Protection of Chinese hamster cells against the cytotoxic and mutagenic effects of alkylating agents by transfection of the Escherichia coli alkyltransferase gene and a truncated derivative.

The cytotoxic and mutagenic effects of various monofunctional and bifunctional alkylating agents have been assessed in V79 Chinese hamster cells that express either the entire O6-alkylguanine (O6AG) and alkylphosphotriester alkyltransferase (ATase) gene (clone 8 cells) or a truncated form that codes only for O6AG ATase activity (clone SB cells). Protection ratios, as determined by D37 values, were greater for clone 8 cells than for SB cells. Significant protection against the mutagenic effects of N-methyl-N-nitrosourea and ethylmethanesulphonate at the hypoxanthine phosphoribosyltransferase (HPRT) locus was observed in clone 8 and SB cells. Streptozotocin and the haloethyl nitrosoureas, chlorozotocin and bis-chloroethylnitrosourea were less efficient in inducing HPRT-deficient mutants and a smaller degree of protection was afforded by the transfected genes. This is possibly due to the propensity of these compounds to induce multi-locus deletions. Southern analysis of DNA from clone 8 and SB cells indicated the presence of multiple copies of the plasmid integrated into clone 8 cells but few copies in clone SB cells. The copy number did not change but ATase levels fell when cells were grown in the absence of G418.