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

Therapeutic and Toxic Effects of Valproic Acid Metabolites

Valproic acid (VPA) and its salts are psychotropic drugs that are widely used in neurological diseases (epilepsy, neuropathic pain, migraine, etc.) and psychiatric disorders (schizophrenia, bipolar affective disorder, addiction diseases, etc.). In addition, the indications for the appointment of valproate have been expanding in recent years in connection with the study of new mechanisms of action of therapeutic and toxic metabolites of VPA in the human body. Thus, VPA is considered a component of disease-modifying therapy for multiple tumors, neurodegenerative diseases (Huntington's disease, Parkinson's disease, Duchenne progressive dystrophy, etc.), and human immunodeficiency syndrome. The metabolism of VPA is complex and continues to be studied. Known pathways of VPA metabolism include: β-oxidation in the tricarboxylic acid cycle (acetylation); oxidation with the participation of cytochrome P-450 isoenzymes (P-oxidation); and glucuronidation. The complex metabolism of VPA explains the diversity of its active and inactive metabolites, which have therapeutic, neutral, or toxic effects. It is known that some active metabolites of VPA may have a stronger clinical effect than VPA itself. These reasons explain the relevance of this narrative review, which summarizes the results of studies of blood (serum, plasma) and urinary metabolites of VPA from the standpoint of the pharmacogenomics and pharmacometabolomics. In addition, a new personalized approach to assessing the cumulative risk of developing VPA-induced adverse reactions is presented and ways for their correction are proposed depending on the patient's pharmacogenetic profile and the level of therapeutic and toxic VPA metabolites in the human body fluids (blood, urine).

Sodium Valproate Modulates the Methylation Status of Lysine Residues 4, 9 and 27 in Histone H3 of HeLa Cells

BACKGROUND

Valproic acid/sodium valproate (VPA), a well-known anti-epileptic agent, inhibits histone deacetylases, induces histone hyperacetylation, promotes DNA demethylation, and affects the histone methylation status in some cell models. Histone methylation profiles have been described as potential markers for cervical cancer prognosis. However, histone methylation markers that can be studied in a cervical cancer cell line, like HeLa cells, have not been investigated following treatment with VPA.

METHODS

In this study, the effect of 0.5 mM and 2.0 mM VPA for 24 h on H3K4me2/me3, H3K9me/me2 and H3K27me/me3 signals as well as on KMT2D, EZH2, and KDM3A gene expression was investigated using confocal microscopy, Western blotting, and RT-PCR. Histone methylation changes were also investigated by Fourier-transform infrared spectroscopy (FTIR).

RESULTS

We found that VPA induces increased levels of H3K4me2/me3 and H3K9me, which are indicative of chromatin activation. Particularly, H3K4me2 markers appeared intensified close to the nuclear periphery, which may suggest their implication in increased transcriptional memory. The abundance of H3K4me2/me3 in the presence of VPA was associated with increased methyltransferase KMT2D gene expression. VPA induced hypomethylation of H3K9me2, which is associated with gene silencing, and concomitant with the demethylase KDM3A, it increased gene expression. Although VPA induces increased H3K27me/me3 levels, it is suggested that the role of the methyltransferase EZH2 in this context could be affected by interactions with this drug.

CONCLUSION

Histone FTIR spectra were not affected by VPA under present experimental conditions. Whether our epigenetic results are consistent with VPA affecting the aggressive tumorous state of HeLa cells, further investigation is required.

X-linked myotubular myopathy is associated with epigenetic alterations and is ameliorated by HDAC inhibition

X-linked myotubular myopathy (XLMTM) is a fatal neuromuscular disorder caused by loss of function mutations in MTM1. At present, there are no directed therapies for XLMTM, and incomplete understanding of disease pathomechanisms. To address these knowledge gaps, we performed a drug screen in mtm1 mutant zebrafish and identified four positive hits, including valproic acid, which functions as a potent suppressor of the mtm1 zebrafish phenotype via HDAC inhibition. We translated these findings to a mouse XLMTM model, and showed that valproic acid ameliorates the murine phenotype. These observations led us to interrogate the epigenome in Mtm1 knockout mice; we found increased DNA methylation, which is normalized with valproic acid, and likely mediated through aberrant 1-carbon metabolism. Finally, we made the unexpected observation that XLMTM patients share a distinct DNA methylation signature, suggesting that epigenetic alteration is a conserved disease feature amenable to therapeutic intervention.

SARS-CoV-2 Infection Can Lead to an Increase in Tacrolimus Levels in Renal Transplant Patients: A Cohort Study

The aim of this study is to evaluate the effect of SARS-CoV-2 infection on serum tacrolimus levels. Tacrolimus levels of 34 transplant patients diagnosed with SARS-CoV-2 in 2020 were compared with their pre-infection values and those of a control group with alternative infections. 20 out of 34 (59%) had high levels. At diagnosis, median tacrolimus level in the SARS-CoV-2 cohort was 9.6 μg/L (2.7-23) compared to 7.9 μg/L in the control group (p = 0.07, 95% CI for difference -0.3-5.8). The ratio of post-infection to pre-infection tacrolimus values was higher in the SARS-CoV-2 group (1.7) compared to the control group (1.25, p = 0.018, 95% CI for difference 0.08-0.89). The acute kidney injury rate was 65% (13 of 20) in SARS-CoV-2 patients with a level >8 μg/dl, compared to 29% (4 of 14) in those with lower levels (p = 0.037). Median length of stay was 10 days among SARS-CoV-2 infected patients with high tacrolimus levels compared to 0 days in the rest (p = 0.04). Four patients with high levels died compared to 2 in the control group. Clinicians should be aware of this potential effect on tacrolimus levels and take appropriate measures.

