Merits and limitations of recombinant models for the study of human P450-mediated drug metabolism and toxicity: An intralaboratory comparison

A wide variety of pharmacological and toxicological properties of drugs are determined by cytochrome P450-mediated metabolism. Characterization of the se pathways and of the P450 isoenzymes involved constitutes an essential pa rt of drug development. Similarly, because P450s are catalyzing the toxicat ion and detoxication of environmental pollutants, an understanding of these reactions facilitates risk assessment in environmental toxicology. Recentl y, a variety of recombinant expression systems has been employed to study t he role of human P450s in these reactions. These include insect, bacterial, yeast, and mammalian models. As these were developed and characterized by different laboratories, evaluation of their merits and limitations is inher ently difficult. To resolve this problem, we have established and character ized the latter three systems and present the key results here. In general, the catalytic properties of P450 isozymes in the various models were rathe r similar. However, taking technical considerations into account as well as the high level of functional expression of P450s achieved in bacteria make this system ideally suited for drug metabolism research, including the gen eration of milligram quantities of metabolites for: structural determinatio ns. For toxicological studies, however, expression of P450s in mammalian ce lls was most appropriate. This is exemplified here by studies into the role of human P450s in the activation and inactivation of chemotherapeutic drug s.