Selective Histone Deacetylase Inhibitors Research Articles

Selective inhibition of histone deacetylase 3 by novel hydrazide based small molecules as therapeutic intervention for the treatment of cancer

A promising hydrazide based small molecule lead as a potent and selective histone deacetylase 3 (HDAC3) inhibitor has been developed from a small series of synthesized novel chemical entities. The lead compound (4e) displayed high HDAC3 inhibitory potency (IC50 = 15.41 nM) and a minimum of 18-fold selectivity over other HDAC isoforms. It also exhibited potent cytotoxicity against several cancer cell lines with minimal toxicity against normal cell lines tested. Compound 4e also enhanced acetylation levels on H3K9, H4K12 and H3K27 both in vitro and in vivo. It also induced cell cycle arrest at the G2/M phase in B16F10 and 4T1 cells. It caused significant apoptosis and upregulated the expression of caspase-3, caspase-7, cytochrome c and downregulated the expression of BCL2 in tumour tissue. In addition, the downregulation of CD44, EGFR and Ki-67 suggested the potential of compound 4e in reducing cell proliferation and metastasis in mice. Further, a marked decrease in the tumour volume was observed with no general toxicity in the major organs when treated with 4e in the 4T1-Luc xenograft mouse model. Therefore, compound 4e is a promising candidate selectively targeting HDAC3 with a significant antitumour activity that can be evaluated further in preclinical and clinical evaluation.

HDAC6 modulates myofibril stiffness and diastolic function of the heart.

Passive stiffness of the heart is determined largely by extracellular matrix and titin, which functions as a molecular spring within sarcomeres. Titin stiffening is associated with the development of diastolic dysfunction (DD), while augmented titin compliance appears to impair systolic performance in dilated cardiomyopathy. We found that myofibril stiffness was elevated in mice lacking histone deacetylase 6 (HDAC6). Cultured adult murine ventricular myocytes treated with a selective HDAC6 inhibitor also exhibited increased myofibril stiffness. Conversely, HDAC6 overexpression in cardiomyocytes led to decreased myofibril stiffness, as did ex vivo treatment of mouse, rat, and human myofibrils with recombinant HDAC6. Modulation of myofibril stiffness by HDAC6 was dependent on 282 amino acids encompassing a portion of the PEVK element of titin. HDAC6 colocalized with Z-disks, and proteomics analysis suggested that HDAC6 functions as a sarcomeric protein deacetylase. Finally, increased myofibril stiffness in HDAC6-deficient mice was associated with exacerbated DD in response to hypertension or aging. These findings define a role for a deacetylase in the control of myofibril function and myocardial passive stiffness, suggest that reversible acetylation alters titin compliance, and reveal the potential of targeting HDAC6 to manipulate the elastic properties of the heart to treat cardiac diseases.

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.

Front Cover: Balancing Histone Deacetylase (HDAC) Inhibition and Drug‐likeness: Biological and Physicochemical Evaluation of Class I Selective HDAC Inhibitors (ChemMedChem 9/2022)

The Front Cover shows the development of a potent and selective histone deacetylase 1 and 2 (HDAC1 and 2) inhibitor that was tailor-made to engage the characteristic “foot-pocket” present in both isoforms. This was achieved by a modular approach aiming to find the perfect balance between selectivity and drug-likeliness through systematic screening and thorough biological evaluation. Cover design by Dr. Christoph Selg. More information can be found in the Research Article by Linda Schäker-Hübner, Finn K. Hansen et al.

HDAC Inhibition as Potential Therapeutic Strategy to Restore the Deregulated Immune Response in Severe COVID-19.