Design, synthesis and anticancer activity of novel valproic acid conjugates with improved histone deacetylase (HDAC) inhibitory activity

Twenty-five valproic acid conjugates have been designed and synthesized. All target compounds were explored for their in vitro anti-proliferative activities using the MTT-based assay against four human cancer cell lines includingliver (HePG2), colon (HCT116), breast (MCF7) and cervical (HeLa) carcinoma cell lines. Out of six valproic acid-amino acid conjugates 2a-f. Only cysteine containing conjugate 2f showed the significant activity (IC₅₀ 9.10 µM against HePG2 and 6.81 µM against HCT116). However conjugate 2j showed broad-spectrum antitumor activity against all cell lines tested. In addition, conjugates 4j and 4k which contains phenyl hydrazide and hydroxamic acid group, respectively, also showed broad spectrum activity. Furthermore, six compounds were screened for HDAC 1-9 isozymes inhibitory activities. Compounds 2j, 4j and 4k manifested a higher inhibitory activity more than valproic acid but less than SAHA. In addition, the in vivo antitumor screening of 2j, 4j and 4k was done and the results have shown that 2j, 4j and 4k, particularly 4j, showed a significant decrease in tumor size and presented a considerable decrease in viable EAC count. Docking study of selectedcompound 4j revealed that it can bind nicely to the binding pocket of HDAC 1, 2, 3, 4 and HDAC 8. The results suggest that compounds 2j, 4j and 4k, particularly 4j, may be promising lead candidates for the development of novel targeted anti-tumor drug potentially via inhibiting HDACs.

Lacosamide at therapeutic concentrations induces histone hyperacetylation in vitro

Inhibition of histone deacetylases (HDACs) and subsequent hyperacetylation of histone proteins lead to altered gene expression associated with therapeutic drug effects, but also with teratogenicity. The only US Food and Drug Administration (FDA)-approved antiepileptic drug that has been consistently shown to induce histone hyperacetylation is valproic acid. More recently, lacosamide was reported to interfere with histone modifications, but histone hyperacetylation was not demonstrated. In the current study we evaluated the effects of lacosamide on histone acetylation in vitro. MDA-MB-231 (triple-negative breast cancer) cells and human placental BeWo cells were exposed for 16 hours to 5-20 μg/ml (20-80 μm) lacosamide. Histone acetylation was evaluated by western blot analysis. We additionally measured HDAC1 activity in the presence of lacosamide. At 5, 10, and 20 μg/ml, lacosamide enhanced histone acetylation in BeWo cells by 1.7-fold (p > 0.05), 3.4-fold (p < 0.05), and 3.0-fold (p > 0.05), respectively. Histone H3 acetylation and total histones H3 and H4 levels were not significantly modified (p > 0.05). The magnitude of change in histone acetylation in MDA-MB-231 cells was smaller (p > 0.05). In contrast to valproic acid, lacosamide did not inhibit HDAC1. Our findings suggest that the effects of lacosamide on gene expression, and the related potential antitumor activity and teratogenicity, may differ from those of valproic acid.

Valproic acid attenuates manganese-induced reduction in expression of GLT-1 and GLAST with concomitant changes in murine dopaminergic neurotoxicity

Exposure to elevated levels of manganese (Mn) causes manganism, a neurological disorder with similar characteristics to those of Parkinson's disease (PD). Valproic acid (VPA), an antiepileptic, is known to inhibit histone deacetylases and exert neuroprotective effects in many experimental models of neurological disorders. In the present study, we investigated if VPA attenuated Mn-induced dopaminergic neurotoxicity and the possible mechanisms involved in VPA's neuroprotection, focusing on modulation of astrocytic glutamate transporters (glutamate aspartate transporter, GLAST and glutamate transporter 1, GLT-1) and histone acetylation in H4 astrocyte culture and mouse models. The results showed that VPA increased promoter activity, mRNA/protein levels of GLAST/GLT-1 and glutamate uptake, and reversed Mn-reduced GLAST/GLT-1 in in vitro astrocyte cultures. VPA also attenuated Mn-induced reduction of GLAST and GLT-1 mRNA/protein levels in midbrain and striatal regions of the mouse brain when VPA (200 mg/kg, i.p., daily, 21 d) was administered 30 min prior to Mn exposure (30 mg/kg, intranasal instillation, daily, 21 d). Importantly, VPA attenuated Mn-induced dopaminergic neuronal damage by reversing Mn-induced decrease of tyrosine hydroxylase (TH) mRNA/protein levels in the nigrostriatal regions. VPA also reversed Mn-induced reduction of histone acetylation in astrocytes as well as mouse brain tissue. Taken together, VPA exerts attenuation against Mn-induced decrease of astrocytic glutamate transporters parallel with reversing Mn-induced dopaminergic neurotoxicity and Mn-reduced histone acetylation. Our findings suggest that VPA could serve as a potential neuroprotectant against Mn neurotoxicity as well as other neurodegenerative diseases associated with excitotoxicity and impaired astrocytic glutamate transporters.

Valproic acid and its congener propylisopropylacetic acid reduced the amount of soluble amyloid-β oligomers released from 7PA2 cells

The amyloid hypothesis of Alzheimer's disease suggests that synaptic degeneration and pathology is caused by the accumulation of amyloid-β (Aβ) peptides derived from the amyloid precursor protein (APP). Subsequently, soluble Aβ oligomers cause the loss of synaptic proteins from neurons, a histopathological feature of Alzheimer's disease that correlates with the degree of dementia. In this study, the production of toxic forms of Aβ was examined in vitro using 7PA2 cells stably transfected with human APP. We show that conditioned media from 7PA2 cells containing Aβ oligomers caused synapse degeneration as measured by the loss of synaptic proteins, including synaptophysin and cysteine-string protein, from cultured neurons. Critically, conditioned media from 7PA2 cells treated with valproic acid (2-propylpentanoic acid (VPA)) or propylisopropylacetic acid (PIA) did not cause synapse damage. Treatment with VPA or PIA did not significantly affect total Aβ42 concentrations; rather these drugs selectively reduced the concentrations of Aβ42 oligomers in conditioned media. In contrast, treatment significantly increased the concentrations of Aβ42 monomers in conditioned media. VPA or PIA treatment reduced the concentrations of APP within lipid rafts, membrane compartments associated with Aβ production. These effects of VPA and PIA were reversed by the addition of platelet-activating factor, a bioactive phospholipid produced following activation of phospholipase A2, an enzyme sensitive to VPA and PIA. Collectively these data suggest that VPA and PIA reduce Aβ oligomers through inhibition of phospholipase A2 and suggest a novel therapeutic approach to Alzheimer's treatment.

A randomized, double-blind, placebo- and risperidone-controlled study on valnoctamide for acute mania

OBJECTIVES

Mood stabilizers administered for bipolar disorder during pregnancy, such as valproic acid, can increase the risk of congenital anomalies in offspring. Valnoctamide is a valproic acid derivative associated with a decreased risk for congenital abnormalities in animals. The present study evaluated the efficacy and safety of valnoctamide monotherapy, compared to placebo, in the treatment of patients in an acute manic episode.

