CKD-506, a novel HDAC6-selective inhibitor, improves renal outcomes and survival in a mouse model of systemic lupus erythematosus

Unveiling Novel Drug Targets and Emerging Therapies for Rheumatoid Arthritis: A Comprehensive Review

Rheumatoid arthritis (RA) is a chronic debilitating autoimmune disease, that causes joint damage, deformities, and decreased functionality. In addition, RA can also impact organs like the skin, lungs, eyes, and blood vessels. This autoimmune condition arises when the immune system erroneously targets the joint synovial membrane, resulting in synovitis, pannus formation, and cartilage damage. RA treatment is often holistic, integrating medication, physical therapy, and lifestyle modifications. Its main objective is to achieve remission or low disease activity by utilizing a "treat-to-target" approach that optimizes drug usage and dose adjustments based on clinical response and disease activity markers. The primary RA treatment uses disease-modifying antirheumatic drugs (DMARDs) that help to interrupt the inflammatory process. When there is an inadequate response, a combination of biologicals and DMARDs is recommended. Biological therapies target inflammatory pathways and have shown promising results in managing RA symptoms. Close monitoring for adverse effects and disease progression is critical to ensure optimal treatment outcomes. A deeper understanding of the pathways and mechanisms will allow new treatment strategies that minimize adverse effects and maintain quality of life. This review discusses the potential targets that can be used for designing and implementing precision medicine in RA treatment, spotlighting the latest breakthroughs in biologics, JAK inhibitors, IL-6 receptor antagonists, TNF blockers, and disease-modifying noncoding RNAs.

Advances in targeting histone deacetylase for treatment of solid tumors

Histone deacetylase (HDAC) serves as a critical molecular regulator in the pathobiology of various malignancies and have garnered attention as a viable target for therapeutic intervention. A variety of HDAC inhibitors (HDACis) have been developed to target HDACs. Many preclinical studies have conclusively demonstrated the antitumor effects of HDACis, whether used as monotherapy or in combination treatments. On this basis, researchers have conducted various clinical studies to evaluate the potential of selective and pan-HDACis in clinical settings. In our work, we extensively summarized and organized current clinical trials, providing a comprehensive overview of the current clinical advancements in targeting HDAC therapy. Furthermore, we engaged in discussions about several clinical trials that did not yield positive outcomes, analyzing the factors that led to their lack of anticipated therapeutic effectiveness. Apart from the experimental design factors, issues such as toxicological side effects, tumor heterogeneity, and unexpected off-target effects also contributed to these less-than-expected results. These challenges have naturally become significant barriers to the application of HDACis. Despite these challenges, we believe that advancements in HDACi research and improvements in combination therapies will pave the way or lead to a broad and hopeful future in the treatment of solid tumors.

Advanced Progress of Histone Deacetylases in Rheumatic Diseases

Rheumatic disease is a disease which is not yet fully clarified to etiology and also involved in a local pathological injury or systemic disease. With the continuous improvement of clinical medical research in recent years, the development process of rheumatic diseases has been gradually elucidated; with the intensely study of epigenetics, it is realized that environmental changes can affect genetics, among which histone acetylation is one of the essential mechanisms in epigenetics. Histone deacetylases (HDACs) play an important role in regulating gene expression in various biological processes, including differentiation, development, stress response, and injury. HDACs are involved in a variety of physiological processes and are promising drug targets in various pathological conditions, such as cancer, cardiac and neurodegenerative diseases, inflammation, metabolic and immune disorders, and viral and parasitic infections. In this paper, we reviewed the roles of HDACs in rheumatic diseases in terms of their classification and function.

Epigenetic mechanisms driving the pathogenesis of systemic lupus erythematosus, systemic sclerosis and dermatomyositis

Autoimmune connective tissue disorders, including systemic lupus erythematosus, systemic sclerosis (SSc) and dermatomyositis (DM), often manifest with debilitating cutaneous lesions and can result in systemic organ damage that may be life-threatening. Despite recent therapeutic advancements, many patients still experience low rates of sustained remission and significant treatment toxicity. While genetic predisposition plays a role in these connective tissue disorders, the relatively low concordance rates among monozygotic twins (ranging from approximately 4% for SSc to about 11%-50% for SLE) have prompted increased scrutiny of the epigenetic factors contributing to these diseases. In this review, we explore some seminal studies and key findings to provide a comprehensive understanding of how dysregulated epigenetic mechanisms can contribute to the development of SLE, SSc and DM.

Identification of new candidate drugs for primary Sjögren's syndrome using a drug repurposing transcriptomic approach

OBJECTIVES

To date, no immunomodulatory drug has demonstrated its efficacy in primary SS (pSS). We sought to analyse potential commonalities between pSS transcriptomic signatures and signatures of various drugs or specific knock-in or knock-down genes.

METHODS

Gene expression from peripheral blood samples of patients with pSS was compared with that of healthy controls in two cohorts and three public databases. In each of the five datasets, we analysed the 150 most up- and downregulated genes between pSS patients and controls with regard to the differentially expressed genes resulting from the biological action on nine cell lines of 2837 drugs, 2160 knock-in and 3799 knock-down genes in the Connectivity Map database.

RESULTS

We analysed 1008 peripheral blood transcriptomes from five independent studies (868 patients with pSS and 140 healthy controls). Eleven drugs could represent potential candidate drugs, with histone deacetylases and PI3K inhibitors among the most significantly associated. Twelve knock-in genes were associated with a pSS-like profile and 23 knock-down genes were associated with a pSS-revert profile. Most of those genes (28/35, 80%) were interferon-regulated.

CONCLUSION

This first drug repositioning transcriptomic approach in SS confirms the interest of targeting interferons and identifies histone deacetylases and PI3K inhibitors as potential therapeutic targets.

Exosomes derived from mesenchymal stem cells primed with disease-condition-serum improved therapeutic efficacy in a mouse rheumatoid arthritis model via enhanced TGF-β1 production

BACKGROUNDS

Rheumatoid arthritis (RA) is a chronic and systemic autoimmune disease characterized by synovial inflammation-mediated progressive destruction of the cartilage and bone, resulting in reduced quality of life. We primed human telomerase reverse transcriptase-overexpressing immortalized human adipose tissue-derived mesenchymal stem cells (iMSCs) with serum derived from a non-human primate RA model and studied the immunomodulatory ability of exosomes obtained from primed iMSCs.

METHODS

After immunophenotyping, nanoparticle tracking analysis, and in vitro functional tests, Dulbecco's phosphate-buffered saline (dPBS, Group C), exosomes derived from the supernatant of iMSCs (Exo-FBS, Group E), exosomes derived from the supernatant of iMSCs primed with RA serum (Exo-RA, Group F), and methotrexate (Group M) were administered in collagen-induced arthritis (CIA) model mice. dPBS was administered to the normal (N) group for comparison (n = 10/group).

