HDAC11 deficiency disrupts oncogene-induced hematopoiesis in myeloproliferative neoplasms

Role of the histone deacetylase family in lipid metabolism: Structural specificity and functional diversity

Lipids play crucial roles in signal transduction. Lipid metabolism is associated with several transcriptional regulators, including peroxisome proliferator activated receptor γ, sterol regulatory element-binding protein 1, and acetyl-CoA carboxylase. In recent years, increasing evidence has suggested that members of the histone deacetylase (HDAC) family play key roles in lipid metabolism. However, the mechanisms by which each member of this family regulates lipid metabolism remain unclear. This review discusses the latest research on the roles played by HDACs in fat metabolism. The role of HDACs in obesity, diabetes, and atherosclerosis has also been discussed. In addition, the interaction of HDACs with the gut microbiome and circadian rhythm has been reviewed, and the future development trend in HDACs has been predicted, which may potentiate therapeutic application of targeted HDACs in related metabolic diseases.

Biological function and small molecule inhibitors of histone deacetylase 11

HDAC11, as a rising star in the histone deacetylase (HDAC) family, has attracted widespread interest in the biomedical field in recent years specially owing to its high defatty-acylase activity compared its innate deacetylase activity. Numerous studies have provided evidence indicating the crucial involvement of HDAC11 in cancers, immune responses, and metabolic processes. Several potent and selective HDAC11 inhibitors have been discovered and identified, which is crucial for exploring the function of HDAC11 and its potential therapeutic applications. Herein, we present a critical overview of the current advances in the biological function of HDAC11 and its inhibitors. We initially discuss the physiological functions of HDAC11 and its pathological roles in relevant diseases. Subsequently, our main focus centers on the design strategy and development process of HDAC11 inhibitors. Additionally, we address significant challenges and outline future directions in this field. This perspective may provide guidance for the further development of HDAC11 inhibitors and their prospects in disease treatment.

Epigenetic regulation of megakaryopoiesis and platelet formation

Platelets, produced by megakaryocytes, play unique roles in physiological processes, such as hemostasis, coagulation, and immune regulation, while also contributing to various clinical diseases. During megakaryocyte differentiation, the morphology and function of cells undergo significant changes due to the programmed expression of a series of genes. Epigenetic changes modify gene expression without altering the DNA base sequence, effectively affecting the inner workings of the cell at different stages of growth, proliferation, differentiation, and apoptosis. These modifications also play important roles in megakaryocyte development and platelet biogenesis. However, the specific mechanisms underlying epigenetic processes and the vast epigenetic regulatory network formed by their interactions remain unclear. In this review, we systematically summarize the key roles played by epigenetics in megakaryocyte development and platelet formation, including DNA methylation, histone modification, and non-coding RNA regulation. We expect our review to provide a deeper understanding of the biological processes underlying megakaryocyte development and platelet formation and to inform the development of new clinical interventions aimed at addressing platelet-related diseases and improving patients' prognoses.

SHP2 inhibition displays efficacy as a monotherapy and in combination with JAK2 inhibition in preclinical models of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocytosis, and primary myelofibrosis, are clonal hematopoietic neoplasms driven by mutationally activated signaling by the JAK2 tyrosine kinase. Although JAK2 inhibitors can improve MPN patients' quality of life, they do not induce complete remission as disease-driving cells persistently survive therapy. ERK activation has been highlighted as contributing to JAK2 inhibitor persistent cell survival. As ERK is a component of signaling by activated RAS proteins and by JAK2 activation, we sought to inhibit RAS activation to enhance responses to JAK2 inhibition in preclinical MPN models. We found the SHP2 inhibitor RMC-4550 significantly enhanced growth inhibition of MPN cell lines in combination with the JAK2 inhibitor ruxolitinib, effectively preventing ruxolitinib persistent growth, and the growth and viability of established ruxolitinib persistent cells remained sensitive to SHP2 inhibition. Both SHP2 and JAK2 inhibition diminished cellular RAS-GTP levels, and their concomitant inhibition enhanced ERK inactivation and increased apoptosis. Inhibition of SHP2 inhibited the neoplastic growth of MPN patient hematopoietic progenitor cells and exhibited synergy with ruxolitinib. RMC-4550 antagonized MPN phenotypes and increased survival of an MPN mouse model driven by MPL-W515L. The combination of RMC-4550 and ruxolitinib, which was safe and tolerated in healthy mice, further inhibited disease compared to ruxolitinib monotherapy, including extending survival. Given SHP2 inhibitors are undergoing clinical evaluation in patients with solid tumors, our preclinical findings suggest that SHP2 is a candidate therapeutic target with potential for rapid translation to clinical assessment to improve current targeted therapies for MPN patients.

Transcriptional Expression of Histone Acetyltransferases and Deacetylases During the Recovery of Acute Exercise in Mouse Hippocampus

Protein acetylation, which is dynamically maintained by histone acetyltransferases (HATs) and deacetylases (HDACs), might play essential roles in hippocampal exercise physiology. However, whether HATs/HDACs are imbalanced during the recovery phase following acute exercise has not been determined. Groups of exercised mice with different recovery periods after acute exercise (0 h, 0.5 h, 1 h, 4 h, 7 h, and 24 h) were constructed, and a group of sham-exercised mice was used as the control. The mRNA levels of HATs and HDACs were detected via real-time quantitative polymerase chain reaction. Lysine acetylation on the total proteins and some specific locations on histones were detected via western blotting, as were various acylation modifications on the total proteins. Except for four unaffected genes (Hdac4, Ncoa1, Ncoa2, and Sirt1), the mRNA expression trajectories of 21 other HATs or HDACs affected by exercise could be categorized into three clusters. The genes in Cluster 1 increased quickly following exercise, with a peak at 0.5 h and/or 1 h, and remained at high levels until 24 h. Cluster 2 genes presented a gradual increase with a delayed peak at 4 h or 7 h postexercise before returning to baseline. The expression of Cluster 3 genes decreased at 0.5 h and/or 1 h, with some returning to overexpression (Hdac1 and Sirt3). Although most HATs were upregulated and half of the affected HDACs were downregulated at 0.5 h postexercise, the global or residue-specific histone acetylation levels were unchanged. In contrast, the levels of several metabolism-related acylation products of total proteins, including acetylation, succinylation, 2-hydroxyisobutyryllysine, β-hydroxybutyryllysine, and lactylation, decreased and mainly occurred on nonhistones immediately after exercise. During the 24-h recovery phase after acute exercise, the transcriptional trajectory of HATs or the same class of HDACs in the hippocampus exhibited heterogeneity. Although acute exercise did not affect the selected sites on histone lysine residues, it possibly incurred changes in acetylation and other acylation on nonhistone proteins.

