title: Increased activity of CYP3A enzyme in primary cultures of rat hepatocytes treated with docetaxel: comparative evaluation with paclitaxel.
abstract: OBJECTIVE
  Docetaxel, a potent antimicrotubule agent widely used in the treatment of ovarian, breast and lung cancer, is extensively metabolized in various animal species, including humans. The metabolism of docetaxel to its primary metabolite, hydroxydocetaxel, is mediated by cytochrome P450 isozymes CYP3A2 and CYP3A4 in rats and humans, respectively. Several substrates of enzymes belonging to the CYP3A subfamily are known to induce different CYP isozymes, including CYP3A enzymes. Recently, paclitaxel, a compound structurally related to docetaxel, has been shown to significantly elevate the expression of CYP3A in rat and human hepatocytes. In this study we investigated the influence of docetaxel, employed at clinically relevant concentrations, on the level and the activity of cytochrome P450 3A in primary cultures of rat hepatocytes.
  
  
  METHODS
  Rat hepatocytes were treated with different concentrations of docetaxel, paclitaxel and other CYP3A inducers. Testosterone 6beta-hydroxylase activity of intact hepatocytes was used as a marker for CYP3A. The immunoreactive CYP3A levels in the S-9 fractions were determined by Western blot analysis.
  
  
  RESULTS
  We observed that by day 3 of drug treatment, docetaxel at concentration in the range of 2.5-10 microM increased the CYP3A enzymatic activity and the immunoreactive CYP3A levels in a concentration-dependent manner. At the 10 microM level, docetaxel caused a twofold increase in the CYP3A activity and a threefold increase in the immunoreactive CYP3A levels. However, the docetaxel-mediated CYP3A activity and enzyme level increase were significantly lower than those mediated by paclitaxel and dexamethasone. A comparison of the testosterone 6beta-hydroxylation activity in hepatocytes treated with these agents at a concentration of 5 microM each yielded the following rank order of induction capacity: dexamethasone > paclitaxel > docetaxel (15-fold, 5-fold, 2.2-fold, respectively).
  
  
  CONCLUSIONS
  Taken together, our findings raise the possibility that docetaxel at clinically relevant concentrations increases CYP3A activity. The potential for docetaxel-mediated changes in the metabolism of other coadministered drugs and its own metabolism, in relation to that due to paclitaxel, are discussed.
authors.affiliation: College of Pharmacy, University of Cincinnati Medical Center, OH 45267-0004, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Nallani
authors.forename: M B
authors.initials: MB
authors.lastname: Genter
authors.forename: P B
authors.initials: PB
authors.lastname: Desai
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D000077143:Docetaxel; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology*; D015151:Immunoblotting; D008297:Male; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis / Q000378:metabolism*; D017239:Paclitaxel / Q000031:analogs & derivatives / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043823:Taxoids
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005938:Glucocorticoids; D043823:Taxoids; D000077143:Docetaxel; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C113764:Cyp2c13 protein, rat; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D017239:Paclitaxel