The histone deacetylase inhibitor Trichostatin A modulates CD4+ T cell responses

BET bromodomain inhibition as a novel strategy for reactivation of HIV-1

The persistence of latent HIV-1 remains a major challenge in therapeutic efforts to eradicate infection. We report the capacity for HIV reactivation by a selective small molecule inhibitor of BET family bromodomains, JQ1, a promising therapeutic agent with antioncogenic properties. JQ1 reactivated HIV transcription in models of latent T cell infection and latent monocyte infection. We also tested the effect of exposure to JQ1 to allow recovery of replication-competent HIV from pools of resting CD4(+) T cells isolated from HIV-infected, ART-treated patients. In one of three patients, JQ1 allowed recovery of virus at a frequency above unstimulated conditions. JQ1 potently suppressed T cell proliferation with minimal cytotoxic effect. Transcriptional profiling of T cells with JQ1 showed potent down-regulation of T cell activation genes, including CD3, CD28, and CXCR4, similar to HDAC inhibitors, but JQ1 also showed potent up-regulation of chromatin modification genes, including SIRT1, HDAC6, and multiple lysine demethylases (KDMs). Thus, JQ1 reactivates HIV-1 while suppressing T cell activation genes and up-regulating histone modification genes predicted to favor increased Tat activity. Thus, JQ1 may be useful in studies of potentially novel mechanisms for transcriptional control as well as in translational efforts to identify therapeutic molecules to achieve viral eradication.

Histone deacetylase inhibitors promote mice corneal allograft survival through alteration of CD4+ effector T cells and induction of Foxp3+ regulatory T cells

Trichostatin A (TSA) is classical Histone deacetylase inhibitors (HDACIs) II which is used in treatment of advanced cutaneous T-cells lymphoma. Our works focused on the roles of TSA on immuno-modulatory. We found that the TSA could induce resting Teff cells into apoptotic cell death and inhibit Teff cells proliferation in a dose-dependent manner. We also observed down-regulation effects of various costimulatory/adhesion molecules on Teff cells and up-regulation of Foxp3 expression on CD4+ CD25+ T cells. Treatment with TSA could improve mice corneal allograft survival by promoting the proportions and allosuppressive function of CD4+ CD25+ regulatory T cells. Our findings suggest that the use of TSA allows the beneficial pharmacological effect on CD4+ CD25- T activation in vitro and enhancement of Foxp3+ Treg cells in vivo.

Neuroprotection by the histone deacetylase inhibitor trichostatin A in a model of lipopolysaccharide-sensitised neonatal hypoxic-ischaemic brain injury

Background

Perinatal brain injury is complex and often associated with both inflammation and hypoxia-ischaemia (HI). In adult inflammatory brain injury models, therapies to increase acetylation are efficacious in reducing inflammation and cerebral injury. Our aim in the present study was to examine the neuropathological and functional effects of the histone deacetylase inhibitor (HDACi) trichostatin A (TSA) in a model of neonatal lipopolysaccharide (LPS)-sensitised HI. We hypothesised that, by decreasing inflammation, TSA would improve injury and behavioural outcome. Furthermore, TSA’s effects on oligodendrocyte development, which is acetylation-dependent, were investigated.

Methods

On postnatal day 8 (P8), male and female mice were exposed to LPS together with or without TSA. On P9 (14 hours after LPS), mice were exposed to HI (50 minutes at 10% O₂). Neuropathology was assessed at 24 hours, 5 days and 27 days post-LPS/HI via immunohistochemistry and/or Western blot analysis for markers of grey matter (microtubule-associated protein 2), white matter (myelin basic protein) and cell death (activated caspase-3). Effects of TSA on LPS or LPS/HI-induced inflammation (cytokines and microglia number) were assessed by Luminex assay and immunohistochemistry. Expression of acetylation-dependent oligodendrocyte maturational corepressors was assessed with quantitative PCR 6 hours after LPS and at 24 hours and 27 days post-LPS/HI. Animal behaviour was monitored with the open-field and trace fear-conditioning paradigms at 25 days post-LPS/HI to identify functional implications of changes in neuropathology associated with TSA treatment.

Results

TSA induced increased Ac-H4 in females only after LPS exposure. Also only in females, TSA reduced grey matter and white matter injury at 5 days post-LPS/HI. Treatment altered animal behaviour in the open field and improved learning in the fear-conditioning test in females compared with LPS/HI-only females at 25 days post-HI. None of the inflammatory mechanisms assessed that are known to mediate neuroprotection by HDACi in adults correlated with improved outcome in TSA-treated neonatal females. Oligodendrocyte maturation was not different between the LPS-only and LPS + TSA-treated mice before or after exposure to HI.

Conclusions

Hyperacetylation with TSA is neuroprotective in the female neonatal mouse following LPS/HI and correlates with improved learning long-term. TSA appears to exert neuroprotection via mechanisms unique to the neonate. Deciphering the effects of age, sex and inflammatory sensitisation in the cerebral response to HDACi is key to furthering the potential of hyperacetylation as a viable neuroprotectant. TSA did not impair oligodendrocyte maturation, which increases the possible clinical relevance of this strategy.

