Breast-cancer extracellular vesicles induce platelet activation and aggregation by tissue factor-independent and -dependent mechanisms.

Introduction: Cancer-associated thrombosis is one of the major causes of worse prognosis among tumor-bearing patients. Extracellular vesicles derived from cancer cells, which can be divided mainly into microvesicles and exosomes, can participate in several tumor progression phenomena. Tumor-derived microvesicles positive for tissue factor (TF) have been associated with thrombotic risk in certain cancer types. Cancer cell-derived exosomes, however, have not. In this study we evaluated the capacity of extracellular vesicles (EVs, containing both microvesicles and exosomes) derived from breast-cancer cell lines in promoting platelet activation, aggregation and plasma coagulation, in experiments that access both TF-dependent and -independent activities.

Materials And Methods: EVs were isolated from the conditioned media of two human mammary carcinoma cell lines: MDA-MB-231 (highly invasive) and MCF-7 (less invasive). TF-independent EV/platelet interaction, platelet P-selectin exposure and aggregation were evaluated. Western blotting, plasma clotting and platelet aggregation in the presence of plasma were performed for the measurement of TF-dependent activity in EVs.

Results: Interaction between MDA-MB-231 EVs and washed platelets led to increased platelet P-selectin exposure and platelet aggregation compared to MCF-7 EVs. MDA-MB-231 EVs had higher TF protein levels and TF-dependent procoagulant activity than MCF-7 EVs. Consequently, TF-dependent platelet aggregation was also induced by MDA-MB-231 EVs, but not by MCF-7 EVs.

Conclusion: Our results suggest that MDA-MB-231 EVs induce TF-independent platelet activation and aggregation, as well as TF-dependent plasma clotting and platelet aggregation by means of thrombin generation. In this context, aggressive breast cancer-derived EVs may contribute to cancer-associated thrombosis.