Structure and function of factor XI

Genetic architecture of epigenetic cortical clock age in brain tissue from older individuals: alterations in CD46 and other loci

The cortical epigenetic clock was developed in brain tissue as a biomarker of brain aging. As one way to identify mechanisms underlying aging, we conducted a GWAS of cortical age. We leveraged postmortem cortex tissue and genotyping array data from 694 participants of the Rush Memory and Aging Project and Religious Orders Study (ROSMAP; 11000,000 SNPs), and meta-analysed ROSMAP with 522 participants of Brains for Dementia Research (5,000,000 overlapping SNPs). We confirmed results using eQTL (cortical bulk and single nucleus gene expression), cortical protein levels (ROSMAP), and phenome-wide association studies (clinical/neuropathologic phenotypes, ROSMAP). In the meta-analysis, the strongest association was rs4244620 (p = 1.29 × 10-7), which also exhibited FDR-significant cis-eQTL effects for CD46 in bulk and single nucleus (microglia, astrocyte, oligodendrocyte, neuron) cortical gene expression. Additionally, rs4244620 was nominally associated with lower cognition, faster slopes of cognitive decline, and greater Parkinsonian signs (n ~ 1700 ROSMAP with SNP/phenotypic data; all p ≤ 0.04). In ROSMAP alone, the top SNP was rs4721030 (p = 8.64 × 10-8) annotated to TMEM106B and THSD7A. Further, in ROSMAP (n = 849), TMEM106B and THSD7A protein levels in cortex were related to many phenotypes, including greater AD pathology and lower cognition (all p ≤ 0.0007). Overall, we identified converging evidence of CD46 and possibly TMEM106B/THSD7A for potential roles in cortical epigenetic clock age.

A pharmacokinetic and pharmacodynamic evaluation of asundexian: a novel factor XIa inhibitor for stroke prevention

INTRODUCTION

Antithrombotic therapy is the mainstay of ischemic stroke prevention. Current drugs (antiplatelets and oral anticoagulants) lead to increased bleeding risks, and the rates of stroke recurrence, despite antithrombotic therapy, are still elevated. There is a need for novel antithrombotic therapies with superior effectiveness but without increased bleeding risk. Factor XIa inhibitors might cover this gap.

AREAS COVERED

This manuscript examines the pharmacokinetic and pharmacodynamic properties of asundexian and the current clinical evidence regarding its application in preventing ischemic stroke.

EXPERT OPINION

Asundexian shows a very favoring pharmacokinetic profile. Despite asundexian being inferior to apixaban for cardioembolic ischemic stroke, it could be useful in patients with non-cardioembolic ischemic stroke. Although antiplatelet therapy is the recommended treatment to prevent non-cardioembolic ischemic stroke, adding an anticoagulant might have beneficial effects through the dual-pathway inhibition strategy. Due to the potential risk of hemorrhagic transformation, there is hesitation to administer anticoagulants early to patients who have recently had an ischemic stroke, especially if they are also on antiplatelet therapy. However, clinical trials on asundexian confirmed its safety for bleeding, even when used with antiplatelets. A phase 3 trial is currently investigating the efficacy of asundexian in preventing non-cardioembolic ischemic stroke.

Substrates, Cofactors, and Cellular Targets of Coagulation Factor XIa

Coagulation factor XI (FXI) has increasingly been shown to play an integral role in several physiologic and pathological processes. FXI is among several zymogens within the blood coagulation cascade that are activated by proteolytic cleavage, with FXI converting to the active serine protease form (FXIa). The evolutionary origins of FXI trace back to duplication of the gene that transcribes plasma prekallikrein, a key factor in the plasma kallikrein-kinin system, before further genetic divergence led to FXI playing a unique role in blood coagulation. While FXIa is canonically known for activating the intrinsic pathway of coagulation by catalyzing the conversion of FIX into FIXa, it is promiscuous in nature and has been shown to contribute to thrombin generation independent of FIX. In addition to its role in the intrinsic pathway of coagulation, FXI also interacts with platelets, endothelial cells, and mediates the inflammatory response through activation of FXII and cleavage of high-molecular-weight kininogen to generate bradykinin. In this manuscript, we critically review the current body of knowledge surrounding how FXI navigates the interplay of hemostasis, inflammatory processes, and the immune response and highlight future avenues for research. As FXI continues to be clinically explored as a druggable therapeutic target, understanding how this coagulation factor fits into physiological and disease mechanisms becomes increasingly important.

The first-in-human study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of the factor XI monoclonal antibody SHR-2004 in healthy subjects

BACKGROUND

Inhibiting the coagulation factor XI (FXI) is a novel strategy for prevention and treatment of thromboembolism without affecting extrinsic coagulation pathways. SHR-2004 is a humanized monoclonal antibody that selectively binds to FXI and factor XIa (FXIa).

RESEARCH DESIGN & METHODS

This randomized, double-blind, dose-escalation, placebo-controlled study evaluated SHR-2004 administered either intravenously (i.v.; Part A) or subcutaneously (s.c.; Part B). In Part A, 24 subjects received a single i.v. dose of SHR-2004 (0.1, 0.3, or 1.0 mg/kg) or placebo. In Part B, 40 subjects received a single s.c. dose of SHR-2004 (0.5, 1.0, 3.0, or 4.5 mg/kg) or placebo.

RESULTS

SHR-2004 was well tolerated. Plasma exposure to SHR-2004 increased in a dose-dependent manner. The geometric mean half-time ranged from 11.6 to 13.0 days. FXI activity decreased, and the activated partial thromboplastin time (APTT) was prolonged after i.v. and s.c. administration in a dose- and time-dependent manner. FXI activity was nearly completely abolished immediately after administering the highest i.v. dose, with the average APTT prolonged to nearly three times of baseline.

CONCLUSION

SHR-2004 is a promising candidate for further development as an anticoagulant drug that exerts effective anticoagulation with minimal risk of bleeding.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov identifier is NCT05369767.

Genome-wide investigation of exogenous female hormones, genetic variation, and venous thromboembolism risk

BACKGROUND

Increased risk of venous thromboembolism (VTE) is a life-threatening side effect for users of oral contraceptives (OCs) or hormone therapy (HT).

OBJECTIVES

To investigate the potential for genetic predisposition to VTE in OC or HT users, we conducted a gene-by-environment case-only meta-analysis of genome-wide association studies (GWAS).

METHODS

Use or nonuse of OCs (7 studies) or HT (8 studies) at the time of the VTE event was determined by pharmacy records or self-report. A synergy index (SI) was modeled for each variant in each study and submultiplicative/supramultiplicative gene-by-environment interactions were estimated. The SI parameters were first meta-analyzed across OC and HT studies and subsequently meta-analyzed to obtain an overall estimate. The primary analysis was agnostic GWAS and interrogated all imputed genotypes using a P value threshold of <5.0 × 10-8; secondary analyses were candidate-based.

RESULTS

The VTE case-only OC meta-analysis included 2895 OC users and 6607 nonusers; the case-only HT meta-analysis included 2434 HT users and 12 793 nonusers. In primary GWAS meta-analyses, no variant reached genome-wide significance, but the smallest P value approached statistical significance: rs9386463 (P = 5.03 × 10-8). We tested associations for 138 candidate variants and identified 2 that exceeded statistical significance (0.05/138 = 3.62 × 10-4): F5 rs6025 (P = 1.87 × 10-5; SI, 1.29; previously observed) and F11 rs2036914 (P = 2.0 × 10-4; SI, 0.91; new observation).

CONCLUSION

The candidate variant approach to identify submultiplictive/supramultiplicative associations between genetic variation and OC and HT use identified a new association with common genetic variation in F11, while the agnostic interrogations did not yield new discoveries.

