Regioselective metabolism of taxoids by human CYP3A4 and 2C8: structure-activity relationship

Drug Metab Dispos. 2002 Apr;30(4):438-45. doi: 10.1124/dmd.30.4.438.


Paclitaxel and docetaxel are metabolized by liver microsomal monooxygenases into inactive metabolites further eliminated from the body via the bile route. In spite of their close chemical structure, the two drugs are oxidized by two different enzymes; CYP2C8 catalyzes the 6-hydroxylation on the taxane ring of paclitaxel, whereas CYP3A4 oxidizes docetaxel on the tert-butyl group of the lateral chain in C13. Since paclitaxel and docetaxel differ only by two substitutions, the role of individual modifications was investigated; the regioselectivity of hydroxylation was assessed by high-pressure liquid chromatography/mass spectrometry, and enzymes implicated in individual reactions were identified using human liver microsomes and recombinant P450 expressed in Ad293 cells. The biotransformation of docetaxel, 10-deacetylpaclitaxel, and 10-deacetylbaccatin III was steadily increased (2- to 5-fold) by the addition of an acetyl group in position 10, suggesting that the presence of a hydrophobic group in position 10 stimulated hydroxylation by P450 proteins. The absence of the lateral chain at C13 in baccatin III severely impaired the metabolism supported by CYP3A4. The presence of a tert-butyl group in the lateral chain of docetaxel favored the hydroxylation on the tert-butyl by CYP3A4, whereas the presence of a phenyl group in the lateral chain facilitated the oxidation on the taxane ring by CYP2C8. Collectively, these data strongly suggested that the structure of the lateral chain and the nature of substituent in position 10 play an important role in determining the regioselective oxidation by P450 proteins and modulate the reaction rate by human liver microsomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids / metabolism
  • Alkaloids / pharmacokinetics
  • Animals
  • Aryl Hydrocarbon Hydroxylases*
  • Biotransformation
  • COS Cells
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme System / metabolism*
  • Docetaxel
  • Humans
  • Hydroxylation
  • Microsomes, Liver / chemistry
  • Microsomes, Liver / metabolism
  • Mixed Function Oxygenases / metabolism*
  • Paclitaxel / analogs & derivatives*
  • Paclitaxel / metabolism*
  • Paclitaxel / pharmacokinetics
  • Recombinant Proteins / metabolism
  • Steroid 16-alpha-Hydroxylase*
  • Steroid Hydroxylases / metabolism*
  • Structure-Activity Relationship
  • Substrate Specificity
  • Taxoids*
  • Triterpenes / metabolism


  • Alkaloids
  • Recombinant Proteins
  • Taxoids
  • Triterpenes
  • Docetaxel
  • baccatin III
  • 10-deacetylbaccatine III
  • Cytochrome P-450 Enzyme System
  • 10-deacetylpaclitaxel
  • Mixed Function Oxygenases
  • Steroid Hydroxylases
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C8 protein, human
  • CYP3A protein, human
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP3A
  • Steroid 16-alpha-Hydroxylase
  • CYP3A4 protein, human
  • Paclitaxel