The radiosensitivity effects of apatinib on the esophageal cancer cell line ECA-109 and its stem-like cells

Abstract

Objective To evaluate the radiosensitivity effects of apatinib on the esophageal cancer cell line ECA-109 and its cancer stem-like cells, and to investigate the underlying mechanism. Methods A serum-free medium (SFM) was used to culture esophageal cancer stem cell line ECA-109 and enrich the esophageal stem-like spheres. ECA-109 and its stem-like cells were divided into control group, drug treatment group, radiation group and drug plus radiation group. Cell proliferations of ECA-109 and its stem-like cells were detected with CCK-8 method. The concentration of vascular endothelial growth factor(VEGF) in the cell culture medium was determined by enzyme linked immunosorbent assay(ELISA). Cell cycle and apoptosis were detected by flow cytometry method. The expressions of CHK2 and P-STAT3 proteins were detected by Western blot assay. Results With the administration with apatinib for 24, 48 and 72 h, the half of the inhibitory concentration (IC50) of ECA-109 stem-like cells was significantly higher than that of the parent cells (t=8.17, 9.29, 18.85, P<0.05) in a time dependent manner (parental cells: r2=0.94-0.97, P<0.05; stem-like cells: r2=0.94-0.98, P<0.05). After administration with different concentrations of apatinib (parental cells: 10 and 20 μmol/L; stem-like cells: 30 and 40 μmol/L) combined with different dose of X-rays (6 and 8 Gy), the proliferations of ECA-109 and its stem-like cells were significantly (t=5.20-39.68, P<0.05) inhibited compared with radiation alone group. VEGF secretion from both ECA-109 cells and its stem like cells were significantly decreased in different manner (t=7.45, P<0.05). Compared with control group, the cell apoptosis rate and the percentages of cells in G2/M phase were significantly increased in drug plus radiation group (t=8.83, 11.59, P<0.05), and the expressions of CHK2 and P-STAT3 were decreased in drug group (t=3.36, 4.10, P<0.05). Compared with radiation group, the expressions of CHK2 and P-STAT3 were decreased in drug plus radiation group (t=9.05, 2.36, P<0.05). Conclusions Apatinib enhanced the radiosensitivity of ECA-109 cells and its stem-like cells, which was much more effective on ECA-109 cells and may be related to the radiation-induced inhibition of VEGF signal pathway that can further inhibit cell proliferation, promote cell apoptosis and induce cell cycle redistribution. The higher intrinsic level of VEGF protein may contribute to radioresistance of ECA-109 stem-like cells. Key words: Esophageal cancer; Apatinib; Vascular endothelial growth factor; Radiation sensitization