RESULTS

Exo-RA had a significantly higher number of exosomes compared to Exo-FBS when measured with nanoparticle tracking analysis or exosome marker CD81, and Transforming growth factor-β1 amounts were significantly higher in Exo-RA than in Exo-FBS. When Exo-FBS or Exo-RA was administered to the collagen-induced arthritis model, serum interleukin (IL)-4 and the proportion of Th2 (CD4+CD25+GATA3+) and M2 (CD11c - CD206+ of CD45+CD64+) cells were significantly increased compared to the control group. Furthermore, Exo-RA could alleviate cartilage damage by significantly lowering the concentrations of proinflammatory cytokines such as tumor necrosis factor-α, keratinocyte chemoattractant, and IL-12p70.

CONCLUSION

Exosomes derived from disease-condition-serum-primed iMSCs ameliorated cartilage damage in a RA model by enhancing TGF-β1 production, inducing Th2 and M2 polarization and lowering proinflammatory cytokines, TNF-α, KC, and IL-12p70 in the host. Patient-derived serum can be used as an iMSC priming strategy in iMSC-derived exosome treatment of RA.

Novel Histone Deacetylase 6 Inhibitor Confers Anti-inflammatory Effects and Enhances Gut Barrier Function

Background/Aims

The purpose of the current study was to examine the anti-inflammatory effects of CKD-506, a novel histone deacetylase 6 inhibitor, on human peripheral blood mononuclear cells (PBMCs) and CD4+ T cells and to explore the relationship between CKD-506 and gut epithelial barrier function.

Methods

Lipopolysaccharide-stimulated human PBMCs from inflammatory bowel disease (IBD) patients were treated with CKD-506, and tumor necrosis factor (TNF)-α expression was measured using an enzyme-linked immunosorbent assay. The proliferation of CD4+ T cells from IBD patients was evaluated using flow cytometric analysis. The effects of CKD-506 on gut barrier function in a cell line and colon organoids, based on examinations of mRNA production, goblet cell differentiation, and E-cadherin recovery, were investigated using quantitative reverse transcription polymerase chain reaction, immunofluorescence, and a fluorescein isothiocyanate-dextran permeability assay.

Results

Secretion of TNF-α, a pivotal pro-inflammatory mediator in IBD, by lipopolysaccharide-triggered PBMCs was markedly decreased by CKD-506 treatment in a dose-dependent manner and to a greater extent than by tofacitinib or tubastatin A treatment. E-cadherin mRNA expression and goblet cell differentiation increased significantly and dose-dependently in HT-29 cells in response to CKD-506, and inhibition of E-cadherin loss after TNF-α stimulation was significantly reduced both in HT-29 cells and gut organoids. Caco-2 cells treated with CKD-506 showed a significant reduction in barrier permeability in a dose-dependent manner.

Conclusions

The present study demonstrated that CKD-506 has anti-inflammatory effects on PBMCs and CD4 T cells and improves gut barrier function, suggesting its potential as a small-molecule therapeutic option for IBD.

HDAC6 inhibition: a significant potential regulator and therapeutic option to translate into clinical practice in renal transplantation

Histone deacetylase 6 (HDAC6), an almost exclusively cytoplasmic enzyme, plays an essential role in many biological processes and exerts its deacetylation-dependent/independent effects on a variety of target molecules, which has contributed to the flourishing growth of relatively isoform-specific enzyme inhibitors. Renal transplantation (RT) is one of the alternatively preferred treatments and the most cost-effective treatment approaches for the great majority of patients with end-stage renal disease (ESRD). HDAC6 expression and activity have recently been shown to be increased in kidney disease in a number of studies. To date, a substantial amount of validated studies has identified HDAC6 as a pivotal modulator of innate and adaptive immunity, and HDAC6 inhibitors (HDAC6i) are being developed and investigated for use in arrays of immune-related diseases, making HDAC6i a promising therapeutic candidate for the management of a variety of renal diseases. Based on accumulating evidence, HDAC6i markedly open up new avenues for therapeutic intervention to protect against oxidative stress-induced damage, tip the balance in favor of the generation of tolerance-related immune cells, and attenuate fibrosis by inhibiting multiple activations of cell profibrotic signaling pathways. Taken together, we have a point of view that targeting HDAC6 may be a novel approach for the therapeutic strategy of RT-related complications, including consequences of ischemia-reperfusion injury, induction of immune tolerance in transplantation, equilibrium of rejection, and improvement of chronic renal graft interstitial fibrosis after transplantation in patients. Herein, we will elaborate on the unique function of HDAC6, which focuses on therapeutical mechanism of action related to immunological events with a general account of the tantalizing potential to the clinic.

Prevention of Atrial Fibrillation: Putting Proteostasis Derailment Back on Track

Despite the many attempts to treat atrial fibrillation (AF), the most common cardiac tachyarrhythmia in the Western world, the treatment efficacy of AF is still suboptimal. A plausible reason for the suboptimal efficacy is that the current treatments are not directed at the underlying molecular mechanisms that drive AF. Recent discoveries revealed that the derailment of specific molecular proteostasis pathways drive electrical conduction disorders, contractile dysfunction and AF. The degree of this so-called 'electropathology' corresponds to the response to anti-AF treatment. Hence, to develop effective therapies to prevent AF, understanding the molecular mechanisms is of key importance. In this review, we highlight the key modulators of proteostasis derailment and describe the mechanisms that explain how they affect electrical and contractile function in atrial cardiomyocytes and AF. The key modulators of proteostasis derailment include (1) exhaustion of cardioprotective heat shock proteins (HSPs), (2) excessive endoplasmic reticulum (ER) stress and downstream autophagic protein degradation, (3) histone deacetylase 6 (HDAC6)-induced microtubule disruption, (4) activation of DNA damage-PARP1 activation and NAD⁺ axis and (5) mitochondrial dysfunction. Furthermore, we discuss druggable targets within these pathways that are involved in the prevention of proteostasis derailment, as well as the targets that aid in the recovery from AF. Finally, we will elaborate on the most favorable druggable targets for (future) testing in patients with AF, as well as drugs with potential benefits for AF recovery.

Design, synthesis, and anti-inflammatory activity characterization of novel brain-permeable HDAC6 inhibitors

Targeting histone deacetylase 6 (HDAC6) has emerged as a promising therapeutic approach for anti-inflammation and related biological pathways, including inflammatory events associated with the brain. In this study, in order to develop brain-permeable HDAC6 inhibitors for anti-neuroinflammation, we report here the design, synthesis, and characterization of a number of N-heterobicyclic analogues that can inhibit HDAC6 with high specificity and strong potency. Among our analogues, PB131 exhibits potent binding affinity and selectivity against HDAC6, with an IC50 value of 1.8 nM and more than 116-fold selectivity over other HDAC isoforms. In addition, PB131 shows good brain penetration, binding specificity, and reasonable biodistribution through our positron emission tomography (PET) imaging studies of [18F]PB131 in mice. Furthermore, we characterized the efficacy of PB131 on regulating neuroinflammation using the mouse microglia model BV2 cells in vitro and the LPS-induced inflammation mouse model in vivo. These data not only indicate the anti-inflammatory activity of our novel HDAC6 inhibitor PB131, but also strengthen the biological functions of HDAC6 and further extend the therapeutic approach inhibiting HDAC6. Our findings show that PB131 displays good brain permeability, high specificity, and strong potency toward inhibiting HDAC6 and is a potential HDAC6 inhibitor for inflammation-related disease treatment, especially neuroinflammation.