The histone deacetylase inhibitor, romidepsin, suppresses cellular immune functions of cutaneous T-cell lymphoma patients

Romidepsin is the second histone deacetylase inhibitor (HDACi) approved for the treatment of advanced stages of cutaneous T-cell lymphoma (CTCL). Recent in vitro data suggest that HDACis suppress immune function although these findings have not been confirmed in patients. Thus, we serially examined the cellular immune function of eight CTCL patients undergoing treatment with three cycles of romidepsin. We measured the patients' natural killer (NK) and dendritic cell (DC) function and performed an in vitro terminal deoxynucleotidyl transferase dUTP nick end labeling assay to measure cellular apoptosis. Patients' NK cell cytolytic activity decreased from baseline to the third cycle of treatment (P = 0.018) but stimulation with a toll-like receptor (TLR) agonist increased this activity (P = 0.018). At baseline, a TLR agonist could both activate patients' DC (P = 0.043) and stimulate interleukin-12 protein production (P = 0.043) but both were suppressed after the first cycle of romidepsin. Finally, we observed increased specificity for romidepsin-induced CD4+ tumor cell apoptosis and dose-dependent increases in cellular apoptosis of healthy cells in multiple lineages (P < 0.05). These findings raise concern that HDACis suppress immune function in CTCL patients and they support the concurrent use of multiple immune stimulatory agents to preserve the host immune response.

Regulation of immune responses by histone deacetylase inhibitors

Both genetic and epigenetic factors are important regulators of the immune system. There is an increasing body of evidence attesting to epigenetic modifications that influence the development of distinct innate and adaptive immune response cells. Chromatin remodelling via acetylation, methylation, phosphorylation, and ubiquitination of histone proteins as well as DNA, methylation is epigenetic mechanisms by which immune gene expression can be controlled. In this paper, we will discuss the role of epigenetics in the regulation of host immunity, with particular emphasis on histone deacetylase inhibitors. In particular, the role of HDAC inhibitors as a new class of immunomodulatory therapeutics will also be reviewed.

Histone/protein deacetylases and T-cell immune responses

Clinical and experimental studies show that inhibition of histone/protein deacetylases (HDAC) can have important anti-neoplastic effects through cytotoxic and proapoptotic mechanisms. There are also increasing data from nononcologic settings that HDAC inhibitors (HDACi) can exhibit useful anti-inflammatory effects in vitro and in vivo, unrelated to cytotoxicity or apoptosis. These effects can be cell-, tissue-, or context-dependent and can involve modulation of specific inflammatory signaling pathways as well as epigenetic mechanisms. We review recent advances in the understanding of how HDACi alter immune and inflammatory processes, with a particular focus on the effects of HDACi on T-cell biology, including the activation and functions of conventional T cells and the unique T-cell subset, composed of Foxp3(+) T-regulatory cells. Although studies are still needed to tease out details of the various biologic roles of individual HDAC isoforms and their corresponding selective inhibitors, the anti-inflammatory effects of HDACi are already promising and may lead to new therapeutic avenues in transplantation and autoimmune diseases.

Trichostatin A reduced phospholipase C gamma-1 transcript and protein contents in MCF-7 breast cancer cells

It has recently been demonstrated that phospholipase C gamma-1 (PLCγ1) activation may contribute to breast carcinoma cell motility and their metastasis. Employing MCF-7 breast cancer cells, we showed the effect of trichostatin A (TSA) on the cellular contents of the PLCγ1 molecule. Using reverse transcription, real-time quantitative PCR and western blot analysis, we demonstrated that TSA reduced the PLCγ1 transcript and protein levels in MCF-7 cells. We also found that TSA decreased the half-life of the PLCγ1 transcript from approximately 7hours to 5hours. Moreover, we observed that protein synthesis appears to be essential in the TSA reduction of PLCγ1 mRNA stability. Since PLCγ1 activation is considered a key factor in the initiation of events that increase malignant cell motility, our observations may support the validity of TSA in anticancer studies.

Histone deacetylase inhibitors in the generation of the anti-tumour immune response

Acetylation of lysine residues acts to modify the function of a wide range of proteins. In histones, it affects chromatin structure, which can impact gene transcription, whereas acetylation of transcription factors and heat-shock proteins affect their activity. Deacetylase inhibitors block the dynamic turnover of acetylation resulting in hyperacetylation of target proteins. This can affect a wide range of cellular functions, and in a wide range of tumour cell types promote cytostatic and cytotoxic effects, but has little effect on normal cells. The inhibitors are being used clinically as anti-cancer agents. Although direct effects of the histone deacetylase (HDAC) inhibitors on cancers are beginning to be elucidated, the prospect of concurrent stimulation of the immune response raises hopes for immune attack of the tumour as part of the initial anti-cancer therapy and long-term immune-surveillance of residual or recurrent tumour. This review will examine the evidence for the generation of anti-tumour immunity after treatment of cancers with HDAC inhibitors.

Foxp3 inhibits HDAC1 activity to modulate gene expression in human T cells

We have previously reported that HIV-1 preferentially infects Foxp3+ Treg cells in vitro and in vivo, and Foxp3 enhances the HIV-1 LTR expression through epigenetic mechanisms in T cells. We report here that histone deacetylase inhibitor (HDACi) failed to further enhance HIV gene expression in FoxP3+ T cells. We discovered that Foxp3 inhibited cellular HDAC activity in T cells, and mutations in the forkhead domain that ablate Foxp3 function also abolished its ability to inhibit HDAC. When co-expressed, Foxp3 specifically inhibited the deacetylase activity of HDAC1. We further showed that Foxp3 was associated with HDAC1, and mutations in the forkhead domain that ablate Foxp3 function in Treg cells also inhibited Foxp3 association with and inhibition of HDAC1. Finally, Foxp3 failed to enhance HIV-1 gene expression in human T cells expressing HDAC1-specific shRNA. We conclude that Foxp3 modulates gene expression in human T cells at least partly by inhibiting HDAC1 activity.

Attenuation of vascular dementia by sodium butyrate in streptozotocin diabetic rats

RATIONALE

Vascular dementia is the second leading cause of dementia, which is strongly associated with diabetes. Diabetes and dementia have become a major public health concern worldwide. At this point of time, it is very important to find the possible pharmacological agents which may be useful in management and therapy of dementia including Alzheimer's disease, vascular dementia, etc.