Engineering novel scaffolds for specific HDAC11 inhibitors against metabolic diseases exploiting deep learning, virtual screening, and molecular dynamics simulations

The prevalence of metabolic diseases is increasing at a frightening rate year by year. The burgeoning development of deep learning enables drug design to be more efficient, selective, and structurally novel. The critical relevance of Histone deacetylase 11 (HDAC11) to the pathogenesis of several metabolic diseases makes it a promising drug target for curbing metabolic disorders. The present study aims to design new specific HDAC11 inhibitors for the treatment of metabolic diseases. Deep learning was performed to learn the properties of existing HDAC11 inhibitors and yield a novel compound library containing 23,122 molecules. Subsequently, the compound library was screened by ADMET properties, Lipinski & Veber rules, traditional machine classification models, and molecular docking, and 10 compounds were screened as candidate HDAC11 inhibitors. The stability of the 10 new molecules was further evaluated by deploying RMSD, RMSF, MM/GBSA, free energy landscape mapping, and PCA analysis in molecular dynamics simulations. As a result, ten compounds, Cpd_17556, Cpd_2184, Cpd_8907, Cpd_7771, Cpd_14959, Cpd_7108, Cpd_12383, Cpd_13153, Cpd_14500and Cpd_21811, were characterized as good HDAC11 inhibitors and are expected to be promising drug candidates for metabolic disorders, and further in vitro, in vivo and clinical trials to demonstrate in the future.

Comparative Structure-Based Virtual Screening Utilizing Optimized AlphaFold Model Identifies Selective HDAC11 Inhibitor

HDAC11 is a class IV histone deacylase with no crystal structure reported so far. The catalytic domain of HDAC11 shares low sequence identity with other HDAC isoforms, which makes conventional homology modeling less reliable. AlphaFold is a machine learning approach that can predict the 3D structure of proteins with high accuracy even in absence of similar structures. However, the fact that AlphaFold models are predicted in the absence of small molecules and ions/cofactors complicates their utilization for drug design. Previously, we optimized an HDAC11 AlphaFold model by adding the catalytic zinc ion and minimization in the presence of reported HDAC11 inhibitors. In the current study, we implement a comparative structure-based virtual screening approach utilizing the previously optimized HDAC11 AlphaFold model to identify novel and selective HDAC11 inhibitors. The stepwise virtual screening approach was successful in identifying a hit that was subsequently tested using an in vitro enzymatic assay. The hit compound showed an IC50 value of 3.5 µM for HDAC11 and could selectively inhibit HDAC11 over other HDAC subtypes at 10 µM concentration. In addition, we carried out molecular dynamics simulations to further confirm the binding hypothesis obtained by the docking study. These results reinforce the previously presented AlphaFold optimization approach and confirm the applicability of AlphaFold models in the search for novel inhibitors for drug discovery.

FT895 Impairs Mitochondrial Function in Malignant Peripheral Nerve Sheath Tumor Cells

Neurofibromatosis type 1 (NF1) stands as a prevalent neurocutaneous disorder. Approximately a quarter of NF1 patients experience the development of plexiform neurofibromas, potentially progressing into malignant peripheral nerve sheath tumors (MPNST). FT895, an HDAC11 inhibitor, exhibits potent anti-tumor effects on MPNST cells and enhances the cytotoxicity of cordycepin against MPNST. The study aims to investigate the molecular mechanism underlying FT895's efficacy against MPNST cells. Initially, our study unveiled that FT895 disrupts mitochondrial biogenesis and function. Post-FT895 treatment, reactive oxygen species (ROS) in MPNST notably increased, while mitochondrial DNA copy numbers decreased significantly. Seahorse analysis indicated a considerable decrease in basal, maximal, and ATP-production-coupled respiration following FT895 treatment. Immunostaining highlighted FT895's role in promoting mitochondrial aggregation without triggering mitophagy, possibly due to reduced levels of XBP1, Parkin, and PINK1 proteins. Moreover, the study using CHIP-qPCR analysis revealed a significant reduction in the copy numbers of promoters of the MPV17L2, POLG, TFAM, PINK1, and Parkin genes. The RNA-seq analysis underscored the prominent role of the HIF-1α signaling pathway post-FT895 treatment, aligning with the observed impairment in mitochondrial respiration. In summary, the study pioneers the revelation that FT895 induces mitochondrial respiratory damage in MPNST cells.

Utilization of AlphaFold models for drug discovery: Feasibility and challenges. Histone deacetylase 11 as a case study

Histone deacetylase 11 (HDAC11), an enzyme that cleaves acyl groups from acylated lysine residues, is the sole member of class IV of HDAC family with no reported crystal structure so far. The catalytic domain of HDAC11 shares low sequence identity with other HDAC isoforms which complicates the conventional template-based homology modeling. AlphaFold is a neural network machine learning approach for predicting the 3D structures of proteins with atomic accuracy even in absence of similar structures. However, the structures predicted by AlphaFold are missing small molecules as ligands and cofactors. In our study, we first optimized the HDAC11 AlphaFold model by adding the catalytic zinc ion followed by assessment of the usability of the model by docking of the selective inhibitor FT895. Minimization of the optimized model in presence of transplanted inhibitors, which have been described as HDAC11 inhibitors, was performed. Four complexes were generated and proved to be stable using three replicas of 50 ns MD simulations and were successfully utilized for docking of the selective inhibitors FT895, MIR002 and SIS17. For SIS17, The most reasonable pose was selected based on structural comparison between HDAC6, HDAC8 and the HDAC11 optimized AlphaFold model. The manually optimized HDAC11 model is thus able to explain the binding behavior of known HDAC11 inhibitors and can be used for further structure-based optimization.

