Advances in oral anticoagulation therapy – What's in the pipeline?

An Update on Betrixaban, The Challenging Anticoagulant Agent for Extended Venous Thromboembolism Prophylaxis

ABSTRACT

Venous thromboembolism (VTE) is a prevalent yet preventable cause of death, particularly among hospitalized patients. Studies have shown that the risk of VTE remains high for up to 6 months after discharge, highlighting the need for extended thromboprophylaxis as a viable treatment approach. Despite the availability of several anticoagulant drugs such as vitamin K antagonists, heparinoids, rivaroxaban, apixaban, edoxaban, and dabigatran, none of them has received approval from the US Food and Drug Administration for long-term thromboprophylaxis. However, an emerging factor Xa inhibitor called betrixaban has shown promising results in Phase II and phase III trials, positioning itself as the first and only US Food and Drug Administration-approved anticoagulant for extended thromboprophylaxis in hospitalized patients after discharge. Betrixaban offers distinct pharmacological characteristics, including a long half-life, low renal excretion, and unique hepatic metabolism, making it an attractive option for various theoretical uses. Numerous articles have been published discussing the safety and efficacy of betrixaban, all of which have emphasized its usefulness and practicality. However, there has been limited discussion regarding its weaknesses and areas of ambiguity. Therefore, this article aimed to explore the challenges faced during the approval process of betrixaban and provide a comprehensive review of the literature on its advantages and disadvantages as a long-term prophylaxis approach for VTE. Furthermore, we aim to identify the ambiguous points that require further investigation in future studies.

Novel oral anticoagulants in intracardiac thrombosis resolution: a case series

Background

Vitamin K antagonists (VKAs) have been regarded as the therapy of choice for intracardiac thrombosis for decades based mostly on observational data. The advent of direct oral anticoagulants (DOACs) has displaced VKAs as the first-line therapy for multiple thrombotic disorders but not for intracardiac thrombosis. Although limited, there is growing evidence that DOACs are effective for intracardiac thrombosis and some data suggest that thrombus resolution might be superior to that with warfarin.

Case summary

Here, we present a series of six patients with left atrial appendage thrombi were treated with a venous thromboembolic dose of DOACs with resolution within 2–6 months with no reported complications.

Discussion

This case series adds to the accumulating evidence supporting the efficacy of DOACs in the treatment of intracardiac thrombi.

Factors Affecting the Formation and Treatment of Thrombosis by Natural and Synthetic Compounds

Venous thromboembolism (VTE) refers to deep vein thrombosis (DVT), whose consequence may be a pulmonary embolism (PE). Thrombosis is associated with significant morbidity and mortality and is the third most common cardiovascular disease after myocardial infarction and stroke. DVT is associated with the formation of a blood clot in a deep vein in the body. Thrombosis promotes slowed blood flow, hypoxia, cell activation, and the associated release of many active substances involved in blood clot formation. All thrombi which adhere to endothelium consist of fibrin, platelets, and trapped red and white blood cells. In this review, we summarise the impact of various factors affecting haemostatic disorders leading to blood clot formation. The paper discusses the causes of thrombosis, the mechanism of blood clot formation, and factors such as hypoxia, the involvement of endothelial cells (ECs), and the activation of platelets and neutrophils along with the effects of bacteria and reactive oxygen species (ROS). Mechanisms related to the action of anticoagulants affecting coagulation factors including antiplatelet drugs have also been discussed. However, many aspects related to the pathogenesis of thrombosis still need to be clarified. A review of the drugs used to treat and prevent thrombosis and natural anticoagulants that occur in the plant world and are traditionally used in Far Eastern medicine has also been carried out.

Direct Determination of Coagulation Factor IIa and Plasmin Activities for Monitoring of Thrombotic State

Background

Current laboratory examinations for hypercoagulable diseases focus on the biomarker content of the activated coagulation cascade and fibrinolytic system. Direct detection of physiologically important protease activities in blood remains a challenge. This study aims to develop a general approach that enables the determination of activities of crucial coagulation factors and plasmin in blood.

Methods

This assay is based on the proteolytic activation of an engineered zymogen of l-phenylalanine oxidase (proPAO), for which the specific blood protease cleavage sites were engineered between the inhibitory and activity domains of proPAO. Specific cleavage of the recombinant proenzyme leads to the activation of proPAO, followed by oxidation and oxygenation of l-phenylalanine, resulting in an increase of chromogenic production when coupled with the Trinder reaction.

Results

We applied this method to determine the activities of both coagulation factor IIa and plasmin in their physiologically relevant basal state and fully activated state in sodium citrate–anticoagulated plasma respectively. Factor IIa and plasmin activities could be dynamically monitored in patients with thrombotic disease who were taking oral anticoagulants and used for assessing the hypercoagulable state in pregnant women.

Conclusions

The high specificity, sensitivity, and stability of this novel assay not only makes it useful for determining clinically important protease activities in human blood and diagnosing thrombotic diseases but also provides a new way to monitor the effectiveness and safety of anticoagulant drugs.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.

Use of dabigatran for treatment of left ventricular thrombus: A tertiary care center experience

Objectives:

Direct oral anticoagulants (DOACs) are now replacing vitamin K oral anticoagulants (VKAs) owing to superior efficacy, rapid action, less bleeding, wider therapeutic range,and fewer food and drug interactions.Unfortunately, the available data on the use of DOACs, particularly dabigatran, for treatment of left ventricular thrombus (LVT) issparse. We have hereby presented the largest study on use of dabigatran in LVT.

Methods:

Retrospective data of patients having LVT as diagnosed by transthoracic echocardiography (TTE) was screened. Patients on dabigatran were included in the study and follow up data of 6 months was obtained through medical records.