OBJECTIVES

To investigate the effect of sodium butyrate on streptozotocin (STZ) diabetes induced vascular dementia in rats.

METHODS

Diabetes and subsequent endothelial dysfunction and dementia were induced in rats by administration of single dose of STZ. Drug treatment was started after 1 month of STZ administration and treatment was continued until the end of the study. Morris water maze (MWM) test was employed for testing learning and memory. Endothelial function was measured on isolated aortic rings using student physiograph. Serum glucose, body weight, serum nitrite/nitrate, aortic superoxide anion generation, brain thiobarbituric acid reactive species (TBARS), reduced glutathione (GSH) levels, and acetylcholinesterase activity were also tested.

RESULTS

STZ treatment produced endothelial dysfunction, impairment of learning and memory, reduction in body weight and serum nitrite/nitrate, and increase in serum glucose, aortic and brain oxidative stress (increased superoxide anion, TBARS, and decreased GSH levels), and brain acetylcholinesterase activity. Treatment of sodium butyrate attenuated diabetes induced impairment of learning, memory, endothelial function, and various biochemical parameters.

CONCLUSIONS

Sodium butyrate may be considered as potential pharmacological agent for the management of diabetes induced vascular dementia.

Phase II study of belinostat in patients with recurrent or refractory advanced thymic epithelial tumors

PURPOSE

Thymic epithelial tumors are rare malignancies, and there is no standard treatment for patients with advanced disease in whom chemotherapy has failed. Antitumor activity of histone deacetylase (HDAC) inhibitors in this disease has been documented, including one patient with thymoma treated with the pan-HDAC inhibitor belinostat.

PATIENTS AND METHODS

Patients with advanced thymic epithelial malignancies in whom at least one line of platinum-containing chemotherapy had failed were eligible for this study. Other eligibility criteria included adequate organ function and good performance status. Belinostat was administered intravenously at 1 g/m(2) on days 1 to 5 of a 21-day cycle until disease progression or development of intolerance. The primary objective was response rate in patients with thymoma.

RESULTS

Of the 41 patients enrolled, 25 had thymoma, and 16 had thymic carcinoma; patients had a median of two previous systemic regimens (range, one to 10 regimens). Treatment was well tolerated, with nausea, vomiting, and fatigue being the most frequent adverse effects. Two patients achieved partial response (both had thymoma; response rate, 8%; 95% CI, 2.2% to 25%), 25 had stable disease, and 13 had progressive disease; there were no responses among patients with thymic carcinoma. Median times to progression and survival were 5.8 and 19.1 months, respectively. Survival of patients with thymoma was significantly longer than that of patients with thymic carcinoma (median not reached v 12.4 months; P = .001). Protein acetylation, regulatory T-cell numbers, and circulating angiogenic factors did not predict outcome.

CONCLUSION

Belinostat has modest antitumor activity in this group of heavily pretreated thymic malignancies. However, the duration of response and disease stabilization is intriguing, and additional testing of belinostat in this disease is warranted.

Histone deacetylase inhibitors for treating a spectrum of diseases not related to cancer

This issue of Molecular Medicine contains 14 original research reports and state-of-the-art reviews on histone deacetylase inhibitors (HDACi's), which are being studied in models of a broad range of diseases not related to the proapoptotic properties used to treat cancer. The spectrum of these diseases responsive to HDACi's is for the most part due to several antiinflammatory properties, often observed in vitro but importantly also in animal models. One unifying property is a reduction in cytokine production as well as inhibition of cytokine postreceptor signaling. Distinct from their use in cancer, the reduction in inflammation by HDACi's is consistently observed at low concentrations compared with the higher concentrations required for killing tumor cells. This characteristic makes HDACi's attractive candidates for treating chronic diseases, since low doses are well tolerated. For example, low oral doses of the HDACi givinostat have been used in children to reduce arthritis and are well tolerated. In addition to the antiinflammatory properties, HDACi's have shown promise in models of neurodegenerative disorders, and HDACi's also hold promise to drive HIV-1 out of latently infected cells. No one molecular mechanism accounts for the non-cancer-related properties of HDACi's, since there are 18 genes coding for histone deacetylases. Rather, there are mechanisms unique for the pathological process of specific cell types. In this overview, we summarize the preclinical data on HDACi's for therapy in a wide spectrum of diseases unrelated to the treatment of cancer. The data suggest the use of HDACi's in treating autoimmune as well as chronic inflammatory diseases.

The therapeutic potential of HDAC inhibitors in the treatment of multiple sclerosis

Multiple sclerosis (MS) is a devastating autoimmune disorder of the central nervous system (CNS) for which there is no efficacious cure. Thanks to numerous preclinical and clinical studies, drugs able to mitigate the inexorable course of the disease have been made available recently. Still, there is a terrible need for compounds capable of reducing the severity of the autoimmune attack and of blocking progression of the disorder. Also, besides the classic immunosuppressive strategies, it is now appreciated that compounds directly targeting neuronal death can be of relevance to the treatment of MS patients. Acetylation homeostasis is a key regulator of both immune cell activation and neuronal survival. Of note, potent histone deacetylase inhibitors (HDACi) endowed with antiinflammatory and neuroprotective properties have been identified. Efficacy of HDACi in experimental models of MS has been reported consistently. In this review, we provide an appraisal of the literature on HDACi and MS, also discussing the mechanisms by which HDACi can suppress the autoimmune attack to the CNS.

