhibiting the activity of HDACs. However, due to the weak stability of the disulfide bond in FK228, it has been difficult to obtain direct evidence for the above conjecture. Thus, improving the stability of the FK228 disulfide bond will help to explore the exact mechanism of FK228. In this study, based on the stability and target-induced covalent properties of the Cysteine-Penicillamine (Cys-Pen) disulfide bond reported previously, the Pen was introduced into the modification of FK228. Specifically, the d-Cys in FK228 was replaced by d-Pen, the total synthetic pathway was optimized, and the novel synthetic FK228 analogue (FK-P) stability was verified. FK-P can also be used as a new drug molecule in the future to participate in the research of related biological mechanisms or the treatment of diseases.

Suberoylanilide Hydroxamic Acid Analogs with Heteroaryl Amide Group and Different Chain Length: Synthesis and Effect on Histone Deacetylase

This review covers the last 25 years of the literature on analogs of suberoylanilide hydroxamic acid (SAHA, known also as vorinostat) acting as an HDAC inhibitor. In particular, the topic has been focused on the synthesis and biological activity of compounds where the phenyl group (the surface recognition moiety, CAP) of SAHA has been replaced by an azaheterocycle through a direct bond with amide nitrogen atom, and the methylene chain in the linker region is of variable length. Most of the compounds displayed good to excellent inhibitory activity against HDACs and in many cases showed antiproliferative activity against human cancer cell lines.

The role of KLF transcription factor in the regulation of cancer progression

Kruppel-like factors (KLFs) are a family of zinc finger transcription factors that have been found to play an essential role in the development of various human tissues, including epithelial, teeth, and nerves. In addition to regulating normal physiological processes, KLFs have been implicated in promoting the onset of several cancers, such as gastric cancer, lung cancer, breast cancer, liver cancer, and colon cancer. To inhibit cancer progression, various existing medicines have been used to modulate the expression of KLFs, and anti-microRNA treatments have also emerged as a potential strategy for many cancers. Investigating the possibility of targeting KLFs in cancer therapy is urgently needed, as the roles of KLFs in cancer have not received enough attention in recent years. This review summarizes the factors that regulate KLF expression and function at both the transcriptional and posttranscriptional levels, which could aid in understanding the mechanisms of KLFs in cancer progression. We hope that this review will contribute to the development of more effective anti-cancer medicines targeting KLFs in the future.

High-yield production of FK228 and new derivatives in a Burkholderia chassis

FK228 (romidepsin) is the only natural histone deacetylases (HDACs) inhibitor approved by FDA to treat cutaneous and peripheral T-cell lymphoma. However, the limited supply and severe cardiotoxicity of FK228 underscore the importance to develop an effective synthetic biology platform for the manufacturing and fine-tuning of this drug lead. In this work, we constructed a Burkholderia chassis for the high-yield production of FK228-family (unnatural) natural products. By virtue of the optimized Burkholderia-specific recombineering system, the biosynthetic gene cluster (BGC) encoding the FK228-like skeleton thailandepsins (tdp) in Burkholderia thailandensis E264 was replaced with an attB integration site to afford the basal chassis KOGC1. The tdp BGC directly captured from E264 was hybridized with the FK228-encoding BGC (dep) using the versatile Red/ET technology. The hybrid BGC (tdp-dep) was integrated into the attB site of KOGC1, resulting in the heterologous expression of FK228. Remarkably, the titer reached 581 mg/L, which is 30-fold higher than that of native producer Chromobacterium violaceum No. 968. This success encouraged us to further engineer the NRPS modules 4 or 6 of hybrid tdp-dep BGC by domain units swapping strategy, and eight new FK228 derivatives (1-8) varying in the composition of amino acids were generated. Especially, the titers of 2 and 3 in KOGC1 were up to 985 mg/L and 453 mg/L, respectively. 2 and 3 displayed stronger cytotoxic activity than FK228. All in all, this work established a robust platform to produce FK228 and its new derivatives in sufficient quantities for anticancer drug development.

Role of epigenetics in carcinogenesis: Recent advancements in anticancer therapy

The role of epigenetics in the etiology of cancer progression is being emphasized for the past two decades to check the impact of chromatin modifiers and remodelers. Histone modifications, DNA methylation, chromatin remodeling, nucleosome positioning, regulation by non-coding RNAs and precisely microRNAs are influential epigenetic marks in the field of progressive cancer sub-types. Furthermore, constant epigenetic changes due to hyper or hypomethylation could efficiently serve as effective biomarkers of cancer diagnosis and therapeutic development. Ongoing research in the field of epigenetics has resulted in the resolutory role of various epigenetic markers and their inhibition using specific inhibitors to arrest their key cellular functions in in-vitro and pre-clinical studies. Although, the mechanism of epigenetics in cancer largely remains unexplored. Nevertheless, various advancements in the field of epigenetics have been made through transcriptome analysis and in-vitro genome targeting technologies to unravel the applicability of epigenetic markers for future cancer therapeutics and management. Therefore, this review emphasizes on recent advances in epigenetic landscapes that could be targeted/explored using novel approaches as personalized treatment modalities for cancer containment.

Selenium-Based Novel Epigenetic Regulators Offer Effective Chemotherapeutic Alternative with Wider Safety Margins in Experimental Colorectal Cancer

Colorectal cancer (CRC) is a major cause of morbidity and mortality worldwide. Despite the critical involvement of epigenetic modifications in CRC, the studies on the chemotherapeutic efficacy of various epigenetic regulators remain limited. Considering the key roles of histone deacetylases (HDACs) in the regulation of diverse cellular processes, several HDAC inhibitors are implied as effective therapeutic strategies. In this context, suberoylanilide hydroxamic acid (SAHA), a 2^nd-generation HDAC inhibitor, showed limited efficacy in solid tumors. Also, side effects associated with SAHA limit its clinical application. Based on the redox-modulatory and HDAC inhbitiory activities of essential trace element selenium (Se), the anti-carcinogenic potential of Se substituted SAHA, namely, SelSA-1 (25 mg kg^-1), was screened for it enhanced anti-tumorigenic role and wider safety profiles in DMH-induced CRC in Balb/c mice. A multipronged approach such as in silico, biochemical, and pharmacokinetics (PK) has been used to screen, characterize, and evaluate these novel compounds in comparison to existing HDAC inhibitor SAHA. This is the first in vivo study indicating the chemotherapeutic potential of Se-based novel epigenetic regulators such as SelSA-1 in any in vivo experimental model of carcinogenesis. Pharmcological and toxicity data indicated better safety margins, bioavailability, tolerance, and elimination rate of SelSA-1 compared to classical HDAC inhibitor SAHA. Further, histological and morphological evidence demonstrated enhanced chemotherapeutic potential of SelSA-1 even at lower pharmacological doses than SAHA. This is the first in vivo study suggesting Se-based novel epigenetic regulators as potential chemotherapeutic alternatives with wider safety margins and enhanced anticancer activities.

