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

Discovery of Highly Selective, Potent, Covalent, and Orally Bioavailable Factor XIIa Inhibitors for the Treatment of Thrombo-Inflammation

Thrombo-inflammation is closely associated with a few severe cardiovascular and infectious diseases. Factor XIIa (FXIIa) in the intrinsic coagulation pathway plays a pivotal role in the development of thrombo-inflammation and its inhibition has emerged as a potential therapeutic approach for thrombo-inflammatory disorders. Nonetheless, as of now, few small-molecule FXIIa inhibitors have demonstrated notable effectiveness against thrombo-inflammation, with none progressing into clinical stages. Herein, we present potent, covalent, reversible, and selective small-molecule FXIIa inhibitors such as 4a and 4j obtained through structure-based drug design. Compounds 4a and 4j showed significant anticoagulation and substantial anti-inflammatory effects in vitro, coupled with exceptional plasma stability. Furthermore, in carrageenan-induced thrombosis models, 4a and 4j demonstrated remarkable dual antithrombotic and anti-inflammatory activity when administered orally. Compound 4j exhibited a favorable safety profile without obvious tissue toxicity in mice, suggesting its potential as an oral therapeutic option for thrombo-inflammation.

Drug repurposing opportunities for chronic kidney disease

The development of targeted drugs for the early prevention and management of chronic kidney disease (CKD) is of great importance. However, the success rates and cost-effectiveness of traditional drug development approaches are extremely low. Utilizing large sample genome-wide association study data for drug repurposing has shown promise in many diseases but has not yet been explored in CKD. Herein, we investigated actionable druggable targets to improve renal function using large-scale Mendelian randomization and colocalization analyses. We combined two population-scale independent genetic datasets and validated findings with cell-type-dependent eQTL data of kidney tubular and glomerular samples. We ultimately prioritized two drug targets, opioid receptor-like 1 and F12, with potential genetic support for restoring renal function and subsequent treatment of CKD. Our findings explore the potential pathological mechanisms of CKD, bridge the gap between the molecular mechanisms of pathogenesis and clinical intervention, and provide new strategies in future clinical trials of CKD.

Recent advances in the discovery and development of drugs targeting the kallikrein-kinin system

BACKGROUND

The kallikrein-kinin system is a key regulatory cascade involved in blood pressure maintenance, hemostasis, inflammation and renal function. Currently, approved drugs remain limited to the rare disease hereditary angioedema. However, growing interest in this system is indicated by an increasing number of promising drug candidates for further indications.

METHODS

To provide an overview of current drug development, a two-stage literature search was conducted between March and December 2023 to identify drug candidates with targets in the kallikrein-kinin system. First, drug candidates were identified using PubMed and Clinicaltrials.gov. Second, the latest publications/results for these compounds were searched in PubMed, Clinicaltrials.gov and Google Scholar. The findings were categorized by target, stage of development, and intended indication.

RESULTS

The search identified 68 drugs, of which 10 are approved, 25 are in clinical development, and 33 in preclinical development. The three most studied indications included diabetic retinopathy, thromboprophylaxis and hereditary angioedema. The latter is still an indication for most of the drug candidates close to regulatory approval (3 out of 4). For the emerging indications, promising new drug candidates in clinical development are ixodes ricinus-contact phase inhibitor for thromboprophylaxis and RZ402 and THR-149 for the treatment of diabetic macular edema (all phase 2).

CONCLUSION

The therapeutic impact of targeting the kallikrein-kinin system is no longer limited to the treatment of hereditary angioedema. Ongoing research on other diseases demonstrates the potential of therapeutic interventions targeting the kallikrein-kinin system and will provide further treatment options for patients in the future.

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.

Effect of factor XI inhibition on tumor cell-induced coagulation activation

BACKGROUND

Cancer-associated thrombosis is a frequent complication in patients with malignancies. While factor XI (FXI)/FXIa inhibition is efficacious in preventing postoperative venous thromboembolism, its role in tumor cell-induced coagulation is less defined.

