HIF-1?/ETS-1 Positive Feedback Pathway Induces Endothelial Transformation In Lung Cancer Cell-new Mechanism Research Of Resistance To Bevacizumab

Lung cancer is a malignant tumor with the highest morbidity and mortality in our country.Approximately,70%of the newly diagnosed patients are at an advanced stage.Radiotherapy and Chemotherapy have entered into a plateau to prolong the survival of patients with lung cancer.The appearance of targeted therapy has brought a dawn for them.As the targeted antiangiogenic drug of VEGF firstly approved by FDA,Bevacizumab is usually used with chemotherapy drugs to improve the therapeutic effect.However,in clinic,Bevacizumab resistance often leads to the treatment failure phenomenon.Therefore,it is urgent to further elucidate the drug-resistance mechanism of Bevacizumab.The newest studies have found a special type of endothelial cell in tumor blood vessels,tumor endothelial-like cell,which is transformed from tumor cells.It has not only the general characteristics of ordinary endothelial cells,and surprisingly also inherits the characteristics of the characteristic mutation,genomic instability and frequent resistance of tumor cells.The production,survival and function of this kind of tumor endothelial-like cells have no dependence upon the VEGF-VEGFR signal.The above characteristics of the tumor endothelial-like cells may be the important reasons for antiangiogenic therapy resistance,and the transformation mechanism is unclear.Studies have found that hypoxia environment could promote the transformation of tumor cells to endothelial-like cells,and the key factor HIF-1could activate the ETS-1 promoter,While the latter regulate downstream multiple angiogenesis related genes,specificity promote tumor angiogenesis and endothelial-like cell growth.Therefore we speculate that hypoxia can induce the transformation of lung cancer cells to lung endothelial-like cells via the HIF-1?/ETS-1 pathway to promote angiogenesis in lung cancer and lead to Bevacizumab resistance.This study found that the expressions of HIF-1? and ETS-1 were positively correlated in non-small cell lung cancer patients,and the tumor tissue with both high expression is in rich blood supply,advanced stage and poor prognosis.The results preliminary prompt HIF-1? and ETS-1 are closely related to the tumor angiogenesis.Further in vivo experiments found that lung cancer cells could express the biological makers of endothelial cells under the condition of hypoxia,own the biological characteristics of endothelial cells,and form the lung cancer endothelial-like cells.This kind of lung endothelial-like cell had the resistance against Bevacizumab(Bevacizumab had an apoptosis rate of 75%on common tumor endothelial cells and 25%on lung cancer endothelial-like cells).The in vivo researches found that the transplanted tumors which from hypoxia lung cancer cells were in rapidly growth,rich blood supply and not sensitive to Bevacizumab therapy.We further analyzed the relationship between HIF-1?/ETS-1 signaling pathway and the transformation from lung cancer to lung endothelial-like cells under hypoxia condition.The resutls found that,compared with VEGF,ETS-1 expression level was more sensitive to hypoxia environment,and the key effect factor of hypoxia HIF-1? could effectively activate the ETS-1 promoter and protein expression.under the condition of normoxia,the upregulation of the expression of the lung cancer cell line ETS-1 could promote the endothelialization of lung cancer endothelial-like cells and promote lung cancer angiogenesis,resulting in Bevacizumab resistance(A549:ETS-lover-expression group:22.3%,ETS-1over-expression+Avastin group:27.13%;H460:ETS-1 over-expression group:12.68%,ETS-1over-expression+Avastin group:15.93%,P>0.05).The downregulation of the expression of the hypoxic cell line ETS-1 could reverse the endothelialization of lung cancer cells to inhibit lung cancer angiogenesis and enhance the antiangiogenic effect of Bevacizumab(A549:Hypoxia+Avastin group:15.3%,Hypoxia+SiRNA-ETS-1+Avastin group:36.15%;H460:Hypoxia+Avastin group:22.02%,Hypoxia+SiRNA-ETS-1+Avastin group:49.81%,P<0.05).In addition this study also found that under the hypoxia condition,the ETS-1 transcription factor could activate the PI3K/AKT/mTOR pathway,which could further strengthen endothelial-like changes of lung cancer cells,and inhibition of PI3K/AKT/mTOR pathway could reverse the process of lung endothelial-like transformation effectively.These results suggested that the positive feedback pathway of HIF-1?/ETS-1 mediated the hypoxia induced transformation of lung cancer cells to lung endothelial-like cells and mediated Bevacizumab resistance.The study enriches the related study on the new mechanisms and signaling pathway of the resistance against antiangiogenic therapy and also provides a new target for clinical treatment of lung cancer to finally provide new inspiration for the marketing of new clinical drugs.