SELECTIVE MECHANISM-BASED INACTIVATION OF RAT CYP2D BY 4-ALLYLOXYMETHAMPHETAMINE

The high selectivity of amphetamine and its derivatives for CYP2D-medi ated oxidations suggested the use of the phenylisopropylamine skeleton as a template for a selective inhibitor of this important enzyme. Acc ordingly, 4-allyloxymethamphetamine (ALLMA) was synthesized and its ab ility to selectively inactivate CYP2D was investigated both in in vitr o and in vivo experiments. Incubation studies with rat liver microsome s demonstrated that this compound suppressed the CYP2D-mediated methyl enedioxymethamphetamine (MDMA) demethylation in a time- and dose-depen dent manner and that the inhibition required the presence of NADPH. Th e development of irreversible inhibition was associated with oxidation at position 4 of the aromatic ring, the common site of CYP2D-mediated oxidation of this group of compounds. In in vivo studies, single dose s of ALLMA (1-10 mg/kg) were administered to adult male Sprague-Dawley rats and liver microsomes were obtained 3 hr later. Methamphetamine p -hydroxylation and low K-m MDMA demethylation activities, both mediate d by CYP2D, were reduced by more than 80% after a dose of 10 mg/kg. Cy tochrome P-450 reactions attributed to P-450s other than CYP2D, such a s aniline p-hydroxylation, the high K-m system of MDMA demethylation a nd the N-demethylation of methamphetamine, benzphetamine, aminopyrine and erythromycin, all appeared to be minimally affected. The importanc e of aromatic ring oxidation in the metabolism is such that inhibition of CYP2D would be expected to cause a significant change in the pharm acokinetics of these compounds. The kinetics of MDMA metabolic activit y in microsomes from ALLMA-pretreated rats were comparable to those fr om female Dark-Agouti rats, an animal model for CYP2D1 deficiency.