OBJECTIVES

We thus aimed to provide mechanistic insights into FXI/FXIa inhibition in tumor cell-induced coagulation activation.

METHODS

Procoagulant activity (PCA) of 4 different tissue factor (TF) expressing tumor cell lines was analyzed by single-stage clotting and thrombin generation assay in the presence of a FXIa inhibitor, BMS-262084 (BMS), an inhibitory FXI antibody (anti-FXI), or peak and trough concentrations of rivaroxaban or tinzaparin. Further, tumor cell-induced platelet aggregation was recorded. Recombinant human TF served as positive control.

RESULTS

Although BMS and anti-FXI potently inhibited FXIa amidolytic activity, both inhibitors efficiently mitigated recombinant human TF- and tumor cell-induced fibrin clot formation and platelet aggregation only in the presence of low TF PCA. The anticoagulant effects showed an inverse correlation with the magnitude of cellular TF PCA expression. Similarly, BMS markedly interfered with tumor cell-induced thrombin generation, with the most prominent effects on peak and total thrombin. In addition, anticoagulant effects of FXIa inhibition by 10 μM BMS were in a similar range to those obtained by 600 nM rivaroxaban and 1.6 μM tinzaparin at low TF PCA levels. However, rivaroxaban and tinzaparin also exerted marked anticoagulant activity at high TF PCA levels.

CONCLUSION

Our findings indicate that FXI/FXIa inhibition interferes with tumor cell-induced coagulation activation only at low TF PCA expression levels, a finding with potential implications for future in vivo studies.

Coumarins as factor XIIa inhibitors: Potency and selectivity improvements using a fragment-based strategy

Previously, we described weak coumarin inhibitors of factor XIIa, a promising target for artificial surface-induced thrombosis and various inflammatory diseases. In this work, we used fragment-based drug discovery approach to improve our coumarin series. First, we screened about 200 fragments for the S1 pocket. The S1 pocket of trypsin-like serine proteases, such as factor XIIa, is highly conserved and is known to drive a major part of the association energy. From the screening, we selected fragments displaying a micromolar activity and studied their selectivity on other serine proteases. Then, these fragments were merged to our coumarin templates, leading to the generation of nanomolar inhibitors. The mechanism of inhibition was further studied by mass spectrometry demonstrating the covalent binding through the formation of an acyl enzyme complex. The most potent compound was tested in plasma to evaluate its stability and efficacy on coagulation assays. It exhibited a plasmatic half-life of 1.9 h and a good selectivity for the intrinsic coagulation pathway over the extrinsic one.

Potential anticoagulant of traditional chinese medicine and novel targets for anticoagulant drugs

BACKGROUND

Anticoagulants are the main drugs used for the prevention and treatment of thrombosis. Currently, anticoagulant drugs are primarily multitarget heparin drugs, single-target FXa inhibitors and FIIa inhibitors. In addition, some traditional Chinese drugs also have anticoagulant effects, but they are not the main direction of treatment at present. But the anticoagulant drugs mentioned above, all have a common side effect is bleeding. Many other anticoagulation targets are under investigation. With further exploration of coagulation mechanism, how to further determine new anticoagulant targets and how to make traditional Chinese medicine play anticoagulant role have become a new field of exploration.

PURPOSE

The purpose of the study was to summarize the recent research progress on coagulation mechanisms, new anticoagulant targets and traditional Chinese medicine.

METHODS

A comprehensive literature search was conducted using four electronic databases, including PubMed, Embase, CNKI, Wanfang database and ClinicalTrials.gov, from the inception of the study to 28 Feb 2023. Key words used in the literature search were "anticoagulation", "anticoagulant targets", "new targets", "coagulation mechanisms", "potential anticoagulant", "herb medicine", "botanical medicine", "Chinese medicine", "traditional Chinese medicine", "blood coagulation factor", keywords are linked with AND/OR. Recent findings on coagulation mechanisms, potential anticoagulant targets and traditional Chinese medicine were studied.

