Figure 5

ACT1 enhances the effectiveness of lapatinib in HER2+ BT474 cells. (A) BT474 cells were treated with vehicle, R-pep (100 μM), or ACT1 (100 μM) in the presence of drug vehicle (DMSO) or lapatinib (1, 10, 50 nM) for 48 hours and assessed for crystal violet staining density and quantitation by OD540. Student’s T-test was used to assess statistical significance. *p ≤ 0.001 when ACT1 compared to either R-pep or vehicle control. (B) Combined treatment with ACT1 and lapatinib impairs BT474 mammosphere formation. BT474 cells were plated in ultra low adhesion 96-well plates for 72 hours, followed by treatment with R-pep (100 μM) or ACT1 (100 μM) in the presence of drug vehicle (DMSO) or lapatinib (50 nM) for 96 hours. At the end of the 7 day assays, wells were assessed for mammosphere number, which was used to calculate the mammosphere forming efficiency of the cells. Student’s T-test was used to assess statistical significance as indicated. ± SEM; n = 4 (A) n = 24 (B).