Effects of high fat diet-induced obesity on pathophysiology, immune cells, and therapeutic efficacy in systemic lupus erythematosus

Prior studies have suggested a strong link between obesity and autoimmune diseases. This study aimed to evaluate the effects of high fat diet (HFD)-induced obesity on the disease pathogenesis, immune cell infiltration, and therapeutic efficacy in systemic lupus erythematosus (SLE). Treatment with methylprednisolone significantly increased the survival in the control diet group, but not in the HFD group. An HFD significantly increased the incidence of severe proteinuria and glucose intolerance. Regardless of the diet, treatment with methylprednisolone significantly decreased the serum levels of anti-dsDNA antibodies, IL-2, IL-10, and interferon γ-induced protein 10 (IP-10), and improved the renal pathology scores. Treatment with methylprednisolone significantly lowered the serum levels of IL-6, MCP-1, and TNF-α in the control diet group, but not in the HFD group. HFD significantly increased the proportions of CD45⁺ and M1 cells and significantly decreased the proportion of M2 cells in white adipose tissue; methylprednisolone treatment significantly rescued this effect. In the HFD group, methylprednisolone treatment significantly decreased the M1:M2 and increased the Foxp3⁺:RORγt⁺ cell in the spleen compared with the untreated group. These data improve our understanding of the effect of HFD on the therapeutic efficacy of corticosteroids in SLE treatment, which could have clinical implications.

First-in-Class Hydrazide-Based HDAC6 Selective Inhibitor with Potent Oral Anti-Inflammatory Activity by Attenuating NLRP3 Inflammasome Activation

In this study, we report the first highly selective HDAC6 inhibitor with hydrazide as the zinc-binding group (ZBG), which displays superior pharmacokinetic properties to the current hydroxamic acid inhibitors. Structure-activity relationship study reveals that ethyl group substituent hydrazide-based ZBG and cap group with more substantial rigidity and larger volume increase the HDAC6 selectivity of designed compounds. Representative inhibitor 35m exhibits potent HDAC6 inhibitory activity with an IC₅₀ value of 0.019 μM. To our surprise, 35m establishes significant improvement in the pharmacokinetic property with much higher AUC_0-inf (10292 ng·h/mL) and oral bioavailability (93.4%) than hydroximic acid-based HDAC6 inhibitors Tubastatin A and ACY-1215. Low-dose 35m remarkably decreases LPS-induced IL-1β release both in vitro and in vivo by blocking the activation of NLRP3, indicating that 35m can be a potential orally active therapeutic agent for the treatment of NLRP3-related diseases.

Design of Fluorogenic Probe Based on Intramolecular Condensation for Specific Detection of HDAC3

It is crucial to develop fluorogenic probes for selective targeting of HDACs to explore the roles of HDACs in the tumor onset and progression as well as HDAC-related drug development. However, considerable non-specific signals were produced by spontaneous hydrolysis and undesirable intermolecular attack of the unstable caging moiety in the detection of HDACs with previous probes. To improve the detection specificity, we proposed an intramolecular condensation strategy by the replacement of the traditional acetamide moiety with a trans-enamide unit. Upon deacetylation by HDACs, rapid intramolecular condensation reaction between newly formed terminal aldehyde and hydrazine moiety would occur to afford highly fluorescent hydrazone product. Systematic studies demonstrated that the probe exhibited an extraordinary selectivity for HDAC3 over other HDAC isoforms and interfering substances. The stability and specificity of the indicator make it a powerful tool for HDAC3 activity detection and HDAC3-related drug development.

Role of Selective Histone Deacetylase 6 Inhibitor ACY-1215 in Cancer and Other Human Diseases

The deacetylation process regulated by histone deacetylases (HDACs) plays an important role in human health and diseases. HDAC6 belongs to the Class IIb of HDACs family, which mainly modifies non-histone proteins located in the cytoplasm. HDAC6 plays a key role in tumors, neurological diseases, and inflammatory diseases. Therefore, targeting HDAC6 has become a promising treatment strategy in recent years. ACY-1215 is the first orally available highly selective HDAC6 inhibitor, and its efficacy and therapeutic effects are being continuously verified. This review summarizes the research progress of ACY-1215 in cancer and other human diseases, as well as the underlying mechanism, in order to guide the future clinical trials of ACY-1215 and more in-depth mechanism researches.

Chasing a Breath of Fresh Air in Cystic Fibrosis (CF): Therapeutic Potential of Selective HDAC6 Inhibitors to Tackle Multiple Pathways in CF Pathophysiology

Compelling new support has been provided for histone deacetylase isoform 6 (HDAC6) as a common thread in the generation of the dysregulated proinflammatory and fibrotic phenotype in cystic fibrosis (CF). HDAC6 also plays a crucial role in bacterial clearance or killing as a direct consequence of its effects on CF immune responses. Inhibiting HDAC6 functions thus eventually represents an innovative and effective strategy to tackle multiple aspects of CF-associated lung disease. In this Perspective, we not only showcase the latest evidence linking HDAC(6) activity and expression with CF phenotype but also track the new dawn of HDAC(6) modulators in CF and explore potentialities and future perspectives in the field.

Histone Deacetylase Isoforms Differentially Modulate Inflammatory and Autoantibody Responses in a Mouse Model of Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease characterized by chronic muscle fatigue and weakness caused by autoantibodies and complement-mediated damage at neuromuscular junctions. Histone deacetylases (HDACs) are crucial epigenetic regulators of proinflammatory gene expression; however, it is unclear whether HDACs modulate chronic inflammation or autoantibody production associated with MG pathogenesis. We examined expression profiles and serum levels of key inflammatory cytokines (IL-6 and IL-21) and acetylcholine receptor (AChR)-specific autoantibodies following pharmacological inhibition of key HDAC isoforms in a mouse model of MG. We found that HDAC inhibition significantly reduced the production of IL-6, but not IL-21, in AChR-stimulated PBMCs and splenocytes (n = 5 per group). Trichostatin (pan-HDAC inhibitor) treatment of MG-PBMCs (n = 2) also exhibited reduced production of induced IL-6. Although HDAC1 inhibition lowered IL-6 levels the most, HDAC2 inhibition depleted intracellular IL-6 and markedly reduced serum anti-AChR IgG2b in EAMG mice. The transcriptomic profiling and pathway mapping also revealed that autoimmunity-linked, major cell signaling pathways were differentially altered by HDAC1/2 inhibition. HDAC inhibition-mediated reduction in IL-6 and autoantibody levels also correlated with milder disease and preservation of muscle AChR in the treated mice. Overall, our findings revealed isoform-specific functional variance of HDACs in reducing inflammation and identified HDAC-regulated many genes underlying specific inflammatory and autoantibody pathways in EAMG. Thus, the study provides a rationale for further research to evaluate the HDACs or their gene targets as a potential adjunct treatment for MG.

