A first-in-human study of DS-1040, an inhibitor of the activated form of thrombin-activatable fibrinolysis inhibitor, in healthy subjects

Cutting-Edge Techniques and Drugs for the Treatment of Pulmonary Embolism: Current Knowledge and Future Perspectives

Pulmonary embolism (PE) is a potentially life-threatening condition requiring prompt diagnosis and treatment. Recent advances have led to the development of newer techniques and drugs aimed at improving PE management, reducing its associated morbidity and mortality and the complications related to anticoagulation. This review provides an overview of the current knowledge and future perspectives on PE treatment. Anticoagulation represents the first-line treatment of hemodynamically stable PE, direct oral anticoagulants being a safe and effective alternative to traditional anticoagulation: these drugs have a rapid onset of action, predictable pharmacokinetics, and low bleeding risk. Systemic fibrinolysis is suggested in patients with cardiac arrest, refractory hypotension, or shock due to PE. With this narrative review, we aim to assess the state of the art of newer techniques and drugs that could radically improve PE management in the near future: (i) mechanical thrombectomy and pulmonary embolectomy are promising techniques reserved to patients with massive PE and contraindications or failure to systemic thrombolysis; (ii) catheter-directed thrombolysis is a minimally invasive approach that can be suggested for the treatment of massive or submassive PE, but the lack of large, randomized controlled trials represents a limitation to widespread use; (iii) novel pharmacological approaches, by agents inhibiting thrombin-activatable fibrinolysis inhibitor, factor Xia, and the complement cascade, are currently under investigation to improve PE-related outcomes in specific settings.

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.

Visualization of Domain- and Concentration-Dependent Impact of Thrombomodulin on Differential Regulation of Coagulation and Fibrinolysis

BACKGROUND

 Thrombomodulin (TM) functions as a dual modulator-anticoagulant and antifibrinolytic potential-by the thrombin-dependent activation of protein C and thrombin-activatable fibrinolysis inhibitor (TAFI). Activated TAFI cleaves the C-terminal lysine of partially degraded fibrin and inhibits both plasminogen binding and its activation on the fibrin surface. We have reported previously that activated platelets initiate fibrin network formation and trigger fibrinolysis after the accumulation of tissue-type plasminogen activator and plasminogen.

OBJECTIVE

 To analyze the effects of domain-deletion variants of TM on coagulation and fibrinolysis at different concentrations.

METHODS

 Domain-deletion variants of TM, such as D123 (all extracellular regions), E3456 (minimum domains for thrombin-dependent activation of protein C and TAFI), and E456 (minimum domains for that of protein C but not TAFI), were used at 0.25 to 125 nM for turbidimetric assay to determine the clotting time and clot lysis time and to visualize fibrin network formation and lysis in platelet-containing plasma.

RESULTS AND CONCLUSIONS

 A low concentration of either D123 or E3456, but not of E456, prolonged clot lysis time, and delayed the accumulation of fluorescence-labeled plasminogen at the activated platelets/dense fibrin area due to effective TAFI activation. Conversely, only the highest concentrations of all three TM variants delayed the clotting time, though fibrin network formation in the vicinity of activated platelets was almost intact. TAFI activation might be affected by attenuation in thrombin activity after the clot formation phase. These findings suggest that the spatiotemporal balance between the anticoagulant and antifibrinolytic potential of TM is controlled in domain- and concentration-dependent manners.

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.

Carboxypeptidase U (TAFIa) Is Rapidly Activated and Deactivated Following Thrombolysis and Thrombectomy in Stroke Patients

The antifibrinolytic enzyme carboxypeptidase U (CPU, TAFIa, CPB2) is an appealing target for the treatment of acute ischemic stroke (AIS). Increased insights in CPU activation and inactivation during thrombolysis (rtPA) with or without endovascular thrombectomy (EVT) are required to develop CPU inhibitors as profibrinolytic agents with optimal benefits/risks. Therefore, CPU kinetics during ischemic stroke treatment were evaluated. AIS patients with documented cerebral artery occlusion receiving rtPA (N = 20) or rtPA + EVT (N = 16) were included. CPU activation during thrombolysis was measured by an ultrasensitive HPLC-based CPU activity method and by an ELISA measuring both CPU and inactivated CPU (CPU + CPUi). Intravenous blood samples were collected at admission and throughout the first 24 h. Additional in situ blood samples were collected in the rtPA + EVT cohort proximal from the thrombus. The NIHSS score was determined at baseline and 24 h. CPU activity and CPU + CPUi levels increased upon rtPA administration and reached peak values at the end of thrombolysis (1 h). High inter-individual variability was observed in both groups. CPU activity decreased rapidly within 3 h, while CPU + CPUi levels were still elevated at 7 h. CPU activity or CPU + CPUi levels were similar in in situ and peripheral samples. No correlation between CPU or CPU + CPUi and NIHSS or thrombus localization was found. The CPU system was rapidly activated and deactivated following thrombolysis and thrombectomy in stroke patients, suggesting that a CPU inhibitor would have to be administered during rtPA infusion and over the next few hours. The high CPU generation variability suggests that some patients may not respond to the treatment. EudraCT number 2017-002760-41.

