Identification of potential classes of glycoligands mediating dynamic endothelial adhesion of human tumor cells

One critical step of metastasis formation is the extravasation of circulating tumor cells from the bloodstream. This process requires the dynamic interaction of cell adhesion molecules like E-selectin on endothelial cells with carbohydrate ligands on tumor cells. To characterize these glycans in a comprehensible approach, the rolling, tethering, and firm adhesion of nine human tumor cell lines on human umbilical vein endothelial cells was analyzed using laminar flow adhesion assays. The tumor cell lines were grouped into three subsets by their canonical E-selectin ligand status (sialyl-Lewis A and X +/+, -/+, -/-) and their adhesiveness was compared after enzymatic, pharmacologic, chemical treatment or antibody blockade of the tumor cells or endothelial cells, respectively. Tumor cells were also screened regarding their glycosyltransferase expression profile. We found that although E-selectin and terminal α2,3-sialic acid largely determined firm adhesion, adhesive events did not exclusively depend on the presence of sialyl-Lewis A and/or sialyl-Lewis X. Nevertheless, two of the three sialyl-Lewis A/X-/- tumor cells additionally or fully depended on vascular cell adhesion molecule-1 for firm adhesion. The significance of O-GalNAc- and N-glycans for adhesion varied remarkably among the tumor cells. The sialyl-Lewis A/X+/+ subset showed glycoprotein-independent adhesion, suggesting a role of glycolipids as well. All sialyl-Lewis A/X-/- tumor cells lacked FUT3 and FUT7 expression as opposed to sialyl-Lewis A/X+/+ or -/+ cell lines. In summary, the glycans on tumor cells mediating endothelial adhesion are not as much restricted to sialyl-Lewis A /X as previously assumed. The present study specifically suggests α2,3-linked sialic acid, O-GalNAc glycans, glycosphingolipids, and FUT3/FUT7 products as promising targets for future studies.

Metastatic Esophageal Carcinoma Cells Exhibit Reduced Adhesion Strength and Enhanced Thermogenesis

Despite continuous improvements in multimodal therapeutic strategies, esophageal carcinoma maintains a high mortality rate. Metastases are a major life-limiting component; however, very little is known about why some tumors have high metastatic potential and others not. In this study, we investigated thermogenic activity and adhesion strength of primary tumor cells and corresponding metastatic cell lines derived from two patients with metastatic adenocarcinoma of the esophagus. We hypothesized that the increased metastatic potential of the metastatic cell lines correlates with higher thermogenic activity and decreased adhesion strength. Our data show that patient-derived metastatic esophageal tumor cells have a higher thermogenic profile as well as a decreased adhesion strength compared to their corresponding primary tumor cells. Using two paired esophageal carcinoma cell lines of primary tumor and lymph nodes makes the data unique. Both higher specific thermogenesis profile and decreased adhesion strength are associated with a higher metastatic potential. They are in congruence with the clinical patient presentation. Understanding these functional, biophysical properties of patient derived esophageal carcinoma cell lines will enable us to gain further insight into the mechanisms of metastatic potential of primary tumors and metastases. Microcalorimetric evaluation will furthermore allow for rapid assessment of new treatment options for primary tumor and metastases aimed at decreasing the metastatic potential.

Role of NO and S-nitrosylation in the Expression of Endothelial Adhesion Proteins That Regulate Leukocyte and Tumor Cell Adhesion

Leukocyte recruitment is one of the most important cellular responses to tissue damage. Leukocyte extravasation is exquisitely regulated by mechanisms of selective leukocyte-endothelium recognition through adhesion proteins in the endothelial cell surface that recognize specific integrins in the activated leukocytes. A similar mechanism is used by tumor cells during metastasis to extravasate and form a secondary tumor. Nitric oxide (NO) has been classically described as an anti-inflammatory molecule that inhibits leukocyte adhesion. However, the evidence available shows also a positive role of NO in leukocyte adhesion. These apparent discrepancies might be explained by the different NO concentrations reached during the inflammatory response, which are highly modulated by the expression of different nitric oxide synthases, along the inflammatory response and by changes in their subcellular locations.

