Anticonvulsant profile and teratogenicity of N-methyl-tetramethylcyclopropyl carboxamide: a new antiepileptic drug

Design and Synthesis of Some Novel 4-(4-substituted aryl) Semicarbazones as Anticonvulsant Agents

In the present study, a series of 4-(4-substituted aryl) semicarbazones were synthesized from substituted anilines and subsequently evaluated for their anticonvulsant activities. The anticonvulsant activities were established by the anticonvulsant drug development (ADD) programme NIH, USA using experimental animal, adult male FCM mice (20–25 g) and adult Sprague-Dawley rats (100–150 g) and screened against electroshock seizure, subcutaneous metrazole and minimal neurotoxicity tests in mice. Compound 7 was found equipotent to carbamazepine in both MES and ScPTZ tests. This study has highlighted the importance of distal alkyl chain which influences the anticonvulsant activity.

Comparative pharmacodynamic and pharmacokinetic analysis of two anticonvulsant halo derivatives of 2,2,3,3-tetramethylcyclopropanecarboxamide, an amide of a cyclic analog of valproic acid

PURPOSE

α-Fluoro-2,2,3,3-tetramethylcyclopropanecarboxamide (α-F-TMCD) and α-Cl-TMCD, are α-halo derivatives of TMCD, the corresponding amide of a cyclopropane analog of valproic acid (VPA). This study aimed to comparatively evaluate the pharmacodynamics and pharmacokinetics of α-F-TMCD and α-Cl-TMCD in rodent models of epilepsy and for antiepileptic drug (AED)-induced teratogenicity. The potential of α-F-TMCD as an antiallodynic and antinociceptive compound was also evaluated.

METHODS

α-F-TMCD and α-Cl-TMCD were synthesized. α-Cl-TMCD anticonvulsant activity was evaluated in comparison to VPA in the mouse maximal-electroshock-seizure (MES), Metrazol (scMet), and 6-Hz psychomotor-seizure tests. Neurotoxicity was assessed by the Rotorod-ataxia test. Induction of neural tube defects (NTDs) by α-Cl-TMCD and α-F-TMCD was evaluated after intraperitoneal administration to a mouse strain highly susceptible to VPA-induced teratogenicity. The ability of α-F-TMCD to reduce pain was evaluated in the rat spinal nerve ligation (SNL) model for neuropathic pain and in the formalin test. α-F-TMCD and α-Cl-TMCD pharmacokinetics was evaluated following intraperitoneal (40 mg/kg) and oral (60 mg/kg) administration to rats.

RESULTS

α-F-TMCD and α-Cl-TMCD had similar potencies in the 6-Hz test and were more potent than VPA in this model and in the scMet test. Neither induced NTDs, and both exhibited wide safety margins. α-F-TMCD was active in the two pain models, and was found to be equipotent to gabapentin in the SNL model (ED(50) = 37 and 32 mg/kg, respectively). Comparative pharmacokinetic analysis showed that α-Cl-TMCD is less susceptible to liver first-pass effect than α-F-TMCD because of lower total (metabolic) clearance and liver extraction ratio.

CONCLUSIONS

Based on their potent anticonvulsant activity and lack of teratogenicity, α-F-TMCD and α-Cl-TMCD have the potential for development as new antiepileptics and central nervous system (CNS) drugs.

Facile synthesis of amide and amine derivatives of 2,2,3,3-tetramethylcyclopropanecarboxylic acid

An efficient one-pot procedure for the synthesis of amide derivatives of 2,2,3,3-tetramethylpropanecarboxylic acid (TMCA) that involves the treating of TMCA in N,N-dimethylacetamide (DMAC) with thionyl chloride and stoichiometric amounts of reactant amines has been developed. The combined reagent TiCl4/NaBH4 was found to be effective for the reduction of the amide derivatives of TMCA to the corresponding amines.