Acetylation in pathogenesis: Revealing emerging mechanisms and therapeutic prospects

Protein acetylation modifications play a central and pivotal role in a myriad of biological processes, spanning cellular metabolism, proliferation, differentiation, apoptosis, and beyond, by effectively reshaping protein structure and function. The metabolic state of cells is intricately connected to epigenetic modifications, which in turn influence chromatin status and gene expression patterns. Notably, pathological alterations in protein acetylation modifications are frequently observed in diseases such as metabolic syndrome, cardiovascular disorders, and cancer. Such abnormalities can result in altered protein properties and loss of function, which are closely associated with developing and progressing related diseases. In recent years, the advancement of precision medicine has highlighted the potential value of protein acetylation in disease diagnosis, treatment, and prevention. This review includes provocative and thought-provoking papers outlining recent breakthroughs in acetylation modifications as they relate to cardiovascular disease, mitochondrial metabolic regulation, liver health, neurological health, obesity, diabetes, and cancer. Additionally, it covers the molecular mechanisms and research challenges in understanding the role of acetylation in disease regulation. By summarizing novel targets and prognostic markers for the treatment of related diseases, we aim to contribute to the field. Furthermore, we discuss current hot topics in acetylation research related to health regulation, including N4-acetylcytidine and liquid-liquid phase separation. The primary objective of this review is to provide insights into the functional diversity and underlying mechanisms by which acetylation regulates proteins in disease contexts.

HDAC11 mediates the ubiquitin-dependent degradation of p53 and inhibits the anti-leukemia effect of PD0166285

Cytarabine-resistant acute myeloid leukemia (AML) is a common phenomenon, necessitating the search for new chemotherapeutics. WEE1 participates in cell cycle checkpoint signaling and inhibitors targeting WEE1 (WEE1i) constitute a potential novel strategy for AML treatment. HDAC (histone deacetylase) inhibitors have been shown to enhance the anti-tumor effects of WEE1i but molecular mechanisms of HDAC remain poorly characterized. In this study, the WEE1 inhibitor PD0166285 showed a relatively good anti-leukemia effect. Notably, PD0166285 can arise the expression of HDAC11 which was negatively correlated with survival of AML patients. Moreover, HDAC11 can reduced the anti-tumor effect of PD0166285 through an effect on p53 stability and the changes in phosphorylation levels of MAPK pathways. Overall, the cell cycle inhibitor, PD0166285, is a potential chemotherapeutic drug for AML. These fundings contribute to a functional understanding of HDAC11 in AML.

HDAC11: A novel target for improved cancer therapy

Histone deacetylase 11 (HDAC11) is a unique member of the histone deacetylase family that plays an important role in the regulation of gene expression and protein function. In recent years, research on the role of HDAC11 in tumors has attracted increasing attention. This review summarizes the current knowledge on the subcellular localization, structure, expression, and functions of HDAC11 in tumors, as well as the regulatory mechanisms involved in its network, including ncRNA and substrates. Moreover, we focus on the progress made in targeting HDAC11 to overcome tumor therapy resistance, and the development of HDAC11 inhibitors for cancer treatment. Collectively, this review provides comprehensive insights into the potential clinical implications of HDAC11 for cancer therapy.

Development of a novel histone deacetylase inhibitor unveils the role of HDAC11 in alleviating depression by inhibition of microglial activation

Histone deacetylases (HDACs) are key epigenetic regulators and classified into four subtypes. Despite the various roles of each HDAC isoform, the lack of selective HDAC inhibitors has limited the elucidation of their roles in biological systems. HDAC11, the sole class-IV HDAC, is highly expressed in the brain, however, the role of HDAC11 in microglia is not fully understood. Based on the modification of MC1568, we developed a novel HDAC inhibitor, 5. Interestingly, 5 suppresses lipopolysaccharide-induced microglial activation by the initiation of autophagy and subsequent inhibition of nitric oxide production. Furthermore, we demonstrated that 5 significantly alleviates depression-like behavior by inhibiting microglial activation in mouse brain. Our discovery reveals that specific pharmacological regulation of HDAC11 induces autophagy and reactive nitrogen species balance in microglia for the first time, which makes HDAC11 a new therapeutic target for depressive disorder.

Recent advances in therapies for primary myelofibrosis

Primary myelofibrosis (PMF), polycythemia vera (PV) and essential thrombocythemia (ET) form the classical BCR-ABL1-negative myeloproliferative neoplasms (MPNs) that are driven by a constitutive activation of JAK2 signaling. PMF as well as secondary MF (post-ET and post-PV MF) are the most aggressive MPNs. Presently, there is no curative treatment, except allogenic hematopoietic stem cell transplantation. JAK inhibitors, essentially ruxolitinib, are the therapy of reference for intermediate and high-risk MF. However, presently the current JAK inhibitors behave mainly as anti-inflammatory drugs, improving general symptoms and spleen size without major impact on disease progression. A better understanding of the genetics of MF, the biology of its leukemic stem cells (LSCs), the mechanisms of fibrosis and of cytopenia and the role of inflammatory cytokines has led to new approaches with the development of numerous therapeutic agents that target epigenetic regulation, telomerase, apoptosis, cell cycle, cytokines and signaling. Furthermore, the use of a new less toxic form of interferon-α has been revived, as it is presently one of the only molecules that targets the mutated clone. These new approaches have different aims: (a) to provide alternative therapy to JAK inhibition; (b) to correct cytopenia; and (c) to inhibit fibrosis development. However, the main important goal is to find new disease modifier treatments, which will profoundly modify the progression of the disease without major toxicity. Presently the most promising approaches consist of the inhibition of telomerase and the combination of JAK2 inhibitors (ruxolitinib) with either a BCL2/BCL-xL or BET inhibitor. Yet, the most straightforward future approaches can be considered to be the development of and/or selective inhibition of JAK2V617F and the targeting MPL and calreticulin mutants by immunotherapy. It can be expected that the therapy of MF will be significantly improved in the coming years.

HDAC6 regulates human erythroid differentiation through modulation of JAK2 signalling

Among histone deacetylases, HDAC6 is unusual in its cytoplasmic localization. Its inhibition leads to hyperacetylation of non-histone proteins, inhibiting cell cycle, proliferation and apoptosis. Ricolinostat (ACY-1215) is a selective inhibitor of the histone deacetylase HDAC6 with proven efficacy in the treatment of malignant diseases, but anaemia is one of the most frequent side effects. We investigated here the underlying mechanisms of this erythroid toxicity. We first confirmed that HDAC6 was strongly expressed at both RNA and protein levels in CD34⁺ -cells-derived erythroid progenitors. ACY-1215 exposure on CD34⁺ -cells driven in vitro towards the erythroid lineage led to a decreased cell count, an increased apoptotic rate and a delayed erythroid differentiation with accumulation of weakly hemoglobinized immature erythroblasts. This was accompanied by drastic changes in the transcriptomic profile of primary cells as shown by RNAseq. In erythroid cells, ACY-1215 and shRNA-mediated HDAC6 knockdown inhibited the EPO-dependent JAK2 phosphorylation. Using acetylome, we identified 14-3-3ζ, known to interact directly with the JAK2 negative regulator LNK, as a potential HDAC6 target in erythroid cells. We confirmed that 14-3-3ζ was hyperacetylated after ACY-1215 exposure, which decreased the 14-3-3ζ/LNK interaction while increased LNK ability to interact with JAK2. Thus, in addition to its previously described role in the enucleation of mouse fetal liver erythroblasts, we identified here a new mechanism of HDAC6-dependent control of erythropoiesis through 14-3-3ζ acetylation level, LNK availability and finally JAK2 activation in response to EPO, which is crucial downstream of EPO-R activation for human erythroid cell survival, proliferation and differentiation.

