The use of heterologously expressed drug metabolizing enzymes--state of the art and prospects for the future.

The first report of the functional, heterologous expression of a mammalian cytochrome P450 (CYP) enzyme occurred more than a decade ago. In the intervening years, these expression systems have been optimized with regard to the specific requirements for production of catalytically active enzymes. In this review, we discuss the strengths and limitations of heterologously expressed enzymes as they affect in vitro drug metabolism studies. Emphasis is given to new applications (screens for CYP inhibition and novel enzyme mixtures) that have been enabled by high level, functional expression of CYP enzymes.