Docetaxel (Taxotere) is not metabolized by recombinant human CYP1B1 in vitro, but acts as an effector of this isozyme.

The objective of this study was to determine whether recombinant human cytochrome P450 1B1 (rhCYP1B1) metabolizes the anticancer agent docetaxel (Taxotere) in vitro. First, the catalytic activities of Supersomes-expressed rhCYP1B1 toward 17beta-estradiol and of rhCYP3A4 toward docetaxel in our conditions were determined. Second, [(14)C]docetaxel at 0.1 and 1 microM was incubated with rhCYP1B1 in the presence of NADPH up to 60 min. No metabolism of docetaxel was detected. Third, several activators of P450 isoenzymes were added to docetaxel incubations with rhCYP1B1, such as 2-chloro 3-pyridine 3-yl 5,6,7,8-tetrahydroindolizine 1-carboxamide, alpha-naphthoflavone, and organic solvents. Again, no metabolism of docetaxel was detected. As a forth step, 10 incubation factors were tested at two levels each in 16 different combinations, using a fractional factorial statistical experimental design. Docetaxel was not metabolized by rhCYP1B1 under any of the combinations. As a final step, the effect of docetaxel on the rhCYP1B1-mediated 7-ethoxyresorufin O-deethylase (EROD) activity was studied, to evaluate if docetaxel can bind to CYP1B1. Alpha-Naphthoflavone (1 microM), a CYP1B1 inhibitor, totally inhibited the EROD activity. Docetaxel at 3, 10, and 30 microM did not show major effects on EROD activity. At 100 microM, docetaxel increased EROD activity by 3.8-fold. Additionally, it was shown that 7-epidocetaxel, which is in equilibrium with docetaxel as a minor compound in solutions, was a potent activator of rhCYP1B1, with a >7-fold increase of EROD activity at 10 microM. In conclusion, docetaxel was not metabolized by recombinant human CYP1B1 in vitro, under any of the conditions tested. Docetaxel was shown to bind to recombinant human CYP1B1 and to act as an effector of this enzyme.