The Use and Value of In Vitro Technologies in Metabolism Studies
The detailed investigation of the metabolism of drugs is one of the key issues in drug development. Several in vitro metabolism assays have been developed over the last two decades, to replace time-consuming and expensive animal studies. These have the potential to speed up drug development and increase drug safety, as they can be used to improve the prediction of the effects of drugs on humans. The key factors to be identified in metabolism are: a) the enzymes involved, and b) the metabolites produced by these enzymes. Cytochromes P450 (CYP-450s) are the key enzymes in drug metabolism. Cloning the genes encoding the CYP-450s, and the genetic engineering of suitable cells for heterologous expression, have provided new cell lines for studies on drug metabolism in vitro, under highly defined conditions. The V79 cell line, derived from Chinese hamster lung fibroblasts, was found to be suitable for heterologous expression, as these cells themselves do not express CYP-450s, thus providing a clean background for genetically engineering for the stable expression of any cloned CYP-450. In this way, V79 cell lines were created which specifically express CYP-450s from human, mouse, rat, and fish. These recombinant V79 cells have been applied in several drug metabolism and toxicity studies.