S62798, a TAFIa inhibitor, accelerates endogenous thrombolysis in a murine model of pulmonary thromboembolism

Abstract

Pulmonary embolism (PE) is the third leading cause of cardiovascular death in western countries. The enhancement of fibrinolysis constitutes a promising approach to treat thrombotic diseases. In patients, venous thrombosis and thromboembolism risks are associated with increased plasma levels of TAFI (Thrombin Activatable Fibrinolysis Inhibitor) antigen as well as the active form TAFIa. S62798 is a competitive, selective and potent human TAFIa inhibitor (IC50±SD=11.2±0.4nM). It is however less potent on mouse TAFIa (IC50±SD=270±39nM). Here, we tested the ability of S62798 to enhance endogenous fibrinolysis in a mouse model of pulmonary thromboembolism. Human Tissue Factor (TF) was injected in C57Bl6 male mice. Ten minutes later, mice (n=4 to 14 per group) were treated (IV) with S62798 (from 0.01 to 100mg/kg) or vehicle (0.9% NaCl). Ten or twenty minutes (min) later, mice were anesthetized and lungs were collected, homogenized and pulmonary fibrin was quantified by ELISA. Results are expressed as ratio of geometric mean of pulmonary fibrin (μg/mL): tested treatment/ vehicle [95% confidence interval (CI)]. Ten minutes after S62798 treatment, pulmonary fibrin deposition was dose-dependently decreased with a Minimal Effective Dose of 0.04mg/kg [90% prediction interval 0.037 - 0.051] and an ED50 of 0.03mg/kg [95% CI: 0.01; 0.06]. Mice were then treated with 0.1mg/kg S62798 or vehicle (10 min after TF induction) and fibrin deposition in lungs was quantified 10 and 20 minutes post S62798 treatment. The level of pulmonary fibrin deposition was significantly decreased (p<0.0001) compared to vehicle group (ratio 0.31 [0.21; 0.45] at 10 min; 0.35 [0.24; 0.51] at 20 min). Finally, the effect of S62798 (1mg/kg) in combination with heparin was evaluated (n=10/group). When administered 10 min before TF injection, heparin (2000IU/kg) significantly (p<0.0001) decreased pulmonary fibrin level (20 min post TF: ratio 0.03 [0.01; 0.05]). When treatment was done in a curative setting (10 min post TF), heparin alone had no effect (p=0.85) on fibrin deposition (ratio 0.96 [0.65; 1.43]) whereas a similar significant (p<0.0001) decreased pulmonary fibrin deposition was observed in response to S62798 alone or associated with heparin (ratio 0.27 [0.18; 0.40] (S62798 alone) and 0.29 [0.20; 0.43] (S62798+heparin)). In this model, curative S62798 treatment, alone or associated to heparin, accelerated clot degradation by potentiating endogenous fibrinolysis and thus decreased pulmonary fibrin deposition. Due to its capacity to enhance endogenous fibrinolysis, S62798, which has completed phase I studies, is expected to be a therapeutic option for intermediate high risk PE patients on top of anticoagulants. With early recanalization, S62798 should rapidly reduce pulmonary artery pressure and resistance, with concomitant improvement in right ventricular function, preserving cardiac function, and reducing acute PE-related morbidity and mortality in these patients. Funding Acknowledgement Type of funding source: None

Phosphinanes and Azaphosphinanes as Potent and Selective Inhibitors of Activated Thrombin-Activatable Fibrinolysis Inhibitor (TAFIa)

“…It is well established in the literature that three main functions are necessary for the recognition by TAFIa of an inhibitor including a carboxylic acid function forming intramolecular salt bridges with two arginine residues (Arg217 and Arg235), a zinc-coordinating group, and a basic moiety forming a salt bridge with Asp348 . The carboxylic acid and the basic function (amine) are usually separated by a 4–5 atom flexible chain (Figure ).…”

“…We determined the EC 50 values for 28a and 28k , which were 378 and 389 nM, respectively. These EC 50 values are significantly higher than the activity observed on human TAFIa (5 and 6 nM respectively, Table ), suggesting a higher activity of these compounds on human TAFIa than in rat TAFIa, as described for mouse TAFIa . The compounds showing in vitro inhibition over 40% were then tested for their duration of action in an in vivo pharmacodynamics model.…”

“…The SBDD led to the identification of 28k that accelerates clot degradation and might increase vessel recanalization in vivo . Acceleration of endogenous fibrinolysis was confirmed in vivo in a murine model of pulmonary thromboembolism after IV administration of 28k . Treatment with a TAFIa inhibitor, such as 28k also known as S62798 , could be a promising therapeutic option to treat patients with pulmonary embolism or ischemic stroke by accelerating blood vessel recanalization and improving patient outcome.…”

Carboxypeptidase U (CPU, TAFIa, CPB2) in Thromboembolic Disease: What Do We Know Three Decades after Its Discovery?

“…A rapid and dose-dependent inhibition of CPU in three different pharmacodynamic assays (ex vivo CPU inhibition and two variants of the in vitro clot lysis assay) was observed in all treated groups [ 95 ]. In a mouse model of pulmonary, thromboembolism, S62798 treatment, alone or associated with heparin, accelerated clot degradation by potentiating endogenous fibrinolysis and decreasing pulmonary fibrin deposition [ 164 ]. These promising data made it worthwhile to pursue clinical development for the treatment of thromboembolic diseases [ 95 ].…”