Effect of a conserved mutation in uridine diphosphate glucuronosyltransferase 1A1 and 1A6 on glucuronidation of a metabolite of flutamide

Objective: We investigated how the conserved mutation (Y486D) changed the kinetic parameters of uridine diphosphate glucuronosyltransferase 1A1 and 1A6 (UGT1A1 and 1A6) for 2-amino-5-nitro-4-trifluoromethylphenol, which is a major metabolite of flutamide, a nonsteroidal antiandrogenic agent. Methods: The wild-type or mutant cDNA-expressed UGT was co-incubated with 2-amino-5-nitro-4-trifluoromethylphenol (aglycone) and uridine diphosphateglucuronic acid (UDP-GA, donor substrate). The glucuronidation of the aglycone was determined. Results: The maximum velocities of the mutant UGT1A1 and UGT1A6 were about 12% and less than 1% of the corresponding wild-type, respectively. The Michaelis constant (K-M) for the aglycone of the wildtype UGT1A1 was double that of the mutant, but the Km for UDP-GA of the wild-type UGT1A1 was not significantly different from that of the mutant. Conclusion: Patients with Y486D may accumulate excessive 2-amino-5-nitro-4-trifluoromethylphenol, which might lead to unexpected toxicity.