The Expression Of Forkhead Box M1(FOXM1) And Its Role In Cisplatin-resistance In Non-small Cell Lung Cancer(NSCLC)

Objective and background: Lung cancer is the leading cause of cancer-related death in the world. Cis-Diaminodichloroplatinum (DDP, cisplatin) is the foundation of the first line chemotherapy in advanced non-small cell lung cancer (NSCLC). However, treatment with this agent is characterized by resistance, both acquired and intrinsic. Forkhead box M1(FoxM1)transcription factor is essential for progression into DNA replication and mitosis and has been shown to play important roles in cell proliferation and apoptosis. Upregulation of FoxM1 expression is closely associated with the occurrence, development and prognosis in various human cancers. New researches confirm that FoxM1 are involved in the DNA damage and apoptosis pathway, which indicates the role of FoxM1 in the multidrug resistance. In this study, we explored the association between FoxM1 and cisplatin resistance of NSCLC from the levels of histopathology and cell lines. These studies provide a strong rationale for the development of FoxM1 based therapeutic strategies aiming to overcome NSCLC cell drug resistance.Methods: (1) Immunohistochemistry was used to detect the expression of FoxM1 in NSCLC. The correlation among the expression of FoxM1 and clinicopathalogic variables, overall survival and sensitivity of cisplatin was analyzed. (2)The drug resistance of A549/DDP cells was evaluated using CCK-8 assay. The FoxM1 expression level of the two cell lines was analyzed using real time PCR and western blot. (3) We utilized RNA interference to knockdown FoxM1 expression in A549/DDP cells and further assessed the cell viability using CCK-8 assay. (4) When overexpressed FoxM1, we constructed eukaryotic expressing vector of FoxM1 gene and transfected A549 cells. The cell viability was analyzed.Results: (1) The expression of FoxM1 protein was detected in the nuclei and cytoplasm of the tumor cells. The positive expression rate of FoxM1 was 36.76%. The expression levels of FoxM1 in advanced cancer stage were significantly higher than those in early stage (P=0.001). The Kaplan-Meier survival curves revealed that there is a significantly negative relation between the expression of FoxM1 and survival time(P=0.001). The Cox multivariate analysis demonstrated that the FoxM1 expression was an independent poor prognostic factor (P=0.039). Among the patients with stageâ…¢B andâ…£who received platinum-based regimen as the first line chemotherapy, the FoxM1 expression level in responding cases was significantly lower than resistance ones(P=0.002). (2) Compared to A549 cells, the FoxM1 mRNA and protein levels of A549/DDP cells incereasd remarkably. (3)When inhibiting the expression of FoxM1 by RNA Interference technology, the sensitivity to cisplatin was enhanced. The IC50 decreased in A549/DDP-siFoxM1 by 76.4% than the control group (P<0.01). (4)When up-regulating the expression of FoxM1 by establishing FoxM1-overexpressing cell models, we observed the opposite phnomenon. The IC50 increased in FoxM1b-pcDNA3.1(+)-A549 by 313% than the control group (P<0.01).Conclusion: The positive expression rate of FoxM1 in NSCLC is associated with advanced pathologic stage and is negatively correlated with prognosis and the chemosensitivity to cisplatin. The FoxM1 expression level in A549/DDP cells in higher than A549 cells. FoxM1 depletion sensitized A549/DDP cells to cisplatin suggesting critical roles of FoxM1 in chemoresistance to cisplatin and raising the possibility of FoxM1 depletion as a promising approach to lung cancer therapy.