Factor XI and coagulation. Factor XI inhibitors - antithrombotic perspectives

Factor XI is a zymogen with an important role in the coagulation cascade. It is activated by FXII, thrombin and or it can be autoactivated. It has a prothrombotic effect after being activated by thrombin, but also through its antifibrinolytic action, stabilizing the formed clot. Hereditary deficiency of FXI causes haemophilia C - a disease manifested by an usually provoked, small to moderate mucosal bleeding. People with severe FXI deficiency have a low risk of thrombotic events. Conversely, increased FXI values have been found to be associated with increased risk of venous thromboembolism and ischemic stroke. Lowering serum FXI levels has become a treatment target for the prevention of thrombotic events. New pharmacological agents - FXI inhibitors - have been investigated in phase II clinical trials, with promising results in terms of efficacy and safety in the prevention of thrombotic events. FXI inhibitors are emerging as new anticoagulant agents with broad indication prospects beyond direct oral anticoagulants and vitamin K antagonists.

Biology of factor XI

ABSTRACT

Unique among coagulation factors, the coagulation factor XI (FXI) arose through a duplication of the gene KLKB1, which encodes plasma prekallikrein. This evolutionary origin sets FXI apart structurally because it is a homodimer with 2 identical subunits composed of 4 apple and 1 catalytic domain. Each domain exhibits unique affinities for binding partners within the coagulation cascade, regulating the conversion of FXI to a serine protease as well as the selectivity of substrates cleaved by the active form of FXI. Beyond serving as the molecular nexus for the extrinsic and contact pathways to propagate thrombin generation by way of activating FIX, the function of FXI extends to contribute to barrier function, platelet activation, inflammation, and the immune response. Herein, we critically review the current understanding of the molecular biology of FXI, touching on some functional consequences at the cell, tissue, and organ level. We conclude each section by highlighting the DNA mutations within each domain that present as FXI deficiency. Together, a narrative review of the structure-function of the domains of FXI is imperative to understand the etiology of hemophilia C as well as to identify regions of FXI to safely inhibit the pathological function of activation or activity of FXI without compromising the physiologic role of FXI.

Emicizumab as a Promising Form of Therapy for Type A Hemophilia - A Review of Current Knowledge from Clinical Trials

Hemophilia is a plasma bleeding disorder characterized by a deficiency of certain blood clotting factors. The most common forms of this disease, i.e., type A and type B, affect approximately 400,000 people worldwide. Without appropriate treatment ensuring the proper coagulation cascade, this disease may lead to serious disability. Minimizing patient discomfort is possible via replacement therapy, consisting of the substitution of a missing coagulation factor via intravenous administration. Frequent medication and the risk related to factor inhibitors are significant disadvantages, necessitating the improvement of current therapies or the development of novel ones. This review examines the humanized bispecific antibody Emicizumab which ensures hemostasis by mimicking the action of the coagulation factor VIII, a deficiency of which causes type A hemophilia. The paper outlines the topic and then summarizes available clinical trials on Emicizumab in type A hemophilia. Several interventional clinical trials have found Emicizumab to be effective in decreasing bleeding episodes and raising patient satisfaction among various hemophilia A populations. Current Emicizumab-related trials are forecast to be completed between 2024 and 2030, and in addition to congenital hemophilia A, the trials cover acquired hemophilia A and patients playing sports. Providing a more comprehensive understanding of Emicizumab may revolutionize the management of hemophilia type A and improve quality of life. Conclusively, Emicizumab is a gentler therapy owing to subcutaneous delivery and fewer injections, which reduces injection-site reactions and makes therapy less burdensome, ultimately decreasing hospital visits and indirect costs.

Factor XI in Carriers of Antiphospholipid Antibodies: Elevated Levels Associated with Symptomatic Thrombotic Cases, While Low Levels Linked to Asymptomatic Cases

Antiphospholipid syndrome (APS) is a thromboinflammatory disorder caused by circulating antiphospholipid autoantibodies (aPL) and characterized by an increased risk of thrombotic events. The pathogenic mechanisms of these antibodies are complex and not fully understood, but disturbances in coagulation and fibrinolysis have been proposed to contribute to the thrombophilic state. This study aims to evaluate the role of an emerging hemostatic molecule, FXI, in the thrombotic risk of patients with aPL. Cross-sectional and observational study of 194 consecutive and unrelated cases with aPL recruited in a single center: 82 asymptomatic (AaPL) and 112 with primary antiphospholipid syndrome (APS). Clinical and epidemiological variables were collected. The profile of aPL was determined. Plasma FXI was evaluated by Western blotting and two coagulation assays (FXI:C). In cases with low FXI, molecular analysis of the F11 gene was performed. FXI:C levels were significantly higher in patients with APS than in patients with AaPL (122.8 ± 33.4 vs. 104.5 ± 27.5; p < 0.001). Multivariate analysis showed a significant association between symptomatic patients with aPL (APS) and high FXI (>150%) (OR = 11.57; 95% CI: 1.47-90.96; p = 0.020). In contrast, low FXI (<70%), mostly caused by inhibitors, was less frequent in the group of patients with APS compared to AaPL (OR = 0.17; 95%CI: 0.36-0.86; p = 0.032). This study suggests that FXI levels may play a causal role in the prothrombotic state induced by aPLs and holds the promise of complementary treatments in APS patients by targeting FXI.

Factor XI Inhibitors: Potential Role in End-Stage Kidney Disease

Patients with end-stage kidney disease (ESKD) experience a high thrombotic risk but are also at increased risk of bleeding. There is an unmet need for safer antithrombotic therapy in patients with ESKD on hemodialysis. Factor XI (FXI) represents an attractive therapeutic target for anticoagulation because of the potential to mitigate the bleeding risks associated with currently approved anticoagulants, especially in patients at high risk of bleeding. FXI inhibition is also an attractive option in settings where coagulation is activated by exposure of the blood to artificial surfaces, including the extracorporeal circuit during hemodialysis. Therapies targeting FXI that are in the most advanced stages of clinical development include antisense oligonucleotides, monoclonal antibodies, and synthetic small molecules, which serve either to lower FXI levels or block its physiological effects. This review article presents the most recent pharmacological data with FXI inhibitors, briefly describes phase 2 and 3 clinical trials with these agents, and critically examines the potential future use of FXI inhibitors for extracorporeal circuit anticoagulation in patients with ESKD. In addition, laboratory monitoring and reversal of FXI inhibitors are briefly discussed.

Congenital factor XI deficiency with multiple tooth extractions (Case report)

Congenital factor XI deficiency (CFXI) is a rare blood disorder that occurs in one of every one million individuals. Given its rarity, there are very few reports of surgical procedures performed in the oral region CFXI patients. The present study reports the case of a 43-year-old man with CFXI who experienced multiple tooth extractions. It also conducted a review of the literature and treatment outline. We preoperatively administered fresh frozen plasma (FFP) before the tooth extraction and continued to transfuse FFP at the rate of 2 units per day from day 1 to 4 of admission. The extractions were divided into two parts, maxillary and mandibular and the teeth extracted on days 2 and 4 of admission. The patient was discharged on day 6 of admission because there was good progress and no postoperative bleeding. Therefore, it was possible to perform multiple tooth extractions without abnormal bleeding in the oral cavity; the chance of bleeding was reduced by administering FFP and increasing local hemostasis in CFXI patients.

Neurological Complications Associated with Hereditary Bleeding Disorders

PURPOSE OF REVIEW

Hereditary bleeding disorders may have a wide variety of clinical presentations ranging from mild mucosal and joint bleeding to severe central nervous system (CNS) bleeding, of which intracranial hemorrhage (ICH) is the most dreaded complication. In this review, we will discuss the pathophysiology of specific hereditary bleeding disorders, namely, hemophilia A, hemophilia B, and von Willebrand disease (vWD); their clinical manifestations with a particular emphasis on neurological complications; a brief overview of management strategies pertaining to neurological complications; and a review of literature guiding treatment strategies.

