Signaling pathways for induction of platelet aggregation by sas tongue cancer cells - A mechanism of hematogenous metastasis

Background: Tongue cancer metastasis is mainly through blood stream and possibly associated with tumor cell-induced platelet aggregation (TCIPA). Methods: Platelet aggregation was induced by different amounts of SAS tongue cancer cells with/without inhibitors and the latent period for induction of platelet aggregation was recorded. Gene expression was analyzed by reverse transcriptase-polymerase chain reaction. Results: SAS cells (4 × 10 ⁴ to 1 × 10 ⁶ cells/ml) induced platelet aggregation in a cell density-dependent manner. The latent period for induction of platelet aggregation reduced from 11.3 min (2 × 10 ⁵ cells/ml) to 0.9 min (5 × 10 ⁵ cells/ml). The extent of platelet aggregation increased from 39% to 76% by 2 × 10 ⁵ and 5 × 10 ⁵ SAS cells. Pre-treatment of SAS cells with aspirin showed little effect on its induction of platelet aggregation. SAS cells expressed tissue factor (TF) mRNA and the SAS cells-induced TCIPA was inhibited by TF neutralization antibody (5-20 μg/ml), heparin (5-10 U/ml), Hirudin fragment 54-65 (50 μg/ml) and D-Phenylalanyl-L-prolyl-L-arginine chloromethyl ketone. But areca nut (AN, a betel quid component known to generate reactive oxygen species (ROS)) extract showed little effect on TF expression in SAS cells. Pre-treatment with U73122 and 2-aminoethoxydiphenylborate inhibited SAS-induced TCIPA. Interestingly, catalase suppressed SAS cells-induced TCIPA, whereas AN extract enhanced this event. Conclusions: These results suggest that tongue cancer cells may induce TCIPA and enhance tumor metastasis. SAS-induced TCIPA is related to TF secretion, thrombin generation and associated with Phospholipase C-Inositol triphosphate signaling and ROS production. Betel quid chewing may potentially promote tongue cancer metastasis.