Relationship of DNA repair processes to mutagenesis and carcinogenesis in mammalian cells. Progress report, August 1, 1977--October 31, 1978

The objective of this research is to compare repair-proficient and repair-deficient mammalian cells with regard to the frequencies of mutation and oncogenic transformation following treatment with mutagenic/carcinogenic agents or environmental pollutants. During the past 15 months we have established methods and conditions for the growth, maintenance, and assay of the mouse embryo cell line C3H/10T1/2 and for infection of this cell with polyoma virus. We have determined the levels of various mutagens and selectants to be used with this cell line. Following treatment of the cells with 0.06% ethylmethane sulfonate (EMS), no cell killing results, but the number of ouabain-resistant (oua/sup R/) mutants induced is higher than the number of spontaneous oua/sup R/ mutants. The frequency of mutation ranged from 4 x 10/sup -8/ to 2.8 x 10/sup -6/. The higher frequencies were obtained when the selectant was applied to cells plated at a low density and when a three-day expression time was allowed between the mutagenic treatment and the application of the selectant. The frequency of oncogenic transformation was higher than the frequency of mutagenesis, by several orders of magnitude, perhaps because of problems with the morphological transformation assay. We are investigating the use of growth in soft agar as an assay for transformation.