Figure 2. Paclitaxel enriches a CSC population with increased TGF-β signaling.

(A and B) SUM159 and BT549 cells were treated with vehicle (control) or 10 nM paclitaxel for 4 days and allowed to recover in fresh media for another 4 days. Cells were trypsinized and analyzed by FACS for (A) ALDH activity and CD44^hi/PROCR⁺ expression (*P < 0.01) or (B) assessed for their ability to form mammospheres (*P = 0.04). (C) SUM159 xenografts were treated with vehicle or 10 and 20 mg/kg/d paclitaxel for 5 consecutive days (treatment started at day 1 and ended at day 6 of x axis). Tumor diameters were measured every 3 days using calipers, and volume in mm³ was calculated as described in Methods. Xenografts were harvested on day 15, dissociated into single cells, and grown as mammospheres. Each bar represents the mean mammosphere number ± SEM (n = 3; *P < 0.05). Original magnification, ×100. (D) Whole lysates from the same SUM159 xenografts as in C were subjected to P-SMAD2, total SMAD2/3, and actin (control) immunoblot analysis. exp, exposure. (E) SUM159 and BT549 cells were treated with vehicle or 5 nM or 10 nM paclitaxel for 4 days and seeded in 24-well plates. Cells were transfected with pCAGA-Luc and Renilla plasmids; luciferase activity was determined 24 hours later using the Dual Luciferase Kit, as described in Methods (n = 3; *P < 0.05). Error bars indicate SEM.