Advances in therapeutic targets-related study on systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic and autoimmunity-mediated diffuse connective tissue disease. The mainstay of treatments for SLE mainly relies on corticosteroids and immunosuppressants, which have a series of unavoidable side effects. Therefore, it is of fundamental importance to search novel therapeutic targets for better treatment with favorable efficacy and minor side effects. Recent studies shed light on potential therapeutic targets for SLE, mainly covering the followings: B-cell/plasmocyte-related targets [B cell activating factor (BAFF), a proliferation-inducing ligand (APRIL), CD20, CD22, CD19/FcγRIIb, Bruton tyrosine kinase (Btk), and proteasome], T cell-related targets [calcineurin, mammalian target of rapamycin (mTOR), regulatory factor X1 (RFX1), and Rho kinase], macrophage-related targets (macrophage migration inhibitory factor), intracellular signaling molecules, cytokines (cereblon, histone deacetylase 6, Janus activated kinase/signal transducer and activator of transcription), co-stimulating factors (CD28/B7, CD40/CD154), IgE autoantibody, and gut microbiome. Among them, belimumab (a humanized monoclonal antibody against B-lymphocyte stimulator) and telitacicept (a recombinant human B-lymphocyte stimulator receptor-antibody fusion protein) have been sequentially approved for the clinical treatment of SLE in China. A variety of new targeted-therapy drugs are in the Phase 2 or Phase 3 clinical trials,among which anifrolumab (a human monoclonal antibody against type I interferon receptor subunit 1) has completed a Phase 3 clinical trial with good responses achieved, although its incidence of herpes zoster is higher than that in the control group. The research progress in both molecular mechanisms and new drug development for different therapeutic targets have greatly promoted our better and in-depth understanding of the pathogenesis of SLE, and have also reflected the complexity and heterogeneity of the disease. Successful development and clinical application of more novel therapies would no doubt usher in a new era of individualized treatment for SLE in the future.

Epigenetics in kidney diseases

Epigenetics examines heritable changes in DNA and its associated proteins except mutations in gene sequence. Epigenetic regulation plays fundamental roles in kidney cell biology through the action of DNA methylation, chromatin modification via epigenetic regulators and non-coding RNA species. Kidney diseases, including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis are multistep processes associated with numerous molecular alterations even in individual kidney cells. Epigenetic alterations, including anomalous DNA methylation, aberrant histone alterations and changes of microRNA expression all contribute to kidney pathogenesis. These changes alter the genome-wide epigenetic signatures and disrupt essential pathways that protect renal cells from uncontrolled growth, apoptosis and development of other renal associated syndromes. Molecular changes impact cellular function within kidney cells and its microenvironment to drive and maintain disease phenotype. In this chapter, we briefly summarize epigenetic mechanisms in four kidney diseases including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis. We primarily focus on current knowledge about the genome-wide profiling of DNA methylation and histone modification, and epigenetic regulation on specific gene(s) in the pathophysiology of these diseases and the translational potential of identifying new biomarkers and treatment for prevention and therapy. Incorporating epigenomic testing into clinical research is essential to elucidate novel epigenetic biomarkers and develop precision medicine using emerging therapies.

Epigenetic linkage of systemic lupus erythematosus and nutrition

The term "epigenetics" refers to a series of meiotically/mitotically inheritable alterations in gene expression, related to environmental factors, without disruption on DNA sequences of bases. Recently, the pathophysiology of autoimmune diseases (ADs) has been closely linked to epigenetic modifications. Actually, epigenetic mechanisms can modulate gene expression or repression of targeted cells and tissues involved in autoimmune/inflammatory conditions acting as keys effectors in regulation of adaptive and innate responses. ADs, as systemic lupus erythematosus (SLE), a rare disease that still lacks effective treatment, is characterized by epigenetic marks in affected cells.Taking into account that epigenetic mechanisms have been proposed as a winning strategy in the search of new more specific and personalized therapeutics agents. Thus, pharmacology and pharmacoepigenetic studies about epigenetic regulations of ADs may provide novel individualized therapies. Focussing in possible implicated factors on development and predisposition of SLE, diet is feasibly one of the most important factors since it is linked directly to epigenetic alterations and these epigenetic changes may augment or diminish the risk of SLE. Nevertheless, several studies have guaranteed that dietary therapy could be a promise to SLE patients via prophylactic actions deprived of side effects of pharmacology, decreasing co-morbidities and improving lifestyle of SLE sufferers.Herein, we review and discuss the cross-link between epigenetic mechanisms on SLE predisposition and development, as well as the influence of dietary factors on regulation epigenetic modifications that would eventually make a positive impact on SLE patients.

A Patent Review on the Current Developments of Benzoxazoles in Drug Discovery

The benzoxazole moiety is widely found in various natural compounds, which are often found to be biologically active. Due to its versatile biological properties, benzoxazole has been incorporated as an essential pharmacophore and substructure in many medicinal compounds. In the past years, numerous benzoxazole derivatives have been synthesised and evaluated for their biological potential. The wide range in therapeutic potential of benzoxazole derivatives is related to the favourable interactions of the benzoxazole moiety with different protein targets. Herein we review the biological activities of benzoxazole derivatives patented within the past six years. Using the Lens database, granted patents issued from 2015 to 2020 were retrieved. The patented benzoxazole derivatives demonstrated excellent activity against various protein targets and diseases, with some reaching clinical trial stage. Pharmacological and medicinal aspects of patented benzoxazole derivatives are discussed. The recent development and drawbacks are also reviewed.