Isoform-selective HDAC Inhibitor Mocetinostat (MGCD0103) Alleviates Myocardial Ischemia/Reperfusion Injury via Mitochondrial Protection through the HDACs/CREB/PGC-1α Signaling Pathway

ABSTRACT

Over the past decade, histone deacetylases (HDACs) has been proven to manipulate development and exacerbation of cardiovascular diseases, including myocardial ischemia/reperfusion injury (MIRI), cardiac hypertrophy, ventricular remodeling, myocardial fibrosis. Inhibition of histone deacetylases, especially class-I HDACs, is potent to protection of ischemic myocardium after ischemia/reperfusion. Herein, we examine whether mocetinostat (MGCD0103, MOCE), a class-I selective HDAC inhibitor in phase-II clinical trial, conducts cardioprotection under ischemia/reperfusion (I/R) in vivo and vitro, if so, reveal its potential pharmacological mechanism to provide an experimental and theoretical basis for mocetinostat usage in a clinical setting. HCMs were exposed to hypoxia and reoxygenation (H/R), with or without mocetinostat treatment. H/R reduced mitochondrial membrane potential (MMP) and induced HCMs apoptosis. Mocetinostat pre-treatment reversed these H/R-induced mitochondrial damage and cellular apoptosis and upregulated CREB, p-CREB and PGC-1α in HCMs during H/R. Transfection with siRNA against PGC-1α or CREB abolished the protective effects of mocetinostat on cardiomyocytes undergoing H/R. In vivo, mocetinostat was demonstrated to protect myocardial injury posed by myocardial ischemia/reperfusion (I/R) via activation of CREB and upregulation of PGC-1α. Mocetinostat (MGCD0103) can protect myocardium from ischemia/reperfusion injury through mitochondrial protection mediated by CREB/PGC-1α pathway. Therefore, activation of the CREB/PGC-1α signaling pathway via inhibition of Class-I HDACs may be a promising new therapeutic strategy for alleviating myocardial reperfusion injury.

Discovery of quinazolinyl-containing benzamides derivatives as novel HDAC1 inhibitors with in vitro and in vivo antitumor activities

A series of quinazolinyl-containing benzamide derivatives were designed, synthesized and evaluated for their in vitro histone deacetylase 1 (HDAC1) inhibitory activities. Compounds 11a surpassed the known class I selective HDAC inhibitor MS-275 in both HDAC1 enzymatic inhibitory activity and cellular anti-proliferative activity against a selected set of cancer cell types (Hut78, K562, Hep3B and HCT116 cells) with no observed effects on human normal cells. In particular, compound 11a inhibited HDAC1 over the other tested HDACs isoforms (HDAC2, HDAC6 and HDAC8) with acceptable safety profiles. Moreover, compound 11a displayed favorable oral pharmacokinetic properties and showed significant antitumor activity in the A549 tumor xenograft model in vivo.

Histone deacetylase-6 modulates amyloid beta-induced cognitive dysfunction rats by regulating PTK2B

The aim of this study was to investigate the effects of histone deacetylase-6 (HDAC6) on the functional and pathological changes of the amyloid beta (Aβ)-induced cognitive dysfunction rats by regulating protein tyrosine kinase 2 beta (PTK2B). Ninety Sprague Dawley rats were randomly divided into nine groups, consisting of five experimental groups and four control groups. In five experimental groups, Aβ1-42 was infused intracerebroventricularly and 3 days later, rats in each group were infused intracerebroventricularly with tubastatin A hydrochloride (TSA), the HDAC6-specific inhibitor (Aβ + TSA group), theophylline, the HDACs agonist (Aβ + Theo group), PF431396 (PF), the PTK2B inhibitor (Aβ + PF group), the combination of PF and theophylline (Aβ + PF + Theo group), and normal saline (Aβ + normal saline group), respectively. Rats in four control groups took normal saline that was equivalent to the volume of Aβ1-42, and 3 days later, TSA (TSA group), theophylline (Theo group), (PF group, or normal saline group) was given at a volume of 5 µL for rats in each group. Our results showed that HDAC6 may not only lead to the deterioration of learning and memory abilities but also elevate the levels of Aβo and Tau phosphorylation in Aβ-induced cognitive dysfunction rats via upregulating PTK2B.

Intracellular fluorescence competition assay for inhibitor engagement of histone deacetylase

An intracellular fluorescence competition assay was developed to assess the capability of inhibitor candidates to engage histone deacetylase (HDAC) inside living cells and thus diminish cell uptake and staining by the HDAC-targeted fluorescent probe APS. Fluorescence cell microscopy and flow cytometry showed that pre-incubation of living cells with candidate inhibitors led to diminished cell uptake of the fluorescent probe. The assay was effective because the fluorescent probe (APS) possessed the required performance properties, including bright fluorescence, ready membrane diffusion, selective intracellular HDAC affinity, and negligible acute cytotoxicity. The concept of an intracellular fluorescence competition assay is generalizable and has broad applicability since it obviates the requirement to use the isolated biomacromolecule target for screening of molecular candidates with target affinity.

The Emerging Role of HDACs: Pathology and Therapeutic Targets in Diabetes Mellitus

Diabetes mellitus (DM) is one of the principal manifestations of metabolic syndrome and its prevalence with modern lifestyle is increasing incessantly. Chronic hyperglycemia can induce several vascular complications that were referred to be the major cause of morbidity and mortality in DM. Although several therapeutic targets have been identified and accessed clinically, the imminent risk of DM and its prevalence are still ascending. Substantial pieces of evidence revealed that histone deacetylase (HDAC) isoforms can regulate various molecular activities in DM via epigenetic and post-translational regulation of several transcription factors. To date, 18 HDAC isoforms have been identified in mammals that were categorized into four different classes. Classes I, II, and IV are regarded as classical HDACs, which operate through a Zn-based mechanism. In contrast, class III HDACs or Sirtuins depend on nicotinamide adenine dinucleotide (NAD+) for their molecular activity. Functionally, most of the HDAC isoforms can regulate β cell fate, insulin release, insulin expression and signaling, and glucose metabolism. Moreover, the roles of HDAC members have been implicated in the regulation of oxidative stress, inflammation, apoptosis, fibrosis, and other pathological events, which substantially contribute to diabetes-related vascular dysfunctions. Therefore, HDACs could serve as the potential therapeutic target in DM towards developing novel intervention strategies. This review sheds light on the emerging role of HDACs/isoforms in diabetic pathophysiology and emphasized the scope of their targeting in DM for constituting novel interventional strategies for metabolic disorders/complications.

