Role of polymorphic human CYP2B6 in cyclophosphamide bioactivation

The role of polymorphic CYP2B6 in cyclophosphamide (CPA) bioactivation was investigated in human liver microsomes. A total of 67 human liver specimens were first genotyped with respect to the CYP2B6*5 and CYP2B6*6 variant alleles. CYP2B6 apoprotein levels in 55 liver microsomal preparations were assessed by immunoblotting. 4-Hydroxy-CPA and hydroxy-bupropion were quantified by using HPLC and LC-MS, respectively. 7-Ethoxy-4-trifluoromethyl coumarin O-deethylase activity was measured fluorometrically. The frequencies of CYP2B6*5 and CYP2B6*6 mutant alleles were 9.0 and 16.4%, respectively. CYP2B6 protein expression was detected in 80% of the samples, with a large variation (0.003-2.234, arbitrary units). There was a high correlation between CYP2B6 apoprotein content and CPA 4-hydroxylation (n=55, r=0.81, P