Human cytochrome P450 and UDP-glucuronosyltransferase reaction phenotyping of MPC-3100, an oral HSP90 inhibitor.

Abstract

e13019 Background: MPC-3100 is an oral synthetic inhibitor of HSP90, in a phase I safety study in cancer patients. Major cytochrome P450 (CYP450) and UDP-glucuronosyltransferase (UGT) isozymes were identified to define the inclusion and exclusion criteria necessary to ensure patient safety. Methods: CYP450 isozymes responsible for the metabolism of MPC-3100 were assessed by two methods. The first entailed the use of recombinant human Supersomes (1A2, 2C8, 2C9, 2C19, 2D6 and 3A4) suspended in phosphate buffer (pH 7.4) with 40 pmoles of CYP450. An NADPH regenerating system was used with a 5 minute pre-incubation prior to adding 10 µM MPC-3100. The second used human donor liver microsomes suspended in phosphate buffer (pH 7.4) with 0.5 mg/mL of protein. The microsomes were pre-incubated with CYP450 isozyme selective chemical inhibitors prior to addition of 10 µM MPC-3100 and NADPH. UGT isozymes responsible for glucuronidation of MPC-3100 and a major oxidative metabolite were identified using recombinant UGT Supersomes suspended in Tris-HCl buffer (pH 7.5) at a final protein concentration of 1 mg/mL. The UGT Supersomes were pre-incubated with alamethicin and the reaction was initiated with UDPGA. The disappearance of MPC-3100 and formation of metabolites was monitored by HPLC-ESI-MS/MS. Results: MPC-3100 was metabolized by CYP450 1A2, 2C19, 2D6 and 3A4, but not by 2C8 or 2C9. With the use of selective chemical inhibitors in pooled human liver microsomes, the percent of MPC-3100 metabolized at 40 minutes was inhibited greatest by azamulin (31.4%), ketoconazole (20.9%) and quinidine (5.5%). MPC-3100 was glucuronidated by UGT 1A3, 1A8 and 1A4, but not by 1A1, 1A6, 1A7, 1A9, 1A10, 2B4, 2B5, 2B15, and 2B17. The major oxidative metabolite of MPC-3100 was a substrate for UGT 1A3, 1A7, 1A9, 1A10, 2B4, 2B17 with 1A1, 1A8, and 2B7 predominating. Conclusions: CYP450 3A4 is the primary isozyme involved in the metabolism of MPC-3100. UGT 1A4 is the major isozyme responsible for direct glucuronidation of MPC-3100; whereas multiple UGTs (1A1, 1A8, and 2B7) are capable of glucuronidating the major oxidative metabolite. Therefore current clinical studies preclude co-administration of potent CYP3A4 inhibitors with MPC-3100.