Metabolic stereoselectivity of cytochrome P450 3A4 towards deoxypodophyllotoxin:: In silico predictions and experimental validation

Deoxypodophyllotoxin is stereoselectively converted into epipodophyllotoxin by recombinant human cytochrome P450 3A4 (CY-P3A4). Further kinetic analysis revealed that the Michaelis-Menten K-m and V-max for hydroxylation of deoxypodophyllotoxin by CYP3A4 at C7 position were 1.93 mu M and 1.48 nmol/min/nmol, respectively. Deoxypodophyllotoxin was subjected to automated docking analysis in order to get better knowledge of the interaction between the CYP3A4 enzyme and the substrate, using the PatchDock algorithm with distance constraints. Automated docking showed that the P-hydrogen atom at C7 position is in the most appropriate binding orientation at the site of oxidation. The docking results are consistent with the experimental data for the bioconversion of deoxypodophyllotoxin into epipodophyllotoxin by CYP3A4. In addition, the effects of five lignans, deoxypodophyllotoxin, epipodophyllotoxin, podophyllotoxin, demethylenedeoxypodophyllotoxin, and demethylenepodophyllotoxin, on CYP3A4 were compared in order to investigate the influence of the methylenedioxy group on the biotransformation process, to give insight into the mode of metabolization and to explain inhibitory activity of lignans. (c) 2007 Elsevier Masson SAS. All rights reserved.