HDAC11, an emerging therapeutic target for metabolic disorders

Histone deacetylase 11 (HDAC11) is the only member of the class IV HDAC, and the latest member identified. It is highly expressed in brain, heart, kidney and some other organs, and located in mitochondria, cytoplasm and nuclei, depending on the tissue and cell types. Although studies in HDAC11 total knockout mice suggest its dispensable features for tissue development and life, it participates in diverse pathophysiological processes, such as DNA replication, tumor growth, immune regulation, oxidant stress injury and neurological function of cocaine. Recent studies have shown that HDAC11 is also critically involved in the pathogenesis of some metabolic diseases, including obesity, diabetes and complications of diabetes. In this review, we summarize the recent progress on the role and mechanism of HDAC11 in the regulation of metabolic disorders, with the focus on its regulation on adipogenesis, lipid metabolism, metabolic inflammation, glucose tolerance, immune responses and energy consumption. We also discuss the property and selectivity of HDAC11 inhibitors and their applications in a variety of in vitro and in vivo models of metabolic disorders. Given that pharmacological and genetic inhibition of HDAC11 exerts a beneficial effect on various metabolic disorders, HDAC11 may be a potential therapeutic target to treat chronic metabolic diseases.

Histone Deacetylases Function in the Control of Early Hematopoiesis and Erythropoiesis

Numerous studies have highlighted the role of post-translational modifications in the regulation of cell proliferation, differentiation and death. Among these modifications, acetylation modifies the physicochemical properties of proteins and modulates their activity, stability, localization and affinity for partner proteins. Through the deacetylation of a wide variety of functional and structural, nuclear and cytoplasmic proteins, histone deacetylases (HDACs) modulate important cellular processes, including hematopoiesis, during which different HDACs, by controlling gene expression or by regulating non-histone protein functions, act sequentially to provide a fine regulation of the differentiation process both in early hematopoietic stem cells and in more mature progenitors. Considering that HDAC inhibitors represent promising targets in cancer treatment, it is necessary to decipher the role of HDACs during hematopoiesis which could be impacted by these therapies. This review will highlight the main mechanisms by which HDACs control the hematopoietic stem cell fate, particularly in the erythroid lineage.

A pan-cancer analysis identifies HDAC11 as an immunological and prognostic biomarker

Histone deacetylase 11 (HDAC11) is aberrantly expressed in many types of cancer, and such abnormalities are associated with tumor immunity and heterogeneous clinical outcomes. Here, we explore the prognostic value and immunological function of HDAC11 across 33 cancer types. We observe HDAC11 is aberrantly expressed in 25 cancer types and positively or negatively associated with prognosis in different cancers. HDAC11 played a protective prognostic role in KIRP, KIRC, LGG, PCPG, READ, and UVM, which was contrary to the conventional opinion that HDAC11 was an oncogenic gene. Moreover, HDAC11 is negatively associated with tumor immune components, most immune checkpoint genes, and key cytokine expression. HDAC11 is correlated with tumor mutational burden in 11 cancer types and with microsatellite instability in 9 cancer types, suggesting HDAC11 may affect a patient's response to immune checkpoint inhibitor (ICI) therapy. In addition, HDAC11 is negatively correlated with the drug sensitivity of oxaliplatin, carmustine, ifosfamide, imexon, lomustine, and BN-2629, indicating the potential synergy between HDAC11 inhibitors and these anti-tumor drugs. In vitro assays indicate that HDAC11 inhibitor SIS17 combined with oxaliplatin shows a synergistic cytotoxic role in K562 cells while SIS17 has an antagonistic effect on the cytotoxic role of oxaliplatin in 769P cells. HDAC11 is also associated with hallmark pathways, including epithelial mesenchymal transition, IL-6/JAK/STAT3, and allograft rejection pathways. Overall, we provide clues regarding the key role of HDAC11 in multiple cancers.

Epigenetic downregulation of Socs2 contributes to mutant N-Ras-mediated hematopoietic dysregulation

RAS mutations occur in a broad spectrum of human hematopoietic malignancies. Activating Ras mutations in blood cells leads to hematopoietic malignancies in mice. In murine hematopoietic stem cells (HSCs), mutant N-Ras^G12D activates Stat5 to dysregulate stem cell function. However, the underlying mechanism remains elusive. In this study, we demonstrate that Stat5 activation induced by a hyperactive Nras mutant, G12D, is dependent on Jak2 activity. Jak2 is activated in Nras mutant HSCs and progenitors (HSPCs), and inhibiting Jak2 with ruxolitinib significantly decreases Stat5 activation and HSPC hyper-proliferation in vivo in Nras^G12D mice. Activation of Jak2-Stat5 is associated with downregulation of Socs2, an inhibitory effector of Jak2/Stat5. Restoration of Socs2 blocks Nras^G12D HSC reconstitution in bone marrow transplant recipients. SOCS2 downregulation is also observed in human acute myeloid leukemia (AML) cells that carry RAS mutations. RAS mutant AML cells exhibited suppression of the enhancer active marker H3K27ac at the SOCS2 locus. Finally, restoration of SOCS2 in RAS mutant AML cells mitigated leukemic growth. Thus, we discovered a novel signaling feedback loop whereby hyperactive Ras signaling activates Jak2/Stat5 via suppression of Socs2.

Summary: Jak2/Stat5 is often considered to be parallel to or upstream of Ras signaling. We have discovered a novel signaling feedback loop whereby hyperactive Ras signaling activates Jak2/Stat5 via suppression of Socs2.

