Enhanced virus transformation of hamster embryo cells in vitro

Since transformation of hamster cells in vitro by simian virus 40 (SV40) is a rare event in a homogeneously infected cell population, physiochemical studies of the events of virus transformation are difficult. Similarly, other deoxyribonucleic acid-containing oncogenic viruses produce transformed-cell foci in vitro with low efficiency. Sublethal doses of X-ray irradiation, as well as preincubation of hamster embryo cells with the radiomimetic analogue, 5-iododeoxyuridine, markedly sensitized hamster embryo cells to SV40 in vitro. Agents were used at dosages which neither produced lethality nor caused neoplastic transformation in the absence of virus. Embryo cells maintained in vitro for long periods of time became increasingly more sensitive to SV40 transformation. Radiation also stimulated transformation by adenovirus 31. Delay in the addition of virus to preirradiated cells reduced the susceptibility to transformation by SV40 which was observed for cells infected immediately after irradiation, suggesting that radiation repair mechanisms or, possibly, release from radiation-induced "mitotic delay" may interfere with the process of neoplastic conversion by SV40.