HDAC3 is a potential validated target for cancer: An overview on the benzamide-based selective HDAC3 inhibitors through comparative SAR/QSAR/QAAR approaches

Negative regulation of HDAC3 transcription by histone acetyltransferase TIP60 in colon cancer

BACKGROUND

Colon cancer is the third most common cancer globally. The expression of histone deacetylase 3 (HDAC3) is upregulated, whereas the expression of tat interactive protein, 60 kDa (TIP60) is downregulated in colon cancer. However, the relationship between HDAC3 and TIP60 in colon cancer has not been clearly elucidated.

OBJECTIVE

We investigated whether TIP60 could regulate the expression of HDAC3 and suppress colon cancer cell proliferation.

METHODS

RNA sequencing data (GSE108834) showed that HDAC3 expression was regulated by TIP60. Subsequently, we generated TIP60-knockdown HCT116 cells and examined the expression of HDAC3 by western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). We examined the expression pattern of HDAC3 in various cancers using publicly available datasets. The promoter activity of HDAC3 was validated using a dual-luciferase assay, and transcription factors binding to HDAC3 were identified using GeneCards and Promo databases, followed by validation using chromatin immunoprecipitation-quantitative polymerase chain reaction. Cell proliferation and apoptosis were assessed using colony formation assays and fluorescence-activated cell sorting analysis of HCT116 cell lines.

RESULTS

In response to TIP60 knockdown, the expression level and promoter activity of HDAC3 increased. Conversely, when HDAC3 was downregulated by overexpression of TIP60, proliferation of HCT116 cells was inhibited and apoptosis was promoted.

CONCLUSION

TIP60 plays a crucial role in the regulation of HDAC3 transcription, thereby influencing cell proliferation and apoptosis in colon cancer. Consequently, TIP60 may function as a tumor suppressor by inhibiting HDAC3 expression in colon cancer cells.

Exploring different classification-dependent QSAR modelling strategies for HDAC3 inhibitors in search of meaningful structural contributors

Histone deacetylase 3 (HDAC3), a Zn2+-dependent class I HDACs, contributes to numerous disorders such as neurodegenerative disorders, diabetes, cardiovascular disease, kidney disease and several types of cancers. Therefore, the development of novel and selective HDAC3 inhibitors might be promising to combat such diseases. Here, different classification-based molecular modelling studies such as Bayesian classification, recursive partitioning (RP), SARpy and linear discriminant analysis (LDA) were conducted on a set of HDAC3 inhibitors to pinpoint essential structural requirements contributing to HDAC3 inhibition followed by molecular docking study and molecular dynamics (MD) simulation analyses. The current study revealed the importance of hydroxamate function for Zn2+ chelation as well as hydrogen bonding interaction with Tyr298 residue. The importance of hydroxamate function for higher HDAC3 inhibition was noticed in the case of Bayesian classification, recursive partitioning and SARpy models. Also, the importance of substituted thiazole ring was revealed, whereas the presence of linear alkyl groups with carboxylic acid function, any type of ester function, benzodiazepine moiety and methoxy group in the molecular structure can be detrimental to HDAC3 inhibition. Therefore, this study can aid in the design and discovery of effective novel HDAC3 inhibitors in the future.

ZNF787 and HDAC1 Mediate Blood-Brain Barrier Permeability in an In Vitro Model of Alzheimer's Disease Microenvironment

The permeability of the blood-brain barrier (BBB) is increased in Alzheimer's disease (AD). This plays a key role in the instigation and maintenance of chronic inflammation during AD. Experiments using AD models showed that the increased permeability of the BBB was mainly caused by the decreased expression of tight junction-related proteins occludin and claudin-5. In this study, we found that ZNF787 and HDAC1 were upregulated in β-amyloid (Aβ)1-42-incubated endothelial cells, resulting in increased BBB permeability. Conversely, the silencing of ZNF787 and HDAC1 by RNAi led to reduced BBB permeability. The silencing of ZNF787 and HDAC1 enhanced the expression of occludin and claudin-5. Mechanistically, ZNF787 binds to promoter regions for occludin and claudin-5 and functions as a transcriptional regulator. Furthermore, we demonstrate that ZNF787 interacts with HDAC1, and this resulted in the downregulation of the expression of genes encoding tight junction-related proteins to increase in BBB permeability. Taken together, our study identifies critical roles for the interaction between ZNF787 and HDAC1 in regulating BBB permeability and the pathogenesis of AD.

Hydroxamic acid derivatives as selective HDAC3 inhibitors: computer-aided drug design strategies

Histone deacetylases (HDACs) are critical epigenetic drug targets that have gained significant attention in the scientific community for the treatment of cancer. The currently marketed HDAC inhibitors lack selectivity for the various HDAC isoenzymes. Here, we describe our protocol for the discovery of novel potential hydroxamic acid based HDAC3 inhibitors through pharmacophore modeling, virtual screening, docking, molecular dynamics (MD) simulation and toxicity studies. The ten pharmacophore hypotheses were established, and their reliability was validated by different ROC (receiving operator curve) analysis. Among them, the best model (Hypothesis 9 or RRRA) was employed for searching SCHEMBL, ZINC and MolPort database to screen out hit molecules as selective HDAC3 inhibitors, followed by different docking stages. MD simulation (50 ns) and MMGBSA study were performed to study the stability of ligand binding modes and with the help of trajectory analysis, to calculate the ligand-receptor complex RMSD (root-mean-square deviation), RMSF (root-mean-square fluctuation) and H-bond distance, etc. Finally, in-silico toxicity studies were performed on top screened molecules and compared with reference drug SAHA and established structure-activity relationship (SAR). The results indicated that compound 31, with high inhibitory potency and less toxicity (probability value 0.418), is suitable for further experimental analysis.Communicated by Ramaswamy H. Sarma.

A Review on Molecular Docking on HDAC Isoforms: Novel Tool for Designing Selective Inhibitors

Research into histone deacetylases (HDACs) has experienced a remarkable surge in recent years. These enzymes are key regulators of several fundamental biological processes, often associated with severe and potentially fatal diseases. Inhibition of their activity represents a promising therapeutic approach and a prospective strategy for the development of new therapeutic agents. A critical aspect of their inhibition is to achieve selectivity in terms of enzyme isoforms, which is essential to improve treatment efficacy while reducing undesirable pleiotropic effects. The development of computational chemistry tools, particularly molecular docking, is greatly enhancing the precision of designing molecules with inherent potential for specific activity. Therefore, it was considered necessary to review the molecular docking studies conducted on the major isozymes of the enzyme in order to identify the specific interactions associated with each selective HDAC inhibitor. In particular, the most critical isozymes of HDAC (1, 2, 3, 6, and 8) have been thoroughly investigated within the scope of this review.

