Fibrinolytic potential of DS-1040, a novel orally available inhibitor of activated thrombin-activatable fibrinolysis inhibitor (TAFIa)

Brain Expression of CPB2 and Effects of Cpb2 Deficiency in Mouse Models of Behavior

BACKGROUND

 Procarboxypeptidase B2 (proCPB2 or TAFI) is a zymogen that after activation cleaves C-terminal basic residues from peptides or proteins with many identified targets. A splice variant of CPB2 has been found in the brain lacking essential residues for its carboxypeptidase function. The aim was to determine CPB2 expression in the brain and effects of CPB2 deficiency (Cpb2 -/-) on behavior.

MATERIALS AND METHODS

 Behavioral effects were tested by comparing Cpb2 -/- mice in short-term (open field and elevated zero maze tests) and long-term (Phenotyper) observations with wild-type (WT) controls.

RESULTS

 Long-term observation compared day 1 (acclimatizing to novel environment) to day 4 (fully acclimatized) with the inactive (day) and active (night) periods analyzed separately. Brain expression of CPB2 mRNA and protein was interrogated in publicly available databases. Long-term observation demonstrated differences between WT and Cpb2 -/- mice in several parameters. For example, Cpb2 -/- mice moved more frequently on both days 1 and 4, especially in the normally inactive periods. Cpb2 -/- mice spent more time on the shelter and less time in it. Differences were more pronounced on day 4 after the mice had fully acclimatized. In short-term observations, no differences were observed between Cpb2 -/- mice and WT mice. Brain expression of CBP2 was not detectable in the human protein atlas. Databases of single-cell RNAseq did not show expression of CPB2 mRNA in either human or mouse brain.

CONCLUSION

 Continuous observation of home-cage behavior suggests that Cpb2 -/- mice are more active than WT mice, show different day-night activity levels, and might have a different way of processing information.

Inhibition of thrombin-activatable fibrinolysis inhibitor via DS-1040 to accelerate clot lysis in patients with acute pulmonary embolism: a randomized phase 1b study

BACKGROUND

The optimal treatment of intermediate-risk pulmonary embolism (PE) in hemodynamically stable patients remains unknown. Fibrinolytics reduce the risk of hemodynamic deterioration but increase bleeding risk. DS-1040, an inhibitor of thrombin-activatable fibrinolysis inhibitor, enhanced endogenous fibrinolytic activity without increasing bleeding risk in preclinical studies.

OBJECTIVES

To evaluate the tolerability and explore the efficacy of DS-1040 in patients with acute PE.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled study, ascending doses of intravenous DS-1040 (20-80 mg) or placebo were added to enoxaparin (1 mg/kg twice daily) in patients with intermediate-risk PE. The primary endpoint was the number of patients with major or clinically relevant nonmajor bleeding. The percentage change in thrombus volume and right-to-left ventricular dimensions, assessed using quantitative computed tomography pulmonary angiography, at baseline and after 12 to 72 hours were used to explore the efficacy of DS-1040.

RESULTS

Of 125 patients with all available data, 38 were randomized to placebo and 87 to DS-1040. The primary endpoint occurred in 1 patient in the placebo group (2.6%) and 4 patients who received DS-1040 (4.6%). One subject experienced major bleeding (DS-1040 80 mg group); no fatal or intracranial bleeding occurred. Thrombus volume was 25% to 45% lower after infusion, with no differences between the DS-1040 and placebo groups. There was no difference in the change from baseline right-to-left ventricular dimensions between the DS-1040 and placebo groups.

CONCLUSION

In patients with acute PE, adding DS-1040 to standard anticoagulation was not associated with an increase in bleeding but did not improve thrombus resolution or right ventricular dilation.

Safety, Pharmacokinetics and Pharmacodynamics of DS-1040, in Combination with Thrombectomy, in Japanese Patients with Acute Ischemic Stroke

Background and Objectives

DS-1040 is a novel inhibitor of the activated form of thrombin-activatable fibrinolysis inhibitor that may have therapeutic potential in thromboembolic diseases, such as acute ischemic stroke (AIS) or pulmonary embolism. We undertook a Phase I clinical trial to investigate the safety, pharmacokinetics, and pharmacodynamics of DS-1040 in Japanese patients who were eligible for thrombectomy following AIS.

Methods

The trial enrolled patients with AIS due to large vessel occlusion, who were planned for thrombectomy within 8 h of symptom onset. Subjects were randomized to receive a single intravenous infusion of placebo or DS-1040 (0.6, 1.2, 2.4 or 4.8 mg) in a sequential-cohort design. The primary endpoints were the incidence of intracranial hemorrhage (ICH) and major extracranial bleeding within 36 and 96 h, respectively, of treatment initiation. Treatment-emergent adverse events (TEAEs) and pharmacokinetic/pharmacodynamic parameters were also assessed.

