A metabolic screening study of trichostatin A (TSA) and TSA-like histone deacetylase inhibitors in rat and human primary hepatocyte cultures

Overview of class I HDAC modulators: Inhibitors and degraders

Class I histone deacetylases (HDACs) are closely associated with the development of a diverse array of diseases, including cancer, neurodegenerative disorders, HIV, and inflammatory diseases. Considering the essential roles in tumorigenesis, class I HDACs have emerged as highly desirable targets for therapeutic strategies, particularly in the field of anticancer drug development. However, the conventional class I HDAC inhibitors faced several challenges such as acquired resistance, inherent toxicities, and limited efficacy in inhibiting non-enzymatic functions of HDAC. To address these problems, novel strategies have emerged, including the development of class I HDAC dual-acting inhibitors, targeted protein degradation (TPD) technologies such as PROTACs, molecular glues, and HyT degraders, as well as covalent inhibitors. This review provides a comprehensive overview of class I HDAC enzymes and inhibitors, by initially introducing their structure and biological roles. Subsequently, we focus on the recent advancements of class I HDAC modulators, including isoform-selective class I inhibitors, dual-target inhibitors, TPDs, and covalent inhibitors, from the perspectives of rational design principles, pharmacodynamics, pharmacokinetics, and clinical progress. Finally, we also provide the challenges and outlines future prospects in the realm of class I HDAC-targeted drug discovery for cancer therapeutics.

Enhanced drug delivery to the reproductive tract using nanomedicine reveals therapeutic options for prevention of preterm birth

Inflammation contributes to nearly 4 million global premature births annually. Here, we used a mouse model of intrauterine inflammation to test clinically used formulations, as well as engineered nanoformulations, for the prevention of preterm birth (PTB). We observed that neither systemic 17a-hydroxyprogesterone caproate (Makena) nor vaginal progesterone gel (Crinone) was sufficient to prevent inflammation-induced PTB, consistent with recent clinical trial failures. However, we found that vaginal delivery of mucoinert nanosuspensions of histone deacetylase (HDAC) inhibitors, in some cases with the addition of progesterone, prevented PTB and resulted in delivery of live pups exhibiting neurotypical development. In human myometrial cells in vitro, the P4/HDAC inhibitor combination both inhibited cell contractility and promoted the anti-inflammatory action of P4 by increasing progesterone receptor B stability. Here, we demonstrate the use of vaginally delivered drugs to prevent intrauterine inflammation-induced PTB resulting in the birth of live offspring in a preclinical animal model.

PTG-0861: A novel HDAC6-selective inhibitor as a therapeutic strategy in acute myeloid leukaemia

Dysregulated Histone Deacetylase (HDAC) activity across multiple human pathologies have highlighted this family of epigenetic enzymes as critical druggable targets, amenable to small molecule intervention. While efficacious, current approaches using non-selective HDAC inhibitors (HDACi) have been shown to cause a range of undesirable clinical toxicities. To circumvent this, recent efforts have focused on the design of highly selective HDACi as a novel therapeutic strategy. Beyond roles in regulating transcription, the unique HDAC6 (with two catalytic domains) regulates the deacetylation of α-tubulin; promoting growth factor-controlled cell motility, cell division, and metastatic hallmarks. Recent studies have linked aberrant HDAC6 function in various hematological cancers including acute myeloid leukaemia and multiple myeloma. Herein, we report the discovery, in vitro characterization, and biological evaluation of PTG-0861 (JG-265), a novel HDAC6-selective inhibitor with strong isozyme-selectivity (∼36× ) and low nanomolar potency (IC₅₀ = 5.92 nM) against HDAC6. This selectivity profile was rationalized via in silico docking studies and also observed in cellulo through cellular target engagement. Moreover, PTG-0861 achieved relevant potency against several blood cancer cell lines (e.g. MV4-11, MM1S), whilst showing limited cytotoxicity against non-malignant cells (e.g. NHF, HUVEC) and CD-1 mice. In examining compound stability and cellular permeability, PTG-0861 revealed a promising in vitro pharmacokinetic (PK) profile. Altogether, in this study we identified a novel and potent HDAC6-selective inhibitor (∼4× more selective than current clinical standards - citarinostat, ricolinostat), which achieves cellular target engagement, efficacy in hematological cancer cells with a promising safety profile and in vitro PK.

