MTT assay

The MTT assay (Sigma-Aldrich; Merck KGaA) was used to measure the viability of MCF-7 and SK-BR-3 cells. The cells were seeded into 96-well plates at a density of 5×10³ cells/well and then cultured in an incubator at 37°C with 5% CO₂. MTT (20 µl) was added into each well to measure cell viability and incubated for another 4 h at 37°C. After incubation, the medium was removed and 150 µl DMSO was added into the wells to dissolve the formazan crystals at 37°C. The cell viability was calculated by measuring the optical density at 490 nm.