RESULTS

The active components extracted from the Chinese medicinal herbs, Salvia miltiorrhiza, Chuanxiong rhizoma, safflower and Panax notoginseng have obvious anticoagulant effects and can be used as potential anticoagulant drugs, but the risk of bleeding is unclear. TF/FVIIa, FVIII, FIX, FXI, FXII, and FXIII have all been evaluated as targets in animal studies or clinical trials. FIX and FXI are the most studied anticoagulant targets, but FXI inhibitors have shown stronger advantages.

CONCLUSION

This review of potential anticoagulants provides a comprehensive resource. Literature analysis suggests that FXI inhibitors can be used as potential anticoagulant candidates. In addition, we should not ignore the anticoagulant effect of traditional Chinese medicine, and look forward to more research and the emergence of new drugs.

Thrombus composition and thrombolysis resistance in stroke

A State of the Art lecture titled "Thrombus Composition and Thrombolysis Resistance in Stroke" was presented at the ISTH Congress in 2022. Intravenous thrombolysis (IVT) remains the only pharmacologic option to re-establish cerebral perfusion at the acute phase of ischemic stroke. IVT is based on the administration of recombinant tissue plasminogen activator with the objective of dissolving fibrin, the major fibrillar protein component of thrombi. Almost 30 years on from its introduction, although the clinical benefits of IVT have been clearly demonstrated, IVT still suffers from a relatively low efficacy, with a rate of successful early recanalization below 50% overall. Analyses of thrombectomy-recovered acute ischemic stroke (AIS) thrombi have shown that apart from occlusion site, thrombus length, and collateral status, AIS thrombus structure and composition are also important modulators of IVT efficacy. In this article, after a brief presentation of IVT principle and current knowledge on IVT resistance, we review recent findings on how compaction and structural alterations of fibrin together with nonfibrin thrombus components such as neutrophil extracellular traps and von Willebrand factor interfere with IVT in AIS. We further discuss how these new insights could soon result in the development of original adjuvant therapies for improved IVT in AIS. Finally, we summarize relevant new data presented during the 2022 ISTH Congress.

Targeting the Contact Pathway of Coagulation for the Prevention and Management of Medical Device-Associated Thrombosis

Hemorrhage remains a major complication of anticoagulants, with bleeding leading to serious and even life-threatening outcomes in rare settings. Currently available anticoagulants target either multiple coagulation factors or specifically coagulation factor (F) Xa or thrombin; however, inhibiting these pathways universally impairs hemostasis. Bleeding complications are especially salient in the medically complex population who benefit from medical devices. Extracorporeal devices-such as extracorporeal membrane oxygenation, hemodialysis, and cardiac bypass-require anticoagulation for optimal use. Nonetheless, bleeding complications are common, and with certain devices, highly morbid. Likewise, pharmacologic prophylaxis to prevent thrombosis is not commonly used with many medical devices like central venous catheters due to high rates of bleeding. The contact pathway members FXI, FXII, and prekallikrein serve as a nexus, connecting biomaterial surface-mediated thrombin generation and inflammation, and may represent safe, druggable targets to improve medical device hemocompatibility and thrombogenicity. Recent in vivo and clinical data suggest that selectively targeting the contact pathway of coagulation through the inhibition of FXI and FXII can reduce the incidence of medical device-associated thrombotic events, and potentially systemic inflammation, without impairing hemostasis. In the following review, we will outline the current in vivo and clinical data encompassing the mechanism of action of drugs targeting the contact pathway. This new class of inhibitors has the potential to herald a new era of effective and low-risk anticoagulation for the management of patients requiring the use of medical devices.

