Figure 7

Topoisomerase I inhibition prevents centrosome separation. A. HCT116 cells synchronized or treated with sn38 as described above were subjected to immunofluorescence analysis. Centrosomes were detected by staining with monoclonal antibody to γ-tubulin. ~ 100 cells were analyzed for each experiment, (n = 3 +/- sd). B. HCT116 cells were treated with sn38 (5 ng/ml, 12.5 nM) and further grown for 7-9 days. Colony formation was then counted using an inverted microscope, and for each cell line, growth of non treated cells was set up at 100%. Clonogenic survival was then plotted as a fraction relative to these untreated cells (n = 5 +/- sd). C. In parallel, the percentage of senescent cells was evaluated as the number of cells expressing SA-β-gal activity (n = 3).