Platelets and Metastasis In Mice and in Humans, Platelets are Important Mediators of Metastatic process Gabriel Gasic, Tatiana Gasic, Carleton Stewart PNAS 61:46-52, 1968

Transfusion of Platelet Rich Plasma Reverses Neuraminidase Effect on Metastasis

Treatment of Mice with Anti-Platelet Serum Produces the Same Effect as Neuraminidase

How do platelets contribute to metastasis?  In many cancer patients platelet numbers are elevated.  Platelets in cancer patients are activated (elevated levels of serum thrombin, von Willebrand factor, VEGF).  Prostacyclin/Thromboxane A2 balance disturbed in many cancer patients.  Hypercoagulable state of blood in many cancer patients  Heparin (an anti-coagulant) protected against pulmonary metastasis in animal models Hypotheis 1. Activation of clotting pathway.

However, Clinical trials that used anti-coagulants (vitamin K antagonists such as warfarin) failed. And yet…. Retrospective analysis indicated that cancer patients that were treated with low doses of heparin before cancer surgery showed improved survival. Cancer patients treated with heparin to combat venous thromboemolism also showed improved survival.

Activated platelets secrete cytokynes such as VEGF A, PDGF, TGF , bFGF that promote Tumor growth and angiogenesis. Cancer patients undergoing chemotherapy experience decrease in platelet counts (thrombosytopenia) and receive platelet transfusion. BUT platelets become activated during storage (secrete P-selectin and VEGF). Transfusion of blood products carries the risk of increased cancer recurrence. Nash et al., Platelets and Cancer. Lancet Oncology 3:425, 2002

Hypotheis 2. Platelets interact directly with tumor cells, and this interaction facilitates metastasis. Two modes of interaction Platelets interact with tumor cells via Integrins (  IIb  3), vWF, fibronectin, fibrinogen P-selectin on platelets binds to tumor cell carbohydrate coat (sialyl Lewis a/x ) Coating of tumor cells by platelets protects tumor cells from killing by immune cells, shear forces, allows them to attach, extravasate, grow and recruit blood vessels

Selectins: ELPELP

Sialyl Lewis A Sialyl Lewis X

sulfatides Selectin Ligands

Tumor cells upregulate sLa/x Progression to invasive phenotype of tumor cells in vitro and tumors in vivo is associated with upregulation of cell surface sLa/x Upregulation of sLa/x is a poor prognostic factor for colon, pancreas and stomach cancers Expression of sLa on colon adenocarcinomas correlates with appearance liver metastasis sLa/x on mucin-type O-glycans is highly correlated with lymphatic and venous metastasis Ugorski et al., Acta Biochimica Polonica 49: , 2002

Experimental Mouse Models: Treatment of tumor cells with O-sialglycosidase (cleaves glycosylated mucins) inhibits tumor mets Treatment of tumor cells with monoclonal Ab to sLa inhibits tumor mets Heparin actually competes with sLa/x for binding to selectins also inhibits tumor mets However, Experiments in mice also showed that levels of sLa/x are important. When too much of sLa/x are present on tumor cell surface (presentation of sLa/x is altered), tumor cells are subject to attack by NK cells. Ohyama et al., EMBO J., 18: , 1999

Selectin Kos Experimental pulmonary mets are attenuated in P-KO mice. Kim et al, PNAS 95:9325, 1998

3-D Reconstruction of Tumor-Platelet-Leukocyte Emboli in Blood Vessels of the Lung Borsig et al (Varki) PNAS 98:3352, 2001 Tumor Cells Platelets Leukocytes

Heparin does not equal Heparin 1.Low MW Heparin fraction does not have the same effect 2.Heparin fragments generated by different heparinases exhibit different effects on tumor growth and metastasis. Fragments resulting from digestion of tumor cell surface with HepIII inhibit tumor growth and metastasis. But fragments resulting from digestion with HepI promote tumor growth! Liu et al, PNAS 99: , 2002

Hypotheis 2. Platelets interact directly with tumor cells, and this interaction facilitates metastasis. Two modes of interaction Platelets interact with tumor cells via Integrins (  IIb  3), vWF, fibronectin, fibrinogen P-selectin on platelets binds to tumor cell carbohydrate coat (sialyl Lewis a/x ) Coating of tumor cells by platelets protects tumor cells from killing by immune cells, shear forces, allows them to attach, extravasate, grow and recruit blood vessels

Treatment of cell lines with trypsin, hrombin or antibodies to fibronectin, vWF,  IIb  3 inhibits tumor cell binding to platelets Treatment of mice with antibodies to vWF,  IIb  3, RGDS peptides, or thrombin attenuate tumor metastasis. Karpatkin et al, J. Clin. Invest 1988 Nierodzik et al, Thromb and Haemostasis 74:282, 1995

Seeding of metastasis is attenuated in the absence of Fibrinogen. Palumbo et al., Blood 96: 3302, 2000

Tumor cells disappear from the lungs in Fg -/- mice!

Targeted disruption of platelet-tumor interactions is worth clinical testing again (Varki) Heparin treatment to inhibit tumor cells association with platelets (as well as inhibiut platelet activation by thrombin) may be of great therapeutic, anti-metastatic effect Other inhibitors of platelet-tumor interactions may be helpful as well