Pharmacophore-based virtual screening, 3D QSAR, Docking, ADMET, and MD simulation studies: An in silico perspective for the identification of new potential HDAC3 inhibitors

Histone deacetylase 3 (HDAC3) is an epigenetic regulator that involves gene expression, apoptosis, and cell cycle progression, and the overexpression of HDAC3 is accountable for several cancers, neurodegeneracy, and many other diseases. Therefore, HDAC3 emerged as a promising drug target for the novel drug design. Here, we carried out the pharmacophore modeling using 50 benzamide-based HDAC3 selective inhibitors and utilized it for PHASE ligand screening to retrieve the hits with similar pharmacophore features. The dataset inhibitors of best hypotheses used to build the 3D QSAR model and the generated 3D QSAR model resulted in good PLS statistics with a regression coefficient (R2) of 0.89, predictive coefficient (Q2) of 0.88, and Pearson-R factor of 0.94 indicating its excellent predictive ability. The hits retrieved from pharmacophore-based virtual screening were subjected to docking against HDAC3 for the identification of potential inhibitors. A total of 10 hitsM1 to M10 were ranked using their scoring functions and further subject to lead optimization. The Prime MM/GBSA, AutoDock binding free energies, and ADMET studies were implemented for the selection of lead candidates. The four ligand molecules M1, M2, M3, and M4 were identified as potential leads against HDAC3 after lead optimization. The top two leads M1 and M2 were subjected to MD simulations for their stability evaluation with HDAC3. The newly designed leads M11 and M12 were identified as HDAC3 potential inhibitors from MD simulations studies. Therefore, the outcomes of the present study could provide insights into the discovery of new potential HDAC3 inhibitors with improved selectivity and activity against a variety of cancers and neurodegenerative diseases.

Selective HDAC3 Inhibitors with Potent In Vivo Antitumor Efficacy against Triple-Negative Breast Cancer

HDAC3 modulation shows promise for breast cancer, including triple-negative cases. Novel pyrazino-hydrazide-based HDAC3 inhibitors were designed and synthesized. Lead compound 4i exhibited potent HDAC3 inhibition (IC50 = 14 nM) with at least 121-fold selectivity. It demonstrated strong cytotoxicity against triple-negative breast cancer cells (IC50: 0.55 μM for 4T1, 0.74 μM for MDA-MB-231) with least normal cell toxicity. Metabolically stable 4i displayed a superior pharmacokinetic profile. A dose-dependent therapeutic efficacy of 4i was observed in a tumor-bearing mouse model. The biomarker analysis with tumor tissues displayed enhanced acetylation on Ac-H3K9, Ac-H3K27, and Ac-H4K12 compared to Ac-tubulin and Ac-SMC3 indicating HDAC3 selectivity of 4i in vivo. The immunoblotting study with tumor tissue showed upregulation of apoptotic proteins caspase-3, caspase-7, and cytochrome c and the downregulation of proliferation markers Bcl-2, CD44, EGFR, and Ki-67. Compound 4i represents a promising candidate for targeted breast cancer therapy, particularly for cases with triple-negative breast cancer.

Recent development of selective inhibitors targeting the HDAC6 as anti-cancer drugs: Structure, function and design

HDAC6, a member of the histone deacetylase family, mainly is a cytosolic protein and regulates cell growth by acting on non-histone substrates, such as α -tubulin, cortactin, heat shock protein HSP90, programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1), that are closely related to the proliferation, invasion, immune escape and angiogenesis of cancer tissues. The approved drugs targeting the HDACs are all pan-inhibitors and have many side effects due to their lack of selectivity. Therefore, development of selective inhibitors of HDAC6 has attracted much attention in the field of cancer therapy. In this review, we will summarize the relationship between HDAC6 and cancer, and discuss the design strategies of HDAC6 inhibitors for cancer treatment in recent years.

Systematic analysis of histone acetylation regulators across human cancers

BACKGROUND

Histone acetylation (HA) is an important and common epigenetic pathway, which could be hijacked by tumor cells during carcinogenesis and cancer progression. However, the important role of HA across human cancers remains elusive.

METHODS

In this study, we performed a comprehensive analysis at multiple levels, aiming to systematically describe the molecular characteristics and clinical relevance of HA regulators in more than 10000 tumor samples representing 33 cancer types.

RESULTS

We found a highly heterogeneous genetic alteration landscape of HA regulators across different human cancer types. CNV alteration may be one of the major mechanisms leading to the expression perturbations in HA regulators. Furthermore, expression perturbations of HA regulators correlated with the activity of multiple hallmark oncogenic pathways. HA regulators were found to be potentially useful for the prognostic stratification of kidney renal clear cell carcinoma (KIRC). Additionally, we identified HDAC3 as a potential oncogene in lung adenocarcinoma (LUAD).

CONCLUSION

Overall, our results highlights the importance of HA regulators in cancer development, which may contribute to the development of clinical strategies for cancer treatment.

Discovery of selective HDAC6 inhibitors based on a multi-layer virtual screening strategy

The abnormal enhancement of histone deacetylase 6 (HDAC6) has been demonstrated to be closely related to the occurrence and development of various malignant tumors, attracting extensive attention as a promising target for cancer therapy. Currently, only limited selective HDAC6 inhibitors have entered clinical trials, making the rapid discovery of selective HDAC6 inhibitors with safety profiles particularly urgent. In this study, a multi-layer virtual screening workflow was established, and the representative compounds screened were biologically evaluated in combination with enzyme inhibitory and anti-tumor cell proliferation experiments. The experimental results showed that the screened compounds L-25, L-32, L-45 and L-81 exhibited nanomolar inhibitory activity against HDAC6, and exerted a certain degree of anti-proliferative activities against tumor cells, especially the cytotoxicity of L-45 to A375 (IC₅₀ = 11.23 ± 1.27 μM) and the cytotoxicity of L-81 against HCT-116 (IC₅₀ = 12.25 ± 1.13 μM). Additionally, the molecular mechanisms underlying the subtype selective inhibitory activities of the selected compounds were further elucidated using computational approaches, and the hotspot residues on HDAC6 contributing to the ligands' binding were identified. In summary, this study established a multi-layer screening scheme to quickly and effectively screen out hit compounds with enzyme inhibitory activity and anti-tumor cell proliferation, providing novel scaffolds for the subsequent anti-tumor drug design based on HDAC6 target.