Inhibition of histone deacetylases in inflammatory bowel diseases

This review, comprised of our own data and that of others, provides a summary overview of histone deacetylase (HDAC) inhibition on intestinal inflammation as well as inflammation-mediated carcinogenesis. Experimental colitis in mice represents an excellent in vivo model to define the specific cell populations and target tissues modulated by inhibitors of HDAC. Oral administration of either suberyolanilide hydroxamic acid (SAHA) or ITF2357 results in an amelioration in these models, as indicated by a significantly reduced colitis disease score and histological score. This effect was paralleled by suppression of proinflammatory cytokines at the site of inflammation as well as specific changes in the composition of cells within the lamina propria. In addition, tumor number and size was significantly reduced in two models of inflammation-driven tumorigenesis, namely interleukin (IL)-10-deficient mice and the azoxymethane-dextran sulfate sodium (DSS) model, respectively. The mechanisms affected by HDAC inhibition, contributing to this antiinflammatory and antiproliferative potency will be discussed in detail. Furthermore, with regard to the relevance in human inflammatory bowel disease, the doses of ITF2357 considered safe in humans and the corresponding serum concentrations are consistent with the efficacious dosing used in our in vivo as well as in vitro experiments. Thus, the data strongly suggest that HDAC inhibitors could serve as a therapeutic option in inflammatory bowel disease.

Rationale for HDAC inhibitor therapy in autoimmunity and transplantation

While there are currently more than 70 ongoing clinical trials of inhibitors of so-called classical HDACs (HDACi) as anticancer therapies, given their potency as antiproliferative and angiostatic agents, HDACi also have considerable therapeutic potential as anti-inflammatory and immunosuppressive drugs. The utility of HDACi as anti-inflammatory agents is dependent upon their proving safe and effective in experimental models. Current pan-HDACi compounds are not well suited to this role, given the broad distribution of target HDACs and their complex and multifaceted mechanisms of action. In contrast, the development of isoform-selective HDACi may provide important new tools for therapy in autoimmunity and transplantation. This chapter discusses which HDACs are worthwhile targets in inflammation and progress toward their therapeutic inhibition, including the use of HDAC subclass and isoform-selective HDACi to promote the functions of Foxp3+ T regulatory cells.

Enhancement of vaccinia virus based oncolysis with histone deacetylase inhibitors

Histone deacetylase inhibitors (HDI) dampen cellular innate immune response by decreasing interferon production and have been shown to increase the growth of vesicular stomatitis virus and HSV. As attenuated tumour-selective oncolytic vaccinia viruses (VV) are already undergoing clinical evaluation, the goal of this study is to determine whether HDI can also enhance the potency of these poxviruses in infection-resistant cancer cell lines. Multiple HDIs were tested and Trichostatin A (TSA) was found to potently enhance the spread and replication of a tumour selective vaccinia virus in several infection-resistant cancer cell lines. TSA significantly decreased the number of lung metastases in a syngeneic B16F10LacZ lung metastasis model yet did not increase the replication of vaccinia in normal tissues. The combination of TSA and VV increased survival of mice harbouring human HCT116 colon tumour xenografts as compared to mice treated with either agent alone. We conclude that TSA can selectively and effectively enhance the replication and spread of oncolytic vaccinia virus in cancer cells.

HDAC activity is required for efficient core promoter function at the mouse mammary tumor virus promoter

Histone deacetylases (HDACs) have been shown to be required for basal or inducible transcription at a variety of genes by poorly understood mechanisms. We demonstrated previously that HDAC inhibition rapidly repressed transcription from the mouse mammary tumor virus (MMTV) promoter by a mechanism that does not require the binding of upstream transcription factors. In the current study, we find that HDACs work through the core promoter sequences of MMTV as well as those of several cellular genes to facilitate transcriptional initiation through deacetylation of nonhistone proteins.

Histone deacetylase 9 activates gamma-globin gene expression in primary erythroid cells

Strategies to induce fetal hemoglobin (HbF) synthesis for the treatment of β-hemoglobinopathies probably involve protein modifications by histone deacetylases (HDACs) that mediate γ-globin gene regulation. However, the role of individual HDACs in globin gene expression is not very well understood; thus, the focus of our study was to identify HDACs involved in γ-globin activation. K562 erythroleukemia cells treated with the HbF inducers hemin, trichostatin A, and sodium butyrate had significantly reduced mRNA levels of HDAC9 and its splice variant histone deacetylase-related protein. Subsequently, HDAC9 gene knockdown produced dose-dependent γ-globin gene silencing over an 80-320 nm range. Enforced expression with the pTarget-HDAC9 vector produced a dose-dependent 2.5-fold increase in γ-globin mRNA (p < 0.05). Furthermore, ChIP assays showed HDAC9 binding in vivo in the upstream Gγ-globin gene promoter region. To determine the physiological relevance of these findings, human primary erythroid progenitors were treated with HDAC9 siRNA; we observed 40 and 60% γ-globin gene silencing in day 11 (early) and day 28 (late) progenitors. Moreover, enforced HDAC9 expression increased γ-globin mRNA levels by 2.5-fold with a simultaneous 7-fold increase in HbF. Collectively, these data support a positive role for HDAC9 in γ-globin gene regulation.

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.

Conditional deletion of histone deacetylase 1 in T cells leads to enhanced airway inflammation and increased Th2 cytokine production

Chromatin modifications, such as reversible histone acetylation, play a key role in the regulation of T cell development and function. However, the role of individual histone deacetylases (HDACs) in T cells is less well understood. In this article, we show by conditional gene targeting that T cell-specific loss of HDAC1 led to an increased inflammatory response in an in vivo allergic airway inflammation model. Mice with HDAC1-deficient T cells displayed an increase in all critical parameters in this Th2-type asthma model, such as eosinophil recruitment into the lung, mucus hypersecretion, parenchymal lung inflammation, and enhanced airway resistance. This correlated with enhanced Th2 cytokine production in HDAC1-deficient T cells isolated from diseased mice. In vitro-polarized HDAC1-deficient Th2 cells showed a similar enhancement of IL-4 expression, which was evident already at day 3 of Th2 differentiation cultures and restricted to T cell subsets that underwent several rounds of cell divisions. HDAC1 was recruited to the Il4 gene locus in ex vivo isolated nonstimulated CD4(+) T cells, indicating a direct control of the Il4 gene locus. Our data provide genetic evidence that HDAC1 is an essential HDAC that controls the magnitude of an inflammatory response by modulating cytokine expression in effector T cells.

