Abstract
Objective To determine the effects of endostatin on the expression of vascular endothelial growth factor receptor-2(VEGFR-2) in non-small cell lung cancer cells (human A549 lung adenocarcinoma cells and human Calu-1 lung carcinoma cells), and to investigate the possible mechanisms underlying its radiosensitizing effect. Methods The CCK8 method was used to determine the inhibitory effect of endostatin on cell proliferation and calculate the drug concentration that caused a 20% reduction in cell proliferation within 24 h (IC20). RT-PCR and Western blot assays were used to assess the mRNA and protein expression of VEGFR-2, proteins within its related signaling pathways, and HIF-1α, respectively. The radiosensitivity of cells in each group was determined by colony formation assay; cell apoptosis and cell cycle distribution were determined by flow cytometry. Comparison of mean values between multiple samples was made by one-way analysis of variance, and comparison of mean values between two samples was made by t test. Results Endostatin significantly inhibited the proliferation of Calu-1 cells (F=50.36, P<0.01) with an IC20 of 296.5 μg/ml; the mRNA and protein expression of VEGFR-2 and HIF-1α was also significantly inhibited in endostatin-treated Calu-1 cells (F=25.43, 10.44, all P<0.05). Moreover, the phosphorylation of Akt, ERK1/2, and p38 was significantly reduced in endostatin-treated Calu-1 cells (F=2.89, 0.24, 1.09, all P<0.05). The radiosensitivity enhancement ratios for Calu-1 cells and A549 cells were 1.38 and 1.09, respectively. Endostatin significantly induced apoptosis (F=44.15, P<0.01) and G2/M blockage (F=104.24, P<0.01) in Calu-1 cells. Conclusions Endostatin induces apoptosis and enhances radiosensitivity in Calu-1 cells with high expression of VEGFR-2, but it has a limited impact on A549 cells with low expression of VEGFR-2. Key words: Endostatin; A549 cell line; Calu-1 cell line; Vascular endothelial growth factor receptor 2; Radiosensitivity
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