MICROSOMAL METABOLISM OF THE 5-LIPOXYGENASE INHIBITOR L-739,010 - EVIDENCE FOR FURAN BIOACTIVATION

The novel 5-lipoxygenase inhibitor [1S,5R]-3-cyano-1-(3-furyl)-6-(6-[3 -(3 o[3.2.1]octanyl)]pyridin-2-yl-methoxyl)naphthalene (L-739,010), wh en administered to rats and rhesus monkeys, was found to produce metab olites which appeared to be covalently bound to plasma proteins. Incub ation of [C-14]L-739,010 with rat liver microsomes did not yield appre ciable amounts of soluble metabolites but resulted in covalent binding to microsomal proteins. The covalent binding was NADPH-dependent and was enhanced by 1.5- and 2-fold in liver microsomes from rats, pretrea ted with phenobarbital and dexamethasone, respectively. Addition of tr iacetyloleandomycin and diethyldithiocarbamate to the incubation mixtu re inhibited the covalent binding by 60% and 46%, respectively. These findings suggest that the cytochrome P450 3A family of enzymes play an important role in the bioactivation of L-739,010. The presence of GSH attenuated the covalent binding by 50%, while methoxylamine, an aldeh yde trapping agent, blocked the covalent binding completely and, concu rrently, produced several soluble metabolic adducts. Subsequently, maj or methoxylamine adducts were identified by LC-MS/MS and NMR as O-meth yloximes of the ring-opened furan moiety of L-739,010. Incubation of L -739,010 with methoxylamine and hepatic microsomes from dog, rhesus mo nkey, and human produced similar metabolic adducts as those formed by rat liver microsomes. Therefore, under these experimental conditions, the furan moiety, which undergoes oxidative cleavage to the highly rea ctive 2-butene-1,4-dialdehyde, represents the major site of L-739,010 biotransformation. This putative reactive intermediate could react wit h microsomal proteins in vitro and physiological proteins in vivo. Sin ce furan bioactivation is believed to be responsible for the toxicity of many furan-containing compounds, the furan moiety of L-739,010 may be regarded as undesirable.