RECENT FINDINGS

ICH is the most significant cause of morbidity and mortality in patients with hemophilia. Adequate control of bleeding with the administration of specific factors or blood products, identification of risk factors for bleeding, and maintaining optimal coagulant activity are essential for appropriately managing CNS bleeding complications in these patients. The administration of specific recombinant factors is tailored to a patient's pharmacokinetics and steady-state levels. During acute bleeding episodes, initial factor activity should be maintained between 80 and 100%. Availability of monoclonal antibody Emicizumab has revolutionized prophylactic therapies in patients with hemophilia. Management of ICH in patients with vWD involves using plasma-derived factor concentrates, recombinant von Willebrand factor, and supportive antifibrinolytic agents individualized to the type and severity of vWD. Hemophilia and vWD are the most common hereditary bleeding disorders that can predispose patients to life-threatening CNS complications-intracranial bleeds, intraspinal bleeding, and peripheral nerve syndromes. Early care coordination with a hematologist can help develop an effective prophylactic regimen to avoid life-threatening bleeding complications in these patients. Further research is needed to evaluate using emicizumab as an on-demand treatment option for acute bleeding episodes in patients with hemophilia.

New Therapeutic Targets for the Prevention and Treatment of Venous Thromboembolism With a Focus on Factor XI Inhibitors

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management.

Structures of factor XI and prekallikrein bound to domain 6 of high-molecular weight kininogen reveal alternate domain 6 conformations and exosites

BACKGROUND

High-molecular weight kininogen (HK) circulates in plasma as a complex with zymogen prekallikrein (PK). HK is both a substrate and a cofactor for activated plasma kallikrein, and the principal exosite interactions occur between PK N-terminal apple domains and the C-terminal D6 domain of HK.

OBJECTIVES

To determine the structure of the complex formed between PK apple domains and an HKD6 fragment and compare this with the coagulation factor XI (FXI)-HK complex.

METHODS

We produced recombinant FXI and PK heavy chains (HCs) spanning all 4 apple domains. We cocrystallized PKHC (and subsequently FXIHC) with a 31-amino acid synthetic peptide spanning HK residues Ser565-Lys595 and determined the crystal structure. We also analyzed the full-length FXI-HK complex in solution using hydrogen deuterium exchange mass spectrometry.

RESULTS

The 2.3Å PKHC-HK peptide crystal structure revealed that the HKD6 sequence WIPDIQ (Trp569-Gln574) binds to the apple 1 domain and HK FNPISDFPDT (Phe582-Thr591) binds to the apple 2 domain with a flexible intervening sequence resulting in a bent double conformation. A second 3.2Å FXIHC-HK peptide crystal structure revealed a similar interaction with the apple 2 domain but an alternate, straightened conformation of the HK peptide where residues LSFN (Leu579-Asn583) interacts with a unique pocket formed between the apple 2 and 3 domains. HDX-MS of full length FXI-HK complex in solution confirmed interactions with both apple 2 and apple 3.

CONCLUSIONS

The alternate conformations and exosite binding of the HKD6 peptide likely reflects the diverging relationship of HK to the functions of PK and FXI.

Polyphosphate as an antithrombotic target and hemostatic agent

Polyphosphate (PolyP) is a polymer comprised of linear phosphate units connected by phosphate anhydride bonds. PolyP exists in a diverse range of eukaryotes and prokaryotes with varied chain lengths ranging from six to thousands of phosphate units. Upon activation, human platelets and neutrophils release short-chain PolyP, along with other components, to initiate the coagulation pathway. Long-chain PolyP derived from cellular or bacterial organelles exhibits higher proinflammatory and procoagulant effects compared to short-chain PolyP. Notably, PolyP has been identified as a low-hemorrhagic antithrombotic target since neutralizing plasma PolyP suppresses the thrombotic process without impairing the hemostatic functions. As an inorganic polymer without uniform steric configuration, PolyP is typically targeted by cationic polymers or recombinant polyphosphatases rather than conventional antibodies, small-molecule compounds, or peptides. Additionally, because of its procoagulant property, PolyP has been incorporated in wound-dressing materials to facilitate blood hemostasis. This review summarizes current studies on PolyP as a low-hemorrhagic antithrombotic target and the development of hemostatic materials based on PolyP.

Investigation of the anticoagulant activity of cyclic sulfated glycosaminoglycan mimetics

Thrombotic disorders are among the leading causes of deaths worldwide. Anticoagulants are frequently prescribed for their prevention and/or treatment. Current anticoagulants, which target either thrombin or factor Xa, are plagued with a number of drawbacks, the most important of which is the increased risk of internal bleeding. To develop better antithrombotic agents, the anticoagulant activity of cyclic glycosaminoglycan mimetics was evaluated. Human plasma clotting assays and enzyme inhibition assays were exploited to evaluate the anticoagulant activity of sulfated β-cyclodextrin (SBCD) and its three analogs: sulfated α-cyclodextrin, β-cyclodextrin, and methylated β-cyclodextrin. In normal human plasma, SBCD selectively doubled the activated partial thromboplastin time (APTT) at ∼9 μg/mL, with no effect on prothrombin time (PT) at the same concentration. Likewise, SBCD doubled APTT at ∼9 μg/mL and at ∼8 μg/mL in antithrombin-deficient plasma and heparin cofactor II-deficient plasma, respectively. Interestingly, the three SBCD derivatives were inactive at the highest concentrations tested which highlighted the importance of the sulfate groups and the size of the molecule. Enzyme assays revealed that SBCD inhibits factor XIa (FXIa) with an IC50 value of ∼20 μg/mL and efficacy of near 100%. SBCD did not inhibit other related proteins including thrombin, factor IXa, factor Xa, factor XIIa, factor XIIIa, plasmin, chymotrypsin, or trypsin at the highest concentrations tested demonstrating a significant selectivity. In Michaelis-Menten kinetics, SBCD decreased the VMAX and increased the KM of FXIa hydrolysis of a tripeptide chromogenic substrate indicating a mixed inhibition mechanism. Together, it appears that SBCD is a potent and selective inhibitor of human FXIa with substantial anticoagulant activity in human plasma. Overall, this study introduces SBCD as a promising lead for further development as a safer anticoagulant.

Thrombogenesis-associated genetic determinants as predictors of thromboembolism and prognosis in cervical cancer

Venous thromboembolism (VTE) is a leading cause of death among cancer patients. Khorana score (KS) is the most studied tool to predict cancer-related VTE, however, it exerts poor sensitivity. Several single-nucleotide polymorphisms (SNPs) have been associated with VTE risk in the general population, but whether they are predictors of cancer-related VTE is a matter of discussion. Compared to other solid tumours, little is known about VTE in the setting of cervical cancer (CC) and whether thrombogenesis-related polymorphisms could be valuable biomarkers in patients with this neoplasia. This study aims to analyse the effect of VTE occurrence on the prognosis of CC patients, explore the predictive capability of KS and the impact of thrombogenesis-related polymorphisms on CC-related VTE incidence and patients' prognosis regardless of VTE. A profile of eight SNPs was evaluated. A retrospective hospital-based cohort study was conducted with 400 CC patients under chemoradiotherapy. SNP genotyping was carried on by using TaqMan® Allelic Discrimination methodology. Time to VTE occurrence and overall survival were the two measures of clinical outcome evaluated. The results indicated that VTE occurrence (8.5%) had a significant impact on the patient's survival (log-rank test, P < 0.001). KS showed poor performance (KS ≥ 3, χ², P = 0.191). PROCR rs10747514 and RGS7 rs2502448 were significantly associated with the risk of CC-related VTE development (P = 0.021 and P = 0.006, respectively) and represented valuable prognostic biomarkers regardless of VTE (P = 0.004 and P = 0.010, respectively). Thus, thrombogenesis-related genetic polymorphisms may constitute valuable biomarkers among CC patients allowing a more personalized clinical intervention.

