4.3. Cell Viability Assay

The cell viability assay was performed using the MTT method. After treatment with 50, 100, 200, 300, 400 and 500 µM of resveratrol; 1, 5, 10, 25, 50, 75 and 100 µM of curcumin; and 1, 5, 10, 25, 50, 75, 100, 150, 200 and 300 µM of piperine for 24 or 48 h, the cells were washed with phosphate buffered saline (PBS) and incubated for 3 h in 0.5 mL of an MTT solution (0.5 mg/mL of PBS) at 37 °C under a 5% CO₂ atmosphere in an incubator. Subsequently, the medium was removed, and 0.5 mL of absolute isopropanol was added to the attached cells. The absorbance of the converted dye in living cells was determined at 595 nm. The cell viability of MCF-7 cells cultured in the presence of the assessed compounds was calculated as a percent of the control cells, and the IC₅₀ values were obtained from dose-response curves. All experiments were performed in triplicate, and the GraphPad Software 6.0 (GraphPad Inc., San Diego, CA, USA) was used for the IC₅₀ calculation.