Results

Nine patients received placebo and 32 patients received DS-1040. There were no cases of symptomatic ICH or major extracranial bleeding with either placebo or DS-1040 after 36 and 96 h. One patient, who received DS-1040 0.6 mg, experienced a subarachnoid hemorrhage that was considered to be drug-related. Three patients died (2 placebo, 1 DS-1040), but no deaths were adjudicated as study drug-related. In vivo exposure to DS-1040 increased in proportion to dosage, but no clear dose-response relationship was seen for D-dimer levels and thrombin-activatable fibrinolysis inhibitor activity.

Conclusions

Single doses of DS-1040 0.6–4.8 mg were well tolerated in Japanese patients with AIS undergoing thrombectomy.

Clinical trial registration number

NCT03198715; JapicCTI-163164.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40261-021-01112-8.

Fibrinogen and Antifibrinolytic Proteins: Interactions and Future Therapeutics

Thrombus formation remains a major cause of morbidity and mortality worldwide. Current antiplatelet and anticoagulant therapies have been effective at reducing vascular events, but at the expense of increased bleeding risk. Targeting proteins that interact with fibrinogen and which are involved in hypofibrinolysis represents a more specific approach for the development of effective and safe therapeutic agents. The antifibrinolytic proteins alpha-2 antiplasmin (α2AP), thrombin activatable fibrinolysis inhibitor (TAFI), complement C3 and plasminogen activator inhibitor-2 (PAI-2), can be incorporated into the fibrin clot by FXIIIa and affect fibrinolysis by different mechanisms. Therefore, these antifibrinolytic proteins are attractive targets for the development of novel therapeutics, both for the modulation of thrombosis risk, but also for potentially improving clot instability in bleeding disorders. This review summarises the main properties of fibrinogen-bound antifibrinolytic proteins, their effect on clot lysis and association with thrombotic or bleeding conditions. The role of these proteins in therapeutic strategies targeting the fibrinolytic system for thrombotic diseases or bleeding disorders is also discussed.

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

Enhancement of fibrinolysis constitutes a promising approach to treat thrombotic diseases. Venous thrombosis and thromboembolism risks are associated with increased plasma levels of TAFI (Thrombin Activatable Fibrinolysis Inhibitor) as well as its active form TAFIa. A new TAFIa inhibitor, namely S62798 has been identified. Its ability to enhance fibrinolysis was investigated both in vitro and in vivo in a mouse model of pulmonary thromboembolism, as well as its effect on bleeding. S62798 is a highly selective human, mouse and rat TAFIa inhibitor (IC₅₀ = 11; 270; 178 nmol/L, respectively). It accelerates lysis of a human clot in vitro, evaluated by thromboelastometry (EC₅₀ = 27 nmol/L). In a rat tail bleeding model, no effect of S62798 treatment was observed up to 20 mg/kg. Enhancement of endogenous fibrinolysis by S62798 was investigated in a mouse model of Tissue Factor-induced pulmonary thromboembolism. Intravenous administration of S62798 decreased pulmonary fibrin clots with a minimal effective dose of 0.03 mg/kg. Finally, effect of S62798 in combination with heparin was evaluated. When treatment of heparin was done in a curative setting, no effect was observed whereas a significantly decreased pulmonary fibrin deposition was observed in response to S62798 alone or in combination with heparin. This study demonstrates that S62798 is a potent TAFIa inhibitor with minimal risk of bleeding. In vivo, curative S62798 intravenous treatment, alone or associated with heparin, accelerated clot lysis by potentiating endogenous fibrinolysis and thus decreased pulmonary fibrin clots. S62798 is expected to be a therapeutic option for pulmonary embolism patients on top of anticoagulants.

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

Selective and potent inhibitors of activated thrombin activatable fibrinolysis inhibitor (TAFIa) have the potential to increase endogenous and therapeutic fibrinolysis and to behave like profibrinolytic agents without the risk of major hemorrhage, since they do not interfere either with platelet activation or with coagulation during blood hemostasis. Therefore, TAFIa inhibitors could be used in at-risk patients for the treatment, prevention, and secondary prevention of stroke, venous thrombosis, and pulmonary embolisms. In this paper, we describe the design, the structure-activity relationship (SAR), and the synthesis of novel, potent, and selective phosphinanes and azaphosphinanes as TAFIa inhibitors. Several highly active azaphosphinanes display attractive properties suitable for further in vivo efficacy studies in thrombosis models.