A phase I pharmacokinetic study of belinostat in patients with advanced cancers and varying degrees of liver dysfunction

AIMS

The histone deacetylase inhibitor belinostat has activity in various cancers. Because belinostat is metabolized by the liver, reduced hepatic clearance could lead to excessive drug accumulation and increased toxicity. Safety data in patients with liver dysfunction are needed for this drug to reach its full potential in the clinic.

METHODS

We performed a phase 1 trial to determine the safety, maximum tolerated dose (MTD) and pharmacokinetics of belinostat in patients with advanced cancer and varying degrees of liver dysfunction.

RESULTS

Seventy-two patients were enrolled and divided into cohorts based on liver function. In patients with mild dysfunction, the MTD was the same as the recommended phase 2 dose (1000 mg/m2 /day). Belinostat was well tolerated in patients with moderate and severe liver dysfunction, although the trial was closed before the MTD in these cohorts could be determined. The mean clearance of belinostat was 661 mL/min/m2 in patients with normal liver function, compared to 542, 505 and 444 mL/min/m2 in patients with mild, moderate and severe hepatic dysfunction. Although this trial was not designed to assess clinical activity, of the 47 patients evaluable for response, 13 patients (28%) experienced stable disease.

CONCLUSION

While a statistically significant difference in clearance indicates increased belinostat exposure with worsening liver function, no relationship was observed between belinostat exposure and toxicity. An assessment of belinostat metabolites revealed significant differences in metabolic pathway capability in patients with differing levels of liver dysfunction. Further studies are needed to establish formal dosing guidelines in this patient population.

Synthesis and Biological Evaluation of Novel Thiazolyl-Coumarin Derivatives as Potent Histone Deacetylase Inhibitors with Antifibrotic Activity

New histone deacetylases (HDAC) inhibitors with low toxicity to non-cancerous cells, are a prevalent issue at present because these enzymes are actively involved in fibrotic diseases. We designed and synthesized a novel series of thiazolyl-coumarins, substituted at position 6 (R = H, Br, OCH₃), linked to classic zinc binding groups, such as hydroxamic and carboxylic acid moieties and alternative zinc binding groups such as disulfide and catechol. Their in vitro inhibitory activities against HDACs were evaluated. Disulfide and hydroxamic acid derivatives were the most potent ones. Assays with neonatal rat cardiac fibroblasts demonstrated low cytotoxic effects for all compounds. Regarding the parameters associated to cardiac fibrosis development, the compounds showed antiproliferative effects, and triggered a strong decrease on the expression levels of both α-SMA and procollagen I. In conclusion, the new thiazolyl-coumarin derivatives inhibit HDAC activity and decrease profibrotic effects on cardiac fibroblasts.

Hydroxamic Acids Constitute a Novel Class of Autotaxin Inhibitors that Exhibit in Vivo Efficacy in a Pulmonary Fibrosis Model

Autotaxin (ATX) catalyzes the hydrolysis of lysophosphatidylcholine (LPC) generating the lipid mediator lysophosphatidic acid (LPA). Both ATX and LPA are involved in various pathological inflammatory conditions, including fibrosis and cancer, and have attracted great interest as medicinal targets over the past decade. Thus, the development of novel potent ATX inhibitors is of great importance. We have developed a novel class of ATX inhibitors containing the zinc binding functionality of hydroxamic acid. Such novel hydroxamic acids that incorporate a non-natural δ-amino acid residue exhibit high in vitro inhibitory potency over ATX (IC₅₀ values 50-60 nM). Inhibitor 32, based on δ-norleucine, was tested for its efficacy in a mouse model of pulmonary inflammation and fibrosis induced by bleomycin and exhibited promising efficacy. The novel hydroxamic ATX inhibitors provide excellent tools for the study of the role of the enzyme and could contribute to the development of novel therapeutic agents for the treatment of fibrosis and other chronic inflammatory diseases.

