Corthrombin

A new class of divalent thrombin inhibitors is described that contains an α‐keto‐amide transition‐state mimetic linking an active site binding group and a group that binds to the fibrinogen‐binding exosite. The X‐ray crystallographic structure of the most potent member of this new class, CVS995, shows many features in common with other divalent thrombin inhibitors and clearly defines the transition‐state‐like binding of the α‐keto‐amide group. The structure of the active site part of the inhibitor shows a network of water molecules connecting both the side‐chain and backbone atoms of thrombin and the inhibitor. Direct peptide analogues of the new transition‐state‐containing divalent thrombin inhibitors were compared using in vitro assays of thrombin inhibition. There was no direct correlation between the binding constants of the peptides and their α‐keto‐amide counterparts. The most potent cv‐keto‐amide inhibitor, CVS995, with a Ki = 1 pM, did not correspond to the most potent divalent peptide and contained a single amino acid deletion in the exosite binding region with respect to the equivalent region of the natural thrombin inhibitor hirudin. The interaction energies of the active site, transition state, and exosite binding regions of these new divalent thrombin inhibitors are not additive.

Background In the pathogenesis of (recurrent) thrombosis, clot-associated thrombin appears to play an important role. Antithrombin III–independent thrombin inhibitors have been shown to neutralize clot-bound thrombin effectively. We compared the sustained antithrombotic effects and the effects on endogenous fibrinolysis of several of these agents with recombinant tick anticoagulant peptide (rTAP), a selective factor Xa inhibitor, and low-molecular-weight heparin (LMWH) in an experimental venous thrombosis model. Methods and Results Rabbits received either recombinant hirudin (rHir), Hirulog-1, CVS#995 (a novel direct inhibitor of thrombin), rTAP, LMWH, or saline. The effect on thrombus growth was assessed by measuring the accretion of 125 I-labeled fibrinogen onto preformed nonradioactive thrombi, and the effect on endogenous fibrinolysis was assessed by measuring the decline in radioactivity of preformed 125 I-labeled thrombi in rabbit jugular veins. All direct thrombin inhibitors induced a sustained antithrombotic effect compared with either LMWH and rTAP. In addition, CVS#995 also further decreased thrombus size after stopping its infusion, which was due to a significant enhancement of endogenous fibrinolysis. Conclusions Direct thrombin inhibition by rHir, Hirulog-1, or CVS#995 induces a sustained antithrombotic effect compared with rTAP and LMWH, which is most likely due to inhibition of clot-bound thrombin. CVS#995 was shown to also enhance the extent of endogenous fibrinolysis to a greater degree compared with rHir and might therefore be an interesting new antithrombotic agent for the treatment of venous and arterial thrombosis.