Cyclophosphamide is used in high doses as a part of the conditioning regimen prior to stem cell transplantation. It is usually given for two or four consecutive days, primarily to facilitate engraftment of donor cells. Cyclophosphamide is a prodrug that is activated in liver by a 4-hydroxylation reaction catalyzed by cytochrome P450 (CYP) enzymes. Several studies have shown that cyclophosphamide induces its own metabolism, which affects its pharmacokinetic parameters after repeated dose (

Chang TK, Yu L et al. Cancer Res 1997; 57:1946–54
and
Schuler U, Ehninger G et al. Cancer Chemother Pharmacol 1987; 20:248–52
). In the present study, we aimed to investigate the effect of repeated doses of cyclophosphamide on the CYPs in rat. mRNA, protein, and enzyme activity levels were investigated. Animals received (200 mg/kg, i.v.) at time 0, 20, 48 h. Additionally another group of animals was treated at 0, 6, 20, 26, 48 and 54 h. At each time point three animals were killed 30 min after the administration (
Xie H, Afsharian P et al. Xenobiotica 2005; 35:239–51
). mRNAs of CYP2B1 and 2B2 were significantly induced up to 458- and 8.3-fold at 6h, 983- and 102-fold at 26 h, and 342- and 33-fold at 54 h. CYP2B protein levels were increased and their peaks was observed at 20 and 48 h. Microsomal activity of CYP2B was determined at three different concentration of cyclophosphamide (1, 0.5, 0.1 mM) by measuring the formation rate of 4-hydroxy-cyclophosphamide (4-OH-CPA). The microsomal activity increased as reflected in an increase in cyclophosphamide 4-hydroxylation at all concentrations used using microsomes from rats treated at 6, 20 and 48 h. A significant increase of 4-hydroxylation of cyclophosphamide (0.1 mM) by 2.9-, 4.4- and 4.2- fold, respectively compared to the control rats. However, a decrease in the hydroxylation rate was observed using microsomes from rats treated at 26 and 54 h and in all concentrations used that might due to hepatotoxicity effect of cyclophosphamide when administered in short time period of repeated dose. A significant (p<0.05) decrease in CPA concentration and a significant (p<0.05) increase in its metabolite (4-OH-CPA) level in plasma were observed with repeated administration of CPA. In conclusion, an induction effect on CYP2B and a substantial up regulation of its mRNA expression were observed after repeated administration of CPA. This information can have a high clinical importance when a dosing schedule for cyclophosphamide considering the polymorphism of CYPs in cancer patient.

Topics:
cyclophosphamide, cytochrome p-450 cyp2b1, cancer, rna, messenger, cytochrome p450, enzymes, hematopoietic stem cell transplantation, hepatotoxicity, metabolites, prodrugs

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2005, The American Society of Hematology
2005
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