Platelet integrin α6ß1 controls lung metastasis through direct binding to cancer cell-derived ADAM9.

Metastatic dissemination of cancer cells, which accounts for 90% of cancer mortality, is the ultimate hallmark of malignancy. Growing evidence suggests that blood platelets have a predominant role in tumor metastasis; however, the molecular mechanisms involved remain elusive. Here, we demonstrate that genetic deficiency of integrin α6ß1 on platelets markedly decreases experimental and spontaneous lung metastasis. In vitro and in vivo assays reveal that human and mouse platelet α6ß1 supports platelet adhesion to various types of cancer cells. Using a knockdown approach, we identified ADAM9 as the major counter receptor of α6ß1 on both human and mouse tumor cells. Static and flow-based adhesion assays of platelets binding to DC-9, a recombinant protein covering the disintegrin-cysteine domain of ADAM9, demonstrated that this receptor directly binds to platelet α6ß1. In vivo studies showed that the interplay between platelet α6ß1 and tumor cell-expressed ADAM9 promotes efficient lung metastasis. The integrin α6ß1-dependent platelet-tumor cell interaction induces platelet activation and favors the extravasation process of tumor cells. Finally, we demonstrate that a pharmacological approach targeting α6ß1 efficiently impairs tumor metastasis through a platelet-dependent mechanism. Our study reveals a mechanism by which platelets promote tumor metastasis and suggests that integrin α6ß1 represents a promising target for antimetastatic therapies.

[Anti-platelets without a bleeding risk: novel targets and strategies]. / Les anti-plaquettaires sans risque de saignement : nouvelles cibles et stratégies.

Anti-platelet agents such as aspirin, clopidogrel and antagonists of integrin αIIbß3 allowed to efficiently reduce morbidity and mortality associated with arterial thrombosis. A major limit of these drugs is that they increase the risk of bleeding. During the last few years, several innovative anti-thrombotic strategies with a potentially low bleeding risk were proposed. These approaches target the collagen receptor glycoprotein (GP) VI, the GPIb/von Willebrand factor axis, the thrombin receptor PAR-1, the activated form of integrin αIIbß3 or the ADP receptor P2Y1. While an antagonist of PAR-1 was recently marketed, the clinical proofs of the efficiency and safety of the other agents remain to be established. This review evaluates these new anti-platelet approaches toward safer anti-thrombotic therapies.

A humanized glycoprotein VI (GPVI) mouse model to assess the antithrombotic efficacies of anti-GPVI agents.

Glycoprotein VI (GPVI) has been proposed as a promising antiplatelet target, because its blockade prevents experimental thrombosis without impairing hemostasis. The objective of this study was to develop a preclinical tool to evaluate the role of human GPVI (hGPVI) in various models of thrombosis and to screen anti-GPVI compounds. A genetically modified mouse strain expressing hGPVI has been developed using a knockin strategy. The mice were viable and fertile and did not present any hematological defects. Approximately 3700 copies of human GPVI were detected at the platelet surface. Platelet aggregation, fibrinogen binding, and P-selectin exposure were normal in response to various agonists. The 9O12.2 Fab fragment directed against human GPVI bound to hGPVI platelets in vitro and ex vivo and markedly reduced collagen- and collagen-related peptide-induced responses. Injection of 9O12.2 into hGPVI animals did not prolong the tail bleeding time but provided protection against lethal thromboembolism induced by a collagen/adrenaline mixture. In addition, 9O12.2 reduced arterial thrombus growth by 44% after superficial laser injury, 43% after deep laser injury in mice pretreated with hirudin, and 48% after mechanical injury. In conclusion, we have developed a humanized mouse model that could be used in preclinical studies to evaluate the effects of anti-GPVI compounds.