Inflammation is a potent promoter of tumor metastasis. The aim of the present study was to explore the function of systemic inflammation in the formation of lung metastasis of breast cancer cells in a mouse model. BALB/c mice were injected intraperitoneally with lipopolysaccharide (LPS) in order to establish an inflammatory animal model and 4T1 murine breast cancer cells were injected through the tail vein to induce lung metastasis. The levels of proinflammatory cytokines were evaluated by ELISA. Metastases on the surface of the lungs were counted and histologically analyzed by hematoxylin and eosin staining. Angiogenesis in the lungs was examined by CD31 immunofluorescence. Mouse pulmonary endothelial cells (MPVECs) were isolated and used to assay endothelial tube formation and determine the protein expression levels of vascular endothelial growth factor (VEGF) in vitro. Serum levels of VEGF and prostaglandin E2 (PGE2), the number and size of metastatic lesions, and the expression levels of cyclooxygenase‑2 were significantly greater in the lungs of LPS‑treated mice, as compared with those in control mice threated with phosphate‑buffered saline. Blood vessel density was also markedly increased in the LPS‑treated mice. These increases were reversed by treatment with celecoxib. In vitro, the protein expression levels of VEGF produced by the PGE2‑treated cells were significantly increased in a concentration‑dependent manner. In addition, the production of VEGF was increased in response to treatment with the PGE2 receptor (EP2) agonist ONO‑AE1‑259‑01; however, this increase was abrogated by treatment with AH6809, an EP2 receptor antagonist. Treatment with PGE2 or VEGF alone promoted the tube formation of MPVECs and this effect was reversed by treatment with celecoxib. These results demonstrated that PGE2 may regulate the release of VEGF by MPVECs through the EP2 receptor pathway and thereby promoted pulmonary angiogenesis and breast cancer metastasis in a mouse model.
Abstract. Vascular endothelial growth factor (VEGF) and its receptors are involved in carcinogenesis, invasion and tumor angiogenesis, but the underlying mechanism by which VEGF promotes tumor metastasis is poorly understood. In this study, we show that in cancer patients high expression of VEGF is correlated with metastasis, and anti-VEGF treatment (bevacizumab) has clinical effects on tumor metastasis. Two human lung carcinoma cell lines (A549 and SPCA1 cells) with distinct VEGF expression were injected intravenously through the lateral tail vein of SCID mice and a murine model was developed. We investigated the association between the expression of VEGF and tumor metastasis by microvessel density, immunohistochemistry and whole mount staining. At sacrifice, in the high VEGF expression A549 cell line group, the induced tumor was distinctively larger in size and multiple metastatic lesions were found in lung tissues. Two specific neutralizing anti-mouse VEGFR1 and VEGFR2 antibodies were administered to the tumor-bearing mice; anti-VEGFR1, but not anti-VEGFR2 treatment produced inhibitive effects on VEGFinduced tumor metastasis. These findings demonstrate that the VEGF-VEGFR1 signaling pathway is crucial for tumor metastasis and the blockade of VEGF-VEGFR1-induced metastasis may provide a novel approach for the prevention and treatment of tumor metastasis.
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