Novel 4-Oxoquinazoline-Based N-Hydroxypropenamides as Histone Deacetylase Inhibitors: Design, Synthesis, and Biological Evaluation

Two series of novel 4-oxoquinazoline-based N-hydroxypropenamides (9a-m and 10a-m) were designed, synthesized, and evaluated for their inhibitory and cytotoxicity activities against histone deacetylase (HDAC). The compounds showed good to potent HDAC inhibitory activity and cytotoxicity against three human cancer cell lines (SW620, colon; PC-3, prostate; NCI-H23, lung cancer). In this series, compounds with the N-hydroxypropenamide functionality impeded at position 7 on the 4-oxoquinazoline skeleton (10a-m) were generally more potent than compounds with the N-hydroxypropenamide moiety at position 6 (9a-m). Also, the N ³-benzyl-substituted derivatives (9h-m, 10h-m) exhibited stronger bioactivity than the N ³-alkyl-substituted ones (9a-e, 10a-e). Two compounds 10l and 10m were the most potent ones. Their HDAC inhibitory activity (IC₅₀ values, 0.041-0.044 μM) and cytotoxicity (IC₅₀ values, 0.671-1.211 μM) were approximately 2- to 3-fold more potent than suberoylanilide hydroxamic acid (SAHA). Some compounds showed up to 10-fold more potent HDAC6 inhibition compared to their inhibitory activity in total HDAC extract assay. Analysis of selected compounds 10l and 10m revealed that these compounds strongly induced both early and late apoptosis and arrested SW620 cells at the G2/M phase. Docking studies were carried out on the HDAC6 isoform for series 10a-m and revealed some important features contributing to the inhibitory activity of synthesized compounds.

Convergent epigenetic regulation of glial plasticity in myelin repair and brain tumorigenesis: A focus on histone modifying enzymes

Brain regeneration and tumorigenesis are complex processes involving in changes in chromatin structure to regulate cellular states at the molecular and genomic level. The modulation of chromatin structure dynamics is critical for maintaining progenitor cell plasticity, growth and differentiation. Oligodendrocyte precursor cells (OPC) can be differentiated into mature oligodendrocytes, which produce myelin sheathes to permit saltatory nerve conduction. OPCs and their primitive progenitors such as pri-OPC or pre-OPC are highly adaptive and plastic during injury repair or brain tumor formation. Recent studies indicate that chromatin modifications and epigenetic homeostasis through histone modifying enzymes shape genomic regulatory landscape conducive to OPC fate specification, lineage differentiation, maintenance of myelin sheaths, as well as brain tumorigenesis. Thus, histone modifications can be convergent mechanisms in regulating OPC plasticity and malignant transformation. In this review, we will focus on the impact of histone modifying enzymes in modulating OPC plasticity during normal development, myelin regeneration and tumorigenesis.

Patel V, Veerasamy R, Sharma PC, Rajak H. Searching for Potential HDAC2 Inhibitors: Structure-activity Relationship Studies on Indole-based Hydroxamic Acids as an Anticancer Agent

Aim:

To predict the most potent indole based HDAC2 inhibitors from several scientific reports through the process of lead identification and SAR development. Background: The current scenario is observing Histone Deacetylase (HDAC) as an alluring molecular target for the designing and development of drugs for cancer treatment.

Background:

The current scenario is observing Histone Deacetylase (HDAC) as an alluring molecular target for the designing and development of drugs for cancer treatment.

Objective:

To identify the lead and establish structure-activity correlation among indole based hydroxamic acid to find out promising HDAC2 based anticancer agent.

Methods:

A dataset containing 59 molecules was analyzed using structure and ligand-based integrated approach comprising atom-based 3D-QSAR (Quantitative Structure-Activity Relationship) and pharmacophore study, e-pharmacophore mapping and molecular modeling methodologies. The finest model was prepared by amalgamating the properties of electronegativity, polarizability, Vander Waals forces and other conformational aspects.

Results:

The result of 3D QSAR analysis, performed for 4 PLS factor, provided the following statistical information: R2 = 0.9461, Q2 = 0.7342 and low standard of deviation SD = 0.1744 for hypothesis ADDDH.10 and R2 = 0.9444, Q2= 0.7858 and again low standard of deviation SD = 0.1795 for hypothesis DDHRR.12. The XP molecular docking showed intermolecular interactions of small molecules with amino acids such as GLY154, HIP145, PHE210, HIE183, internal H2O and Zn2+.

Conclusion:

The interpretation of data generated as a result of this investigation clearly hints about the better biological activity of test compounds as compared to SAHA. Hence, the outcome of these structure and ligand-based integrated studies could be employed for the design of novel arylindole derivatives as a potent HDAC inhibitor.

Exploration of certain 1,3-oxazole- and 1,3-thiazole-based hydroxamic acids as histone deacetylase inhibitors and antitumor agents

Several novel series of hydroxamic acids bearing 2-benzamidooxazole/thiazole (5a-g, 6a-g) or 2-phenylsulfonamidothiazole (8a-c) were designed and synthesized. The compounds were obtained straightforwards via a two step pathway, starting from commercially available ethyl 2-aminooxazole-4-carboxylate or ethyl 2-aminothiazole-4-carboxylate. Biological evaluation showed that these hydroxamic acids generally exhibited good cytotoxicity against three human cancer cell lines (SW620, colon; PC-3, prostate; NCI-H23, lung cancer), with IC₅₀ values in low micromolar range and comparable to that of SAHA. These compounds also comparably inhibited HDACs with IC₅₀ values in sub-micromolar range (0.010-0.131 µM) and some compounds (e.g 5f, IC₅₀, 0.010 µM) were even more potent than SAHA (IC₅₀, 0.025 µM) in HDAC inhibition. Representative compounds 6a and 8a appeared to arrest the SW620 cell cycle at G2 phase and significantly induced both early and late apoptosis of SW620 colon cancer cells. Docking experiments on HDAC2 and HDAC6 isozymes revealed favorable interactions at the tunnel of the HDAC active site which positively contributed to the inhibitory activity of synthesized compound. The binding affinity predicted by docking program showed good correlation with the experimental IC₅₀ values. This study demonstrates that simple 1,3-oxazole- and 1,3-thiazole-based hydroxamic acids are also promising as antitumor agents and HDAC inhibitors and these results should provide valuable information for further design of more potent HDAC inhibitors and antitumor agents.

