Cancer microvesicles induce tissue factor-related procoagulant activity in endothelial cells in vitro.

: Microvesicles associated with tissue factor (TF) may play a role in cancer-related venous thromboembolism; however, not much is known about their interaction with the tumour stroma, especially the endothelium or any procoagulant changes seen because of this interaction. Using a head and neck squamous cell carcinoma line (UMSCC81B) and human umbilical vein endothelial cells (HUVECs), this study explored the interaction of cancer microvesicles released into cell culture media with endothelial cells in vitro, and assessed the procoagulant activity resulting from this interaction. Cell-free media containing UMSCC81B cancer microvesicles supported coagulation in a concentration-dependent manner, suggesting TF and microvesicle presence, this media was then added to HUVECs and flow cytometry analysis showed a subpopulation of HUVECs that had acquired a significantly high expression of TF, which was dependent upon the concentration of UMSCC81B media containing microvesicles present and confocal microscopy confirmed HUVECs associated with labelled microvesicles. The range of TF-positive HUVECs was determined to be 0, 4.2(±1.4), 12.5(±3.72), and 45.9(±18.7)% for microvesicle-positive media concentration of 0, 25, 50, and 100%, respectively, which resulted in decreasing prothrombin values of more than 600 (no clot), 126.4, 65.8, and 47.8 s. Our results demonstrate that procoagulant microvesicles shed by UMSCC81B induced a procoagulant effect in HUVECs through increased clotting activity and cell membrane surface expression of TF.