Affiliations: Institute of Biotechnology, Brandenburg University of Technology Cottbus-Senftenberg, Senftenberg, Germany
Corresponding author: S. Kammerer, Institute of Biotechnology, Brandenburg University of Technology Cottbus-Senftenberg, Universitätsplatz 1, 01968 Senftenberg, Germany. Tel.: +49 3573 85 934; E-mail: [email protected].
Abstract: The liver is the place of biotransformation, where drugs or other substances are metabolized. Cytochrome P450 oxidoreductases (CYPs) play a prominent role in these processes and thus sufficient CYP expression levels are the prerequisite for physiologically relevant liver metabolism or toxicity studies. Human primary hepatocytes, the most popular in vitro liver model for such studies, have several limiting properties: poor availability, rapid dedifferentiation, substantial donor variability and restricted proliferation capacity in vitro. This prompted many research groups to develop alternative models for the investigation of biotransformation-related questions. The hepatoblastoma-derived HepG2 cell line is a highly proliferative and easy to handle in vitro model, but has the disadvantage that expression levels of relevant CYP enzymes are dramatically downregulated. The generation of CYP-overexpressing HepG2 cells is a way to overcome this disadvantage and such cells were used as in vitro alternative to primary hepatocytes. Coding sequences of various CYP isoforms were transiently or stably introduced into HepG2 cells by using viral transduction or transfection reagents. With the frequently used adenoviral transduction, the level of recombinant enzyme activity usually is high within a time window of several days and simultaneous expression of several CYP enzymes is possible. High expression levels can also be achieved with lentiviral transduction which is stable upon virus integration into the host genome. Transient and stable CYP-expressing HepG2 cells serve as a convenient tool for toxicity studies and risk assessment of drugs or other substances undergoing biotransformation, clearance and drug-drug interaction. Furthermore, they can be used for rapid identification of CYP enzymes relevant to a specific reaction or screening for CYP enzyme inhibitors. The use of CYP-overexpressing HepG2 systems also have some disadvantages, such as the cancerous cell origin und their lack of other liver specific functions. The broad spectrum of possible applications of these CYP-expressing HepG2 cells, especially in the early phase of drug development, can quickly and easily provide important information about drug metabolism in the liver and toxicity behaviour of potential metabolites. In this way, unsuitable drug candidates can be excluded at an early stage of pharmacological studies in order to safe costs and to reduce in vivo animal trials.
Keywords: Biotransformation, Cytochrome P450, drug-induced hepatotoxicity, drug metabolism, HepG2, liver in vitro model, primary human hepatocytes, viral