Minipig and Human Metabolism of Aldehyde Oxidase Substrates: In Vitro–In Vivo Comparisons

The importance of aldehyde oxidase (AOX) is becoming increasingly recognized in the prediction of human pharmacokinetic parameters from animal data. The objectives of these studies were to ascertain whether an in vitro–in vivo correlation existed in the clearance and metabolic pathways of AOX substrates and to establish whether the minipig represented an appropriate non-rodent model for man in the pre-clinical development of drugs metabolized by AOX. Using the AOX substrates carbazeran, 6-deoxypenciclovir and zaleplon, clearance was estimated from in vitro depletion experiments with minipig and human liver cytosol and microsomes and scaled before comparison with data generated in parallel in vivo studies in minipigs. In vitro and in vivo metabolic pathways were characterized by LC–MS/MS. Scaling of in vitro metabolism data to predict in vivo clearance underestimated in vivo values, although the rank order of clearance for the three compounds was preserved. Prediction of human in vivo clearance from scaled minipig in vivo data produced results which correlated well with published clinical values. Overall, this study is the first to compare minipig in vitro metabolism data with in vivo pharmacokinetic data for compounds metabolized by AOX and provides a scientific rationale for the selection of this species as a model for humans in the development of drugs which are substrates of AOX.