The COVID-19 pandemic has had a devastating impact worldwide and has been a great challenge for the scientific community. Vaccines against SARS-CoV-2 are now efficiently lessening COVID-19 mortality, although finding a cure for this infection is still a priority. An unbalanced immune response and the uncontrolled release of proinflammatory cytokines are features of COVID-19 pathophysiology and contribute to disease progression and worsening. Histone deacetylases (HDACs) have gained interest in immunology, as they regulate the innate and adaptative immune response at different levels. Inhibitors of these enzymes have already proven therapeutic potential in cancer and are currently being investigated for the treatment of autoimmune diseases. We thus tested the effects of different HDAC inhibitors, with a focus on a selective HDAC6 inhibitor, on immune and epithelial cells in in vitro models that mimic cells activation after viral infection. Our data indicate that HDAC inhibitors reduce cytokines release by airway epithelial cells, monocytes and macrophages. This anti-inflammatory effect occurs together with the reduction of monocytes activation and T cell exhaustion and with an increase of T cell differentiation towards a T central memory phenotype. Moreover, HDAC inhibitors hinder IFN-I expression and downstream effects in both airway epithelial cells and immune cells, thus potentially counteracting the negative effects promoted in critical COVID-19 patients by the late or persistent IFN-I pathway activation. All these data suggest that an epigenetic therapeutic approach based on HDAC inhibitors represents a promising pharmacological treatment for severe COVID-19 patients.

HDAC3 Inhibition Improved Urinary Concentrating Defect in Hypokalemia by Promoting AQP2 Transcription

Hypokalemia is a common electrolyte disturbance frequently encountered in clinical medicine. Animals with hypokalemia had a significant arginine vasopressin (AVP)‐resistant polyuria with reduced expression of aquaporin 2 (AQP2) levels in the collecting ducts of the kidneys. The precise molecular mechanisms of hypokalemia‐induced nephrogenic diabetes insipidus remain unresolved. AVP induced a marked increase in histone H3K27 acetylation (H3K27ac) across the body of the AQP2 gene, in the promoter and in upstream of the AQP2 transcriptional start site in mouse mpkCCD cell line (PMID: 29572403). The purpose of the present study was to investigate whether enhanced histone acetylation prevented decreased AQP2 expression and improved urinary concentrating defect in rats with hypokalemia. Male Wistar rats were fed potassium‐free diet with or without 4‐phenylbutyric acid (4‐PBA) or a selective inhibitor of histone deacetylase 3 (HDAC3) RGFP966 for 4 days. 4‐PBA or RGFP966 markedly increased AQP2 mRNA and protein levels in kidney inner medulla of rats with hypokalemia, which was associated with decreased urine output and increased urinary osmolality. Protein expression of H3K27ac was markedly decreased in kidney inner medulla of hypokalemic rats, which was significantly prevented by 4‐PBA or RGFP966. Expression of H3K27ac was decreased in primary cultured inner medullary collecting duct cells (IMCD) or mpkCCD cells cultured in potassium‐deprivation media, in particular, H3K27ac in the promoter region of AQP2 was markedly decreased, which was associated with reduced mRNA levels of AQP2. Protein expression of HDAC3 was significantly upregulated in both mpkCCD and IMCD cells in response to potassium deprivation; the binding of HDAC3 to the promoter of AQP2 was also dramatically increased. RGFP966 significantly increased expression of H3K27ac and AQP2 protein and enhanced the binding of H3K27ac to AQP2 in mpkCCD cells. In conclusion, HDAC3 inhibition prevented downregulation of AQP2 and improved urinary concentrating defect induced by potassium deprivation, likely through enhancing acetylation of H3K27 and transcription of AQP2.

