title: The effect of cyclophosphamide with and without dexamethasone on cytochrome P450 3A4 and 2B6 in human hepatocytes.
abstract: The purpose of this study was to characterize the concentration-response effects of cyclophosphamide (CPA) with and without dexamethasone (DEX; 10 microM) on the expression of CYP3A4 and CYP2B6 in cultured human hepatocytes at concentrations representative of standard- and high-dose CPA therapy (25 to 750 microM). CPA produced concentration-dependent increases in CYP3A4 and CYP2B6 activity and immunoreactive protein that peaked at 250 and 125 microM, respectively, and declined thereafter. The inductive effect of CPA alone and in combination with DEX was greater in magnitude for CYP2B6 compared with CYP3A4. To further examine the inductive effect of CPA on CYP3A4, CPA (250 microM) and DEX (10 microM) alone and in combination were examined in 10 hepatocyte preparations. The combination of CPA and DEX yielded higher rates of 6beta-hydroxytestosterone formation than either agent alone. However, the effect was less than additive in human hepatocyte cultures with relatively high baseline CYP3A4 activity and additive or synergistic in human hepatocyte cultures with relatively low baseline CYP3A4 activity. Induction index was highly correlated with CYP3A4 baseline activity for both CPA (r(2) = 0.75) and CPA plus DEX (r(2) = 0.85). To investigate the potential mechanism for CPA-induced increases in CYP3A4 activity, the ability of CPA alone and in combination with DEX to activate pregnane X receptor (PXR) was explored using transient transfection assays. CPA produced a dose-dependent increase in PXR activation that was maximal at the highest CPA concentration studied (500 microM). The addition of DEX to CPA resulted in a minor increase in PXR activation compared with CPA alone. These results indicate that CPA alone and in combination with DEX differentially induces the expression of CYP3A4 and 2B in a concentration-dependent manner, which may be mediated partially through activation of PXR. The impact of these effects on the efficacy and toxicity of CPA therapy warrants further investigation.
authors.affiliation: Division of Pharmacotherapy, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. celeste_lindley@unc.edu
authors.forename: Celeste
authors.initials: C
authors.lastname: Lindley
authors.forename: Geraldine
authors.initials: G
authors.lastname: Hamilton
authors.forename: Jeannine S
authors.initials: JS
authors.lastname: McCune
authors.forename: Stephanie
authors.initials: S
authors.lastname: Faucette
authors.forename: Stacy S
authors.initials: SS
authors.lastname: Shord
authors.forename: Roy L
authors.initials: RL
authors.lastname: Hawke
authors.forename: Hongbing
authors.initials: H
authors.lastname: Wang
authors.forename: Darryl
authors.initials: D
authors.lastname: Gilbert
authors.forename: Summer
authors.initials: S
authors.lastname: Jolley
authors.forename: Bingfang
authors.initials: B
authors.lastname: Yan
authors.forename: Edward L
authors.initials: EL
authors.lastname: LeCluyse
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis / Q000378:metabolism*; D002478:Cells, Cultured; D003520:Cyclophosphamide / Q000494:pharmacology*; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D004338:Drug Combinations; D003907:Dexamethasone; D003520:Cyclophosphamide; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C104464:CYP3A protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating