Direct Activation of Factor X by Some Cancer Cells: Evaluation by an Amidolytic Assay

The procoagulant activity of cells from some experimental tumors isolated in culture or as cell suspensions fron ascitic fluid was investigated. Cells from Lewis Lung carcinoma (primary and metastasis), Ehrlich carcinoma ascites and JK sarcoma ascites markedly shortened the recalcification time of normal, F.VIII and F.VII-deficient, not of F.X-deficient human plasma. This suggests a direct activation of coagulation F.X. To verify this assumption, cells were incubated with a BaS0₄-eluate of normal (N.E.) or F.VII-deficient (VII-D.E.) human serum (as a source of F.X) and CaCl₂. The chromogenic substrate S-2222 was used for monitoring F. Xa generation. Substrate cleavage occurred to different degrees with all cell types; it was similar both with VII-D.F. and N.F., proportional to cell number and incubation period and was not influenced by hirudin. When tested separately, neither the eluate nor the cells had any amidolytic activity. Our assay readily discriminated between direct and F.VII-mediated activation of F.X. Indeed when cells with thrombopla-stin-like activity (mouse embryo fibroblasts) were tested, the rate of S-2222 cleavage was markedly lower with VII-D.E. than with N.E. Cells from sarcoma 180 ascites were completely inactive in both plasma recalcification time and amidolytic assay. It is concluded that cells from some experimental tumors directly activate F.X.(Supported by CNR (Italy), and NIK, NCI (USA).