Cytokine-mediated tumor-endothelial cell interaction in metastasis

The role of superoxide anions in the development of distant tumour recurrence

We hypothesise that reactive oxygen species (ROS) released from activated polymorphonuclear leucocytes during surgery play a crucial role in enhanced tumour recurrence seen after surgery. Therefore, the effect of ROS on adhesion of tumour cells to microvascular endothelium in a reproducible human in vitro model was studied. Preincubation of microvascular endothelial cells with the superoxide anion producing xanthine–xanthine oxidase complex significantly increased adhesion of the human colon carcinoma cells HT29 (167% vs control, P<0.01), Caco2 (164% vs control, P<0.01) and of the pancreas carcinoma cells PanC1 (180% vs control, P<0.01). Addition of the antioxidant enzymes superoxide dismutase or catalase significantly decreased tumour cell adhesion (P<0.01). Exposure of endothelial cells to superoxide anions increased the apoptotic rate to 7.9 times the normal rate. Additionally, exposure increased expression of the endothelial adhesion molecules E-Selectin, ICAM-1, and VCAM-1 of maximally 170% vs control (P<0.01). In conclusion, this study shows that superoxide anions promote the adherence of tumour cells to the microvasculature by inducing endothelial apoptosis that subsequently induces the expression of various adhesion molecules for tumour cells. This indicates that by tackling the production of ROS preventing tumour recurrence at distant sites might be feasible.

Discovery of Inhibitors of MCF-7 Tumor Cell Adhesion to Endothelial Cells and Investigation on their Mode of Action

Metastasis, the main reason for high mortality of cancer, is a multistep process. One important step in this process is the adhesion of tumor cells to vascular endothelium at sites distant from primary tumors during hematogenous dissemination. In order to investigate and quantify the adhesion of tumor cells to endothelial cells we developed an in vitro model using MCF-7 breast cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC). The tumor cells were specifically labeled with a fluorescent dye for quantification; for increasing the amount of adherent cells, HUVEC monolayers were stimulated with phorbol ester before the addition of the tumor cells. Due to previous reports that products of several P450 enzymes contribute to the progression of certain kinds of cancer, inhibitors of CYP5 (thromboxane A(2) synthase), CYP17 (17alpha-hydroxylase-C17, 20-lyase), and CYP19 (aromatase) were tested in this in vitro model for their potency to reduce cancer cell adhesion. Within each series of P450 inhibitors, compounds with high inhibitory activity on tumor cell adhesion were identified. At an initial concentration of 100 microM, BW26, a potent inhibitor of CYP5, reduced tumor cell adhesion of MCF-7 to HUVECs to 15%, BW40 (CYP17) to 29%, and SU5a (CYP19) to 11% of the corresponding controls (no inhibitor). Reduction of tumor cell adhesion was shown to occur in a concentration-dependent manner. In addition to these inhibitors of CYP5, CYP17, and CYP19, liarozole, known to be a potent inhibitor of CYP26 (retinoic acid-4-hydroxylase) and ATRA (all-trans-retinoic acid) metabolism, was able to reduce tumor cell adhesion to 51% of the initial rate. Experiments elucidating the mode of action of these compounds revealed that inhibition of the mentioned CYP enzymes is not responsible for their ability to reduce tumor cell adhesion.

Particle diameter influences adhesion under flow

The diameter of circulating cells that may adhere to the vascular endothelium spans an order of magnitude from approximately 2 microm (e.g., platelets) to approximately 20 microm (e.g., a metastatic cell). Although mathematical models indicate that the adhesion exhibited by a cell will be a function of cell diameter, there have been few experimental investigations into the role of cell diameter in adhesion. Thus, in this study, we coated 5-, 10-, 15-, and 20-microm-diameter microspheres with the recombinant P-selectin glycoprotein ligand-1 construct 19.ek.Fc. We compared the adhesion of the 19.ek.Fc microspheres to P-selectin under in vitro flow conditions. We found that 1) at relatively high shear, the rate of attachment of the 19.ek.Fc microspheres decreased with increasing microsphere diameter whereas, at a lower shear, the rate of attachment was not affected by the microsphere diameter; 2) the shear stress required to set in motion a firmly adherent 19.ek.Fc microsphere decreased with increasing microsphere diameter; and 3) the rolling velocity of the 19.ek.Fc microspheres increased with increasing microsphere diameter. These results suggest that attachment, rolling, and firm adhesion are functions of particle diameter and provide experimental proof for theoretical models that indicate a role for cell diameter in adhesion.