CKD-506: A novel HDAC6-selective inhibitor that exerts therapeutic effects in a rodent model of multiple sclerosis

Despite advances in therapeutic strategies for multiple sclerosis (MS), the therapy options remain limited with various adverse effects. Here, the therapeutic potential of CKD-506, a novel HDAC6-selective inhibitor, against MS was evaluated in mice with myelin oligodendrocyte glycoprotein35-55 (MOG35-55)-induced experimental autoimmune encephalitis (EAE) under various treatment regimens. CKD-506 exerted prophylactic and therapeutic effects by regulating peripheral immune responses and maintaining blood-brain barrier (BBB) integrity. In MOG35-55-re-stimulated splenocytes, CKD-506 decreased proliferation and downregulated the expression of IFN-γ and IL-17A. CKD-506 downregulated the levels of pro-inflammatory cytokines in the blood of EAE mice. Additionally, CKD-506 decreased the leakage of intravenously administered Evans blue into the spinal cord; CD4+ T cells and CD4-CD11b+CD45+ macrophage/microglia in the spinal cord was also decreased. Moreover, CKD-506 exhibited therapeutic efficacy against MS, even when drug administration was discontinued from day 15 post-EAE induction. Disease exacerbation was not observed when fingolimod was changed to CKD-506 from day 15 post-EAE induction. CKD-506 alleviated depression-like behavior at the pre-symptomatic stage of EAE. In conclusion, CKD-506 exerts therapeutic effects by regulating T cell- and macrophage-mediated peripheral immune responses and strengthening BBB integrity. Our results suggest that CKD-506 is a potential therapeutic agent for MS.

Chronic HDAC6 Activation Induces Atrial Fibrillation Through Atrial Electrical and Structural Remodeling in Transgenic Mice

Atrial fibrillation (AF) is a relatively common complication of hypertension. Chronic hypertension induces cardiac HDAC6 catalytic activity. However, whether HDAC6 activation contributes to hypertension-induced AF is still uncertain. We examined whether chronic cardiac HDAC6 activation-induced atrial remodeling, leading to AF induction.The HDAC6 constitutively active transgenic (TG) (HDAC6 active TG) mouse overexpressing the active HDAC6 protein, specifically in cardiomyocytes, was created to examine the effects of chronic HDAC6 activation on atrial electrical and structural remodeling and AF induction in HDAC6 active TG and non-transgenic (NTG) mice. Left atrial burst pacing (S₁S₁ = 30 msec) for 15-30 sec significantly increased the frequency of sustained AF in HDAC6 active-TG mice compared with NTG mice. Left steady-state atrial pacing (S₁S₁ = 80 msec) decreased the atrial conduction velocity in isolated HDAC6 active TG compared with NTG mouse atria. The atrial size was similar between HDAC6 active TG and NTG mice. In contrast, atrial interstitial fibrosis increased in HDAC6 active TG compared with that of NTG mouse atria. While protein expression levels of both CX40 and CX43 were similar between HDAC6 active TG and NTG mouse atria, a heterogeneous distribution of CX40 and CX43 occurred in HDAC6 active-TG mouse atria but not in NTG mouse atria. Gene expression of interleukin 6 increased in HDAC6 active TG compared with NTG mouse atria.Chronic cardiac HDAC6 activation induced atrial electrical and structural remodeling, and sustained AF. Hypertension-induced cardiac HDAC6 catalytic activity may play important roles in the development of AF.

Correlation analysis between expression of histone deacetylase 6 and clinical parameters in IgA nephropathy patients

Background

It has been demonstrated that histone deacetylase 6 (HDAC6) is involved in various kidney diseases in experimental study. However, correlation between HDAC6 and clinical parameters in IgA nephropathy (IgAN) patients is still unknown.

Methods

A total of 46 human kidney biopsy specimens with IgAN were selected as observation group, specimens of normal renal cortex tissue that was not affected by the tumor from patients with renal carcinoma (n = 7) served as control. We investigated the relationship between HDAC6 and clinical parameters in IgAN.

Results

HDAC6 was highly expressed in human kidney biopsy specimens with IgAN compared with control group, while the number of acetyl histone H3 positive cells were significantly decreased. There was a statistical difference in the indexes of albumin, estimated glomerular filtration rate (eGFR), serum urea, serum creatinine, serum uric acid, β2-microglobulin, cystatin C, cholesterol, high-density lipoprotein, low-density lipoprotein, and HDAC6 positive area among the different Oxford Classification (p < 0.05). The expression of HDAC6 was different in various eGFR levels, the expression of HDAC6 increased with the decreasing of eGFR level, the expression of acetyl histone H3 decreased with the decreasing of eGFR level. In addition, the expression of HDAC6 positively correlated with Masson trichrome positive area, serum urea, serum creatinine, β2 macroglobulin, and cystatin C, while negatively correlated with eGFR and acetyl histone H3. Multivariate linear regression analysis demonstrated that eGFR and cystatin C were independently associated with HDAC6, respectively (p < 0.05).

Conclusions

These results suggested that high level of HDAC6 expression in IgAN is correlated with renal dysfunction.

Selective Targeting of Epigenetic Readers and Histone Deacetylases in Autoimmune and Inflammatory Diseases: Recent Advances and Future Perspectives

Histone deacetylases (HDACs) and bromodomain-containing proteins (BCPs) play a key role in chromatin remodeling. Based on their ability to regulate inducible gene expression in the context of inflammation and cancer, HDACs and BCPs have been the focus of drug discovery efforts, and numerous small-molecule inhibitors have been developed. However, dose-limiting toxicities of the first generation of inhibitors, which typically target multiple HDACs or BCPs, have limited translation to the clinic. Over the last decade, an increasing effort has been dedicated to designing class-, isoform-, or domain-specific HDAC or BCP inhibitors, as well as developing strategies for cell-specific targeted drug delivery. Selective inhibition of the epigenetic modulators is helping to elucidate the functions of individual epigenetic proteins and has the potential to yield better and safer therapeutic strategies. In accordance with this idea, several in vitro and in vivo studies have reported the ability of more selective HDAC/BCP inhibitors to recapitulate the beneficial effects of pan-inhibitors with less unwanted adverse events. In this review, we summarize the most recent advances with these strategies, discussing advantages and limitations of these approaches as well as some therapeutic perspectives, focusing on autoimmune and inflammatory diseases.

m6A RNA Methylation in Systemic Autoimmune Diseases-A New Target for Epigenetic-Based Therapy?

The general background of autoimmune diseases is a combination of genetic, epigenetic and environmental factors, that lead to defective immune reactions. This erroneous immune cell activation results in an excessive production of autoantibodies and prolonged inflammation. During recent years epigenetic mechanisms have been extensively studied as potential culprits of autoreactivity. Alike DNA and proteins, also RNA molecules are subjected to an extensive repertoire of chemical modifications. N6-methyladenosine is the most prevalent form of internal mRNA modification in eukaryotic cells and attracts increasing attention due to its contribution to human health and disease. Even though m6A is confirmed as an essential player in immune response, little is known about its role in autoimmunity. Only few data have been published up to date in the field of RNA methylome. Moreover, only selected autoimmune diseases have been studied in respect of m6A role in their pathogenesis. In this review, I attempt to present all available research data regarding m6A alterations in autoimmune disorders and appraise its role as a potential target for epigenetic-based therapies.

Endothelial dysfunction and cardiovascular risk in lupus nephritis: New roles for old players?

