Assessment of the hepatic CYP reductase null mouse model and its potential application in drug discovery.

CYP Oxidoreductase (Por) is the essential electron donor for all CYP enzymes and is responsible for the activation of CYP. The Taconic Hepatic CYP Reductase Null (HRN) mouse model possesses a targeted mutation that results in liver-specific deletion of the Por gene thereby resulting in a disruption of CYP metabolism in the liver. The objectives of these studies were to further characterize the HRN mouse using probe drugs metabolized by CYP. In addition, tumor exposure in xenograft tumor bearing HRN immune-compromised (nude) mice was also determined. In HRN mice following intravenous (iv) administration of midazolam, clearance (CL) was reduced by ∼80% compared to wild-type mice (WT). After oral administration, the AUC of midazolam was increased by ∼20-fold in HRN mice compared to WT mice; this greater effect suggests that hepatic first pass plays a role in the oral CL of midazolam. A 50% and an 80% decrease in CL were also observed in HRN mice following iv administration of docetaxel and theophylline, resp...