Search for "indicators" of neoplastic conversion in vitro.

Certain responses of mouse and hamster cells to polyoma virus were examined with respect to their specificity as "indicators" of neoplastic conversion in vitro. These responses included the development of transplantation antigens and changes in morphologic growth pattern, cytology, karyology, rates of proliferation, and glycolytic activities. Under limited conditions, i.e., in short-term, slow-growing cultures, the morphologic change in growth pattern and increases in glycolytic activity and proliferation rate induced by polyoma virus appeared to correlate with neoplastic conversion. However, in long-term or rapidly growing short-term cultures, similar morphologic patterns occurred in cells that subsequently tested as non-neoplastic. Also, such patterns could be induced by polyoma virus in cells already neoplastic. Cells that had undergone "spontaneous" neoplastic conversion frequently showed none of these morphologic features of virus-transformed cells. Prolonged culture of cells without added virus resulted in increased glycolytic activities and proliferation rates equivalent to those of virus-transformed cells. These changes occurred in at least one cell line long before evidence of neoplastic conversion. The cytologic changes in the virus-treated neoplastic cells were similar to those usually associated with neoplastic cells in vivo and may possibly serve as sensitive indicators of in vitro neoplastic conversion. From the observations of this study, the change in morphologic growth pattern is interpreted not as loss of "contact inhibition," but as a proliferative response accompanied by decreased adhesion of cells to the glass substrate.