Enhancement of adriamycin-induced killing after delayed plating of plateau-phase V79-cells.

Unfed plateau-phase cultures of Chinese hamster V79-cells were treated for 1 h with various amounts of adriamycin in the range between 0 and 10 micrograms ml-1 and subsequently either immediately trypsinized and plated to assay for survival, or reincubated in medium collected from replicate plateau-phase cultures and returned to the incubator for various periods of time before plating. Significantly less killing was observed, for the same adriamycin dose, in cells treated in the plateau-phase and plated immediately thereafter as compared to cells treated while actively growing. When cell trypsinization and plating was delayed for up to 22 h, a significant increase in killing was observed, and the survival curve obtained approached that observed after treatment with adriamycin of growing cells. Initially almost exponential kinetics were observed for this potentiation of adriamycin-induced cell killing with a t37 of approximately 2 h. Cell survival was still decreasing after 22 h of post-treatment incubation in the plateau phase, with no clear indication for approaching a plateau. However, longer incubations, to establish a plateau, were not possible due to degeneration of the cultures. Flow cytometry measurements of the intracellular adriamycin content showed only a small difference between exponentially growing and plateau-phase cells despite the significant differences in the number of cells per culture at the time of treatment. The rate at which adriamycin-related fluorescence decayed after adriamycin treatment was slightly higher for cells trypsinized and exposed to fresh medium than for cells kept in the plateau-phase. The results indicate the importance of the physiological state and the post-treatment incubation conditions of cells for the final effect of adriamycin on survival.