Discovery of Teleost Plasma Kallikrein/Coagulation Factor XI-Like Gene from Channel Catfish (Ictalurus punctatus) and the Evidence that the Protein Encoded by it Acts as a Lectin

Mammalian plasma kallikrein (PK) and coagulation factor XI (fXI) are serine proteases that play in the kinin-kallikrein cascade and in the blood clotting pathway. These proteases share sequence homology and have four apple domains (APDs) and a serine protease domain (SPD) from their N-terminus to C-terminus. No homologs of these proteases are believed to be present in fish species, except for lobe-finned fish. Fish, however, have a unique lectin, named kalliklectin (KL), which is composed of APDs only. In the present study, we found genomic sequences encoding a protein with both APDs and SPD in a few cartilaginous and bony fishes, including the channel catfish Ictalurus punctatus, using bioinformatic analysis. Furthermore, we purified two ~ 70 kDa proteins from the blood plasma of the catfish using mannose-affinity and gel filtration chromatography sequentially. Using de novo sequencing with quadrupole time-of-flight tandem mass spectrometry, several internal amino acid sequences in these proteins were mapped onto possible PK/fXI-like sequences that are thought to be splicing variants. Exploration of APD-containing proteins in the hagfish genome database and phylogenetic analysis suggested that the PK/fXI-like gene originated from hepatocyte growth factor, and that the gene was acquired in a common ancestor of jawed fish. Synteny analysis provided evidence for chromosomal translocation around the PK/fXI-like locus that occurred in the common ancestor of holosteans and teleosts after separation from the lobe-finned fish lineage, or gene duplication into two chromosomes, followed by independent gene losses. This is the first identification of PK/fXI-like proteins in teleosts.

New pharmacotherapeutic options for oral anticoagulant treatment in atrial fibrillation patients aged 65 and older: factor XIa inhibitors and beyond

INTRODUCTION

Although much progress has been made using anticoagulation for stroke prevention in patients with non-valvular atrial fibrillation, bleeding is still a major concern.

AREAS COVERED

This article reviews current pharmacotherapeutic options in this setting. Particular emphasis is placed on the ability of the new molecules to minimize the bleeding risk in elderly patients. A systematic search of PubMed, Web of Science, and the Cochrane Library up to March 2023 was carried out.

EXPERT OPINION

Contact phase of coagulation is a possible new target for anticoagulant therapy. Indeed, congenital or acquired deficiency of contact phase factors is associated with reduced thrombotic burden and limited risk of spontaneous bleeding. These new drugs seem particularly suitable for stroke prevention in elderly patients with non-valvular atrial fibrillation in whom the hemorrhagic risk is high. Most of anti Factor XI (FXI) drugs are for parenteral use only. A group of small molecules are for oral use and therefore are candidates to substitute direct oral anticoagulants (DOACs) for stroke prevention in elderly patients with atrial fibrillation. Doubts remain on the possibility of impaired hemostasis. Indeed, a fine calibration of inhibition of contact phase factors is crucial for an effective and safe treatment.

Designing Smaller, Synthetic, Functional Mimetics of Sulfated Glycosaminoglycans as Allosteric Modulators of Coagulation Factors

Natural glycosaminoglycans (GAGs) are arguably the most diverse collection of natural products. Unfortunately, this bounty of structures remains untapped. Decades of research has realized only one GAG-like synthetic, small-molecule drug, fondaparinux. This represents an abysmal output because GAGs present a frontier that few medicinal chemists, and even fewer pharmaceutical companies, dare to undertake. GAGs are heterogeneous, polymeric, polydisperse, highly water soluble, synthetically challenging, too rapidly cleared, and difficult to analyze. Additionally, GAG binding to proteins is not very selective and GAG-binding sites are shallow. This Perspective attempts to transform this negative view into a much more promising one by highlighting recent advances in GAG mimetics. The Perspective focuses on the principles used in the design/discovery of drug-like, synthetic, sulfated small molecules as allosteric modulators of coagulation factors, such as antithrombin, thrombin, and factor XIa. These principles will also aid the design/discovery of sulfated agents against cancer, inflammation, and microbial infection.

Fluorescent Activity-Based Probe To Image and Inhibit Factor XIa Activity in Human Plasma

Anticoagulation therapy is a mainstay of the treatment of thrombotic disorders; however, conventional anticoagulants trade antithrombotic benefits for bleeding risk. Factor (f) XI deficiency, known as hemophilia C, rarely causes spontaneous bleeding, suggesting that fXI plays a limited role in hemostasis. In contrast, individuals with congenital fXI deficiency display a reduced incidence of ischemic stroke and venous thromboembolism, indicating that fXI plays a role in thrombosis. For these reasons, there is intense interest in pursuing fXI/factor XIa (fXIa) as targets for achieving antithrombotic benefit with reduced bleeding risk. To obtain selective inhibitors of fXIa, we employed libraries of natural and unnatural amino acids to profile fXIa substrate preferences. We developed chemical tools for investigating fXIa activity, such as substrates, inhibitors, and activity-based probes (ABPs). Finally, we demonstrated that our ABP selectively labels fXIa in the human plasma, making this tool suitable for further studies on the role of fXIa in biological samples.

Pharmacology and Clinical Development of Factor XI Inhibitors

Therapeutic anticoagulation is indicated for a variety of circumstances and conditions in several fields of medicine to prevent or treat venous and arterial thromboembolism. According to the different mechanisms of action, the available parenteral and oral anticoagulant drugs share the common principle of hampering or blocking key steps of the coagulation cascade, which unavoidably comes at the price of an increased propensity to bleed. Hemorrhagic complications affect patient prognosis both directly and indirectly (ie, by preventing the adoption of an effective antithrombotic strategy). Inhibition of factor XI (FXI) has emerged as a strategy with the potential to uncouple the pharmacological effect and the adverse events of anticoagulant therapy. This observation is based on the differential contribution of FXI to thrombus amplification, in which it plays a major role, and hemostasis, in which it plays an ancillary role in final clot consolidation. Several agents were developed to inhibit FXI at different stages (ie, suppressing biosynthesis, preventing zymogen activation, or impeding the biological action of the active form), including antisense oligonucleotides, monoclonal antibodies, small synthetic molecules, natural peptides, and aptamers. Phase 2 studies of different classes of FXI inhibitors in orthopedic surgery suggested that dose-dependent reductions in thrombotic complications are not paralleled by dose-dependent increases in bleeding compared with low-molecular-weight heparin. Likewise, the FXI inhibitor asundexian was associated with lower rates of bleeding compared with the activated factor X inhibitor apixaban in patients with atrial fibrillation, although no evidence of a therapeutic effect on stroke prevention is available so far. FXI inhibition could also be appealing for patients with other conditions, including end-stage renal disease, noncardioembolic stroke, or acute myocardial infarction, for which other phase 2 studies have been conducted. The balance between thromboprophylaxis and bleeding achieved by FXI inhibitors needs confirmation in large-scale phase 3 clinical trials powered for clinical end points. Several of such trials are ongoing or planned to define the role of FXI inhibitors in clinical practice and to clarify which FXI inhibitor may be most suited for each clinical indication. This article reviews the rationale, pharmacology, results of medium or small phase 2 studies, and future perspectives of drugs inhibiting FXI.

Factor XI inhibitors: what should clinicians know

PURPOSE OF REVIEW

Factor XI (FXI) inhibitors were developed to address unmet needs and limitations of current anticoagulants and are currently being studied in several indications. In this paper, we review the rationale for the development of these agents and summarize what clinicians should know about drugs that target FXI.

RECENT FINDINGS

Patients with FXI deficiency may have a lower risk of venous thromboembolism and cardiovascular events and have a variable but generally mild bleeding diathesis. FXI has been proposed as a target for anticoagulants due to the potential for reduction in thrombosis with a lower risk of bleeding than current anticoagulant agents. Several classes of drugs that target FXI are under development, of which three classes (small molecule inhibitors, antisense oligonucleotides and monoclonal antibodies) have been studied in Phase II trials. At least three large Phase III trial programs are planned or are underway, and will study the efficacy and safety of FXI inhibitors in tens of thousands of patients across a variety of indications including atrial fibrillation, stroke and cancer-associated venous thromboembolism.

