Metabolism of Flutamide in Diet Control Fischer 344 and Brown Norway ´ F 344 Rats, and Its Hydroxylation and Conjugation by Human CYP450s and UDP-Glucuronosyltransferases
HEBRON C. CHANG1*, JOHN E. SENG2, JULIAN E. A. LEAKEY2 AND JAY GANDY3
1. Division of Biochemical Toxicology, National Center for Toxicological Research, FDA, 3900 NCTR Rd., HFT-110, Jefferson AR 72079, U.S.A
2. Division of Chemistry, National Center for Toxicological Research, FDA, Jefferson AR 72079, U.S.A.
3. Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, U.S.A.
(Received: March 20, 2000; Accepted: June 2, 2000)
ABSTRACT
In our current report, flutamide (2-methyl-N-[4-nitro-3-(trifluoromethyl)-phenyl] propanamide) treated diet control and non limited-fed Fischer 344 (F344) and Brown Norway (BN) ´ F344 rats showed that diet control reduces spontaneous and flutamide-induced hyperplasia(1). In this continued study, we found that serum concentrations of active metabolite of flutamide, 2-hydroxyflutamide (OH-flu), were 181 ± 26.6 ng/mL and 68 ± 8.0 ng/mL (p<0.05), in non-limited fed and diet control F344 rats. In BN ´ F344 rats, the serum concentrations of 2-OH-flutamide were 232± 57 ng/mL and 52±6 ng/mL (p<0.05) in non-limited fed and diet control animals. In diet control groups, liver microsomes from flutamide-treated F344 rats showed high 7-ethoxyresorufin O-deethylase (EROD) activity, while 7-Benzoxyresorufin O-dealkylase (BROD) activity was not affected significantly. Both rat and human liver microsomes showed flutamide oxidation activity. Human liver microsomes showed 10 times higher activity than rat liver microsomes (0.673±0.04 vs 0.063 ± 0.008 nmol OH-flu/min/mg protein). Microsomes from human tissues such as colon, colon cancer, kidney, bladder, pancreas, prostate, prostate cancer, or ovarian cancer, showed no or non-detectable activity for flutamide hydroxylation. CYP450 1A1, 1A2, 1B1 and 2C19 from human lymphoblastoid cell lines, oxidized flutamide to OH-flu in vitro with activities from 0.118 ±0.005 to 0.275 ±0.010 nmol/min/mg protein. Microsomes isolated from human kidney, colon, and liver showed UDP-glucuronosyltransferase (UGT) activity for glucuronidation of OH-flu. Human kidney showed the highest activity. Several human recombinant UGTs (1A1, 1A4, 1A6, 1A7, 1A9, and 1A10) also showed glucuronidation activity for OH-flu. It was found that UGT1A6 was more active than other human UGTs.
Key words: flutamide, diet restricted, non limited-fed, hydroxylation, glucuronidation, CYP450, UDP-glucuronosyltransferase