Histone/protein deacetylase inhibitors increase suppressive functions of human FOXP3+ Tregs

Histone/protein deacetylases (HDACs) decrease histone and protein acetylation, typically leading to suppression of gene transcription and modulation of various protein functions. We found significant differences in expression of HDAC before and after stimulation of human T regulatory (Treg) and T effector cells, suggesting the potential for future selective targeting of Tregs with HDAC inhibitors (HDACi). Use of various HDACi small molecules enhanced, by up to 4.5-fold (average 2-fold), the suppressive functions of both freshly isolated and expanded human Tregs, consistent with our previous murine data. HDACi use increased Treg expression of CTLA-4, a key negative regulator of immune response, and we found a direct and significant correlation between CTLA-4 expression and Treg suppression. Hence, HDACi compounds are promising pharmacologic tools to increase Treg suppressive functions, and this action may potentially be of use in patients with autoimmunity or post-transplantation.

Butyrate-induced cell death and differentiation are associated with distinct patterns of ROS in HT29-derived human colon cancer cells

To investigate the role of reactive oxygen species (ROS) induced by butyrate in tumor cells, we compared HT29R, an HT29-derived human colon cancer cell line refractory to butyrate-induced cell differentiation but highly sensitive to cell death, with the differentiation-positive HT29-12 and HT29-21 cell lines (exhibiting low sensitivity to butyrate-induced cell death), with respect to levels of butyrate-induced free radicals (FRs), ROS, and H(2)O(2). Dose-dependent increase of FRs (as determined by electron spin resonance spectroscopy) and ROS (dichlorofluorescein assay) was induced in HT29R, but not in HT29-12 and HT29-21 cells, where, in contrast to HT29R, a dose-dependent increase of H(2)O(2) release (phenol red assay) was induced by butyrate. The mode of butyrate-induced cell death in HT29R cells was of a mixed type with necrosis predominating, which, however, switched to apoptosis as the major type of cell death in the presence of the drugs 1,5-dihydroxyisoquinoline, resveratrol, or cyclosporine A. The results suggest that FRs and ROS induced by butyrate in HT29R cells are products of cell death, while H(2)O(2) induced in HT29-12 and HT29-21 cells is functionally related to cell differentiation.

Histone deacetylase inhibitors prevent activation of tumour-reactive NK cells and T cells but do not interfere with their cytolytic effector functions

Histone deacetylase inhibitors (HDIs) exert direct tumour-toxic activity and sensitise tumour cells for other therapeutic regimens as well as the cytotoxic effects of activated immune cells. However, the HDI suberoylanilide hydroxamic acid (SAHA; vorinostat) interfered with the IL-2 activation of human NK cells and the priming of human tumour-specific T cells. In contrast, NK or T cells which were activated in the absence of HDIs became resistant to their immunosuppressive action. Therefore, as a therapeutic strategy, first the patient's immune system might be stimulated and then HDIs could sensitise the tumours for the attack of the pre-activated immune effector cells.

HDAC inhibitors and neurodegeneration: at the edge between protection and damage

The use of histone deacetylase inhibitors (HDACIs) as a therapeutic tool for neurodegenerative disorders has been examined with great interest in the last decade. The functional response to treatment with broad-spectrum inhibitors however, has been heterogeneous: protective in some cases and detrimental in others. In this review we discuss potential underlying causes for these apparently contradictory results. Because HDACs are part of repressive complexes, the functional outcome has been characteristically attributed to enhanced gene expression due to increased acetylation of lysine residues on nucleosomal histones. However, it is important to take into consideration that the up-regulation of diverse sets of genes (i.e. pro-apoptotic and anti-apoptotic) may orchestrate different responses in diverse cell types. An alternative possibility is that broad-spectrum pharmacological inhibition may target nuclear or cytosolic HDAC isoforms, with distinct non-histone substrates (i.e. transcription factors; cytoskeletal proteins). Thus, for any given neurological disorder, it is important to take into account the effect of HDACIs on neuronal, glial and inflammatory cells and define the relative contribution of distinct HDAC isoforms to the pathological process. This review article addresses how opposing effects on distinct cell types may profoundly influence the overall therapeutic potential of HDAC inhibitors when investigating treatments for neurodegenerative disorders.

Immunomodulatory effects of deacetylase inhibitors: therapeutic targeting of FOXP3+ regulatory T cells

Classical zinc-dependent histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and also from many non-histone proteins, including the transcription factor FOXP3, a key regulator of the development and function of regulatory T cells. Many HDAC inhibitors are in cancer clinical trials, but a subset of HDAC inhibitors has important anti-inflammatory or immunosuppressive effects that might be of therapeutic benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of HDAC inhibitors to enhance the production and suppressive functions of FOXP3(+) regulatory T cells. Understanding which HDACs contribute to the regulation of the functions of regulatory T cells may further stimulate the development of new class- or subclass-specific HDAC inhibitors with applications beyond oncology.

