Influence of Methylnitrosourea on Malignant Transformation of Mouse Embryo Cells in Tissue Culture

Summary

The powerful methylating carcinogen methylnitrosourea (MNUA) enhanced the malignant transformation of inbred Swiss mouse embryo cells. This effect was observed sometimes after single treatment with MNUA and frequently after multiple treatment with MNUA in cell lines carried in tissue culture for 14 weeks or longer. The antecedent changes suggest that malignant transformation is a stepwise process in which increased plating efficiency of treated cells appears first, followed by the appearance of morphologically transformed colonies, and finally by the capacity of such cell lines to grow as tumors in irradiated hosts. A search for murine leukemia virus in some of the transformed cell lines was negative.