Tetramethylcyclopropyl analogue of the leading antiepileptic drug, valproic acid: evaluation of the teratogenic effects of its amide derivatives in NMRI mice

BACKGROUND

Although valproic acid (VPA) is used extensively for treating various kinds of epilepsy, it causes hepatotoxicity and teratogenicity. In an attempt to develop a more potent and safer second generation to VPA drug, the amide derivatives of the tetramethylcyclopropyl VPA analogue, 2,2,3,3-tetramethylcyclopropanecarboxamide (TMCD), N-methyl-TMCD (MTMCD), 4-(2,2,3,3-tetramethylcyclopropanecarboxamide)-benzenesulfonamide (TMCD-benzenesulfonamide), and 5-(TMCD)-1,3,4-thiadiazole-2-sulfonamide (TMCD-thiadiazolesulfonamide) were synthesized and shown to have more potent anticonvulsant activity than VPA. Teratogenic effects of these CNS-active compounds were evaluated in Naval Medical Research Institute (NMRI) mice susceptible to VPA-induced teratogenicity by comparing them to those of VPA.

METHODS

Pregnant NMRI mice were given a single sc injection of either VPA or TMC-amide derivatives on gestation day 8.5, and then the live fetuses were examined to detect any external malformations on gestation day 18. After double-staining for bone and cartilage, their skeletons were examined.

RESULTS

In contrast to VPA, which induced NTDs in a high number of fetuses at 2.4-4.8 mmol/kg, TMCD, TMCD-benzenesulfonamide, and TMCD-thiadiazolesulfonamide at 4.8 mmol/kg and MTMCD at 3.6 mmol/kg did not induce a significant number of NTDs. TMCD-thiadiazolesulfonamide exhibited a potential to induce limb defects in fetuses. Skeletal examination also revealed that fetuses exposed to all four of the tetramethylcyclopropanecarboxamide derivatives developed vertebral and rib abnormalities less frequently than those exposed to VPA. Our results established that TMCD, MTMCD, and TMCD-benzenesulfonamide are distinctly less teratogenic than VPA in NMRI mice.

CONCLUSIONS

The CNS-active amides containing a tetramethylcyclopropanecarbonyl moiety demonstrated better anticonvulsant potency compared to VPA and a lack of teratogenicity, which makes these compounds good second-generation VPA antiepileptic drug candidates.

Anticonvulsant efficacy of valproate-like carboxylic acids: a potential target for anti-bipolar therapy

BACKGROUND

Bipolar disorder (BPD) is a severe and chronic illness, with a lifetime prevalence of approximately 1.5%. Despite the availability of some mood stabilizing drugs including lithium, valproate (valproic acid), lamotrigine and carbamazepine, BPD is characterized by high rates of recurrence, as treatment with these and other drugs is ineffective for and not well-tolerated by a significant percentage of patients. Most drugs currently used for the maintenance treatment of BPD are anticonvulsants (e.g., valproate, carbamazepine and lamotrigine).

OBJECTIVES

The aim of this paper is to review the studies characterizing the anticonvulsant efficacy of valproate-like carboxylic acids and related compounds, some of which may have potential for the treatment of manic-depressive illness.

RESULTS

The data reviewed herein demonstrate clearly that some dietary fatty acids and other valproate-like carboxylic acids exhibit potent anticonvulsant activity, and may thus be candidates for mood stabilizing treatment options for BPD.

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.

Effect of Conantokin G on NMDA receptor-mediated spontaneous EPSCs in cultured cortical neurons