Submassive Pulmonary Embolism: Current Perspectives and Future Directions

Submassive pulmonary embolism (PE) lies on a spectrum of disease severity between standard and high-risk disease. By definition, patients with submassive PE have a worse outcome than the majority of those with standard-risk PE, who are hemodynamically stable and lack imaging or laboratory features of cardiac dysfunction. Systemic thrombolytic therapy has been proven to reduce mortality in patients with high-risk disease; however, its use in submassive PE has not demonstrated a clear benefit, with haemodynamic improvements being offset by excess bleeding. Furthermore, meta-analyses have been confusing, with conflicting results on overall survival and net gain. As such, significant interest remains in optimising thrombolysis, with recent efforts in catheter-based delivery as well as upcoming studies on reduced systemic dosing. Recently, long-term cardiorespiratory limitations following submassive PE have been described, termed post-PE syndrome. Studies on the ability of thrombolytic therapy to prevent this condition also present conflicting evidence. In this review, we aim to clarify the current evidence with respect to submassive PE management, and also to highlight shortcomings in current definitions and prognostic factors. Additionally, we discuss novel therapies currently in preclinical and early clinical trials that may improve outcomes in patients with submassive PE.

Association of Thrombin-Activatable Fibrinolysis Inhibitor with Acute Pulmonary Embolism

BACKGROUND

 Thrombin-activatable fibrinolysis inhibitor (TAFI) inhibits fibrinolysis and high levels may have an association with thrombosis. The aim of the current study was to investigate the association of TAFI antigen levels with pulmonary thromboembolism (PTE).

PATIENTS AND METHODS

 A case-control study was conducted with 29 patients with PTE and 17 age- and gender-matched control individuals. Plasma levels of TAFI were measured at the time of diagnosis, then at 3 and 6 months after the event.

RESULTS

 Initial TAFI levels (%) were higher in patients with PTE than in the control group Initial TAFI levels (%) were higher in patients with PTE than in the control group (190,0 [65,0-250,0] vs 133,0 [83,0-153,0]; p = 0.003). TAFI levels significantly decreased at the third and sixth months after initial diagnosis (p < 0.05). The percentage reductions in TAFI levels were 12 and 36.8% at 3 and 6 months, respectively. The Odss ratio (OR) of TAFI level for PTE was found to be 1.024 (95% CI: 1.007-1.040; p = 0.005). There was no significant correlation of initial TAFI levels with age, gender, smoking status, history of thrombosis, pulmonary artery pressure, and D-dimer levels (p > 0.05). In the sixth month of treatment, patients with residual thrombosis were seen to have similar baseline levels and reductions of TAFI as patients without residual thrombosis (p > 0.05).

CONCLUSION

 The result of this study suggests that high TAFI levels may have a role in the occurrence of PTE without impact on treatment outcome.

Activated platelet-based inhibition of fibrinolysis via thrombin-activatable fibrinolysis inhibitor activation system

Our previous real-time imaging studies directly demonstrated the spatiotemporal regulation of clot formation and lysis by activated platelets. In addition to their procoagulant functions, platelets enhanced profibrinolytic potential by augmenting the accumulation of tissue-type plasminogen activator (tPA) and plasminogen, in vivo in a murine microthrombus model, and in vitro in a platelet-containing plasma clot model. To clarify the role of thrombin-activatable fibrinolysis inhibitor (TAFI), which regulates coagulation-dependent anti-fibrinolytic potential, we analyzed tPA-induced clot lysis times in platelet-containing plasma. Platelets prolonged clot lysis times in a concentration-dependent manner, which were successfully abolished by a thrombomodulin-neutralizing antibody or an activated TAFI inhibitor (TAFIaI). The results obtained using TAFI- or factor XIII-deficient plasma suggested that TAFI in plasma, but not in platelets, was essential for this prolongation, though its cross-linkage with fibrin was not necessary. Confocal laser scanning microscopy revealed that fluorescence-labeled plasminogen accumulated on activated platelet surfaces and propagated to the periphery, similar to the propagation of fibrinolysis. Plasminogen accumulation and propagation were both enhanced by TAFIaI, but only accumulation was enhanced by thrombomodulin-neutralizing antibody. Labeled TAFI also accumulated on both fibrin fibers and activated platelet surfaces, which were Lys-binding-site-dependent and Lys-binding-site-independent, respectively. Finally, TAFIaI significantly prolonged the occlusion times of tPA-containing whole blood in a microchip-based flow chamber system, suggesting that TAFI attenuated the tPA-dependent prolongation of clot formation under flow. Thus, activated platelet surfaces are targeted by plasma TAFI, to attenuate plasminogen accumulation and fibrinolysis, which may contribute to thrombogenicity under flow.

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.

Selective inhibition of carboxypeptidase U may reduce microvascular thrombosis in rat experimental stroke

BACKGROUND

Carboxypeptidase U (CPU, CPB2, TAFIa) is a potent attenuator of fibrinolysis. The inhibition of CPU is thus an interesting strategy for improving thrombolysis.

OBJECTIVES

The time course of CPU generation and proCPU consumption were assessed in an experimental rat model of acute ischemic stroke (AIS). In addition, the effects of the selective CPU inhibitor AZD9684 on CPU kinetics, microvascular thrombosis (MT), and AIS outcome were evaluated.

METHODS

Rats were subjected to transient middle cerebral artery occlusion (tMCAO) and received recombinant tissue-type plasminogen activator (tPA), a specific CPU inhibitor (AZD9684), combination therapy of tPA and AZD9684, or saline for 1 hour using a randomized treatment regime. CPU and proCPU levels were determined at five time points and assessed in light of outcome parameters (a.o.: infarct volume and fibrin[ogen] deposition as a measure for MT).

RESULTS

Clear activation of the CPU system was observed after AIS induction, in both saline- and tPA-treated rats. Maximal CPU activities were observed at treatment cessation and were higher in tPA-treated animals compared to the saline group. Concomitant proCPU consumption was more pronounced in tPA-treated rats. AZD9684 suppressed the CPU activity and reduced fibrin(ogen) deposition, suggesting a reduction of MT. Nonetheless, a significant decrease in infarct volume was not observed.

CONCLUSIONS

A pronounced activation of the CPU system was observed during tMCAO in rats. Selective inhibition of CPU with AZD9684 was able to reduce fibrin(ogen) deposition and brain edema, suggesting a reduction of MT but without a significant effect on final infarct volume.

Acute treatment of venous thromboembolism

All patients with venous thromboembolism (VTE) should receive anticoagulant treatment in the absence of absolute contraindications. Initial anticoagulant treatment is crucial for reducing mortality, preventing early recurrences, and improving long-term outcome. Treatment and patient disposition should be tailored to the severity of clinical presentation, to comorbidities, and to the potential to receive appropriate care in the outpatient setting. Direct oral anticoagulants (DOACs) used in fixed doses without laboratory monitoring are the agents of choice for the treatment of acute VTE in the majority of patients. In comparison with conventional anticoagulation (parenteral anticoagulants followed by vitamin K antagonists), these agents showed improved safety (relative risk [RR] of major bleeding, 0.61; 95% confidence interval [CI], 0.45-0.83) with a similar risk of recurrence (RR, 0.90; 95% CI, 0.77-1.06). Vitamin K antagonists or low molecular weight heparins are still alternatives to DOACs for the treatment of VTE in specific patient categories such as those with severe renal failure or antiphospholipid syndrome, or cancer, respectively. In addition to therapeutic anticoagulation, probably less than 10% of patients require reperfusion by thrombolysis or interventional treatments; those patients are hemodynamically unstable with acute pulmonary embolism, and a minority of them have proximal limb-threatening deep vein thrombosis (DVT). The choice of treatment should be driven by the combination of evidence from clinical trials and by local expertise. The majority of patients with acute DVT and a proportion of selected hemodynamically stable patients with acute pulmonary embolism can be safely managed as outpatients.

