Effect of Thrombin Treatment of Tumor Cells on Adhesion of Tumor Cells to Platelets in Vitro and Tumor Metastasis in Vivo1

Seven different tumor cell lines (human melanoma SK MEL 28; hamster melanoma HM29; murine melanomas B16F10 and amelanotic melanoma B16a; human colon carcinoma 11("IX:murine colon carcinoma CT26; and murine Lewis lung carcinoma) were treated with thrombin at 0.5-1 unit/ml and examined for their ability to bind to adherent platelets; HM29 was studied for its ability to bind to fibronectin and von Willebrand factor; .»1611.B16F10, and B16a were studied for their ability to form pulmonary metastasis after i.v. injection of thrombin-treated tumor cells; CT26 was studied for its ability to grow s.c. Five of 7 thrombintreated tumor cell lines increased their adhesion to adherent platelets 2to 3-fold. HM29 increased its adherence to fibronectin and von Willebrand factor 2to 3-fold. CT26, B16F1, B16F10, and B16a increased experimental pulmonary metastasis 10to 156-fold. Thrombin-treated CT26 cells demonstrated 2-fold greater growth in vivoafter s.c. injection. The mechanism of enhanced adhesion of thrombin-treated tumor cells to platelets required the platelet integrin GPHb-GPIIIa since it could be inhibited by agents known to block adhesion of ligands to CPIIb-GPIIIa (monoclonal antibody 10E5, tetrapeptide RGDS, disintegrin Albolabrin); as well as a "GPIIb-GPIIIa-like" structure on tumor cells since it could be inhibited by treatment of thrombin-treated tumor cells with 10E5 and RGDS. The thrombin effect on tumor cells was optimum at l h of incubation with thrombin, did not require active thrombin on the tumor cell surface, and did not require protein synthesis (not inhibited by cycloheximide). Thus, thrombin-treated tumor cells markedly enhance pulmonary metastasis. It is suggested that this may be secondary to thrombin-induced enhanced adhesion as well as growth of tumor cells.