Abstract
Saos-2 cells, derived from a primary human osteosarcoma, caused dose-dependent platelet aggregation in heparinised human platelet-rich plasma. Saos-2 tumour cell-induced platelet aggregation (TCIPA) was completely inhibited by hirudin but unaffected by apyrase. The cell suspension shortened the plasma recalcification times of normal, factor VIII-deficient and factor IX-deficient human plasmas in a dose-dependent manner. However, the cell suspension did not affect the recalcification time of factor VII-deficient plasma. Moreover, a monoclonal antibody (MAb) against human tissue factor completely abolished TCIPA. Flow cytometric analysis using anti-integrin MAbs as the primary binding ligands demonstrated that the integrin receptors alpha v beta 3, alpha 5 beta 1 and alpha 6 beta 1 were present of Saos-2 cells, which might mediate tumour cell adhesion to extracellular matrix. Rhodostomin, an Arg-Gly-Asp (RGD)-containing snake venom peptide which antagonises the binding of fibrinogen to platelet membrane glycoprotein IIb/IIIa, prevented Saos-2 TCIPA as well as tumour cell adhesion to vitronectin, fibronectin and collagen type I. Likewise, the synthetic peptide Gly-Arg-Gly-Asp-Ser (GRGDS) showed a similar effect. On a molar basis, rhodostomin was about 18,000 and 1000 times, respectively, more potent than GRGDS in inhibiting TCIPA and tumour cell adhesion.