Induction of differentiation in F9 cells and activation of peroxisome proliferator-activated receptor delta by valproic acid and its teratogenic derivatives

Is the peroxisome proliferator-activated receptor gamma a putative target for epilepsy treatment? Current evidence and future perspectives

The peroxisome proliferator-activated receptor gamma (PPARγ), which belongs to the family of nuclear receptors, has been mainly studied as an important factor in metabolic disorders. However, in recent years the potential role of PPARγ in different neurological diseases has been increasingly investigated. Especially, in the search of therapeutic targets for patients with epilepsy the question of the involvement of PPARγ in seizure control has been raised. Epilepsy is a chronic neurological disorder causing a major impact on the psychological, social, and economic conditions of patients and their families, besides the problems of the disease itself. Considering that the world prevalence of epilepsy ranges between 0.5% - 1.0%, this condition is the fourth for importance among the other neurological disorders, following migraine, stroke, and dementia. Among others, temporal lobe epilepsy (TLE) is the most common form of epilepsy in adult patients. About 65% of individuals who receive antiseizure medications (ASMs) experience seizure independence. For those in whom seizures still recur, investigating PPARγ could lead to the development of novel ASMs. This review focuses on the most important findings from recent investigations about the potential intracellular PPARγ-dependent processes behind different compounds that exhibited anti-seizure effects. Additionally, recent clinical investigations are discussed along with the promising results found for PPARγ agonists and the ketogenic diet (KD) in various rodent models of epilepsy.

Valproic acid autoinduction: a case-based review

Although valproic acid (VPA) induces the metabolism of multiple other drugs, the clinical reports of VPA autoinduction are rare. A comprehensive literature search yielded only one published case series, which provided the rationale to conduct a review of the published cases along with a new case of VPA autoinduction. Although there may be myriad of reasons for lack of published cases of VPA autoinduction, potential underreporting may be one of the core reasons. Lack of understanding into the highly complex metabolism of VPA may also make it difficult to recognize and report VPA autoinduction. However, it is important to mention that in addition to autoinduction increased elimination of VPA may be mediated by several pharmacokinetic (PK) factors, such as drug interactions, genetic polymorphisms of metabolic enzymes, and protein displacement reactions. As VPA is metabolized by multiple metabolic pathways, the risk for drug interactions is relatively high. There is also a growing evidence for high genetic inducibility of some enzymes involved in VPA metabolism. Protein displacement reactions with VPA increase the biologically active and readily metabolizable free fraction and pose a diagnostic challenge as they are usually not requested by most clinicians. Thus, monitoring of free fraction with total VPA levels may prevent clinically serious outcomes and optimize VPA treatment in clinically challenging patients. This case-based review compares the clinical data from three published cases and a new case of VPA autoinduction to enhance clinicians' awareness of this relatively rare but clinically relevant phenomenon along with a discussion of potential underlying mechanisms.

Molecular Targets and Early Response Biomarkers for the Prediction of Developmental Toxicity In Vitro

There is an urgent need for new in vitro methods to predict the potential developmental toxicity of candidate drugs in the early lead identification and optimisation process. This would lead to a reduction in the total number of animals required in full-scale developmental toxicology studies, and would improve the efficiency of drug development. However, suitable in vitro systems permitting robust high-throughput screening for this purpose, for the most part, remain to be designed. An understanding of the mechanisms involved in developmental toxicity may be essential for the validation of in vitro tests. Early response biomarkers — even a single one — could contribute to reducing assay time and facilitating automation. The use of toxicogenomics approaches to study in vitro and in vivo models in parallel may be a powerful tool in defining such mechanisms of action and the molecular targets of toxicity, and also for use in finding possible biomarkers of early response. Using valproic acid as a model substance, the use of DNA microarrays to identify teratogen-responsive genes in cell models is discussed. It is concluded that gene expression in P19 mouse embryocarcinoma cells represents a potentially suitable assay system, which could be readily used in a tiered testing system for developmental toxicity testing.

An Atomic Force Microscope Study Revealed Two Mechanisms in the Effect of Anticancer Drugs on Rate-Dependent Young's Modulus of Human Prostate Cancer Cells

Mechanical properties of cells have been recognized as a biomarker for cellular cytoskeletal organization. As chemical treatments lead to cell cytoskeletal rearrangements, thereby, modifications of cellular mechanical properties, investigating cellular mechanical property variations provides insightful knowledge to effects of chemical treatments on cancer cells. In this study, the effects of eight different anticancer drugs on the mechanical properties of human prostate cancer cell (PC-3) are investigated using a recently developed control-based nanoindentation measurement (CNM) protocol on atomic force microscope (AFM). The CNM protocol overcomes the limits of other existing methods to in-liquid nanoindentation measurement of live cells on AFM, particularly for measuring mechanical properties of live cells. The Young's modulus of PC-3 cells treated by the eight drugs was measured by varying force loading rates over three orders of magnitude, and compared to the values of the control. The results showed that the Young's modulus of the PC-3 cells increased substantially by the eight drugs tested, and became much more pronounced as the force load rate increased. Moreover, two distinct trends were clearly expressed, where under the treatment of Disulfiram, paclitaxel, and MK-2206, the exponent coefficient of the frequency- modulus function remained almost unchanged, while with Celebrex, BAY, Totamine, TPA, and Vaproic acid, the exponential rate was significantly increased.

A Phase I Protocol of Hydralazine and Valproic Acid in Advanced, Previously Treated Solid Cancers

Smokers experience aberrant gene promoter methylation in their bronchial cells, which may predispose to the development of neoplasia. Hydralazine is a DNA demethylating agent, and valproic acid is a histone deacetylase inhibitor, and both have modest but synergistic anticancer activity in vitro. We conducted a phase I trial combining valproic acid and hydralazine to determine the maximally tolerated dose (MTD) of hydralazine in combination with a therapeutic dose of valproic acid in patients with advanced, unresectable, and previously treated solid cancers. Twenty females and nine males were enrolled, with a median age of 57 years and a median ECOG performance status of 0. Grade 1 lymphopenia and fatigue were the most common adverse effects. Three subjects withdrew for treatment-related toxicities occurring after the DLT observation period, including testicular edema, rash, and an increase in serum lipase accompanied by hyponatremia in one subject each. A true MTD of hydralazine in combination with therapeutic doses of valproic acid was not reached in this trial, and the planned upper limit of hydralazine investigated in this combination was 400 mg/day without grade 3 or 4 toxicities. A median number of two treatment cycles were delivered. One partial response by Response Evaluation Criteria In Solid Tumors criteria was observed, and five subjects experienced stable disease for 3 to 6 months. The combination of hydralazine and valproic acid is simple, nontoxic, and might be appropriate for chemoprevention or combination with other cancer treatments. This trial supports further investigation of epigenetic modification as a new therapeutic strategy.

Valproic acid enhances Oct4 promoter activity through PI3K/Akt/mTOR pathway activated nuclear receptors

Valproic acid (VPA) has been shown to increase the reprogramming efficiency of induced pluripotent stem cells (iPSC) from somatic cells, but the mechanism by which VPA enhances iPSC induction has not been defined. Here we demonstrated that VPA directly activated Oct4 promoter activity through activation of the PI3K/Akt/mTOR signaling pathway that targeted the proximal hormone response element (HRE, -41∼-22) in this promoter. The activating effect of VPA is highly specific as similar compounds or constitutional isomers failed to instigate Oct4 promoter activity. We further demonstrated that the upstream 2 half-sites in this HRE were essential to the activating effect of VPA and they were targeted by a subset of nuclear receptors, such as COUP-TFII and TR2. These findings show the first time that NRs are implicated in the VPA stimulated expression of stem cell-specific factors and should invite more investigation on the cooperation between VPA and NRs on iPSC induction.