Design, Synthesis, and Cytotoxic Evaluation of Novel Lupane Triterpenoid Derived Hydroxamates

A series of new hydroxamate derivatives of lupane triterpenoids has been designed and successfully synthesized. The synthesized compounds were evaluated for their in vitro antitumor activity using the 3-[4,5-dimethylthiazol-2-yl]−2,5-diphenyltetrazolium bromide-based assay against the human cancer cell lines KB and HepG2. Most of these derivatives possess at least moderate cytotoxic activity and the hydroxamate derivative compounds 3c, 3e, 7a, and 15b could be lead compounds for further optimization to develop novel anticancer agents.

Novel Conjugated Quinazolinone-Based Hydroxamic Acids: Design, Synthesis and Biological Evaluation

BACKGROUND

The target-based approach to drug discovery currently attracts a great deal of interest from medicinal chemists in anticancer drug discovery and development. Histone deacetylase (HDAC) inhibitors represent an extensive class of targeted anti-cancer agents. Among the most explored structure moieties, hydroxybenzamides and hydroxypropenamides have been demonstrated to have potential HDAC inhibitory effects. Several compounds of these structural classes have been approved for clinical uses to treat different types of cancer, such as vorinostat and belinostat.

AIMS

This study aims at developing novel HDAC inhibitors bearing conjugated quinazolinone scaffolds with potential cytotoxicity against different cancer cell lines.

METHODS

A series of novel N-hydroxyheptanamides incorporating conjugated 6-hydroxy-2 methylquinazolin- 4(3H)-ones (15a-l) was designed, synthesized and evaluated for HDAC inhibitory potency as well as cytotoxicity against three human cancer cell lines, including HepG-2, MCF-7 and SKLu-1. Molecular simulations were finally performed to gain more insight into the structureactivity relationships.

RESULTS

It was found that among novel conjugated quinazolinone-based hydroxamic acids synthesized, compounds 15a, 15c and 15f were the most potent, both in terms of HDAC inhibition and cytotoxicity. Especially, compound 15f displayed up to nearly 4-fold more potent than SAHA (vorinostat) in terms of cytotoxicity against MCF-7 cell line with IC₅₀ value of 1.86 μM, and HDAC inhibition with IC₅₀ value of 6.36 μM. Docking experiments on HDAC2 isozyme showed that these compounds bound to HDAC2 with binding affinities ranging from -10.08 to -14.93 kcal/mol compared to SAHA (-15.84 kcal/mol). It was also found in this research that most of the target compounds seemed to be more cytotoxic toward SKLu-1than MCF-7 and HepG-2.

CONCLUSION

The resesrch results suggest that some hydroxamic acids could emerge for further evaluation and the results are well served as basics for further design of more potent HDAC inhibitors and antitumor agents.

Design and synthesis of diazine-based panobinostat analogues for HDAC8 inhibition

Guided by computational analysis, herein we report the design, synthesis and evaluation of four novel diazine-based histone deacetylase inhibitors (HDACis). The targets of interest (TOI) are analogues of panobinostat, one of the most potent and versatile HDACi reported. By simply replacing the phenyl core of panobinostat with that of a diazine derivative, docking studies against HDAC2 and HDAC8 revealed that the four analogues exhibit inhibition activities comparable to that of panobinostat. Multistep syntheses afforded the visualized targets TOI1, TOI2, TOI3-rev and TOI4 whose biological evaluation confirmed the strength of HDAC8 inhibition with TOI4 displaying the greatest efficacy at varying concentrations. The results of this study lay the foundation for future design strategies toward more potent HDACis for HDAC8 isozymes and further therapeutic applications for neuroblastoma.

Epigenetic regulation of oligodendrocyte myelination in developmental disorders and neurodegenerative diseases

Oligodendrocytes are the critical cell types giving rise to the myelin nerve sheath enabling efficient nerve transmission in the central nervous system (CNS). Oligodendrocyte precursor cells differentiate into mature oligodendrocytes and are maintained throughout life. Deficits in the generation, proliferation, or differentiation of these cells or their maintenance have been linked to neurological disorders ranging from developmental disorders to neurodegenerative diseases and limit repair after CNS injury. Understanding the regulation of these processes is critical for achieving proper myelination during development, preventing disease, or recovering from injury. Many of the key factors underlying these processes are epigenetic regulators that enable the fine tuning or reprogramming of gene expression during development and regeneration in response to changes in the local microenvironment. These include chromatin remodelers, histone-modifying enzymes, covalent modifiers of DNA methylation, and RNA modification-mediated mechanisms. In this review, we will discuss the key components in each of these classes which are responsible for generating and maintaining oligodendrocyte myelination as well as potential targeted approaches to stimulate the regenerative program in developmental disorders and neurodegenerative diseases.

Epigenetic polypharmacology: A new frontier for epi-drug discovery

Recently, despite the great success achieved by the so-called "magic bullets" in the treatment of different diseases through a marked and specific interaction with the target of interest, the pharmacological research is moving toward the development of "molecular network active compounds," embracing the related polypharmacology approach. This strategy was born to overcome the main limitations of the single target therapy leading to a superior therapeutic effect, a decrease of adverse reactions, and a reduction of potential mechanism(s) of drug resistance caused by robustness and redundancy of biological pathways. It has become clear that multifactorial diseases such as cancer, neurological, and inflammatory disorders, may require more complex therapeutic approaches hitting a certain biological system as a whole. Concerning epigenetics, the goal of the multi-epi-target approach consists in the development of small molecules able to simultaneously and (often) reversibly bind different specific epi-targets. To date, two dual histone deacetylase/kinase inhibitors (CUDC-101 and CUDC-907) are in an advanced stage of clinical trials. In the last years, the growing interest in polypharmacology encouraged the publication of high-quality reviews on combination therapy and hybrid molecules. Hence, to update the state-of-the-art of these therapeutic approaches avoiding redundancy, herein we focused only on multiple medication therapies and multitargeting compounds exploiting epigenetic plus nonepigenetic drugs reported in the literature in 2018. In addition, all the multi-epi-target inhibitors known in literature so far, hitting two or more epigenetic targets, have been included.