3D CRISPR screen in prostate cancer cells reveals PARP inhibitor sensitization through TBL1XR1-SMC3 interaction

Poly(ADP-ribose) (PAR) polymerase inhibitors (PARPi) either have been approved or being tested in the clinic for the treatment of a variety of cancers with homologous recombination deficiency (HRD). However, cancer cells can develop resistance to PARPi drugs through various mechanisms, and new biomarkers and combination therapeutic strategies need to be developed to support personalized treatment. In this study, a genome-wide CRISPR screen was performed in a prostate cancer cell line with 3D culture condition which identified novel signals involved in DNA repair pathways. One of these genes, TBL1XR1, regulates sensitivity to PARPi in prostate cancer cells. Mechanistically, we show that TBL1XR1 interacts with and stabilizes SMC3 on chromatin and promotes γH2AX spreading along the chromatin of the cells under DNA replication stress. TBL1XR1-SMC3 double knockdown (knockout) cells have comparable sensitivity to PARPi compared to SMC3 knockdown or TBL1XR1 knockout cells, and more sensitivity than WT cells. Our findings provide new insights into mechanisms underlying response to PARPi or platin compounds in the treatment of malignancies.

The emerging roles of HDACs and their therapeutic implications in cancer

Deregulation of protein post-translational modifications is intensively involved in the etiology of diseases, including degenerative diseases, inflammatory injuries, and cancers. Acetylation is one of the most common post-translational modifications of proteins, and the acetylation levels are controlled by two mutually antagonistic enzyme families, histone acetyl transferases (HATs) and histone deacetylases (HDACs). HATs loosen the chromatin structure by neutralizing the positive charge of lysine residues of histones; whereas HDACs deacetylate certain histones, thus inhibiting gene transcription. Compared with HATs, HDACs have been more intensively studied, particularly regarding their clinical significance. HDACs extensively participate in the regulation of proliferation, migration, angiogenesis, immune escape, and therapeutic resistance of cancer cells, thus emerging as critical targets for clinical cancer therapy. Compared to HATs, inhibitors of HDAC have been clinically used for cancer treatment. Here, we enumerate and integratethe mechanisms of HDAC family members in tumorigenesis and cancer progression, and address the new and exciting therapeutic implications of single or combined HDAC inhibitor (HDACi) treatment.

Nickel nanoparticles induce epithelial-mesenchymal transition in human bronchial epithelial cells via the HIF-1α/HDAC3 pathway

We and others have previously demonstrated that exposure to nickel nanoparticles (Nano-Ni) caused fibrogenic and carcinogenic effects; however, the underlying mechanisms are still not fully understood. This study aimed to investigate the effects of Nano-Ni on epithelial-mesenchymal transition (EMT) in human bronchial epithelial cells (BEAS-2B) and its underlying mechanisms since EMT is involved in both cancer pathogenesis and tissue fibrosis. Our results showed that exposure to Nano-Ni, compared to the control Nano-TiO2, caused a remarkable decrease in the expression of E-cadherin and an increase in the expression of vimentin and α-SMA, indicating an inducible role of Nano-Ni in EMT development in human bronchial epithelial cells. HIF-1α nuclear accumulation, HDAC3 upregulation, and decreased histone acetylation were also observed in the cells exposed to Nano-Ni, but not in those exposed to Nano-TiO2. Pretreatment of the cells with a specific HIF-1α inhibitor, CAY10585, or HIF-1α-specific siRNA transfection prior to Nano-Ni exposure resulted in the restoration of E-cadherin and abolished Nano-Ni-induced upregulation of vimentin and α-SMA, suggesting a crucial role of HIF-1α in Nano-Ni-induced EMT development. CAY10585 pretreatment also attenuated the HDAC3 upregulation and increased histone acetylation. Inhibition of HDAC3 with specific siRNA significantly restrained Nano-Ni-induced reduction in histone acetylation and restored EMT-related protein expression to near control levels. In summary, our findings suggest that exposure to Nano-Ni promotes the development of EMT in human bronchial epithelial cells by decreasing histone acetylation through HIF-1α-mediated HDAC3 upregulation. Our findings may provide information for further understanding of the molecular mechanisms of Nano-Ni-induced fibrosis and carcinogenesis.

miR-589-5p Inhibits Cell Proliferation by Targeting Histone Deacetylase 3 in Triple Negative Breast Cancer

BACKGROUND

Histone deacetylase 3 (HDAC3) is a potential oncogene that is significantly up-regulated in patients with breast cancer. MicroRNAs (miRs) are a group of small non-coding and regulatory RNAs which have recently been proposed as promising molecules for breast cancer target therapy. In the current study, we investigated the impact of miR-589-5p/ HDAC3 axis on cancer cell development in triple negative breast cancer (TNBC) cells.

METHODS

In-silico analysis determined that miR-589-5p potentially targets HDAC3. We evaluated the HDAC3 and mir-589-5p expression levels in clinical samples and breast cancer cell lines including MDA-MB-231, MDA-MB-468, MCF-7 and MCF-10A. HDAC3 was knocked out to investigate its role on cancer cell progression. Anti-cancerous role of the miR-589-5p was assessed using an expression vector. We evaluated possible alteration in the cell cycle progression, cell viability and cell proliferation, after transient transfection.

RESULTS

HDAC3 was over-expressed in TNBC clinical samples and breast cancer cell lines compared to non-cancerous controls while miR-589-5p was down regulated in cancer cells. Suppression of HDAC3 decreased the cell viability, cell proliferation and colony formation. Similar results were observed after over-expression of the miR-589-5p. Dual-Luciferase reporter assay confirmed the direct targeting of HDAC3 by miR-589-5p.

CONCLUSION

Our results showed that miR-589-5p mediates its anti-proliferative effects on breast cancer cells via targeting HDAC3. These findings suggest that the miR-589-5p/ HDAC3 axis could be considered as a possible therapeutic strategy in TNBC.