Aromatic C‐F Interactions Influence Binding Mode of Inhibitors in HDAC6

Fluorine is increasingly being incorporated into pharmaceuticals to modulate their physical properties. Furthermore, 18F can be utilized in positron emission tomography (PET) probes for in vivo imaging. Bavarostat is a selective inhibitor of histone deacetylase 6 (HDAC6), and when derivatized with 18F is used to map out HDAC6 localisation within the brain. As HDAC6 is implicated in Alzheimer’s disease due to its function as a Tau deacetylase, it may serve as an effective biomarker for this disease. The active site cavity of HDAC6 contains two phenylalanine residues that form an aromatic crevice, F583 and F643, that engage in offset π‐π interactions with phenylhydroxymate binding groups. Moreover, the fluoroaromatic ring of Bavarostat orientates such that the C–F group binds in the aromatic crevice instead of being exposed to solvent. Structure activity relationships were determined for a series of fluorophenylhydroxymates to inform the design of fluorinated inhibitors of HDAC6 as well PET probes. Our studies show the aromatic crevice of HDAC6 preferentially binds C–F groups in this series of inhibitors. The inhibitors show differences in zinc binding orientations, likely due to the electronic influence of fluorine on the hydroxymate zinc‐binding group.

Lysine deacetylases (KDACs) regulate PKCõ phosphorylation in response to muscle atrophy

Post‐translational modifications (PTMs) such as acetylation and phosphorylation have been implicated in contractile dysfunction and muscle wasting. Indeed, lysine deacetylase (KDAC) inhibitors attenuate muscle atrophy and delay muscle damage in response to nutrient deprivation, in models of metabolic dysfunction and genetic models of muscle disease (e.g. muscle dystrophy). Historically, lysine acetylation was studied in the regulation of gene transcription, where for instance HDACs remove acetyl groups on lysine residues of histone proteins to suppress gene expression. However, recent evidence demonstrates that non‐histone proteins are acetylated; functioning in protein stability, intracellular signaling, mitochondrial function and muscle contraction. Using C2C12 myotubes stimulated with dexamethasone (Dex) as a model of muscle atrophy, we report that KDAC inhibition using Trichostatin A (TSA) restored myotube size and attenuated Dex‐induced atrophy genes, Murf1 and Atrogin‐1. Despite our current understanding for lysine acetylation in muscle physiology; a role for KDACs in the regulation of muscle signal transduction remains a ‘black box.’ We report that protein kinase C delta (PKCδ) phosphorylation decreased at threonine 505 (T505) and serine 643 (S643), residues important for PKCδ activity, in myotubes in response to muscle atrophy. Interestingly, PKCδ phosphorylation was restored in myotubes treated with a pan‐HDAC inhibitor (TSA) or a class I selective HDAC inhibitor (Apicidin) targeting HDAC1, ‐2, and ‐3 in response to Dex. Moreover, we observed that Dex induced skeletal muscle atrophy rapidly in mice, with weight loss noted by day 3 post Dex and muscle weight loss noted by day 7. Similar to our findings in C2C12 myotubes, Dex attenuated phosphorylation of PKCδ at S643, while KDAC inhibition restored or increased PKCδ phosphorylation at both T505 and S643 in the tibialis anterior. These findings suggest that KDACs act as endogenous regulators of skeletal muscle atrophy through the regulation of PKCδ phosphorylation. Consistent with this hypothesis, we report that KDAC inhibition could not restore myotube size in response to Dex in the presence of a PKCδ inhibitor or when overexpressing a dominant negative PKCδ. Combined, these suggest a non‐canonical role for KDACs in the regulation of muscle physiology outside of its role in chromatin condensation and gene regulation.

HDAC6 knockout alleviates pristane-induced lupus

Abstract Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by excessive inflammation and production of pathogenic antibodies. Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase. It has been reported that selective HDAC6 inhibition decreases inflammation in lupus mice models. C57BL/6 mice develop SLE-like symptoms following pristane injection. In this study, sex and age-matched wild type and HDAC6−/− mice on the C57BL/6 background were administered 0.5 ml pristane or PBS intraperitoneally (i.p.) at 8–12 weeks-of-age and were euthanized 10 days later. At sacrifice, body weight and spleen weight were measured, sera were collected, splenocytes and peritoneal cells were harvested for flow cytometry. We found pristane administration increased the spleen weight with no difference between WT mice and HDAC6−/− mice. Flow cytometry results showed that there was no difference in T cell or B cell populations in the spleen. Pristane administration promoted the population of CD11b+ Ly6Chigh inflammatory monocytes and CD11b+Ly6G+ neutrophils. Peritoneal recruitment of these inflammatory monocytes and neutrophils in HDAC6−/− mice was significantly decreased compared to the WT mice. Pristane administration also induced the interferon (IFN) signature genes, like Mx1, Oas1a, Irf7, Irf9, Cxcl10, Isg15. qRT-PCR revealed that these IFN signature genes were decreased in HDAC6−/− mice compared to the WT mice. In summary, our results show that HDAC6 knockout inhibits the recruitment of inflammatory monocytes and neutrophils in the peritoneum in early inflammation response to pristane. HDAC6 deletion also inhibited the expression of IFN signature genes with pristine stimulation.