Novel antithrombotic strategies for treatment of venous thromboembolism

Venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), is the third most common cause of vascular death after heart attack and stroke. Anticoagulation therapy is the cornerstone of VTE treatment. Despite such therapy, up to 50% of patients with DVT develop postthrombotic syndrome, and up to 4% of patients with PE develop chronic thromboembolic pulmonary hypertension. Therefore, better therapies are needed. Although direct oral anticoagulants are more convenient and safer than warfarin for VTE treatment, bleeding remains the major side effect, particularly in cancer patients. Factor XII and factor XI have emerged as targets for new anticoagulants that may be safer. To reduce the complications of VTE, attenuation of thrombin activatable fibrinolysis inhibitor activity is under investigation in PE patients to enhance endogenous fibrinolysis, whereas blockade of leukocyte interaction with the vessel wall is being studied to reduce the inflammation that contributes to postthrombotic syndrome in DVT patients. Focusing on these novel antithrombotic strategies, this article explains why safer anticoagulants are needed, provides the rationale for factor XII and XI as targets for such agents, reviews the data on the factor XII- and factor XI-directed anticoagulants under development, describes novel therapies to enhance fibrinolysis and decrease inflammation in PE and DVT patients, respectively, and offers insights into the opportunities for these novel VTE therapies.

Impaired Spontaneous/Endogenous Fibrinolytic Status as New Cardiovascular Risk Factor?: JACC Review Topic of the Week

Endogenous fibrinolysis is a powerful natural defense mechanism against lasting arterial thrombotic occlusion. Recent prospective studies have shown that impaired endogenous fibrinolysis (or hypofibrinolysis) can be detected in a significant number of patients with acute coronary syndrome (ACS) using global assays and is a strong marker of future cardiovascular risk. This novel risk biomarker is independent of traditional cardiovascular risk factors and unaffected by antiplatelet therapy. Most prospective prognostic data have been obtained using a global assay using native whole blood at high shear or plasma turbidimetric assays, which are described herein. Tests of endogenous fibrinolysis could be used to identify patients with ACS who, despite antiplatelet therapy, remain at high cardiovascular risk. This review discusses the impact of currently available medications and those in development that favorably modulate fibrinolytic status and may offer a potential new avenue to improve outcomes in ACS.

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.

Improving fibrinolysis in venous thromboembolism: impact of fibrin structure

Introduction. Fibrinolysis is of key importance in maintaining vessel patency. Impaired fibrinolysis associated with more compact fibrin structure has been shown in patients with venous thromboembolism (VTE), including deep-vein thrombosis and pulmonary embolism (PE). Currently, recombinant or modified plasminogen activators are the only commonly available thrombolytic agents. However, they are fraught with side effects and suboptimal effectiveness. Areas covered. Based on the available literature, the current evidence linking fibrinolysis with VTE and potential therapeutic targets among fibrinolysis proteins are presented. Expert opinion. Prolonged clot lysis time has been reported as a new predictor of first-time and recurrent VTE, including PE. Anticoagulant therapy, including non-vitamin K antagonist oral anticoagulants, has a favorable impact on fibrinolysis in VTE patients. Several VTE risk factors are also related to lower efficiency of fibrinolysis and their treatment improve fibrinolysis, in part by alterations to fibrin properties. There is an increasing number of studies aiming at developing novel profibrinolytic therapeutic agents for treatment of VTE patients, mostly targeting the antifibrinolytic proteins, i.e. antiplasmin, plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor.

First-in-Human Study to Assess the Safety, Pharmacokinetics, and Pharmacodynamics of an Oral Formulation of DS-1040, an Inhibitor of the Activated Form of Thrombin-Activatable Fibrinolysis Inhibitor, in Healthy Subjects

