Proteinase-Activated Receptor 1, 3 Expression in Primary Human Carcinoma Cells.

The coagulation system is regularly activated in patients with cancer, especially with lung cancer and gastrointestinal tumors. Up to 30% of these patients suffer from thromboembolic complications. Obviously, activation of thrombin occurs in the natural course of cancer. During tumor progression, many patients develop malignant effusions; treatment is complicated by increased resistance of tumor cells to chemotherapy. Thrombin-mediated activation of cellular receptor(s), such as proteinase-activated receptor-1(PAR-1), plays an important role in tumor growth, local progression, and distant metastasis. Our hypothesis is, that tumor cells that express PAR-1 have a survival benefit if they are activated by thrombin within the malignant effusion. We harvested primary cancer cells from pleural and peritoneal effusions of 110 patients with different carcinomas. In 22 cases we were able to establish long time cultures (2 pancreatic, 4 colon, 3 SCLC, 5 NSCLC, 3 mesothelioma, 1 gastric, 1 rectum, 1 breast, 1 melanoma and 1 NHL). We detected PAR-1, 3 expression using reverse transcription-polymerase chain reaction (RT-PCR) and fluorescence activated cell sorting (FACS) scan. We found that in 76% the primary cancer cells were PAR-1 positive using RT-PCR assays, and in 70% the expression of PAR-1 receptor was positive using FACS scan. In contrast, we found that PCR for PAR-3 was positive in only 37.5% and the expression of the receptor in 6%. As a sign of thrombin activation, we regularly found increased levels of prothrombin fragment F1+2 in the malignant effusions compared to serum of patients (12.0 +/− 4.1 nmol/L vs 1.9 +/− 0.4 nmol/L).

In summary, we found that most of the primary cancer cells in malignant effusions exhibit a positive PAR-1 expression, but PAR-3 expression is low. Also, thrombin is activated in most malignant effusions as shown by prothrombin fragment 1+2 elevation. Further experiments will show if these cell-biological mechanisms aggravate cellular resistance in primary tumor cells found in malignant effusion in end-stage cancer. Therapeutic consequences, such as therapeutic thrombin inhibition in addition to chemotherapy are discussed.