P-305 - Synthesis of novel selective histone deacetylase inhibitors for the development of a suitable 18F-labelled radiotracer for the molecular imaging of HDAC1 in brain tumours

P-305 - Synthesis of novel selective histone deacetylase inhibitors for the development of a suitable 18F-labelled radiotracer for the molecular imaging of HDAC1 in brain tumours

Design, synthesis, and biological evaluation of histone deacetylase inhibitor with novel salicylamide zinc binding group.

Introduction:Histone deacetylases (HDACs) have emerged as important therapeutic targets for various diseases, such as cancer and neurological disorders. Although a majority of HDAC inhibitors use hydroxamic acids as zinc binding groups, hydroxamic acid zinc-binding groups suffer from poor bioavailability and nonspecific metal-binding properties, necessitating a new zinc-binding group. Salicylic acid and its derivatives, well-known for their therapeutic value, have also been reported to chelate zinc ions in a bidentate fashion. This drew our attention towards replacing hydroxamic acid with salicylamide as a zinc-binding group.Methods:In this study, for the first time, compound 5 possessing a novel salicylamide zinc-binding group was synthesized and evaluated biologically for its ability to inhibit various HDAC isoforms and induce acetylation upon α-tubulin and histone H3 among MDA-MB-231 cells.Results:Compound 5 exhibits selective inhibition against class I HDAC isoforms (HDAC1, 2, and 3) over class II and IV HDAC isoforms (HDAC4, 6, and 11). The exposure of MDA-MB-231 cells to compound 5 efficiently induced the acetylation of more histone H3 than α-tubulin, suggesting that compound 5 is a class I selective HDAC inhibitor. Moreover, the molecular docking study indicated that the salicylamide zinc-binding group of compound 5 coordinates the active zinc ion of class I HDAC2 in a bidentate fashion.Conclusion:Overall, salicylamide represents a novel zinc-binding group for the development of class I selective HDAC inhibitors.Graphical abstract:

Synthesis and structure-activity relationship of thiol-based histone deacetylase 6 inhibitors.

Selective histone deacetylase 6 (HDAC6) inhibitors are safe and well-tolerated with less off-target effect. However, most available HDAC6 inhibitors contain hydroxamate as a zinc-binding group (ZBG), and their unfavorable pharmacokinetic properties along with potential genotoxicity limited wide application in diverse diseases. Therefore, we designed and synthesized a series of selective HDAC6 inhibitors utilizing thiol as the ZBG and discussed their structure-activity relationship based on molecular docking. In particular, compound 21, obtained by constantly step-by-step simplification and evolution based on Ricolinostat, a specific HDAC6 inhibitor in Phase II, unexpectedly showed high selectivity (29-fold) and moderate potency (73nM). Utilizing pyrimidine as a linker in thiol-based HDAC6 inhibitors produces an utterly novel structure, which might display different pharmacokinetic properties and genotoxicity.

Selective Inhibitors of Histone Deacetylase 10 (HDAC-10).

