Endostar Synergizes with Radiotherapy to Inhibit Angiogenesis of Cervical Cancer in a Subcutaneous Xenograft Mouse Model

Background: To investigate the synergic effect and underlying mechanism of Endostar, a recombinant human endostatin used for antiangiogenesis, in radiotherapy for cervical cancer.Methods: The Cell Counting Kit-8 (CCK-8) assay and plate cloning experiment were first employed to analyze the proliferation of HeLa and SiHa cervical cancer cells and human umbilical vein vascular endothelial cells (HUVECs). Flow cytometry was used to detect apoptosis and cell cycle progression. A tube formation assay was used to assess angiogenesis in vitro. The expression of gamma H2A histone family member X (-y-H2AX) and activation of the vascular endothelial growth factor receptor (VEGFR) signaling pathway were detected by immunofluorescence and western blotting, respectively. In a HeLa xenograft model, tumor tissue expression of CD31 and alpha smooth muscle actin and serum expression of VEGF-A were detected by immunohistochemistry (IHC) and enzyme-linked immunosorbent assay, respectively.Results: The CCK-8 and plate cloning assays showed that Endostar and radiotherapy synergistically inhibited the growth of HUVECs but not HeLa and SiHa cells. The flow cytometric results showed that Endostar only promoted radiotherapy-induced apoptosis and G2/M phase arrest in HUVECs (p < 0.05). Endostar combined with radiotherapy also significantly inhibited tube formation by HUVECs (p < 0.05). Furthermore, Endostar inhibited the radiotherapy-induced expression of -yH2AX (p < 0.05) and phosphorylation of VEGFR2/PI3K/AKT/DNA-PK in HUVECs (p < 0.05). IHC showed that Endostar enhanced the inhibitory effect of radiotherapy on the microvessel density in xenograft tumor tissues (p < 0.05), as well as serum VEGF-A expression (p < 0.05). The tumor volume in the combination therapy groups (1200 mm3) was significantly lower than in the control group (2500 mm3; p < 0.05).Conclusions: Our findings provide experimental evidence and a theoretical basis for the application of Endostar in combination with irradiation for anti-cervical cancer treatment.