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

Procarboxypeptidase U (proCPU, TAFI, proCPB2) is a basic carboxypeptidase zymogen that is converted by thrombin(-thrombomodulin) or plasmin into the active carboxypeptidase U (CPU, TAFIa, CPB2), a potent attenuator of fibrinolysis. As CPU forms a molecular link between coagulation and fibrinolysis, the development of CPU inhibitors as profibrinolytic agents constitutes an attractive new concept to improve endogenous fibrinolysis or to increase the efficacy of thrombolytic therapy in thromboembolic diseases. Furthermore, extensive research has been conducted on the in vivo role of CPU in (the acute phase of) thromboembolic disease, as well as on the hypothesis that high proCPU levels and the Thr/Ile325 polymorphism may cause a thrombotic predisposition. In this paper, an overview is given of the methods available for measuring proCPU, CPU, and inactivated CPU (CPUi), together with a summary of the clinical data generated so far, ranging from the current knowledge on proCPU concentrations and polymorphisms as potential thromboembolic risk factors to the positioning of different CPU forms (proCPU, CPU, and CPUi) as diagnostic markers for thromboembolic disease, and the potential benefit of pharmacological inhibition of the CPU pathway.

Safety and Pharmacokinetics of DS-1040 Drug-Drug Interactions With Aspirin, Clopidogrel, and Enoxaparin

DS-1040, a novel low-molecular-weight inhibitor of activated thrombin-activatable fibrinolysis inhibitor, is under development for the treatment of thromboembolic diseases including venous thromboembolism and acute ischemic stroke. Here we describe the results of 3 studies that evaluated the safety and tolerability of DS-1040 along with the effect on DS-1040 pharmacokinetic (PK) parameters, when dosed alone or when coadministered with aspirin (NCT02071004), clopidogrel (NCT02560688), or enoxaparin in healthy subjects. Concomitant administration of single-dose DS-1040 with multiple-dose aspirin, multiple-dose clopidogrel, or single-dose enoxaparin, consistent with clinically relevant dose regimens, was safe and well tolerated with no serious treatment-emergent adverse events (TEAEs), TEAEs leading to discontinuation, bleeding-related TEAEs, and no significant changes in coagulation parameters. DS-1040 did not prolong bleeding time when administered concomitantly with aspirin or clopidogrel. In the aspirin study, DS-1040 PK was evaluated following the concomitant administration with multiple-dose aspirin, where the plasma DS-1040 exposure (peak plasma concentration [C_max ] and area under the concentration-time curve [AUC_inf ]) was to be similar to the data previously published in the first-in-human study of DS-1040 in healthy subjects. The PK parameters of DS-1040 coadministered with clopidogrel were similar to those of DS-1040 alone, with small increases in geometric means for C_max (7%) and AUC_last (9%). When coadministered with enoxaparin, the PK parameters of DS-1040 were not affected (1.1% and 1.5% decreases in geometric means for C_max and AUC_last , respectively). Therefore, concomitant administration of DS-1040 and clopidogrel or enoxaparin did not demonstrate PK drug-drug interactions.

Combined effect of a direct oral anticoagulant edoxaban and an inhibitor of activated thrombin-activatable fibrinolysis inhibitor on clot lysis

Fibrinolysis is regulated by the thrombin/thrombin-activatable fibrinolysis inhibitor (TAFI) system. Thus, anticoagulants and inhibitors of TAFI are expected to accelerate fibrinolysis. The combined effects of an anticoagulant and a TAFIa inhibitor on fibrinolysis remain unknown. The aim of this study was to evaluate the combined effect of edoxaban, an oral direct factor Xa (FXa) inhibitor, and a TAFIa inhibitor, potato tuber carboxypeptidase inhibitor (PCI) on tissue-type plasminogen activator (t-PA)-induced clot lysis in human plasma in vitro. Pooled human plasma (containing 180 ng/mL t-PA and 0.1 nM thrombomodulin) was mixed with edoxaban and/or PCI. Clot formation was induced by 2.5 pM tissue factor and 4 µM phospholipids and clot lysis time was examined. Plasma plasmin-α2 antiplasmin complex (PAP) concentration was measured as a marker of plasmin generation. Edoxaban or PCI alone significantly shortened the t-PA-induced clot lysis time and plasma PAP concentration. The combination of these compounds significantly accelerated the clot lysis compared with the inhibitors alone. Addition of PCI (0.3, 1, and 3 μg/mL) to 75 ng/mL edoxaban increased plasma PAP concentration compared with edoxaban alone; however, compared with PCI alone only the combination of 0.3 μg/mL PCI + 75 ng/mL edoxaban showed the significant increase in PAP concentration. Concomitant use of an oral direct FXa inhibitor, edoxaban, and a TAFIa inhibitor, PCI, significantly accelerate fibrinolysis via enhancement of plasmin generation. These results suggest that the combination of edoxaban and a TAFIa inhibitor might be beneficial for the treatment of thromboembolic diseases.