AP2α transcriptional activity is essential for retinoid-induced neuronal differentiation of mesenchymal stem cells

Pre-activation of the retinoid signaling pathway by all-trans retinoic acid facilitates neuronal differentiation of mesenchymal stem cells. Using protein/DNA based screening assays, we identified activator protein 2α as an important downstream target of all-trans retinoic acid. Although all-trans retinoic acid treatment significantly increased activator protein 2α transcriptional activity, it did not affect its expression. Inhibition of activator protein 2α with dominant-negative mutants reduced ATRA-induced differentiation of mesenchymal stem cells into neurons and reversed its associated functional recovery of memory impairment in the cell-based treatment of a hypoxic-ischemic brain damage rat model. Dominant-negative mutants of activator protein 2α inhibited the expression of neuronal markers which were induced by retinoic acid receptor β activation. All-trans retinoic acid treatment increased phosphorylation of activator protein 2α and resulted in its nuclear translocation. This was blocked by siRNA-mediated knockdown of retinoic acid receptor β. Furthermore, we found that retinoic acid receptor β directly interacted with activator protein 2α. In summary, the regulation of all-trans retinoic acid on activator protein 2α transcriptional activity was mediated by activation of retinoic acid receptor β and subsequent phosphorylation and nuclear translocation of activator protein 2α. Our results strongly suggest that activator protein 2α transcriptional activity is essential for all-trans retinoic acid-induced neuronal differentiation of mesenchymal stem cells.

Effects of lithium and valproic acid on gene expression and phenotypic markers in an NT2 neurosphere model of neural development

Mood stabilising drugs such as lithium (LiCl) and valproic acid (VPA) are the first line agents for treating conditions such as Bipolar disorder and Epilepsy. However, these drugs have potential developmental effects that are not fully understood. This study explores the use of a simple human neurosphere-based in vitro model to characterise the pharmacological and toxicological effects of LiCl and VPA using gene expression changes linked to phenotypic alterations in cells. Treatment with VPA and LiCl resulted in the differential expression of 331 and 164 genes respectively. In the subset of VPA targeted genes, 114 were downregulated whilst 217 genes were upregulated. In the subset of LiCl targeted genes, 73 were downregulated and 91 were upregulated. Gene ontology (GO) term enrichment analysis was used to highlight the most relevant GO terms associated with a given gene list following toxin exposure. In addition, in order to phenotypically anchor the gene expression data, changes in the heterogeneity of cell subtype populations and cell cycle phase were monitored using flow cytometry. Whilst LiCl exposure did not significantly alter the proportion of cells expressing markers for stem cells/undifferentiated cells (Oct4, SSEA4), neurons (Neurofilament M), astrocytes (GFAP) or cell cycle phase, the drug caused a 1.4-fold increase in total cell number. In contrast, exposure to VPA resulted in significant upregulation of Oct4, SSEA, Neurofilament M and GFAP with significant decreases in both G2/M phase cells and cell number. This neurosphere model might provide the basis of a human-based cellular approach for the regulatory exploration of developmental impact of potential toxic chemicals.

Dissecting the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in colon, breast, and lung carcinogenesis

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a promising drug target since its agonists increase serum high-density lipoprotein; decrease low-density lipoprotein, triglycerides, and insulin associated with metabolic syndrome; improve insulin sensitivity; and decrease high fat diet-induced obesity. PPARβ/δ agonists also promote terminal differentiation and elicit anti-inflammatory activities in many cell types. However, it remains to be determined whether PPARβ/δ agonists can be developed as therapeutics because there are reports showing either pro- or anti-carcinogenic effects of PPARβ/δ in cancer models. This review examines studies reporting the role of PPARβ/δ in colon, breast, and lung cancers. The prevailing evidence would suggest that targeting PPARβ/δ is not only safe but could have anti-carcinogenic protective effects.

Homeobox gene Rhox5 is regulated by epigenetic mechanisms in cancer and stem cells and promotes cancer growth

Background

Homeobox genes murine Rhox5 and human RHOXF1 are expressed in early embryonic stages and then mostly restricted to germline tissues in normal adult, yet they are aberrantly expressed in cancer cells in vitro and in vivo . Here we study the epigenetic regulation and potential functions of Rhox5 gene.

Findings

In Rhox5 -silenced or extremely low expresser cells, we observed low levels of active histone epigenetic marks (H3ac, H4ac and H3K4me2) and high levels of repressive mark H3K9me2 along with DNA hypermethylation in the promoter. In Rhox5 low expresser cells, we typically observed modest levels of both active and repressive histone marks along with moderate DNA methylation. In Rhox5 highly expressed CT26 cancer cells, we observed DNA hypomethylation along with high levels of both active and repressive histone marks. Epigenetic drugs (retinoic acid and MS-275) induced F9 cell differentiation with enhanced Rhox5 expression and dynamic changes of epigenetic marks. Finally, Rhox5 knockdown by small hairpin RNA (shRNA) in CT26 colon cancer decreased cell proliferation and migration in vitro and tumor growth in vivo .

Conclusions

Both DNA methylation and histone methylation/acetylation play key roles in modulating Rhox5 expression in various cell types. The stem cell-like "bivalent domain", an epigenetic feature originally identified in key differentiation genes within stem cells, exists in the Rhox5 gene promoter in not only embryonic stem cells but also cancer cells, cancer stem cells, and differentiated Sertoli cells. As Ras signaling-dependent Rhox5 expression promotes tumor growth, Rhox5 may be an ideal target for therapeutic intervention in cancer.

Interpreting clinical assays for histone deacetylase inhibitors

As opposed to genetics, dealing with gene expressions by direct DNA sequence modifications, the term epigenetics applies to all the external influences that target the chromatin structure of cells with impact on gene expression unrelated to the sequence coding of DNA itself. In normal cells, epigenetics modulates gene expression through all development steps. When "imprinted" early by the environment, epigenetic changes influence the organism at an early stage and can be transmitted to the progeny. Together with DNA sequence alterations, DNA aberrant cytosine methylation and microRNA deregulation, epigenetic modifications participate in the malignant transformation of cells. Their reversible nature has led to the emergence of the promising field of epigenetic therapy. The efforts made to inhibit in particular the epigenetic enzyme family called histone deacetylases (HDACs) are described. HDAC inhibitors (HDACi) have been proposed as a viable clinical therapeutic approach for the treatment of leukemia and solid tumors, but also to a lesser degree for noncancerous diseases. Three epigenetic drugs are already arriving at the patient's bedside, and more than 100 clinical assays for HDACi are registered on the National Cancer Institute website. They explore the eventual additive benefits of combined therapies. In the context of the pleiotropic effects of HDAC isoforms, more specific HDACi and more informative screening tests are being developed for the benefit of the patients.

Molecular and therapeutic potential and toxicity of valproic acid

Valproic acid (VPA), a branched short-chain fatty acid, is widely used as an antiepileptic drug and a mood stabilizer. Antiepileptic properties have been attributed to inhibition of Gamma Amino Butyrate (GABA) transaminobutyrate and of ion channels. VPA was recently classified among the Histone Deacetylase Inhibitors, acting directly at the level of gene transcription by inhibiting histone deacetylation and making transcription sites more accessible. VPA is a widely used drug, particularly for children suffering from epilepsy. Due to the increasing number of clinical trials involving VPA, and interesting results obtained, this molecule will be implicated in an increasing number of therapies. However side effects of VPA are substantially described in the literature whereas they are poorly discussed in articles focusing on its therapeutic use. This paper aims to give an overview of the different clinical-trials involving VPA and its side effects encountered during treatment as well as its molecular properties.

Histone deacetylase inhibitors induce cytochrome P450 2B by activating nuclear receptor constitutive androstane receptor

Valproic acid, a histone deacetylase (HDAC) inhibitor, induces the cytochrome P450 2B subfamily. However, the effects of HDAC inhibitors on CYP2B induction are still not fully understood. Nuclear receptor constitutive androstane receptor (CAR) is a key regulator of CYP2B induction. In this study, we investigated the effect of HDAC inhibitors on CAR-mediated CYP2B induction. The expression of CYP2B6 mRNA was induced in HepG2 cells stably expressing mouse CAR (Ym17) by HDAC inhibitors including valproic acid, phenylbutyrate, and trichostatin A. HDAC inhibitors activated the phenobarbital-responsive enhancer module of the CYP2B6 promoter in transient transfection reporter assays with Ym17 cells. Furthermore, HDAC inhibitors synergistically augmented the effect of the CAR ligand, 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, in the transactivation of CYP2B6 mRNA and the promoter assay in Ym17 cells. Intraperitoneal injection of HDAC inhibitors induced Cyp2b10 mRNA in wild-type mice. However, such induction was not observed in CAR(-/-) mice. Immunoprecipitation demonstrated that CAR formed a complex with HDACs. HDAC inhibitors diminished the binding between CAR and HDAC1 and augmented the binding of steroid receptor coactivator-1 (SRC-1) to CAR. Furthermore, small interfering RNA knockdown of HDAC1 increased CYP2B6 mRNA expression. These results provide novel insight into the mechanism by which HDAC inhibitors affect gene expression of CYP2B6. HDAC inhibitors have the potential to up-regulate CYP2B6 through the dissociation of HDAC1 and recruitment of SRC-1 to receptor CAR.

