PT  - JOURNAL ARTICLE
AU  - Stevens, Jeffrey C.
AU  - White, Rebecca B.
AU  - Hsu, Shih Hsein
AU  - Martinet, Michel
TI  - Human Liver CYP2B6-Catalyzed Hydroxylation of RP 73401
DP  - 1997 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1389--1395
VI  - 282
IP  - 3
4099  - http://jpet.aspetjournals.org/content/282/3/1389.short
4100  - http://jpet.aspetjournals.org/content/282/3/1389.full
SO  - J Pharmacol Exp Ther1997 Sep 01; 282
AB  - RP 73401 is a potent inhibitor of cyclic nucleotide phosphodiesterase type IV. RP 73401 is metabolized by human liver microsomes almost exclusively by transhydroxylation of the cyclopentyl group to RPR 113406. Liquid chromatography/mass spectrometry/mass spectrometry analysis of plasma from patients given RP 73401 also revealed a molecular ion and fragmentation consistent with RPR 113406. Thus, the objective was to determine the oxidative enzyme(s) responsible for RP 73401 hydroxylation. Kinetic constants of RP 113406 formation ranged from 8 to 26 μM and 0.83 to 5.99 nmol/min/mg protein forKm and Vmax , respectively (n = 3). Enzyme activity varied 23-fold among 15 human liver microsome samples and correlated with CYP2A6-catalyzed coumarin hydroxylase (r2 = 0.85, P < .01) and CYP2B6-catalyzed 7-ethoxytrifluoromethylcoumarin O-deethylase (r2 = 0.82, P < .01) activities. Chemical inhibition studies showed a 63% decrease in RP 73401 hydroxylation by 500 μM orphenadrine. Coumarin (10 μM), however, did not inhibit RP 73401 hydroxylation. Also, anti-CYP2B1 IgG produced 85% inhibition of RP 73401 hydroxylation, but only a negligible decline in coumarin hydroxylase activity. Of the 10 expressed P450 forms studied, only CYP2B6 catalyzed RP 73401 hydroxylation. Finally, expressed CYP2B6 showed a high affinity (K m = 22.5 μM) for RP 73401 hydroxylation, similar to the human liver microsome studies. The American Society for Pharmacology and Experimental Therapeutics