New CNS-active drugs which are second-generation valproic acid: can they lead to the development of a magic bullet?:

Efficacy of antiepileptic tetramethylcyclopropyl analogues of valproic acid amides in a rat model of neuropathic pain

Antiepileptic drugs (AEDs) are widely utilized in the management of neuropathic pain. The AED valproic acid (VPA) holds out particular promise as it engages a variety of different anticonvulsant mechanisms simultaneously. However, the clinical use of VPA is limited by two rare but potentially life-threatening side effects: teratogenicity and hepatotoxicity. We have synthesized several tetramethylcyclopropyl analogues of VPA amides that are non-teratogenic, and are likely to be non-hepatotoxic, and that exhibit good antiepileptic efficacy. In the present study we have assessed the antiallodynic activity of these compounds in comparison to VPA and gabapentin (GBP) using the rat spinal nerve ligation (SNL) model of neuropathic pain. TMCA (2,2,3,3-tetramethylcyclopropanecarboxylic acid, 100-250 mg/kg), TMCD (2,2,3,3-tetramethylcyclopropanecarboxamide, 40-150 mg/kg), MTMCD (N-methyl-TMCD, 20-100 mg/kg), and TMCU (2,2,3,3-tetramethylcyclopropanecarbonylurea, 40-240 mg/kg) all showed dose-related reversal of tactile allodynia, with ED(50) values of 181, 85, 41, and 171 mg/kg i.p., respectively. All were more potent than VPA (ED(50)=269 mg/kg). An antiallodynic effect was obtained for TMCD, MTMCD and TMCU at plasma concentrations as low as 23, 6 and 22 mg/L, respectively. MTMCD was found to be non-toxic, non-sedative and equipotent to gabapentin, currently the leading AED in neuropathic pain treatment. Tetramethylcyclopropyl analogues of VPA amides have potential to become a new series of drugs for neuropathic pain treatment.

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.

Could valerian have been the first anticonvulsant?

PURPOSE

To assess the available evidence for the belief that valerian, highly recommended in the past for treating epilepsy, possessed real anticonvulsant effectiveness.

METHODS

Review of available literature.

RESULTS

In 1592, Fabio Colonna, in his botanical classic Phytobasanos, reported that taking powdered valerian root cured his own epilepsy. Subsequent reports of valerian's anticonvulsant effectiveness appeared. By the late 18th and early 19th centuries, it was often regarded as the best available treatment for the disorder. Valerian preparations yield isovaleric acid, a substance analogous to valproic acid and likely to possess anticonvulsant properties, as isovaleramide does. In favorable circumstances, high valerian doses can be calculated to have sometimes provided potentially effective amounts of anticonvulsant substance for epilepsy patients.

CONCLUSIONS

Valerian probably did possess the potential for an anticonvulsant effect, but the uncertain chemical composition and content of valerian preparations, and their odor and taste, made it unlikely that they could ever prove satisfactory in widespread use.

Tetramethylcyclopropyl Analogue of a Leading Antiepileptic Drug, Valproic Acid. Synthesis and Evaluation of Anticonvulsant Activity of Its Amide Derivatives

Although valproic acid (VPA) is an extensively used antiepileptic drug for treatment of various kinds of epilepsies, it has been proven to possess two life-threatening side effects: hepatotoxicity and teratogenicity. Amide and urea derivatives of 2,2,3,3-tetramethylcyclopropanecarboxylic acid (TMCA) were prepared to discover lead compounds with clinical potential. In the amide and alkylamide series of TMCA derivatives, N-methoxy-2,2,3,3-tetramethylcyclopropanecarboxamide (21) was one of the most active compounds, having the subcutaneous metrazol test (scMet) ED50 values of 35 mg/kg in rats and 74 mg/kg in mice. In the maximal electroshock-induced seizure test (MES), this compound had ED50 values of 108 mg/kg in rats and 115 mg/kg in mice. Compound 21 was 18.5 and 4.5 times more potent than VPA in the corresponding rat tests. The most active compound in the series of urea derivatives was 2,2,3,3-tetramethylcyclopropanecarbonylurea (25), possessing MES ED50 values of 29 mg/kg in rats and 90 mg/kg in mice. In the scMet test this compound had ED50 values of 92 mg/kg in rats and 125 mg/kg in mice. The median toxic dose (TD50) in rats was 538 mg/kg, providing compound 25 with a wide safety margin and a protective index (TD50/ED50) of 18.5 in the MES test, which is about 12 times greater than that of VPA. Compounds 21 and 25 have the potential for development as novel potent and safe central nervous system active drugs with a broad spectrum of antiepileptic activity.