Structure-function studies for the panacea, valproic acid

The anticonvulsant properties of VPA (valproic acid), a branched short-chain fatty acid, were serendipitously discovered in 1963. Since then, therapeutic roles of VPA have increased to include bipolar disorder and migraine prophylaxis, and have more recently been proposed in cancer, Alzheimer's disease and HIV treatment. These numerous therapeutic roles elevate VPA to near 'panacea' level. Surprisingly, the mechanisms of action of VPA in the treatment of many of these disorders remain unclear, although it has been shown to alter a wide variety of signalling pathways and a small number of direct targets. To analyse the mechanism of action of VPA, a number of studies have defined the structural characteristics of VPA-related compounds giving rise to distinct therapeutic and cellular effects, including adverse effects such as teratogenicity and hepatotoxicity. These studies raise the possibility of identifying target-specific novel compounds, providing better therapeutic action or reduced side effects. This short review will describe potential therapeutic pathways targeted by VPA, and highlight studies showing structural constraints necessary for these effects.

Nuclear receptors: the controlling force in drug metabolism of the liver?

The body is in a constant battle to achieve homeostasis; indeed, the robustness with which it can respond to moves away from homeostasis is a vital part in the survival of the organism as a whole. There thus exists a need for a network of sensors that are able to capture, interpret, and respond to alterations in chemical levels that move the body away from homeostasis and this applies to both endogenous and exogenous chemicals. With respect to external chemicals (xenobiotics), this xenosensing is often carried out through specific interactions with cellular receptors. The phenomenon of 'xenosensing' has attracted much interest of late, whereby xenobiotics interact with receptors resulting in the activation of a battery of genes mediating oxidative drug metabolism, conjugation, and transport, thereby enhancing the elimination of the xenobiotic by the organism. However, this beneficial response is counterbalanced by the increasingly recognized role of nuclear receptors in mediating drug-drug interactions via enzyme induction or the production of toxicity through interaction with endogenous pathways. This review will focus on the role of nuclear receptors in mediating these effects, and how such knowledge will contribute to a mechanism-based risk assessment for xenobiotics.

Clinical and biological effects of valproic acid as a histone deacetylase inhibitor on tumor and surrogate tissues: phase I/II trial of valproic acid and epirubicin/FEC

PURPOSE

The aim was to study the biological and molecular effects of the histone deacetylase (HDAC) inhibitor, valproic acid, in patients with solid tumor malignancies.

EXPERIMENTAL DESIGN

A phase I dose escalation of valproic acid given on days 1 to 3 followed by epirubicin (day 3) was followed by a dose expansion of valproic acid combined with 5-fluorouracil, epirubicin, and cyclophosphamide (FEC100). Pharmacodynamic and pharmacokinetic studies entailed valproic acid and epirubicin plasma levels and their interaction, the effects of valproic acid on histone acetylation in peripheral blood mononuclear cells (PBMC) and tumor cells at baseline and day 3, and baseline expression of HDAC2 and HDAC6 as therapeutic targets.

RESULTS

Forty-four patients were enrolled in the phase I part, with a disease-specific cohort expansion of 15 breast cancer patients (median age, 55 years; range, 28-66 years) receiving 120 mg/kg/day valproic acid followed by FEC100. Partial responses were seen in 9 of 41 (22%) patients during the phase I part. Objective responses were seen in 9 of 14 (64%) evaluable patients at the dose expansion with a median number of 6 administered cycles. Predominant toxicities were valproic acid-associated somnolence and epirubicin-induced myelosuppression. Valproic acid plasma levels were associated with short-term, reversible depletion of WBC and neutrophils within 48 hours. Histone acetylation in tumor samples and in PBMCs correlated with valproic acid levels and was further linked to baseline HDAC2 but not to HDAC6 expression.

CONCLUSION

Valproic acid is a clinically relevant HDAC inhibitor, and PBMCs may serve as a surrogate for tumor histone acetylation in solid tumor malignancies. HDAC2 should be further considered as a relevant therapeutic target.

Anti-leukemic activity of valproic acid and imatinib mesylate on human Ph+ ALL and CML cells in vitro

The armamentarium of anti-leukemic drugs has increased substantially since anti-leukemic activities were recently found for a variety of non-classical cytostatic drugs, among them the histone deacetylase (HDAC) inhibitor valproic acid (VPA). This study investigated the effect of VPA on proliferation and apoptosis of human Philadelphia chromosome-positive (Ph+) acute lymphatic (ALL) and chronic myeloid leukemia (CML) cells and on colony formation of human chronic-phase CML progenitor cells. Strong anti-proliferative and pro-apoptotic effects of VPA were observed on human ALL and CML cell lines at concentrations achievable in vivo. These effects were most pronounced in ALL cell lines as well as in primary ALL cells. Notably, VPA revealed enhanced activity with imatinib mesylate, nilotinib, the farnesyl transferase inhibitor SCH66336, interferon-alpha and cytosine arabinoside. VPA inhibited the growth of colony-forming cells from 12 Ph+ chronic-phase CML patients but also of those from normal healthy controls in a dose-dependent fashion. HDAC-inhibiting activity of VPA was confirmed on ALL and CML cells. In conclusion, VPA, whether alone or in combination with other non-classical anti-leukemic compounds, exerts significant anti-leukemic effects on human ALL and CML cells.

Epigenetic mechanisms in AML - a target for therapy

Epigenetics refers to a stable, mitotically perpetuated regulatory mechanism of gene expression without an alteration of the coding sequence. Epigenetic mechanism include DNA methylation and histone tail modifications. Epigenetic regulation is part of physiologic development and becomes abnormal in neoplasia, where silencing of critical genes by DNA methylation or histone deacetylation can contribute to leukemogenesis as an alternative to deletion or loss-of-function mutation. In acute myelogenous leukemia (AML), aberrant DNA methylation can be observed in multiple functionally relevant genes such as p15, p 73, E-cadherin, ID 4, RARbeta2. Abnormal activities of histone tail-modifying enzymes have also been seen in AML, frequently as a direct result of chromosomal translocations. It is now clear that these epigenetic changes play a significant role in development and progression of AML, and thus constitute important targets of therapy. The aim of targeting epigenetic effector protein or "epigenetic therapy" is to reverse epigenetic silencing and reactive various genes to induce a therapeutic effect such as differentiation, growth arrest, or apoptosis. Recent clinical studies have shown the relative safety and efficacy of such epigenetic therapies.

Role of peroxisome-proliferator-activated receptor beta/delta (PPARbeta/delta) in gastrointestinal tract function and disease

PPARbeta/delta (peroxisome-proliferator-activated receptor beta/delta) is one of three PPARs in the nuclear hormone receptor superfamily that are collectively involved in the control of lipid homoeostasis among other functions. PPARbeta/delta not only acts as a ligand-activated transcription factor, but also affects signal transduction by interacting with other transcription factors such as NF-kappaB (nuclear factor kappaB). Constitutive expression of PPARbeta/delta in the gastrointestinal tract is very high compared with other tissues and its potential physiological roles in this tissue include homoeostatic regulation of intestinal cell proliferation/differentiation and modulation of inflammation associated with inflammatory bowel disease and colon cancer. Analysis of mouse epithelial cells in the intestine and colon has clearly demonstrated that ligand activation of PPARbeta/delta induces terminal differentiation. The PPARbeta/delta target genes mediating this effect are currently unknown. Emerging evidence suggests that PPARbeta/delta can suppress inflammatory bowel disease through PPARbeta/delta-dependent and ligand-independent down-regulation of inflammatory signalling. However, the role of PPARbeta/delta in colon carcinogenesis remains controversial, as conflicting evidence suggests that ligand activation of PPARbeta/delta can either potentiate or attenuate this disease. In the present review, we summarize the role of PPARbeta/delta in gastrointestinal physiology and disease with an emphasis on findings in experimental models using both high-affinity ligands and null-mouse models.