Conantokin G (Con G), derived from the venom of Conus geographus, is the most characterized natural peptide antagonist targeted to N-methyl-D-aspartate (NMDA) receptors. Although Con G is known to bind to the glutamate binding site on the NR2 subunit of the receptor, it is unclear whether it can allosterically modulate the function of the receptor through the glycine binding site on the NR1 subunit. This study was designed to evaluate the action of Con G on NMDA receptor-mediated spontaneous excitatory postsynaptic currents (sEPSCs) and its modulation by glycine in cultured cortical neurons (13-19 days in vitro) using the whole cell patch-clamp technique. Con G inhibited NMDA receptor-mediated sEPSCs in a concentration-dependent manner. Also, the potency of Con G decreased as a function of time in culture. The inhibition of EPSCs observed after application of Con G in the presence of high (10 microM) and nominal (no added) concentrations of glycine was not different at 13 days in vitro (DIV). Furthermore, similar results were obtained with experiments on Con G-induced inhibition of NMDA-evoked whole cell currents. These results indicate that glycine concentrations do not have a direct effect on Con G-induced inhibition of NMDA currents. In addition, age dependency in the action of Con G on cortical neurons in vitro suggests that this model system would be useful in examining the effects of different agonists/antagonists on native synaptic NMDA receptors.

Molecular approaches to developmental malformations using analogous forms of valproic acid

The teratogenic potential of valproic acid has been well established both in experimental models and in human clinical studies. Evidence from many previous studies has shown that VPA is an appropriate drug model for studying chemical structure-teratogenicity relationships. Using molecular techniques of DNA microarray (GeneChip system) or quantitative real-time polymerase chain reaction with low teratogenic VPA analogs as comparative control drugs, we attempted to identify the genes involved with the molecular mechanisms of VPA teratogenicity in the neural tube and the axial skeleton of the mouse embryo. The recent development of DNA microarray enables a genome-wide approach to the identification of genes correlated with the teratogenicity of chemicals (teratogenomics). The VPA-induced changes in gene expression seen during mouse embryogenesis provides information for understanding how VPA disrupts normal embryonic development, and also provides leads for the development of safer medicines.

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.

Preclinical Profiling and Safety Studies of ABT-769: A Compound with Potential for Broad-spectrum Antiepileptic Activity

PURPOSE

The objective of this study was to characterize the antiseizure and safety profiles of ABT-769 [(R)-N-(2 amino-2-oxoethyl)spiro[2,5]octane-1-carboxamide].

METHODS

ABT-769 was tested for protection against maximal electroshock and pentylenetetrazol-induced seizures in the mouse and for suppression of electrically kindled amygdala seizures and spontaneous absence-like seizures in the rat. The central nervous system safety profile was evaluated by using tests of motor coordination and inhibitory avoidance. The potential for liver toxicity was assessed in vitro by using a mitochondrial fatty acid beta-oxidation assay. Teratogenic potential was assessed in the mouse.

RESULTS

ABT-769 blocked maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol-induced seizures with median effective dose (ED50) values of 0.25, 0.38, and 0.11 mmol/kg, p.o., respectively. No tolerance was evident in the intravenous pentylenetetrazol test after twice-daily dosing of ABT-769 (0.3 mmol/kg, p.o.) for 4 days. ABT-769 blocked absence-like spike-wave discharge (ED50, 0.15 mmol/kg, p.o.) and shortened the cortical and amygdala afterdischarge duration of kindled seizures (1 and 3 mmol/kg, p.o.). The protective indices (ED50 rotorod impairment/ED50 seizure protection) were 4.8, 3.2, and 10.9 in the maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol seizure tests, respectively. ABT-769 did not affect inhibitory avoidance performance (0.1-1 mmol/kg, p.o.). ABT-769 did not affect mitochondrial fatty acid beta-oxidation or induce neural tube defects.

CONCLUSIONS

ABT-769 is an efficacious antiseizure agent in animal models of convulsive and nonconvulsive epilepsy and has a favorable safety profile. ABT-769 has a broad-spectrum profile like that of valproic acid. Its profile is clearly different from those of carbamazepine, phenytoin, lamotrigine, topiramate, vigabatrin, and tiagabine.

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.

Valproate decreases inositol biosynthesis

BACKGROUND

Lithium and valproate (VPA) are used for treating bipolar disorder. The mechanism of mood stabilization has not been elucidated, but the role of inositol has gained substantial support. Lithium inhibition of inositol monophosphatase, an enzyme required for inositol recycling and de novo synthesis, suggested the hypothesis that lithium depletes brain inositol and attenuates phosphoinositide signaling. Valproate also depletes inositol in yeast, Dictyostelium, and rat neurons. This raised the possibility that the effect is the result of myo-inositol-1-phosphate (MIP) synthase inhibition.