Histone deacetylases: salesmen and customers in the post-translational modification market

HDACs (histone deacetylases) are enzymes that remove the acetyl moiety from N-epsilon-acetylated lysine residues in histones and non-histone proteins. In recent years, it has turned out that HDACs themselves are also subject to post-translational modification. Such structural alterations can determine the stability, localization, activity and protein-protein interactions of HDACs. This subsequently affects the modification of their substrates and the co-ordination of cellular signalling networks. Intriguingly, physiologically relevant non-histone proteins are increasingly found to be deacetylated by HDACs, and aberrant deacetylase activity contributes to several severe human diseases. Targeting the catalytic activity of these enzymes and their post-translational modifications are therefore attractive targets for therapeutical intervention strategies. To achieve this ambitious goal, details on the molecular mechanisms regulating post-translational modifications of HDACs are required. This review summarizes aspects of the current knowledge on the biological role and enzymology of the phosphorylation, acetylation, ubiquitylation and sumoylation of HDACs.

Using histone deacetylase inhibitors to enhance Foxp3(+) regulatory T-cell function and induce allograft tolerance

The histone/protein deacetylase inhibitor (HDACi), trichostatin A (TsA), increases the production and suppressive function of Foxp3(+) regulatory T cells (T(regs)), at least in part, by promoting the acetylation of Foxp3 protein itself. Acetylation of Foxp3 is required for effective binding of Foxp3 to the promoter of the interleukin-2 (IL-2) gene and the suppression of IL-2 expression. We have sought to identify agents that had similar effects on T(regs), but without the associated toxicity of TsA. This review summarizes the contrasting effects of various HDACis on T(reg) functions in vitro and in vivo. Agents that block primarily class I HDAC had minimal or no effect on T(reg) suppression, whereas multiple inhibitors of both class I and class II HDAC enhanced T(reg) suppression in vitro and in vivo. These data indicate tools for further analysis of T(reg) functions, and point to a critical role of class II HDAC in the regulation of T(regs). Such knowledge has direct implications for the development of in vivo approaches to treat autoimmune and other inflammatory diseases.

HDAC inhibitors in models of inflammation-related tumorigenesis

Histone deacetylase (HDAC) inhibitors have been described in detail for their anti-proliferative potency. Recently, an anti-inflammatory property was characterized in vitro and in vivo. This dual efficacy of HDAC inhibitors is highly attractive, since chronic inflammations such as ulcerative colitis are associated with an increased risk of developing carcinomas. Additionally, in models of colitis and inflammation-induced tumorigenesis inflammation as well as tumor development was significantly inhibited by HDAC inhibitor treatment. The mechanisms involved reach beyond the simple regulation of histone acetylation and deacetylation. The currently known key target structures and mechanisms mediating this dual effect will be discussed in this review.

Blocking TH17-polarizing cytokines by histone deacetylase inhibitors in vitro and in vivo

Histone deacetylase (HDAC) inhibitors are small molecules inducing cell-cycle arrest, differentiation, and apoptosis, currently undergoing clinical trials as anticancer drugs. In addition, emerging evidence suggests HDAC inhibitors may have anti-inflammatory and immunomodulatory properties as well, although the molecular mechanisms remain poorly defined. Given the central role of dendritic cells (DC) in the induction and maintenance of the inflammatory and immune response, we investigated the effects of HDAC inhibitors on the maturation and activation of human monocyte-derived DC in the presence of LPS and IFN-gamma. Our results show that the production of T(H)1- and T(H)17-inducing cytokines, namely IL-12 and IL-23, was inhibited by trichostatin A (72% and 52%, respectively) and suberoylanilide hydroxamic acid (86% and 83%). Strikingly, HDAC inhibitors were effective if added simultaneously as well as after the proinflammatory challenge, and their effect was not associated to a reduction of expression or function of LPS/IFN-gamma receptors. These findings were confirmed in two different murine models. In addition, HDAC inhibitors selectively blocked the production of T(H)1-attracting chemokines CXCL9, CXCL10, and CXCL11. The reduction of T(H)1- and T(H)17-inducing cytokines as well as T(H)1-attracting chemokines may represent relevant mechanisms through which HDAC inhibitors at nonproapoptotic doses exert their immunomodulatory properties.

Evaluating epigenetic landmarks in the brain of multiple sclerosis patients: a contribution to the current debate on disease pathogenesis

The evidence suggesting a role of epigenetics in the definition of complex trait diseases is rapidly increasing. The gender prevalence of multiple sclerosis, the low level concordance in homozygous twins and the linkage to several genetic loci, suggest an epigenetic component to the definition of this demyelinating disorder. While the immune etio-pathogenetic mechanism of disease progression has been well characterized, still relatively little is known about the initial events contributing to onset and progression of the demyelinating lesion. This article addresses the challenging question of whether loss of the mechanisms of epigenetic regulation of gene expression in the myelinating cells may contribute to the pathogenesis of multiple sclerosis, by affecting the repair process and by modulating the levels of enzymes involved in neo-epitope formation. The role of altered post-translational modifications of nucleosomal histones and DNA methylation in white matter oligodendroglial cells are presented in terms of pathogenetic concepts and the relevance to therapeutic intervention is then discussed.

Cutting edge: chromatin remodeling as a molecular basis for the enhanced functionality of memory CD8 T cells

Memory CD8 T cells, unlike their naive precursors, are capable of rapidly producing high levels of cytokines, killing target cells, and proliferating into numerous secondary effectors immediately upon Ag encounter. This ready-to-respond state contributes to their superior ability to confer protective immunity, yet the underlying molecular basis remains unknown. In this study, we show that memory CD8 T cells have increased histone acetylation compared with naive CD8 T cells; however, those activated without CD4 T cell help ("unhelped") remain hypoacetylated and fail to develop into functional, protective memory. Treatment with a histone deacetylase inhibitor during activation results in increased histone acetylation in unhelped CD8 T cells and restores their ability to differentiate into functional memory cells capable of immediate cytokine production and providing protective immunity. These results demonstrate that CD4 T help-dependent chromatin remodeling provides a molecular basis for the enhanced responsiveness of memory CD8 T cells.