Ligand activation of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) attenuates carbon tetrachloride hepatotoxicity by downregulating proinflammatory gene expression

Peroxisome proliferator-activated receptor (PPAR) beta/delta-null mice exhibit exacerbated hepatotoxicity in response to administration of carbon tetrachloride (CCl(4)). To determine whether ligand activation of the receptor protects against chemical toxicity in the liver, wild-type and PPARbeta/delta-null mice were administered CCl(4) with or without coadministration of the highly specific PPARbeta/delta ligand GW0742. Biomarkers of liver toxicity, including serum alanine aminotransferase (ALT) and hepatic tumor necrosis factor (TNF) alpha mRNA, were significantly higher in CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. Hepatic expression of TNF-like weak inducer of apoptosis receptor (TWEAKr) and S100 calcium-binding protein A6 (S100A6/calcyclin), genes involved in nuclear factor kappa B signaling, was higher in the CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. GW0742 treatment resulted in reduced serum ALT concentration and lower expression of CCl(4)-induced TNF-alpha, S100A6, monocyte chemoattractant protein-1 (MCP1), and TWEAKr in wild-type mice, and these effects were not observed in PPARbeta/delta-null mice. Expression of TNF-alpha was higher in PPARbeta/delta-null primary hepatocytes in response to interleukin-1beta treatment compared to wild-type hepatocytes, but GW0742 did not significantly modulate TNF-alpha expression in hepatocytes from either genotype. While PPARbeta/delta-null hepatic stellate exhibited higher rates of proliferation compared to wild-type cells, GW0742 did not affect alpha-smooth muscle actin expression in these cells. Combined, these findings demonstrate that ligand activation of PPARbeta/delta protects against chemically induced hepatotoxicity by downregulating expression of proinflammatory genes. Hepatocytes and hepatic stellate cells do not appear to directly mediate the inhibitory effects of ligand activation of PPARbeta/delta in liver, suggesting the involvement of paracrine and autocrine events mediated by hepatic cells.

Neuronal peroxisome proliferator-activated receptor gamma signaling: regulation by mood-stabilizer valproate

Valproate (Depakote) remains an effective medication for the prevention and treatment of seizures in epilepsy and of mood symptoms in bipolar disorder. Both of these disorders are severe and debilitating, and both warrant further medication options as well as a better understanding of the side effects associated with their current treatments. Although a number of molecular and cellular processes have been found to be altered by valproate, the medication's therapeutic mechanism has not been fully elucidated. In this paper, peroxisome proliferator-activated receptor (PPAR) signaling was examined to determine valproate's effects on this transcriptional regulatory system in neuronal tissue. PPAR signaling has been found to affect a number of biochemical processes, including lipid metabolism, cellular differentiation, insulin sensitivity, and cell survival. When primary neuronal cultures were treated with valproate, a significant decrease in PPARgamma signaling was observed. This effect was demonstrated through a change in nuclear quantities of PPARgamma receptor and decreased DNA binding of the receptor. Valproate also caused gene expression changes and a change to the peroxisome biochemistry consistent with a decrease of PPARgamma signaling. These biochemical changes may have functional consequences for either valproate's therapeutic mechanism or for its neurological side effects and merit further investigation.

Phase I trial of histone deacetylase inhibition by valproic acid followed by the topoisomerase II inhibitor epirubicin in advanced solid tumors: a clinical and translational study

PURPOSE

To determine the safety, toxicity, and maximum-tolerated dose of a sequence-specific combination of the histone deacetylase inhibitor (HDACi), valproic acid (VPA), and epirubicin in solid tumor malignancies and to define the clinical feasibility of VPA as an HDACi.

PATIENTS AND METHODS

Patients were treated with increasing doses of VPA (days 1 through 3) followed by epirubicin (day 3) in 3-week cycles. The study evaluated pharmacokinetic and pharmacodynamic end points, toxicities, and tumor response.

RESULTS

Forty-eight patients were enrolled, and 44 received at least one cycle of therapy. Patients (median age, 54 years; range, 39 to 78 years) received the following doses of VPA: 15, 30, 45, 60, 75, 90, 100, 120, 140, and 160 mg/kg/d. Dose-limiting toxicities were somnolence (n = 1), confusion (n = 3), and febrile neutropenia (n = 1). No exacerbation of epirubicin-related toxicities was observed. Partial responses were seen across different tumor types in nine patients (22%), and stable disease/minor responses were seen in 16 patients (39%), despite a median number of three prior regimens (range, zero to 10 prior regimens). Patients received a median number of four treatment cycles (range, one to 10 cycles), and treatment was stopped after reaching maximal epirubicin doses rather than progression in 13 (32%) of 41 patients patients. Total and free VPA plasma concentrations increased linearly with dose and correlated with histone acetylation in peripheral-blood mononuclear cells.

CONCLUSION

The maximum-tolerated dose and recommended phase II dose was VPA 140 mg/kg/d for 48 hours followed by epirubicin 100 mg/m2. Sustained plasma concentrations of VPA exceeding those required for in vitro synergy were achieved with acceptable toxicity. Noteworthy antitumor activity was observed in heavily pretreated patients and historically anthracycline-resistant tumors.

Valproic acid induces CYP3A4 and MDR1 gene expression by activation of constitutive androstane receptor and pregnane X receptor pathways

In our study, we tested the hypothesis whether valproic acid (VPA) in therapeutic concentrations has potential to affect expression of CYP3A4 and MDR1 via constitutive androstane receptor (CAR) and pregnane X receptor (PXR) pathways. Interaction of VPA with CAR and PXR nuclear receptors was studied using luciferase reporter assays, real-time reverse transcriptase polymerase chain reaction (RT-PCR), electrophoretic mobility shift assay (EMSA), and analysis of CYP3A4 catalytic activity. Using transient transfection reporter assays in HepG2 cells, VPA was recognized to activate CYP3A4 promoter via CAR and PXR pathways. By contrast, a significant effect of VPA on MDR1 promoter activation was observed only in CAR-cotransfected HepG2 cells. These data well correlated with up-regulation of CYP3A4 and MDR1 mRNAs analyzed by real-time RT-PCR in cells transfected with expression vectors encoding CAR or PXR and treated with VPA. In addition, VPA significantly up-regulated CYP3A4 mRNA in primary hepatocytes and augmented the effect of rifampicin. EMSA experiments showed VPA-mediated augmentation of CAR/retinoid X receptor alpha heterodimer binding to direct repeat 3 (DR3) and DR4 responsive elements of CYP3A4 and MDR1 genes, respectively. Finally, analysis of specific CYP3A4 catalytic activity revealed its significant increase in VPA-treated LS174T cells transfected with PXR. In conclusion, we provide novel insight into the mechanism by which VPA affects gene expression of CYP3A4 and MDR1 genes. Our results demonstrate that VPA has potential to up-regulate CYP3A4 and MDR1 through direct activation of CAR and/or PXR pathways. Furthermore, we suggest that VPA synergistically augments the effect of rifampicin in transactivation of CYP3A4 in primary human hepatocytes.

The histone deacetylase (HDAC) inhibitor valproic acid as monotherapy or in combination with all-trans retinoic acid in patients with acute myeloid leukemia

BACKGROUND

Valproic acid (VPA) inhibits histone deacetylase activity and, synergizing with all-trans retinoic acid (ATRA), achieves differentiation induction of myeloid blast cells in vitro.

METHODS

We used VPA in 58 patients with acute myeloid leukemia (AML) who were too old and/or medically unfit to receive intensive chemotherapy (32 AML secondary to myelodysplastic syndrome [MDS], 22 de novo AML, 4 AML secondary to myeloproliferative syndrome). VPA serum concentrations were 50-100 mug/mL. Thirty-one patients received VPA monotherapy. ATRA was added later in 13 patients who did not respond or who relapsed. Another 27 patients received VPA plus ATRA from the start. Median treatment duration was 93 days for VPA and 88 days for ATRA.

RESULTS

The response rate was only 5% according to International Working Group (IWG) criteria for AML but was 16% when IWG response criteria for MDS were used, which capture hematologic improvement and stabilization of the disease. These endpoints, which are not necessarily correlated with diminishing blast counts, are relevant for the patients' quality of life. Among 23 patients with a peripheral blast count > 5%, 6 (26%) showed a diminishing blast count, and 5 of these had a complete peripheral blast clearance.

CONCLUSIONS

Future trials should combine VPA with chemotherapy or demethylating agents.

