Received for publication September 27, 2004.
Revised April 6, 2005.
Accepted for publication April 6, 2005.

Contribution of CYP3A5 to hepatic and renal ifosfamide N-dechloroethylation

Abstract

Ifosfamide nephrotoxicity is attributed to the formation of a toxic metabolite - chloroacetaldehyde via N-dechloroethylation, a reaction catalyzed by CYP3A and CYP2B6. Because allelic variants of CYP3A5 are associated with polymorphic expression of microsomal CYP3A5 in human liver and kidneys, we hypothesized that ifosfamide N-dechloroethylation depends on CYP3A5 genotype. Methods: We compared ifosfamide N-dechloroethylation activity in cDNA-expressed CYP3A4 and CYP3A5. Ifosfamide N-dechloroethylation was also assessed in liver (N=20) and kidney (N=21) microsomes from human donors with different CYP3A5 genotypes. Results: Ifosfamide N-dechloroethylation was catalyzed by recombinant CYP3A5 at a rate comparable to recombinant CYP3A4. In human liver microsomes matched for CYP3A4 protein content, N-dechloroethylation was more than 2-fold higher in those from donors carrying CYP3A5*1 allele that express CYP3A5 relative to those from donors homozygous for the mutant CYP3A5*3. Correlation analysis revealed that ifosfamide N-dechloroethylation was associated with CYP3A4 and CYP3A5 protein concentration, but not with age, sex or CYP2B6 protein concentration. In hepatic microsomes not expressing CYP3A5 protein, ifosfamide N-dechloroethylation was inhibited 53-61% and 0-3% by monoclonal antibodies specific for CYP3A4/5 or CYP2B6, respectively. Ifosfamide N-dechloroethylation was not detected in renal microsomes from CYP3A5*3/*3 donors, whereas it was readily measurable in the four kidneys isolated from CYP3A5*1 carriers, which was almost completely inhibited by a CYP3A inhibitor - ketoconazole. CYP2B6 protein could not be detected in this panel of human renal microsomes. Conclusions: CYP3A5*1 genotype is associated with greater rates of ifosfamide N-dechloroethylation in human liver and kidneys.

Key words: anticancer agents, CYP3A, extrahepatic cytochrome P450, pharmacogenomics, renal disposition

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