CROSSTALK BETWEEN PLATELETS AND CANCER CELLS: Do cancer cells interact with transfused platelets?

Abstract

In Australia, oncology patients receive up to 60% of platelet transfusions. Interactions between platelets and cancer cells in oncology patients are well documented, notably, crosstalk between the C-type like lectin receptor on platelets and podoplanin (PDPN) on malignant cells. Described here is the first in-vitro investigation of crosstalk between stored apheresis platelets and cancer cells. Platelets were stored for 7 days at 20-24°C with constant agitation. During storage, samples were taken and interactions with HepG2, H226 and A549 cells were examined. The potential of malignant cells to induce platelet aggregation was measured using light transmission aggregometry with 1.25 mM CaCl2 (n=5), and platelet phenotypes were determined using flow cytometry (n=3), as was titration of an antibody to block PDPN (n=5). Blocking the interaction between platelets and malignant cells was examined using LTA (n=3). A 24-well plate assay was developed to investigate the interactions between platelets and malignant cells (n=3) using 1.25 mM CaCl2 and 2.5 mM GPRP. Changes within groups were analysed by one-way ANOVA, and two-way ANOVA; p<0.05 was significant. HepG2, H226 and A549 cells induced platelet aggregation, which was reduced when platelets were stored for longer. Blocking PDPN with an anti-PDPN antibody did not prevent cancer cell induced aggregation, suggesting multiple pathways may mediate platelet aggregation. The interactions of platelets with malignant cells in a 24-well plate led to a reduction in platelet receptors and increased platelet activation with release of CD62P and externalisation of phosphatidylserine. TGF-ß release was highest following the incubation of platelets with A549 cells with GPRP and CaCl2. In conclusion, the incubation of platelets with cells derived from solid tumour induced platelet activation and aggregation, leading to a marked reduction of platelet glycoproteins. These alterations were more marked during early platelet storage.