Quantitative and qualitative studies of chemical transformation of cloned C3H mouse embryo cells sensitive to postconfluence inhibition of cell division.

A line of C3H mouse embryo cells (C3H/10T1/2 clone 8) sensitive to postconfluence inhibition of cell division was used for a variety of quantitative and qualitative studies of chemical oncogenesis in culture. The polycyclic hydrocarbons (PH), 3-methylcholanthrene, dibenz[a,h]anthracene, and 7,12-dimethylbenz[a]anthracene, caused varying degrees of cytotoxicity and produced morphologically and malignantly transformed foci in these cells with a dose-dependent frequency, while N -methyl- N ′-nitro- N -nitrosoguanidine was toxic but did not transform under the same conditions. Transformation frequency was related to cell density at the time of treatment and to the duration of treatment with PH. After treatment of the cells with the PH, three types of morphologically altered foci were identified. Foci of each type were cloned and inoculated into irradiated syngeneic mice. Two of the three types of foci gave rise to fibrosarcomas when cells were inoculated at Passages 2 to 4 after cloning. The determination of transformation frequency in this system includes only these two types of malignantly transformed foci. The third type of focus was morphologically minimally altered but did not give rise to tumors under the same conditions. Control cells did not produce tumors. The saturation densities of several transformed lines were shown to be greater than the control line and did not correlate with the growth rate of the cells. The antimycotic agent amphotericin B (Fungizone) interfered with transformation when it was present in the medium at the time of exposure of the cells to the PH.