In systemic lupus erythematosus (SLE) patients, most of the clinical manifestation share a vascular component triggered by endothelial dysfunction. Endothelial cells (ECs) activation occurs both on the arterial and venous side, and the high vascular density of kidneys accounts for the detrimental outcomes of SLE through lupus nephritis (LN). Kidney damage, in turn, exerts a negative feedback on the cardiovascular (CV) system aggravating risk factors for CV diseases such as hypertension, stroke and coronary syndrome among others. Despite the intensive investigation on SLE and LN, the role of endothelial dysfunction, as well as the underlying mechanisms, remains to be fully understood, with no specifically targeted pharmacological treatment. It is not known, in fact, if the activation pathway(s) in venous ECs are similar to the one in arterial ECs and doubts persist on the shared manifestation of microcirculation compared to macrocirculation. In this work, we aim to review the recent literature about the role of endothelial activation and dysfunction in the development of CV complications in SLE and LN patients. We, therefore, focus on arteriovenous similarities and differences and on specific pathways of great vessels compared to capillaries. Critically summarising the available data is of pivotal importance for both basic researchers and clinicians in order to develop and test new pharmacological approaches in the treatment of basic components of SLE and LN.

Novel Selective Histone Deacetylase 6 (HDAC6) Inhibitors: A Patent Review (2016-2019)

BACKGROUND

Many human diseases are associated with dysregulation of HDACs. HDAC6 exhibits deacetylase activity not only to histone protein but also to non-histone proteins such as α- tubulin, HSP90, cortactin, and peroxiredoxin. These unique functions of HDAC6 have gained significant attention in the medicinal chemistry community in recent years. Thus a great deal of effort has devoted to developing selective HDAC6 inhibitors for therapy with the hope to minimize the side effects caused by pan-HDAC inhibition.

OBJECTIVE

The review intends to analyze the structural feature of the scaffolds, to provide useful information for those who are interested in this field, as well as to spark the future design of the new inhibitors.

METHODS

The primary tool used for patent searching is SciFinder. All patents are retrieved from the following websites: the World Intellectual Property Organization (WIPO®), the United States Patent Trademark Office (USPTO®), Espacenet®, and Google Patents. The years of patents covered in this review are between 2016 and 2019.

RESULTS

Thirty-six patents from seventeen companies/academic institutes were classified into three categories based on the structure of ZBG: hydroxamic acid, 1,3,4-oxadiazole, and 1,2,4-oxadiazole. ZBG connects to the cap group through a linker. The cap group can tolerate different functional groups, including amide, urea, sulfonamide, sulfamide, etc. The cap group appears to modulate the selectivity of HDAC6 over other HDAC subtypes.

CONCLUSION

Selectively targeting HDAC6 over other subtypes represents two fold advantages: it maximizes the pharmacological effects and minimizes the side effects seen in pan-HDAC inhibitors. Many small molecule selective HDAC6 inhibitors have advanced to clinical studies in recent years. We anticipate the approval of selective HDAC6 inhibitors as therapeutic agents in the near future.

Recent Advances in Lupus B Cell Biology: PI3K, IFNγ, and Chromatin

In the autoimmune disease Systemic Lupus Erythematosus (SLE), autoantibodies are formed that promote inflammation and tissue damage. There has been significant interest in understanding the B cell derangements involved in SLE pathogenesis. The past few years have been particularly fruitful in three domains: the role of PI3K signaling in loss of B cell tolerance, the role of IFNγ signaling in the development of autoimmunity, and the characterization of changes in chromatin accessibility in SLE B cells. The PI3K pathway coordinates various downstream signaling molecules involved in B cell development and activation. It is governed by the phosphatases PTEN and SHIP-1. Murine models lacking either of these phosphatases in B cells develop autoimmune disease and exhibit defects in B cell tolerance. Limited studies of human SLE B cells demonstrate reduced expression of PTEN or increased signaling events downstream of PI3K in some patients. IFNγ has long been known to be elevated in both SLE patients and mouse models of lupus. New data suggests that IFNγR expression on B cells is required to develop autoreactive germinal centers (GC) and autoantibodies in murine lupus. Furthermore, IFNγ promotes increased transcription of BCL6, IL-6 and T-bet in B cells, which also promote GC and autoantibody formation. IFNγ also induces epigenetic changes in human B cells. SLE B cells demonstrate significant epigenetic reprogramming, including enhanced chromatin accessibility at transcription factor motifs involved in B cell activation and plasma cell (PC) differentiation as well as alterations in DNA methylation and histone modifications. Histone deacetylase inhibitors limit disease development in murine lupus models, at least in part via their ability to prevent B cell class switching and differentiation into plasma cells. This review will discuss relevant discoveries of the past several years pertaining to these areas of SLE B cell biology.

M-134, a novel HDAC6-selective inhibitor, markedly improved arthritic severity in a rodent model of rheumatoid arthritis when combined with tofacitinib

BACKGROUND

Although tofacitinib has shown highly significant efficacy for rheumatoid arthritis (RA), there are still a considerable number of patients that are non-responders owing to its limited effectiveness and various adverse effects. Thus, alternative options with better efficacy and lower toxicity are desired. Here, M-134, a recently developed HDAC6 inhibitor, was examined for its therapeutic potential when combined with tofacitinib in a rat model of RA.

METHODS

The single or combined administration of M-134 and tofacitinib was examined in complete Freund's adjuvant-induced arthritis (AIA) or collagen-induced arthritis (CIA) rodent models. To evaluate the therapeutic and adverse effects, the following factors were observed: macroscopic or microscopic scoring of all four paws; the expression of ICAM-1, VCAM-1, and IP-10 in the joints and that of various cytokines and chemokines in the plasma; the weight of the thymus and the liver; and changes in hematological enzymes.

RESULTS

Combination treatment showed strong synergistic effects as measured by the clinical score and histological changes, without adverse effects such as weight loss in the thymus and increased liver enzymes (ALT and AST). Additionally, it also reduced ICAM-1, VCAM-1, and IP-10 expression in the joints, and M-134 increased the efficacy of tofacitinib by regulating various cytokines, such as interleukin (IL)-1β, IL-17, and TNF-α, in the serum of AIA rats. Differences in the cytokine expression for each drug were found in the CIA model.

CONCLUSIONS

M-134 and tofacitinib combination therapy is a potential option for the treatment of RA through the regulation of cytokines, chemokines, and adhesion molecules.

