miRNA-1246 in extracellular vesicles secreted from metastatic tumor induces drug resistance in tumor endothelial cells.

Tumor endothelial cells (TECs) reportedly exhibit altered phenotypes. We have demonstrated that TECs acquire drug resistance with the upregulation of P-glycoprotein (P-gp, ABCB1), contrary to traditional assumptions. Furthermore, P-gp expression was higher in TECs of highly metastatic tumors than in those of low metastatic tumors. However, the detailed mechanism of differential P-gp expression in TECs remains unclear. miRNA was identified in highly metastatic tumor extracellular vesicles (EVs) and the roles of miRNA in endothelial cell resistance were analyzed in vitro and in vivo. In the present study, we found that treatment of highly metastatic tumor-conditioned medium induced resistance to 5-fluorouracil (5-FU) with interleukin-6 (IL-6) upregulation in endothelial cells (ECs). Among the soluble factors secreted from highly metastatic tumors, we focused on EVs and determined that miR-1246 was contained at a higher level in highly metastatic tumor EVs than in low metastatic tumor EVs. Furthermore, miR-1246 was transported via the EVs into ECs and induced IL-6 expression. Upregulated IL-6 induced resistance to 5-FU with STAT3 and Akt activation in ECs in an autocrine manner. These results suggested that highly metastatic tumors induce drug resistance in ECs by transporting miR-1246 through EVs.

Correlation between endothelial CXCR7 expression and clinicopathological factors in oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) impairs functionality and sensuousness resulting in poor quality of life. Biomarkers can predict disease trajectory and lead to effective treatments. Transcriptomics have identified genes that are upregulated in tumor endothelial cells (TECs) compared with normal endothelial cells (NECs). Among them, chemokine receptor 7 (CXCR7) is highly expressed in TECs of several cancers and involved in angiogenesis of TECs. However, levels of CXCR7 in OSCC blood vessels have not been fully investigated. In this study, we analyzed the correlation between CXCR7 expression in TECs and clinicopathological factors in OSCC. Immunohistochemistry for CXCR7 and CD34 was performed on 59 OSCC tissue specimens resected between 1996 and 2008 at Hokkaido University Hospital. CXCR7 expression in blood vessels was evaluated by the ratio of CXCR7+/CD34+ blood vessels. CXCR7 expression was 42% and 19% in tumor and non-tumor parts, respectively, suggesting that CXCR7 expression is higher in TECs than in NECs. CXCR7 expression in TECs correlated with advanced T-stage and cancer stage. Overall survival and disease-free survival rates were higher in low-expressing CXCR7 patients than in high-expressing. These results suggest that CXCR7 expression in blood vessels may be a useful diagnostic and prognostic marker for OSCC patients.

Tumor endothelial cells with high aldehyde dehydrogenase activity show drug resistance.

Tumor blood vessels play an important role in tumor progression and metastasis. We previously reported that tumor endothelial cells (TEC) exhibit several altered phenotypes compared with normal endothelial cells (NEC). For example, TEC have chromosomal abnormalities and are resistant to several anticancer drugs. Furthermore, TEC contain stem cell-like populations with high aldehyde dehydrogenase (ALDH) activity (ALDHhigh TEC). ALDHhigh TEC have proangiogenic properties compared with ALDHlow TEC. However, the association between ALDHhigh TEC and drug resistance remains unclear. In the present study, we found that ALDH mRNA expression and activity were higher in both human and mouse TEC than in NEC. Human NEC:human microvascular endothelial cells (HMVEC) were treated with tumor-conditioned medium (tumor CM). The ALDHhigh population increased along with upregulation of stem-related genes such as multidrug resistance 1, CD90, ALP, and Oct-4. Tumor CM also induced sphere-forming ability in HMVEC. Platelet-derived growth factor (PDGF)-A in tumor CM was shown to induce ALDH expression in HMVEC. Finally, ALDHhigh TEC were resistant to fluorouracil (5-FU) in vitro and in vivo. ALDHhigh TEC showed a higher grade of aneuploidy compared with that in ALDHlow TEC. These results suggested that tumor-secreting factor increases ALDHhigh TEC populations that are resistant to 5-FU. Therefore, ALDHhigh TEC in tumor blood vessels might be an important target to overcome or prevent drug resistance.