The role of histone deacetylase 3 in breast cancer

It has been recently revealed that Histone Deacetylase (HDAC) 3, a unique member of the HDACs family, can trigger and progress cancers by alternation in genes expression and proteins activity. Epigenetic modifications by HDACs have been studied well in various cancer cells. Recent studies have focused on the HDAC enzymes as a possible target in cancer therapy. There are significant documents on upregulation of HDAC3 in breast cancer (BC) cells which suggest an oncogenic role for this enzyme. Interestingly, some studies showed that HDAC3 inhibition could be considered as a promising target in breast cancer therapy, and thus far, several inhibitors from different nature have been introduced. In this review, we discussed the function and highlight the existing inhibitors of HDAC3 in BC pathogenesis and therapy.

Silencing of histone deacetylase 3 suppresses the development of esophageal squamous cell carcinoma through regulation of miR-494-mediated TGIF1

BACKGROUND

Deacetylation of histones by histone deacetylase 3 (HDAC3) acts importantly in modulating apoptosis, DNA damage and cellular progression. Herein, we aimed to unravel the functional role of HDAC3 in a lethal disease, esophageal squamous cell carcinoma (ESCC).

METHODS

The expression of HDAC3 in clinically collected ESCC tissues was determined by RT-qPCR and immunohistochemistry. As revealed from bioinformatics analysis, the putative relations between HDAC3 and microRNA-494 (miR-494) and between miR-494 and transforming growth factor beta (TGFβ)-inducing factor 1 (TGIF1) were further verified by chromatin immunoprecipitation and dual-luciferase reporter gene assay. Functional roles of shRNA-mediated depletion of HDAC3, miR-494 mimic and overexpressed TGIF1 were explored by gain- and loss-of-function assays with regard to ESCC cell biological behaviors. A nude mouse model of ESCC was developed for in vivo validation.

RESULTS

HDAC3 was highly expressed in ESCC tissues, suggestive of poor prognosis while TGIF1 was upregulated and miR-494 was downregulated. Mechanistic investigation revealed that HDAC3 inhibited miR-494 expression and TGIF1 was a direct target of miR-494. Furthermore, silencing HDAC3 or overexpressing miR-494 was demonstrated to suppress aggressive phenotypes of ESCC cells both in vitro through the activated TGFβ signaling pathway and in vivo, while TGIF1 overexpression induced opposite results.

CONCLUSION

Collectively, our findings provided demonstration regarding the oncogenic property of HDAC3 in ESCC via the miR-494/TGIF1/TGFβ axis.

Why 90% of clinical drug development fails and how to improve it?

Ninety percent of clinical drug development fails despite implementation of many successful strategies, which raised the question whether certain aspects in target validation and drug optimization are overlooked? Current drug optimization overly emphasizes potency/specificity using structure‒activity-relationship (SAR) but overlooks tissue exposure/selectivity in disease/normal tissues using structure‒tissue exposure/selectivity–relationship (STR), which may mislead the drug candidate selection and impact the balance of clinical dose/efficacy/toxicity. We propose structure‒tissue exposure/selectivity–activity relationship (STAR) to improve drug optimization, which classifies drug candidates based on drug's potency/selectivity, tissue exposure/selectivity, and required dose for balancing clinical efficacy/toxicity. Class I drugs have high specificity/potency and high tissue exposure/selectivity, which needs low dose to achieve superior clinical efficacy/safety with high success rate. Class II drugs have high specificity/potency and low tissue exposure/selectivity, which requires high dose to achieve clinical efficacy with high toxicity and needs to be cautiously evaluated. Class III drugs have relatively low (adequate) specificity/potency but high tissue exposure/selectivity, which requires low dose to achieve clinical efficacy with manageable toxicity but are often overlooked. Class IV drugs have low specificity/potency and low tissue exposure/selectivity, which achieves inadequate efficacy/safety, and should be terminated early. STAR may improve drug optimization and clinical studies for the success of clinical drug development.

The role of protein acetylation in carcinogenesis and targeted drug discovery

Protein acetylation is a reversible post-translational modification, and is involved in many biological processes in cells, such as transcriptional regulation, DNA damage repair, and energy metabolism, which is an important molecular event and is associated with a wide range of diseases such as cancers. Protein acetylation is dynamically regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) in homeostasis. The abnormal acetylation level might lead to the occurrence and deterioration of a cancer, and is closely related to various pathophysiological characteristics of a cancer, such as malignant phenotypes, and promotes cancer cells to adapt to tumor microenvironment. Therapeutic modalities targeting protein acetylation are a potential therapeutic strategy. This article discussed the roles of protein acetylation in tumor pathology and therapeutic drugs targeting protein acetylation, which offers the contributions of protein acetylation in clarification of carcinogenesis, and discovery of therapeutic drugs for cancers, and lays the foundation for precision medicine in oncology.

Combining histone deacetylase inhibitors (HDACis) with other therapies for cancer therapy

Histone deacetylases (HDACs) play an important role in regulating the expression of genes involved in tumorigenesis and tumor maintenance, and hence they have been considered as key targets in cancer therapy. As a novel category of antitumor agents, histone deacetylase inhibitors (HDACis) can induce cell cycle arrest, apoptosis, and differentiation in cancer cells, ultimately combating cancer. Although in the United States, the use of HDACis for the treatment of certain cancers has been approved, the therapeutic efficacy of HDACis as a single therapeutic agent in solid tumorshas been unsatisfactory and drug resistance may yet occur. To enhance therapeutic efficacy and limit drug resistance, numerous combination therapies involving HDACis in synergy with other antitumor therapies have been studied. In this review, we describe the classification of HDACs. Moreover, we summarize the antitumor mechanism of the HDACis for targeting key cellular processes of cancers (cell cycle, apoptosis, angiogenesis, DNA repair, and immune response). In addition, we outline the major developments of other antitumor therapies in combination with HDACis, including chemotherapy, radiotherapy, phototherapy, targeted therapy, and immunotherapy. Finally, we discuss the current state and challenges of HDACis-drugs combinations in future clinical studies, with the aim of optimizing the antitumor effect of such combinations.