Factor XII Explored with AlphaFold - Opportunities for Selective Drug Development

Medical device associated thrombosis is an important clinical problem. This type of thrombosis can result from Factor XII (FXII) binding to non-natural surface materials and subsequent activation of the contact pathway. This drives the development of new therapeutic strategies to block this pathway and information on the structural properties of FXII should catalyse this quest. Presently, there is no publicly available crystal structure of full-length FXII. However, the AlphaFold Protein Structure Database provides a model structure. We here explore this model in combination with previous structure-function studies to identify opportunities for selective pharmacological blockade of the contribution of FXII in medical device associated thrombosis. Previous studies demonstrated that FXII activation is dependent on molecular cleavage after R353. We subsequently proposed that protein conformation protects this cleavage site to ensure zymogen quiescence and prevent inappropriate FXII activation. The AlphaFold model shows that a small loop containing R353 indeed is buried in the globular molecule. This is the result of intra-molecular interactions between the (N-terminal) Fibronectin type II domain, (central) kringle and (C-terminal) protease domain, in a structure that resembles a three-point harness. Furthermore, this interaction pushes the intermediate domains, as well as the flexible proline-rich region (PRR), outward while encapsulating R353 in the molecule. The outward directed positively charged patches are likely to be involved in binding to anionic surfaces. The binding of FXII to surfaces (and several monoclonal antibodies) acccelerates its activation by inducing conformational changes. For prevention of medical device associated thrombosis, it is therefore important to target the surface binding sites of FXII without causing structural changes.

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.

Noonan syndrome with RAF1 gene mutations in a newborn with cerebral haemorrhage

Background

Noonan syndrome is an autosomal dominant genetic disorder that can occur in men and women and has a sporadic or family history. NS can lead to abnormal bleeding, but cerebral haemorrhage is rare. This is the first case of cerebral haemorrhage with a RAF1 gene mutation that originated in the neonatal period.

Case presentation

This case presents a newborn with a RAF1 gene mutation resulting in NS complicated with an abnormality of chromosome 46, X, del (Y) (q12). In the course of treatment, the baby's breathing suddenly increased. After an MRI examination of the skull, haemorrhaging was found in multiple parts of the brain.

Conclusions

After symptomatic treatment, the baby recovered well, but the main cause of cerebral haemorrhage was not found.

Characterization of congenital factor XII deficiency in Taiwanese patients: identification of one novel and one common mutation

Background

Factor XII (FXII) deficiency is an interesting condition that causes prolonged activated partial thromboplastin time without bleeding diathesis. FXII may be not important in hemostasis, but still plays roles in thrombosis and inflammation. In order to raise clinical awareness about this condition, we studied patients with severe FXII deficiency and their relatives.

Methods

Consecutive severely FXII deficient patients presenting from 1995 to 2020 were recruited from two medical centers in Taiwan. Index patients and their families were tested for FXII function, antigen and F12 gene. F12 variants were constructed into the pIRES-hrGFP vector and expressed on human embryonic kidney cells (HEK293T). FXII antigen and activity were analyzed.

Results

We found five severely FXII deficient patients, three women and two men, aged 44–71 years. FXII antigen results ranged from undetectable to 43.7%. Three different mutations were identified: c.1681C>A (p.Gly542Ser), c.1561G>A (p.Glu502Lys), and a novel mutation c.1556T>A (p.Leu500Gln). HEK293T cells expressed consistently low FXII activity with all mutations. FXII antigen expression was similar to the wild type in c.1681C>A (p.Gly542Ser), but reduced in c.1556T>A (p.Leu500Gln) and c.1561G>A (p.Glu502Lys).

Conclusions

We report five unrelated patients with severe FXII deficiency, one of whom carried a novel, cross-reacting material negative mutation c.1556T>A (p.Leu500Gln).