Cucurbitacin IIb improved active chromatin-induced systemic lupus erythematosus via balancing the percentage of Th17 and Treg cells

The pathogenesis of systemic lupus erythematosus (SLE) is closely associated with aberrant immune system. Here, the aim of our study was to explore the regulation of cucurbitacin IIb (CuIIb) to Th17/Treg cells in SLE. Compared with normal mice, the percentage of Treg cells was downregulated in SLE mouse model, and Th17 was upregulated. Meantime, the production of Treg-related transcription factor (foxp3) in SLE model mouse was reduced, and the production of Th17-related transcription factor (RORγt) was increased. After treatment with CuIIb, the percentage of Treg cells in SLE mice was partly upregulated, and Th17 cells percentage was downregulated. The expression of foxp3 and RORγt in SLE mice were promoted and inhibited by CuIIb treatment, respectively. SLE-induced kidney injury also was improved by CuIIb treatment. In vitro, we demonstrated again that CuIIb upregulated the percentage of Treg cells in lymphocytes from SLE mice, and downregulated the percentage of Th17 cells. Highly expressed IL-6 and IL17, and lowly expressed IL-10 and TGF-β in lymphocytes from SLE mice were repressed and facilitated by CuIIb treatment, respectively. Overall, our data proved that CuIIb improved kidney injury in SLE mice through balancing the percentage of Th17 and Treg cells. Our data provided a reliable evidence to support the potential of CuIIb in SLE treatment.

Therapeutic potential of CKD-506, a novel selective histone deacetylase 6 inhibitor, in a murine model of rheumatoid arthritis

OBJECTIVES

Histone deacetylase (HDAC) 6 promotes inflammation. We investigated the anti-arthritic effects of CKD-506, a novel HDAC6 inhibitor, in vitro and in a murine model of arthritis as a novel treatment option for rheumatoid arthritis (RA).

METHODS

HDAC6 was overexpressed in mouse peritoneal macrophages and RAW 264.7 cells, and the effects of a HDAC6 inhibitor CKD-506 on cytokine production and activity of NF-κB and AP-1 signaling were examined. Peripheral blood mononuclear cells (PBMCs) from RA patients and fibroblast-like synoviocytes (FLS) were activated in the presence of CKD-506. Next, regulatory T cells (Tregs) were induced from RA patients and co-cultured with healthy effector T cells (Teffs) and cell proliferation was analyzed by flow cytometry. Finally, the effects of the inhibitor on the severity of arthritis were assessed in a murine model of adjuvant-induced arthritis (AIA).

RESULTS

Overexpression of HDAC6 induced macrophages to produce TNF-α and IL-6. The inhibitory effect of CKD-506 was mediated via blockade of NF-κB and AP-1 activation. HDAC6 inhibition reduced TNF-α and IL-6 production by activated RA PBMCs. CKD-506 inhibited production of MMP-1, MMP-3, IL-6, and IL-8 by activated FLS. In addition, CKD-506 inhibited proliferation of Teffs directly and indirectly by improving iTreg function. In AIA rats, oral CKD-506 improved clinical arthritis in a dose-dependent manner. A combination of sub-therapeutic CKD-506 and methotrexate exerted a synergistic effect.

CONCLUSION

The novel HDAC6 inhibitor CKD-506 suppresses inflammatory responses by monocytes/macrophages, improves Treg function, and ameliorates arthritis severity in a murine model of RA. Thus, CKD-506 might be a novel and effective treatment option for RA.

Histone Deacetylase 6 as a Therapeutic Target in B cell-associated Hematological Malignancies

B lymphocytes play a critical role in humoral immunity. Abnormal B cell development and function cause a variety of hematological malignancies such as myeloma, B cell lymphoma, and leukemia. Histone deacetylase 6 (HDAC6) inhibitors alone or in combination with other drugs have shown efficacy in several hematological malignancies, including those resistant to targeted therapies. Mechanistically, HDAC6 inhibitors promote malignant tumor cell apoptosis by inhibiting protein degradation, reinvigorating anti-tumor immunity, and inhibiting cell survival signaling pathways. Due to their specificity, HDAC6 inhibitors represent a very promising and feasible new development pipeline for high-efficacy drugs with limited side effects. This article reviews recent progress in the mechanisms of action of HDAC6 inhibitors for the treatment of B cell-associated hematological malignancies, such as multiple myeloma and B cell non-Hodgkin lymphoma, which are often resistant to targeted therapies.

Novel Histone Deacetylase 6 Inhibitor CKD-506 Inhibits NF-κB Signaling in Intestinal Epithelial Cells and Macrophages and Ameliorates Acute and Chronic Murine Colitis

BACKGROUND

Selective blocking of HDAC6 has become a promising strategy in treating inflammatory bowel disease. CKD-506 is a novel isoform-selective inhibitor of histone deacetylase 6. The present study was performed to evaluate the effect of CKD-506 on the NF-κB signaling pathway in intestinal epithelial cells (IECs) and macrophages and on murine models of acute and chronic colitis.

METHODS

RAW264RAW264.7 murine macrophages and COLO 205 human IECs were pretreated with CKD-506 and then stimulated with lipopolysaccharides (LPS). Cytokine expression of TNF-α, interleukin (IL)-6, IL-8, and IL-10 was measured by ELISA. The effect of CKD-506 on NF-κB signaling was evaluated by Western blotting of IκBα phosphorylation/degradation and electrophoretic mobility shift assay. In vivo studies were performed using a dextran sulfate sodium (DSS)-induced acute colitis model, a chronic colitis model in IL-10 knockout mice, and an adoptive transfer model. Colitis was quantified by the disease activity index, colon length, and histopathologic evaluation.

RESULTS

CKD-506 suppressed the expression of pro-inflammatory cytokines such as IL-6, IL-8, and TNF-α in IECs and macrophages. CKD-506 strongly inhibited IκBα phosphorylation/degradation and the DNA-binding activity of NF-κB. Oral administration of CKD-506 attenuated DSS-induced acute colitis and chronic colitis in IL-10-/- and adoptive transfer models. CKD-506 ameliorated weight loss, disease activity, and histopathologic score in colitis mice and downregulated IκBα phosphorylation and pro-inflammatory cytokine production significantly.

CONCLUSIONS

CKD-506 blocked NF-κB signaling in IECs and macrophages and ameliorated experimental acute and chronic murine colitis models, which suggests that CKD-506 is a promising candidate for inflammatory bowel disease treatment as a small molecular medicine.

Epigenetic Therapy as a Putative Molecular Target to Modulate B Cell Biology and Behavior in the Context of Immunological Disorders

Histone Deacetylase- (HDAC-) dependent epigenetic mechanisms have been widely explored in the last decade in different types of malignancies in preclinical studies. This effort led to the discovery and development of a range of new HDAC inhibitors (iHDAC) with different chemical properties and selective abilities. In fact, hematological malignancies were the first ones to have new iHDACs approved for clinical use, such as Vorinostat and Romidepsin for cutaneous T cell lymphoma and panobinostat for multiple myeloma. Besides these promising already approved iHDACs, we highlight a range of studies focusing on the HDAC-dependent epigenetic control of B cell development, behavior, and/or function. Here, we highlight 21 iHDACs which have been studied in the literature in the context of B cell development and/or dysfunction mostly focused on B cell lymphomagenesis. Regardless, we have identified 55 clinical trials using 6 out of 21 iHDACs to approach their putative roles on B cell malignancies; none of them focuses on peritoneal B cell populations. Since cells belonging to this peculiar body compartment, named B1 cells, may contribute to the development of autoimmune pathologies, such as lupus, a better understanding of the HDAC-dependent epigenetic mechanisms that control its biology and behavior might shed light on iHDAC use to manage these immunological dysfunctions. In this sense, iHDACs might emerge as a promising new approach for translational studies in this field. In this review, we discuss a putative role of iHDACs in the modulation of peritoneal B cell subpopulation's balance as well as their role as therapeutic agents in the context of chronic diseases mediated by peritoneal B cells.