A phase I study of panobinostat and ruxolitinib in patients with primary myelofibrosis (PMF) and post--polycythemia vera/essential thrombocythemia myelofibrosis (post--PV/ET MF)

Ruxolitinib, a selective JAK1/JAK2 inhibitor, is the current first line therapy for myelofibrosis (MF), which reduces symptomatology and splenomegaly, but does not clearly modify disease course. Panobinostat, a histone deacetylase inhibitor, was shown to be safe and tolerable in phase I and II trials and demonstrated clinical activity in approximately a third of treated patients. Combination therapy of ruxolitinib and panobinostat showed synergistic activity in a preclinical MF model, which prompted clinical evaluation of this combination in both ruxolitinib naïve and treated MF patients. Herein, we report the results of an investigator-initiated, dose escalation, phase I trial of ruxolitinib and panobinostat in 15 patients with primary MF and post-polycythemia vera/essential thrombocythemia MF. This combination treatment proved to be safe and tolerable without dose limiting thrombocytopenia and a maximum tolerated dose of both agents in combination was not determined. The majority of patients maintained stable disease with this combination treatment and 40 % attained a clinical improvement (spleen n = 5, anemia n = 1) by modified IWG-MRT at the end of 6 cycles. This is one of the first attempts of rationally designed, JAK inhibitor-based, combination therapy studies and exemplifies the feasibility of such an approach in patients with advanced MF.

Chromatin modification and epigenetic control in functional nerve regeneration

The repair and functional recovery of the nervous system is a highly regulated process that requires the coordination of many different components including the proper myelination of regenerated axons. Dysmyelination and remyelination failures after injury result in defective nerve conduction, impairing normal nervous system functions. There are many convergent regulatory networks and signaling mechanisms between development and regeneration. For instance, the regulatory mechanisms required for oligodendrocyte lineage progression could potentially play fundamental roles in myelin repair. In recent years, epigenetic chromatin modifications have been implicated in CNS myelination and functional nerve restoration. The pro-regenerative transcriptional program is likely silenced or repressed in adult neural cells including neurons and myelinating cells in the central and peripheral nervous systems limiting the capacity for repair after injury. In this review, we will discuss the roles of epigenetic mechanisms, including histone modifications, chromatin remodeling, and DNA methylation, in the maintenance and establishment of the myelination program during normal oligodendrocyte development and regeneration. We also discuss how these epigenetic processes impact myelination and axonal regeneration, and facilitate the improvement of current preclinical therapeutics for functional nerve regeneration in neurodegenerative disorders or after injury.

Evaluation of entinostat alone and in combination with standard-of-care cytotoxic agents against rhabdomyosarcoma xenograft models

BACKGROUND

Entinostat, a selective class I histone deacetylase inhibitor, has been reported to enhance the activity of cytotoxic agents and suppress expression of PAX3-FOXO1 in alveolar rhabdomyosarcoma (ARMS).

PROCEDURES

Entinostat was tested against three rhabdomyosarcoma cell lines using 96-hour drug exposure. Entinostat alone or in binary combination with vincristine, actinomycin D or cyclophosphamide was tested in ARMS and two embryonal rhabdomyosarcoma (ERMS) xenograft models. Tumor growth was measured at weekly intervals. Drug-induced changes in acetylated histone H3(K9) and entinostat pharmacokinetics were determined.

RESULTS

In vitro, the IC₅₀ concentration of entinostat ranged from 280 to 1300 nM. In vivo, entinostat significantly inhibited the growth of only Rh10 xenografts. For most studies, entinostat did not potentiate the activity of the cytotoxic agent. Exceptions included the vincristine and entinostat combination for Rh10 and the entinostat and actinomycin D combination for Rh10 and Rh18, although the effects were modest. For Rh18, the combination of entinostat with vincristine showed evidence of an antagonistic interaction compared with single-agent vincristine. Pharmacokinetic studies showed the average C_max was 569.4 ng/mL (1.51 μM) with T_max at 15 minutes, and total exposure (AUC_{0-12 h} ) was 435.6 h × ng/mL. Entinostat treatment increased acetylated histone H3.

CONCLUSIONS

Entinostat demonstrated modest antitumor activity in only one of four models at dose and shedule that gave drug exposures relevant to human treatment. The addition of entinostat to standard-of-care cytotoxic agents was in most instances no more effective than the cytotoxic agents used alone. Entinostat demonstrated target inhibition with increased histone 2A acetylation.

The thioredoxin system and cancer therapy: a review

Thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH are key members of the Trx system that is involved in redox regulation and antioxidant defense. In recent years, several researchers have provided information about the roles of the Trx system in cancer development and progression. These reports indicated that many tumor cells express high levels of Trx and TrxR, which can be responsible for drug resistance in tumorigenesis. Inhibition of the Trx system may thus contribute to cancer therapy and improving chemotherapeutic agents. There are now a number of effective natural and synthetic inhibitors with chemotherapy applications possessing antitumor activity ranging from oxidative stress induction to apoptosis. In this article, we first described the features and functions of the Trx system and then reviewed briefly its correlations with cancer. Finally, we summarized the present knowledge about the Trx/TrxR inhibitors as anticancer drugs.

Design, Synthesis and Biological Evaluation of Novel N-hydroxyheptanamides Incorporating 6-hydroxy-2-methylquinazolin-4(3H)-ones as Histone Deacetylase Inhibitors and Cytotoxic Agents

BACKGROUND

Target-based approach to drug discovery currently attracts a great deal of interest from medicinal chemists in anticancer drug discovery and development worldwide, and Histone Deacetylase (HDAC) inhibitors represent an extensive class of targeted anti-cancer agents. Among the most explored structure moieties, hydroxybenzamides and hydroxypropenamides have been demonstrated to have potential HDAC inhibitory effects. Several compounds of these structural classes have been approved for clinical uses to treat different types of cancer, such as vorinostat and belinostat.

AIMS

This study aims at developing novel HDAC inhibitors bearing quinazolinone scaffolds with potential cytotoxicity against different cancer cell lines.

