Analysis of SP cells by CKI treatment. (A) MCF-7 cells were labeled with Hoechst 33342 and analyzed by flow cytometry or with the addition of Verapamil. The percentage of SP cells appeared as the Hoechst low fraction in the P3 is about 2.7%. (B) MCF-7 cells were treated with CKI (30 μl/ml, 50 μl/ml, 70 μl/ml) for 48 h, and SP cells were analyzed by flow cytometry. P3 gate is the percentage of SP cells. Data from a representative experiment (from a total of three) are shown.