Influence of culture passages on growth kinetics, xenobiotic metabolism, chromosomal stability and transformation in a clonal fetal hamster lung epithelial cell line.

M3E3/C3 is a clonal fetal hamster lung epithelial cell line which is used for studies of epithelial differentiation as well as for in vitro toxicologic tests. In this study growth kinetics, xenobiotic metabolism, chromosomal stability and transformation were investigated at increasing culture passage numbers up to 150. Cells of higher passages grew faster and reached higher cell densities than the cells of lower ones. As an indicator of xenobiotic metabolism we measured the activity of 7-ethoxycoumarin-deethylase (ECD), an enzyme belonging to the mixed function oxidase system. Up to passage number 100 the ECD activity strongly increased, followed by a slight decrease in additional passages. The chromosomal stability was assessed by the induction of micronuclei by benzo[a]pyrene (BaP) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). More micronuclei were always detected in cells of higher passages than of lower passages. The capability of cells to be transformed to anchorage independent growth by chemical carcinogens was examined using a soft agar test. After carcinogen exposure with BaP and MNNG, cells of higher passages showed higher transformation frequencies than cells of lower passages. Many cells at passage 150 exhibited an especially high soft agar growth even without carcinogen treatment and were therefore characterized as spontaneously transformed. These results show that metabolic and genetic characteristics of permanently growing cells differ remarkably depending on the culture passage. This has always to be considered when permanently growing cells are used for toxicological studies.