METHODS

A 3-week, double-blind, randomized, placebo- and risperidone-controlled, parallel group trial was conducted on 173 patients in an acute manic episode. Patients were randomized to receive valnoctamide 1500 mg/d (n=71), risperidone 6 mg/d (n=32), or matching placebo (n=70). The primary outcome measure was the change in Young Mania Rating Scale (YMRS) scores.

RESULTS

Valnoctamide did not differ significantly from placebo on any of the study endpoints (YMRS, Positive and Negative Syndrome Scale, and the Clinical Global Impression Scale for Bipolar Disorder [CGI-BP] scales; all P>.60). Mixed models for repeated measures showed that risperidone produced significantly more improvement than placebo in the overall bipolar disorder CGI-BP severity scale (P=.036), and the CGI-BP severity scale for mania (P=.021). The Kaplan-Meier survival curve revealed higher all-cause discontinuation rates (mainly due to lack of efficacy) in the valnoctamide group compared to the other study groups (P=.026). Patients with higher valnoctamide plasma levels had a numerically higher YMRS response, but this was not statistically significant.

CONCLUSIONS

Valnoctamide was well tolerated at 1500 mg/d but lacked efficacy in the treatment of symptoms in patients with acute mania. Possible differences between the biological mechanisms of action of valproic acid and valnoctamide are discussed.

Novel valproic aminophenol amides with enhanced glial cell viability effect

In this work, ortho-aminophenols were attached to valproic acid, resulting in seven novel anticancer drug prototypes.

Pharmacogenomics and histone deacetylase inhibitors

The histone deacetylase inhibitor valproic acid (VPA) has been used for many decades in neurology and psychiatry. The more recent introduction of the histone deacetylase inhibitors (HDIs) belinostat, romidepsin and vorinostat for treatment of hematological malignancies indicates the increasing popularity of these agents. Belinostat, romidepsin and vorinostat are metabolized or transported by polymorphic enzymes or drug transporters. Thus, genotype-directed dosing could improve pharmacotherapy by reducing the risk of toxicities or preventing suboptimal treatment. This review provides an overview of clinical studies on the effects of polymorphisms on the pharmacokinetics, efficacy or toxicities of HDIs including belinostat, romidepsin, vorinostat, panobinostat, VPA and a number of novel compounds currently being tested in Phase I and II trials. Although pharmacogenomic studies for HDIs are scarce, available data indicate that therapy with belinostat (UGT1A1), romidepsin (ABCB1), vorinostat (UGT2B17) or VPA (UGT1A6) could be optimized by upfront genotyping.

N-(2-hydroxyphenyl)-2-propylpentanamide, a valproic acid aryl derivative designed in silico with improved anti-proliferative activity in HeLa, rhabdomyosarcoma and breast cancer cells

Epigenetic alterations are associated with cancer and their targeting is a promising approach for treatment of this disease. Among current epigenetic drugs, histone deacetylase (HDAC) inhibitors induce changes in gene expression that can lead to cell death in tumors. Valproic acid (VPA) is a HDAC inhibitor that has antitumor activity at mM range. However, it is known that VPA is a hepatotoxic drug. Therefore, the aim of this study was to design a set of VPA derivatives adding the arylamine core of the suberoylanilide hydroxamic acid (SAHA) with different substituents at its carboxyl group. These derivatives were submitted to docking simulations to select the most promising compound. The compound 2 (N-(2-hydroxyphenyl)-2-propylpentanamide) was the best candidate to be synthesized and evaluated in vitro as an anti-cancer agent against HeLa, rhabdomyosarcoma and breast cancer cell lines. Compound 2 showed a better IC₅₀ (μM range) than VPA (mM range) on these cancer cells. And also, 2 was particularly effective on triple negative breast cancer cells. In conclusion, 2 is an example of drugs designed in silico that show biological properties against human cancer difficult to treat as triple negative breast cancer.

Valpromide Inhibits Lytic Cycle Reactivation of Epstein-Barr Virus

Reactivation of Epstein-Barr virus (EBV) from latency into the lytic phase of its life cycle allows the virus to spread among cells and between hosts. Valproic acid (VPA) inhibits initiation of the lytic cycle in EBV-infected B lymphoma cells. While VPA blocks viral lytic gene expression, it induces expression of many cellular genes, because it is a histone deacetylase (HDAC) inhibitor. Here we show, using derivatives of VPA, that blockade of EBV reactivation is separable from HDAC inhibition. Valpromide (VPM), an amide derivative of valproic acid that is not an HDAC inhibitor, prevented expression of two EBV genes, BZLF1 and BRLF1, that mediate lytic reactivation. VPM also inhibited expression of a viral late gene, but not early genes, when BZLF1 was exogenously expressed. Unlike VPA, VPM did not activate lytic expression of Kaposi's sarcoma-associated herpesvirus. Expression of cellular immediate-early genes, such as FOS and EGR1, is kinetically upstream of the EBV lytic cycle. VPM did not activate expression of these cellular immediate-early genes but decreased their level of expression when induced by butyrate, an HDAC inhibitor. VPM did not alter expression of several other cellular immediate-early genes, including STAT3, which were induced by the HDAC inhibitors in cells refractory to lytic induction. Therefore, VPM selectively inhibits both viral and cellular gene expression. VPA and VPM represent a new class of antiviral agents. The mechanism by which VPA and VPM block EBV reactivation may be related to their anticonvulsant activity.

IMPORTANCE

Epstein-Barr virus, (EBV), a human tumor virus, establishes a life-long latent infection. Reactivation of EBV into the lytic phase of its life cycle allows the virus to spread. Previously, we showed that EBV reactivation was blocked by valproic acid (VPA), an inhibitor of cellular histone deacetylases (HDACs). VPA alters the expression of thousands of cellular genes. In this study, we demonstrate that valpromide (VPM), an amide derivative of valproic acid that is not an HDAC inhibitor, prevented initiation of the EBV lytic cycle. VPA induced lytic reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV), but VPM did not. Unlike VPA, VPM did not activate cellular immediate-early gene expression. VPM is a new type of antiviral agent. VPM will be useful in probing the mechanism of EBV lytic reactivation and may have therapeutic application.

