The Center for Alternatives to Animal Testing is an academic center affiliated with the Division of Toxicological Sciences in the Department of Environmental Health Sciences of the Johns Hopkins University Bloomberg School of Public Health.

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Research Grants 2002-2003

Evaluation of CYP3A Induction with Engineered Cell Lines

Bingfang Yan, DVM, PhD
University of Rhode Island, Kingston, Rhode Island

Drugs entering the human body undergo extensive chemical conversions through an array of diverse catalytic proteins referred to as drug-metabolizing enzymes. Among them, cytochrome P450 (CYP) enzymes rank first among the phase I biotransformation enzymes in terms of catalytic versatility and the number of drugs they metabolize. Approximately twelve CYP enzymes are involved in drug-metabolism with CYP3A enzymes being the most abundant and responsible for the metabolism of two thirds of drugs. CYP3A induction by many drugs is known as an important contributing factor to many failures of therapy or severe toxicity. Recent studies demonstrate that activation of the pregnane X receptor (PXR) is responsible for CYP3A induction by many drugs, providing a rationale for establishing an in vitro screening system. The objective of the proposed studies is to develop a PXR-based in vitro screening system for CYP3A induction. Stable transfectants have been prepared to express steady levels of the PXR and to harbor a PXR responsive reporter. In the final period of support, we will focus on the optimization of the screening conditions such as selection of the best responsive transfectants. Screening of CYP3A inducers has been exclusively dependent upon the use of human hepatocytes and animals. The availability of human livers and the use of a large number of animals are the primary limited factors in rapidly and accurately predicting the effects of drugs on CYP3A expression. The screening system to be established will significantly reduce the number of animal use and ease the supply of human tissues.