Effect of fractionated radiation on the proliferation of CICs. ZsGreen-cODC expression and cell membrane PKH26 staining was analyzed in MCF-7 or T47D monolayer cultures before and after radiation treatment. Cells were stained with PKH26, plated, and treated with the appropriate radiation dose. Representative histograms of PKH26 fluorescence in the total population, non-tumorigenic and CICs populations in MCF-7 (A) and T47D (D). Calculated numbers of cell divisions in MCF-7 (B) and T47D (E). Red bars: Total population; Blue bars: Non-tumorigenic cells; Green bars: CICs. Quantification of non-dividing CICs after fractionated radiation MCF-7 (C) and T47D (F). White bars: untreated; Black bars: fractionated radiation; Grey bars: biological equivalent 8.5 Gy treatment. Data from means (+/- SEM) of at least three independent experiments are shown.