Valeric acid induces cell cycle arrest at G1 phase in CHO cell cultures and improves recombinant antibody productivity

To find a more effective chemical reagent for improved monoclonal antibody (mAb) production, eight chemical reagents (curcumin, quercein, DL-sulforaphane, thymidine, valeric acid, phenyl butyrate, valproic acid, and lithium chloride) known to induce cell cycle arrest were examined individually as chemical additives to recombinant CHO (rCHO) cell cultures producing mAb. Among these chemical additives, valeric acid showed the best production performance. Valeric acid decreased specific growth rate (μ), but increased culture longevity and specific mAb productivity (qmAb ) in a dose-dependent manner. The beneficial effect of valeric acid on culture longevity and qmAb outweighed its detrimental effect on μ, resulting in 2.9-fold increase in the maximum mAb concentration when 1.5 mM valeric acid was added to the cultures. Furthermore, valeric acid did not negatively affect the mAb quality attributes with regard to aggregation, charge variation, and galactosylation. Unexpectedly, galactosylation of the mAb increased by the 1.5 mM valeric acid addition. Taken together, the results obtained here demonstrate that valeric acid is an effective chemical reagent to increase mAb production in rCHO cells.

Valproic Acid Limits Pancreatic Recovery after Pancreatitis by Inhibiting Histone Deacetylases and Preventing Acinar Redifferentiation Programs

The mechanisms by which drugs induce pancreatitis are unknown. A definite cause of pancreatitis is due to the antiepileptic drug valproic acid (VPA). On the basis of three crucial observations-that VPA inhibits histone deacetylases (HDACs), HDACs mediate pancreas development, and aspects of pancreas development are recapitulated during recovery of the pancreas after injury-we hypothesized that VPA does not cause injury on its own, but it predisposes patients to pancreatitis by inhibiting HDACs and provoking an imbalance in pancreatic recovery. In an experimental model of pancreatic injury, we found that VPA delayed recovery of the pancreas and reduced acinar cell proliferation. In addition, pancreatic expression of class I HDACs (which are the primary VPA targets) increased in the midphase of pancreatic recovery. VPA administration inhibited pancreatic HDAC activity and led to the persistence of acinar-to-ductal metaplastic complexes, with prolonged Sox9 expression and sustained β-catenin nuclear activation, findings that characterize a delay in regenerative reprogramming. These effects were not observed with valpromide, an analog of VPA that lacks HDAC inhibition. This is the first report, to our knowledge, that VPA shifts the balance toward pancreatic injury and pancreatitis through HDAC inhibition. The work also identifies a new paradigm for therapies that could exploit epigenetic reprogramming to enhance pancreatic recovery and disorders of pancreatic injury.

An in vitro model for synaptic loss in neurodegenerative diseases suggests a neuroprotective role for valproic acid via inhibition of cPLA2 dependent signalling

Many neurodegenerative diseases present the loss of synapses as a common pathological feature. Here we have employed an in vitro model for synaptic loss to investigate the molecular mechanism of a therapeutic treatment, valproic acid (VPA). We show that amyloid-β (Aβ), isolated from patient tissue and thought to be the causative agent of Alzheimer's disease, caused the loss of synaptic proteins including synaptophysin, synapsin-1 and cysteine-string protein from cultured mouse neurons. Aβ-induced synapse damage was reduced by pre-treatment with physiologically relevant concentrations of VPA (10 μM) and a structural variant propylisopropylacetic acid (PIA). These drugs also reduced synaptic damage induced by other neurodegenerative-associated proteins α-synuclein, linked to Lewy body dementia and Parkinson's disease, and the prion-derived peptide PrP82-146. Consistent with these effects, synaptic vesicle recycling was also inhibited by these proteins and protected by VPA and PIA. We show a mechanism for this damage through aberrant activation of cytoplasmic phospholipase A2 (cPLA2) that is reduced by both drugs. Furthermore, Aβ-dependent cPLA2 activation correlates with its accumulation in lipid rafts, and is likely to be caused by elevated cholesterol (stabilising rafts) and decreased cholesterol ester levels, and this mechanism is reduced by VPA and PIA. Such observations suggest that VPA and PIA may provide protection against synaptic damage that occurs during Alzheimer's and Parkinson's and prion diseases.

Valnoctamide, a non-teratogenic amide derivative of valproic acid, inhibits arachidonic acid activation in vitro by recombinant acyl-CoA synthetase-4

OBJECTIVE

Valproic acid (VPA), a mood stabilizer used for treating bipolar disorder (BD), uncompetitively inhibits acylation of arachidonic acid (AA) by recombinant AA-selective acyl-CoA synthetase 4 (Acsl4) at an enzyme inhibition constant (Ki ) of 25 mM. Inhibition may account for VPA's ability to reduce AA turnover in brain phospholipids of unanesthetized rats and to be therapeutic in BD. However, VPA is teratogenic. We tested whether valnoctamide (VCD), a non-teratogenic amide derivative of a VPA chiral isomer, which had antimanic potency in a phase III BD trial, also inhibits recombinant Acsl4.

METHODS

Rat Acsl4-flag protein was expressed in Escherichia coli. We used Michaelis-Menten kinetics to characterize and quantify the ability of VCD to inhibit conversion of AA to AA-CoA by recombinant Acsl4 in vitro.

RESULTS

Acsl4-mediated activation of AA to AA-CoA by Acsl4 was inhibited uncompetitively by VCD, with a Ki of 6.38 mM.

CONCLUSIONS

VCD's ability to uncompetitively inhibit AA activation to AA-CoA by Acsl4, at a lower Ki than VPA, suggests that, like VPA, VCD may reduce AA turnover in rat brain phospholipids. If so, VCD and other non-teratogenic Acsl4 inhibitors might be considered further for treating BD.

Propylisopropylacetic acid (PIA), a constitutional isomer of valproic acid, uncompetitively inhibits arachidonic acid acylation by rat acyl-CoA synthetase 4: a potential drug for bipolar disorder

BACKGROUND

Mood stabilizers used for treating bipolar disorder (BD) selectively downregulate arachidonic acid (AA) turnover (deacylation-reacylation) in brain phospholipids, when given chronically to rats. In vitro studies suggest that one of these, valproic acid (VPA), which is teratogenic, reduces AA turnover by inhibiting the brain long-chain acyl-CoA synthetase (Acsl)4 mediated acylation of AA to AA-CoA. We tested whether non-teratogenic VPA analogues might also inhibit Acsl4 catalyzed acylation, and thus have a potential anti-BD action.