HDACs and the epigenetic plasticity of cancer cells: Target the complexity

Cancer cells must adapt to the hostile conditions of the microenvironment in terms of nutrition, space, and immune system attack. Mutations of DNA are the drivers of the tumorigenic process, but mutations must be able to hijack cellular functions to sustain the spread of mutant genomes. Transcriptional control is a key function in this context and is controlled by the rearrangement of the epigenome. Unlike genomic mutations, the epigenome of cancer cells can in principle be reversed. The discovery of the first epigenetic drugs triggered a contaminating enthusiasm. Unfortunately, the complexity of the epigenetic machinery has frustrated this enthusiasm. To develop efficient patient-oriented epigenetic therapies, we need to better understand the nature of this complexity. In this review, we will discuss recent advances in understanding the contribution of HDACs to the maintenance of the transformed state and the rational for their selective targeting.

Comprehensive Analysis of the Differential Expression and Prognostic Value of Histone Deacetylases in Glioma

Gliomas are the most common and aggressive malignancies of the central nervous system. Histone deacetylases (HDACs) are important targets in cancer treatment. They regulate complex cellular mechanisms that influence tumor biology and immunogenicity. However, little is known about the function of HDACs in glioma. The Oncomine, Human Protein Atlas, Gene Expression Profiling Interactive Analysis, Broad Institute Cancer Cell Line Encyclopedia, Chinese Glioma Genome Atlas, OmicShare, cBioPortal, GeneMANIA, STRING, and TIMER databases were utilized to analyze the differential expression, prognostic value, and genetic alteration of HDAC and immune cell infiltration in patients with glioma. HDAC1/2 were considerable upregulated whereas HDAC11 was significantly downregulated in cancer tissues. HDAC1/2/3/4/5/7/8/11 were significantly correlated with the clinical glioma stage. HDAC1/2/3/10 were strongly upregulated in 11 glioma cell lines. High HDCA1/3/7 and low HDAC4/5/11 mRNA levels were significantly associated with overall survival and disease-free survival in glioma. HDAC1/2/3/4/5/7/9/10/11 are potential useful biomarkers for predicting the survival of patients with glioma. The functions of HDACs and 50 neighboring genes were primarily related to transcriptional dysregulation in cancers and the Notch, cGMP-PKG, and thyroid hormone signaling pathways. HDAC expression was significantly correlated with the infiltration of B cells, CD4+ T cells, CD8+ T cells, macrophages, neutrophils, and dendritic cells in glioma. Our study indicated that HDACs are putative precision therapy targets and prognostic biomarkers of survival in glioma patients.

A novel HDAC11 inhibitor potentiates the tumoricidal effects of cordycepin against malignant peripheral nerve sheath tumor through the Hippo signaling pathway

Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder. Clinically, the hallmarks of NF1 include skin pigmentation and cutaneous neurofibroma. Some NF1 patients develop plexiform neurofibroma (PN) since early childhood. Pathologically, PN contains abundant Schwann cells, blood vessels and connective tissues, which may transform into a malignant peripheral nerve sheath tumor (MPNST). MPNST is a highly invasive sarcoma without any effective therapy. Recently, both in vitro and in vivo studies showed that cordycepin can inhibit the growth of MPNST cells. Cordycepin causes cell cycle arrest at G2/M phase and downregulates the protein levels of α-tubulin, p53 and Sp1. Herein, the present study revealed that the HDAC11 inhibitor, FT895, can synergistically enhance the tumoricidal effect of cordycepin against MPNST cells in vitro. Treatment with the combination of cordycepin and FT895 reduced the size of MPNST in the xenograft mouse model. The combined treatment decreased the protein levels of α-tubulin and KIF18A, which may disrupt the microtubule organization leading to the mis-segregation of chromosomes and aneuploidy. Moreover, the expression levels of TEAD1 and its co-activator TAZ, the candidate proteins in hippo signaling pathway, were suppressed after combined treatment. Sequence analysis found a few binding sites for the transcription factor, TEAD1 in the promoter regions of TUBA1B, KIF18A, TEAD1, TAZ, YAP, TP53 and SP1 genes. ChIP-qPCR assay showed that the combined treatment decreases the binding of TEAD1 to the promoters of TUBA1B, KIF18A, TEAD1, TAZ and YAP genes in STS26T cells. The reduced binding to TP53 and SP1 promoters was also found in S462TY cells, which was further confirmed by immunoblotting. The down-regulation of these important transcriptional factors may contribute to the vulnerability of MPNST. In summary, HDAC11 inhibitor, FT895 can potentiate the tumoricidal effect of cordycepin to suppress the MPNST cell growth, which was probably mediated by the dysfunction of hippo-signaling pathway.

GM-CSF impairs erythropoiesis by disrupting erythroblastic island formation via macrophages

Anemia is a significant complication of chronic inflammation and may be related to dysregulated activities among erythroblastic island (EBI) macrophages. GM-CSF was reported to be upregulated and attracted as a therapeutic target in many inflammatory diseases. Among EBIs, we found that the GM-CSF receptor is preferentially and highly expressed among EBI macrophages but not among erythroblasts. GM-CSF treatment significantly decreases human EBI formation in vitro by decreasing the adhesion molecule expression of CD163. RNA-sequence analysis suggests that GM-CSF treatment impairs the supporting function of human EBI macrophages during erythropoiesis. GM-CSF treatment also polarizes human EBI macrophages from M2-like type to M1-like type. In addition, GM-CSF decreases mouse bone marrow (BM) erythroblasts as well as EBI macrophages, leading to a reduction in EBI numbers. In defining the molecular mechanism at work, we found that GM-CSF treatment significantly decreases the adhesion molecule expression of CD163 and Vcam1 in vivo. Importantly, GM-CSF treatment also decreases the phagocytosis rate of EBI macrophages in mouse BM as well as decreases the expression of the engulfment-related molecules Mertk, Axl, and Timd4. In addition, GM-CSF treatment polarizes mouse BM EBI macrophages from M2-like type to M1-like type. Thus, we document that GM-CSF impairs EBI formation in mice and humans. Our findings support that targeting GM-CSF or reprogramming EBI macrophages might be a novel strategy to treat anemia resulting from inflammatory diseases.

