title: Dexamethasone induction of taxol metabolism in the rat.
abstract: This study examined the effect of dexamethasone (DEX), 100 mg/kg/day for 3 days, on [3H]taxol metabolism in liver microsomes and hepatocytes of male and female Sprague-Dawley rats. In control rats, two isomeric monohydroxylated metabolites, M1 and M2, were formed. The formation of both metabolites was 2-3 times greater in the male than in the female animals. After DEX treatment, M1 increased 2.6-fold in the male animals and 6.5-fold in the female animals. This was accompanied by similar increases in hepatic cytochrome P4503A protein and testosterone 6 beta-hydroxylation. Three additional metabolites (U1, U2, and U3) were formed in the DEX-treated animals only. Isolation of these metabolites from rat hepatocyte incubates by reversed-phase HPLC permitted structure identification of U2 and U3, using tandem MS. The mass spectrum of U3 was consistent with deacetylation of taxol, whereas the mass spectrum of U2 was consistent with deacetylation of the monohydroxylated taxol metabolite M2. A comparison of HPLC and MS data for U3 with those of standard 10-deacetyltaxol suggested that the site of deacetylation might be the 4-position of the taxane ring. Preliminary observations indicate that the deacetylation is caused by a DEX-inducible cytochrome P450.
authors.affiliation: Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston 29425, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Anderson
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: G N
authors.initials: GN
authors.lastname: Kumar
authors.forename: J M
authors.initials: JM
authors.lastname: McMillan
authors.forename: U K
authors.initials: UK
authors.lastname: Walle
authors.forename: T
authors.initials: T
authors.lastname: Walle
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D017239:Paclitaxel / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005938:Glucocorticoids; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D017239:Paclitaxel