Breast cancer cells display differential cytotoxic responses to 3-bromo-2-oxopropionate-1-propyl ester (3-BrOP): triple-negative beast cancer (TNBC) cells are more sensitive to 3-BrOP compared to estrogen receptor (ER)-positive cells. (A) Representative profile of fluorescence-activated cell sorting (FACS) analysis after annexin-V/PI staining. After treatment with 3-BrOP (up to 75 μM) for 24 hours, MDA468 and MCF7 cells were assayed for cell death. Number shown in each panel indicates percentage of the annexin-V and PI double-negative cells (viable). (B) Cell death induced by 50 μM 3- BrOP for 24 hours in breast cancer cells detected by flow cytometric analysis (annexin V/PI double staining, left panel). 3-BrOP induced cell death in a dose dependent manner in breast cancer cells (right panel). (C) Representative profile of FACS analysis after rhodamine 123 staining. MCF7 and MDA468 were treated with 3-BrOP (up to 75 μM) for 24 hours , the mitochondrial outer membrane potential was then assessed by rhodamine 123 labeling and the reduction of rhodamine 123 fluorescence intensity indicates impaired mitochondrial membrane potential. The number shown in each panel indicates the percentage of cells with mitochondrial potential loss. (D) Loss of membrane potential induced by 50 μM 3-BrOP for 24 hours in breast cancer cells detected by flow cytometric analysis (left panel). 3-BrOP induced loss of membrane potential in a dose-dependent manner in breast cancer cells (right panel). The bar graph represents mean ± SD from results of three experiments. Triple+: BT474 cells; ER+: MCF7, T47D, ZR751; Her+: SKBR3, Triple-: BT20, MDA468, MDA231, MDA436.