Alternative splicing in disease and therapy

Alternative splicing is the major source of proteome diversity in humans and thus is highly relevant to disease and therapy. For example, recent work suggests that the long-sought-after target of the analgesic acetaminophen is a neural-specific, alternatively spliced isoform of cyclooxygenase 1 (COX-1). Several important diseases, such as cystic fibrosis, have been linked with mutations or variations in either cis-acting elements or trans-acting factors that lead to aberrant splicing and abnormal protein production. Correction of erroneous splicing is thus an important goal of molecular therapies. Recent experiments have used modified oligonucleotides to inhibit cryptic exons or to activate exons weakened by mutations, suggesting that these reagents could eventually lead to effective therapies.

The Activity of Antiepileptic Drugs as Histone Deacetylase Inhibitors

PURPOSE

Valproic acid (VPA), one of the widely used antiepileptic drugs (AEDs), was recently found to inhibit histone deacetylases (HDACs). HDAC inhibitors of a wide range of structures, such as hydroxamic acids, carboxylic acids, and cyclic tetrapeptides, have various effects on transformed and nontransformed cells, including neuromodulation and neuroprotection. The aim of this study was to assess comparatively the activity of traditional and newer AEDs as HDAC inhibitors.

METHODS

After incubation of HeLa cells with the tested AEDs, histone hyperacetylation was assessed by immunoblotting with an antibody specific to acetylated histone H4. Direct HDAC inhibition by AEDs was estimated by using HeLa nuclear extract as an HDACs source and an acetylated lysine substrate.

RESULTS

We found that in addition to VPA, topiramate (TPM) inhibited HDACs with apparent Ki values of 2.22 +/- 0.67 mM. Although levetiracetam (LEV) had no direct effect on HDACs, its major carboxylic acid metabolite in humans, 2-pyrrolidinone-n-butyric acid (PBA), inhibited HDACs with Ki values of 2.25 +/- 0.78 mM. The AEDs LEV, phenobarbital, phenytoin, carbamazepine, ethosuximide, gabapentin, and vigabatrin did not inhibit HDACs. The compounds that directly inhibited HDACs also induced the accumulation of acetylated histone H4 in HeLa cells. The effects of TPM and PBA on histone acetylation were significant at 0.25 mM and 1 mM, respectively.

CONCLUSIONS

We found that in addition to VPA, the newer AED TPM and the major metabolite of LEV, PBA, are able to induce histone hyperacetylation in human cells, although with lower potencies than VPA.

Metabolism of a new antiepileptic drug, N-methyl-tetramethylcyclopropanecarboxamide, and anticonvulsant activity of its metabolites

N-methyl-tetramethylcyclopropanecarboxamide (MTMCD) is a new antiepileptic drug (AED) structurally related to valproic acid (VPA) that has a broad spectrum of anticonvulsant activity including models of therapy-resistant epilepsy. The purpose of this study was to identify in vivo metabolites of MTMCD that could contribute to its anticonvulsant efficacy. The metabolism of MTMCD was studied in mice, in human liver microsomes (HLM), and in recombinant human CYP isoforms with focus on formation of the hydroxylation product, N-hydroxymethyl-tetramethylcyclopropanecarboxamide (OH-MTMCD) and the N-demethylation product tetramethylcyclopropanecarboxamide (TMCD). The anticonvulsant activity of MTMCD's metabolites was evaluated in the maximal electroshock (MES), subcutaneous metrazole (s.c. Met), and in the 6Hz model in mice. In mice, OH-MTMCD was identified as a phase I metabolite of MTMCD and detected in plasma and brain after administration of MTMCD. In human liver microsomes MTMCD was biotransformed to OH-MTMCD but not to TMCD. Chemical inhibition studies suggested that MTMCD hydroxylation is mainly mediated by CYP 2A6 and CYP 2C19, which was confirmed using cDNA-expressed P450 isozymes. OH-MTMCD was a broad-spectrum anticonvulsant and possessed significant anticonvulsant activity in mouse models of partial and generalized seizures (ED50 values 75-220mg/kg), but was less potent than MTMCD. As OH-MTMCD was also present at lower concentrations than MTMCD in mouse brain, it is likely that MTMCD itself and not one of its metabolites is responsible for its activity in therapy-resistant epilepsy.

Amidic modification of valproic acid reduces skeletal teratogenicity in mice

BACKGROUND

The antiepileptic drug valproic acid (VPA) is well known to cause neural tube and skeletal defects in both humans and animals. The amidic VPA analogues valpromide (VPD) and valnoctamide (VCD) have much lower teratogenicity than VPA inducing exencephaly in mice. The objective of this study was to investigate the teratogenic effects of VPA, VPD, and VCD on the skeleton of NMRI mice.

METHODS

Pregnant NMRI mice were given a single subcutaneous injection of VPA (400 and 800 mg/kg), VPD (800 mg/kg), or VCD (800 mg/kg) on the morning of gestation day (GD) 8. Cesarean section was carried out on GD 18. Live fetuses were double-stained for bone and cartilage and their skeletons were examined.