SUMMARY

FXI inhibitors were developed with the hope of attenuating thrombosis with reduced bleeding/impairment of haemostasis. These agents have shown promise in preliminary trials with a low rate of bleeding. Ongoing Phase III investigations will inform the utility of these agents in clinical practice.

BJTJ-1837, a novel FXI activation-blocking antibody

Background

Factor (F)XI contributes to thrombosis development while it plays a limited role in normal hemostasis. FXI targeting has the potential for preventing and treating thrombosis with little bleeding risk.

Objectives

The aim of this study was to develop novel antibody therapeutics against FXI for the treatment of thrombosis-related diseases.

Methods

Mouse hybridoma technology was applied to screen for anti-FXI antibodies. Surface plasma resonance, enzyme inhibition, activated partial thromboplastin time, and prothrombin time assays were conducted to characterize the binding affinity and activity of antibodies. A cynomolgus monkey arterial venous shunt model was applied to validate the antithrombotic activities.

Results

A humanized antibody, BJTJ-1837, reported here bound to the protease domain of FXI and activated FXI with high affinity. BJTJ-1837 fully inhibited the activation of FXI by activated FXII and thrombin. BJTJ-1837 also demonstrated strong anticoagulant activity in human and cynomolgus monkey plasma as measured by activated partial thromboplastin time. Moreover, BJTJ-1837 showed favorable antithrombotic activity with a dose-dependent protection in an arterial venous shunt thrombosis model in cynomolgus monkeys without the bleeding adverse effect. Furthermore, BJTJ-1837 displayed favorable pharmacokinetic and pharmacodynamic properties and good developability.

Conclusion

As a potential antithrombotic therapeutic agent with a safe profile, BJTJ-1837 is a very promising FXI activation-blocking antibody candidate.

Harnessing the cyclization strategy for new drug discovery

The design of new ligands with high affinity and specificity against the targets of interest has been a central focus in drug discovery. As one of the most commonly used methods in drug discovery, the cyclization represents a feasible strategy to identify new lead compounds by increasing structural novelty, scaffold diversity and complexity. Such strategy could also be potentially used for the follow-on drug discovery without patent infringement. In recent years, the cyclization strategy has witnessed great success in the discovery of new lead compounds against different targets for treating various diseases. Herein, we first briefly summarize the use of the cyclization strategy in the discovery of new small-molecule lead compounds, including the proteolysis targeting chimeras (PROTAC) molecules. Particularly, we focus on four main strategies including fused ring cyclization, chain cyclization, spirocyclization and macrocyclization and highlight the use of the cyclization strategy in lead generation. Finally, the challenges including the synthetic intractability, relatively poor pharmacokinetics (PK) profiles and the absence of the structural information for rational structure-based cyclization are also briefly discussed. We hope this review, not exhaustive, could provide a timely overview on the cyclization strategy for the discovery of new lead compounds.

Factor XI, a potential target for anticoagulation therapy for venous thromboembolism

Venous thromboembolism (VTE) is a common cause of mortality and disability in hospitalized patients, and anticoagulation is an essential therapeutic option. Despite the increasing use of direct oral anticoagulants, complications and adverse drug reactions still occur in patients with VTE. Within 5 years, 20% of patients with VTE experience recurrence, and 50% of patients with deep vein thrombosis develop post-thrombotic syndrome. Furthermore, bleeding due to anticoagulants is a side effect that must be addressed. Therefore, safer and more effective anticoagulant strategies with higher patient compliance are urgently needed. Available epidemiological evidence and animal studies have shown that factor XI (FXI) inhibitors can reduce thrombus size and loosen the thrombus structure with a relatively low risk of bleeding, suggesting that FXI has an important role in thrombus stabilization and is a safer target for anticoagulation. Recent clinical trial data have also shown that FXI inhibitors are as effective as enoxaparin and apixaban in preventing VTE, but with a significantly lower incidence of bleeding. Furthermore, FXI inhibitors can be administered daily or monthly; therefore, the monitoring interval can be longer. Additionally, FXI inhibitors can prolong the activated partial thromboplastin time without affecting prothrombin time, which is an easy and common test used in clinical testing, providing a cost-effective monitoring routine for patients. Consequently, the inhibition of FXI may be an effective strategy for the prevention and treatment of VTE. Enormous progress has been made in the research strategies for FXI inhibitors, with abelacimab already in phase III clinical trials and most other inhibitors in phase I or II trials. In this review, we discuss the challenges of VTE therapy, briefly describe the structure and function of FXI, summarize the latest FXI/activated FXI (FXIa) inhibitor strategies, and summarize the latest developments in clinical trials of FXI/FXIa inhibitors.

SHR2285, the first selectively oral FXIa inhibitor in China: Safety, tolerability, pharmacokinetics and pharmacodynamics combined with aspirin, clopidogrel or ticagrelor

Purpose: To evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of SHR2285, the first oral coagulation factor XIa (FXIa) inhibitor developed in China in combination with aspirin, clopidogrel or ticagrelor in healthy subjects. Methods: This study was a single-center, randomized, double-blind, placebo-controlled (only SHR2285) design (NCT04945616). A total of 52 healthy subjects, 29 male and 23 female, were completed in this study. The subjects were divided into three groups: A, B and C, 16 subjects in group A [aspirin + clopidogrel + placebo or SHR2285 200 mg bid (1:3, 4 received placebo and 12 received SHR2285)] 16 subjects in group B [aspirin + clopidogrel + placebo or SHR2285 300 mg bid (1:3, 3 received placebo and 13 received SHR2285)] and 20 subjects in group C (aspirin + ticagrelor + placebo or SHR2285 300 mg bid (2:3, 8 received placebo and 12 received SHR2285)), respectively. All groups were administered orally for six consecutive days. Safety, tolerability, pharmacokinetics and pharmacodynamics parameters were assessed. Results: 1) SHR2285 was well tolerated, and all adverse events were mild. There was no evidence of an increased risk of bleeding. 2) After 6 days of twice-daily administration, SHR2285 could reach a steady state. The mean half-life of SHR2285 in group A, group B and group C was 13.9 h, 14.5 h and 13.8 h, respectively. 3) SHR2285 markedly inhibited FXI activity and prolonged activated partial thromboplastin time (APTT). In group A, group B and group C, the mean maximum inhibition rate of FXI activity was 84.8%, 89.3% and 92.2% and the mean maximum prolongation of APTT was 2.08-fold, 2.36-fold and 2.26-fold, respectively. Conclusion: These data suggest that SHR2285, a potential oral FXIa inhibitor, is expected to become a novel, safe and effective anticoagulant when combined with aspirin, clopidogrel or ticagrelor.

Blocking domain 6 of high molecular weight kininogen to understand intrinsic clotting mechanisms

Background

The contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation of this system contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding of this pathway is needed.

Methods

We performed coagulation assays in normal human plasma and various factor-deficient plasmas. To evaluate how HK-mediated PK and FXI activation contributes to coagulation, we used an anti-HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI.

Results

FXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti-HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI in this process. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK-deficient plasma, which was not due to feedback activation of FXII.

Conclusions

This study improves our understanding of HK-mediated coagulation and provides an explanation for the absence of bleeding in HK-deficient individuals. 3E8 specifically prevented HK-mediated FXI activation; therefore, it could be used to prevent contact activation-mediated thrombosis without altering hemostasis.

Single-Dose Pharmacokinetics of Milvexian in Participants with Normal Renal Function and Participants with Moderate or Severe Renal Impairment

OBJECTIVE

The aim of this study was to assess the effect of moderate or severe renal impairment on the pharmacokinetic (PK) properties of milvexian.

