Figure 4. Melatonin reverses DDP chemoresistance in NPC DDP-resistant cells. (A, B) The cell viability of the CNE2/DDP (A) and 5-8F/DDP (B) cells treated with melatonin (2 mM) was determined by CCK-8 assay. (C, D) Images (C) and quantification (D) of transwell migration and invasion assays. (E) Images (up) and quantification (down) clonogenic colony formation assays of the CNE2/DDP and 5-8F/DDP cells treated with melatonin for 2 weeks. All of the experiments were performed at least three times. Data presented are the mean ± SD; **P < 0.01, *P < 0.05 compared with control using Student t-test.