Valproic acid induces growth arrest, apoptosis, and senescence in medulloblastomas by increasing histone hyperacetylation and regulating expression of p21Cip1, CDK4, and CMYC

Valproic acid is a well-tolerated anticonvulsant that has been identified recently as a histone deacetylase inhibitor. To evaluate the antitumor efficacy and mechanisms of action of valproic acid in medulloblastoma and supratentorial primitive neuroectodermal tumor (sPNET), which are among the most common malignant brain tumors in children with poor prognosis, two medulloblastoma (DAOY and D283-MED) and one sPNET (PFSK) cell lines were treated with valproic acid and evaluated with a panel of in vitro and in vivo assays. Our results showed that valproic acid, at clinically safe concentrations (0.6 and 1 mmol/L), induced potent growth inhibition, cell cycle arrest, apoptosis, senescence, and differentiation and suppressed colony-forming efficiency and tumorigenicity in a time- and dose-dependent manner. The medulloblastoma cell lines were more responsive than the sPNET cell line and can be induced to irreversible suppression of proliferation and significantly reduced tumorigenicity by 0.6 and 1 mmol/L valproic acid. Daily i.p. injection of valproic acid (400 mg/kg) for 28 days significantly inhibited the in vivo growth of DAOY and D283-MED s.c. xenografts in severe combined immunodeficient mice. With Western hybridization and real-time reverse transcription-PCR, we further showed that the antitumor activities of valproic acid correlated with induction of histone (H3 and H4) hyperacetylation, activation of p21, and suppression of TP53, CDK4, and CMYC expression. In conclusion, valproic acid possesses potent in vitro and in vivo antimedulloblastoma activities that correlated with induction of histone hyperacetylation and regulation of pathways critical for maintaining growth inhibition and cell cycle arrest. Therefore, valproic acid may represent a novel therapeutic option in medulloblastoma treatment.

The Toxicology of Ligands for Peroxisome Proliferator-Activated Receptors (PPAR)

Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that modulate target gene expression in response to endogenous and exogenous ligands. Ligands for the PPARs have been widely developed for the treatment of various diseases including dyslipidemias and diabetes. While targeting selective receptor activation is an established therapeutic approach for the treatment of various diseases, a variety of toxicities are known to occur in response to ligand administration. Whether PPAR ligands produce toxicity via a receptor-dependent and/or off-target-mediated mechanism(s) is not always known. Extrapolation of data derived from animal models and/or in vitro models, to humans, is also questionable. The different toxicities and mechanisms associated with administration of ligands for the three PPARs will be discussed, and important data gaps that could increase our current understanding of how PPAR ligands lead to toxicity will be highlighted.

TCDD induces c-jun expression via a novel Ah (dioxin) receptor-mediated p38-MAPK-dependent pathway

The aryl hydrocarbon receptor (AhR) has a fundamental role during postnatal liver development and is essential for mediating dioxin toxicity. However, the genetic programs mediating, both, the toxic and physiological effects downstream of the transcription factor AhR are in major parts unknown. We have identified the proto-oncogene c-jun as a novel target gene of AhR. Induction of c-jun depends on activation of p38-mitogen-activated protein kinase (MAPK) by an AhR-dependent mechanism. None of the kinases that are known to phosphorylate p38-MAPK is activated by AhR. Neither the dephosphorylation rate of p38-MAPK is reduced. Furthermore, increased p38-MAPK phosphorylation in response to dioxins does not require ongoing transcription. These findings establish activating 'cross-talk' with MAPK signaling as a novel principle of AhR action, which is apparently independent of the AhR's function as a DNA-binding transcriptional activator.

The role of peroxisome proliferator-activated receptor-beta/delta in epithelial cell growth and differentiation

The physiological and pharmacological roles of peroxisome proliferator-activated receptor-beta (PPARbeta-also referred to as PPARdelta) are just beginning to emerge. It has recently become clear that PPARbeta has a function in epithelial tissues, but controversy exists due to inconsistencies in the literature. There is strong evidence that ligand activation of PPARbeta can induce terminal differentiation of keratinocytes, with a concomitant inhibition of cell proliferation. However, the role of PPARbeta in keratinocyte-specific apoptosis is less clear. Additionally, the role of PPARbeta in colonic epithelium remains unclear due to conflicting evidence suggesting that ligand activation of PPARbeta can potentiate, as well as attenuate, intestinal cancer. Recent studies revealed that ligand activation of PPARbeta can induce fatty acid catabolism in skeletal muscle and is associated with improved insulin sensitivity, attenuated weight gain and elevated HDL levels thus demonstrating promising potential for targeting PPARbeta for treating obesity, dyslipidemias and type 2 diabetes. Therefore, it becomes critical to determine the safety of PPARbeta ligands. This review focuses on recent literature describing the role of PPARbeta in epithelial tissues and highlights critical discrepancies that need to be resolved for a more comprehensive understanding of how this receptor modulates epithelial homeostasis.

Histone deacetylases inhibition and tumor cells cytotoxicity by CNS-active VPA constitutional isomers and derivatives

The tumor cells toxicity of the antiepileptic drug valproic acid (VPA) has been associated with the inhibition of histone deacetylases (HDACs). We have assessed, in comparison to VPA, the HDACs inhibition and tumor cells cytotoxicities of CNS-active VPA's constitutional isomers, valnoctic acid (VCA), propylisopropylacetic acid (PIA), diisopropylacetic acid (DIA), VPA's cyclopropyl analogue 2,2,3,3-tetramethylcyclopropanecarboxylic acid (TMCA) and VPA's metabolites, 2-ene-VPA and 4-ene-VPA, all possessing, as does VPA, eight carbon atoms in their structures. The aim was to define structural components of the VPA molecule that are involved in HDACs inhibition and tumor cells cytotoxicity. HDACs inhibition by the above-mentioned compounds was estimated using an acetylated lysine substrate and HeLa nuclear extract as a HDACs source. SW620 cells were used for assessing HDACs inhibition in vivo. The cytotoxicity of these compounds was assessed in SW620 and 1106mel cells. HDAC inhibition potency was the highest for VPA and 4-ene-VPA (IC(50)=1.5mM each). 2-Ene-VPA inhibited HDACs with IC(50)=2.8mM. IC(50) values of the other tested compounds for HDACs inhibition were higher than 5mM, 4-ene-VPA and VPA induced histone hyperacetylation in SW620 cells. 4-Ene-VPA and VPA at 2mM each were also most potent in reducing cell viability, to 59+/-2.0% and 67.3+/-5.4%, respectively, compared to control. VCA, PIA, DIA, TMCA, 2-ene-VPA and valpromide (VPD) did not reduce viability to less than 80%. All tested compounds did not significantly affect the cell cycle of SW620 cells. In conclusion, in comparison to the VPA derivatives and constitutional isomers tested in this study, VPA had the optimal chemical structure in terms of HDACs inhibition and tumor cells cytotoxicity.

Modulation of peroxisome proliferator-activated receptor delta activity affects neural cell adhesion molecule and polysialyltransferase ST8SiaIV induction by teratogenic valproic acid analogs in F9 cell differentiation

It has been suggested that the teratogenic effects of the antiepileptic drug valproic acid (VPA) is reflected in vitro by the differentiation of F9 cells, activation of peroxisome proliferator-activated receptor delta (PPARdelta), and inhibition of histone deacetylases (HDACs). The aim of this study was to identify genes involved in the differentiation of F9 cells induced by VPA, teratogenic VPA derivatives, or the HDAC inhibitor trichostatin A (TSA) and to characterize the role of PPARdelta. Treatment of the cells with teratogenic VPA derivatives or TSA induced differentiation of F9 cells, mRNA, and protein expression of the neural cell adhesion molecule (NCAM) as well as activated the 5'-flanking region of the NCAM promoter, whereas nonteratogenic VPA derivatives had no effect at all. The polysialyltransferases [ST8SiaIV (PST1) and ST8SiaII] are responsible for the addition of polysialic acid (PSA) to NCAM. The mRNA expression of PST1 was highly induced by only teratogenic VPA derivatives and TSA. As shown by fluorescence-activated cell sorting analysis the level of PSA was higher after treatment of F9 cells with teratogenic VPA derivatives. It is interesting that overexpression of the PPARdelta but not PPARalpha or PPARgamma in F9 cells resulted in higher induction of NCAM mRNA and protein expression and of PST1 mRNA expression (and a higher PSA level) than in mock-transfected F9 cells. Furthermore, repression of PPARdelta activity in F9 cells inhibited these effects. We conclude that NCAM and PST1 are molecular markers in F9 cell differentiation caused by treatment with teratogenic VPA compounds or TSA and suggest that in addition to HDAC inhibition PPARdelta is involved in the signaling pathway.