Plasma cell dependence on histone/protein deacetylase 11 reveals a therapeutic target in multiple myeloma

The clinical utility of histone/protein deacetylase (HDAC) inhibitors in combinatorial regimens with proteasome inhibitors for patients with relapsed and refractory multiple myeloma (MM) is often limited by excessive toxicity due to HDAC inhibitor promiscuity with multiple HDACs. Therefore, more selective inhibition minimizing off-target toxicity may increase the clinical effectiveness of HDAC inhibitors. We demonstrated that plasma cell development and survival are dependent upon HDAC11, suggesting this enzyme is a promising therapeutic target in MM. Mice lacking HDAC11 exhibited markedly decreased plasma cell numbers. Accordingly, in vitro plasma cell differentiation was arrested in B cells lacking functional HDAC11. Mechanistically, we showed that HDAC11 is involved in the deacetylation of IRF4 at lysine¹⁰³. Further, targeting HDAC11 led to IRF4 hyperacetylation, resulting in impaired IRF4 nuclear localization and target promoter binding. Importantly, transient HDAC11 knockdown or treatment with elevenostat, an HDAC11-selective inhibitor, induced cell death in MM cell lines. Elevenostat produced similar anti-MM activity in vivo, improving survival among mice inoculated with 5TGM1 MM cells. Elevenostat demonstrated nanomolar ex vivo activity in 34 MM patient specimens and synergistic activity when combined with bortezomib. Collectively, our data indicated that HDAC11 regulates an essential pathway in plasma cell biology establishing its potential as an emerging theraputic vulnerability in MM.

Roles of Histone Deacetylases in Acute Myeloid Leukemia With Fusion Proteins

Accurate orchestration of gene expression is critical for the process of normal hematopoiesis, and dysregulation is closely associated with leukemogenesis. Epigenetic aberration is one of the major causes contributing to acute myeloid leukemia (AML), where chromosomal rearrangements are frequently found. Increasing evidences have shown the pivotal roles of histone deacetylases (HDACs) in chromatin remodeling, which are involved in stemness maintenance, cell fate determination, proliferation and differentiation, via mastering the transcriptional switch of key genes. In abnormal, these functions can be bloomed to elicit carcinogenesis. Presently, HDAC family members are appealing targets for drug exploration, many of which have been deployed to the AML treatment. As the majority of AML events are associated with chromosomal translocation resulting in oncogenic fusion proteins, it is valuable to comprehensively understand the mutual interactions between HDACs and oncogenic proteins. Therefore, we reviewed the process of leukemogenesis and roles of HDAC members acting in this progress, providing an insight for the target anchoring, investigation of hyperacetylated-agents, and how the current knowledge could be applied in AML treatment.

Characterization of Histone Deacetylase Mechanisms in Cancer Development

Over decades of studies, accumulating evidence has suggested that epigenetic dysregulation is a hallmark of tumours. Post-translational modifications of histones are involved in tumour pathogenesis and development mainly by influencing a broad range of physiological processes. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are pivotal epigenetic modulators that regulate dynamic processes in the acetylation of histones at lysine residues, thereby influencing transcription of oncogenes and tumour suppressor genes. Moreover, HDACs mediate the deacetylation process of many nonhistone proteins and thus orchestrate a host of pathological processes, such as tumour pathogenesis. In this review, we elucidate the functions of HDACs in cancer.

Hydroxytyrosol Acetate Inhibits Vascular Endothelial Cell Pyroptosis via the HDAC11 Signaling Pathway in Atherosclerosis

Hydroxytyrosol acetate (HT-AC), a natural polyphenolic compound in olive oil, exerts an anti-inflammatory effect in cardiovascular diseases (CVDs). Pyroptosis is a newly discovered form of programmed inflammatory cell death and is suggested to be involved in the atherosclerosis (AS) process. However, the effect of HT-AC on vascular endothelial cell pyroptosis remains unknown. Thus, we aimed to investigate the effect of HT-AC on vascular endothelial cell pyroptosis in AS and related signaling pathways. In vivo studies showed that HT-AC alleviated the formation of atherosclerotic lesions and inhibited pyroptosis in the aortic intima of ApoE^−/− mice fed a high-fat diet (HFD) for 12 weeks. In vitro, we found that HT-AC treatment of human umbilical vein endothelial cells (HUVECs) alleviated tumor necrosis factor-alpha (TNF-α)-induced pyroptosis by decreasing the number of PI positive cells, decreasing the enhanced protein expressions of activated caspase-1 and gasdermin D (GSDMD), as well as by decreasing the release of pro-inflammatory interleukin (IL)-1β and IL-6. Besides, HT-AC down-regulated HDAC11 expression in the aortic intima of HFD-fed ApoE^−/− mice and TNF-α-stimulated HUVECs. To determine the underlying mechanism of action, molecular docking and drug affinity responsive target stability (DARTS) were utilized to identify whether HDAC11 protein is a target of HT-AC. The molecular docking result showed good compatibility between HT-AC and HDAC11. DARTS study's result showed that HDAC11 protein may be a target of HT-AC. Further study demonstrated that knockdown of HDAC11 augmented the inhibition of HT-AC on pyroptosis in TNF-α-stimulated HUVECs. These findings indicate that HT-AC might prevent vascular endothelial pyroptosis through down-regulation of HDAC11 related signaling pathway in AS.

HDAC11: a multifaceted histone deacetylase with proficient fatty deacylase activity and its roles in physiological processes

The histone deacetylases (HDACs) family of enzymes possess deacylase activity for histone and nonhistone proteins; HDAC11 is the latest discovered HDAC and the only member of class IV. Besides its shared HDAC family catalytical activity, recent studies underline HDAC11 as a multifaceted enzyme with a very efficient long-chain fatty acid deacylase activity, which has open a whole new field of action for this protein. Here, we summarize the importance of HDAC11 in a vast array of cellular pathways, which has been recently highlighted by discoveries about its subcellular localization, biochemical features, and its regulation by microRNAs and long noncoding RNAs, as well as its new targets and interactors. Additionally, we discuss the recent work showing the consequences of HDAC11 dysregulation in brain, skeletal muscle, and adipose tissue, and during regeneration in response to kidney, skeletal muscle, and vascular injuries, underscoring HDAC11 as an emerging hub protein with physiological functions that are much more extensive than previously thought, and with important implications in human diseases.

Novel Pathophysiological Mechanisms of Thrombosis in Myeloproliferative Neoplasms

PURPOSE OF REVIEW

Thrombosis remains a leading cause of morbidity and mortality in BCR/ABL negative myeloproliferative neoplasms (MPN). Circulating blood cells are both increased in quantity and qualitatively abnormal in MPN, resulting in an increased thrombotic risk. Herein, we review recently elucidated mechanisms of MPN thrombosis and discuss implications of drugs currently under investigation for MPN.

