VE-1902-A direct thrombin inhibitor with reversible covalent mechanism of action shows efficacy with reduced bleeding in rodent models of thrombosis

An automated analysis method enabling the screening of covalent thrombin and factor XIIa inhibitors via liquid chromatography-mass spectrometry

An automated sample preparation and separation method for the analysis of various enzyme-inhibitor combinations using liquid chromatography (LC) coupled to mass spectrometry (MS) is presented. As conventional anticoagulants have several drawbacks, the most severe being the elevated risk of internal bleedings, it is necessary to develop new-generation anticoagulants with reduced side effects. Therefore, the screening of potential inhibitors against anticoagulation targets like thrombin and FXIIa is important to design a potent and selective inhibitor. To facilitate the analysis of numerous enzyme-inhibitor covalent complexes, automation of the analysis using an LC system with a user-defined injection sequence is helpful. The developed method ensures comparable reaction conditions like reaction time and temperature for all enzyme-inhibitor complexes. Furthermore, it prevents time-consuming manual sample preparation and potential manual errors. To achieve good reproducibility with relative standard deviation of approximately 3% for three-fold determination, multiple cleaning steps were added to the automated sample preparation. Subsequently, this method was applied to screen a variety of 15 aminopyrazole- and aminotriazole-based inhibitors with a covalent mechanism of action against thrombin and to test two covalent inhibitors for FXIIa. Successful complex formation and acylation of the catalytic center of the enzymes was monitored using deconvoluted mass spectra and the matching mass shifts of the acyl moiety of the analyzed inhibitors. The inhibitors' structure directly influenced reaction yields. Sterically demanding aminotriazoles and acyl moieties both affected the product formation negatively. However, the screening yielded several promising candidates for new covalent thrombin inhibitors, which might find their application as prospective anticoagulants.

Discovery of novel N-acylpyrazoles as potent and selective thrombin inhibitors

Direct oral anticoagulants (DOACs), which includes thrombin and factor Xa inhibitors, have emerged as the preferred therapeutics for thrombotic disorders, penetrating a market previously dominated by warfarin and heparin. This article describes the discovery and profiling of a novel series of N-acylpyrazoles, which act as selective, covalent, reversible, non-competitive inhibitors of thrombin. We describe in vitro stability issues associated with this chemotype and, importantly, demonstrate that N-acylpyrazoles successfully act in vivo as anticoagulants in basic thrombotic animal models. Crucially, this anticoagulant nature is unaccompanied by the higher bleeding risk profile that has become an undesirable characteristic of the DTIs and factor Xa inhibitors. We propose that the N-acylpyrazole chemotype shows intriguing promise as next-generation oral anticoagulants.

Amide-functionalized 1,2,4-Triazol-5-amines as Covalent Inhibitors of Blood Coagulation Factor XIIa and Thrombin

To counteract thrombosis, new safe and efficient antithrombotics are required. We herein report the design, synthesis, and biological activity of a series of amide-functionalized acylated 1,2,4-triazol-5-amines as selective inhibitors of blood coagulation factor XIIa and thrombin. The introduction of an amide moiety into the main scaffold of 3-aryl aminotriazoles added certain three-dimensional properties to synthesized compounds and allowed them to reach binding sites in FXIIa and thrombin previously unaddressed by non-functionalized 1,2,4-triazol-5-amines. Among synthesized compounds, one quinoxaline-derived aminotriazole bearing N-butylamide moiety inhibited FXIIa with the IC50 value of 28 nM, whereas the N-phenylamide-derived aminotriazole inhibited thrombin with the IC50 value of 41 nM. Performed mass-shift experiments and molecular modeling studies proved the covalent mechanism of FXIIa and thrombin inhibition by synthesized compounds. In plasma coagulation tests, developed aminotriazoles showed anticoagulant properties mainly affecting the intrinsic blood coagulation pathway, activation of which is associated with thrombosis but is negligible for hemostasis.

Pyrazole-Based Thrombin Inhibitors with a Serine-Trapping Mechanism of Action: Synthesis and Biological Activity

New antithrombotic drugs are needed to combat thrombosis, a dangerous pathology that causes myocardial infarction and ischemic stroke. In this respect, thrombin (FIIa) represents an important drug target. We herein report the synthesis and biological activity of a series of 1H-pyrazol-5-amine-based thrombin inhibitors with a serine-trapping mechanism of action. Among synthesized compounds, flexible acylated 1H-pyrazol-5-amines 24e, 34a, and 34b were identified as potent 16-80 nM thrombin inhibitors, which showed practically no off-targeting effect against other physiologically relevant serine proteases. To prove that synthesized compounds are covalent thrombin inhibitors, the most potent derivative 24e (FIIa IC₅₀ = 16 nM) was studied in a mass-shift assay, where it has been shown that 24e transfers its acyl moiety (pivaloyl) to the catalytic Ser195 of thrombin. Performed herein docking studies also confirmed the covalent mechanism of thrombin inhibition by synthesized compounds. Acylated aminopyrazoles found during this study showed only limited effects on plasma coagulation in activated partial thrombin time (aPTT) and prothrombin time (PT) in vitro assays. However, such thrombin inhibitors are expected to have virtually no effect on bleeding time and can be used as a starting point for developing a safer alternative to traditional non-covalent anticoagulants.