METHODS

Inositol was measured by gas chromatography. Human prefrontal cortex MIP synthase activity was assayed in crude homogenate. INO1 was assessed by Northern blotting. Growth cones morphology was evaluated in cultured rat neurons.

RESULTS

We found a 20% in vivo reduction of inositol in mouse frontal cortex after acute VPA administration. As hypothesized, inositol reduction resulted from decreased MIP synthase activity: .21-.28 mmol/LVPA reduced the activity by 50%. Among psychotropic drugs, the effect is specific to VPA. Accordingly, only VPA upregulates the yeast INO1 gene coding for MIP synthase. The VPA derivative N-methyl-2,2,3,3,-tetramethyl-cyclopropane carboxamide reduces MIP synthase activity and has an affect similar to that of VPA on rat neurons, whereas another VPA derivative, valpromide, poorly affects the activity and has no affect on neurons.

CONCLUSIONS

The rate-limiting step of inositol biosynthesis, catalyzed by MIP synthase, is inhibited by VPA; inositol depletion is a first event shown to be common to lithium and VPA.

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.

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.

Pharmacokinetic-pharmacodynamic relationships of (2S,3S)-valnoctamide and its stereoisomer (2R,3S)-valnoctamide in rodent models of epilepsy

PURPOSE

Racemic valnoctamide (VCD) is a central nervous system-active drug commercially available in Europe. VCD possesses two chiral centers and, therefore, it exists as a mixture of four stereoisomers. The purpose of this study was to evaluate the anticonvulsant activity of two VCD stereoisomers in comparison with VCD (racemate), valpromide (VPD), and valproic acid (VPA) and to study their pharmacokinetic-pharmacodynamic relationships.

METHODS

The ability of racemic VCD, (2S,3S)-VCD, (2R,3S)-VCD and VPD to block partial seizures was studied in the 6Hz psychomotor seizure model in mice and in the hippocampal kindled rat. The ability of (2S,3S)-VCD and (2R,3S)-VCD to prevent generalized seizures was evaluated in the maximum electroshock (MES) and subcutaneous metrazole (sc Met) seizure tests. The PK of (2S,3S)-VCD, (2R,3S)-VCD, and VPD was studied in the mice utilized in the 6Hz model.

RESULTS

All of the tested compounds were effective in the models tested. No significant difference in ED50 values was observed but the plasma and brain EC50 values of (2R,3S)-VCD in the 6Hz model at 32 mA stimulation were 2-fold higher than the EC50 values of (2S,3S)-VCD. An excellent pharmacokinetic-pharmacodynamic correlation was found between the plasma and brain concentrations of the VCD stereoisomers and their anticonvulsant effect in mice. Stereoselectivity was observed in clearance, volume of distribution, and in brain-to-plasma AUC ratio at a dose of 25 mg/kg, but the difference disappeared at higher doses as the clearance of the stereoisomers decreased and their half-life increased. For (2R,3S)-VCD the brain-to-plasma AUC ratio doubled at the tested dose range, while it remained constant for (2S,3S)-VCD.

CONCLUSIONS

Racemic VCD, VPD, (2R,3S)-VCD, and (2S,3S)-VCD are effective anticonvulsants in animal models of partial seizures and are more potent than VPA. The more favorable brain penetration of (2S,3S)-VCD and its lower EC50 value in the 6Hz test provides one advantage over (2R,3S)-VCD as a new antiepileptic drug.

