4T1 SP cells are more tumorigenic than 4T1 non-SP cells. 4T1 cells stained with Hoechst 33342 dye were sorted into PI–/live, SP, and non-SP groups, and 8 × 103 cells from each group were injected orthotopically into the mammary fat pad of syngeneic BALB/c mice (n = 8). (A) Tumor volume was measured after tumor cell challenge, and (B) primary tumors were harvested and weighed 29 days after tumor cell challenge. (C) The lungs of each mouse were also harvested, and the number of tumor foci was quantified. The data represent the mean and SEM of tumor volume, tumor weight, and number of tumor foci, respectively. Data represent 1 of 2 experiments. Single-cell suspensions were created from (D) 3 PI–/live-derived tumors, (E) 3 SP-derived tumors, and (F) 1 non-SP–derived tumor, stained with Hoechst 33342 dye and analyzed by FACS to determine the repopulation potential of each group in vivo. (G) Percentage of repopulation of the non-SP compartment in SP-derived tumors and the percentage of repopulation of the SP compartment in non-SP–derived tumors. Data represent the mean and SEM of the percentage of repopulation. *P < .05.