The Use of Gene Ontology Term and KEGG Pathway Enrichment for Analysis of Drug Half-Life

A drug's biological half-life is defined as the time required for the human body to metabolize or eliminate 50% of the initial drug dosage. Correctly measuring the half-life of a given drug is helpful for the safe and accurate usage of the drug. In this study, we investigated which gene ontology (GO) terms and biological pathways were highly related to the determination of drug half-life. The investigated drugs, with known half-lives, were analyzed based on their enrichment scores for associated GO terms and KEGG pathways. These scores indicate which GO terms or KEGG pathways the drug targets. The feature selection method, minimum redundancy maximum relevance, was used to analyze these GO terms and KEGG pathways and to identify important GO terms and pathways, such as sodium-independent organic anion transmembrane transporter activity (GO:0015347), monoamine transmembrane transporter activity (GO:0008504), negative regulation of synaptic transmission (GO:0050805), neuroactive ligand-receptor interaction (hsa04080), serotonergic synapse (hsa04726), and linoleic acid metabolism (hsa00591), among others. This analysis confirmed our results and may show evidence for a new method in studying drug half-lives and building effective computational methods for the prediction of drug half-lives.

Heat shock protein 90 (Hsp90): A novel antifungal target against Aspergillus fumigatus

Invasive aspergillosis is a life-threatening and difficult to treat infection in immunosuppressed patients. The efficacy of current anti-Aspergillus therapies, targeting the cell wall or membrane, is limited by toxicity (polyenes), fungistatic activity and some level of basal resistance (echinocandins), or the emergence of acquired resistance (triazoles). The heat shock protein 90 (Hsp90) is a conserved molecular chaperone involved in the rapid development of antifungal resistance in the yeast Candida albicans. Few studies have addressed its role in filamentous fungi such as Aspergillus fumigatus, in which mechanisms of resistance may differ substantially. Hsp90 is at the center of a complex network involving calcineurin, lysine deacetylases (KDAC) and other client proteins, which orchestrate compensatory repair mechanisms of the cell wall in response to the stress induced by antifungals. In A. fumigatus, Hsp90 is a trigger for resistance to high concentrations of caspofungin, known as the paradoxical effect. Disrupting Hsp90 circuitry by different means (Hsp90 inhibitors, KDAC inhibitors and anti-calcineurin drugs) potentiates the antifungal activity of caspofungin, thus representing a promising novel antifungal approach. This review will discuss the specific features of A. fumigatus Hsp90 and the potential for antifungal strategies of invasive aspergillosis targeting this essential chaperone.

Melatonin treatment induces interplay of apoptosis, autophagy, and senescence in human colorectal cancer cells

In Asia, the incidence of colorectal cancer has been increasing gradually due to a more Westernized lifestyle. The aim of study is to determine the interaction between melatonin-induced cell death and cellular senescence. We treated HCT116 human colorectal adenocarcinoma cells with 10 μm melatonin and determined the levels of cell death-related proteins and evaluated cell cycle kinetics. The plasma membrane melatonin receptor, MT1, was significantly decreased by melatonin in a time-dependent manner, whereas the nuclear receptor, RORα, was increased only after 12 hr treatment. HCT116 cells, which upregulated both pro-apoptotic Bax and anti-apoptotic Bcl-xL in the early response to melatonin treatment, activated autophagic as well as apoptotic machinery within 18 hr. Melatonin decreased the S-phase population of the cells to 57% of the control at 48 hr, which was concomitant with a reduction in BrdU-positive cells in the melatonin-treated cell population. We found not only marked attenuation of E- and A-type cyclins, but also increased expression of p16 and p-p21. Compared to the cardiotoxicity of Trichostatin A in vitro, single or cumulative melatonin treatment induced insignificant detrimental effects on neonatal cardiomyocytes. We found that 10 μm melatonin activated cell death programs early and induced G1-phase arrest at the advanced phase. Therefore, we suggest that melatonin is a potential chemotherapeutic agent for treatment of colon cancer, the effects of which are mediated by regulation of both cell death and senescence in cancerous cells with minimized cardiotoxicity.

Identification of a key lysine residue in heat shock protein 90 required for azole and echinocandin resistance in Aspergillus fumigatus