The tick and I: Parasite-host interactions between ticks and humans

Ticks, particularly hard ticks (Ixodidae), which are among the most important vectors of dangerous infectious agents, feed on their hosts for extended periods of time. With this lifestyle, numerous adaptations have evolved in ticks and their hosts, the pharmacological importance of which is increasingly being recognized. Many bioactive substances in tick saliva are being considered as the basis of new drugs. For example, components of tick cement can be developed into tissue adhesives or wound closures. Analgesic and antipruritic salivary components inhibit histamine or bradykinin, while other tick-derived molecules bind opioid or cannabinoid receptors. Tick saliva inhibits the extrinsic, intrinsic, or common pathway of blood coagulation with implications for the treatment of thromboembolic diseases. It contains vasodilating substances and affects wound healing. The broad spectrum of immunomodulatory and immunosuppressive effects of tick saliva, such as inhibition of chemokines or cellular immune responses, allows development of drugs against inflammation in autoimmune diseases and/or infections. Finally, modern vaccines against ticks can curb the spread of serious infections. The medical importance of the complex tick-host interactions is increasingly being recognized and translated into first clinical applications. Using selected examples, an overview of the mutual adaptations of ticks and hosts is given here, focusing on their significance to medical advance.

Factor IX(a) inhibitors: an updated patent review (2003-present)

INTRODUCTION

Anticoagulation with no bleeding complications is the current objective of drug discovery programs in the area of treating and/or preventing thromboembolism. Despite the promises of therapeutics targeting factors XI(a) and XII(a), none has been approved thus far. Clinically used thrombin- and/or factor Xa-based anticoagulants continue to be associated with a significant bleeding risk which limits their safe use in a broad range of thrombotic patients. Research findings in animals and humans indicate that it is possible to target factor IX(a) (FIX(a)) to achieve anticoagulation with a limited risk of bleeding.

AREAS COVERED

A review of patents literature has retrieved >35 patents on the development of molecules targeting FIX(a) since 2003. Small molecules, antibodies, and aptamers have been developed to target FIX(a) to potentially promote effective and safer anticoagulation. Most of these agents are in the pre-clinical development phase and few have been tested in clinical trials.

EXPERT OPINION

FIX(a) system is being considered to develop new anticoagulants with fewer bleeding complications. Our survey indicates that the number of FIX(a)-targeting agents is mediocre. The agents under development are diverse. Although additional development is essential, moving one or more of these agents to the clinic will facilitate achieving better clinical outcomes.

Hemostasis in neonatal ECMO

Extracorporeal membrane oxygenation (ECMO) is a life-saving support for cardio-respiratory function. Over the last 50 years, the extracorporeal field has faced huge technological progress. However, despite the improvements in technique and materials, coagulation problems are still the main contributor to morbidity and mortality of ECMO patients. Indeed, the incidence and survival rates of the main hemorrhagic and thrombotic complications in neonatal respiratory ECMO are relevant. The main culprit is related to the intrinsic nature of ECMO: the contact phase activation. The exposure of the human blood to the non-endothelial surface triggers a systemic inflammatory response syndrome, which chronically activates the thrombin generation and ultimately leads to coagulative derangements. Pre-existing illness-related hemostatic dysfunction and the peculiarity of the neonatal clotting balance further complicate the picture. Systemic anticoagulation is the management's mainstay, aiming to prevent thrombosis within the circuit and bleeding complications in the patient. Although other agents (i.e., direct thrombin inhibitors) have been recently introduced, unfractionated heparin (UFH) is the standard of care worldwide. Currently, there are multiple tests exploring ECMO-induced coagulopathy. A combination of the parameters mentioned above and the evaluation of the patient's underlying clinical context should be used to provide a goal-directed antithrombotic strategy. However, the ideal algorithm for monitoring anticoagulation is currently unknown, resulting in a large inter-institutional diagnostic variability. In this review, we face the features of the available monitoring tests and approaches, mainly focusing on the role of point-of-care (POC) viscoelastic assays in neonatal ECMO. Current gaps in knowledge and areas that warrant further study will also be addressed.