The Mechanism Of IGF-1R Inhibition Enhances Radiosensitivity In Nasopharyngeal Carcinoma Cells

Objective : To explore the mechanism of IGF-1R inhibitor OSI-906 enhance the radiosensitivity in nasopharyngeal carcinoma cell line.Methods:The basic levels of p IGF-1R examined by Western blot using 5 cell lines of nasopharyngeal carcinoma cells;Then,we examined the effect of IGF,OSI-906 and the combination of IGF-1 with OSI-906 on cell proliferation by MTT assay;Then,the activation of AKT and ERK1/2 which are the downstream of IGF-1R,were detected after treatment with irradiation,IGF-1,OSI-906 alone,or the combination of IGF-1 with OSI-906 and combination of OSI-906 with irradiation.The cell-cycle arrest and apoptosis in NPC cell after various treatments were detected by Flow Cytometry.Clonogenic survival assays were also performed after treatments by IGF-1,OSI-906 and the combination of irradiation with OSI-906;Finally,the effect of DNA damage was assessed by examining gH2 AX protein level and gH2 AX foci assay.All the quantitate data were statistically analyzed with GraphPad Prism 5 software.Results: The expression levels of pIGF-1R were varied in each NPC cell line.Moderate levels of p IGF-1R existed in CNE-2 and SUNE-1 cells,and therefore were selected as the research object.IGF-1 enhances NPC cells proliferation and OSI-906 significantly inhibit NPC cells proliferation.Meanwhile,OSI-906 antaagonized the effect of IGF-1.IGF-1 and IR induced activation of IGF-1R,as well as,pAKT,pERK obviously,and OSI-906 induced suppresssesion of IGF-1R,reduced the expression level of p IGF-1R,pAKT,pERK.Treatment with OSI-906 or IR alone led to a few cells under G2/M arrest and the combination of OSI-906 with IR significantly increased percentage of cells in G2/M phase.Treatment with OSI-906 or IR alone could induce apoptosis in NPC cells when compared with untreated cells and the combination of OSI-906 with IR induced a more cells undergoing apoptosis.Clonogenic survival assays showed that IGF-1 increased the survival fraction of NPC cells after IR,whereas the OSI-906 treatment significantly reduced the survival fraction and reversed the effect of IGF-1 on the radiation in NPC cells.At the same time,OSI-906 reverse the effect of IGF-1.In addition,OSI-906 in combination with X-ray increases the expression of gH2 AX,which is the typical marker of double-strain DNA damage compared with enposure to IR,IGF-1 in combination with X-ray reduced the expression of gH2 AX,increased the repair of DNA damage,whereas the administration of OSI-906 reversed the effect induced by IGF-1.Conclusion: OSI-906 inhibited multiple signaling pathways,reduced the repair of DNA damage,changed the cell cycle,increased the cell apoptosis,induced genome instability and reversed the radioresistance induced by IGF-1 in NPC cells that might be the potential mechanisms to enhance the radiosensitivity in NPC cells.