Introduction of Cytochrome P-450 Genes into V79 Chinese Hamster Cells to Generate New Mutagenicity Test Systems

Usually, cultivated cells have poor capabilities to metabolize promutagens and procarcinogens. This is particularly true for cells that grow fast and have a high cloning efficiency, as is the case with V79 Chinese hamster cells. For this reason, these cells are being extensively used in mutagenicity tests. But, due to the fact that particularly these cells lack cytochrome P-450 activities, promutagens and procarcinogens have to be incubated with an exogenous metabolizing system, e.g. liver homogenate preparations, in order to generate reactive metabolites. These extracellularly generated metabolites are then given to V79 cells in order to check for their potency to mutate the chromosomal DNA in the test cell which is usually measured by counting HPRT- cell clones surviving in 6-thio- guanine containing selection medium. By doing so, one may encounter two serious problems. First, if metabolites carry charges it might very well be that these metabolites cannot cross the cellular membrane and thus, never reach their target molecule in the cell which is the chromosomal DNA or the cellular proteins. Second, metabolites may be further metabolized in the liver homogenate and turned into non-reactive compounds before the reactive intermediate ever had a chance to enter the cell. In any case, those metabolites would remain undetected in test systems such as the V79 cell in combination with extracellular metabolization.