METHODS

Rat Acsl4-flag protein was expressed in Escherichia coli, and the ability of three VPA analogues, propylisopropylacetic acid (PIA), propylisopropylacetamide (PID) and N-methyl-2,2,3,3-tetramethylcyclopropanecarboxamide (MTMCD), and of sodium butyrate, to inhibit conversion of AA to AA-CoA by Acsl4 was quantified using Michaelis-Menten kinetics.

RESULTS

Acsl4-mediated conversion of AA to AA-CoA in vitro was inhibited uncompetitively by PIA, with a Ki of 11.4mM compared to a published Ki of 25mM for VPA, while PID, MTMCD and sodium butyrate had no inhibitory effect.

CONCLUSIONS

PIA's ability to inhibit conversion of AA to AA-CoA by Acsl4 in vitro suggests that, like VPA, PIA may reduce AA turnover in brain phospholipids in unanesthetized rats, and if so, may be effective as a non-teratogenic mood stabilizer in BD patients.

Conserved valproic-acid-induced lipid droplet formation in Dictyostelium and human hepatocytes identifies structurally active compounds

Lipid droplet formation and subsequent steatosis (the abnormal retention of lipids within a cell) has been reported to contribute to hepatotoxicity and is an adverse effect of many pharmacological agents including the antiepileptic drug valproic acid (VPA). In this study, we have developed a simple model system (Dictyostelium discoideum) to investigate the effects of VPA and related compounds in lipid droplet formation. In mammalian hepatocytes, VPA increases lipid droplet accumulation over a 24-hour period, giving rise to liver cell damage, and we show a similar effect in Dictyostelium following 30 minutes of VPA treatment. Using ³H-labelled polyunsaturated (arachidonic) or saturated (palmitic) fatty acids, we shown that VPA treatment of Dictyostelium gives rise to an increased accumulation of both types of fatty acids in phosphatidylcholine, phosphatidylethanolamine and non-polar lipids in this time period, with a similar trend observed in human hepatocytes (Huh7 cells) labelled with [³H]arachidonic acid. In addition, pharmacological inhibition of β-oxidation in Dictyostelium phenocopies fatty acid accumulation, in agreement with data reported in mammalian systems. Using Dictyostelium, we then screened a range of VPA-related compounds to identify those with high and low lipid-accumulation potential, and validated these activities for effects on lipid droplet formation by using human hepatocytes. Structure-activity relationships for these VPA-related compounds suggest that lipid accumulation is independent of VPA-catalysed teratogenicity and inositol depletion. These results suggest that Dictyostelium could provide both a novel model system for the analysis of lipid droplet formation in human hepatocytes and a rapid method for identifying VPA-related compounds that show liver toxicology.

Histone deacetylase inhibition enhances self renewal and cardioprotection by human cord blood-derived CD34 cells

Background

Use of peripheral blood- or bone marrow-derived progenitors for ischemic heart repair is a feasible option to induce neo-vascularization in ischemic tissues. These cells, named Endothelial Progenitors Cells (EPCs), have been extensively characterized phenotypically and functionally. The clinical efficacy of cardiac repair by EPCs cells remains, however, limited, due to cell autonomous defects as a consequence of risk factors. The devise of “enhancement” strategies has been therefore sought to improve repair ability of these cells and increase the clinical benefit.

Principal Findings

Pharmacologic inhibition of histone deacetylases (HDACs) is known to enhance hematopoietic stem cells engraftment by improvement of self renewal and inhibition of differentiation in the presence of mitogenic stimuli in vitro. In the present study cord blood-derived CD34⁺ were pre-conditioned with the HDAC inhibitor Valproic Acid. This treatment affected stem cell growth and gene expression, and improved ischemic myocardium protection in an immunodeficient mouse model of myocardial infarction.

Conclusions

Our results show that HDAC blockade leads to phenotype changes in CD34⁺ cells with enhanced self renewal and cardioprotection.

Targeting the epigenome: effects of epigenetic treatment strategies on genomic stability in healthy human cells

Epigenetic treatment concepts have long been ascribed as being tumour-selective. Over the last decade, it has become evident that epigenetic mechanisms are essential for a wide range of intracellular functions in healthy cells as well. Evaluation of possible side-effects and their underlying mechanisms in healthy human cells is necessary in order to improve not only patient safety, but also to support future drug development. Since epigenetic regulation directly interacts with genomic and chromosomal packaging density, increasing genomic instability may be a result subsequent to drug-induced epigenetic modifications. This review highlights past and current research efforts on the influence of epigenetic modification on genomic stability in healthy human cells.

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.

Simple inhibitors of histone deacetylase activity that combine features of short-chain fatty acid and hydroxamic acid inhibitors

Butyric acid and trichostatin A (TSA) are anti-cancer compounds that cause the upregulation of genes involved in differentiation and cell cycle regulation by inhibiting histone deacetylase (HDAC) activity. In this study we have synthesized and evaluated compounds that combine the bioavailability of short-chain fatty acids, like butyric acid, with the bidentate binding ability of TSA. A series of analogs were made to examine the effects of chain length, simple aromatic cap groups, and substituted hydroxamates on the compounds' ability to inhibit rat-liver HDAC using a fluorometric assay. In keeping with previous structure-activity relationships, the most effective inhibitors consisted of longer chains and hydroxamic acid groups. It was found that 5-phenylvaleric hydroxamic acid and 4-benzoylbutyric hydroxamic acid were the most potent inhibitors with IC50's of 5 microM and 133 microM respectively.

Hepatoprotection and lethality rescue by histone deacetylase inhibitor valproic acid in fatal hemorrhagic shock

BACKGROUND

Pharmacological histone deacetylase (HDAC) inhibitors, such as known anticonvulsant valproic acid (VPA), demonstrate cytoprotective effects and increase acetylation of nuclear histones, promoting transcriptional activation of deregulated genes. Therefore, we examined protective effects of VPA administration in lethal hemorrhage and analyzed the patterns of hepatic histone acetylation.

METHODS

Male Wistar Kyoto rats were pretreated with VPA (n = 10) and 2-methyl-2-pentenoic acid (2M2P), structural VPA analog with limited HDAC inhibiting activity (2M2P; n = 8), at 300 mg/kg/dose, administered subcutaneously, 24 hour and immediately before lethal, if untreated, hemorrhage was induced by removing the 60% of total blood volume. Both drugs were dissolved in normal saline (NS) and rats pretreated with corresponding volume of NS served as control group (n = 8). Time to death, the degree of histone acetylation in liver, HDAC activity and markers of cytotoxicity (alpha-glutathione S-transferase, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, and lactate), and apoptosis were analyzed.