From ancient leech to direct thrombin inhibitors and beyond: New from old

Medicinal leeches have been used in health care since before written history, with widely varying popularity over the centuries. Nowadays, medicinal leech therapy is mainly used in plastic and reconstructive microsurgery, with new interesting potential therapeutic applications in many other diseases. The leech's best-known salivary product, hirudin - one of the most powerful natural anticoagulants - was the only remedy to prevent blood clotting until the discovery of heparin. Starting from hirudin, pharmacological research succeeded in developing new anticoagulants, which represent a cornerstone of prevention and treatment of thromboembolic disease. While we are perhaps on the threshold of a new era of anticoagulation, with the development of FXI and XII inhibitors and direct reversible covalent thrombin inhibitors, which promise to achieve effective anticoagulation without bleeding risk. This review retraces the intriguing journey of these drugs in cardiovascular disease, highlighting the fil rouge that links the ancient leech to the current and oncoming antithrombotic therapy. We think that knowledge of the past is key to understanding and appreciating the present and to seize future opportunities.

Microscale Parallel Synthesis of Acylated Aminotriazoles Enabling the Development of Factor XIIa and Thrombin Inhibitors

Herein we report a microscale parallel synthetic approach allowing for rapid access to libraries of N-acylated aminotriazoles and screening of their inhibitory activity against factor XIIa (FXIIa) and thrombin, which are targets for antithrombotic drugs. This approach, in combination with post-screening structure optimization, yielded a potent 7 nM inhibitor of FXIIa and a 25 nM thrombin inhibitor; both compounds showed no inhibition of the other tested serine proteases. Selected N-acylated aminotriazoles exhibited anticoagulant properties in vitro influencing the intrinsic blood coagulation pathway, but not extrinsic coagulation. Mechanistic studies of FXIIa inhibition suggested that synthesized N-acylated aminotriazoles are covalent inhibitors of FXIIa. These synthesized compounds may serve as a promising starting point for the development of novel antithrombotic drugs.

Drugs in phase I and II clinical development for the prevention of stroke in patients with atrial fibrillation

INTRODUCTION

Atrial fibrillation is the most frequently diagnosed cardiac arrhythmia globally and is associated with ischemic stroke and heart failure. Patients with atrial fibrillation are typically prescribed long-term anticoagulants in the form of either vitamin K antagonists or non-vitamin K antagonist oral anticoagulants; however, both carry a potential risk of adverse bleeding.

AREAS COVERED

This paper sheds light on emerging anticoagulant agents which target clotting factors XI and XII, or their activated forms - XIa and XIIa, respectively, within the intrinsic coagulation pathway. The authors examined data available on PubMed, Scopus, and the clinical trials registry of the United States National Library of Medicine (www.clinicaltrials.gov).

EXPERT OPINION

Therapies targeting factors XI or XII can yield anticoagulant efficacy with the potential to reduce adverse bleeding. Advantages for targeting factor XI or XII include a wider therapeutic window and reduced bleeding. Long-term follow-up studies and a greater understanding of the safety and efficacy are required. Atrial fibrillation is a chronic disease and therefore the development of oral formulations is key.

Factor XII(a) inhibitors: a review of the patent literature

Introduction: Blood coagulation factor XII (FXII) is an emerging and potentially safe drug target, which dysregulation is associated with thrombosis, hereditary angioedema, and (neuro)inflammation. At the same time, FXII-deficiency is practically asymptomatic. Industrial and academic institutions have developed a number of potential therapeutic agents targeting either FXII zymogen or its active form FXIIa for the treatment of thrombotic and inflammatory conditions associated with the activity of this enzyme.Areas covered: A short overview of the FXII(a) structure and function, underlining its suitability as a drug target, is given. The article reviews patents reported over the last three decades on FXII(a)-targeting therapeutic agents. These agents include small molecules, proteins, peptides, oligonucleotides, siRNAs, and monoclonal antibodies.Expert opinion: The performed analysis of patents revealed that many FXII(a) inhibitors are in the early preclinical stage, while several already showed efficacy in vivo animal models of thrombosis, sepsis, hereditary angioedema, and multiple sclerosis. Two anti-FXIIa agents namely tick protein Ir-CPI and monoclonal antibody CSL312 are currently in human clinical trials. The results of these trials and further studies of FXII(a) pathophysiological functions will encourage the development of new FXII(a) inhibitors.