4.3. Cell Viability Assay

We performed an MTT assay to examine the viability of 4T1 cells treated with OST. Briefly, 4T1 cells (4000 cells/well) were seeded into 96-well plates to culture for 24 h, followed by treatment of the cells with different concentrations of OST (0, 25, 50, 75, 100, 125, and 150 μM). After treatment for 24, 48, and 72 h, 100 μL DMEM basal culture and 15 μL MTT solution (5 mg/mL in PBS) were added to each well and incubated for 4 h at 37 °C. Finally, the culture supernatant in the wells was aspirated, and 150 μL of dimethyl sulfoxide was added to each well and shaken for 10 min at room temperature to melt the crystals. Absorbance was measured at 490 nm using a multifunctional enzyme marker. The percentage of cell viability was calculated from the mean optical density (OD) values of the wells using the following formula: cell viability (%) = (OD _Test /OD _Control) × 100.