METHODS

A series of novel N-hydroxyheptanamides incorporating 6-hydroxy-2 methylquinazolin-4(3H)-ones (14a-m) was designed, synthesized and evaluated for HDAC inhibitory potency as well as cytotoxicity against three human cancer cell lines, including HepG-2 (liver cancer), MCF-7 (breast cancer) and SKLu-1 (lung cancer). Molecular simulations were finally carried out to gain more insight into the structure-activity relationships. ADME-T predictions for selected compounds were also performed to predict some important features contributing to the absorption profile of the present hydroxamic derivatives.

RESULTS

It was found that the N-hydroxyheptanamide 14i and 14j were the most potent, both in terms of HDAC inhibition and cytotoxicity. These compounds displayed up to 21-71-fold more potent than SAHA (suberoylanilide hydroxamic acid, vorinostat) in terms of cytotoxicity, and strong inhibition against the whole cell HDAC enzymes with IC₅₀ values of 7.07-9.24μM. Docking experiments on HDAC2 isozyme using Autodock Vina showed all compounds bound to HDAC2 with relatively higher affinities (from -7.02 to -11.23 kcal/mol) compared to SAHA (-7.4 kcal/mol). It was also found in this research that most of the target compounds seemed to be more cytotoxic toward breast cancer cells (MCF-7) than liver (HepG2), and lung (SKLu-1) cancer cells.

Brain region-specific regulation of histone acetylation and efflux transporters in mice

Multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) protect the brain by restricting the passage of chemicals across the blood-brain barrier. Prior studies have demonstrated the epigenetic regulation of MDR1 and BCRP in cancer cells treated with histone deacetylase (HDAC) inhibitors that enhance histone acetylation and gene transcription. In the present study, we tested the in vivo effects of two HDAC inhibitors, valproic acid (VPA; 400 mg/kg) and apicidin (5 mg/kg), on Mdr1 and Bcrp transporter expression in brain regions of adult male mice injected intraperitoneally daily for 7 days. VPA increased Mdr1 protein expression in the striatum (70%) and Bcrp protein in the midbrain (30%). Apicidin enhanced striatal Mdr1 protein (30%) and hippocampal Bcrp protein (20%). Transporter induction correlated with increased histone H3 acetylation in discrete brain regions. In conclusion, HDAC inhibitors upregulate transporter proteins in vivo, which may be important in regulating regional xenobiotic disposition within the brain.

Unfolded Protein Response (UPR) in Survival, Dormancy, Immunosuppression, Metastasis, and Treatments of Cancer Cells

The endoplasmic reticulum (ER) has diverse functions, and especially misfolded protein modification is in the focus of this review paper. With a highly regulatory mechanism, called unfolded protein response (UPR), it protects cells from the accumulation of misfolded proteins. Nevertheless, not only does UPR modify improper proteins, but it also degrades proteins that are unable to recover. Three pathways of UPR, namely PERK, IRE-1, and ATF6, have a significant role in regulating stress-induced physiological responses in cells. The dysregulated UPR may be involved in diseases, such as atherosclerosis, heart diseases, amyotrophic lateral sclerosis (ALS), and cancer. Here, we discuss the relation between UPR and cancer, considering several aspects including survival, dormancy, immunosuppression, angiogenesis, and metastasis of cancer cells. Although several moderate adversities can subject cancer cells to a hostile environment, UPR can ensure their survival. Excessive unfavorable conditions, such as overloading with misfolded proteins and nutrient deprivation, tend to trigger cancer cell death signaling. Regarding dormancy and immunosuppression, cancer cells can survive chemotherapies and acquire drug resistance through dormancy and immunosuppression. Cancer cells can also regulate the downstream of UPR to modulate angiogenesis and promote metastasis. In the end, regulating UPR through different molecular mechanisms may provide promising anticancer treatment options by suppressing cancer proliferation and progression.

Increased MDR1 Transporter Expression in Human Brain Endothelial Cells Through Enhanced Histone Acetylation and Activation of Aryl Hydrocarbon Receptor Signaling

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) is a critical efflux transporter that extrudes chemicals from the blood-brain barrier (BBB) and limits neuronal exposure to xenobiotics. Prior studies in malignant cells demonstrated that MDR1 expression can be altered by inhibition of histone deacetylases (HDAC), enzymes that modify histone structure and influence transcription factor binding to DNA. Here, we sought to identify the mechanisms responsible for the up-regulation of MDR1 by HDAC inhibitors in human BBB cells. Immortalized human brain capillary endothelial (hCMEC/D3) cells were treated with HDAC inhibitors and assessed for MDR1 expression and function. Of the HDAC inhibitors profiled, valproic acid (VPA), apicidin, and suberoylanilide hydroxamic acid (SAHA) increased MDR1 mRNA and protein levels by 30-200%, which corresponded with reduced intracellular accumulation of the MDR1 substrate rhodamine 123. Interestingly, induction of MDR1 mRNA by HDAC inhibitors mirrored increases in the expression of the aryl hydrocarbon receptor (AHR) and its target gene cytochrome P450 1A1. To explore the role of AHR in HDAC inhibitor-mediated regulation of MDR1, a pharmacological activator (β-naphthoflavone, βNF) and inhibitor (CH-223191, CH) of AHR were tested. The induction of MDR1 in cells treated with SAHA was amplified by βNF and attenuated by CH. Furthermore, SAHA increased the binding of acetylated histone H3K9/K14 and AHR proteins to regions of the MDR1 promoter that contain AHR response elements. In conclusion, HDAC inhibitors up-regulate the expression and activity of the MDR1 transporter in human brain endothelial cells by increasing histone acetylation and facilitating AHR binding at the MDR1 promoter.

HDAC Inhibitors Induce BDNF Expression and Promote Neurite Outgrowth in Human Neural Progenitor Cells-Derived Neurons

Besides its key role in neural development, brain-derived neurotrophic factor (BDNF) is important for long-term potentiation and neurogenesis, which makes it a critical factor in learning and memory. Due to the important role of BDNF in synaptic function and plasticity, an in-house epigenetic library was screened against human neural progenitor cells (HNPCs) and WS1 human skin fibroblast cells using Cell-to-Ct assay kit to identify the small compounds capable of modulating the BDNF expression. In addition to two well-known hydroxamic acid-based histone deacetylase inhibitors (hb-HDACis), SAHA and TSA, several structurally similar HDAC inhibitors including SB-939, PCI-24781 and JNJ-26481585 with even higher impact on BDNF expression, were discovered in this study. Furthermore, by using well-developed immunohistochemistry assays, the selected compounds were also proved to have neurogenic potential improving the neurite outgrowth in HNPCs-derived neurons. In conclusion, we proved the neurogenic potential of several hb-HDACis, alongside their ability to enhance BDNF expression, which by modulating the neurogenesis and/or compensating for neuronal loss, could be propitious for treatment of neurological disorders.

