4.1. Cell Culture and Chemical Treatment

Human OSCC cell lines HN22 and HSC-3 were obtained from Dankook University (Cheonan, Korea) and Hokkaido University (Hokkaido, Japan), respectively. Both cell lines were cultured in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum and antibiotics at 37 °C in a 5% CO2 incubator. All experiments were performed after the cells reached 50–60% confluence. NCTD was purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA) and was treated at concentrations ranging from 0 to 30 μM for 6–48 h. SB203580 (a p38 MAPK inhibitor) was purchased from Calbiochem (San Diego, CA, USA). Each chemical was dissolved in dimethyl sulfoxide (DMSO), aliquoted, and stored at −20 °C.