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.