Heat shock protein 90 (Hsp90) is an essential chaperone involved in the fungal stress response that can be harnessed as a novel antifungal target for the treatment of invasive aspergillosis. We previously showed that genetic repression of Hsp90 reduced Aspergillus fumigatus virulence and potentiated the effect of the echinocandin caspofungin. In this study, we sought to identify sites of posttranslational modifications (phosphorylation or acetylation) that are important for Hsp90 function in A. fumigatus. Phosphopeptide enrichment and tandem mass spectrometry revealed phosphorylation of three residues in Hsp90 (S49, S288, and T681), but their mutation did not compromise Hsp90 function. Acetylation of lysine residues of Hsp90 was recovered after treatment with deacetylase inhibitors, and acetylation-mimetic mutations (K27A and K271A) resulted in reduced virulence in a murine model of invasive aspergillosis, supporting their role in Hsp90 function. A single deletion of lysine K27 or an acetylation-mimetic mutation (K27A) resulted in increased susceptibility to voriconazole and caspofungin. This effect was attenuated following a deacetylation-mimetic mutation (K27R), suggesting that this site is crucial and should be deacetylated for proper Hsp90 function in antifungal resistance pathways. In contrast to previous reports in Candida albicans, the lysine deacetylase inhibitor trichostatin A (TSA) was active alone against A. fumigatus and potentiated the effect of caspofungin against both the wild type and an echinocandin-resistant strain. Our results indicate that the Hsp90 K27 residue is required for azole and echinocandin resistance in A. fumigatus and that deacetylase inhibition may represent an adjunctive anti-Aspergillus strategy.

Kinetic and thermodynamic rationale for suberoylanilide hydroxamic acid being a preferential human histone deacetylase 8 inhibitor as compared to the structurally similar ligand, trichostatin a

Of the different hydroxamate-based histone deacetylase (HDAC) inhibitors, suberoylanilide hydroxamic acid (SAHA) has been approved by the Food and Drug Administration for the treatment of T-cell lymphoma. Interestingly, a structurally similar inhibitor, trichostatin A (TSA), which has a higher in vitro inhibitory potency against HDAC8, reportedly shows poor efficacy in clinical settings. To gain molecular insight into this discriminatory feature, we performed transient kinetic and isothermal titration calorimetric studies for the interaction of SAHA and TSA with the recombinant form of human HDAC8. The transient kinetic data revealed that the binding of both inhibitors to the enzyme showed biphasic profiles, which represented an initial encounter of the enzyme with the inhibitor followed by the isomerization of the transient enzyme-inhibitor complexes. The temperature-dependent transient kinetic studies with these inhibitors revealed that the bimolecular process is primarily dominated by favorable enthalpic changes, as opposed to the isomerization step, which is solely contributed by entropic changes. The standard binding enthalpy (ΔH°) of SAHA, deduced from the transient kinetic as well as the isothermal titration calorimetric experiments, was 2-3 kcal/mol higher than that of TSA. The experimental data presented herein suggest that SAHA serves as a preferential (target-specific and -selective) HDAC8 inhibitor as compared to TSA. Arguments that the detailed kinetic and thermodynamic studies may guide the rational design of HDAC inhibitors as therapeutic agents are presented.

HDAC inhibitors in experimental liver and kidney fibrosis

Histone deacetylase (HDAC) inhibitors have been extensively studied in experimental models of cancer, where their inhibition of deacetylation has been proven to regulate cell survival, proliferation, differentiation and apoptosis. This in turn has led to the use of a variety of HDAC inhibitors in clinical trials. In recent years the applicability of HDAC inhibitors in other areas of disease has been explored, including the treatment of fibrotic disorders. Impaired wound healing involves the continuous deposition and cross-linking of extracellular matrix governed by myofibroblasts leading to diseases such as liver and kidney fibrosis; both diseases have high unmet medical needs which are a burden on health budgets worldwide. We provide an overview of the potential use of HDAC inhibitors against liver and kidney fibrosis using the current understanding of these inhibitors in experimental animal models and in vitro models of fibrosis.

Primary hepatocyte cultures for pharmaco-toxicological studies: at the busy crossroad of various anti-dedifferentiation strategies

Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.

Comparison of genotoxicant-modified transcriptomic responses in conventional and epigenetically stabilized primary rat hepatocytes with in vivo rat liver data

The concept of mechanistic toxicogenomics implies that compound-induced changes in gene expression profiles provide valuable information about their mode of action. A growing number of research groups have presented evidence that whole-genome gene expression profiling techniques might be used as tools for in vivo and in vitro generation of gene signatures and elucidation of molecular mechanisms after exposure to toxic compounds. An important issue to be investigated is the in vivo relevance of in vitro-obtained data. In the current study, we compare the gene expression profiles generated in vitro, after exposing conventional and epigenetically stabilized primary rat hepatocytes to well-known genotoxic hepatocarcinogens (aflatoxin B1, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and 2-nitrofluorene) with those derived in vivo after oral exposure of rats to these compounds. Similar statistical tools were applied on both sets of data. The major molecular pathways affected in the in vivo setting were DNA damage, detoxification and cell survival response, as previously described. In the conventional hepatocyte cultures, two of the three genotoxicants showed quite similar responses as in vivo with respect to these pathways. The third compound (2-nitrofluorene) revealed in vitro response which was not observed in vivo. In the epigenetically stabilized hepatocytes, in contrast to what was expected, the responses were less relevant for the in vivo situation. This study highlights the importance of in vitro/in vivo comparison of data that are generated using in vitro models and shows that conventional primary rat hepatocyte cultures represent an appropriate in vitro model to retrieve mechanistic information on the exposure to genotoxicants.

