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Drug Metabolism and Disposition Fast Forward
First published on February 9, 2009; DOI: 10.1124/dmd.108.025700

0090-9556/09/3705-1017-1024$20.00
DMD 37:1017-1024, 2009

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A Predominate Role of CYP1A2 for the Metabolism of Nabumetone to the Active Metabolite, 6-Methoxy-2-naphthylacetic Acid, in Human Liver Microsomes

Miia Turpeinen, Ute Hofmann, Kathrin Klein, Thomas Mürdter, Matthias Schwab, and Ulrich M. Zanger

Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Stuttgart, Germany (M.T., U.H., K.K., T.M., M.S., U.M.Z.); Department of Clinical Pharmacology, University Hospital Tuebingen, Tuebingen, Germany (M.S.); and Department of Pharmacology and Toxicology, University of Oulu, Oulu, Finland (M.T.)

Nabumetone, a widely used nonsteroidal anti-inflammatory drug, requires biotransformation into 6-methoxy-2-naphthylacetic acid (6-MNA), a close structural analog to naproxen, to achieve its analgesic and anti-inflammatory effects. Despite its wide use, the enzymes involved in metabolism have not been identified. In the present study, several in vitro approaches were used to identify the cytochrome P450 (P450) enzyme(s) responsible for 6-MNA formation. In human liver microsomes (HLMs) 6-MNA formation displayed monophasic Michaelis-Menten kinetics with apparent Km and Vmax values (mean ± S.D.) of 75.1 ± 15.3 µM and 1304 ± 226 pmol/min/mg protein, respectively, and formation rate of 6-MNA varied approximately 5.5-fold (179–983 pmol/min/mg protein). 6-MNA activity correlated strongly with both CYP1A2-mediated phenacetin O-deethylation activity and CYP1A2 protein content (r = 0.85 and 0.74, respectively; p < 0.0001 for both). Additional correlations were found with model activities of CYP2C19 and CYP3A4. Of 11 cDNA-expressed recombinant P450s used, recombinant CYP1A2 was the major form catalyzing the 6-MNA formation with an apparent Km of 45 µM and Vmax of 8.7 pmol/min/pmol P450. Minor fractions were catalyzed by recombinant P450s CYP1A1, CYP2B6, CYP2C19, CYP2D6, and CYP2E1. Experiments with P450-selective chemical inhibitors and monoclonal anti-P450 antibodies showed that furafylline, a mechanism-based inhibitor CYP1A2, and anti-CYP1A2 antibody markedly inhibited 6-MNA formation, whereas inhibitors for other P450s did not show significant inhibitory effects. Taken together, these studies indicate that the formation of the active metabolite of nabumetone, 6-MNA, is predominantly catalyzed by CYP1A2 in HLMs with only minor contribution of other P450s.

Address correspondence to: Miia Turpeinen, Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Auerbachstrasse 112, D-70376 Stuttgart, Germany. E-mail: miia.turpeinen{at}ikp-stuttgart.de






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