Design, synthesis and binding mode of interaction of novel small molecule o-hydroxy benzamides as HDAC3-selective inhibitors with promising antitumor effects in 4T1-Luc breast cancer xenograft model

Histone deacetylase 3 (HDAC3) is one of the most promising targets to develop anticancer therapeutics. In continuation of our quest for selective HDAC3 inhibitors, a series of small molecules having o-hydroxy benzamide as the novel zinc binding group (ZBG) has been introduced for the first time that can be able to produce good HDAC3-selectivity over other HDACs. The most promising HDAC3 inhibitors, 11a and 12b, displayed promising in vitro anticancer activities with less toxicity to normal kidney cells. These compounds significantly upregulate histone acetylation and induce apoptosis with a G2/M phase arrest in B16F10 cells. Compound 11a exhibited potent antitumor efficacy in 4T1-Luc breast cancer xenograft mouse model in female Balb/c mice. It also showed significant tumor growth suppression with no general toxicity and extended survival rates post-tumor resection. It significantly induced higher ROS generation, leading to apoptosis. No considerable toxicity was noticed in major organs isolated from the compound 11a-treated mice. Compound 11a also induced the upregulation of acH3K9, acH4K12, caspase-3 and caspase-7 as analyzed by immunoblotting with treated tumor tissue. Overall, HDAC3 selective inhibitor 11a might be a potential lead for the clinical translation as an emerging drug candidate.

Histone deacetylase 3 (HDAC3) as an important epigenetic regulator of kidney diseases

Development and progression of many kidney diseases are substantially influenced by aberrant protein acetylation modifications of gene expression crucial for kidney functions. Histone deacetylase (HDAC) expression alterations are detected from renal samples of patients and animal models of various kidney diseases, and the administrations of HDAC inhibitors display impressive renal protective effects in vitro and in vivo. However, when the expression alterations of multiple HDACs occur, not all the HDACs causally affect the disease onset or progression. Identification of a single HDAC as a disease-causing factor will allow subtype-targeted intervention with less side effect. HDAC3 is a unique HDAC with distinct structural and subcellular distribution features and co-repressor dependency. HDAC3 is required for kidney development and its aberrations actively participate in many pathological processes, such as cancer, cardiovascular diseases, diabetes, and neurodegenerative disorders, and contribute significantly to the pathogenesis of kidney diseases. This review will discuss the recent studies that investigate the critical roles of HDAC3 aberrations in kidney development, renal aging, renal cell carcinoma, renal fibrosis, chronic kidney disease, polycystic kidney disease, glomerular podocyte injury, and diabetic nephropathy. These studies reveal the distinct characters of HDAC3 aberrations that act on different molecules/signaling pathways under various renal pathological conditions, which might shed lights into the epigenetic mechanisms of renal diseases and the potentially therapeutic strategies.

Repression of the miR-627-5p by histone deacetylase 3 contributes to hypoxia-induced hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one of the most common solid tumors globally. Our previous studies revealed that miR-627-5p suppresses HCC progression via targeting BCL3/CCND1 pathway. However, the molecular mechanism by which miR-627-5p was downregulated in HCC remains to be further elucidated. As a hallmark of solid tumors, hypoxia results in the rapid growth, strongly potential invasion and high frequent metastasis of cancer cells. Hypoxia-inducible factors (HIFs), mainly including HIF-1 and HIF-2, are the classical transcription factors which mediate hypoxia-related gene transcription. Here, we demonstrated that miR-627-5p was repressed by hypoxia in a HIF-1-dependent manner in HCC cells. But HIF-1 regulated miR-627-5p expression not directly through the hypoxia-response element (HRE) sites of MIR627 gene. In contrast, histone deacetylase 3 (HDAC3) was identified as a HIF-1 target gene, and the occupancy of HIF-1 to HRE site was essential for hypoxia-mediated HDAC3 induction. And upregulated HDAC3 was closely related to the malignant clinical and pathological characteristics and worse prognosis of HCC. Furthermore, HDAC3-mediated histone deacetylation in promoter region of MIR627 was critical for hypoxia-mediated miR-627-5p repression. And miR-627-5p mediated the effects of hypoxic condition on HCC progression. Thus, this study has revealed that miR-627-5p was repressed by hypoxia under the mediation of HDAC3 in HCC, and there existed a HIF-1α/HDAC3/miR-627-5p/BCL3/CCND1 signal pathway in HCC.

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

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

KDELR2 promotes breast cancer proliferation via HDAC3-mediated cell cycle progression

Background

Histone deacetylases (HDACs) engage in the regulation of various cellular processes by controlling global gene expression. The dysregulation of HDACs leads to carcinogenesis, making HDACs ideal targets for cancer therapy. However, the use of HDAC inhibitors (HDACi) as single agents has been shown to have limited success in treating solid tumors in clinical studies. This study aimed to identify a novel downstream effector of HDACs to provide a potential target for combination therapy.

Methods

Transcriptome sequencing and bioinformatics analysis were performed to screen for genes responsive to HDACi in breast cancer cells. The effects of HDACi on cell viability were detected using the MTT assay. The mRNA and protein levels of genes were determined by quantitative reverse transcription‐PCR (qRT‐PCR) and Western blotting. Cell cycle distribution and apoptosis were analyzed by flow cytometry. The binding of CREB1 (cAMP‐response element binding protein 1) to the promoter of the KDELR (The KDEL (Lys‐Asp‐Glu‐Leu) receptor) gene was validated by the ChIP (chromatin immunoprecipitation assay). The association between KDELR2 and protein of centriole 5 (POC5) was detected by immunoprecipitation. A breast cancer‐bearing mouse model was employed to analyze the effect of the HDAC3‐KDELR2 axis on tumor growth.

Results

KDELR2 was identified as a novel target of HDAC3, and its aberrant expression indicated the poor prognosis of breast cancer patients. We found a strong correlation between the protein expression patterns of HADC3 and KDELR2 in tumor tissues from breast cancer patients. The results of the ChIP assay and qRT‐PCR analysis validated that HDAC3 transactivated KDELR2 via CREB1. The HDAC3‐KDELR2 axis accelerated the cell cycle progression of cancer cells by protecting the centrosomal protein POC5 from proteasomal degradation. Moreover, the HDAC3‐KDELR2 axis promoted breast cancer cell proliferation and tumorigenesis in vitro and in vivo.

Conclusion

Our results uncovered a previously unappreciated function of KDELR2 in tumorigenesis, linking a critical Golgi‐the endoplasmic reticulum traffic transport protein to HDAC‐controlled cell cycle progression on the path of cancer development and thus revealing a potential therapeutical target for breast cancer.