DS-1040, a low-molecular-weight imidazole derivative, inhibits the enzymatic activity of thrombin-activatable fibrinolysis inhibitor (TAFIa), enhancing endogenous tissue plasminogen activator-triggered fibrinolysis. This first-in-human, randomized, placebo-controlled, phase 1 study evaluated the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of an oral formulation of DS-1040. Healthy adults (aged 20-45 years; N = 56) were randomized 3:1 to receive DS-1040 orally administered as single ascending doses (50, 100, 200, or 400 mg) or placebo, or DS-1040 multiple ascending doses (100 mg once daily, 200 mg once daily, or 150 mg twice daily) or placebo for 14 days. Safety, PK, and PD parameters were assessed. All doses of DS-1040 were well tolerated; no serious/severe adverse events (AEs) or discontinuations due to AEs occurred. DS-1040 had no effect on coagulation parameters, and no treatment-related trends in the bleeding time were observed. DS-1040 exposure (peak concentration and area under the concentration-time curve) increased in a dose-proportional manner across the single-dose range. With multiple doses, steady state was achieved by day 7 with minimal accumulation (mean accumulation ratio 1.15-1.25), and the PK was time-independent. After 72 hours, approximately 10% of the DS-1040 400-mg single dose was recovered in urine as intact parent drug. The mean terminal half-life ranged from 17.2 to 24.9 hours, which was similar to previous intravenous administration data. Dose-dependent inhibition of total TAFIa activity was observed following single and multiple doses of oral DS-1040. The safety and PK/PD profiles of oral DS-1040 in healthy subjects support further clinical development.

Fibrinolysis: strategies to enhance the treatment of acute ischemic stroke

Stroke is a major cause of disability worldwide, and is the second leading cause of death after ischemic heart disease. Until recently, tissue-type plasminogen activator (t-PA) was the only treatment for acute ischemic stroke. If administered within 4.5 h of symptom onset, t-PA improves the outcome in stroke patients. Mechanical thrombectomy is now the preferred treatment for patients with acute ischemic stroke resulting from a large-artery occlusion in the anterior circulation. However, the widespread use of mechanical thrombectomy is limited by two factors. First, only ⁓ 10% of patients with acute ischemic stroke have a proximal large-artery occlusion in the anterior circulation and present early enough to undergo mechanical thrombectomy within 6 h; an additional 9-10% of patients presenting within the 6-24-h time window may also qualify for the procedure. Second, not all stroke centers have the resources or expertise to perform mechanical thrombectomy. Nonetheless, patients who present to hospitals where thrombectomy is not an option can receive intravenous t-PA, and those with qualifying anterior circulation strokes can then be transferred to tertiary stroke centers where thrombectomy is available. Therefore, despite the advances afforded by mechanical thrombectomy, there remains a need for treatments that improve the efficacy and safety of thrombolytic therapy. In this review, we discuss: (i) current treatment options for acute ischemic stroke; (ii) the mechanism of action of fibrinolytic agents; and (iii) potential strategies to manipulate the fibrinolytic system to promote endogenous fibrinolysis or to enhance the efficacy of fibrinolytic therapy.

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

An activated thrombin-activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis by removing C-terminal lysine/arginine residues from partially degraded fibrin. We have identified a novel low-molecular-weight inhibitor of TAFIa, DS-1040, to be potentially useful for treating thrombotic diseases. In this study, we investigated its in vitro pharmacological profile and in vivo effects in animal models of microthrombosis and bleeding. DS-1040 inhibited human TAFIa and carboxypeptidase N (CPN) in vitro with IC₅₀ values of 5.92 and 3.02 × 10⁶ nmol/L, respectively, suggesting that DS-1040 is highly selective for TAFIa over CPN. DS-1040 did not affect platelet aggregation and coagulation time. In a tissue factor-induced rat microthrombosis model, intravenously administered DS-1040 reduced existing fibrin clots in the lung, whereas post-treatment with enoxaparin had limited effect. Both intravenously and orally administered DS-1040 elevated plasma D-dimer levels with similar plasma exposures of DS-1040. DS-1040 significantly augmented plasma D-dimer level on top of silent dose of recombinant tissue-plasminogen activator (t-PA), suggesting DS-1040 enhances fibrinolytic activity of t-PA. In addition, DS-1040 did not prolong the tail bleeding time beyond its efficacy dose. These results indicate that DS-1040 is a potent, selective, intravenously/orally available inhibitor of TAFIa with minimum risk of bleeding. DS-1040 is a potential novel fibrinolysis enhancer useful in treating thrombotic diseases.

