2.2 Cell viability assay

Cell viability was evaluated by MTT assay. Briefly, Sk-Mel-28, A375, IGR37, LU-1205, MV3, normal melanocytes were seeded in 96-well plates at 5 × 10³ cells/well containing 0.1 ml growth medium and incubated overnight, followed by treatment with indicated concentrations for 24, 48, and 72 h. 20μl of MTT solution were then added to each well and incubated for 4 h at 37°C. Formazan crystals were dissolved in 150 μl of DMSO and quantitated spectrophotometrically at a wavelength of 570nm with a micro-plate reader to obtain absorbance values. Cell viability was expressed as percentage change compared to the control. The IC₅₀ value was determined by curve fitting of the sigmoidal dose-response curve. The experiments were independently performed for three times.