RESULTS

VPA-pretreated animals demonstrated five-fold increase in survival duration. At 12 hours posthemorrhage, 70% (VPA) and 12% (2M2P) pretreated rats were alive versus 0% in NS group. Hyperacetylation of histones H2A, H3, and H4 indicated the presence of active genes and correlated with survival (VPA > 2M2P > NS). Hemorrhage-induced increases in lactate, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase were alleviated by VPA. Moreover, alpha-glutathione S-transferase release, indicative of liver damage, was completely abolished.

CONCLUSION

VPA offers considerable protection in severe hemorrhagic shock. The role of HDAC inhibition is suggested in mediating prosurvival actions of VPA.

Mechanisms of action of the mood stabilizer valproate: a focus on GSK-3 inhibition

Valproate is the most widely prescribed antiepileptic drug worldwide, and it is also used in the treatment of bipolar affective disorder, migraine headache and cancer. However, the therapeutic mechanism of action of valproate in these illness states is not understood. This article reviews the pharmacological effects of valproate that may explain its therapeutic efficacy. It focuses on the hypothesis that inhibition of glycogen synthase kinase-3 by valproate is a crucial therapeutic mechanism of this drug in the treatment of bipolar affective disorder. Other cellular pathways and signaling molecules that are targets of valproate (such as inositol de novo biosynthesis, histone deacetylase, protein kinase C, γ-aminobutyric acid, the extracellular signal-regulated kinase pathway and others) are also discussed.

Antiepileptic drugs in non-epilepsy disorders: relations between mechanisms of action and clinical efficacy

Antiepileptic drugs (AEDs) are used extensively to treat multiple non-epilepsy disorders, both in neurology and psychiatry. This article provides a review of the clinical efficacy of AEDs in non-epilepsy disorders based on recently published preclinical and clinical studies, and attempts to relate this efficacy to the mechanism of action of AEDs and pathophysiological processes associated with the disorders. Some newer indications for AEDs have been established, while others are under investigation. The disorders where AEDs have been demonstrated to be of clinical importance include neurological disorders, such as essential tremor, neuropathic pain and migraine, and psychiatric disorders, including anxiety, schizophrenia and bipolar disorder. Many of the AEDs have various targets of action in the synapse and have several proposed relevant mechanisms of action in epilepsy and in other disorders. Pathophysiological processes disturb neuronal excitability by modulating ion channels, receptors and intracellular signalling pathways, and these are targets for the pharmacological action of various AEDs. Attention is focused on the glutamatergic and GABAergic synapses. In psychiatric conditions such as schizophrenia and bipolar disorder, AEDs such as valproate, carbamazepine and lamotrigine appear to have clear roles based on their effect on intracellular pathways. On the other hand, some AEDs, e.g. topiramate, have efficacy for nonpsychiatric disorders including migraine, possibly by enhancing GABAergic and reducing glutamatergic neurotransmission. AEDs that seem to enhance GABAergic neurotransmission, e.g. tiagabine, valproate, gabapentin and possibly levetiracetam, may have a role in treating neurological disorders such as essential tremor, or anxiety disorders. AEDs with effects on voltage-gated sodium or calcium channels may be advantageous in treating neuropathic pain, e.g. gabapentin, pregabalin, carbamazepine, oxcarbazepine, lamotrigine and valproate. Co-morbid conditions associated with epilepsy, such as mood disorders and migraine, may often respond to treatment with AEDs. Other possible disorders where AEDs may be of clinical importance include cancer, HIV infection, drug and alcohol abuse, and also in neuroprotection. A future challenge is to evaluate the second-generation AEDs in non-epilepsy disorders and to design clinical trials to study their effects in such disorders in paediatric patients. Differentiation between the main mechanisms of action of the AEDs needs more consideration in drug selection for tailored treatment of the various non-epilepsy disorders.

Modifications of Antiepileptic Drugs for Improved Tolerability and Efficacy

Introduction

A large number of antiepileptic drugs (AEDs) are available today, but they may not be satisfactory regarding clinical efficacy, tolerance, toxicity or pharmacokinetic properties. The purpose of this review is to focus upon the rationale behind the chemical modifications of several recently marketed AEDs or drugs in development and to categorize them according to the main purposes for the improvements: better efficacy or tolerability accompanied by improved pharmacokinetic properties.

Material and Method

AEDs that have been chemically modified to new derivatives during the last years are reviewed based on recent publications and PubMed-searches.

Results and Discussion

Improvement in pharmacokinetic parameters may affect both tolerability and efficacy. Modifications to improve tolerability include various valproate analogues, divided into aliphatic amides, cyclic derivatives or amino acid conjugates. Furthermore, there are the carbamazepine analogues oxcarbazepine and eslicarbazepine, the felbamate analogues fluorofelbamate and carisbamate (RWJ 33369), and the lamotrigine analogue JZP-4. The levetiracetam analogues brivaracetam and seletracetam and the derivatives of gabapentin, pregabalin and XP13512, have improved selectivity compared to their parent compounds. Other new drugs have new mechanisms of action related to GABA and glutamate receptors; the glutamate antagonists like topiramate (talampanel and NS-1209), and GABAA receptor agonists, benzodiazepine or progesterone analogues (ELB-139 and ganaxolone).

Conclusion

Further challenges for development of new AEDs include investigations of target molecules affected by pathophysiological processes and detailed structure-activity relationships with focus on stereoselectivity. These potential drugs may become of importance in future drug therapy in epilepsy and other CNS disorders.

