ABSTRACT
Objective To investigate the effect of signal transducer and activator of transcription-3(STAT-3)-mediated non-dependent vascular endothelial growth factor receptor-2(VEGFR-2) pathway on the radiosensitivity of non-small cell lung cancer (NSCLC) cells and its possible mechanism.Methods NSCLC cells were divided into control group, apatinib (VEGFR-2 inhibitor) group, apatinib+S3I-201(STAT-3 inhibitor) group, radiation (RT) group, RT+apatinib group, and RT+apatinib+S3I-201 group.Q-PCR and Western blot were used to measure the mRNA and protein expression of VEGFR-2, STAT-3, other proteins involved in the signaling pathway, hypoxia-inducible factor 1α(HIF-1α), and cyclin D1.The cellular radiosensitivity was determined by colony-forming assay and cell apoptosis and cell cycle distribution were evaluated by flow cytometry.Results For Calu-1 cells, there was no significant difference in the expression of VEGFR-2 mRNA and STAT-3 mRNA between the apatinib group and the control group (P>0.05);the apatinib group had significantly lower expression of HIF-1α mRNA and cyclin D1 mRNA than the control group (P<0.05);the apatinib+S3I-201 group had significantly lower mRNA and phosphorylated protein expression of VEGFR-2, STAT-3, and related downstream target proteins than the control group (F=304.54, P<0.01;F=118.99, P<0.01, F=144.34, P<0.01;F=529.66, P<0.01);compared with the control group, the apatinib+S3I-201 group and the apatinib group showed increases in apoptosis rate and proportion of cells in G2+M phase, and the apatinib+S3I-201 group had significantly greater increases than the apatinib group (F=72.37, P<0.01).Compared with Calu-1 cells, the radiosensitizing effect of apatinib on A549 cells was limited (SER[sensitizer enhancement ratio]=1.39).The radiosensitizing effect of apatinib+S3I-201 on A549 cells was significantly higher than that of apatinib (SER:1.72 vs.1.39, P=0.000).Conclusions The inhibition of STAT-3 can enhance the radiosensitivity of NSCLC cells.When VEGFR-2 is inhibited by apatinib, activated STAT-3 regulates the expression of cyclin D1 directly or indirectly to affect the radiosensitivity of NSCLC cells.The inhibition of VEGFR-2 and STAT-3 has a good radiosensitizing effect on NSCLC cells.
ABSTRACT
Hypoxia results from long-term anti-angiogenic therapy and can stimulate hypoxia-inducible factors (HIFs). HIF-induced hy-poxia signaling is involved in various steps in tumor invasive-metastatic cascade. On the one hand, HIFs regulate epithelial-mesenchy-mal transition. On the other hand, the characteristics of pericytes around vessels and the links among endothelial cells can change;thus, tumor cells can more easily intravasate into blood vessels, survive in peripheral blood, and then reach specific organs, ultimately resulting in metastasis. This review discusses the emerging mechanisms of long-term anti-angiogenic therapy and the occurrence of metastasis.