Histone acetylation balance is one epigenetic mechanism controlling gene expression associated with disease progression. It has been observed that histone deacetylase 10 (HDAC-10) isozyme contributes to the chemotherapy resistance; in addition, the poor clinical outcome observed in patients with aggressive solid tumors, such as neuroblastoma, has been associated with its overexpression. Moreover, HDAC-10 selective inhibition suppresses the autophagic response, thus providing an improved risk-benefit profile compared to cytotoxic cancer chemotherapy drugs. On these bases, HDAC-10 is becoming an emerging target for drug design. Due to the rapid progress in the development of next-generation HDAC inhibitors, this review article aims to provide an overview on novel selective or dual HDAC-8/10 inhibitors, as new leads for cancer chemotherapy, able to avoid the severe side-effects of several actual approved "pan" HDAC inhibitors. A literature search was conducted in MedLine, PubMed, Caplus, SciFinder Scholar databases from 2015 to the present. Since the disclosure that the HDAC-6 inhibitor Tubastatin A was able to bind HDAC-10 efficiently, several related analogues were synthesized and tested. Both tricyclic (25-30) and bicyclic (31-42) derivatives were considered. The best pharmacological profile was shown by 36 (HDAC-10 pIC50 = 8.4 and pIC50 towards Class I HDACs from 5.2-6.4). In parallel, based on the evidence that high levels of HDAC-8 are a marker of poor prognosis in neuroblastoma treatment, dual HDAC-8/10 inhibitors were designed. The hydroxamic acid TH34 (HDAC-8 and 10 IC50 = 1.9 μM and 7.7 μM, respectively) and the hybrid derivatives 46d, 46e and 46g were the most promising both in terms of potency and selectivity. Literature surveys indicate several structural requirements for inhibitory potency and selectivity towards HDAC-10, e.g., electrostatic and/or hydrogen bond interactions with E274 and complementarity to the P(E,A) CE motif helix.

Bone tissue engineering using 3D silk scaffolds and human dental pulp stromal cells epigenetic reprogrammed with the selective histone deacetylase inhibitor MI192

Epigenetics plays a critical role in regulating mesenchymal stem cells’ (MSCs) fate for tissue repair and regeneration. There is increasing evidence that the inhibition of histone deacetylase (HDAC) isoform 3 can enhance MSC osteogenesis. This study investigated the potential of using a selective HDAC2 and 3 inhibitor, MI192, to promote human dental pulp stromal cells (hDPSCs) bone-like tissue formation in vitro and in vivo within porous Bombyx Mori silk scaffolds. Both 2 and 5 wt% silk scaffolds were fabricated and characterised. The 5 wt% scaffolds possess thicker internal lamellae, reduced scaffold swelling and degradation rates, whilst increased compressive modulus in comparison to the 2 wt% silk scaffold. MI192 pre-treatment of hDPSCs on 5 wt% silk scaffold significantly enhanced hDPSCs alkaline phosphatase activity (ALP). The expression of osteoblast-related genes (RUNX2, ALP, Col1a, OCN) was significantly upregulated in the MI192 pre-treated cells. Histological analysis confirmed that the MI192 pre-treated hDPSCs-silk scaffold constructs promoted bone extracellular matrix (ALP, Col1a, OCN) deposition and mineralisation compared to the untreated group. Following 6 weeks of subcutaneous implantation in nude mice, the MI192 pre-treated hDPSCs-silk scaffold constructs enhanced the vascularisation and extracellular matrix mineralisation compared to untreated control. In conclusion, these findings demonstrate the potential of using epigenetic reprogramming and silk scaffolds to promote hDPSCs bone formation efficacy, which provides evidence for clinical translation of this technology for bone augmentation.Graphical abstract

HDAC3 promotes pulmonary fibrosis by activating NOTCH1 and STAT1 signaling and up-regulating inflammasome components AIM2 and ASC