Comparative analysis of the effects of four mood stabilizers in SH-SY5Y cells and in primary neurons

OBJECTIVES

The mood-stabilizing drug valproic acid (VPA) exerts a neurotrophic effect on the human neuroblastoma cell line, SH-SY5Y. We aimed to establish whether other mood-stabilizing drugs have a similar action and which signalling pathways mediate this process.

METHODS

We analysed the effects of the mood stabilizers VPA, lithium, carbamazepine and lamotrigine on proliferation, survival, neurite outgrowth and extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) activation using the SH-SY5Y cell line. We also compared their effects in primary neurons.

RESULTS

We found that VPA promotes neurite outgrowth and prevents cell death in SH-SY5Y cells, but has no effect on cell proliferation. This neurotrophic effect does not involve inhibition of glycogen synthase kinase-3, histone deacetylase or prolyl oligopeptidase; the effect also does not seem to involve protein kinase C. In contrast, VPA activates ERK/MAPK and the survival effect of VPA is blocked by inhibition of the ERK/MAPK signalling pathway. Moreover, other activators of ERK/MAPK, such as epidermal growth factor and phorbol 12-myristate 13-acetate, mimic the neurotrophic effects of VPA. Other mood stabilizers do not activate ERK/MAPK and do not promote neurite outgrowth or survival of SH-SY5Y cells. In contrast, both lithium and VPA activate ERK/MAPK in rat primary cortical neurons.

CONCLUSIONS

We investigated four mood stabilizers that are effective in the treatment of bipolar disorder. Our results suggest that, while some mood stabilizers may have additional neuroprotective effects, activation of ERK/MAPK does not appear to be a mechanism common to all mood-stabilizing drugs.

Peroxisome proliferator-activated receptor-beta/delta inhibits epidermal cell proliferation by down-regulation of kinase activity

Recent work has shown that peroxisome proliferator-activated receptor beta (PPARbeta) attenuates cell proliferation and skin carcinogenesis, and this is due in part to regulation of ubiquitin C expression. In these studies, the role of PPARbeta in modulating ubiquitin-dependent protein kinase Calpha (PKCalpha) levels and phosphorylation signaling pathways was evaluated. Intracellular phosphorylation analysis showed that phosphorylated PKCalpha and other kinases were lower in wild-type mouse skin treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) as compared with PPARbeta-null mouse skin. No differences in expression levels of other PKC isoforms present in skin were observed. Lower ubiquitination of PKCalpha was found in TPA-treated PPARbeta-null skin as compared with wild-type, and inhibition of ubiquitin-dependent proteasome degradation prevented TPA-induced down-regulation of PKCalpha. The activity of PKCalpha and downstream signaling kinases is enhanced, and expression of cyclooxygenase-2 (COX-2) is significantly greater, in PPARbeta-null mouse skin in response to TPA compared with wild-type mouse skin. Inhibition of PKCalpha or COX-2 reduced cell proliferation in TPA-treated PPARbeta-null keratinocytes in a dose-dependent manner, whereas it only slightly influenced cell proliferation in wild-type keratinocytes. Combined, these studies provide strong evidence that PPARbeta attenuates cell proliferation by modulating PKCalpha/Raf1/MEK/ERK activity that may be due in part to reduced ubiquitin-dependent turnover of PKCalpha.

Valproate-induced alterations in human theca cell gene expression: clues to the association between valproate use and metabolic side effects

Valproic acid (VPA) is an anti-epileptic drug that has been associated with polycystic ovary syndrome (PCOS)-like symptoms, including increased ovarian androgen production. The hyperandrogenemia likely reflects the stimulatory action of VPA on theca cell androgen synthesis and has been correlated to its activity as a histone deacteylase inhibitor in these cells. To determine whether VPA induces a PCOS-like genomic phenotype, we compared the gene expression profiles of untreated (UNT) normal, VPA-treated normal, and UNT PCOS theca cells. Hierarchal cluster analysis demonstrated similarities in the gene expression profiles of VPA-treated normal and PCOS theca cells. Statistical analysis identified 1,050 transcripts that have significantly altered mRNA abundance in both VPA-treated normal and UNT PCOS theca cells compared with normal UNT theca cells. Among these 1,050 transcripts were cAMP-GEFII and TRB3, which have increased and decreased mRNA abundance, respectively. The altered abundance of these two mRNAs was correlated to increased basal and insulin-induced phosphorylation of protein kinase B (Akt/PKB). Thus these studies indicate that VPA- and PCOS-induced changes in gene expression enhance Akt/PKB signal transduction in human theca cells. Furthermore, common changes in gene expression in PCOS and VPA-treated normal theca cells suggest a possible mechanism for the development of PCOS-like symptoms, including increased steroid synthesis and arrested follicle development in women receiving chronic VPA therapy.

The mood stabilizer valproic acid stimulates GABA neurogenesis from rat forebrain stem cells

Valproate, an anticonvulsant drug used to treat bipolar disorder, was studied for its ability to promote neurogenesis from embryonic rat cortical or striatal primordial stem cells. Six days of valproate exposure increased by up to fivefold the number and percentage of tubulin beta III-immunopositive neurons, increased neurite outgrowth, and decreased by fivefold the number of astrocytes without changing the number of cells. Valproate also promoted neuronal differentiation in human fetal forebrain stem cell cultures. The neurogenic effects of valproate on rat stem cells exceeded those obtained with the neurotrophins brain-derived growth factor (BDNF) or NT-3, and slightly exceeded the effects obtained with another mood stabilizer, lithium. No effect was observed with carbamazepine. Most of the newly formed neurons were GABAergic, as shown by 10-fold increases in neurons that immunostained for GABA and the GABA-synthesizing enzyme GAD65/67. Double immunostaining for bromodeoxyuridine and tubulin beta III showed that valproate increased by four- to fivefold the proliferation of neuronal progenitors derived from rat stem cells and increased cyclin D2 expression. Valproate also regulated the expression of survival genes, Bad and Bcl-2, at different times of treatment. The expression of prostaglandin E synthase, analyzed by quantitative RT-PCR, was increased by ninefold as early as 6 h into treatment by valproate. The enhancement of GABAergic neuron numbers, neurite outgrowth, and phenotypic expression via increases in the neuronal differentiation of neural stem cell may contribute to the therapeutic effects of valproate in the treatment of bipolar disorder.

Treatment of myelodysplastic syndromes with valproic acid alone or in combination with all-trans retinoic acid

Valproic acid (VPA) has been shown to inhibit histone deacetylase activity and to synergize with all-trans retinoic acid (ATRA) in the differentiation induction of acute myelogenous leukemia (AML) blasts in vitro. We treated 18 patients with myelodysplastic syndromes (MDS) and AML secondary to MDS (sAML/MDS) with VPA monotherapy (serum concentrations 346-693 μM [50-100 μg/mL]). Five patients received VPA and ATRA (80 mg/m2/d, days 1-7, every other week). Response according to international working group (IWG) criteria was observed in 8 patients (44%) on VPA monotherapy, including 1 partial remission. Median response duration was 4 months (range, 3-9 months). Four of 5 patients relapsing were treated with VPA + ATRA, 2 of them responding again. Among 5 patients receiving VPA + ATRA from the start, none responded according to IWG criteria, but 1 patient with sAML/MDS achieved a marked reduction in peripheral and marrow blasts. Thus, VPA is of therapeutic benefit for patients with MDS, and ATRA may be effective when added later.

Increased human cytomegalovirus replication in fibroblasts after treatment with therapeutical plasma concentrations of valproic acid

Valproic acid (2-propylpentanoic acid, VPA), an effective inhibitor of histone deacetylases (HDAC) is used for the treatment of epilepsia. In this study, structure-activity relationships for the action of structurally modified VPA derivatives on human cytomegalovirus (HCMV) replication and HDAC inhibition were defined. Pretreatment of human foreskin fibroblasts with VPA (0.125-1mM) caused a concentration-dependent increase of HCMV immediate early and antigen late antigen expression. Structure-activity relationships of VPA derivatives for HCMV stimulation were compared to those for teratogenic action and those for HDAC inhibition. Side chain elongation and introduction of a triple bond in 4-position of the other chain caused teratogenicity, stimulated HCMV replication, and increased HDAC inhibition, as demonstrated by enhanced levels of acetylated histones. Teratogenic VPA derivatives with a branched chain in 3-position as well as a non-teratogenic anticonvulsive active VPA derivative did not stimulate HCMV or accumulation of acetylated histones. This demonstrates a strict correlation between inhibition of HDAC and increased HCMV replication.