RECENT FINDINGS

Recent studies highlight that in JAK2^V617F granulocytes and platelets, thrombo-inflammatory genes are upregulated. Furthermore, in JAK2^V617F granulocytes, protein expression of integrin CD11b, tissue factor, and leukocyte alkaline phosphatase are all increased. Overall, myeloid cells, namely neutrophils, may contribute in several ways, such as through increased adhesion via β1 integrin binding to VCAM1, increased infiltration, and enhanced inducibility to extrude neutrophil extracellular traps. Non-myeloid inflammatory cells may also contribute via secretion of cytokines. With regard to red blood cells, number, rigidity, adhesion, and generation of microvesicles may lead to increased vascular resistance as well as increased cell-cell interactions that promote rolling and adhesion. Platelets may also contribute in a similar fashion. Lastly, the vasculature is also increasingly appreciated, as several studies have demonstrated increased endothelial expression of pro-coagulant and pro-adhesive proteins, such as von Willebrand factor or P-selectin in JAK2^V617F endothelial cells. With the advent of molecular diagnostics, MPN therapeutics are advancing beyond cytoreduction. Our increased understanding of pro-inflammatory and thrombotic pathophysiology in MPN provides a rational basis for evaluation of in-development MPN therapeutics to reduce thrombosis.

Current Methods of Post-Translational Modification Analysis and Their Applications in Blood Cancers

Post-translational modifications (PTMs) add a layer of complexity to the proteome through the addition of biochemical moieties to specific residues of proteins, altering their structure, function and/or localization. Mass spectrometry (MS)-based techniques are at the forefront of PTM analysis due to their ability to detect large numbers of modified proteins with a high level of sensitivity and specificity. The low stoichiometry of modified peptides means fractionation and enrichment techniques are often performed prior to MS to improve detection yields. Immuno-based techniques remain popular, with improvements in the quality of commercially available modification-specific antibodies facilitating the detection of modified proteins with high affinity. PTM-focused studies on blood cancers have provided information on altered cellular processes, including cell signaling, apoptosis and transcriptional regulation, that contribute to the malignant phenotype. Furthermore, the mechanism of action of many blood cancer therapies, such as kinase inhibitors, involves inhibiting or modulating protein modifications. Continued optimization of protocols and techniques for PTM analysis in blood cancer will undoubtedly lead to novel insights into mechanisms of malignant transformation, proliferation, and survival, in addition to the identification of novel biomarkers and therapeutic targets. This review discusses techniques used for PTM analysis and their applications in blood cancer research.

Protein Acetylation at the Interface of Genetics, Epigenetics and Environment in Cancer

Metabolic reprogramming is an emerging hallmark of cancer and is driven by abnormalities of oncogenes and tumor suppressors. Accelerated metabolism causes cancer cell aggression through the dysregulation of rate-limiting metabolic enzymes as well as by facilitating the production of intermediary metabolites. However, the mechanisms by which a shift in the metabolic landscape reshapes the intracellular signaling to promote the survival of cancer cells remain to be clarified. Recent high-resolution mass spectrometry-based proteomic analyses have spotlighted that, unexpectedly, lysine residues of numerous cytosolic as well as nuclear proteins are acetylated and that this modification modulates protein activity, sublocalization and stability, with profound impact on cellular function. More importantly, cancer cells exploit acetylation as a post-translational protein for microenvironmental adaptation, nominating it as a means for dynamic modulation of the phenotypes of cancer cells at the interface between genetics and environments. The objectives of this review were to describe the functional implications of protein lysine acetylation in cancer biology by examining recent evidence that implicates oncogenic signaling as a strong driver of protein acetylation, which might be exploitable for novel therapeutic strategies against cancer.

Epigenetic Dysregulation of Myeloproliferative Neoplasms

This article reviews the genetic data on epigenetic modifying mutations in myeloproliferative neoplasms and their clinical implications, preclinical studies exploring our current understanding of how mutations in epigenetic modifying proteins cooperate with myeloproliferative neoplasms drivers to promote disease progression, and recent advances in novel therapeutics supporting the role of targeting epigenetic pathways to treat fibrotic progression.

HDAC11 Regulates Glycolysis through the LKB1/AMPK Signaling Pathway to Maintain Hepatocellular Carcinoma Stemness

Hepatocellular carcinoma (HCC) contains a subset of cancer stem cells (CSC) that cause tumor recurrence, metastasis, and chemical resistance. Histone deacetylase 11 (HDAC11) mediates diverse immune functions and metabolism, yet little is known about its role in HCC CSCs. In this study, we report that HDAC11 is highly expressed in HCC and is closely related to disease prognosis. Depletion of HDAC11 in a conditional knockout mouse model reduced hepatocellular tumorigenesis and prolonged survival. Loss of HDAC11 increased transcription of LKB1 by promoting histone acetylation in its promoter region, thereby activating the AMPK signaling pathway and inhibiting the glycolysis pathway, which in turn leads to the suppression of cancer stemness and HCC progression. Furthermore, HDAC11 overexpression reduced HCC sensitivity to sorafenib. Collectively, these data propose HDAC11 as a new target for combination therapy in patients with kinase-resistant HCC. SIGNIFICANCE: This study finds that HDAC11 suppresses LKB1 expression in HCC to promote cancer stemness, progression, and sorafenib resistance, suggesting the potential of targeting HDAC11 to treat HCC and overcome kinase inhibitor resistance.

Metabolic Vulnerabilities and Epigenetic Dysregulation in Myeloproliferative Neoplasms

The Janus kinase 2 (JAK2)-driven myeloproliferative neoplasms (MPNs) are associated with clonal myelopoiesis, elevated risk of death due to thrombotic complications, and transformation to acute myeloid leukemia (AML). JAK2 inhibitors improve the quality of life for MPN patients, but these approved therapeutics do not readily reduce the natural course of disease or antagonize the neoplastic clone. An understanding of the molecular and cellular changes requisite for MPN development and progression are needed to develop improved therapies. Recently, murine MPN models were demonstrated to exhibit metabolic vulnerabilities due to a high dependence on glucose. Neoplastic hematopoietic progenitor cells in these mice express elevated levels of glycolytic enzymes and exhibit enhanced levels of glycolysis and oxidative phosphorylation, and the disease phenotype of these MPN model mice is antagonized by glycolytic inhibition. While all MPN-driving mutations lead to aberrant JAK2 activation, these mutations often co-exist with mutations in genes that encode epigenetic regulators, including loss of function mutations known to enhance MPN progression. In this perspective we discuss how altered activity of epigenetic regulators (e.g., methylation and acetylation) in MPN-driving stem and progenitor cells may alter cellular metabolism and contribute to the MPN phenotype and progression of disease. Specific metabolic changes associated with epigenetic deregulation may identify patient populations that exhibit specific metabolic vulnerabilities that are absent in normal hematopoietic cells, and thus provide a potential basis for the development of more effective personalized therapeutic approaches.