Synthesis, biological evaluation, and molecular docking analysis of novel linker-less benzamide based potent and selective HDAC3 inhibitors

A series of novel linker-less benzamides with different aryl and heteroaryl cap groups have been designed, synthesized, and screened as potent histone deacetylase (HDAC) inhibitors with promising anticancer activity. Two lead compounds 5e and 5f were found as potent and highly selective HDAC3 inhibitors over other Class-I HDACs and HDAC6. Compound 5e bearing a 6-quinolinyl moiety as the cap group was found to be a highly potent HDAC3 inhibitor (IC₅₀ = 560 nM) and displayed 46-fold selectivity for HDAC3 over HDAC2, and 33-fold selectivity for HDAC3 over HDAC1. The synthesized compounds possess antiproliferative activities against different cancer cell lines and significantly less cytotoxic to normal cells. Molecular Docking studies of compounds 5e and 5f reveal a similar binding mode of interactions as CI994 at the HDAC3 active site. These observations agreed with the in vitro HDAC3 inhibitory activities. Significant enhancement of the endogenous acetylation level on H3K9 and H4K12 was found when B16F10 cells were treated with compounds 5e and 5f in a dose-dependent manner. The compounds induced apoptotic cell death in Annexin-V/FITC-PI assay and caused cell cycle arrest at G2/M phase of cell cycle in B16F10 cells. These compounds may serve as potential HDAC3 inhibitory anticancer therapeutics.

First-in-Class Selective HDAC6 Inhibitor (ACY-1215) Has a Highly Favorable Safety Profile in Patients with Relapsed and Refractory Lymphoma

LESSONS LEARNED

Oral selective HDAC6 inhibitors could allow for decreased toxicity compared to pan-class inhibitors, and increased ease of use. ACY-1215 is well tolerated and led to disease stabilization in 50% of patients treated on a twice-daily dosing schedule. Rational drug combinations with ACY-1215 improve efficacy in patients with lymphoma. Biomarkers such as XBP-1 level or HDAC6-score may improve patient selection.

BACKGROUND

ACY-1215, ricolinostat, is an oral, first-in-class isoform-selective HDAC6 inhibitor. HDAC6 is a class IIb deacetylase and plays a critical role in protein homeostasis via the unfolded protein response (UPR). Lymphocytes generate a large repertoire of antibodies and depend on an activated UPR to maintain proteostasis. Lymphomas utilize this biology to evade programmed cell death. In preclinical models of lymphoma, ACY-1215 disrupted proteostasis, triggering apoptosis.

METHODS

We translated these findings into a multi-institution, open-label, dose-escalation phase Ib/II study aimed to determine the safety and efficacy in patients with relapsed and refractory lymphoma.

RESULTS

Twenty-one patients with heavily pretreated lymphoma were accrued. Patients in the phase Ib portion were enrolled on one of two dose cohorts [Arm A: 160 mg daily (n = 3) or Arm B: 160 mg twice daily (n = 10)]. ACY-1215 was well tolerated. There were no dose limiting toxicities. Most adverse events were grade 1-2, including diarrhea (57%), nausea (57%), and fatigue (43%). Grade 3-4 toxicities were rare and included anemia (9.5%) and hypercalcemia (9.5%). An additional 8 patients were enrolled on the phase II portion, at 160 mg twice daily. Sixteen patients were evaluable for response. ACY-1215 did not result in any complete or partial responses in patients treated. Eight patients had stable disease (50%) lasting a median duration of 4.5 months, all of whom were treated twice daily. Disease progressed in eight patients (50%) at cycle 2. Five patients were not evaluable due to disease progression prior to cycle 2. The median PFS was 56 days.

CONCLUSION

ACY-1215 is an oral selective HDAC6 inhibitor that was safe in patients with relapsed and refractory lymphoid malignancies and led to disease stabilization in half of the evaluable patients.

HDAC6 as privileged target in drug discovery: A perspective

HDAC6, a class IIB HDAC isoenzyme, stands unique in its structural and physiological functions. Besides histone modification, largely due to its cytoplasmic localization, HDAC6 also targets several non-histone proteins including Hsp90, α-tubulin, cortactin, HSF1, etc. Thus, it is one of the key regulators of different physiological and pathological disease conditions. HDAC6 is involved in different signaling pathways associated with several neurological disorders, various cancers at early and advanced stage, rare diseases and immunological conditions. Therefore, targeting HDAC6 has been found to be effective for various therapeutic purposes in recent years. Though several HDAC6 inhibitors (HDAC6is) have been developed till date, only two ACY-1215 (ricolinostat) and ACY-241 (citarinostat) are in the clinical trials. A lot of work is still needed to pinpoint strictly selective as well as potent HDAC6i. Considering the recent crystal structure of HDAC6, novel HDAC6is of significant therapeutic value can be designed. Notably, the canonical pharmacophore features of HDAC6is consist of a zinc binding group (ZBG), a linker function and a cap group. Significant modifications of cap function may lead to achieve better selectivity of the inhibitors. This review details the study about the structural biology of HDAC6, the physiological and pathological role of HDAC6 in several disease states and the detailed structure-activity relationships (SARs) of the known HDAC6is. This detailed review will provide key insights to design novel and highly effective HDAC6i in the future.

Ketogenic Diet Elicits Antitumor Properties through Inducing Oxidative Stress, Inhibiting MMP-9 Expression, and Rebalancing M1/M2 Tumor-Associated Macrophage Phenotype in a Mouse Model of Colon Cancer

Many advanced cancers are characterized by metabolic disorders. A dietary therapeutic strategy was proposed to inhibit tumor growth through administration of low-carbohydrate, average-protein, and high-fat diet, which is also known as ketogenic diet (KD). In vivo antitumor efficacy of KD on transplanted CT26⁺ tumor cells in BALB/c mice was investigated. The results showed that the KD group had significantly higher blood β-hydroxybutyrate and lower blood glucose levels when compared with the normal diet group. Meanwhile, KD increased intratumor oxidative stress, and TUNEL staining showed KD-induced apoptosis against tumor cells. Interestingly, the distribution of CD16/32⁺ and iNOS⁺ M1 tumor-associated macrophages (TAMs) increased in the KD-treated group, with concomitantly less arginase-1⁺ M2 TAMs. Moreover, KD treatment downregulated the protein expression of matrix metalloproteinase-9 in CT26⁺ tumor-bearing mice. Western blot analysis demonstrated that the expression levels of HDAC3/PKM2/NF-κB 65/p-Stat3 proteins were reduced in the KD-treated group. Taken together, our results indicated that KD can prevent the progression of colon tumor via inducing intratumor oxidative stress, inhibiting the expression of the MMP-9, and enhancing M2 to M1 TAM polarization. A novel potential mechanism was identified that KD can prevent the progression of colon cancer by regulating the expression of HDAC3/PKM2/NF-κB65/p-Stat3 axis.

