Use of transgenic cell lines in mechanistic studies of drug metabolism

Heterologously expressed human drug-metabolizing enzyme systems in a variet y of hosts (mammalian cell lines, baculovirus/insect cells, yeast and Esche richia toil) have their distinct advantages for particular studies of biotr ansformation or mechanistic processes, In contrast to classical iii vitro s ystems such as tissue slices. hepatocytes or subcellular fractions, express ed enzymes allow the study of single enzyme reactions in isolation. Further more, metabolic reactions of enzymes expressed only in minor amounts in hum an tissue can be assessed. Here we present an overview of how recombinant e nzymes are bring used in biotransformation studies and we will present seve ral examples of applications of recombinant cytochrome P450 preparations du ring drug development. It is beyond the scope of this overview to describe all experimental procedures in detail since they art: based on published te chniques unless otherwise indicated. Examples of applications of recombinan t cytochrome P450 prep preparations include the involvement of human metabo lizing enzymes in a metabolic pathway and their metabolic products, mechani stic studies to determine specific drug-drug interactions at the metabolic level and detection of mechanism-based inactivation of drug-metabolizing en zymes. Heterologous expression systems offer a constant and reproducible so urer of human drug-metabolizing enzymes that are easily available by standa rd laboratory techniques. Considering the constraints on the availability a nd use of human tissue it is likely that these systems will be widely used in the future, But, because of the unequal distribution of individual drug- metabolizing enzymes in man, extrapolation needs to be done carefully. (C) 1999 Elsevier Science Ltd. All rights reserved.