Cell migration assay

C28/I2 cells were seeded at 2 × 10⁴ cells per well in a 12-well plate (Corning) and allowed to attach overnight. A scratch was introduced to the confluent cells in each well with a 200-μl sterile pipette tip. Cells were allowed to grow for 0, 3, 6, 12 and 24 h in basic medium supplemented with or without 5% PEP solution. Cell migration of each group was captured in real time using the Incucyte^® S3 Live Cell Analysis System (Essen BioScience, MI, USA) and the cell migration rate was analyzed in ImageJ (v.1.8.0; NIH, MD, USA).