Disruption of insulin-like growth factor 1 receptor activity diminished the breast cancer stem cell population. (A) Two populations of insulin-like growth factor 1 receptor (IGF-1R)+/IGF-1R- (BC0145) or IGF-1Rhi/IGF-1Rlo (BC0244) cells were sorted as described in Figure 1B and the mammosphere formation capability determined in the presence of 0.1% dimethylsulfoxide (DMSO) or 1 μM picropodophyllin (PPP). *P <0.05; #P <0.01. (B) The mammosphere forming capability of AS-B145 or AS-B244 cells under PPP or 0.1% DMSO treatment was determined. *P <0.05; #P <0.01. (C) Cells were transfected with 100 nM of negative control siRNA (ctrl siRNA) or IGF-1R specific siRNA (IGF-1R KD) and cells were harvested to determine the mammosphere forming capability. *P <0.05; #P <0.01. (D) IGF-1R+ BC0145 or IGF-1Rhi BC0244 cells were sorted, transduced with sh-Luc or sh-IGF-1R lentivirus and the tumorigenicity determined in NOD/SCID mice. All experiments were repeated independently at least twice and results shown were from a representative experiment. ALDH, aldehyde dehydrogenase.