A fluctuation analysis of the rate of reexpression of the metastatic potential in a nonmetastatic mutant of the MDAY-D2 murine tumor.

A fluctuation analysis was performed on cell populations of a nonmetastatic, wheat germ agglutinin-resistant mutant (MDW4-1) of the murine MDAY-D2 tumor in order to determine the spontaneous frequency of occurrence of metastatic revertants during in vitro proliferation. A number of clones derived from the MDW4-1 mass culture were expanded in vitro and equal samples were inoculated intravenously into groups of DBA/2 mice. The number of metastatic cells present in each clonal population was estimated on the basis of the mean survival time per animal group, by making reference to a standard dose-response relationship. The final calculation indicated that metastatic cells arise randomly in vitro at a rate of 2 X 10(-5) cell per MDW4-1 cell per generation (upper estimate). The lower estimate of the rate reveals that only few metastatic revertants preexisted prior to inoculation when wheat germ agglutinin-sensitive cells are counterselected in the presence of the lectin. We conclude that the reexpression of the metastatic potential in the MDW4-1 tumor cell line may occur spontaneously, outside the host-selective environment, and may be linked to the loss of the wheat germ agglutinin-resistance phenotype.