METHODS

This open-label, parallel-group study assessed the PK, safety, and tolerability of a single oral 60 mg dose of milvexian in participants with normal renal function (n = 8; estimated glomerular filtration rate [eGFR] ≥ 90 mL/min/1.73 m2) and participants with moderate (n = 8; eGFR ≥ 30 to ≤ 59 mL/min/1.73 m2) or severe (n = 8; eGFR < 30 mL/min/1.73 m2) renal impairment. Regression analysis was performed using linear regression of log-transformed PK parameters versus eGFR.

RESULTS

Milvexian was well tolerated, with no deaths, serious adverse events, or serious bleeding reported. The maximum milvexian concentration (Cmax) was similar for all groups. Based on a regression analysis of milvexian concentration versus eGFR, participants with eGFR values of 30 and 15 mL/min/1.73 m2, respectively, had area under the curve (AUC) values that were 41% and 54% greater than in participants with normal renal function. Median time to maximum concentration (Tmax) was similar for the three groups (4.5-5.0 h). The half-life increased for participants with moderate (18.0 h) or severe (17.7 h) renal impairment compared with those with normal renal function (13.8 h).

CONCLUSION

A single dose of milvexian 60 mg was safe and well tolerated in participants with normal renal function and moderate or severe renal impairment. There was a similar increase in milvexian exposure between the moderate and severe renal groups.

CLINICAL TRIALS REGISTRATION

This study was registered with ClinicalTrials.gov (NCT03196206, first posted 22 June 2017).

Liver-heart cross-talk mediated by coagulation factor XI protects against heart failure

Tissue-tissue communication by endocrine factors is a vital mechanism for physiologic homeostasis. A systems genetics analysis of transcriptomic and functional data from a cohort of diverse, inbred strains of mice predicted that coagulation factor XI (FXI), a liver-derived protein, protects against diastolic dysfunction, a key trait of heart failure with preserved ejection fraction. This was confirmed using gain- and loss-of-function studies, and FXI was found to activate the bone morphogenetic protein (BMP)-SMAD1/5 pathway in the heart. The proteolytic activity of FXI is required for the cleavage and activation of extracellular matrix-associated BMP7 in the heart, thus inhibiting genes involved in inflammation and fibrosis. Our results reveal a protective role of FXI in heart injury that is distinct from its role in coagulation.

Molecular heterogeneity of factor XI deficiency in Tunisia

Factor XI (FXI) deficiency is a rare inherited bleeding disorder that is highly prevalent in Ashkenazi Jewish ancestry but sporadically observed in most ethnic groups. It is heterogeneous both in clinical presentation and in genetic causality. Although a large spectrum of mutations associated with this disorder has been reported in several populations, genetic data of FXI deficiency in Tunisia are poorly described. The purpose of this study was to determine the molecular basis of FXI deficiency among Tunisian patients. Fourteen index cases from nine unrelated families with FXI deficiency, referred to Hemophilia Treatment Center of Aziza Othmana Hospital, were included in this study. The patients' F11 genes were amplified by PCR and subjected to direct DNA sequencing analysis. Sequencing analysis of F11 genes identified three distinct mutations; the Jewish type II nonsense mutation E117X, one previously reported missense mutation E602Q and one novel missense mutation V271M, which led to the disruption of the third apple domain structure of FXI. Furthermore, seven polymorphisms previously described, were also detected: C321F, c. 294A>G, -138 A>C, p.D125D, p.T249T, p.G379G, p.D551D. This report represents the first genetic study analyzing the molecular characteristics of factor XI deficiency within Tunisian population. Identification of the Jewish type II mutation in two families, as well as one missense previously reported mutation and one novel mutation confirmed the genetic heterogeneity of this disorder. Screening a large number of Tunisian factor XI deficient would reveal the spectrum mutations causing factor XI deficiency in Tunisia.

Effects of Itraconazole and Diltiazem on the Pharmacokinetics and Pharmacodynamics of Milvexian, A Factor XIa Inhibitor

INTRODUCTION

Modulation of Factor XIa (FXIa) may provide a novel mechanism for systemic anticoagulation with the potential to improve the risk-benefit profile observed with existing anticoagulants through greater efficacy or a safer bleeding profile. This study assessed the effects of co-administration with strong and moderate CYP3A inhibitors itraconazole and diltiazem, respectively, on the pharmacokinetic and pharmacodynamic properties of milvexian, a Factor XIa inhibitor.

METHODS

This was an open-label, non-randomized, two-period crossover study in healthy participants. In period 1, participants received a single oral dose of milvexian (30 mg) on day 1, followed by a washout on days 2 and 3. In period 2, participants received multiple oral doses of itraconazole (200 mg) or diltiazem (240 mg) with a single dose of milvexian.

RESULTS

A total of 28 participants entered the treatment period. Following itraconazole co-administration, milvexian exposure was increased; AUC(0-T), AUC(INF), and C24 were 2.5-, 2.5-, and 3.8-fold higher, while mean Cmax was 28% higher versus milvexian alone. Diltiazem co-administration also increased milvexian exposure; AUC(0-T), AUC(INF), and C24 were 38, 38, and 64% higher, and mean Cmax was 9.6% higher versus milvexian alone. Prolongation of activated partial thromboplastin time was observed with milvexian in a concentration-dependent fashion irrespective of co-administration with itraconazole or diltiazem. Administration of a single dose of milvexian, alone or in combination with itraconazole or diltiazem, was generally safe and well tolerated; there were no deaths or serious adverse events.

CONCLUSIONS

A moderate increase in milvexian exposure was observed following co-administration of itraconazole while a minimal increase was seen with diltiazem, consistent with the involvement of CYP3A metabolism and P-glycoprotein in drug absorption/elimination. Milvexian was generally safe and well tolerated in healthy participants.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov (NCT02807909; submitted June 17, 2016).

Pharmacological profile of asundexian, a novel, orally bioavailable inhibitor of factor XIa

BACKGROUND

Activated coagulation factor XI (FXIa) contributes to the development and propagation of thrombosis but plays only a minor role in hemostasis; therefore, it is an attractive antithrombotic target.

OBJECTIVES

To evaluate the pharmacology of asundexian (BAY 2433334), a small molecule inhibitor targeting FXIa, in vitro and in various rabbit models.

METHODS

The effects of asundexian on FXIa activity, selectivity versus other proteases, plasma thrombin generation, and clotting assays were evaluated. Antithrombotic effects were determined in FeCl2 - and arterio-venous (AV) shunt models. Asundexian was administered intravenously or orally, before or during thrombus formation, and with or without antiplatelet drugs (aspirin and ticagrelor). Potential effects of asundexian on bleeding were evaluated in ear-, gum-, and liver injury models.

RESULTS

Asundexian inhibited human FXIa with high potency and selectivity. It reduced FXIa activity, thrombin generation triggered by contact activation or low concentrations of tissue factor, and prolonged activated partial thromboplastin time in human, rabbit, and various other species, but not in rodents. In the FeCl2 -injury models, asundexian reduced thrombus weight versus control, and in the arterial model when added to aspirin and ticagrelor. In the AV shunt model, asundexian reduced thrombus weight when administered before or during thrombus formation. Asundexian alone or in combination with antiplatelet drugs did not increase bleeding times or blood loss in any of the models studied.

CONCLUSIONS

Asundexian is a potent oral FXIa inhibitor with antithrombotic efficacy in arterial and venous thrombosis models in prevention and intervention settings, without increasing bleeding.

