Cell viability assay

Cell viability was assessed using the MTT assay (Roche Diagnosis, Indianapolis, IN). Briefly, melanoma cell lines were seeded onto 96 well plates for following overnight incubation. Five replicated wells were put up for each group. Then cells were treated with melatonin or vemurafenib by indicated dose. Finally, the effect for cell viability was assessed by the absorbance of the supernatant at a wavelength of 450 nm comparing to the vehicle-treated control group. The drug concentration required to cause 50% cell growth inhibition (IC₅₀) was determined by interpolation from dose-response curves.