CYP3A4-mediated oxidation of lisofylline to lisofylline 4,5-diol in human liver microsomes.

The cytochrome P450s responsible for the conversion of lisofylline, a drug being developed to prevent the complications of high-dose chemotherapy, to lisofylline 4,5-diol, one of two principal metabolites in human liver microsomes, were evaluated. Lisofylline diol formation in microsomes prepared from five adult human livers was biphasic, with respective Km values of 0.0230+/-0.015 and 4.23+/-2.8 mM (mean +/- SD) and respective Vmax values of 0.0565+/-0.052 and 0.429+/-0.15 nmol/min/mg of protein. Through studies with isoform selective chemical inhibitors, CYP3A4 was implicated as the low Km enzyme from 89.0+/-11.2% inhibition of lisofylline 4,5-diol formation by troleandomycin at 50 microM substrate and CYP2A6 was implicated as the high Km enzyme. The formation of lisofylline 4,5-diol by these enzymes was confirmed with cDNA-expressed human CYP3A4 and CYP2A6.