Results:

Of the 15 patients included in the study, the most frequent etiology was ischemic heart disease (67%), including 7 patients of STEMI (47%), followed by non-ischemic cardiomyopathy in 5 patients (33%). Only one patient, with STEMI, developed mild gastrointestinal bleeding at 3 months. Complete clot resolution was seen in 2 patients (13%) at first week of follow up and total 5 patients (33%) at the end of second week. The rate of clot resolution at 1 month, 3 months, and 6 months were 80%, 93% and 100%, respectively. The median duration required for complete clot resolution was 30 days (IQR=14-30).

Conclusion:

Dabigatran appears to be safe, highly efficacious and results in rapid LV clot resolution. DOACs may be a suitable alternative to warfarin in treatment of LV thrombus. However, larger studies are required to validate this hypothesis.

Use of direct oral anticoagulants in the treatment of left ventricular thrombi: A tertiary center experience and review of the literature

Direct oral anticoagulants can potentially provide a more convenient oral alternative for the management of left ventricular thrombi than Warfarin. These medications do not require frequent monitoring and have less drug-drug interactions. Randomized controlled trials are needed to further demonstrate their efficacy and safety in this setting.

Design, synthesis and biological evaluation of anthranilamide derivatives as potential factor Xa (fXa) inhibitors

Factor Xa (fXa) is a crucial player in various thromboembolic disorders. Inhibition of fXa can provide safe and effective antithrombotic effects. In this study, a series of anthranilamide compounds were designed by utilizing structure-based design strategies. Optimization at P1 and P4 groups led to the discovery of compound 16g: a highly potent, selective fXa inhibitor with pronounced in vitro anticoagulant activity. Moreover, 16g also displayed excellent in vivo antithrombotic activity in the rat venous thrombosis (VT) and arteriovenous shunt (AV-SHUNT) models. The bleeding risk evaluation showed that 16g had a safer profile than that of betrixaban at 1 mg/kg and 5 mg/kg dose. Additionally, 16g also exhibited satisfactory PK profiles. Eventually, 16g was selected to investigate its effect on hypoxia-reoxygenation- induced H9C2 cell viability. MTT results showed that H9C2 cell viability can be remarkably alleviated by 16g.

Current and emerging pharmacotherapy for ischemic stroke prevention in patients with atrial fibrillation

Introduction: Atrial fibrillation (AF) is associated with high morbidity and mortality rates due to thromboembolic complications, and anticoagulation is central to the management of this common arrhythmia to prevent acute thromboembolic events. The traditional anticoagulants: heparin, fondaparinux, and vitamin K antagonists (VKA, e.g. warfarin, acenocoumarol or phenprocoumin) have long served as pharmacotherapy for ischemic stroke prophylaxis. Areas covered: In this review article, the authors provide an overview on current and emerging pharmacotherapy for ischemic stroke prevention. Furthermore, they review the data from novel therapeutic targets in the coagulation cascade, and investigational anticoagulant drugs currently assessed in preclinical and clinical studies. Expert opinion: The introduction of nonvitamin K antagonist oral anticoagulants (NOACs) was an important milestone, as these drugs show relative efficacy, safety, and convenience compared to the VKAs. Nevertheless, their clinical use still has some limitations with, for example, patients with severe renal impairment and those with mechanical heart valves, high bleeding risks, lack of standard laboratory monitoring and (some) reversal agents. To overcome some of these limitations, various attempts are now underway to discover new strategies and targets via the hemostatic pathway in order to develop new coagulation inhibiting drugs.

Pharmacokinetic drug interactions of the non-vitamin K antagonist oral anticoagulants (NOACs)

The use of warfarin, the most commonly prescribed oral anticoagulant, is being questioned by clinicians worldwide due to warfarin several limitations (a limited therapeutic window and significant variability in dose-response among individuals, in addition to a potential for drug-drug interactions). Therefore, the need for non-vitamin K antagonist oral anticoagulants (NOACs) with a rapid onset of antithrombotic effects and a predictable pharmacokinetic (PK) and pharmacodynamic (PD) profile led to the approval of five new drugs: the direct factor Xa (F-Xa) inhibitors rivaroxaban, apixaban, edoxaban and betrixaban (newly approved by FDA) and the direct thrombin (factor-IIa) inhibitor dabigatran etexilate. The advantages of NOACs over warfarin are a fixed-dosage, the absence of the need for drug monitoring for changes in anti-coagulation and fewer clinically significant PK and PD drug-drug interactions. NOACs exposure will likely be increased by the administration of strong P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4-inhibitors and may increase the risk of bleeds. On the contrary, P-gp inducers could significantly decrease the NOACs plasma concentration with an associated reduction in their anticoagulant effects. This manuscript gives an overview of NOACs PK profiles and their drug-drug interactions potential. This is meant to be of help to physicians in choosing the best therapeutic approach for their patients.

Novel FXa Inhibitor Identification through Integration of Ligand- and Structure-Based Approaches

Factor Xa (FXa), a vitamin K-dependent serine protease plays a pivotal role in the coagulation cascade, one of the most interesting targets for the development of new anticoagulants. In the present work, we performed a virtual screening campaign based on ligand-based shape and electrostatic similarity search and protein-ligand docking to discover novel FXa-targeted scaffolds for further development of inhibitors. From an initial set of 260,000 compounds from the NCI Open database, 30 potential FXa inhibitors were identified and selected for in vitro biological evaluation. Compound 5 (NSC635393, 4-(3-methyl-4H-1,4-benzothiazin-2-yl)-2,4-dioxo-N-phenylbutanamide) displayed an IC₅₀ value of 2.02 nM against human FXa. The identified compound may serve as starting point for the development of novel FXa inhibitors.