To investigate the effects of TPGS on intracellular Ca2+ levels, MCF-7-ADR cells were inoculated into 6-well plates (1 × 106 cells/well) and cultured in medium containing different TPGS concentrations (16, 80, and 400 µg/mL) for 48 h. Cells were then centrifuged at 8000 rpm at 4 °C for 5 min and washed twice in cold PBS. Next, the fluorescent fluo-3 AM probe was diluted in PBS (1:1000), added to cells, and incubated at 37 °C for 0.5 h before washing twice in PBS. Fluorescence at 528 nm was determined by flow cytometry in the FL1 channel.