Histone deacetylase inhibitors induce medulloblastoma cell death independent of HDACs recruited in REST repression complexes

BACKGROUND

Repressor element 1-silencing transcription factor (REST) acts as a transcriptional repressor by recruiting several chromatin modifiers, including histone deacetylase (HDAC). Elevated REST expression in medulloblastoma has been associated with tumor progression nevertheless, the tumor shows high sensitivity to HDAC inhibitors (HDACi). However, the functional implications of REST and its requirement for HDACi-induced anti-cancer effects are not well understood.

METHODS

In this study, the expression of REST was evaluated across the medulloblastoma subgroups and subtypes using published gene expression data. Further, the expression of REST was modulated using the CRISPR/Cas9 knockout and shRNA knockdown in the Daoy medulloblastoma cell line.

RESULTS

The results of this study showed that the expression of REST is elevated in most medulloblastoma subgroups compared to the non-cancerous cerebellum. Blocking of REST expression resulted in increasing the expression of REST-regulated genes, a moderate decrease in the fraction of the cells in the S-phase, and reducing the cells' migration ability. However, REST deficiency did not lead to a marked decrease in the Daoy cell viability and sensitivity to HDACi.

CONCLUSION

The findings of this study indicate that REST is not essential for sustaining the proliferation/viability of the Daoy cells. It also revealed that the anti-proliferative effect of HDACi is independent of REST expression.

Bifunctional HDAC Therapeutics: One Drug to Rule Them All?

Histone deacetylase (HDAC) enzymes play crucial roles in epigenetic gene expression and are an attractive therapeutic target. Five HDAC inhibitors have been approved for cancer treatment to date, however, clinical applications have been limited due to poor single-agent drug efficacy and side effects associated with a lack of HDAC isoform or complex selectivity. An emerging strategy aiming to address these limitations is the development of bifunctional HDAC therapeutics-single molecules comprising a HDAC inhibitor conjugated to another specificity targeting moiety. This review summarises the recent advancements in novel types of dual-targeting HDAC modulators, including proteolysis-targeting chimeras (PROTACs), with a focus on HDAC isoform and complex selectivity, and the future potential of such bifunctional molecules in achieving enhanced drug efficacy and therapeutic benefits in treating disease.

Checkpoint regulator B7x is epigenetically regulated by HDAC3 and mediates resistance to HDAC inhibitors by reprogramming the tumor immune environment in colorectal cancer

HDAC inhibitors are efficacious for treating lymphoma, but display limited efficacy in treating solid tumors. Here, we investigated the relationship between HDAC inhibitor resistance and the tumor immune environment in colorectal cancer. Our data indicated that among the investigated immune factors, B7x expression was enhanced in HDAC inhibitor-resistant colorectal cancer models in vitro and in vivo. In addition, gene manipulation results demonstrated that xenograft mice with tumors derived from a B7x-overexpressing CT-26 colorectal cancer cell line were resistant to HDAC inhibitor treatment. Notably, we found that there is a negative relationship between HDAC and B7x expression in both colorectal cancer cell lines and patients’ tumors. Furthermore, our data indicated that elevated expression of B7x was related to a poor prognosis in colorectal tumor patients. Interestingly, treatment with a specific inhibitor or siRNA of HDAC3, but not HDAC2, 6, and 8, resulted in obvious upregulation of B7x expression in colorectal cancer cells. In addition, our data showed that a cell line with high HDAC3 expression and low B7x expression had decreased enrichment of acetylated histone H3 in the promoter region of the gene encoding B7x. This pattern was reversed by addition of HDAC3 inhibitors. Mechanistically, we found that HDAC3 regulated B7x transcription by promoting the binding of the transcription activator C/EBP-α with the B7x promoter region. Importantly, our data indicated that an antibody neutralizing B7x augmented the response to HDAC inhibitor in the colorectal cancer xenograft model and the lung metastasis model by increasing the ratios of both CD4-positive and CD8-positive T cells. In summary, we demonstrated a role of B7x in HDAC inhibitor resistance and identified the mechanism that dysregulates B7x in colorectal cancer. Our work provides a novel strategy to overcome HDAC inhibitor resistance.

Matrix metalloproteinase-9 (MMP-9) and its inhibitors in cancer: A minireview

Matrix metalloproteinases (MMPs) are zinc dependent proteolytic metalloenzyme. MMP-9 is one of the most complex forms of matrix metalloproteinases. MMP-9 has the ability to degrade the extracellular matrix (ECM) components and has important role in the pathophysiological functions. Overexpression and dysregulation of MMP-9 is associated with various diseases. Thus, regulation and inhibition of MMP-9 is an important therapeutic approach for combating various diseases including cancer. Inhibitors of MMP-9 can be used as anticancer agents. Till date no selective MMP-9 inhibitors passed the clinical trials. In this review the structure, activation, function and inhibitors of MMP-9 are mainly focused. Some highly active and/or selective MMP-9 inhibitors have been discussed which may be helpful to explore the structural significance of MMP-9 inhibitors. This study may be useful to design new potent and selective MMP-9 inhibitors against cancer in future.

Design, synthesis, and biological evaluation of novel nicotinamide derivatives as potential histone deacetylase-3 inhibitors

The selected nicotinamide-based HDACi displayed selectivity towards HDAC3 over pan HDAC and exhibited potent cytotoxicity against the used cell lines.

In silico Design of Novel Histone Deacetylase 4 Inhibitors: Design Guidelines for Improved Binding Affinity

Histone deacetylases (HDAC) are being targeted for a number of diseases such as cancer, inflammatory disease, and neurological disorders. Within this family of 18 isozymes, HDAC4 is a prime target for glioma, one of the most aggressive brain tumors reported. Thus, the development of HDAC4 inhibitors could present a novel therapeutic route for glioma. In this work, molecular docking studies on cyclopropane hydroxamic acid derivatives identified five novel molecular interactions to the HDAC4 receptor that could be harnessed to enhance inhibitor binding. Thus, design guidelines for the optimization of potent HDAC4 inhibitors were developed which can be utilized to further the development of HDAC4 inhibitors. Using the developed guidelines, eleven novel cyclopropane hydroxamic acid derivatives were designed that outcompeted all original cyclopropane hydroxamic acids HDAC4 inhibitors studied in silico. The results of this work will be an asset to paving the way for further design and optimization of novel potent HDAC4 inhibitors for gliomas.

