2.4. Cell Viability Assay

Cell proliferation of MDA-MB-231 cancer cells upon treatment with usenamine A was measured as follows. In total, 8 × 10³ cells were seeded into 96-well plates, incubated overnight, then exposed for 48 h to different concentrations of the developed drug. Then, 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl-2 tetrazolium bromide (MTT) solution was added to each well, and the cells were incubated at 37 °C under 5% CO₂ for 4 h. The culture medium was removed, and 100 μL DMSO was added to each well to dissolve formazan crystals. Cell viability was measured by reading the absorbance of the resulting solution at 490 nm using a spectrophotometer (DTX880, Beckman Coulter, CA, USA).