CONTRIBUTION OF CYP3A5 TO HEPATIC AND RENAL IFOSFAMIDEN-DECHLOROETHYLATION

Abstract

ABSTRACT:Ifosfamide nephrotoxicity is attributed to the formation of a toxic metabolite, chloroacetaldehyde, via N-dechloroethylation, a reaction that is purportedly 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. We compared ifosfamide N-dechloroethylation activity in cDNA-expressed CYP3A4 and CYP3A5. Ifosfamide Ndechloroethylation was also assessed in liver (N ‫؍‬ 20) and kidney (N ‫؍‬ 21) microsomes from human donors with different CYP3A5 genotypes. Ifosfamide N-dechloroethylation was catalyzed by recombinant CYP3A5 at a rate comparable with recombinant CYP3A4. In human liver microsomes matched for CYP3A4 protein content, N-dechloroethylation was more than 2-fold higher in that from donors carrying CYP3A5*1 allele that express CYP3A5 relative to that from donors homozygous for the mutant CYP3A5*3. Correlation analysis revealed that ifosfamide N-dechloroethylation was significantly 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 to 61% and 0 to 3% by monoclonal antibodies specific for CYP3A4/5 or CYP2B6, respectively. Ifosfamide N-dechloroethylation was not detected in renal microsomes obtained from CYP3A5*3/*3 donors. In contrast, it was readily measurable in microsomes isolated from four kidneys of CYP3A5*1 carriers, which was almost completely inhibited by the CYP3A inhibitor ketoconazole. CYP2B6 protein could not be detected in this panel of human renal microsomes. In conclusion, CYP3A5*1 genotype is associated with higher rates of ifosfamide N-dechloroethylation in human liver and kidneys.

Cytochrome P450 3A-Dependent Metabolism of a Potent and Selective γ-Aminobutyric AcidAα2/3 Receptor Agonist in Vitro: Involvement of Cytochrome P450 3A5 Displaying Biphasic Kinetics

“…Measurable levels of M1 and M2 were detected for both CYP3A5 preparations containing b 5 . Similar to those observed previously (Klees et al, 2005;McCune et al, 2005), the turnover rates obtained by the CYP3A5 ϩ OR ϩ b 5 preparation were higher than those of a b 5 -supplemented CYP3A5 ϩ OR preparation (data not shown). However, the rate of metabolite formation in the presence of both CYP3A5 preparations was lower than in the presence of the CYP3A4 preparation without the addition of b 5 (Fig.…”

Selective Metabolism of Vincristine in Vitro by Cyp3a5

“…The supernatant (25-50 l) was directly assayed by HPLC with UV detection. CYP3A activity can be stimulated by the addition or coexpression of cytochrome b 5 , and this effect may be P450-selective such that activities of CYP3A4 and CYP3A5 may be altered (McCune et al, 2005). Thus, the Michaelis-Menten parameters of CYP3A4 and CYP3A5 were determined with enzyme preparations containing cDNA-expressed enzyme alone, with coexpressed cytochrome b 5 , and with added cytochrome b 5 (PanVera Corp.) at a molar ratio of 3:1 immediately preceding the incubations.…”

Cytochrome P450 in Cancer Susceptibility and Treatment

“…The CYP2B6*1/*6 and *6/*6 genotypes have been linked with lower catalytic activity and protein expression in liver, increased plasma IFO, and higher rates of CAAassociated toxicity [283]. Carriers of CYP3A5*1 catalyzed the detoxification pathway to DCE at a faster rate leading to a increased CAA and higher risk of nephrotoxicity due to its ability to rapidly degrade in blood [286].…”