In vitro biotransformation of 3,4-dihydro-6-hydroxy-2,2-dimethyl-7-methoxy-1(2H)-benzopyran (CR-6), a potent lipid peroxidation inhibitor and nitric oxide scavenger, in rat liver microsomes

The in vitro metabolism of 3,4-dihydro-6-hydroxy-2,2-dimethyl-7-methoxy- 1(2H)-benzopyran (CR-6), a potent lipid peroxidation inhibitor and scavenger of nitric oxide and peroxynitrite species that is currently in phase II trials for antitumoral therapy, has been investigated in rat liver microsomes in the presence of NADP(H). Five major metabolites were identified by comparison with authentic standards, namely, the quinone 2-(3′-hydroxy-3′- methylbutyl-5-methoxy-1,4-benzoquinone (2a) and its ring-closed spiro form oxaspiro[4.5]-2,2-dimethyl-8-methoxy-dec-8-ene-7,10-dione (2b), the hydroquinone 2-(3′-hydroxy-3′-methylbutyl)-5-methoxyhydroquinone (3), the hydroxylated metabolite 3,4-dihydro-4,6-dihydroxy-2,2-dimethyl-7-methoxy-1(2H)- benzopyran (4), and the catechol 3,4-dihydro-6,7-dihydroxy-2,2-dimethyl-1(2H)- benzopyran (5). When the incubations were carried out in the presence of GSH, the HPLC peaks corresponding to the quinone metabolites 2a/b were absent and two novel products were formed showing MS fragmentation patterns consistent with the structure of GSH conjugates of quinone 2a. The time dependence on the formation of metabolites 2a,b and 3 was measured in incubations induced with phenobarbital (PB), dexamethasone, and β-naphthoflavone (βNF). For the dexamethasone-induced microsomes, the amount of hydroquinone 3 decreased from minute 10 to minute 30 while that of 2a,b increased in a complementary manner. Similar effects were observed for the incubations carried out using PB- and βNF-induced microsomes. On the other hand, CR-6 inhibited 7-ethoxyresorufin O-dealkylation activity (IC