Development of In Vitro Methods to Predict Induction of CYP1A2 and CYP3A4 in Humans

The important role of cytochrome P450 (CYP) drug-metabolizing enzymes has been studied for many years, and the potential liabilities of inducing these enzymes are well understood. Though several mechanisms of induction have been studied, a growing consensus is developing that the aryl hydrocarbon receptor (AHR) and the pregnane X receptor (PXR) have evolved as the primary mechanisms responsible for clinically relevant drug-drug interactions caused by induction of drug-metabolizing factors. AHR and PXR have been identified as inducers of a variety of Phase I and Phase II drug-metabolizing enzymes, drug transporters, and other factors involved in drug metabolism. Though many genes are induced through these regulating factors, CYP1A2 and CYP3A4 have been the most reliable biomarkers to identify compounds with potential induction liabilities through AHR and PXR, respectively. Here are presented several in vitro methods to detect AHR- and PXR-mediated induction of CYP1A2 and CYP3A4 in fresh and cryopreserved primary human hepatocytes, stable transfectants, and transiently transfected immortalized cells.