New histone deacetylase inhibitors as potential therapeutic tools for advanced prostate carcinoma

The anti-epileptic drug valproic acid is also under trial as an anti-cancer agent due to its histone deacetylase (HDAC) inhibitory properties. However, the effects of valproic acid (VPA) are limited and concentrations required for exerting anti-neoplastic effects in vitro may not be reached in tumour patients. In this study, we tested in vitro and in vivo effects of two VPA-derivatives (ACS2, ACS33) on pre-clinical prostate cancer models. PC3 and DU-145 prostate tumour cell lines were treated with various concentrations of ACS2 or ACS33 to perform in vitro cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and to evaluate tumour cell adhesion to endothelial cell monolayers. Analysis of acetylated histones H3 and H4 protein expression was performed by western blotting. In vivo tumour growth was conducted in subcutaneous xenograft mouse models. Tumour sections were assessed by immunohistochemistry for histone H3 acetylation and proliferation. ACS2 and ACS33 significantly up-regulated histone H3 and H4 acetylation in prostate cancer cell lines. In micromolar concentrations both compounds exerted growth arrest in PC3 and DU-145 cells and prevented tumour cell attachment to endothelium. In vivo, ACS33 inhibited the growth of PC3 in subcutaneous xenografts. Immunohistochemistry and western blotting confirmed increased histone H3 acetylation and reduced proliferation. ACS2 and ACS33 represent novel VPA derivatives with superior anti-tumoural activities, compared to the mother compound. This investigation lends support to the clinical testing of ACS2 or ACS33 for the treatment of prostate cancer.

Inhibition of histone deacetylase as a new mechanism of teratogenesis

Histone deacetylases (HDACs) are nuclear and cytoplasmic enzymes that deacetylate a number of substrates, of which histones are the best known and described in the literature. HDACs are present in eukaryotic and bacteria cells, and are fundamental for a number of cellular functions, including correct gene expression. Surprisingly, only up to 20% of the whole genome is controlled by HDACs, but key processes for survival, proliferation, and differentiation have been strictly linked to HDAC enzyme functioning. The use of HDAC inhibitors (HDACi) has been proposed for the treatment of neoplastic diseases. Their effectiveness has been suggested for a number of liquid and solid tumors, particularly acute promyelocytic leukemia (APL). The role of HDACs in embryo development is currently under investigation. Published data indicate knockout phenotype analysis to be of particular interest, in which a number of HDACs play a key role during development. Little data have been published on the effects of HDACi on embryonic development, although for valproic acid (VPA), literature from the 1980s described its teratogenic effects in experimental animals and humans. To date, all tested HDACi have shown teratogenic effects similar to those described for VPA when tested in zebrafish, Xenopus laevis, and mice. HDACs were also able to alter embryo development in invertebrates and plants. A model, similar to that proposed in APL, involving retinoic acid receptors (RAR) and tissue specific Hox gene expression, is suggested to explain the HDAC effects on embryo development.

Thoracic skeletal defects and cardiac malformations: a common epigenetic link?

Congenital heart defects (CHDs) are the most common birth defects in humans. In addition, cardiac malformations represent the most frequently identified anomaly in teratogenicity experiments with laboratory animals. To explore the mechanisms of these drug-induced defects, we developed a model in which pregnant rats are treated with dimethadione, resulting in a high incidence of heart malformations. Interestingly, these heart defects were accompanied by thoracic skeletal malformations (cleft sternum, fused ribs, extra or missing ribs, and/or wavy ribs), which are characteristic of anterior-posterior (A/P) homeotic transformations and/or disruptions at one or more stages in somite development. A review of other teratogenicity studies suggests that the co-occurrence of these two disparate malformations is not unique to dimethadione, rather it may be a more general phenomenon caused by various structurally unrelated agents. The coexistence of cardiac and thoracic skeletal malformations has also presented clinically, suggesting a mechanistic link between cardiogenesis and skeletal development. Evidence from genetically modified mice reveals that several genes are common to heart development and to formation of the axial skeleton. Some of these genes are important in regulating chromatin architecture, while others are tightly controlled by chromatin-modifying proteins. This review focuses on the role of these epigenetic factors in development of the heart and axial skeleton, and examines the hypothesis that posttranslational modifications of core histones may be altered by some developmental toxicants.

Valproic Acid: second generation

The manuscript focuses on structure-activity relationship studies of CNS-active compounds derived from valproic acid (VPA) that have the potential to become second-generation VPA drugs. Valproic acid is one of the four most widely prescribed antiepileptic drugs (AEDs) and is effective (and regularly approved) in migraine prophylaxis and in the treatment of bipolar disorders. Valproic acid is also currently undergoing clinical trials in cancer patients. Valproic acid is the least potent of the established AEDs and its use is limited by two rare but potentially life-threatening side effects, teratogenicity and hepatotoxicity. Because AEDs treat the symptoms (seizure) and not the cause of epilepsy, epileptic patients need to take AEDs for a long period of time. Consequently, there is a substantial need to develop better and safer AEDs. To become a successful second-generation VPA, the new drug should possess the following characteristics: broad-spectrum antiepileptic activity, better potency than VPA, lack of teratogenicity and hepatotoxicity, and a favorable pharmacokinetic profile compared with VPA including a low potential for drug interactions.

The antiepileptic and anticancer agent, valproic acid, induces P-glycoprotein in human tumour cell lines and in rat liver

BACKGROUND AND PURPOSE

The antiepileptic drug valproic acid, a histone deacetylase (HDAC) inhibitor, is currently being tested as an anticancer agent. However, HDAC inhibitors may interact with anticancer drugs through induction of P-glycoprotein (P-gp, MDR1) expression. In this study we assessed whether valproic acid induces P-gp function in tumour cells. We also investigated effects of valproic acid on the mRNA for P-gp and the cytochrome P450, CYP3A, in rat livers.

EXPERIMENTAL APPROACH

Effects of valproic acid on P-gp were assessed in three tumour cell lines, SW620, KG1a and H4IIE. Accumulation of acetylated histone H3 in rats' livers treated for two or seven days with valproic acid was evaluated using a specific antibody. Hepatic expression of the P-gp genes, mdr1a, mdr1b and mdr2, was determined by real-time polymerase chain reaction. The effects of valproic acid on CYP3A were assessed by Northern blot analysis and CYP3A activity assays.

KEY RESULTS

Valproic acid (0.5-2.0 mM) induced P-gp expression and function up to 4-fold in vitro. The effect of a series of valproic acid derivatives on P-gp expression in SW620 and KG1a cells correlated with their HDAC inhibition potencies. Treatment of rats with 1 mmol kg(-1) valproic acid for two and seven days increased hepatic histone acetylation (1.3- and 3.5-fold, respectively) and the expression of mdr1a and mdr2 (2.2-4.1-fold). Valpromide (0.5-2.0 mM) did not increase histone acetylation or P-gp expression in rat livers, but induced CYP3A expression.

