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 ∼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 Cmax 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.
Footnotes
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Send reprint requests to: Deborah Nicoll-Griffith, Ph.D., Senior Research Fellow, Merck Frosst Centre for Therapeutic Research, P.O. Box 1005, Pointe Claire-Dorval, Québec, Canada, H9R 4P8. E-mail: deborah_nicoll_griffith{at}merck.com
- Abbreviations used are::
- CYP
- cytochrome P450
- APCI
- atmospheric pressure chemical ionization
- βNF
- β-naphthoflavone
- DEX
- dexamethasone
- DFP
- 5,5-dimethyl-3-(2-isopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone
- DFH (M1)
- 5,5-dimethyl-3-(2-hydroxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone
- DFHP (M2)
- 5,5-dimethyl-3-(2–3′-hydroxyisopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone
- HPLC
- high-performance liquid chromatography
- LC/MS
- liquid chromatography/mass spectrometry
- AUC
- area under the plasma concentration versus time curve
- Cmax
- maximum plasma concentration
- Received May 24, 2000.
- Accepted October 30, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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