Cytochrome P450 (CYP) enzymes rank first among tne phase I bio-transformation enzymes in terms of catalytic versatility and the number of xenobiotics they metabolize. Therefore, induction of CYP enzymes contributes significantly to drug-drug interactions and plays key roles in the detoxication and bioactivation of xenobiotics. The Food and Drug Administration request all new drugs be tested for CYP induction, and pharmaceutical industries are very interested in establishing CYP induction profiles of drug candidates early so that appropriate decisions can be made for further development. Studies of molecular signaling have demonstrated that CYP induction is primarily achieved by receptor-mediated transactivation. The receptor-mediated action requires interactions with other proteins (e.g., co-repressor and co-activator). Some of the interactions exhibit an inducer-dependent manner, providing a molecular basis for developing an in vitro screening system described in this application. In this system, two plasmids encoding respective receptor and its interactive protein will be transformed into yeast strains harboring two reporter genes: HIS3 and B galactosidase. The presence of a CYP inducer will alter the interaction (e.g., dissociation or association) between the receptor and its reactive protein, thus change the expression of the reporter genes. Monitoring of the reporter activities will reflect the inductive effect of a chemical on CYP enzymes. The important features of this screening system are:: unlimited availability, high sensitivity, superior specificity and suitability for high throughput screening. The proposed studies will focus on the aryl hydrocarbon receptor for CYPIA and lB, the constitutive androstane receptor for CYP2B, 2C and 3A, the pregnane X receptor for CYP3A and the peroxisome proliferator-activated receptor-a for CYP4A. These CYP enzymes collectively involve the metabolism of more than 80 percent drugs and other xenobiotics.
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