Identification of cytochrome P4503A as the major subfamily responsible for the metabolism of roquinimex in man

1. Roquinimex, a novel immunomodulator, is metabolized in liver microsomes from mouse and rat via cytochrome P450s to four hydroxylated and two demethylated metabolites (R1−6). The study investigated which cytochrome P450 enzyme(s) is responsible for the metabolism of roquinimex in man. 2. Enzyme kinetic analysis demonstrated an apparent K_m = 1.28-7.00mm and V_max = 50-159 pmol·mg⁻¹ microsomal protein·min⁻¹ for the primary metabolites in human liver microsomes. The sum of Cl_int for the primary pathways was 0.167 μl·mg⁻¹ microsomal protein·min⁻¹. 3. A correlation between the formation rate of R1-6 and 6β-hydroxylation of testosterone was obtained within a panel of liver microsomes from 11 individuals (r² = 0.72-0.97). Furthermore, significant inhibition (<90%) of roquinimex primary metabolism was demonstrated by ketoconazole and troleandomycin, specific inhibitors of CYP3A4 as well as with anti-CYP3A4 antibodies. Moreover, a similar metabolite pattern was produced from roquinimex by incubation with cDNA-expressed CYP3A4 as by human liver microsomes. 4. In conclusion, these data indicate a major role for CYP3A4 in the formation of roquinimex primary metabolites in human liver microsomes.