Small molecule HDAC inhibitors: Promising agents for breast cancer treatment

Breast cancer, a heterogeneous disease, is the most frequently diagnosed cancer and the second leading cause of cancer-related death among women worldwide. Recently, epigenetic abnormalities have emerged as an important hallmark of cancer development and progression. Given that histone deacetylases (HDACs) are crucial to chromatin remodeling and epigenetics, their inhibitors have become promising potential anticancer drugs for research. Here we reviewed the mechanism and classification of histone deacetylases (HDACs), association between HDACs and breast cancer, classification and structure-activity relationship (SAR) of HDACIs, pharmacokinetic and toxicological properties of the HDACIs, and registered clinical studies for breast cancer treatment. In conclusion, HDACIs have shown desirable effects on breast cancer, especially when they are used in combination with other anticancer agents. In the coming future, more multicenter and randomized Phase III studies are expected to be conducted pushing promising new therapies closer to the market. In addition, the design and synthesis of novel HDACIs are also needed.

krCRISPR: an easy and efficient strategy for generating conditional knockout of essential genes in cells

Background

CRISPR/Cas9 system is a powerful tool for knocking out genes in cells. However, genes essential for cell survival cannot be directly knocked out. Traditionally, generation of conditional knockout cells requires multiple steps.

Results

In this study, we developed an easy and efficient strategy to generate conditional knockout cells by using double episomal vectors – one which expresses gRNA and Cas9 nuclease, and the other expresses an inducible rescue gene. Using this system which we named “krCRISPR” (knockout-rescue CRISPR), we showed that essential genes, HDAC3 and DNMT1, can be efficiently knocked out. When cells reach a desired confluency, the exogenous rescue genes can be silenced by the addition of doxycycline. Furthermore, the krCRISPR system enabled us to study the effects of the essential gene mutations on cells. We showed that the P507L mutation in DNMT1 led to downregulation of global DNA methylation in cells, indicating that it is a disease-causing mutation.

Conclusions

The krCRISPR system offers an easy and efficient platform that facilitates the study of essential genes’ function.

Electronic supplementary material

The online version of this article (10.1186/s13036-019-0150-y) contains supplementary material, which is available to authorized users.

Apoptosis Induction byHistone Deacetylase Inhibitors in Cancer Cells: Role of Ku70

Histone deacetylases (HDACs) are a group of enzymes that regulate gene transcription by controlling deacetylation of histones and non-histone proteins. Overexpression of HDACs is found in some types of tumors and predicts poor prognosis. Five HDAC inhibitors are approved for the treatment of cutaneous T-cell lymphoma, peripheral T-cell lymphoma, and multiple myeloma. Treatment with HDAC inhibitors regulates gene expression with increased acetylated histones with unconfirmed connection with therapy. Apoptosis is a key mechanism by which HDAC inhibitors selectively kill cancer cells, probably due to acetylation of non-histone proteins. Ku70 is a protein that repairs DNA breaks and stabilizes anti-apoptotic protein c-FLIP and proapoptotic protein Bax, which is regulated by acetylation. HDAC inhibitors induce Ku70 acetylation with repressed c-FLIP and activated Bax in cancer cells. Current studies indicate that Ku70 is a potential target of HDAC inhibitors and plays an important role during the induction of apoptosis.

Cytotoxic Activity of the Histone Deacetylase 3-Selective Inhibitor Pojamide on MDA-MB-231 Triple-Negative Breast Cancer Cells

We examined the effects of the ferrocene-based histone deacetylase-3 inhibitor Pojamide (N¹-(2-aminophenyl)-N⁸-ferrocenyloctanediamide) and its two derivatives N¹-(2-aminophenyl)-N⁶-ferrocenyladipamide and N¹-(2-aminophenyl)-N⁸-ferroceniumoctanediamide tetrafluoroborate on triple-negative MDA-MB-231 breast cancer cells. Viability/growth assays indicated that only the first two compounds at 70 μM concentration caused an approximate halving of cell number after 24 h of exposure, whereas the tetrafluoroborate derivative exerted no effect on cell survival nor proliferation. Flow cytometric and protein blot analyses were performed on cells exposed to both Pojamide and the ferrocenyladipamide derivative to evaluate cell cycle distribution, apoptosis/autophagy modulation, and mitochondrial metabolic state in order to assess the cellular basis of the cytotoxic effect. The data obtained show that the cytotoxic effect of the two deacetylase inhibitors may be ascribed to the onset of non-apoptotic cell death conceivably linked to a down-regulation of autophagic processes and an impairment of mitochondrial function with an increase in intracellular reactive oxygen species. Our work expands the list of autophagy-regulating drugs and also provides a further example of the role played by the inhibition of autophagy in breast cancer cell death. Moreover, the compounds studied may represent attractive and promising targets for subsequent molecular modeling for anti-neoplastic agents in malignant breast cancer.

Histone deacetylase 8 (HDAC8) and its inhibitors with selectivity to other isoforms: An overview

The histone deacetylases (HDACs) enzymes provided crucial role in transcriptional regulation of cells through deacetylation of nuclear histone proteins. Discoveries related to the HDAC8 enzyme activity signified the importance of HDAC8 isoform in cell proliferation, tumorigenesis, cancer, neuronal disorders, parasitic/viral infections and other epigenetic regulations. The pan-HDAC inhibitors can confront these conditions but have chances to affect epigenetic functions of other HDAC isoforms. Designing of selective HDAC8 inhibitors is a key feature to combat the pathophysiological and diseased conditions involving the HDAC8 activity. This review is concerned about the structural and positional aspects of HDAC8 in the HDAC family. It also covers the contributions of HDAC8 in the pathophysiological conditions, a preliminary discussion about the recent scenario of HDAC8 inhibitors. This review might help to deliver the structural, functional and computational information in order to identify and design potent and selective HDAC8 inhibitors for target specific treatment of diseases involving HDAC8 enzymatic activity.