Abstract: Objective To investigate the potential molecular mechanism of nimotuzumab in its capacity of enhancing lung cancer cell radiosensitivity in vitro.Methods Lung cancer A549 cells were pretreated with or without nimotuzumab for 24h before exposure to radiation.Clonogenic survival assay was performed and the single-hit muti-target model was applied to evaluate the radiosensitivity related parameters.Then cell cycle distribution by flow ctyometry after different doses of radiation were analyzed.EGFR activation was examined,the levels of AKT with its phosphorylaed form and that of p27 in A549 cells at different time point were detected by Western blot.Results Pretreatment with nimotuzumab reduced clonogenic survival after radiation and the sensitivity enhancing ratio was 1.36.The combination of nimotuzumab and radiation treatment led to a significant S phase reduction.EGFR activation was greatly inhibited after pretreating with nimotuzumab,despite it could be activated by radiation.The levels of AKT did not alter between nimotuzumab combined with radiation group and radiation group,but the radiation-induced phosphorylation of AKT were greatly inhibited in the group pretreated with nimotuzumab.On the contrary,the suppressed p27 expression by radiation was substantially elevated after pretreatment with nimotuzumab.Conclusion Our results revealed that the possible mechanism of nimotuzumab enhancing the lung cancer cell radiosensitivity was that nimotuzumab inhibited the radiation-induced activation of EGFR,which directly inhibited the activation of its downstreaming AKT.On the other hand,nimotuzumab increased the expression of p27,which is associated with the redistribution of cell cycle.

Key words: Nimotuzumab, EGFR, Lung cancer, Radiosensitivity, Radiotherapy