A Common Missense Variant Causing Factor XI Deficiency and Increased Bleeding Tendency in Maine Coon Cats

Hereditary factor XI (FXI) deficiency is characterized as an autosomal mild to moderate coagulopathy in humans and domestic animals. Coagulation testing revealed FXI deficiency in a core family of Maine Coon cats (MCCs) in the United States. Factor XI-deficient MCCs were homozygous for a guanine to adenine transition resulting in a methionine substitution for the highly conserved valine-516 in the FXI catalytic domain. Immunoblots detected FXI of normal size and quantity in plasmas of MCCs homozygous for V516M. Some FXI-deficient MCCs experienced excessive post-operative/traumatic bleeding. Screening of 263 MCCs in Europe revealed a mutant allele frequency of 0.232 (23.2%). However, V516M was not found among 100 cats of other breeds. Recombinant feline FXI-M516 (fFXI-M516) expressed ~4% of the activity of wild-type fFXI-V516 in plasma clotting assays. Furthermore, fFXIa-M516 cleaved the chromogenic substrate S-2366 with ~4.3-fold lower catalytic efficacy (kcat/Km) than fFXIa-V516, supporting a conformational alteration of the protease active site. The rate of FIX activation by fFXIa-M516 was reduced >3-fold compared with fFXIa-V516. The common missense variant FXI-V516M causes a cross-reactive material positive FXI deficiency in MCCs that is associated with mild-moderate bleeding tendencies. Given the prevalence of the variant in MCCs, genotyping is recommended prior to invasive procedures or breeding.

The role of thrombin in haemostasis

Thrombin is a multifunctional serine protease generated in injured cells. The generation of thrombin in coagulation plays a central role in the functioning of haemostasis. The last enzyme in the coagulation cascade is thrombin, with the function of cleaving fibrinogen to fibrin, which forms the fibrin clot of a haemostatic plug. Although thrombin primarily converts fibrinogen to fibrin, it also has many other positive regulatory effects on coagulation. Thrombin has procoagulant, inflammatory, cellular proliferation and anticoagulant effects. In coagulation system, thrombin has two very distinct roles. Firstly, it acts as a procoagulant when it converts fibrinogen into an insoluble fibrin clot, activates factor (F) XIII, activates thrombin activatable fibrinolysis inhibitor (TAFI) and activates FV, FVIII and FXI. Thrombin also enhances platelet adhesion by inactivating a disintegrin and metalloprotease with thrombospondin type1 motif (ADAMTS13). However, when thrombin activates protein C, it acts as an anticoagulant. A natural anticoagulant pathway that supplies regulation of the blood coagulation system contains protein C, which is the key component. This is accomplished by the specific proteolytic inactivation of FV and FVIII. In this review, the multiple roles of thrombin in the haemostatic response to injury are studied in addition to the cofactors that determine thrombin activity and how thrombin activity is thought to be coordinated.

Safety, pharmacokinetics, and pharmacodynamics of milvexian in healthy Japanese participants

This randomized, double-blind, placebo-controlled, multiple ascending-dose study evaluated safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple doses of milvexian, an oral small-molecule FXIa inhibitor, in healthy Japanese participants. Participants received oral milvexian daily under fasted (50 mg and 200 mg) or fed conditions (500 mg) or placebo over 14 days; 24 participants (8/cohort: 6 milvexian; 2 placebo) were planned. Due to an unblinding event, participants in one cohort (200 mg daily) were discontinued, and a second cohort enrolled; 32 participants were included in safety and pharmacodynamic analyses, and 24/32 in pharmacokinetic analyses. Milvexian up to 500 mg daily for 14 days was generally well tolerated, with no deaths, serious adverse events, or discontinuations due to adverse events. Milvexian exposure increased between 50-mg and 200-mg doses. Median Tmax was similar with 50-mg and 200-mg doses (2.5-3.0 h) and delayed under fed conditions (500 mg, 7.0-8.0 h). Median T1/2 was similar across doses (8.9-11.9 h). Multiple oral milvexian administrations resulted in concentration-related prolongation of aPTT and decreased FXI clotting activity. Milvexian was generally safe and well tolerated. The pharmacokinetic and pharmacodynamic profile of milvexian demonstrates suitability for further clinical development in Japanese participants.

Anti-HK antibody reveals critical roles of a 20-residue HK region for Aβ-induced plasma contact system activation

Alzheimer's disease (AD) is a neurodegenerative disorder and the leading cause of dementia. Vascular abnormalities and neuroinflammation play roles in AD pathogenesis. Plasma contact activation, which leads to fibrin clot formation and bradykinin release, is elevated in many AD patients, likely due to the ability of AD's pathogenic peptide β-amyloid (Aβ) to induce its activation. Since overactivation of this system may be deleterious to AD patients, the development of inhibitors could be beneficial. Here, we show that 3E8, an antibody against a 20-amino acid region of high molecular weight kininogen's (HK) domain 6, inhibits Aβ-induced intrinsic coagulation. Mechanistically, 3E8 inhibits contact system activation by blocking the binding of prekallikrein (PK) and factor XI (FXI) to HK, thereby preventing their activation and the continued activation of factor XII (FXII). The 3E8 antibody can also disassemble HK/PK and HK/FXI complexes in normal human plasma in the absence of a contact system activator due to its strong binding affinity for HK, indicating its prophylactic ability. Furthermore, the binding of Aβ to both FXII and HK is critical for Aβ-mediated contact system activation. These results suggest that a 20-amino acid region of HK's domain 6 plays a critical role in Aβ-induced contact system activation, and this region may provide an effective strategy to inhibit or prevent contact system activation in related disorders.

Discovery of Milvexian, a High-Affinity, Orally Bioavailable Inhibitor of Factor XIa in Clinical Studies for Antithrombotic Therapy

Factor XIa (FXIa) is an enzyme in the coagulation cascade thought to amplify thrombin generation but has a limited role in hemostasis. From preclinical models and human genetics, an inhibitor of FXIa has the potential to be an antithrombotic agent with superior efficacy and safety. Reversible and irreversible inhibitors of FXIa have demonstrated excellent antithrombotic efficacy without increased bleeding time in animal models (Weitz, J. I., Chan, N. C. Arterioscler. Thromb. Vasc. Biol. 2019, 39 (1), 7-12). Herein, we report the discovery of a novel series of macrocyclic FXIa inhibitors containing a pyrazole P2' moiety. Optimization of the series for (pharmacokinetic) PK properties, free fraction, and solubility resulted in the identification of milvexian (BMS-986177/JNJ-70033093, 17, FXIa Ki = 0.11 nM) as a clinical candidate for the prevention and treatment of thromboembolic disorders, suitable for oral administration.

Milvexian, an orally bioavailable, small-molecule, reversible, direct inhibitor of factor XIa: In vitro studies and in vivo evaluation in experimental thrombosis in rabbits

BACKGROUND

Milvexian (BMS-986177/JNJ-70033093) is an orally bioavailable factor XIa (FXIa) inhibitor currently in phase 2 clinical trials.

OBJECTIVES

To evaluate in vitro properties and in vivo characteristics of milvexian.

METHODS

In vitro properties of milvexian were evaluated with coagulation and enzyme assays, and in vivo profiles were characterized with rabbit models of electrolytic-induced carotid arterial thrombosis and cuticle bleeding time (BT).

RESULTS

Milvexian is an active-site, reversible inhibitor of human and rabbit FXIa (Ki 0.11 and 0.38 nM, respectively). Milvexian increased activated partial thromboplastin time (APTT) without changing prothrombin time and potently prolonged plasma APTT in humans and rabbits. Milvexian did not alter platelet aggregation to ADP, arachidonic acid, or collagen. Milvexian was evaluated for in vivo prevention and treatment of thrombosis. For prevention, milvexian 0.063 + 0.04, 0.25 + 0.17, and 1 + 0.67 mg/kg+mg/kg/h preserved 32 ± 6*, 54 ± 10*, and 76 ± 5%* of carotid blood flow (CBF) and reduced thrombus weight by 15 ± 10*, 45 ± 2*, and 70 ± 4%*, respectively (*p < .05; n = 6/dose). For treatment, thrombosis was initiated for 15 min and CBF decreased to 40% of control. Seventy-five minutes after milvexian administration, CBF averaged 1 ± 0.3, 39 ± 10, and 66 ± 2%* in groups treated with vehicle and milvexian 0.25 + 0.17 and 1 + 0.67 mg/kg+mg/kg/h, respectively (*p < .05 vs. vehicle; n = 6/group). The combination of milvexian 1 + 0.67 mg/kg+mg/kg/h and aspirin 4 mg/kg/h intravenous did not increase BT versus aspirin monotherapy.

