Induction and isolation of frameshift mutants in cultured Chinese hamster DON cells.

Induction, isolation and characterization of frameshift mutants were studied by using a Chinese hamster Don (CHD) cell line. ICR-191, known to be a potent frameshift mutagen, was used for the induction of frameshift mutations. The drug (10(-5) M), as well as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and ethyl methanesulfonate (EMS), increased significantly the frequency of forward mutations from 8-azaguanine (8-AG) sensitivity (8-AGs) to resistance (8-AGr) over the untreated control to an extent of about 100-fold. 21 8-AGr mutants were isolated from the AP-01 (a sub-line of CHD) cells after treatment with appropriate concentrations of ICR-191 (10(-5) and 1.36 X 10(-5) M), and subsequently several reclonal mutants were tested for their ability to revert to 8-AG susceptibility after treatment with the three mutagens and a carcinogen, 2-nitrofluorene (2-NF), known to be a frameshift mutagen. Among the 8-AGr mutants tested, clone ICR-014 or ICR-172 showed a significant increase in reversion frequency over the control level only after treatment with ICR-191 or 2-NF, respectively; but not with the other two mutagens. These results suggest that each of these two kinds of mutant has a different frameshift mutation in one of the loci controlling 8-AG resistibility. It was also found that the hypoxanthine--guanine phosphoribosyl transferase (HGPRT) activities in clones ICR-014 and ICR-172 were 1.9 and 34% of that of the original AP-01 cells, respectively.