Analysis of the thrombotic and fibrinolytic activities of tumor cell-derived extracellular vesicles.

Exosomes and microvesicles (MVs) are small extracellular vesicles secreted by tumor cells and are suggested to contribute to the thrombotic events that commonly occur in patients with advanced malignancies. Paradoxically, these vesicles have been reported to also possess fibrinolytic activity. To determine whether thrombotic or fibrinolytic activity is a predominant characteristic of these extracellular vesicles, we prepared exosomes and MVs from 2 breast cancer cell lines (MDA-MB-231 and MCF7), a lung cancer cell line (A549), and a leukemia cell line (NB4) and assayed their thrombotic and fibrinolytic activities. We observed that thrombotic activity was a common feature of MVs but not exosomes. Exosomes and/or MVs from several cell lines, with the exception of the A549 cell line, displayed fibrinolytic activity toward a pure fibrin clot, but only exosomes from MDA-MB-231 cells could degrade a fibrin clot formed in plasma. Increasing the malignant potential of MCF7 cells decreased the thrombotic activity of their MVs but did not alter their fibrinolytic activity. Decreasing the malignant potential of NB4 cells did not alter the thrombotic or fibrinolytic activity of their MVs or exosomes. Finally, the incubation of MDA-MB-231 cell-derived exosomes with A549 cells increased plasmin generation by these cells. Our data indicate that MVs generally have thrombotic activity, whereas thrombotic activity is not commonly observed for exosomes. Furthermore, exosomes and MVs generally do not display fibrinolytic activity under physiological conditions.