Preservation of hepatocellular functionality in cultures of primary rat hepatocytes upon exposure to 4-Me2N-BAVAH, a hydroxamate-based HDAC-inhibitor

Great efforts are being put in the development/optimization of reliable and highly predictive models for high-throughput screening of efficacy and toxicity of promising drug candidates. The use of primary hepatocyte cultures, however, is still limited by the occurrence of phenotypic alterations, including loss of xenobiotic biotransformation capacity. In the present study, the differentiation-stabilizing effect of a new histone deacetylase inhibitor 5-(4-dimethylaminobenzoyl)-aminovaleric acid hydroxamide (4-Me(2)N-BAVAH), a structural Trichostatin A (TSA)-analogue with a more favourable pharmaco-toxicological profile, was studied at a genome-wide scale by means of microarray analysis. Several genes coding for xenobiotic biotransformation enzymes were found to be positively regulated upon exposure to 4-Me(2)N-BAVAH. For CYP1A1/2B1/3A2, these observations were confirmed by qRT-PCR and immunoblot analysis. In addition, significantly higher 7-ethoxyresorufin-O-deethylase and 7-pentoxyresorufin-O-dealkylase activity levels were measured. These effects were accompanied by an increased expression of CCAAT/enhancer binding protein alpha and hepatic nuclear factor (HNF)4α, but not of HNF1α. Finally, 4-Me(2)N-BAVAH was found to induce histone H3 acetylation at the proximal promoter of the albumin, CYP1A1 and CYP2B1 genes, suggesting that chromatin remodelling is directly involved in the transcriptional regulation of these genes. In conclusion, histone deacetylase inhibitors prove to be efficient agents for better maintaining a differentiated hepatic phenotype in rat hepatocyte cultures.

The histone deacetylase inhibitor, trichostatin A, inhibits the development of 2,4-dinitrofluorobenzene-induced dermatitis in NC/Nga mice

Repetitive skin contact with a chemical hapten like 2,4-dinitrofluorobenzene (DNFB) evokes an atopic dermatitis (AD)-like dermatitis reaction in NC/Nga mice maintained under specific pathogen-free (SPF) conditions. The histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), modulates the expression of several genes by inhibiting the activity of HDACs. Furthermore, TSA has been reported to suppress inflammatory cytokine expression and to induce T cell-suppression by increasing regulatory T cell (T reg cell) numbers. In addition, histone deacetylase inhibitors (HDACi) are currently undergoing clinical trials for the treatment of inflammatory disorders. In the present study, we examined whether treatment with TSA suppresses AD-like skin lesions in NC/Nga mice treated with DNFB under SPF conditions. Intraperitoneal (i.p.) administration of TSA to DNFB-treated NC/Nga mice was found to inhibit ear thickness increases and the skin lesions induced by DNFB. Furthermore, IL-4 production by CD4+ T cells from the lymph nodes of DNFB-treated NC/Nga mice was significantly inhibited by TSA, although levels of IFN-γ were not. Flow cytometric analysis of lymphocytes showed an increase in CD4+ CD25+ T cell proportions in mice given TSA-i.p. These findings suggest that TSA suppresses the development of AD-like dermatitis in DNFB-treated NC/Nga mice by reducing IL-4 production and increasing the T reg cell population.

