Transformation of oral keratinocytes in vitro by 4-nitroquinoline N-oxide

Normal rat oral keratinocytes have been transformed with the carcinogen 4-nitroquinoline N-oxide (4NQO) in vitro. The morphology, growth characteristics, ability to grow without anchorage and tumorigenicity in athymic mice was examined in 12 selected cell lines. Each of the lines could be assigned to one of two general groups. The first group of cell lines although showing some morphological signs of transformation and the ability to be subcultured beyond passage 15 were not anchorage independent or able to form tumours in athymic mice. The second group of cell lines showed distinct signs of morphological transformation, could be serially subcultured without 3T3 feeder cells, were anchorage independent and tumorigenic in athymic mice. Anchorage independence was more common at higher passages and with increased 4NQO treatment and correlated well with a decreased reliance on 3T3 feeder cell support. The anchorage-independent phenotype was closely associated with the ability to form tumours in athymic mice. This same sequence of phenotypic changes has been demonstrated in rat oral keratinocytes after 4NQO treatment in vivo indicating that during carcinogenesis, cell populations progress through the same stages whether proliferation occurs in vitro or in vivo. There is some evidence to suggest, however, that the time interval between stages may be altered when carcinogenesis takes place in vitro.