Platelet Cloaking of Cancer Cells: Platelet Adhesiveness, Effect of Vascular Shear and Access of Chemotherapeutic Agents.
Darragh J Crowley, Karl Egan, Eimear Dunne, Sharon A O'Toole, Cara Martin, Paul A Smyth, Dermot Kenny, Orla M Sheils, John J O'Leary. Trinity College Dublin, Ireland; Royal College of Surgeons in Ireland, Dublin, Ireland; Coombe Women and Infants University Hospital, Dublin, Ireland
Background: Recent studies have demonstrated the important role of platelets in metastasis. Tumour cell induced platelet aggregation (TCIPA), where circulating tumour cells (CTCs) may become 'cloaked' with platelets, has implications for chemotherapeutic efficacy, CTC-endothelium adhesion and CTC extravasation. CTC-platelet cloaking kinetics are poorly understood. We examined (A) platelet-cancer cell adhesion, (B) the role of vascular shear in platelet cloak formation and (C) the impact of platelet cloaking on chemotherapeutic responses.
Design: A: Cell lines representing normal ovarian epithelium and a spectrum of ovarian cancer were studied. Gel filtered platelets were prepared from whole blood from healthy volunteers, loaded with calcein AM dye and applied to cell lines for 45 minutes. Total fluorescence and residual fluorescence following three washes, indicative of platelet adhesion, was recorded. Adhesion was calculated against total fluorescence and a fibrinogen positive control. P-selectin expression as a measure of activated platelets was also assessed by flow cytometry. B: Cone and plate viscometry was used to examine shear and non-shear effects on platelet cloaking of cancer cells. Suspensions of platelets and tumour cells were sheared for 15 minutes at 37oC at a constant shear rate of 200s-1. C: Cell survival and apoptosis was measured in platelet-cloaked and uncloaked ovarian cell lines treated with paclitaxel or 5-fluorouracil.
Results: Cancer cells demonstrated varying adhesiveness and a dose-dependent ability to activate p-selectin after platelet exposure. Cloaking of cancer cells occurred under venous shear, with infrequent cloaking in static conditions. Cloaked cancer cells demonstrated significantly greater cell survival (p<0.05) in the presence of chemotherapeutic agents than uncloaked cells.
Conclusions: Cancer cells form platelet cloaks, which is dependent on vascular shear. Platelet cloaking reduces chemotherapeutic efficacy in cancer cells. The role of platelets in the metastatic highway appears to be important with potentially serious outcomes for patients with cloaked CTCs. This work is supported the Irish Health Research Board (HRB) PhD Programme in Molecular Medicine: From Genes to Function. *Joint first authors
Category: Gynecologic & Obstetrics
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 106, Tuesday Afternoon