BackgroundPre-clinical studies suggest that pan-inhibitors for histone deacetylases (HDACs) may benefit the treatment of pulmonary fibrosis (PF). However, HDAC3-specific roles or mechanisms during PF development are poorly understood. MethodsThe expression of HDAC3 and the impacts of RGFP966, a selective HDAC3 inhibitor, were examined in a bleomycin-induced PF mouse model and in TGF-β-challenged MRC-5 cells. H&E and Masson staining were employed to reveal the pathological changes in lung; Western blot to assess expressions of biomarkers related to fibrosis and epithelial-mesenchymal transition (EMT), activations of Notch1 and signal transducer and activator of transcription 1 (STAT1) signaling, and levels of inflammasome components, absent in melanoma 2 (AIM2) and apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC); ELISA to measure productions of proinflammatory interleukin (IL)-1β and IL-18; cycloheximide chase assay and coimmunoprecipitation to monitor the protein stability and acetylation of Notch intracellular domain 1 (NICD1) and STAT1, respectively. ResultsHDAC3 was induced in in vitro and in vivo PF models, which was associated with elevated expressions of fibrosis-related biomarkers, EMT markers, and pro-inflammatory cytokines, activations of Notch1 and STAT1 signaling, and up-regulated inflammasome components, AIM2 and ASC. All the fibrotic phenotypes were potently inhibited by RGFP966, which boosted the acetylation of NICD1 and STAT1, accelerated the degradation of NICD1, and inhibited STAT1 phosphorylation. Overexpressing NICD1 or STAT1 restored the fibrotic phenotypes suppressed by RGFP966. ConclusionsHDAC3 promoted EMT, inflammation, and PF development by activating Notch1 and STAT1 signaling. Therefore, targeting HDAC3, Notch1 or STAT1 signaling may ameliorate PF development.

Validation of HDAC8 Inhibitors as Drug Discovery Starting Points to Treat Acute Kidney Injury.

Acute kidney injury (AKI), a sudden loss of kidney function, is a common and serious condition for which there are no approved specific therapies. While there are multiple approaches to treat the underlying causes of AKI, no targets have been clinically validated. Here, we assessed a series of potent, selective competitive inhibitors of histone deacetylase 8 (HDAC8), a promising therapeutic target in an AKI setting. Using biochemical assays, zebrafish AKI phenotypic assays, and human kidney organoid assays, we show that selective HDAC8 inhibitors can lead to efficacy in increasingly stringent models. One of these, PCI-34051, was efficacious in a rodent model of AKI, further supporting the potential for HDAC8 inhibitors and, in particular, this scaffold as a therapeutic approach to AKI.

Binary quantitative activity-activity relationship (QAAR) studies to explore selective HDAC8 inhibitors: In light of mathematical models, DFT-based calculation and molecular dynamic simulation studies

Histone deacetylase 8 (HDAC8) selectivity over other HDACs is a major concern of interest, since HDAC8 has been implicated as a potential drug target of many diseases including haematological malignancy. Quantitative activity-activity relationship (QAAR) study is a good strategy to explore the possible features to design HDAC8 selective inhibitors. Here, a mathematical framework has been constructed to understand the important molecular fragments responsible for HDAC8 selectivity over HDAC1, 2 and 3. This study also deals with binary QAAR-based HDAC8 selectivity screening of some in-house molecules and understanding the toxicity of the in-house molecules using DFT-based descriptors. Further, this study explores the possible binding mechanism of in-house compounds with HDAC8 by molecular dynamic simulation. Hence, the comparative learning amongst the mathematical models, DFT-based calculation and molecular dynamic simulation methods will surely enrich the scientific community to design selective HDAC8 inhibitors in future.

HDAC3 inhibition improves urinary-concentrating defect in hypokalaemia by promoting AQP2 transcription.

