PLATELET ACTIVATION BY CELLS ISOLATED FROM HUMAN TUMOR-TISSUES - EFFECT OF CYCLOOXYGENASE BLOCKADE

We have studied in a homologous system the effect on different platele t functions of cells isolated from 26 human tumor tissues (11 breast c arcinomas, 11 colon carcinomas, 2 pancreatic carcinomas, 1 gastric car cinoma and 1 esophageal carcinoma). Tumor cells (10(5)/ml) significant ly increased platelet adhesion to glass beads; they were also found to possess a potent platelet aggregating activity and aggregation was ac companied by significant release of ATP and platelet derived growth fa ctor (PDGF) and by production of TXB2. Preincubation of platelets with a low concentration (1 muM) of indobufen, a cyclooxygenase inhibitor, significantly reduced tumor cell induced TXB2 production and ATP rele ase, while the other platelet functions were not modified. Higher conc entrations of the drug (10 or 100 muM) were also able to inhibit tumor cell-induced platelet aggregation and PDGF release, while platelet ad hesion to glass beads was unchanged even at these doses. Finally, prei ncubation of neoplastic cells with indobufen (400 muM) had no effect o n their ability to induce platelet aggregation, TXB2 production and AT P release. These data demonstrate that cyclooxygenase blockade in plat elets has different effects on several platelet functions activated by the tumor cells that were investigated.