Nimotuzumab abrogates acquired radioresistance of KYSE-150R esophageal cancer cells by inhibiting EGFR signaling and cellular DNA repair

Background: Acquired radioresistance of cancer is common after repeated irradiation and often leads to treatment failure. This study aimed to examine the effects of nimotuzumab on acquired radioresistance in human esophageal carcinoma cells and to investigate its underlying mechanisms. Methods: The radioresistant human esophageal carcinoma cell line KYSE-150R was generated by using fractionated irradiation. KYSE-150R cells were pretreated with or without nimotuzumab before ionizing radiation. Cell growth and colony formation were measured to quantitate the effects of radiation. The gamma-H2AX foci assay was employed to determine cellular DNA-repairing capacity. The phosphorylation of key molecules involved in the epidermal growth factor receptor (EGFR) signaling pathway and cellular DNA repair was measured by Western blot analysis. Results: Nimotuzumab enhanced radiation-induced inhibition on cell growth and clonogenic survival in KYSE-150R cells. The average number of gamma-H2AX foci increased in the irradiated cells treated with nimotuzumab. Nimotuzumab inhibited phosphorylation of the EGFR and its downstream molecules AKT and ERK. Phosphorylation of the DNA repair-related proteins DNA-PKcs, ATM, and RAD51 was also inhibited by nimotuzumab. Conclusions: These results indicate that nimotuzumab can inhibit key cancer survival mechanisms, the EGFR signaling pathway, and DNA repair and thereby reverse acquired radioresistance in KYSE-150R cell line.