The Roles of Histone Deacetylases and Their Inhibitors in Cancer Therapy

Genetic mutations and abnormal gene regulation are key mechanisms underlying tumorigenesis. Nucleosomes, which consist of DNA wrapped around histone cores, represent the basic units of chromatin. The fifth amino group (Nε) of histone lysine residues is a common site for post-translational modifications (PTMs), and of these, acetylation is the second most common. Histone acetylation is modulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs), and is involved in the regulation of gene expression. Over the past two decades, numerous studies characterizing HDACs and HDAC inhibitors (HDACi) have provided novel and exciting insights concerning their underlying biological mechanisms and potential anti-cancer treatments. In this review, we detail the diverse structures of HDACs and their underlying biological functions, including transcriptional regulation, metabolism, angiogenesis, DNA damage response, cell cycle, apoptosis, protein degradation, immunity and other several physiological processes. We also highlight potential avenues to use HDACi as novel, precision cancer treatments.

Finding a Jill for JAK: Assessing Past, Present, and Future JAK Inhibitor Combination Approaches in Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm hallmarked by the upregulation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway with associated extramedullary hematopoiesis and a high burden of disease-related symptoms. While JAK inhibitor therapy is central to the management of MF, it is not without limitations. In an effort to improve treatment for MF patients, there have been significant efforts to identify combination strategies that build upon the substantial benefits of JAK inhibition. Early efforts to combine agents with additive therapeutic profiles have given way to rationally designed combinations hoping to demonstrate clinical synergism and modify the underlying disease. In this article, we review the preclinical basis and existing clinical data for JAK inhibitor combination strategies while highlighting emerging strategies of particular interest.

Histone Deacetylase 11 Knockdown Blocks Larval Development and Metamorphosis in the Red Flour Beetle, Tribolium castaneum

Post-translational modifications (PTM) such as methylation, acetylation, phosphorylation, and ubiquitination of histones and other proteins regulate expression of genes. The acetylation levels of these proteins are determined by the balance of expression of histone acetyltransferase (HATs) and histone deacetylases (HDACs). We recently reported that class I HDACs (HDAC1 and HDAC3) play important roles in juvenile hormone (JH) suppression of metamorphosis in the red flour beetle, Tribolium castaneum. Here, we report on the function of a single class IV HDAC member, HDAC11. Injection of dsRNA targeting T. castaneum HDAC11 gene into newly molted last instar larvae induced knockdown of the target gene and arrested larval development and prevented metamorphosis into the pupal stage. Dark melanized areas were detected in larvae that showed developmental arrest and mortality. Developmental expression studies showed an increase in HDAC11 mRNA levels beginning at the end of the penultimate larval stage. These higher levels were maintained during the final instar larval and pupal stages. A JH analog, hydroprene, suppressed HDAC11 expression in the larvae. Sequencing of RNA isolated from control and dsHDAC11 injected larvae identified several differentially expressed genes, including those involved in JH action, ecdysone response, and melanization. The acetylation levels of core histones showed an increase in TcA cells exposed to dsHDAC11. Also, an increase in histone H3 acetylation, specifically H3K9, H3K18 and H3K27, were detected in HDAC11 knockdown larvae. These studies report the function of HDAC11 in insects other than Drosophila for the first time and show that HDAC11 influences the acetylation levels of histones and expression of multiple genes involved in T. castaneum larval development.

Givinostat: an emerging treatment for polycythemia vera

INTRODUCTION

Polycythemia vera (PV), a Philadelphia chromosome-negative myeloproliferative neoplasm, is characterized by panmyelosis, pancytosis, and a JAK2 mutation. Patients are at increased risk of thrombohemorrhagic events, and progression to myelofibrosis or acute leukemia. Current treatments include aspirin, phlebotomy, and cytoreductive drugs (most commonly hydroxyurea). Givinostat is a potent, class I/II histone deacetylase (HDAC) inhibitor that is in phase I/II clinical trials in PV. Givinostat was well tolerated and yielded promising clinico-hematological responses. A phase III study of givinostat versus hydroxyurea in high-risk PV patients is planned.

AREAS COVERED

We present an overview of PV, current treatment guidelines, and the putative mechanism(s) of action of givinostat. We discuss the preclinical and clinical studies of givinostat in PV and briefly review approved and investigational competitor compounds.

EXPERT OPINION

HDAC inhibitors have long been known to be active in PV, but chronic toxicities can be challenging. Givinostat, however, is active and well tolerated, and is entering a pivotal Phase III randomized trial. Givinostat offers the possibility of replacing hydroxyurea as the standard first-line cytoreductive choice for PV patients. This would completely change the current therapeutic paradigm and guidelines for PV management. Although surrogate clinical study endpoints may suffice for regulatory purposes, thrombosis reduction and prevention of disease progression remain most important to patients and clinicians.

Histone deacetylase (HDAC) inhibitors in cancer: a patent review (2017-present)

Introduction: Histone deacetylase (HDAC) inhibitors play a crucial role in restoring the balance of acetylation and deacetylation of lysine residues of histones and non-histone proteins, which are applied to treat several diseases including cancer.Area covered: This review covers recent efforts in the synthesis and applications of inhibitors and hybrid inhibitors targeting HDAC from 2017 to 2019.Expert opinion: HDACs are important epigenetic targets and HDAC inhibitors have become important biologically active compounds for the treatment of cancers. Among the recent patents available, most of them place emphasis on HDAC selective inhibitors and multitarget HDAC inhibitors. Although great accomplishments have been achieved in developing HDAC selective inhibitors, there is still an urgent need for discovery of novel HDAC inhibitors with new zinc-binding groups avoiding the unfavorable pharmacokinetics profiles of hydroxamic acid. Apart from cancer therapy, HDAC inhibitors have recently been considered as a new strategy in treating other human diseases, such as alcohol use disorder (AUD), neurological disorders, age-related diseases, and so forth.