Effects of histone deacetylase inhibitor SAHA on effector and FOXP3+regulatory T cells in rhesus macaques

Suberoylanilide hydroxamic acid (SAHA) a histone deacetylase inhibitor (HDACi), is clinically approved for treatment of cutaneous T-cell lymphoma. Although the exact underlying mechanisms are unknown, HDACi arrests the cell cycle in rapidly proliferating tumor cells and promote their apoptosis. HDACi were also recently shown to enhance the production and suppressive functions of Foxp3+ regulatory T (Treg) cells in rodents, leading us to begin to investigate the actions of HDACi on rhesus monkey T cells for the sake of potential preclinical applications. In this study, we show that SAHA inhibits polyclonal activation and proliferation of rhesus T cells and that the antiproliferative effects are due to inhibition of T-effector (Teff) cells and enhancement of Treg cells. Cryopreserved rhesus macaque splenocytes were CFSE labeled, stimulated with anti-CD3/anti-CD28 and cultured for 5 days in the presence of varying concentrations of SAHA. Samples were then costained to evaluate CD4 and CD8 expression. Concentrations of SAHA (10 and 5 micromol/L) were toxic to splenocytes. Proliferation was inhibited by 57% in CD4 cells and 47% in CD8 cells when unseparated splenocytes were cultured with 3 micromol/L SAHA. Effector cells alone showed decreased inhibition to proliferation when cultured with 3 micromol/L and 1 micromol/L SAHA when compared to Teff plus Treg cells. Our data suggest that SAHA can be used as part of an immunosuppressive protocol to enhance graft survival by limiting Teff cell proliferation as well as increasing Treg cells, thereby promoting tolerance.

Trichostatin A down-regulates CYP19 transcript and protein levels in MCF-7 breast cancer cells

Epidemiological and experimental evidence implicates estrogens in the etiology and progression of breast cancer. The biosynthesis of estrogens from androgens is catalyzed by an enzymatic complex designated as aromatase (CYP19). Using quantitative real-time PCR and Western blot analysis, we demonstrated that trichostatin A (TSA) histone deacetylase inhibitor significantly reduced CYP19 transcript and protein contents in MCF-7 breast cancer cells. We also found that TSA lowered CYP19 transcript stability and significantly decreased the transcript's half-life from approximately 6h to 3.5h. Our results from experiments with a protein biosynthesis inhibitor suggest the involvement of an RNase and/or mRNA stabilization protein in CYP19 transcript stabilization. Since malignant tissue aromatase is a significant estrogen producer involved in breast tumor progression, our findings may have clinical implication.

Histone deacetylase regulation of immune gene expression in tumor cells

Epigenetic modifications of chromatin, such as histone acetylation, are involved in repression of tumor antigens and multiple immune genes that are thought to facilitate tumor escape. The status of acetylation in a cell is determined by the balance of the activities of histone acetyltransferases and histone deacetylases. Inhibitors of histone deacetylase (HDACi) can enhance the expression of immunologically important molecules in tumor cells and HDACi treated tumor cells are able to induce immune responses in vitro and in vivo. Systemic HDACi are in clinical trails in cancer and also being used in several autoimmune disease models. To date, 18 HDACs have been reported in human cells and more than thirty HDACi identified, although only a few immune targets of these inhibitors have been identified. Here, we discuss the molecular pathways employed by HDACi and their potential role in inducing immune responses against tumors. We review data suggesting that selection of target specific HDACi and combinations with other agents and modalities, including those that activate stress pathways, may further enhance the efficacy of epigenetic therapies.

Trichostatin A and oncolytic HSV combination therapy shows enhanced antitumoral and antiangiogenic effects

Oncolytic herpes simplex viruses (HSVs) possess direct oncolytic and antiangiogenic activities and are promising anticancer agents, but their efficacy, when used as single agents, leaves room for improvement. We investigated whether combination therapy of HSV with histone deacetylase inhibitor trichostatin A (TSA), an agent that also targets cancer cells and tumor vasculature, would result in enhanced efficacy. In vitro, TSA and G47Delta showed strong synergy of action against proliferating endothelial cells, varying degrees of synergistic action against most cancer cell lines, but no effect in quiescent, normal endothelial and prostate epithelial cells. Synergy is dependent on viral replication; however, it is not dependent on the dosing sequence of TSA and G47Delta, viral genetic alterations, infectivity, or replication kinetics of G47Delta. Using an isogenic cell system, we found that a high level of cellular cyclin D1 is also critically important for the interaction. Normal cells with low cyclin D1 levels were not subjected to toxicity by either agent. In tumor cells and proliferating endothelial cells, the combination treatment enhanced the inhibition of cyclin D1 and vascular endothelial growth factor (VEGF). Concurrent systemic TSA and intratumoral G47Delta administration resulted in enhanced antiangiogenesis and enhanced antitumoral efficacy in animal models. Therefore, combination treatment with TSA and oncolytic HSV provides a novel approach to cancer therapy.

A shifting paradigm: histone deacetylases and transcriptional activation

Transcriptional repression and silencing have been strongly associated with hypoacetylation of histones. Accordingly, histone deacetylases, which remove acetyl groups from histones, have been shown to participate in mechanisms of transcriptional repression. Therefore, current models of the role of acetylation in transcriptional regulation focus on the acetylation status of histones and designate histone acetyltransferases, which add acetyl groups to histones, as transcriptional coactivators and histone deacetylases as corepressors. In recent years, an accumulation of studies have shown that these enzymes also target non-histone proteins and that histone deacetylases have clear roles as coactivators at a variety of genes, some of which are key regulators of cell growth and survival. This review summarizes the evidence for histone deacetylases as coactivators and provides models of coactivation mechanisms, some of which integrate roles of acetylated histones and non-histone proteins in transcription.