This study investigated whether enhanced histone acetylation, achieved by inhibiting histone deacetylases (HDACs), could prevent decreased aquaporin-2 (AQP2) expression during hypokalaemia. Male Wistar rats were fed a potassium-free diet with or without 4-phenylbutyric acid (4-PBA) or the selective HDAC3 inhibitor RGFP966 for 4days. Primary renal inner medullary collecting duct (IMCD) cells and immortalized mouse cortical collecting duct (mpkCCD) cells were cultured in potassium-deprivation medium with or without HDAC inhibitors. 4-PBA increased the levels of AQP2 mRNA and protein in the kidney inner medullae in hypokalaemic (HK) rats, which was associated with decreased urine output and increased urinary osmolality. The level of acetylated H3K27 (H3K27ac) protein was decreased in the inner medullae of HK rat kidneys; this decrease was mitigated by 4-PBA. The H3K27ac levels were decreased in IMCD and mpkCCD cells cultured in potassium-deprivation medium. Decreased H3K27ac in the Aqp2 promoter region was associated with reduced Aqp2 mRNA levels. HDAC3 protein expression was upregulated in mpkCCD and IMCD cells in response to potassium deprivation, and the binding of HDAC3 to the Aqp2 promoter was also increased. RGFP966 increased the levels of H3K27ac and AQP2 proteins and enhanced binding between H3K27ac and AQP2 in mpkCCD cells. Furthermore, RGFP966 reversed the hypokalaemia-induced downregulation of AQP2 and H3K27ac and alleviated polyuria in rats. RGFP966 increased interstitial osmolality in the kidney inner medullae of HK rats but did not affect urinary cAMP levels. HDAC inhibitors prevented the downregulation of AQP2 induced by potassium deprivation, probably by enhancing H3K27 acetylation.

Novel biphenyl-based scaffold as potent and selective histone deacetylase 6 (HDAC6) inhibitors: Identification, development and pharmacological evaluation

A series of novel biphenyl-based scaffold derivatives were identified as selective histone deacetylase 6 (HDAC6) inhibitors through an in-house compound library screening approach. The biological evaluation indicated that most of target compounds exhibited moderate to good inhibitory activity and selectivity against HDAC6. Especially, compound C10 was identified as a potent and highly selective HDACs inhibitor, with HDAC1 IC50 value of 3600 nM, HDAC6 IC50 value of 23 nM, and the HDAC1/6 selectivity index of 157. Moreover, C10 displayed robust anti-proliferative activity, induced cancer cells apoptosis, increased the level of acetylated α-tubulin and inhibited cancer cells migration in vitro. C10 showed significant antitumor efficacy (TGI: 75%) in CT26 colon carcinoma xenograft model in mice with no considerable toxicity in vivo. More importantly, C10 could also activate antitumor immunity so as to synergistically exert antitumor effects in vivo. Overall, our findings have provided a new avenue for design, development and investigation into the mechanism underlying the antitumor efficacy of selective HDAC6 inhibitors.

Selected Histone Deacetylase Inhibitors Reverse the Frataxin Transcriptional Defect in a Novel Friedreich's Ataxia Induced Pluripotent Stem Cell-Derived Neuronal Reporter System.

Friedreich’s ataxia (FRDA) is a neurodegenerative disorder caused by the expansion of guanine–adenine–adenine repeats within the first intron of the frataxin (FXN) gene. The location and nature of the expansion have been proven to contribute to transcriptional repression of FXN by decreasing the rate of polymerase II (RNA polymerase II) progression and increasing the presence of histone modifications associated with a heterochromatin-like state. Targeting impaired FXN transcription appears as a feasible option for therapeutic intervention, while no cure currently exists. We created a novel reporter cell line containing an FXN-Nanoluciferase (FXN-NLuc) fusion in induced pluripotent stem cells (iPSCs) reprogrammed from the fibroblasts of patients with FRDA, thus allowing quantification of endogenous FXN expression. The use of iPSCs provides the opportunity to differentiate these cells into disease-relevant neural progenitor cells (NPCs). NPCs derived from the FXN-NLuc line responded to treatments with a known FXN inducer, RG109. Results were validated by quantitative PCR and Western blot in multiple FRDA NPC lines. We then screened a commercially available library of compounds consisting of molecules targeting various enzymes and pathways critical for silencing or activation of gene expression. Only selected histone deacetylase inhibitors were capable of partial reactivation of FXN expression. This endogenous, FRDA iPSC-derived reporter can be utilized for high-throughput campaigns performed in cells most relevant to disease pathology in search of FXN transcription activators.