*4.4. Cell Proliferation Assay*

B16-F10 cells (0.5 × 10<sup>4</sup> cells/well) were seeded in 96-well culture plates in 100 μL of culture medium and incubated for 24 h. Subsequently, 100 μL of complete medium without or with various concentrations of PSS (100, 200, 400, 600, 800, 1000 μg/mL) were added. After incubation for 48 h, 10 μL of resazurin solution (1 mg/mL) was then added to each well, and the cells were incubated for another 4 h. The fluorescence of each well was measured at 544 nm and 595 nm by a microplate reader (SpetraMAX i3, Molecular Devices, Sunnyvale, CA, USA).
