Metabolism of N,N-Dipropyl-2-[4-Methoxy-3-(2-Phenyl-Ethoxy)-Phenyl]-Ethyl-Amine-Monohydrochloride (NE-100), A Novel Sigma Ligand: Contribution of Cytochrome P450 Forms Involved in the Formation of Individual Metabolites in Human Liver and Small Intestine

Prediction of oral clearance fromin vitrometabolic data using recombinant CYPs: Comparison among well-stirred, parallel-tube, distributed and dispersion models

Intrinsic clearances (CLint-HLM-total) for the metabolism of NE-100, metoprolol, clarithromycin (CAM), lornoxicam and tenoxicam were predicted from in vitro data with recombinant cytochorme P450s (CYPs) using relative activity factor (RAF) and then compared with CLint-HLM observed in human liver microsomes (HLM). The predicted CLint-HLM-total correlated well with the observed CLint-HLM in HLM. When oral clearances (CLoral) of low-clearance drugs such as metoprolol, CAM, lornoxicam and tenoxicam were predicted from the in vitro data using four physiological models (well-stirred, parallel tube, distributed and dispersion models), the predicted CLoral corresponded well with the observed CLoralin vivo and were similar among the four models. For a high-clearance drug, the predicted CLoral of NE-100 in extensive CYP2D6 metabolizers (EMs) was substantially different between individual models, although the predicted CLoral in a poor metabolizer of CYP2D6 (PMs) was similar. The CLoral ratio of NE-100 between the EMs and the PMs predicted from the dispersion model, which leads to a reliable prediction for the high-clearance drug, was 48.4, but the ratio decreased depending on the increase of the NE-100 plasma concentration. The results suggest that the CLoral decrease in the EMs is caused by saturation of NE-100 metabolism mediated by CYP2D6 and is based on increases in plasma NE-100 concentrations dependent on the dose of NE-100. The study suggests that the RAF and the in vitro-in vivo scaling approaches are useful for predicting CLoral from in vitro data with recombinant CYPs without using HLM and hepatocytes.

Prediction of differences in in vivo oral clearance of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl] ethylamine monohydrochloride (NE-100) between extensive and poor metabolizers from in vitro metabolic data in human liver microsomes lacking CYP2D6 activity and recombinant CYPs

1. It has previously been reported that N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) was predominantly metabolized by cytochrome P450 (CYP) 2D6 in human liver microsomes (HLM). In the present study, the contribution of CYP forms involved in the formation of the major metabolites of NE-100 in human liver lacking CYP2D6 activity (PM-HLM) has been predicted by use of in vitro kinetic data on recombinant CYPs microsomes (rCYPs). 2. In PM-HLM, NE-100 is predicted to be metabolized to N-despropyl-NE-100 (NE-098), p-hydroxy-NE-100 (NE-152) and m-hydroxyl-NE-100 (NE-163), but not to O-demethy-NE-100 (NE-125), which is a major metabolite in pooled human liver microsomes (EM-HLM). The relative activity factor approach assumed that NE-098 formation is predominantly catalysed by CYP3A4 and CYP2C9 and the NE-152+163mix (a mixture of two hydroxylated metabolites, NE-152 and NE-163) formation is only catalysed by CYP3A4. 3. The predicted contribution rates of CYP3A4 and CYP2C9 for NE-098 formation were 58.1 and 34.6%, respectively, in PM-HLM. These predicted results were strongly supported by kinetic and inhibition studies using PM-HLM. The intrinsic clearance of NE-100 predicted from rCYPs (the predicted CLint-HLM-total) corresponded to those observed from EM- and PM-HLM (the observed CLint-HLM). 4. The in vivo oral clearance (CLoral) of NE-100 in extensive metabolizers and poor metabolizers of CYP2D6 was predicted to be 50times higher in extensive metabolizers than poor metabolizers using in vitro-in vivo scaling method based on the dispersion model. These data suggest that polymorphism of CYP2D6 might greatly affect NE-100 metabolism in vivo.