Dose-Dependent Transformation of Cells of Human Fibroblast Cell Strain MSU-1.1 by Cobalt-60 Gamma Radiation and Characterization of the Transformed Cells

Cells from an infinite-life-span near-diploid human fibroblast cell strain, MSU-1.1, were transformed after a single exposure to60 Co γ radiation. The frequency of transformation as measured by the number of induced foci per 106 cells was a linear function of dose. Cells from 13 independent foci from γ-irradiated cell populations and one from a nonirradiated cell population were isolated, clonally expanded and assayed for characteristics of malignantly transformed cells. Eight of the 13 focus-derived cell strains from the irradiated populations formed tumors in athymic mice with latent periods (time required for the tumors to reach 1 cm in diameter) of 4-27 weeks. Of these 8 cell strains, 3 were fully growth factor-independent, formed large colonies (>120 μm in diameter) in 0.33% agarose at a high frequency (50%), and produced malignant tumors with a mean latency of 6 weeks or less at all sites injected. Four others formed colonies in agarose at a slightly lower frequency, were only partially growth facto...