Figure 2.

Clonogenic survival after paclitaxel treatment is affected by cell growth density at the time of treatment. (A) SKBR3 cells were grown at the at the three different cell growth densities and then treated with paclitaxel (20 nM) for 12 h. All cells were then washed extensively and the indicated numbers of cells (either 500 or 2,500) of each treatment group were plated into new plates with fresh drug-free media. The cells were then left to grow undisturbed for 10 d. All plates were then fixed, stained, and the colonies counted. Plates containing the same number of cells for each group of cells were prepared in triplicate, fixed, and stained identically, with the resulting numbers of colonies averaged. The experiment was repeated three times, with similar results. Representative plates containing identically treated cells of each original growth density are shown. (B) Bar graphs showing the percentages of cells of each growth density forming colonies after treatment with paclitaxel as described. Each data point and its standard deviation (error bars) represents the results from at least six different plates of cells. Open star indicates a significant difference between the low density and the high density groups with the associated p value.