Valproic acid teratogenicity: a toxicogenomics approach

Embryonic development is a highly coordinated set of processes that depend on hierarchies of signaling and gene regulatory networks, and the disruption of such networks may underlie many cases of chemically induced birth defects. The antiepileptic drug valproic acid (VPA) is a potent inducer of neural tube defects (NTDs) in human and mouse embryos. As with many other developmental toxicants however, the mechanism of VPA teratogenicity is unknown. Using microarray analysis, we compared the global gene expression responses to VPA in mouse embryos during the critical stages of teratogen action in vivo with those in cultured P19 embryocarcinoma cells in vitro. Among the identified VPA-responsive genes, some have been associated previously with NTDs or VPA effects [vinculin, metallothioneins 1 and 2 (Mt1, Mt2), keratin 1-18 (Krt1-18)], whereas others provide novel putative VPA targets, some of which are associated with processes relevant to neural tube formation and closure [transgelin 2 (Tagln2), thyroid hormone receptor interacting protein 6, galectin-1 (Lgals1), inhibitor of DNA binding 1 (Idb1), fatty acid synthase (Fasn), annexins A5 and A11 (Anxa5, Anxa11)], or with VPA effects or known molecular actions of VPA (Lgals1, Mt1, Mt2, Id1, Fasn, Anxa5, Anxa11, Krt1-18). A subset of genes with a transcriptional response to VPA that is similar in embryos and the cell model can be evaluated as potential biomarkers for VPA-induced teratogenicity that could be exploited directly in P19 cell-based in vitro assays. As several of the identified genes may be activated or repressed through a pathway of histone deacetylase (HDAC) inhibition and specificity protein 1 activation, our data support a role of HDAC as an important molecular target of VPA action in vivo.

Activation of peroxisome proliferator-activated receptor delta stimulates the proliferation of human breast and prostate cancer cell lines

The nuclear receptor peroxisome proliferator-activated receptor delta [PPARdelta/beta (NR1C2)] has been implicated in colorectal carcinogenesis by various molecular genetic observations. These observations have recently been supported by studies of activation of PPARdelta by pharmacological agents. Here we present the first report of the stimulation of breast and prostate cancer cell growth using PPARdelta selective agonists. Activation of PPARdelta with compound F stimulated proliferation in breast (T47D, MCF7) and prostate (LNCaP, PNT1A) cell lines, which are responsive to sex hormones. Conversely, we have found that several steroid-independent cell lines, including colon lines, were unresponsive to compound F. These findings were confirmed with an additional high-affinity PPARdelta agonist, GW501516. Conditional expression of PPARdelta in MCF7 Tet-On cells resulted in a doxycycline-enhanced response to GW501516, thus providing direct genetic evidence for the role of PPARdelta in the proliferative response to this drug. Activation of PPARdelta in T47D cells resulted in increased expression of the proliferation marker Cdk2 and also vascular endothelial growth factor alpha (VEGFalpha) and its receptor, FLT-1, thus, suggesting that PPARdelta may initiate an autocrine loop for cellular proliferation and possibly angiogenesis. Consistent with this hypothesis, we demonstrated a pro-proliferative effect of GW501516 on human umbilical vein endothelial cell cultures and found that GW501516 also regulated the expression of VEGFalpha and FLT-1 in these cells. Our observations provide the first evidence that activation of PPARdelta can result in increased growth in breast and prostate cancer cell lines and primary endothelial cells and supports the possibility that PPARdelta antagonists may be of therapeutic value in the treatment of breast and prostate cancer.

Valproic acid inhibits angiogenesis in vitro and in vivo

Valproic acid (VPA) is a widely used antiepileptic agent that is undergoing clinical evaluation for anticancer therapy. We assessed the effects of VPA on angiogenesis in vitro and in vivo. In human umbilical vein endothelial cells, therapeutically relevant concentrations of VPA (0.25 to 1 mM) inhibited proliferation, migration, and tube formation. VPA 1 mM inhibited endothelial cell proliferation by 51 +/- 5%, migration by 86 +/- 11%, and tube formation by 82 +/- 3%. These changes were preceded by the hyperacetylation of histone H4, indicating the inhibition of histone deacetylase (HDAC), and a decreased expression of the endothelial nitric-oxide synthase (eNOS). The inhibition of endothelial cell tube formation by VPA was prevented by addition of the nitric oxide donor (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA NONOate). The anticonvulsive active VPA derivative 2-ethyl-4-methylpentanoic acid, which does not inhibit HDAC, did not affect endothelial cell proliferation, tube formation, or eNOS expression. VPA was also found to inhibit angiogenesis in vivo in the chicken chorioallantoic membrane assay and in a Matrigel plug assay in mice. Embryos from VPA-treated mice showed disturbed vessel formation. These results indicate that therapeutic plasma levels of VPA inhibit angiogenesis by a mechanism involving a decrease in eNOS expression preceded by HDAC inhibition.

Antiepileptic drugs inhibit cell growth in the human breast cancer cell line MCF7

Several antiepileptic drugs (AEDs) are associated with anti-cancer activity. At the same time, many AEDs alter endocrine function with phenytoin (PHT) and phenobarbital (PB) causing-reduced free fractions of sex-steroid hormones, while VPA induces hyperandrogenism. Changes in sex-steroid hormone levels are known to affect apoptosis in endocrine tissue. The aim of the study was to investigate the influence of the antiepileptic drugs PHT, PB, VPA and lamotrigine (LTG) on estrogen-stimulated cell growth of human breast cancer cells (MCF-7), and to evaluate whether this effect could be related to a direct estrogen receptor (ER) binding. VPA reduced cell growth at therapeutically relevant concentrations; half-maximum effect of VPA on cell growth was 230 microM. PHT (100 microM) and PB (10 microM) reduced cell growth by 47 and 21%, respectively. None of the drugs had affinity to isolated estrogen receptors, and excess of estrogen was not able to abolish the growth inhibition provoked by VPA. However, sub-therapeutic concentrations of VPA (100 microM) mimicked estrogen by inducing cell growth (11%) in an estrogen-depleted medium, an effect that was abolished by adding an estrogen receptor antagonist. In conclusion; the estrogen receptor appear to be indirectly activated by sub-therapeutic concentrations of VPA, but therapeutic concentrations of VPA inhibits cell growth by mechanisms that do not seem to involve the estrogen receptor or estrogen stimulation.

Valproyl-CoA and esterified valproic acid are not found in brains of rats treated with valproic acid, but the brain concentrations of CoA and acetyl-CoA are altered

Sodium valproate and lithium are used to treat bipolar disorder. In rats, both reduce the turnover of arachidonic acid in several brain phospholipids, suggesting that arachidonate turnover is a common target of action of these mood stabilizers. However, the mechanisms by which these drugs reduce arachidonate turnover in brain are not the same. Lithium decreases turnover by reducing the activity and expression of the 85-kDa type IVA cytosolic phospholipase A2 (cPLA2); valproate does not affect cPLA2 activity or expression. To test whether valproate alters neural membrane order by direct esterification into phospholipid or by interrupting intermediary CoA metabolism, we measured valproyl-CoA, esterified valproate, and short chain acyl-CoAs in brains from control rats and rats treated chronically with sodium valproate. Valproyl-CoA and esterified forms of valproate were not found in brain with detection limits of 25 and 37.5 pmol/g brain(-1), respectively. Valproate treatment did result in a 1.4-fold decrease and 1.5-fold increase in the brain concentrations of free CoA and acetyl-CoA when compared to control. Therefore the reduction of brain arachidonic acid turnover by chronic valproate in rats is not related to the formation of valproyl-CoA or esterified valproate, but may involve changes in the intermediary metabolism of CoA and short chain acyl-CoA.

