Generation of metastatic variants in populations of mutator and amplificator mutants.

Genetic instability has been hypothesized by P. C. Nowell and other investigators to be an important aspect of tumor progression that leads to the generation of metastatic variants. In this study we examined the rate of generation of metastatic variants in mutant cell lines having increased rates of spontaneous mutation and gene amplification. Parallel clonal populations of the spontaneous mutation rate mutant thy-49 and the gene amplification mutants YMP1 and YMP7 and their respective wild types were generated and grown to a critical population size. The number of metastatic variants in each clonal population was then determined following iv injection into nude mice. Lung tumors were scored 3-4 weeks after injection of cells, and the mean number per clonal population was determined. Analysis of the means with the Luria-Delbruck fluctuation test showed no significant differences in the rate of generation of metastatic variants produced in the genetically unstable lines compared to their normal counterparts. This study suggests that increased spontaneous mutation and gene amplification rates in mammalian cells are not sufficient on their own to increase the rate of generation of metastatic variants.