title: Application of rat hepatocyte culture to predict in vivo metabolic auto-induction: studies with DFP, a cyclooxygenase-2 inhibitor.
abstract: The drug candidate DFP [5,5-dimethyl-3-(2-isopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone] is a selective cyclooxygenase-2 inhibitor under evaluation for analgesic and anti-inflammatory therapy. The in vitro metabolic pathways (rat microsomes) involve hydroxylation of the isopropyl side chain at either of two positions, the methyl or the methine, thus producing a hydroxylated metabolite (DFHP) or a dealkylated metabolite (DFH). DFH formation was the major pathway. Using hepatic microsomes from rats treated with agents that induce specific CYP isozymes, it was shown that the dexamethasone-inducible rat CYP3A isozyme(s) play a major role in DFH formation. The roles of CYP3A1 and -3A2 were confirmed with genetically engineered rat CYP enzymes. The potential for induction of rat CYP3A by DFP was evaluated by incubating DFP in rat hepatocyte cultures and measuring the CYP3A levels. Both CYP3A immunoreactive protein and enzyme activity were induced in a dose-dependent manner. The induction was confirmed in vivo by dosing rats with DFP at 100 mg/kg for 4 days. Microsomes prepared from the excised livers showed that DFP gave approximately 55% of the induction observed with dexamethasone, as determined by Western blot. In vitro metabolic auto-induction of DFP was assessed by measuring the metabolism of DFP in hepatocytes treated with DFP. DFH formation was significantly enhanced in the DFP-treated cells. In vivo, treating rats with DFP at doses of 10 to 100 mg/(kg.day) for 13 weeks indicated that DFP induced its own metabolism. The C(max) and plasma drug area under the curve values during the thirteenth week were significantly lower than that on the first day, and the effect was dose-dependent.
authors.affiliation: Merck Frosst Centre for Therapeutic Research, P.O. Box 1005, Pointe Claire-Dorval, Québec, Canada, H9R 4P8. deborah_nicoll_griffith@merck.com
authors.forename: D A
authors.initials: DA
authors.lastname: Nicoll-Griffith
authors.forename: J M
authors.initials: JM
authors.lastname: Silva
authors.forename: N
authors.initials: N
authors.lastname: Chauret
authors.forename: S
authors.initials: S
authors.lastname: Day
authors.forename: Y
authors.initials: Y
authors.lastname: Leblanc
authors.forename: P
authors.initials: P
authors.lastname: Roy
authors.forename: J A
authors.initials: JA
authors.lastname: Yergey
authors.forename: R
authors.initials: R
authors.lastname: Dixit
authors.forename: D
authors.initials: D
authors.lastname: Patrick
mesh_terms: D000478:Alkylation; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001555:Benzene Derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D001711:Biotransformation; D018929:Cell Culture Techniques / Q000379:methods; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000378:metabolism / Q000493:pharmacokinetics*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005663:Furans / Q000378:metabolism / Q000493:pharmacokinetics*; D022781:Hepatocytes / Q000201:enzymology*; D006900:Hydroxylation; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008297:Male; D009249:NADP / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis* / Q000378:metabolism; D011237:Predictive Value of Tests; D011451:Prostaglandin-Endoperoxide Synthases; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C404485:3-2(-propyloxy)-(4-methylsulfonylphenyl)-(5,5-dimethyl)furanone; D001555:Benzene Derivatives; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D005663:Furans; D007527:Isoenzymes; D009249:NADP; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C465138:Cyp3a23-3a1 protein, rat; D051544:Cytochrome P-450 CYP3A; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D010089:Oxidoreductases, N-Demethylating