Safe(r) anticoagulation

Interactions between depolymerized fucosylated glycosaminoglycan and coagulation proteases or inhibitors

Fucosylated glycosaminoglycan (FG) is a structurally novel glycosaminoglycan derivative, and it has potent anticoagulant activity. Depolymerized FG (dFG) is a selective factor Xase (FXase, FIXa-FVIIIa complex) inhibitor and it has antithrombotic action without major bleeding risks. In this study, we report the effects of dFG-3 (Mw ~14kDa) on the catalysis rates of factor IIa (FIIa), factor Xa (FXa) and factor IXa (FIXa) inhibition by antithrombin (AT), and the kinetic of the interactions between coagulation proteases or inhibitors and dFG-3 were also studied using biolayer interferometry (BLI) technology. We found that dFG-3 had much weaker catalysis activity of coagulation proteases inhibition by AT compared with heparin (UFH). The binding affinity of AT bound to dFG-3 was lower than UFH, and the UFH-AT interaction fitted well with biphasic-binding model while dFG-3-AT interaction was monophasic-binding, suggesting dFG-3 might not have allosteric activation effect on AT. The results are consistent with AT-independent inhibitory activities of dFG-3. dFG-3 could strongly bind to FIXa with much higher affinity than UFH, further explained the reason for its potent FXase inhibitory activity. Additionally, the binding ability of dFG-3 and FIXa decreased with decreasing molecular, and the fucose side chains and carboxyl groups of dFG-3 might be required for its high affinity binding with FIXa. Our data supports further the investigation of dFG-3 as a promising anticoagulant drug inhibiting the intrinsic FXase by binding to FIXa.

Characterization of the thrombin generation potential of leukemic and solid tumor cells by calibrated automated thrombography

BACKGROUND

Thrombin, the final enzyme of blood coagulation, is a multifunctional serine protease also involved in the progression of cancer. Tumor cells may activate blood coagulation proteases through the expression of procoagulant activities. However, specific information about the thrombin generation potential of malignant tissues is lacking. In this study we applied a single global coagulation test, the calibrated automated thrombogram assay, to characterize the specific procoagulant phenotypes of different tumor cells.

DESIGN AND METHODS

Malignant hematologic cells (i.e. NB4, HEL, and K562) or solid tumor cells (i.e. MCF-7 breast cancer and H69 small cell lung cells) were selected for the study. The calibrated automated thrombo-gram assay was performed in normal plasma and in plasma samples selectively deficient in factor VII, XII, IX or X, in the absence or presence of a specific anti-tissue factor antibody. Furthermore, cell tissue factor levels were characterized by measuring antigen, activity and mRNA expression.

RESULTS

In normal plasma, NB4 induced the highest thrombin generation, followed by MCF-7, H69, HEL, and K562 cells. The anti-tissue factor antibody, as well as deficiencies of factors VII, IX and XII affected the thrombin generation potential of malignant cells to different degrees, allowing differentiation of the two different pathways of blood clotting activation - by tissue factor or contact activation. The thrombin generation capacity of NB4 and MCF-7 cells was tissue factor-dependent, as it was highly sensitive to inhibition by anti-tissue factor antibody and factor VII deficiency, while the thrombin generation capacity of H69, HEL and K562 was contact activation-dependent, as no thrombin was generated by these cells in factor XII-deficient plasma.

CONCLUSIONS

This study demonstrates that the calibrated automated thrombogram assay is capable of quantifying, characterizing, and comparing the thrombin generation capacity of different tumor cells. This provides a useful tool for understanding the key factors determining the global pro-coagulant profile of tumors, which is important for addressing specific targeted therapy for the prevention of thrombosis and for cancer.