Stable heat-resistant clones selected from wild-type and surface variants of B-16 melanoma

Stable heat-resistant clones were selected from wild-type B-16 melanoma cells and from three of their surface variants resistant to the lectins wheat-germ agglutinin, ricin and concanavalin A. The selection procedure included three or four cycles of heating the cells in culture at 43 degrees C for 2-1/2 to 3-1/2 h interspersed with growth at 37 degrees C. The survivability of the heat-resistant (HR) variant cells at elevated temperatures of 43 degrees C for 160 min and 45 degrees C for 40 min was 2-4 logs greater than that of their respective parents. This acquired property of heat resistance appeared to be a stable phenomenon, persisting in these cell lines for more than 80 generations. One HR variant cell line carried in tissue culture for 250 generations showed no change in the heat-resistance characteristic. Acquisition of resistance appeared to be a gradual process with intermediate stages preceding the more pronounced degree of resistance. These newly selected HR variants join the existing surface variants of B-16 melanoma to result in a large family of variants from the same cell lineage to make this system a powerful tool for studying the relationship between heat sensitivity, metastasis and hyperthermia treatment of cancer.