AKT methylation by SETDB1 promotes AKT kinase activity and oncogenic functions

Aberrant activation of Akt disturbs proliferation, survival and metabolic homeostasis of various human cancers. Thus, it is critical to understand upstream signaling pathways governing Akt activation. Here, we report that Akt undergoes SETDB1-mediated lysine-methylation to promote its activation, which is antagonized by the Jumonji-family demethylase, KDM4B. Notably, compared with wild-type mice, mice harboring non-methylated mutant Akt1 not only exhibited reduced body size, but also were less prone to carcinogen-induced skin tumors in part due to reduced Akt activation. Mechanistically, Phosphatidylinositol (3,4,5)-trisphosphate (PIP₃) interaction with Akt facilitates its interaction with SETDB1 for subsequent Akt methylation, which in turn sustains Akt phosphorylation. Pathologically, genetic alterations including SETDB1 amplification aberrantly promote Akt methylation to facilitate its activation and oncogenic functions. Thus, Akt methylation is an important step synergizing with PI3K signaling to control Akt activation, suggesting that targeting the SETDB1 signaling could be a potential therapeutic strategy for combatting hyperactive Akt-driven cancers.

Quinazolin-4(3H)-one-Based Hydroxamic Acids: Design, Synthesis and Evaluation of Histone Deacetylase Inhibitory Effects and Cytotoxicity

The present article describes the synthesis and biological activity of various series of novel hydroxamic acids incorporating quinazolin-4(3H)-ones as novel small molecules targeting histone deacetylases. Biological evaluation showed that these hydroxamic acids were potently cytotoxic against three human cancer cell lines (SW620, colon; PC-3, prostate; NCI-H23, lung). Most compounds displayed superior cytotoxicity than SAHA (suberoylanilide hydroxamic acid, Vorinostat) in term of cytotoxicity. Especially, N-hydroxy-7-(7-methyl-4-oxoquinazolin-3(4H)-yl)heptanamide (5b) and N-hydroxy-7-(6-methyl-4-oxoquinazolin-3(4H)-yl)heptanamide (5c) (IC₅₀ values, 0.10-0.16 μm) were found to be approximately 30-fold more cytotoxic than SAHA (IC₅₀ values of 3.29-3.67 μm). N-Hydroxy-7-(4-oxoquinazolin-3(4H)-yl)heptanamide (5a; IC₅₀ values of 0.21-0.38 μm) was approximately 10- to 15-fold more potent than SAHA in cytotoxicity assay. These compounds also showed comparable HDAC inhibition potency with IC₅₀ values in sub-micromolar ranges. Molecular docking experiments indicated that most compounds, as represented by 5b and 5c, strictly bound to HDAC2 at the active binding site with binding affinities much higher than that of SAHA.

Current Status of HDAC Inhibitors in Cutaneous T-cell Lymphoma

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of lymphomas that are characterized by primary skin involvement. Mycosis fungoides (MF) and Sézary syndrome (SS), the two most common subtypes of CTCL, can be difficult to manage clinically as there are few effective treatment options available. Recently, histone deacetylase inhibitors (HDACi) have emerged as promising therapies with favorable adverse effect profiles, compared with traditional chemotherapies. In this article, we review the published literature to evaluate the role of HDACi in the treatment of CTCL. Specifically, we (1) briefly discuss the molecular rationale for the use of HDACi in CTCL; (2) compare the efficacy, tolerability, and adverse effects of HDACi; (3) review the cardiac safety data; and (4) discuss optimization of therapy with HDACi in the treatment of CTCL.

Design, Synthesis and Evaluation of Novel 3/4-((Substituted benzamidophenoxy) methyl)-N-hydroxybenzamides/propenamides as Histone Deacetylase Inhibitors and Antitumor Agents

BACKGROUND

Histone Deacetylase (HDAC) inhibitors represent an extensive class of targeted anticancer agents. Among the most explored structure moieties, hydroxybenzamides and hydroxypropenamides have been demonstrated to have potential HDAC inhibitory effects. Several compounds of these structural classes have been approved for clinical uses to treat different types of cancer, such as givinostat (ITF2357) and belinostat (PXD-101).

AIMS

This study aims at developing novel HDAC inhibitors bearing N-hydroxybenzamides and Nhydroxypropenamides scaffolds with potential cytotoxicity against different cancer cell lines.

METHODS

Two new series of N-hydroxybenzamides and N-hydroxypropenamides analogues (4a-j, 6a-j) designed based on the structural features of nexturastat A, AR-42, and PXD-101, were synthesized and evaluated for HDAC inhibitory potency as well as cytotoxicity against three human cancer cell lines (SW620 (colorectal adenocarcinoma), PC3 (prostate adenocarcinoma), and NCI-H23 (adenocarcinoma, non-small cell lung cancer). Molecular simulations were finally carried out to gain more insight into the structure-activity relationships.

RESULTS

It was found that the N-hydroxypropenamides (6a-e) displayed very good HDAC inhibitory potency and cytotoxicity. Various compounds, e.g. 6a-e, especially compound 6e, were up to 5-fold more potent than suberanilohydroxamic acid (SAHA) in terms of cytotoxicity. These compounds also comparably inhibited HDACs with IC50 values in the sub-micromolar range. Docking experiments showed that these compounds bound to HDAC2 at the enzyme active binding site with the same binding mode of SAHA, but with higher binding affinities.

CONCLUSIONS

The two series of N-hydroxybenzamides and N-hydroxypropenamides designed and synthesized were potential HDAC inhibitors and antitumor agents. Further development of these compounds should be warranted.