A patent review of histone deacetylase 6 inhibitors in neurodegenerative diseases (2014-2019)

Introduction: Histone deacetylase 6 (HDAC6) is unique in comparison with other zinc-dependent HDAC family members. An increasing amount of evidence from clinical and preclinical research demonstrates the potential of HDAC6 inhibition as an effective therapeutic approach for the treatment of cancer, autoimmune diseases, as well as neurological disorders. The recently disclosed crystal structures of HDAC6-ligand complexes offer further means for achieving pharmacophore refinement, thus further accelerating the pace of HDAC6 inhibitor discovery in the last few years.Area covered: This review summarizes the latest clinical status of HDAC6 inhibitors, discusses pharmacological applications of selective HDAC6 inhibitors in neurodegenerative diseases, and describes the patent applications dealing with HDAC6 inhibitors from 2014-2019 that have not been reported in research articles.Expert opinion: Phenylhydroxamate has proven a very useful scaffold in the discovery of potent and selective HDAC6 inhibitors. However, weaknesses of the hydroxamate function such as metabolic instability and mutagenic potential limit its application in the neurological field, where long-term administration is required. The recent invention of oxadiazole-based ligands by pharmaceutical companies may provide a new opportunity to optimize the druglike properties of HDAC6 inhibitors for the treatment of neurodegenerative diseases.

HDAC6-an Emerging Target Against Chronic Myeloid Leukemia?

Imatinib became the standard treatment for chronic myeloid leukemia (CML) about 20 years ago, which was a major breakthrough in stabilizing the pathology and improving the quality of life of patients. However, the emergence of resistance to imatinib and other tyrosine kinase inhibitors leads researchers to characterize new therapeutic targets. Several studies have highlighted the role of histone deacetylase 6 (HDAC6) in various pathologies, including cancer. This protein effectively intervenes in cellular activities by its primarily cytoplasmic localization. In this review, we will discuss the molecular characteristics of the HDAC6 protein, as well as its overexpression in CML leukemic stem cells, which make it a promising therapeutic target for the treatment of CML.

The Pathogenic Role of Dysregulated Epigenetic Modifications in Autoimmune Diseases

Autoimmune diseases can be chronic with relapse of inflammatory symptoms, but it can be also acute and life-threatening if immune cells destroy life-supporting organs, such as lupus nephritis. The etiopathogenesis of autoimmune diseases has been revealed as that genetics and environmental factors-mediated dysregulated immune responses contribute to the initiation and development of autoimmune disorders. However, the current understanding of pathogenesis is limited and the underlying mechanism has not been well defined, which lows the development of novel biomarkers and new therapeutic strategies for autoimmune diseases. To improve this, broadening and deepening our understanding of pathogenesis is an unmet need. As genetic susceptibility cannot explain the low accordance rate of incidence in homozygous twins, epigenetic regulations might be an additional explanation. Therefore, this review will summarize current progress of studies on epigenetic dysregulations contributing to autoimmune diseases, including SLE, rheumatoid arthritis (RA), psoriasis, type 1 diabetes (T1D), and systemic sclerosis (SSc), hopefully providing opinions on orientation of future research, as well as discussing the clinical utilization of potential biomarkers and therapeutic strategies for these diseases.

How Does Chirality Determine the Selective Inhibition of Histone Deacetylase 6? A Lesson from Trichostatin A Enantiomers Based on Molecular Dynamics

Histone deacetylase 6 (HDAC6) plays a key role in a variety of neurological disorders, which makes it attractive drug target for the treatment of Alzheimer's disease, Parkinson's disease, and memory/learning impairment. The selectivity of HDAC6 inhibitors (sHDAC6Is) are widely considered to be susceptible to the sizes of their Cap group and the physicochemical properties of their linker or zinc-binding group, which makes the discovery of new sHDAC6Is extremely difficult. With the discovery of the distinct selectivity between Trichostatin A (TSA) enantiomers, the chirality residing in the connective units between TSA's Cap and linker shows a great impact on its selectivity. However, the mechanism underlining ( S)-TSA's selectivity is still elusive, and the way chirality switches the selective ( S)-TSA to nonselective ( R)-TSA is unknown. In this study, multiple computational approaches were collectively applied to explore, validate, and differentiate the binding modes of two TSA enantiomers in HDACs (especially the HDAC6) at atomic level. First, two nonconservative residues (G200/M205 and Y197/F202 in HDAC1/6) in loop3 and four conservative residues deep inside the hydrophobic binding pocket were discovered as the decisive residues of ( S)-TSA's selectivity toward HDAC6. Then, a novel mechanism underlying the selectivity of ( S)-TSA toward HDAC6 was proposed, which was composed of the trigger by two nonconservative residues F202 and M205 in HDAC6 and a subsequently improved fit of ( S)-TSA deep inside HDAC6's hydrophobic binding pocket. TSA enantiomers were used as a molecular probe to explore the mechanism underlying sHDAC6Is' selectivity in this study. Because of their decisive roles in ( S)-TSA's selectivity to HDAC6, both F202 and M205 in HDAC6 should be especially considered in the discovery of novel sHDAC6Is.

Regulation of Chemokines and Cytokines by Histone Deacetylases and an Update on Histone Decetylase Inhibitors in Human Diseases

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) counteract with each other to regulate gene expression by altering chromatin structure. Aberrant HDAC activity was reported in many human diseases including wide range of cancers, viral infections, cardiovascular complications, auto-immune diseases and kidney diseases. HDAC inhibitors are small molecules designed to block the malignant activity of HDACs. Chemokines and cytokines control inflammation, immunological and other key biological processes and are shown to be involved in various malignancies. Various HDACs and HDAC inhibitors were reported to regulate chemokines and cytokines. Even though HDAC inhibitors have remarkable anti-tumor activity in hematological cancers, they are not effective in treating many diseases and many patients relapse after treatment. However, the role of HDACs and cytokines in regulating these diseases still remain unclear. Therefore, understanding exact mechanisms and effector functions of HDACs are urgently needed to selectively inhibit them and to establish better a platform to combat various malignancies. In this review, we address regulation of chemokines and cytokines by HDACs and HDAC inhibitors and update on HDAC inhibitors in human diseases.