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 ReversesNeuraminidase Effect on Metastasis

Treatment of Mice with Anti-Platelet SerumProduces 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 manycancer patients.Hypercoagulable state of blood in many cancer patientsHeparin (an anti-coagulant) protected against pulmonarymetastasis 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 asVEGF A, PDGF, TGF, bFGF that promoteTumor growth and angiogenesis.

Cancer patients undergoing chemotherapy experiencedecrease 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 thisinteraction facilitates metastasis.

Two modes of interaction

Platelets interact with tumor cells viaIntegrins (IIb3), vWF, fibronectin, fibrinogen

P-selectin on platelets binds to tumor cellcarbohydrate coat (sialyl Lewisa/x)

Coating of tumor cells by platelets protects tumor cells fromkilling by immune cells, shear forces, allows them to attach,extravasate, grow and recruit blood vessels

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Selectins:E

L

P

Sialyl Lewis A

Sialyl Lewis X

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sulfatides

Selecti

n Ligands

Tumor cells upregulate sLa/x

•Progression to invasive phenotype of tumor cellsin vitro and tumors in vivo is associated with upregulation of cell surface sLa/x

•Upregulation of sLa/x is a poor prognostic factorfor colon, pancreas and stomach cancers

•Expression of sLa on colon adenocarcinomascorrelates with appearance liver metastasis

sLa/x on mucin-type O-glycans is highly correlated withlymphatic and venous metastasis

Ugorski et al., Acta Biochimica Polonica 49:303-311, 2002

Experimental Mouse Models:

Treatment of tumor cells with O-sialglycosidase(cleaves glycosylated mucins) inhibits tumor mets

Treatment of tumor cells with monoclonal Ab tosLa inhibits tumor mets

Heparin actually competes with sLa/x for bindingto 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., 18:1516-1525, 1999

Selectin Kos

Experimental pulmonary mets are attenuated inP-KO mice.

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Kim et al, PNAS 95:9325, 1998

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3-D Reconstruction of Tumor-Platelet-LeukocyteEmboli 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 exhibitdifferent effects on tumor growth and metastasis.

Fragments resulting from digestion of tumor cell surface withHepIII inhibit tumor growth and metastasis. But fragmentsresulting from digestion with HepI promote tumor growth!

Liu et al, PNAS 99: 568-573, 2002

Hypotheis 2.Platelets interact directly with tumor cells, and thisinteraction facilitates metastasis.

Two modes of interaction

Platelets interact with tumor cells viaIntegrins (IIb3), vWF, fibronectin, fibrinogen

P-selectin on platelets binds to tumor cellcarbohydrate coat (sialyl Lewisa/x)

Coating of tumor cells by platelets protects tumor cells fromkilling 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,

IIb3 inhibits tumor cell binding to platelets

Treatment of mice with antibodies to

vWF, IIb3, RGDS peptides,

or thrombin

attenuate tumor metastasis.

Karpatkin et al, J. Clin. Invest 1988Nierodzik et al, Thromb and Haemostasis 74:282, 1995

Seeding of metastasis is attenuated in the absence ofFibrinogen.

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Palumbo et al., Blood 96: 3302, 2000

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

Targeted disruption of platelet-tumorinteractions is worth clinical testing

again (Varki)

Heparin treatment to inhibit tumor cells associationwith platelets (as well as inhibiut platelet activation by

thrombin) may be of great therapeutic, anti-metastatic effect

Other inhibitors of platelet-tumor interactions may behelpful as well