CONCLUSIONS

Valproic acid increased P-gp expression and function in human tumour cell lines and in rat liver. The clinical significance of this increase merits further investigation.

New antiepileptic drugs that are second generation to existing antiepileptic drugs

In the last decade, 10 new antiepileptic drugs (AEDs) have been introduced that offer appreciable advantages in terms of their favourable pharmacokinetics, improved tolerability and lower potential for drug interactions. However, despite the large therapeutic range of old and new AEDs, approximately 30% of the patients with epilepsy are still not seizure free and, consequently, there is a substantial need to develop new AEDs. The new AEDs currently in development can be divided into two categories: drugs with completely new chemical structures such as lacosamide (formally harkoseride), retigabine, rufinamide and talampanel; and drugs that are derivatives or analogues of existing AEDs that can be regarded as second-generation or follow-up compounds of established AEDs. This article focuses on the second category and thus critically reviews the following second-generation compounds: eslicarbazepine acetate or BIA-2-093 and 10-hydroxy carbazepine (carbamazepine derivatives); valrocemide and NPS 1776 (isovaleramide; valproic acid derivatives); pregabalin and XP13512 (gabapentin derivatives); brivaracetam (ucb 34714) and seletracetam (ucb 44212; levetiracetam derivatives); and fluorofelbamate (a felbamate derivative). In addition, a series of valproic acid derivatives that are currently in preclinical stage has also been evaluated because some lead compounds of this series have a promising potential to become new antiepileptics and CNS drugs. For any of these follow-up compounds to become a successful second generation to an existing AED, it has to be more potent, safer and possess favourable pharmacokinetics, including low potential for pharmacokinetic and pharmacodynamic drug interactions.

VALPROIC ACID PREVENTS HEMORRHAGE-ASSOCIATED LETHALITY AND AFFECTS THE ACETYLATION PATTERN OF CARDIAC HISTONES

Pharmacological inhibitors of histone deacetylases (HDAC) demonstrate cytoprotective effects both in vitro and in vivo. In this study, we investigated whether valproic acid (VPA), a known mood stabilizer and anticonvulsant with HDAC-inhibiting activity, improves survival following otherwise lethal hemorrhage in rats. We found that preinsult injection of VPA (300 mg/kg, twice) prolonged the survival of severely hypotensive animals up to 5 times. VPA treatment increased the acetylation of nonhistone and histone proteins in the rat heart. The pattern of modifications of individual histones revealed hyperacetylation of histones H2A, H3, and H4, indicating the presence of active genes. Expression of HSP70 and superoxide dismutase, implicated in the modulation of vitality, was increased by VPA. Our results reveal that VPA offers considerable protection in the hemorrhagic shock model and suggest a role for HDAC inhibition in mediating VPA actions.

Antineoplastic effects of the DNA methylation inhibitor hydralazine and the histone deacetylase inhibitor valproic acid in cancer cell lines

Background

Among the epigenetic alterations occurring in cancer, DNA hypermethylation and histone hypoacetylation are the focus of intense research because their pharmacological inhibition has shown to produce antineoplastic activity in a variety of experimental models. The objective of this study was to evaluate the combined antineoplastic effect of the DNA methylation inhibitor hydralazine and the histone deacetylase inhibitor valproic acid in a panel of cancer cell lines.

Results

Hydralazine showed no growth inhibitory effect on cervical, colon, breast, sarcoma, glioma, and head & neck cancer cell lines when used alone. On the contrary, valproic acid showed a strong growth inhibitory effect that is potentiated by hydralazine in some cell lines. Individually, hydralazine and valproic acid displayed distinctive effects upon global gene over-expression but the number of genes over-expressed increased when cells were treated with the combination. Treatment of HeLa cells with hydralazine and valproic acid lead to an increase in the cytotoxicity of gemcitabine, cisplatin and adriamycin. A higher antitumor effect of adriamycin was observed in mice xenografted with human fibrosarcoma cells when the animals were co-treated with hydralazine and valproic acid.

Conclusion

Hydralazine and valproic acid, two widely used drugs for cardiovascular and neurological conditions respectively have promising antineoplastic effects when used concurrently and may increase the antitumor efficacy of current cytotoxic agents.

S-2-PENTYL-4-PENTYNOIC HYDROXAMIC ACID AND ITS METABOLITE S-2-PENTYL-4-PENTYNOIC ACID IN THE NMRI-EXENCEPHALY-MOUSE MODEL: PHARMACOKINETIC PROFILES, TERATOGENIC EFFECTS, AND HISTONE DEACETYLASE INHIBITION ABILITIES OF FURTHER VALPROIC ACID HYDROXAMATES AND AMIDES

Structure-activity relationship studies of valproic acid (VPA) derivatives have revealed a quantitative correlation between histone deacetylase (HDAC) inhibition and induction of neural tube defects (NTDs) in the NMRI-exencephaly-mouse model, but this correlation has been, so far, limited to congeners with a carboxylic acid function. Whereas the classical HDAC inhibitor trichostatin A is active only as a hydroxamate but not as a carboxylic acid, we found that neither VPA amides nor hydroxamates inhibit HDACs, but can cause NTDs; e.g., 2-pentyl-4-pentynoic hydroxamic acid with its S-enantiomer being the potent teratogen. We therefore investigated the hypothesis that hydroxamic acid derivatives of VPA might be metabolized in vivo and may possibly be pro-teratogenic, as had been shown for valpromide but not valproic hydroxamic acid. We developed two stereoselective quantification methods based on chiral derivatization of VPA hydroxamates with (1R,2S,5R)-(-)-menthylchloroformate and carboxylic acid derivatives with (S)-(-)-1-naphthylethylamine, followed by gas chromatography-nitrogen phosphor detector analysis of biological samples. We then determined the pharmacokinetic profiles of S-2-pentyl-4-pentynoic hydroxamic acid and of S-2-pentyl-4-pentynoic acid in mice. S-2-Pentyl-4-pentynoic hydroxamic acid was found to be extensively metabolized to the corresponding carboxylic acid without affecting the stereochemistry at position C2. Furthermore, the metabolite S-2-pentyl-4-pentynoic acid was found to be very stable in vivo, with an extended half-life of 4.2 h compared with that of VPA, 1.4 h. Comparison of the individual HDAC inhibition abilities of additional VPA amides and hydroxamates, as measured by cellular and enzymatic assays, led us to the conclusion that both classes of VPA derivatives can be pro-teratogenic.