In vitro differentiation of embryonic and adult stem cells into hepatocytes: state of the art

Stem cells are a unique source of self-renewing cells within the human body. Before the end of the last millennium, adult stem cells, in contrast to their embryonic counterparts, were considered to be lineage-restricted cells or incapable of crossing lineage boundaries. However, the unique breakthrough of muscle and liver regeneration by adult bone marrow stem cells at the end of the 1990s ended this long-standing paradigm. Since then, the number of articles reporting the existence of multipotent stem cells in skin, neuronal tissue, adipose tissue, and bone marrow has escalated, giving rise, both in vivo and in vitro, to cell types other than their tissue of origin. The phenomenon of fate reprogrammation and phenotypic diversification remains, though, an enigmatic and rare process. Understanding how to control both proliferation and differentiation of stem cells and their progeny is a challenge in many fields, going from preclinical drug discovery and development to clinical therapy. In this review, we focus on current strategies to differentiate embryonic, mesenchymal(-like), and liver stem/progenitor cells into hepatocytes in vitro. Special attention is paid to intracellular and extracellular signaling, genetic modification, and cell-cell and cell-matrix interactions. In addition, some recommendations are proposed to standardize, optimize, and enrich the in vitro production of hepatocyte-like cells out of stem/progenitor cells.

Aminoglycoside-induced histone deacetylation and hair cell death in the mouse cochlea

Post-translational modification of histones is an important form of chromatin regulation impacting transcriptional activation. Histone acetyltransferases, for example, acetylate lysine residues on histone tails thereby enhancing gene transcription, while histone deacetylases (HDACs) remove those acetyl groups and repress gene transcription. Deficient histone acetylation is associated with pathologies, and histone deacetylase inhibitors have been studied in the treatment of cancer and neurodegenerative diseases. Here we explore histone acetylation in cochlear sensory cells following a challenge with gentamicin, an aminoglycoside antibiotic known to cause loss of auditory hair cells and hearing. The addition of the drug to organotypic cultures of the mouse organ of Corti decreased the acetylation of histone core proteins (H2A Ack5, H2B Ack12, H3 Ack9, and H4 Ack8) followed by a loss of sensory cells. Protein levels of HDAC1, HDAC3 and HDAC4 were increased while the histone acetyltransferases such as CREB-binding protein and p300 remained unchanged. We next hypothesized that protecting histone acetylation should prevent cell death and tested the effects of HDAC-inhibitors on the actions of gentamicin. Co-treatment with trichostatin A maintained near-normal levels of acetylation of histone core proteins in cochlear hair cells and attenuated gentamicin-induced cell death. The addition of sodium butyrate also rescued hair cells from damage by gentamicin. The results are consistent with an involvement of deficient histone acetylation in aminoglycoside-induced hair cell death and point to the potential value of HDAC-inhibitors in protection from the side effects of these drugs.

Histone deacetylase inhibitors through click chemistry

Histone deacetylase inhibitors (HDACi) are a relatively new class of chemotherapy agents. Herein, we report a click-chemistry based approach to the synthesis of HDACi. Fourteen agents were synthesized from the combination of two alkyne and seven azido precursors. The inhibition of HDAC1 and HDAC8 was then determined by in vitro enzymatic assays, after which the cytotoxicity was evaluated in the NCI human cancer cell line screen. A lead compound 5 g (NSC746457) was discovered that inhibited HDAC1 at an IC(50) value of 104 +/- 30 nM and proved quite potent in the cancer cell line screen with GI(50) values ranging from 3.92 microM to 10 nM. Thus, this click HDACi design has provided a new chemical scaffold that has not only revealed a lead compound, but one which is easily amendable to further structural modifications given the modular nature of this approach.

The histone deacetylase inhibitor trichostatin A upregulates regulatory T cells and modulates autoimmunity in NZB/W F1 mice

We sought to determine if the histone deacetylase inhibitor (HDI), trichostatin A (TSA), would alter systemic lupus erythematosus (SLE) in NZB/W mice. Fourteen to sixteen-week-old female NZB/W F1 mice were given TSA (1.0mg/kg body weight (BW)) intraperitonealy (i.p.) daily, TSA (1.0mg/kg BW) i.p.+anti-CD25 (250mg/mouse) i.p. every third day, only anti-CD25 (250mg/mouse) i.p., DMSO or isotype IgG. Disease progression was assessed as they aged. Mice were sacrificed at 26 or 38 weeks of age, tissues collected and evaluated. At 36 weeks, TSA-treated animals had decreased anti-double stranded DNA (dsDNA) autoantibodies and decreased protein excretion compared to controls. Spleen size and the percentage of CD4+CD69+ cells were decreased, with an increase in CD4+CD25+ T cells in the TSA-treated mice. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis of T cells showed a decrease in IL-6 production but an increase in TGF-beta1 and Foxp3 in the TSA-treated animals. Kidney analysis showed a decrease in IgG and C3 deposition, decrease in pathologic glomerular disease and renal MCP-1, MMP-9, and IL-6 mRNA expression. Anti-CD25-treated mice euthanized at 26 weeks of age showed decreased Foxp3+CD4+CD25+ T cells compared to TSA-treated mice. These data suggest TSA administration modulates lupus-like disease, in part, by increasing T regulatory cells.

