Metabolism of vanoxerine, 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl) piperazine, by human cytochrome P450 enzymes

Vanoxerine (1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piper azine; GBR12909) is a promising agent for the treatment of cocaine dependen ce. Knowledge of the major pathway for GBR12909 metabolism is important for prediction of the likelihood of drug-drug interactions, which may affect t he therapeutic clinical outcome, when this agent is used in cocaine-depende nt individuals receiving multiple drug therapy. We studied biotransformatio n of GBR12909 in human liver microsomes (n = 4), human hepatocytes, and mic rosomes containing cDNA-expressed human P450 isoforms with GBR12909 concent rations within the range of steady-state plasma concentrations detected in healthy volunteers. A high-pressure liquid chromatography assay was used to measure parent GBR12909 and its primary metabolite. GBR12909 was metaboliz ed by human liver microsomes, hepatocytes, and cDNA-expressed human P450s t o a single metabolite. Ketoconazole, a selective inhibitor of CYP3A, reduce d GBR12909 biotransformation in human liver microsomes and primary hepatocy tes; by 92 +/- 2 and 92.4 +/- 0.4%, respectively. Quercetin (an inhibitor o f CYP2C8/3A4) was a less effective inhibitor producing 62 +/- 22% inhibitio n in human liver microsomes and 54 +/- 35% in hepatocytes. Other P450 selec tive inhibitors did not decrease GBR12909 biotransformation more than 29% i n either human liver microsomes or hepatocytes with the exception of chlorz oxazone (CYP2E1), which inhibited GBR12909 biotransformation by 71.4 +/- 18 .5% in primary human hepatocytes. Ciprofloxacin (CYP1A2), sulfaphenazole (C YP2C9), quinidine (CYP2D6), chlorzoxazone (CYP2E1), and mephenytoin (CYP2C1 9) did not demonstrate statistically significant inhibition (p > 0.05) of G BR12909 biotransformation in liver microsomes. cDNA-expressed P450 3A4 meta bolized GBR12909 to a greater extent than 2C8 and 2E1. These data suggest t he possibility that multiple P450 isoforms may be involved in human GBR1290 9 metabolism but that CYP3A appears to be the major enzyme responsible for human GBR12909 biotransformation.