Vasohibin-1 as a Novel Prognostic Factor for Head and Neck Squamous Cell Carcinoma.

AIM: We evaluated the prognostic value of vasohibin-1 (VASH1) expression in head and neck squamous cell carcinoma. MATERIALS AND METHODS: Immunohistochemistry for VASH1 and cluster of differentiation 34 (CD34) was performed on 61 head and neck squamous cell carcinoma specimens. The association between VASH1 expression in the tumour and clinical outcomes was analyzed statistically. RESULTS: VASH1 staining in normal tissue adjacent to cancerous tissue was negative, whereas it was positive in tumour blood vessels and AE1/AE3 and Ki67-positive tumour cells. Therefore, we examined the association between VASH1 expression in the tumour and clinical outcomes. Patients with high VASH1 expression in tumour had significantly shorter disease-free survival and more frequently had lymph node recurrence than those with low VASH1 expression. CONCLUSION: These results suggest that VASH1 expression is associated with tumour progression and may be useful as a prognostic marker of head and neck squamous cell carcinoma.

Tumor endothelial cells express high pentraxin 3 levels.

It has been described that tumor progression has many similarities to inflammation and wound healing in terms of the signaling processes involved. Among biological responses, angiogenesis, which is necessary for tumor progression and metastasis, is a common hallmark; therefore, tumor blood vessels have been considered as important therapeutic targets in anticancer therapy. We focused on pentraxin 3 (PTX3), which is a marker of cancer-related inflammation, but we found no reports on its expression and function in tumor blood vessels. Here we showed that PTX3 is expressed in mouse and human tumor blood vessels based on immunohistochemical analysis. We found that PTX3 is upregulated in primary mouse and human tumor endothelial cells compared to normal endothelial cells. We also showed that PTX3 plays an important role in the proliferation of the tumor endothelial cells. These results suggest that PTX3 is an important target for antiangiogenic therapy.

Tumor angiogenesis--characteristics of tumor endothelial cells.

Tumor blood vessels provide nutrition and oxygen to the tumor, resulting in tumor progression. They also act as gatekeepers, inducing tumor metastasis. Thus, targeting tumor blood vessels is an important strategy in cancer therapy. Tumor endothelial cells (TECs), which line the inner layer of blood vessels of the tumor stromal tissue, are the main targets of anti-angiogenic therapy. Because new tumor blood vessels generally sprout from pre-existing vasculature, they have been considered to be the same as normal blood vessels. However, tumor blood vessels demonstrate a markedly abnormal phenotype that includes several important morphological changes. The degree of angiogenesis is determined by the balance between the angiogenic stimulators and inhibitors released by the tumor and host cells. Recent studies have revealed that TECs also exhibit altered characteristics which depend on the tumor microenvironment. Here, we review recent studies on TEC abnormalities and heterogeneity with respect to tumor progression and consider their therapeutic implications.

Inhibition of multidrug transporter in tumor endothelial cells enhances antiangiogenic effects of low-dose metronomic paclitaxel.

Tumor angiogenesis plays an important role in tumor progression and metastasis. Tumor endothelial cells (TECs) are a therapeutic target of antiangiogenic chemotherapy that was recently developed and is currently being investigated in the clinic with promising results. Low-dose chemotherapy, which is the long-term administration of relatively low doses of chemotherapeutic agents, has been proposed for targeting tumor angiogenesis in various types of cancers. Although the efficacy of low-dose chemotherapy has been confirmed in several clinical models, some studies show insufficient therapeutic effect for malignant cancers. As a possible mechanism of the treatment failure, it has been considered that tumor cells may acquire resistance to this therapy. However, drug resistance by TECs may also be due to another mechanism for resistance of tumor cells to low-dose chemotherapy. We reported elsewhere that TECs were resistant to the anticancer drug paclitaxel, which is a mitotic inhibitor, concomitant with P-glycoprotein up-regulation. Verapamil, a P-glycoprotein inhibitor, abrogated TEC resistance in vitro. Herein, we demonstrated that verapamil coadministration enhanced the effects of low-dose paclitaxel concomitant with inhibiting tumor angiogenesis in a preclinical in vivo mouse melanoma xenograft model. Furthermore, verapamil coadministration reduced lung metastasis. These results suggest that inhibiting P-glycoprotein in TECs may be a novel strategy for low-dose chemotherapy targeting TECs.