DNA repair and sensitivity of mouse embryo fibroblasts to methyl methanesulphonate and N-methyl-N'-nitro-N-nitrosoguanidine.

: DNA repair synthesis and cytotoxicity were evaluated in early passage mouse embryo fibroblasts from five inbred strains (B10, CBA, C3H/A, DBA/2, BALB/c) and in BALB/3T3 IL-2 cells after the cultures had been treated for 3 h with methyl methanesulphonate (MMS) or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). In the presence of hydroxyurea, the incorporation of tritiated thymidine into the MMS- or MNNG-treated cells derived from B10, CBA, C3H/A or DBA/2 mice, was, at the concentrations used, significantly higher than into controls untreated with the mutagens. Under analogous experimental conditions there was no detectable DNA repair synthesis in two kinds of cells derived from BALB/c mice. MNNG was more cytotoxic to the cells derived from BALB/c mice than to those of the four remaining strains. The sensitivity of all kinds of early passage mouse fibroblasts to MMS was similar at each MMS concentration tested. Cloning efficiency of BALB/3T3 IL-2 cells exposed to MMS at the concentration of 10(-3) or 10(-4) M did not differ from that of untreated controls. The latter cells treated with MNNG at the concentration of 10(-4) or 2 X 10(-4) M did not develop colonies.