Gas chromatographic determination of novel valproyl taurinamide derivatives in mouse and dog plasma

Valproyl taurinamides are a novel group of compounds that possess anticonvulsant activity. In this study a gas chromatographic micromethod was developed for the quantification of selected valproyl taurinamides and some of their metabolites in biological samples. Valproyl taurinamide (VTD), N-methyl valproyl taurinamide (M-VTD), N,N-dimethyl valproyl taurinamide (DM-VTD) and N-isopropyl valproyl taurinamide (I-VTD) were analyzed in mouse and dog plasma and in dog urine using gas chromatography. Flame ionization detection and mass spectrometric detection were compared. The plasma samples were prepared by solid-phase extraction using C(18) cartridges. The urine samples were prepared by liquid-liquid extraction. The sample volume used was 100 microl of dog plasma, 50 microl of mouse plasma and 20 microl of dog or mouse urine. The quantification range of the method was 1.5-50 mg/l in dog plasma (VTD only), 2.5-250 mg/l in mouse plasma (0.7-90 pmol injected) and 0.04-2 mg/ml in dog urine (VTD only). The inter-day precision in plasma and urine samples was around 10% for all quantified concentrations except LOQ (15-20%). The accuracy for all four compounds was between 90 and 110% within the entire concentration range. The developed method was suitable for quantification of a series of CNS-active valproyl taurineamide derivatives in biological samples at relevant in vivo concentrations.

Characterization of the anticonvulsant profile and enantioselective pharmacokinetics of the chiral valproylamide propylisopropyl acetamide in rodents

1. Propylisopropyl acetamide (PID) is a new chiral amide derivative of valproic acid. The purpose of this study was to evaluate the anticonvulsant activity of PID in rodent models of partial, secondarily generalized and sound-induced generalized seizures which focus on different methods of seizure induction, both acute stimuli, and following short-term plastic changes as a result of kindling, and to assess enantioselectivity and enantiomer-enantiomer interactions in the pharmacokinetics and pharmacodynamics of racemic PID and its pure enantiomers in rodents. 2. Anticonvulsant activity of (S)-PID, (R)-PID and racemic PID was evaluated in the 6 Hz psychomotor seizure model in mice, in the hippocampal kindled rat, and in the Frings audiogenic seizure susceptible mouse. The pharmacokinetics of (S)-PID and (R)-PID was studied in mice and rats. 3. In mice (S)-PID, (R)-PID and racemic PID were effective in preventing the 6 Hz seizures with (R)-PID being significantly (P < 0.05) more potent (ED(50) values 11 mg kg(-1), 46 mg kg(-1) and 57 mg kg(-1) at stimulation intensities of 22, 32 and 44 mA, respectively) than (S)-PID (ED(50) values 20 mg kg(-1), 73 mg kg(-1) and 81 mg kg(-1) at stimulation intensities of 22, 32 and 44 mA, respectively). (S)-PID, (R)-PID and racemic PID also blocked generalized seizures in the Frings mice (ED(50) values 16 mg kg(-1), 20 mg kg(-1) and 19 mg kg(-1) respectively). 4. In the hippocampal kindled rat a dose of 40 mg kg(-1) of (R)- and (S)-PID prevented the secondarily generalized seizure, whereas racemic PID also blocked the expression of partial seizures following an i.p. dose of 40 mg kg(-1). Racemic PID also significantly increased the seizure threshold in this model. 5. Mechanistic studies showed that PID did not affect voltage-sensitive sodium channels or kainate-, GABA- or NMDA- evoked currents. 6. The pharmacokinetics of PID was enantioselective following i.p. administration of individual enantiomers to mice, with (R)-PID having lower clearance and longer half-life than (S)-PID. In rats and mice, no enantioselectivity in the pharmacokinetics of PID was observed following administration of the racemate, which may be due to enantiomer-enantiomer interaction. 7. This study demonstrated that PID has both enantioselective pharmacokinetics and pharmacodynamics. The better anticonvulsant potency of (R)-PID in comparison to (S)-PID may be due to its more favorable pharmacokinetic profile. The enhanced efficacy of the racemate over the individual enantiomers in the kindled rat may be explained by a pharmacokinetic enantiomer-enantiomer interaction in rats. This study also showed the importance of studying the pharmacokinetics and pharmacodynamics of chiral drugs following administration of the individual enantiomers as well as the racemic mixture.