An integrated in vitro model for simultaneous assessment of drug uptake, metabolism, and efflux.

The absorption, distribution, metabolism, and excretion (ADME) of drugs in vivo are to a large extent dependent on different transport and metabolism routes. Elucidation of this complex transport-metabolism interplay is a major challenge in drug development and at present no in vitro models suitable for this purpose are at hand. The aim of this study was to develop flexible, well-controlled, easy-to-use, integrated cell models, where drug transport and drug metabolism processes could be studied simultaneously. HEK293 cells stably transfected with the organic anion transporting polypeptide 1B1 (OATP1B1) were subjected to either transient transfection or adenoviral infection to introduce the genes expressing cytochrome P450 3A4 (CYP3A4), NADPH cytochrome P450 oxidoreductase (POR), cytochrome b5 (CYB5A), and multidrug resistance protein 1 (MDR1), in different combinations. Thereafter, the time and concentration-dependent transport and metabolism of two well-characterized statins, atorvastatin (acid and lactone forms) and simvastatin (acid form), were determined in the different models. The results show that CYP3A4-dependent metabolism of the more hydrophilic atorvastatin acid was dependent on OATP1B1 uptake and influenced by MDR1 efflux. In contrast, the metabolism of the more lipophilic atorvastatin lactone was not affected by active transport, whereas the metabolism of simvastatin acid was less influenced by active transport than atorvastatin acid. Our results, together with the models being applicative for any combination of drug transporters and CYP metabolizing enzymes of choice, provide proof-of-concept for the potential of the new integrated cell models presented as valuable screening tools in drug discovery and development.