Lipopolysaccharide induces inflammation and facilitates lung metastasis in a breast cancer model via the prostaglandin E2-EP2 pathway.

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 cyclooxygenase­2 were significantly greater in the lungs of LPS­treated mice, as compared with those in control mice threated with phosphate­buffered saline. Blood vessel density was also markedly increased in the LPS­treated mice. These increases were reversed by treatment with celecoxib. In vitro, the protein expression levels of VEGF produced by the PGE2­treated cells were significantly increased in a concentration­dependent manner. In addition, the production of VEGF was increased in response to treatment with the PGE2 receptor (EP2) agonist ONO­AE1­259­01; 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.

Celecoxib attenuates cachectic events in mice by modulating the expression of vascular endothelial growth factor.

Chronic inflammation is one of the main symptoms of cancer cachexia, and cyclooxygenase 2 inhibitors, such as celecoxib, may be beneficial in counteracting the major symptoms of this syndrome. In the current study, celecoxib was orally administered to BALB/c male mice with colon 26 adenocarcinoma. Tumor growth, survival rate, body weight and food intake of the mice with cancer cachexia were recorded during the experiments. The host inflammatory response was assessed by morphological observations and hematoxylin-eosin staining. The serum levels of vascular endothelial growth factor (VEGF), granulocyte-macrophage colony-stimulating factor, interleukin-6 and tumor necrosis factor-α in mice with cancer cachexia were measured by ELISA. Celecoxib administration attenuated the decline in body weight and food intake of mice with cancer cachexia, and improved the survival rate of cachectic mice. Erythrocyte counts and hemoglobin concentration significantly increased in cachectic mice receiving celecoxib compared with control cachectic mice. Notably, celecoxib administration significantly reduced the serum level of VEGF in mice with colon 26 adenocarcinoma, and the cachectic events were also relieved by treatment with a VEGF antibody. The cyclooxygenase 2 inhibitor celecoxib produced positive therapeutic effects in mice with cancer cachexia. This function was regulated at least partly by downregulation of serum levels of VEGF.

Systemic inflammation promotes lung metastasis via E-selectin upregulation in mouse breast cancer model.

Systemic inflammation might modulate the microenvironment in the lungs and promotes metastasis. E-selectin, an inflammation inducible endothelial cell adhesion molecule, has been reported to play an important role in homing metastatic cancer cells. To study the effects of E-selectin expression induced by systemic inflammation on breast cancer metastasis, we first treated BALB/c mice with lipopolysaccharide (LPS) to induce systemic inflammation. Pulmonary tissues were analyzed by wet/dry ratio, hematoxylin and eosin (H&E) staining and immunohistochemistry. Then 4T1 cells were injected via tail vein. Lung surface metastasis was counted and detected by histological analysis. LPS-induced E-selectin expression and tumor cells adhesion were assessed by western blotting and immunofluorescence. The circulating levels of proinflammatory cytokines in sera were evaluated by ELISA. Our results showed that a significant increase in breast cancer metastasis to lungs was observed in LPS-treated mice vs. the PBS-treated mice, accompanying with an increased E-selectin expression in pulmonary tissue of LPS-treated mice. In vitro studies showed a significant elevation of E-selectin production in MPVECs which enhanced the adhesion activity of 4T1 cells. Treatment with anti-E-selectin antibody significantly reduced the development of metastasis in vivo, and significantly reduced the adhesion of 4T1 cells to MPVECs in vitro. Our results suggest that systemic inflammation may increase the expression of E-selectin which mediated the lung metastasis of breast cancer in mouse model.

Primary tumor regulates the pulmonary microenvironment in melanoma carcinoma model and facilitates lung metastasis.

PURPOSE: Lung is a common site for the occurrence of melanoma metastasis, the mechanism by which primary melanoma affects the lungs before tumor cells arrival is poorly understood. The aim of this study was to explore lung microenvironment response to primary melanoma in the premetastatic phase. METHODS: Melanoma cells (B16) were implanted into the Balb/c mice back, pulmonary inflammation response was analyzed by wet/dry ratios and H&E staining, the relationship between inflammation cells and metastatic foci was analyzed by bone marrow transplant mouse model, pulmonary vasculature was further analyzed by whole mount staining, and the circulating levels of proinflammatory cytokines in sera were evaluated by mouse cytokine array. RESULTS: In the premetastatic stage, significant inflammation response in lungs was induced by a distant primary melanoma, inflammation cells colonize in premetastatic sites before tumor cells arrived, and the sites of inflammation cells clusters are tumor metastasis sites. VEGF, M-CSF and TNF-α may be the underlying factors responsible for the increased metastasis in the B16-bearing mice. Treatment with celecoxib had effects on inflammation response and reduced cancer metastasis. CONCLUSIONS: In the premetastatic phase, the melanoma induces pulmonary inflammation response, changes the lung environment and then facilitates lung metastasis. Thus, inhibition of lung inflammation may provide potential targets for the prevention of metastasis.

Tumor-derived vascular endothelial growth factor (VEGF)-a facilitates tumor metastasis through the VEGF-VEGFR1 signaling pathway.

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 VEGF-induced 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.