HDAC inhibitor reduces cytokine storm and facilitates induction of chimerism that reverses lupus in anti-CD3 conditioning regimen

In allogeneic hematopoietic cell transplantation (HCT), donor T cell-mediated graft versus host leukemia (GVL) and graft versus autoimmune (GVA) activity play critical roles in treatment of hematological malignancies and refractory autoimmune diseases. However, graft versus host disease (GVHD), which sometimes can be fatal, remains a major obstacle in classical HCT, where recipients are conditioned with total body irradiation or high-dose chemotherapy. We previously reported that anti-CD3 conditioning allows donor CD8(+) T cells to facilitate engraftment and mediate GVL without causing GVHD. However, the clinical application of this radiation-free and GVHD preventative conditioning regimen is hindered by the cytokine storm syndrome triggered by anti-CD3 and the high-dose donor bone marrow (BM) cells required for induction of chimerism. Histone deacetylase (HDAC) inhibitors such as suberoylanilide hydroxamic acid (SAHA) are known to induce apoptosis of cancer cells and reduce production of proinflammatory cytokines by nonmalignant cells. Here, we report that SAHA inhibits the proliferative and cytotoxic activity of anti-CD3-activated T cells. Administration of low-dose SAHA reduces cytokine production and ameliorates the cytokine storm syndrome triggered by anti-CD3. Conditioning with anti-CD3 and SAHA allows induction of chimerism with lower doses of donor BM cells in old nonautoimmune and autoimmune lupus mice. In addition, conditioning with anti-CD3 and SAHA allows donor CD8(+) T cell-mediated GVA activity to reverse lupus glomerulonephritis without causing GVHD. These results indicate that conditioning with anti-CD3 and HDAC inhibitors represent a radiation-free and GVHD-preventative regimen with clinical application potential.

Deacetylase inhibition promotes the generation and function of regulatory T cells

Histone/protein deacetylases (HDACs) regulate chromatin remodeling and gene expression as well as the functions of more than 50 transcription factors and nonhistone proteins. We found that administration of an HDAC inhibitor (HDACi) in vivo increased Foxp3 gene expression, as well as the production and suppressive function of regulatory T cells (T(reg) cells). Although T(reg) cells express multiple HDACs, HDAC9 proved particularly important in regulating Foxp3-dependent suppression. Optimal T(reg) function required acetylation of several lysines in the forkhead domain of Foxp3, and Foxp3 acetylation enhanced binding of Foxp3 to the Il2 promoter and suppressed endogenous IL-2 production. HDACi therapy in vivo enhanced T(reg)-mediated suppression of homeostatic proliferation, decreased inflammatory bowel disease through T(reg)-dependent effects, and, in conjunction with a short course of low-dose rapamycin, induced permanent, T(reg)-dependent cardiac and islet allograft survival and donor-specific allograft tolerance. Our data show that use of HDACi allows the beneficial pharmacologic enhancement of both the numbers and suppressive function of Foxp3(+) T(reg) cells.

Trichostatin A, sodium butyrate, and 5-aza-2′-deoxycytidine alter the expression of glucocorticoid receptor α and β isoforms in Hut-78 T- and Raji B-lymphoma cell lines

The glucocorticoid receptor (GR) is mainly expressed as nine-exon alternatively spliced variants, encoding functional GRalpha and nonfunctional GRbeta. Overexpression of GRbeta splice variant was found in glucocorticoid-resistant patients with some autoimmune diseases and hematological malignancies. Employing reverse transcription, real-time quantitative PCR, and western blot analysis, we determined an effect of trichostatin A (TSA), sodium butyrate (NaBu) and 5-aza-2'-deoxycytidine (5-dAzaC) on GRalpha and GRbeta expression in Hut-78 T- and Raji B-lymphoma cell lines. We found that TSA, NaBu, and 5-dAzaC significantly increase the expression of GRalpha transcript and protein, whereas GRbeta transcript and protein expression was profoundly decreased in Hut-78 T- and Raji B- lymphoma cell lines. Our observation suggests that changes of epigenetic milieu inside cells may alter the expression of GRalpha and GRbeta isoforms.

Valproic acid and other histone deacetylase inhibitors induce microglial apoptosis and attenuate lipopolysaccharide-induced dopaminergic neurotoxicity

Valproic acid (VPA), a widely prescribed drug for seizures and bipolar disorder, has been shown to be an inhibitor of histone deacetylase (HDAC). Our previous study has demonstrated that VPA pretreatment reduces lipopolysaccharide (LPS)-induced dopaminergic (DA) neurotoxicity through the inhibition of microglia over-activation. The aim of this study was to determine the mechanism underlying VPA-induced attenuation of microglia over-activation using rodent primary neuron/glia or enriched glia cultures. Other histone deacetylase inhibitors (HDACIs) were compared with VPA for their effects on microglial activity. We found that VPA induced apoptosis of microglia cells in a time- and concentration-dependent manner. VPA-treated microglial cells showed typical apoptotic hallmarks including phosphatidylserine externalization, chromatin condensation and DNA fragmentation. Further studies revealed that trichostatin A (TSA) and sodium butyrate (SB), two structurally dissimilar HDACIs, also induced microglial apoptosis. The apoptosis of microglia was accompanied by the disruption of mitochondrial membrane potential and the enhancement of acetylation levels of the histone H3 protein. Moreover, pretreatment with SB or TSA caused a robust decrease in LPS-induced pro-inflammatory responses and protected DA neurons from damage in mesencephalic neuron-glia cultures. Taken together, our results shed light on a novel mechanism whereby HDACIs induce neuroprotection and underscore the potential utility of HDACIs in preventing inflammation-related neurodegenerative disorders such as Parkinson's disease.