Tumor cell-platelet interactions are regarded as an initial crucial step in hematogenous
metastasis. Platelets protect
tumor cells from immune surveillance in the blood, mediate vascular arrest, facilitate
tumor extravasation, growth, and finally angiogenesis in the metastatic foci.
Tumor cells aggregate platelets in the bloodstream by activation of the plasmatic coagulation cascade and by direct contact formation. Antimetastatic activities of unfractionated or
low molecular weight heparin (UFH/
LMWH) can undoubtedly be related to attenuated platelet activation, but molecular mechanisms and contribution of contact formation vs. coagulation remain to be elucidated. Using a set of non-
anticoagulant heparin derivatives varying in size or degree of sulfation as compared with UFH, we provide insight into the relevance of contact formation for platelet activation. Light transmission aggregometry and
ATP release assays confirmed that only those
heparin derivatives with
P-selectin blocking capacities were able to attenuate
breast cancer cell-induced platelet activation, while pentasaccharide
fondaparinux was without effects. Furthermore, a role of
P-selectin in platelet activation and signaling could be confirmed by
proteome profiler arrays detecting platelet
kinases. In this study, we demonstrate that
heparin blocks
tumor cell-induced coagulation. Moreover, we identify platelet
P-selectin, which obviously acts as molecular switch and controls aggregation and secretion of procoagulant platelets.