RESULTS

Significant increases in fetal loss and exencephaly rate were observed with VPA at 800 mg/kg compared to the vehicle control. There were no significant differences between either VPD or VCD and the control groups for any parameter at cesarean section. A number of abnormalities were dose-dependently induced at high incidences by VPA in both the cartilage and bone of vertebrae, ribs and sternum. In contrast, lower frequencies of abnormality were exhibited with VPD and VCD than VPA in all skeletons affected by VPA.

CONCLUSIONS

These findings clearly indicate that VPD and VCD are distinctly less teratogenic than VPA in the induction of not only neural tube defects, but also skeletal abnormalities. A structure-teratogenicity relationship of VPA on the skeleton is suspected.

Teratogenicity of valproate conjugates with anticonvulsant activity in mice

Valproic acid (VPA) is an effective antiepileptic medication, the use of which in females of childbearing age is complicated by its ability to induce birth defects, including neural tube defects (NTDs), in exposed embryos. In experimental settings, VPA reproducibly induces NTDs in laboratory animals such as the highly inbred SWV/Fnn mice. In search of new, efficacious derivatives of VPA that lack toxicity, the conjugates of VPA with amantadine (VPA-AMA) and N-3-aminopropyl-2-pyrrolidinone (VPA-PYR) have been synthesized and evaluated for their anticonvulsant activity. In the present study, the authors evaluated the teratogenicity potential of VPA-AMA and VPA-PYR using a well-established mouse model for antiepileptic drug teratogenicity. All tested compounds were injected intraperitoneally to pregnant dams on gestational day 8.5, and the fetuses examined on day 18.5. At the highest dose tested (3.61 mmol/kg), VPA-PYR was maternally lethal, whereas VPA-AMA induced excessive embryonic lethality. At a dose of 2.20 mmol/kg, VPA-PYR was not teratogenic to the exposed embryos; VPA-AMA induced NTDs in 8.2% of embryos, VPA caused 5.5% NTDs. 0.80 mmol/kg amantadine induced NTDs in 2.2% of the exposed fetuses. In conclusion, VPA-AMA has a comparable teratogenicity as does VPA, and it is proposed that the teratogenicity of VPA-AMA is due to the parent compound. Additional studies are needed to fully define and understand the structure-teratogenicity relationships of VPA analogues.

Anticonvulsant activity, teratogenicity and pharmacokinetics of novel valproyltaurinamide derivatives in mice

1 The purpose of this study was to synthesize novel valproyltaurine (VTA) derivatives including valproyltaurinamide (VTD), N-methyl-valproyltaurinamide (M-VTD), N,N-dimethyl-valproyltaurinamide (DM-VTD) and N-isopropyl-valproyltaurinamide (I-VTD) and evaluate their structure-pharmacokinetic-pharmacodynamic relationships with respect to anticonvulsant activity and teratogenic potential. However, their hepatotoxic potential could not be evaluated. The metabolism and pharmacokinetics of these derivatives in mice were also studied. 2 VTA lacked anticonvulsant activity, but VTD, DM-VTD and I-VTD possessed anticonvulsant activity in the Frings audiogenic seizure susceptible mice (ED(50) values of 52, 134 and 126 mg kg(-1), respectively). 3 VTA did not have any adverse effect on the reproductive outcome in the Swiss Vancouver/Fnn mice following a single i.p. injection of 600 mg kg(-1) on gestational day (GD) 8.5. VTD (600 mg kg(-1) at GD 8.5) produced an increase in embryolethality, but unlike valproic acid, it did not induce congenital malformations. DM-VTD and I-VTD (600 mg kg(-1) at GD 8.5) produced a significant increase in the incidence of gross malformations. The incidence of birth defects increased when the length of the alkyl substituent or the degree of N-alkylation increased. 4 In mice, N-alkylated VTDs underwent metabolic N-dealkylation to VTD. DM-VTD was first biotransformed to M-VTD and subsequently to VTD. I-VTD's fraction metabolized to VTD was 29%. The observed metabolic pathways suggest that active metabolites may contribute to the anticonvulsant activity of the N-alkylated VTDs and reactive intermediates may be formed during their metabolism. In mice, VTD had five to 10 times lower clearance (CL), and three times longer half-life than I-VTD and DM-VTD, making it a more attractive compound than DM-VTD and I-VTD for further development. VTD's extent of brain penetration was only half that observed for the N-alkylated taurinamides suggesting that it has a higher intrinsic activity that DM-VTD and I-VTD. 5 In conclusion, from this series of compounds, although VTD caused embryolethality, this compound emerged as the most promising new antiepileptic drug, having a preclinical spectrum characterized by the highest anticonvulsant potential, lowest potential for teratogenicity and favorable pharmacokinetics.