Global analysis of histone lysine acetylation and proteomic changes in EC109 cells treated with the histone deacetylase inhibitor FK228

FK228 is a selective inhibitor of histone deacetylases that exhibits marked antitumor activity in cancer cells and xenograft models. However, the effect of FK228 on the global profile of histone lysine acetylation and the proteome of EC109 cells remains poorly understood. The present study aimed at analyzing histone lysine acetylation and identifying the proteomic changes in EC109 cells following treatment with FK228, using the stable isotope labelling by amino acids in cell culture technique and a high-sensitivity mass spectrometer. In total, 87 acetylation sites and 3,515 proteins revealed changes in response to FK228 treatment. Of the 87 acetylation sites, 25 were quantifiable and 19 were quantified with ratio of >1.3. Notably, no downregulated lysine acetylation (Kac) sites were quantified in the present study and the 62 unquantified Kac sites were only identified in the FK228-treated cells. Bioinformatic analysis revealed that these quantifiable proteins were primarily involved in multiple biological functions and metabolic pathways as well as in protein complexes. The results of the present study revealed the extensive lysine acetylome and proteome in EC109 cells and expanded upon the current understanding of the anticancer mechanism of FK228 in EC109 cells.

Epigenetic modifications-insight into oligodendrocyte lineage progression, regeneration, and disease

Myelination by oligodendrocytes in the central nervous system permits high-fidelity saltatory conduction from neuronal cell bodies to axon terminals. Dysmyelinating and demyelinating disorders impair normal nervous system functions. Consequently, an understanding of oligodendrocyte differentiation that moves beyond the genetic code into the field of epigenetics is essential. Chromatin reprogramming is critical for steering stage-specific differentiation processes during oligodendrocyte development. Fine temporal control of chromatin remodeling through ATP-dependent chromatin remodelers and sequential histone modifiers shapes a chromatin regulatory landscape conducive to oligodendrocyte fate specification, lineage differentiation, and maintenance of cell identity. In this Review, we will focus on the biological functions of ATP-dependent chromatin remodelers and histone deacetylases in myelinating oligodendrocyte development and implications for myelin regeneration in neurodegenerative diseases.

Chromatin remodeling and epigenetic regulation of oligodendrocyte myelination and myelin repair

Oligodendrocytes are essential for the development, function, and health of the vertebrate central nervous system. These cells maintain axon myelination to ensure saltatory propagation of action potentials. Oligodendrocyte develops from neural progenitor cells, in a step-wise process that involves oligodendrocyte precursor specification, proliferation, and differentiation. The lineage progression requires coordination of transcriptional and epigenetic circuits to mediate the stage-specific intricacies of oligodendrocyte development. Epigenetic mechanisms involve DNA methylation, histone modifications, ATP-dependent chromatin remodeling, and non-coding RNA modulation that regulate the chromatin state over regulatory genes, which must be expressed or repressed to establish oligodendrocyte identity and lineage progression. In this review, we will focus on epigenetic programming associated with histone modification enzymes, chromatin remodeling, and non-coding RNAs that regulate oligodendrocyte lineage progression, and discuss how these mechanisms might be harnessed to induce myelin repair for treatment of demyelinating diseases such as multiple sclerosis.

Epigenetic actions of environmental factors and promising drugs for cancer therapy

Carcinogenesis is known to be primarily associated with gene mutations. Recently, increasing evidence has suggested that epigenetic events also serve crucial roles in tumor etiology. Environmental factors, including nutrition, toxicants and ethanol, are involved in carcinogenesis through inducing epigenetic modifications, such as DNA methylation, histone deacetylase and miRNA regulation. Studying epigenetic mechanisms has facilitated the development of early diagnostic strategies and potential therapeutic avenues. Modulation at the epigenetic level, including reversing epigenetic modifications using targeted drugs, has demonstrated promise in cancer therapy. Therefore, identifying novel epigenetic biomarkers and therapeutic targets has potential for the future of cancer therapy. The present review discusses the environmental factors involved in epigenetic modifications and potential drug candidates for cancer therapy.

Antiproliferative effects of TSA, PXD‑101 and MS‑275 in A2780 and MCF7 cells: Acetylated histone H4 and acetylated tubulin as markers for HDACi potency and selectivity

Inhibition of histone deacetylase enzymes (HDACs) has been well documented as an attractive target for the development of chemotherapeutic drugs. The present study investigated the effects of two prototype hydroxamic acid HDAC inhibitors, namely Trichostatin A (TSA) and Belinostat (PXD-101) and the benzamide Entinostat (MS-275) in A2780 ovarian carcinoma and MCF7 breast adenocarcinoma cells. The three HDACi inhibited the proliferation of A2780 and MCF7 cells at comparable levels, below the µM range. Enzyme inhibition assays in a cell-free system showed that TSA was the most potent inhibitor of total HDAC enzyme activity followed by PXD-101 and MS-275. Incubation of A2780 and MCF7 cells with the hydroxamates TSA and PXD-101 for 24 h resulted in a dramatic increase of acetylated tubulin induction (up to 30-fold for TSA). In contrast to acetylated tubulin, western blot analysis and flow cytometry indicated that the induction of acetylated histone H4 was considerably smaller. The benzamide MS-275 exhibited nearly a 2-fold induction of acetylated histone H4 and an even smaller induction of acetylated tubulin in A2780 and MCF7 cells. Taken together, these data suggest that although the three HDACi were equipotent in inhibiting proliferation of MCF7 and A2780 cells, only the benzamide MS-275 did not induce acetylated tubulin expression, a marker of class IIb HDACs.

The discovery and development of romidepsin for the treatment of T-cell lymphoma

INTRODUCTION

Romidepsin is a potent and selective inhibitor of histone deacetylases (HDCAi). It is also the only bicyclic inhibitor to undergo clinical assessment and is considered a promising drug for the treatment of T-cell lymphomas. The cellular action of romidepsin results in enhanced histone acetylation, as well as the acetylation of other nuclear or cytoplasmic proteins, influencing cell cycle, apoptosis, and angiogenesis. In phase II studies involving patients with relapsed or refractory of cutaneous T-cell lymphoma (CTCL) and peripheral T-cell lymphoma (PTCL), romidepsin produced overall response rates (ORR) of 34-35% and 25-38%, with complete response (CR) rates of 6% and 15-18%, respectively. Areas covered: This review summarizes the development of romidepsin, the mechanisms behind its antineoplastic action and its pharmacology. It also covers its pharmacokinetic and pharmacodynamic properties, as well as the preclinical and clinical data on its activity in T-cell lymphoma. Expert opinion: Since there are only few effective therapies available for T-cell lymphomas, romidepsin is a valuable option for relapsed/refractory patients with both CTCL and PTCL. It's also generally well tolerated, and gives potentially durable responses for patients with advanced and symptomatic disease. Combinations of romidepsin with other antineoplastic agents may also further improve drug response and outcomes in T-cell lymphoma.