Carboxypeptidase B2 and carboxypeptidase N in the crosstalk between coagulation, thrombosis, inflammation, and innate immunity

Two basic carboxypeptidases, carboxypeptidase B2 (CPB2) and carboxypeptidase N (CPN) are present in plasma. CPN is constitutively active, whereas CPB2 circulates as a precursor, procarboxypeptidase B2 (proCPB2), that needs to be activated by the thrombin-thrombomodulin complex or plasmin bound to glycosaminoglycans. The substrate specificities of CPB2 and CPN are similar; they both remove C-terminal basic amino acids from bioactive peptides and proteins, thereby inactivating them. The complement cascade is a cascade of proteases and cofactors activated by pathogens or dead cells, divided into two phases, with the second phase only being triggered if sufficient C3b is present. Complement activation generates anaphylatoxins: C3a, which stimulates macrophages; and C5a, which is an activator and attractant for neutrophils. Pharmacological intervention with inhibitors has shown that CPB2 delays fibrinolysis, whereas CPN is responsible for systemic inactivation of C3a and C5a. Among mice genetically deficient in either CPB2 or CPN, in a model of hemolytic-uremic syndrome, Cpb2-/- mice had the worst disease, followed by Cpn-/- mice, with wild-type (WT) mice being the most protected. This model is driven by C5a, and shows that CPB2 is important in inactivating C5a. In contrast, when mice were challenged acutely with cobra venom factor, the reverse phenotype was observed; Cpn-/- mice had markedly worse disease than Cpb2-/- mice, and WT mice were resistant. These observations need to be confirmed in humans. Therefore, CPB2 and CPN have different roles. CPN inactivates C3a and C5a generated spontaneously, whereas proCPB2 is activated at specific sites, where it inactivates bioactive peptides that would overwhelm CPN.

Pulmonary embolism

Pulmonary embolism (PE) is caused by emboli, which have originated from venous thrombi, travelling to and occluding the arteries of the lung. PE is the most dangerous form of venous thromboembolism, and undiagnosed or untreated PE can be fatal. Acute PE is associated with right ventricular dysfunction, which can lead to arrhythmia, haemodynamic collapse and shock. Furthermore, individuals who survive PE can develop post-PE syndrome, which is characterized by chronic thrombotic remains in the pulmonary arteries, persistent right ventricular dysfunction, decreased quality of life and/or chronic functional limitations. Several important improvements have been made in the diagnostic and therapeutic management of acute PE in recent years, such as the introduction of a simplified diagnostic algorithm for suspected PE as well as phase III trials demonstrating the value of direct oral anticoagulants in acute and extended treatment of venous thromboembolism. Future research should aim to address novel treatment options (for example, fibrinolysis enhancers) and improved methods for predicting long-term complications and defining optimal anticoagulant therapy parameters in individual patients, and to gain a greater understanding of post-PE syndrome.

Tissue-type plasminogen activator transgenic rats for evaluating inhibitors of the activated form of thrombin-activatable fibrinolysis inhibitor

No rodent models are currently available for evaluating inhibitors of the activated form of thrombin-activatable fibrinolysis inhibitor (TAFIa) without exogenous supplementation of tissue-type plasminogen activator (tPA). Characterization of tPA transgenic rats as a tool for the nonclinical evaluation of TAFIa inhibitors is the objective of the current study. tPA transgenic rats were subjected to rat models of tissue-factor-induced thromboembolism, FeCl₃-induced deep vein thrombosis (DVT) and arterial thrombosis, and tail bleeding. Potato tuber carboxypeptidase inhibitor (PCI), a selective TAFIa inhibitor, was used as an experimental compound at doses of 0.1, 1, or 10 mg/kg, and its antithrombotic effects and bleeding prolongation effect were compared with nontransgenic rats. Intravenous PCI showed significant and dose-related increase in plasma d-dimer levels in the tissue-factor-induced thromboembolism model. Intravenous PCI also significantly and dose-dependently reduced thrombus weights in the two thrombosis models only in the tPA transgenic rats. These results suggest that sensitive in-vivo evaluation of TAFIa inhibitors can be achieved using tPA transgenic rats without exogenous supplementation of recombinant tPA. On the other hand, no statistically significant prolongation of bleeding times by PCI was observed in either strain, whereas increased bleeding times were observed with 10 mg/kg of intravenous recombinant tPA, suggesting that the low bleeding risk of TAFIa inhibitors is further confirmed in the tPA transgenic rats whose basal tPA levels are elevated. tPA transgenic rats may be beneficial for the pharmacological and toxicological evaluation of TAFIa inhibitors and further confirm that TAFIa is a promising target for various thrombotic disorders.