Selective Targeting of αvβ5 Integrin in HepG2 Cell Line by RGDechi15D Peptide

Recently, the research community has become increasingly concerned with the receptor αvβ5, a member of the well-known integrin family. Different ongoing studies have evidenced that αvβ5 integrin regulates not only physiological processes but also a wide array of pathological events, suggesting the receptor as a valuable biomarker to specifically target for therapeutic/diagnostic purposes. Remarkably, in some tumors the involvement of the receptor in cell proliferation, tumor dissemination and angiogenesis is well-documented. In this scenario, the availability of a selective αvβ5 antagonist without ‘off-target’ protein effects may improve survival rate in patients with highly aggressive tumors, such as hepatocellular carcinoma. We recently reported a cyclic peptide, RGDechi15D, obtained by structure-activity studies. To our knowledge it represents the first peptide-based molecule reported in the literature able to specifically bind αvβ5 integrin and not cross react with αvβ3. Here we demonstrated the ability of the peptide to diminish both adhesion and invasion of HepG2 cells, an in vitro model system for hepatocellular carcinoma, to reduce the cell proliferation through an apoptotic process, and to interfere with the PI3K pathway. The peptide, also decreases the formation of new vessels in endothelial cells. Taken together these results indicate that the peptide can be considered a promising molecule with properties suited to be assessed in the future for its validation as a selective therapeutic/diagnostic weapon in hepatocarcinoma.

The pretubulysin-induced exposure of collagen is caused by endothelial cell retraction that results in an increased adhesion and decreased transmigration of tumor cells

Microtubule-targeting agents (MTAs) are the most widely used chemotherapeutic drugs. Pretubulysin (PT), a biosynthetic precursor of the myxobacterial tubulysins, was recently identified as a novel MTA. Besides its strong anti-tumoral activities, PT attenuates tumor angiogenesis, exerts anti-vascular actions on tumor vessels and decreases cancer metastasis formation in vivo. The aim of the present study was to analyze the impact of PT on the interaction of endothelial and tumor cells in vitro to gain insights into the mechanism underlying its anti-metastatic effect. The influence of PT on tumor cell adhesion and transmigration onto/through the endothelium as well as its influence on cell adhesion molecules and the chemokine system CXCL12/CXCR4 was investigated. Treatment of human endothelial cells with PT increased the adhesion of breast cancer cells to the endothelial monolayer, whereas their transmigration through the endothelium was strongly reduced. Interestingly, the PT-induced upregulation of ICAM-1, VCAM-1 and CXCL12 were dispensable for the PT-evoked tumor cell adhesion. Tumor cells preferred to adhere to collagen exposed within PT-triggered endothelial gaps via β1-integrins on the tumor cell surface. Taken together, our study provides, at least in part, an explanation for the anti-metastatic potential of PT.

Diaphanous-related formin 1 as a target for tumor therapy

Formins nucleate actin and stabilize microtubules (MTs). Expression of the formin Diaphanous homolog 1 (DIAPH1) is increased in malignant colon carcinoma cells, while expression of DIAPH3 is up-regulated in breast and prostate carcinoma cells. Both DIAPH1 isoforms are required to stabilize interphase MTs of cancer cells, and it has been shown that loss of this function decreases the metastatic potential of these cells. Moreover, depletion of DIAPH3 increases the sensitivity of breast and prostate carcinoma cells to taxanes. In contrast with DIAPH1 + 3, DIAPH2 regulates metaphase MTs of tumor cells by stabilizing binding of kinetochore MTs to chromosomes. Depletion of DIAPH2 impairs chromosome alignment, thus proper chromosome segregation during mitosis. In summary, expression of DIAPH formins in tumor cells is essential for stabilizing interphase or metaphase MTs, respectively. Thus, it would be very interesting to analyze if tumor cells exhibiting low DIAPH expression are more sensitive to taxanes than those with high DIAPH expression.

Proinflammatory adhesion molecules facilitate polychlorinated biphenyl-mediated enhancement of brain metastasis formation

Polychlorinated biphenyls (PCBs) are environmental toxicants that cause vascular inflammation and facilitate the development of brain metastases. The crucial event in metastasis formation is adhesion of blood-borne tumor cells to the vascular endothelium, followed by their transcapillary migration. The aim of the present study was to examine the mechanisms of PCB118-induced brain metastasis formation at the blood-brain barrier level with the focus on tumor cell adhesion to the brain endothelium. PCB118 was administered orally to wild-type or intercellular cell adhesion molecule-1 (ICAM-1)-deficient mice, followed by an injection of Lewis lung carcinoma cells into the carotid artery. Treatment with PCB118 resulted in enhanced development of brain metastases. Injection of tumor cells induced overexpression of ICAM-1 and vascular endothelial cell adhesion molecule-1 (VCAM-1) in brain endothelium that was further potentiated in mice exposed to PCB118. PCB118 did not affect the number of adhered and extravasated tumor cells in ICAM-1-deficient mice. Additional in vitro studies indicated that VCAM-1-neutralizing antibody protected against PCB118-induced adhesion of tumor cells to cultured brain endothelial cells. These results indicate that exposure to selected PCB congeners, such as PCB118, induces adhesion and transcapillary migration of tumor cells. This process is facilitated by proinflammatory adhesion molecules and results in potentiation of brain metastasis formation.