Tumor endothelial cells (TECs) are therapeutic targets in anti-angiogenic therapy. Contrary to the traditional assumption, TECs can be genetically abnormal and might also acquire drug resistance. In this study, mouse TECs and normal ECs were isolated to investigate the drug resistance of TECs and the mechanism by which it is acquired. TECs were more resistant to paclitaxel with the up-regulation of multidrug resistance (MDR) 1 mRNA, which encodes the P-glycoprotein, compared with normal ECs. Normal human microvascular ECs were cultured in tumor-conditioned medium (CM) and became more resistant to paclitaxel through MDR1 mRNA up-regulation and nuclear translocation of Y-box-binding protein 1, which is an MDR1 transcription factor. Vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and Akt were activated in human microvascular ECs by tumor CM. We observed that tumor CM contained a significantly high level of VEGF. A VEGFR kinase inhibitor, Ki8751, and a phosphatidylinositol 3-kinase-Akt inhibitor, LY294002, blocked tumor CM-induced MDR1 up-regulation. MDR1 up-regulation, via the VEGF-VEGFR pathway in the tumor microenvironment, is one of the mechanisms of drug resistance acquired by TECs. We observed that VEGF secreted from tumors up-regulated MDR1 through the activation of VEGFR2 and Akt. This process is a novel mechanism of the acquisition of drug resistance by TECs in the tumor microenvironment.

Oral leukoplakia (OL) is a clinically diagnosed preneoplastic lesion of the oral cavity with an increased oral cancer risk. However, the risk of malignant transformation is still difficult to assess. The objective of the present study was to examine the expression patterns of aldehyde dehydrogenase 1 (ALDH1) and podoplanin in OL, and to determine their roles in predicting oral cancer development. In the present study, the expression patterns of ALDH1 and podoplanin were determined in samples from 79 patients with OL. The association between protein expression and clinicopathological parameters, including oral cancer-free survival, was analyzed during a mean follow-up period of 3.4 years. Expression of ALDH1 and podoplanin was observed in 61 and 67% patients, respectively. Kaplan-Meier analysis demonstrated that the expression of the proteins was correlated with the risk of progression to oral cancer. Multivariate analysis revealed that expression of ALDH1 and podoplanin was associated with 3.02- and 2.62-fold increased risk of malignant transformation, respectively. The malignant transformation risk of OL was considerably higher in cases with expression of both proteins. Point-prevalence analysis revealed that 66% of patients with co-expression of ALDH1 and podoplanin developed oral cancer. Taken together, our data indicate that ALDH1 and podoplanin expression patterns in OL are associated with oral cancer development, suggesting that ALDH1 and podoplanin may be useful biomarkers to identify OL patients with a substantially high oral cancer risk.

Recent studies have demonstrated a relationship between oral bacteria and systemic inflammation. Endothelial cells (ECs), which line blood vessels, control the opening and closing of the vascular barrier and contribute to hematogenous metastasis; however, the role of oral bacteria‐induced vascular inflammation in tumor metastasis remains unclear. In this study, we examined the phenotypic changes in vascular ECs following Streptococcus mutans (S. mutans) stimulation in vitro and in vivo. The expression of molecules associated with vascular inflammation and barrier‐associated adhesion was analyzed. Tumor metastasis was evaluated after intravenous injection of S. mutans in murine breast cancer hematogenous metastasis model. The results indicated that S. mutans invaded the ECs accompanied by inflammation and NF‐κB activation. S. mutans exposure potentially disrupts endothelial integrity by decreasing vascular endothelial (VE)‐cadherin expression. The migration and adhesion of tumor cells were enhanced in S. mutans‐stimulated ECs. Furthermore, S. mutans‐induced lung vascular inflammation promoted breast cancer cell metastasis to the lungs in vivo. The results indicate that oral bacteria promote tumor metastasis through vascular inflammation and the disruption of vascular barrier function. Improving oral hygiene in patients with cancer is of great significance in preventing postoperative pneumonia and tumor metastasis.

Epidemiological relationships between cancer and cardiovascular diseases have been reported, but a molecular basis remains unclear. Some proteoglycans that strongly bind low‐density‐lipoprotein (LDL) are abundant both in atherosclerotic regions and in high metastatic‐tumor tissue. LDL retention is crucial for the initiation of atherosclerosis, although its contribution to malignancy of cancer is not known. In our study, we show the importance of the accumulation of LDL in tumor metastasis. We demonstrated that high metastatic‐tumor tissue contains high amounts of LDL and forms more oxidized LDL (ox‐LDL). Interestingly, lectin‐like ox‐LDL receptor 1 (LOX‐1), a receptor for ox‐LDL and a recognized key molecule for cardiovascular diseases, was highly expressed in tumor endothelial cells (TECs). Neutrophils are important for ox‐LDL formation. Since we observed the accumulation and activation of neutrophils in HM‐tumors, we evaluated the involvement of LOX‐1 in neutrophil migration and activation. LOX‐1 induced neutrophil migration via CCL2 secretion from TECs, which was enhanced by ox‐LDL. Finally, we show genetic manipulation of LOX‐1 expression in TECs or tumor stroma tended to reduce lung metastasis. Thus, the LOX‐1/ox‐LDL axis in TECs may lead to the formation of a high metastatic‐tumor microenvironment via attracting neutrophils.

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