FoxM1 Confers To Stemness And Participates In Resistance To Cisplatin In Osteosarcoma

Purpose:Osteosarcoma is the most common malignancy in adolescents and children with the exception of leukemia and lymphoma.Adjuvant chemotherapy is still the main treatment in addition to surgical treatment.However,resistance to chemotherapeutic drugs reduces the therapeutic effect and affects the prognosis of patients.Cancer stem cells have increased resistance to chemotherapy drugs.FoxM1 is a vital pro-proliferative factor and regulates the cell cycle.Studies have shown that increasing FoxM1 expression can enhance drug resistance,and inhibiting its expression reduces drug resistance.Therefore,we explored whether FoxM1 is involved in the resistance of osteosarcoma cells to cisplatin by promoting tumor stem cells.Whether FoxM1inhibitor can improve the drug resistance of osteosarcoma and increase the sensitivity of cisplatin to drugs.Methods:1. Stably over-expressed FoxM1 cell MG-63F and empty vector control cell MG-63V were established by lentiviral transfection.2. MTT assay was used to detect the drug sensitivity to cisplatin in OS cells.3.The expression of FoxM1 and tumor stem cell-like markers Sox-2,Oct-4 and Nanog were detected by Western blot analysis.4.Microsphere formation ability was measured using a serum-free culture suspension cloned assay.5.The effect of FoxM1 inhibitor Thiostrepton on expression of tumor stem cell-like markers,microsphere formation ability and cisplatin drug sensitivity were detected.6.59 cases of osteosarcoma specimens archived from May 2008 to December 2016were collected from the Department of Pathology of the Affiliated Hospital of Anhui Medical University and clinical pathological data were collected;Sox-2 expression in osteosarcoma tissue was measured by immunohistochemistry（IHC）;Making Kaplan-Meier survival curve to analyze the relationship between Sox-2 expression and clinical prognosis;Spearman rank sum test was used to test the correlation between FoxM1 expression and Sox-2 expression in osteosarcoma.Results:1.MG-63R were stably grew and passaged on a concentration of 2μg/m L cisplatin.Compared with the parental cells,the IC₅₀ of MG-63R increased from 1.27 to 7.36,the expression of FoxM1 was significantly increased.2. Compared with the parental cells,tumor stem cell-like markers,Sox-2,Oct-4 and Nanog in MG-63R was significantly increased;the number of suspended microsphere was also significantly increased.3. Overexpressing FoxM1 cell MG-63F were successfully constructed and the expression level of FoxM1 was significantly increased.After treatment with 4μmol/L thiostrepton in MG-63F,the expression of FoxM1 was significantly decreased.4. Compared with the control group,The expression of tumor stem cell-like markers were significantly increased.The average number of microspheres were increased from14 to 25.MG-63F were more resistant to cisplatin and the IC50 was increased from0.96 to 31.23.5. After treatment with 4μmol/L thiostrepton in MG-63F,the expression of FoxM1 was significantly decreased and the sensitivity to cisplatin was significantly increased;both the expression of tumor stem cell-like markers and the number of microspheres were significantly reduced.6. There was no correlation between FoxM1 expression and Sox-2 expression and clinicopathological features such as gender,age,tumor size,and location.Compared with stageⅠand stageⅡpatients,the high positive rate of Sox-2 was significantly higher in stageⅢpatients,and the difference was statistically significant（P<0.05）.The survival curve showed that the higher the Sox-2 expression level,the lower the overall survival rate（P<0.05）.Sox-2 expression level was positively correlated with FoxM1 expression level.Conclusion:1.Overexpression of FoxM1 may confer to cisplatin resistance by promoting tumor stemness in osteosarcoma cells.2.FoxM1 inhibition may sensitize osteosarcoma drug-resistant cells to cisplatin by reversing tumor stemness.