Differential survival of cell subpopulations in spheroids after treatment with bleomycin.

The cytotoxic effect of bleomycin (BLM) on Chinese hamster V79-cells grown as spheroids is compared to that on monolayer cultures in exponential vs. plateau phase of growth. Cells treated as intact spheroids with BLM (50 micrograms/ml for 1 h) are more sensitive than monolayer cultures. Cell subpopulations derived from different zones of the spheroids survive BLM-treatment to different degrees: When treated as single cells in suspension, the formerly "outer" cells are less affected than the "inner" cells. Within intact spheroids, however, progressive cellular resistance with increasing distance from the outer rim is found.