Sp family of transcription factors is involved in valproic acid-induced expression of Galphai2

Valproic acid-induced gene expression has been attributed to the DNA-binding activity of the transcription factor activator protein 1 (AP-1). Using K562 cells, we have studied valproic acid-induced transcription from the human Galpha(i2) gene promoter, which lacks AP-1-binding motifs. We find that valproic acid-induced expression of Galpha(i2) is inhibited by mithramycin A, a compound that interferes with Sp1 binding to GC boxes in DNA. Three Sp1-binding sequences, located at +68/+75, -50/-36, and -92/-85 in the promoter, accounted for about 60% of this transcriptional effect, as judged by transient transfection assays. Electrophoretic mobility shift assays indicated that these sites bind members of the Sp family of transcription factors. Binding to DNA was inhibited by mithramycin A and was greater in nuclear extracts from cells treated with valproic acid than in control cells. Okadaic acid, calyculin A, and fostriecin, which are potent inhibitors of protein phosphatase, suppressed the transcriptional response to valproic acid. This inhibitory effect was not observed when promoter constructs containing mutations in the referenced Sp1-binding sites were used for transfections. In nuclear extracts from cells cultured in the presence of these inhibitors, the binding of Sp1/Sp3 to DNA probes was much less than in control cells. Alkaline phosphatase treatment of nuclear extracts resulted in enhanced binding of Sp proteins to the DNA probes. These results are consistent with the idea that dephosphorylating conditions enhanced Sp binding to the DNA probes as well as Sp-mediated transcription induced by valproic acid. This study demonstrates that the gene expression-inducing effect of valproic acid occurs, in part, through the Sp family of transcription factors.

Teratogenic phthalate esters and metabolites activate the nuclear receptors PPARs and induce differentiation of F9 cells

Industrial plasticizers such as phthalates can induce peroxisome proliferation. Some phthalates such as di-2-ethyl-hexyl-phthalate (DEHP) and its metabolites mono-2-ethyl-hexyl-phthalate and 2-ethyl-hexanoic acid are also known teratogens. Recently, we introduced two in vitro test systems consisting of F9 teratocarcinoma cell differentiation and activation of peroxisome proliferator-activated receptor (PPAR)-ligand-binding domain in Chinese hamster ovary-reporter cells for the detection of teratogenic compounds related to the antiepileptic drug valproic acid. We now applied these methods to the class of phthalate esters and their metabolites by testing 2 diphthalate esters and 19 monophthalate esters in vitro. In the F9 cell assay only five compounds, mono-2-ethyl-hexyl-phthalate, mono-1-methyl-heptyl-phthalate, mono-benzyl-phthalate, benzyl-butyl-phthalate, and 2-ethyl-hexanoic acid were found to induce F9 cell differentiation. The other test compounds were not able to induce differentiation of F9 cells. Three compounds (mono-methyl-phthalate, mono-ethyl-phthalate, and mono-2,2-dimethyl-1-phenyl-propyl-phthalate, and phthalic acid di-methyl-ester were found not to interact with any PPARs. All other phthalate esters activated PPARs. Most compounds activated PPARalpha and PPARgamma. Interestingly PPARgamma in most cases was activated stronger than PPARalpha. Only the five test compounds, mono-2-ethyl-hexyl-phthatate, mono-1-methyl-heptyl-phthalate, mono-benzyl-phthalate, benzyl-butyl-phthalate, and 2-ethyl-hexanoic acid activated PPARdelta and interacted with a specific PPARdelta-response element. These are the same compounds that induced F9 cell differentiation and three of them are known teratogenic compounds. It is concluded that phthatate esters are acting like hormones by activating PPARs. The combination of F9 cell differentiation assay and PPARdelta activation assay detected possible teratogenic phthalate-ester and derivatives. Therefore the test systems seem useful for a screening test system in the early development of new plasticizers.

Anticonvulsant valproic acid inhibits cardiomyocyte differentiation of embryonic stem cells by increasing intracellular levels of reactive oxygen species

BACKGROUND

The anticonvulsant valproic acid (VPA) exerts teratogenic properties and has been demonstrated to cause neural tube defects and malformations of the heart. The effect of VPA on the differentiation of cardiomyocytes from pluripotent murine embryonic stem cells (ES cells) was investigated.

METHODS

Embryoid bodies derived from ES cells were treated with different concentrations of VPA and the differentiation of cardiomyocytes was monitored by immunohistochemical staining for sarcomeric alpha-actinin. Cytotoxicity was evaluated by the use of the dead cell stain SYTOX green. Intracellular levels of reactive oxygen species (ROS) within the tissue were evaluated by the use of the redox-sensitive dye dichlorodihydrofluorescein diacetate (H2DCFDA).

RESULTS

VPA retarded the growth of ES cell-derived embryoid bodies but did not exert cytotoxic effects. The compound dose-dependently inhibited the development of spontaneously beating clusters of cardiomyocytes within embryoid bodies grown from ES cells and reduced the extension of beating areas of cardiac cells. Furthermore, VPA significantly increased ROS levels, indicating that VPA altered the intracellular redox balance. To investigate whether the inhibition of cardiomyocyte differentiation by VPA was owing to increased ROS overwhelming the intracellular antioxidative defense, the compound was coadministered with the free radical scavenger vitamin E.

CONCLUSIONS

This treatment significantly restored cardiomyogenic differentiation, indicating that VPA inhibits cardiomyogenesis of ES cells by increasing intracellular ROS levels.

Epilepsy and pregnancy: Report of an Epilepsy Research Foundation Workshop

Pregnancy in women with epilepsy (WWE) is known to be associated with a higher risk of congenital malformations than is associated with pregnancy in non-epileptic women. Several factors have been identified to account for the increased risk, including the direct teratogenic effects of antiepileptic drug (AED) therapy, indirect effects of these drugs by interfering with folate metabolism, genetic abnormalities in drug or folate metabolism, and possibly an arrhythmogenic effect of maternal drug therapy on the embryonic heart, leading to ischaemia in developing tissues. A harmful effect of maternal seizures on the developing embryo has not been proven, although seizures and status epilepticus account for most of the excess maternal mortality in women with epilepsy. Abrupt withdrawal of drug therapy by the mother may be an important contributory factor. Less is known about the psychomotor development of children born to mothers with epilepsy because few studies have been designed to follow their progress throughout childhood. Retrospective studies suggest that impaired cognitive development may be associated with maternal drug therapy, particularly valproate. There is an urgent need to evaluate these risks and, with this in mind, several prospective registers have been set up to collect data from pregnancies in women with epilepsy.

Anti-tumor mechanisms of valproate: a novel role for an old drug

Valproic acid (VPA, 2-propylpentanoic acid) is an established drug in the long-term therapy of epilepsy. During the past years, it has become evident that VPA is also associated with anti-cancer activity. VPA not only suppresses tumor growth and metastasis, but also induces tumor differentiation in vitro and in vivo. Several modes of action might be relevant for the biological activity of VPA: (1) VPA increases the DNA binding of activating protein-1 (AP-1) transcription factor, and the expression of genes regulated by the extracellular-regulated kinase (ERK)-AP-1 pathway; (2) VPA downregulates protein kinase C (PKC) activity; (3) VPA inhibits glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of the Wnt signaling pathway; (4) VPA activates the peroxisome proliferator-activated receptors PPARgamma and delta; (5) VPA blocks HDAC (histone deacetylase), causing hyperacetylation. The findings elucidate an important role of VPA for cancer therapy. VPA might also be useful as low toxicity agent given over long time periods for chemoprevention and/or for control of residual minimal disease.

Valproic acid defines a novel class of HDAC inhibitors inducing differentiation of transformed cells

Histone deacetylases (HDACs) play important roles in transcriptional regulation and pathogenesis of cancer. Thus, HDAC inhibitors are candidate drugs for differentiation therapy of cancer. Here, we show that the well-tolerated antiepileptic drug valproic acid is a powerful HDAC inhibitor. Valproic acid relieves HDAC-dependent transcriptional repression and causes hyperacetylation of histones in cultured cells and in vivo. Valproic acid inhibits HDAC activity in vitro, most probably by binding to the catalytic center of HDACs. Most importantly, valproic acid induces differentiation of carcinoma cells, transformed hematopoietic progenitor cells and leukemic blasts from acute myeloid leukemia patients. More over, tumor growth and metastasis formation are significantly reduced in animal experiments. Therefore, valproic acid might serve as an effective drug for cancer therapy.