The role of constitutive androstane receptor in oxazaphosphorine-mediated induction of drug-metabolizing enzymes in human hepatocytes

Pharm Res. 2011 Aug;28(8):2034-44. doi: 10.1007/s11095-011-0429-2. Epub 2011 Apr 13.


Purpose: To investigate the roles of the constitutive androstane receptor (CAR) in cyclophosphamide (CPA)- and ifosfamide (IFO)-mediated induction of hepatic drug-metabolizing enzymes (DME).

Methods: Induction of DMEs was evaluated using real-time RT-PCR and Western blotting analysis in human primary hepatocyte (HPH) cultures. Activation of CAR, pregnane X receptor (PXR), and aryl hydrocarbon receptor by CPA and IFO was assessed in cell-based reporter assays in HepG2 cells and/or nuclear translocation assays in HPHs.

Results: CYP2B6 reporter activity was significantly enhanced by CPA and IFO in HepG2 cells co-transfected with CYP2B6 reporter plasmid and a chemical-responsive human CAR variant (CAR1 + A) construct. Real-time RT-PCR and Western blotting analysis in HPHs showed that both CPA and IFO induced the expressions of CYP2B6 and CYP3A4. Notably, treatment of HPHs with CPA but not IFO resulted in significant nuclear accumulation of CAR, which represents the initial step of CAR activation. Further studies in HPHs demonstrated that selective inhibition of PXR by sulforaphane preferentially repressed IFO- over CPA-mediated induction of CYP2B6.

Conclusion: These results provide novel insights into the differential roles of CAR in the regulation of CPA- and IFO-induced DME expression and potential drug-drug interactions.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aryl Hydrocarbon Hydroxylases / biosynthesis*
  • Aryl Hydrocarbon Hydroxylases / genetics
  • Cells, Cultured
  • Constitutive Androstane Receptor
  • Cyclophosphamide / pharmacology*
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP3A / biosynthesis*
  • Cytochrome P-450 CYP3A / metabolism
  • Drug Interactions
  • Enzyme Induction / drug effects
  • Hep G2 Cells
  • Hepatocytes / enzymology*
  • Hepatocytes / metabolism*
  • Humans
  • Ifosfamide / pharmacology*
  • Inactivation, Metabolic
  • Liver / enzymology
  • Liver / metabolism
  • Oxidoreductases, N-Demethylating / biosynthesis*
  • Oxidoreductases, N-Demethylating / genetics
  • Pregnane X Receptor
  • Receptors, Aryl Hydrocarbon / metabolism
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Steroid / metabolism


  • Constitutive Androstane Receptor
  • Pregnane X Receptor
  • Receptors, Aryl Hydrocarbon
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Steroid
  • Cyclophosphamide
  • Aryl Hydrocarbon Hydroxylases
  • CYP2B6 protein, human
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Oxidoreductases, N-Demethylating
  • Ifosfamide