Effect of cell density on cell survival after high-dose irradiation.

<p>(a) Influence of the number of seeded cells on the shape of the survival curve of MCF7 cells in the colony formation assay. A significant decrease (P<0.0001) in surviving fraction (SF) after 12 Gy was found when seeding 50,000 cells/T25 flask (open symbol) compared with 10,000 cells/T25 flask. This resulted in an increased downward curvature of the survival curve (n = 7). (b) SF after 12 Gy (SF12) for different numbers of seeded cells (MCF7: 5–50×10³/T25 flask) confirmed a significant inverse correlation (P<0.0001) with cell numbers (n = 5). (c) Feeder cell experiment to test the effect of high-dose (20 Gy) irradiated cell numbers on colony formation of unirradiated cells (MCF7). The experimental design is shown above the data diagram. A significant inverse correlation (P<0.0001) between the number of irradiated feeder cells per T25 flask and the normalized plating efficiency of unirradiated MCF7 cells was observed (n = 3). Mean±standard errors are shown.