Cell viability determination

NPC cells in culture medium were seeded at a density of 4000 cells/well in a 96-well plate (100 μl per well) and incubated overnight. Palbociclib (Selleck Chemicals, S1116) was dissolved in cell culture medium to concentrations of 0–20 μM and added to the NPC cell cultures. The viability of the cells was examined on Days 1, 3 and 5 of culture. SAHA was diluted from a stock solution (100 mg/ml) into culture medium and used at various treatment concentrations (0–0.5 μM). The concentration of DMSO (vehicle) was less than 0.001% in the culture with the highest concentration of SAHA. Cisplatin (Sigma, 479,306) was diluted with dimethylformamide (DMF) to a stock concentration of 40 mM.

A resazurin (Sigma, R7017) stock solution (0.02% w/v dissolved in PBS) was added to the cells (10% v/v) to determine cell viability after drug treatment. After incubation with resazurin for 4 h, the amount of the fluorescent product resorufin in the cultures was measured at excitation/emission wavelengths of 530/590 nm using a Victor 3 Plate Reader (PerkinElmer). Growth inhibition in each well was calculated as: (viability_control-viability_drug) / viability_control *100%.