Differential effects of hydroxamate histone deacetylase inhibitors on cellular functionality and gap junctions in primary cultures of mitogen-stimulated hepatocytes

Histone deacetylase (HDAC)-inhibitors are well known to induce proliferative blocks and concomitant differentiation boosts in a plethora of tumor cells. Despite their promising potential as clinical therapeutics, however, the biological outcome of HDAC-inhibitors in non-tumorous cells has been poorly documented. We previously reported that the HDAC-inhibitor trichostatin A (TSA) and its metabolically more stable structural analogue 5-(4-dimethylaminobenzoyl)-aminovaleric acid hydroxamide (4-Me2N-BAVAH) cause cell cycle arrests in primary cultures of mitogen-stimulated hepatocytes. The present study was set up to explore whether this proliferative block in non-tumorous cells is also associated with inducing effects on the differentiated hepatocellular phenotype, a scenario that is usually observed in tumorous cells. In particular, the molecular actions of TSA and 4-Me2N-BAVAH on hepatic functionality and gap junctions, gatekeepers of liver homeostasis, in primary cultures of mitogen-stimulated hepatocytes are investigated. Both HDAC-inhibitors were found to promote albumin secretion and CYP1A1 gene transcription and functionality, whereas CYP2B1 gene transcription and activity were only slightly enhanced. The protein production of the gap junction component Cx26 was downregulated, whereas Cx32 expression was upregulated in response to HDAC-inhibition. Furthermore, TSA increased protein levels of the non-specific hepatocellular Cx43, whereas 4-Me2N-BAVAH rather diminished its expression. These data provide new insight into the biological impact of HDAC-inhibitors on the homeostatic balance in hepatocytes, being major executors of xenobiotic biotransformation and primary targets of drug-induced toxicity.

Histone deacetylases and repression of the gonadotropin genes

The roles of chromatin modifications in transcription have been studied extensively; however, there remains a dearth of information explaining how extracellular signals induce changes in chromatin at a specific gene locus. The gonadotropins provide an example of genes that undergo significant fluctuations in their expression, and are regulated by gonadotropin-releasing hormone (GnRH) through a membrane-bound receptor. GnRH displaces histone deacetylases (HDACs) from gonadotropin genes in immature mouse gonadotropes, and some of the pathways have been elucidated. This GnRH effect likely comprises a mechanism involved in altering reproductive potential and provides a model for studying the regulation of derepression. This paper reviews the role of HDACs in repression of the gonadotropin genes and the mechanisms through which GnRH overcomes their actions.

Inhibition of NF-kappaB activation by the histone deacetylase inhibitor 4-Me2N-BAVAH induces an early G1 cell cycle arrest in primary hepatocytes

OBJECTIVE

Benzoylaminoalkanohydroxamic acids, including 5-(4-dimethylaminobenzoyl)aminovaleric acid hydroxamide (4-Me(2)N-BAVAH), are structural analogues of Trichostatin A, a naturally occurring histone deacetylase inhibitor (HDACi). 4-Me(2)N-BAVAH has been shown to induce histone hyperacetylation and to inhibit proliferation in Friend erythroleukaemia cells in vitro. However, the molecular mechanisms have remained unidentified.

MATERIALS AND METHODS

In this study, we evaluated the effects of 4-Me(2)N-BAVAH on proliferation in non-malignant cells, namely epidermal growth factor-stimulated primary rat hepatocytes.

RESULTS AND CONCLUSION

We have found that 4-Me(2)N-BAVAH inhibits HDAC activity at non-cytotoxic concentrations and prevents cells from responding to the mitogenic stimuli of epidermal growth factor. This results in an early G(1) cell cycle arrest that is independent of p21 activity, but instead can be attributed to inhibition of cyclin D1 transcription through a mechanism involving inhibition of nuclear factor-kappaB activation. In addition, 4-Me(2)N-BAVAH delays the onset of spontaneous apoptosis in primary rat hepatocyte cultures as evidenced by down-regulation of the pro-apoptotic proteins Bid and Bax, and inhibition of caspase-3 activation.