CONCLUSIONS

Milvexian is an effective antithrombotic agent with limited impact on hemostasis, even when combined with aspirin in rabbits. This study supports inhibition of FXIa with milvexian as a promising antithrombotic therapy with a wide therapeutic window.

First-in-human study of milvexian, an oral, direct, small molecule factor XIa inhibitor

Milvexian (BMS-986177/JNJ-70033093) is a small molecule, active-site inhibitor of factor XIa (FXIa) being developed to prevent and treat thrombotic events. The safety, tolerability, pharmacokinetics (PKs), and pharmacodynamics (PDs) of milvexian were assessed in a two-part, double-blind, placebo-controlled, sequential single ascending dose (SAD) and multiple ascending dose (MAD) study in healthy adults. Participants in SAD panels (6 panels of 8 participants; n = 48) were randomized (3:1) to receive milvexian (4, 20, 60, 200, 300, or 500 mg) or placebo. The 200- and 500-mg panels investigated the pharmacokinetic impact of a high-fat meal. Participants in MAD panels (7 panels of 8 participants; n = 56) were randomized (3:1) to receive milvexian (once- or twice-daily) or placebo for 14 days. All milvexian dosing regimens were safe and well-tolerated, with only mild treatment-emergent adverse events and no clinically significant bleeding events. In SAD panels, maximum milvexian plasma concentration occurred 3 h postdose in all fasted panels. The terminal half-life (T1/2 ) ranged from 8.3 to 13.8 h. In fasted panels from 20 to 200 mg, absorption was dose-proportional; results at higher doses (300 and 500 mg) were consistent with saturable absorption. Food increased milvexian bioavailability in a dose-dependent fashion. In MAD panels, steady-state milvexian plasma concentration was reached within 3 and 6 dosing days with once- and twice-daily dosing, respectively. Renal excretion was less than 20% in all panels. Prolongation of activated partial thromboplastin time was observed and was directly related to drug exposure. These results suggest that the safety, tolerability, PK, and PD properties of milvexian are suitable for further clinical development.

Pharmacokinetics, pharmacodynamics and safety of BAY 2433334, a novel activated factor XI inhibitor, in healthy volunteers: A randomized phase 1 multiple-dose study

Aim

To evaluate BAY 2433334, an oral activated factor XI (FXIa) inhibitor, in volunteers.

Methods

Phase 1 study of healthy men at a German centre. Part A: randomized, single‐blind, multiple dose‐escalation study of BAY 2433334 (25/50/100 mg once daily [OD]) vs. placebo. Part B: similar design to Part A; evaluated BAY 2433334 25 mg twice daily. Part C: nonrandomized, open‐label study; evaluated potential interactions between BAY 2433334 (25/75 mg OD) and midazolam (7.5 mg), a CYP3A4 index substrate. Primary variables: treatment‐emergent adverse events (TEAEs; Parts A and B); area under the plasma concentration–time curve (AUC) and maximum plasma concentration of midazolam and α‐hydroxymidazolam (Part C). Study period: 18 days plus follow‐up visit.

Results

Parts A and B: 36 participants randomized to BAY 2433334; 12 to placebo. Part C: 48 participants assigned to BAY 2433334 plus midazolam. BAY 2433334 was well tolerated in all study parts. AUC and maximum plasma concentration of BAY 2433334 in plasma appeared dose proportional over 25–100 mg OD, with low‐to‐moderate variability in pharmacokinetic parameters. Multiple dosing caused minor‐to‐moderate accumulation and a mean terminal half‐life (15.8–17.8 h) supporting once‐daily dosing. Dose‐dependent FXIa activity inhibition and activated partial thromboplastin time prolongation were observed. BAY 2433334 appeared to have a minor effect on AUC for midazolam (ratio [90% confidence interval]: 1.1736 [1.0963–1.2564]) and α‐hydroxymidazolam (0.9864 [0.9169–1.0612]) only for BAY 2433334 75 mg OD on day 10.

Conclusion

Multiple dosing of BAY 2433334 in healthy volunteers was well tolerated, with a predictable pharmacokinetic/pharmacodynamic profile and no clinically relevant CYP3A4 induction or inhibition.

Genetic analysis of compound heterozygous pathogenic variants of the F11 gene in two Chinese patients with hereditary factor XI deficiency

The aim of this study was to explore the molecular pathogenesis of two families with compound heterozygous hereditary factor XI deficiency. All the exons, flanking sequences, 5' and 3' untranslated regions of the F11 gene were analysed by direct DNA sequencing. The suspected variants were confirmed by reverse sequencing. Bioinformatics softwares were used to analysis the conservation and the possible impact of these pathogenic variants. Genetic analysis revealed c.689G > T and c.1556G > A variants of F11 gene in family A; c.1107C > A and c.1557G > C variants of F11 gene in family B. These variants sites were highly conserved among homologous species. Bioinformatics and structural analysis demonstrated these variants were pathogenic and could affect the protein structure. The c.689G > T, c.1556G > A, c.1107C > A and the c.1557G > C heterozygous variants might be responsible for the decrease of FXI levels in probands. In addition, c.689G > T (NM_000128.4) is a novel pathogenic variant site, which has not been reported.

F9 missense mutations impairing factor IX activation are associated with pleiotropic plasma phenotypes

BACKGROUND

Circulating dysfunctional factor IX (FIX) might modulate distribution of infused FIX in hemophilia B (HB) patients. Recurrent substitutions at FIX activation sites (R191-R226, >300 patients) are associated with variable FIX activity and antigen (FIXag) levels.

OBJECTIVES

To investigate the (1) expression of a complete panel of missense mutations at FIX activation sites and (2) contribution of F9 genotypes on the FIX pharmacokinetics (PK).

METHODS

We checked FIX activity and antigen and activity assays in plasma and after recombinant expression of FIX variants and performed an analysis of infused FIX PK parameters in patients (n = 30), mostly enrolled in the F9 Genotype and PK HB Italian Study (GePKHIS; EudraCT ID2017-003902-42).

RESULTS

The variable FIXag amounts and good relation between biosynthesis and activity of multiple R191 variants results in graded moderate-to-mild severity of the R191C>L>P>H substitutions. Recombinant expression may predict the absence in the HB mutation database of the benign R191Q/W/K and R226K substitutions. Equivalent changes at R191/R226 produced higher FIXag levels for R226Q/W/P substitutions, as also observed in p.R226W female carrier plasma. Pharmacokinetics analysis in patients suggested that infused FIX Alpha distribution and Beta elimination phases positively correlated with endogenous FIXag levels. Mean residence time was particularly prolonged (79.4 h, 95% confidence interval 44.3-114.5) in patients (n = 7) with the R191/R226 substitutions, which in regression analysis were independent predictors (β coefficient 0.699, P = .004) of Beta half-life, potentially prolonged by the increasing over time ratio between endogenous and infused FIX.

CONCLUSIONS

FIX activity and antigen levels and specific features of the dysfunctional R191/R226 variants may exert pleiotropic effects both on HB patients' phenotypes and substitutive treatment.

Factor XI deficiency and delayed hemorrhages after resection of choroid plexus papilloma: illustrative case

BACKGROUND

Factor XI deficiency, also known as hemophilia C, is a rare inherited bleeding disorder that may leave routine coagulation parameters within normal range. Depending on the mutation subtype, prolonged activated partial thromboplastin time may occasionally be found. The disease has an autosomal transmission, with an estimated prevalence in the general population of approximately 1 in 1 million. Heterozygosis accounts for partial deficits, but the tendency to bleed is unrelated to the measured activity of factor XI. Diagnosis usually follows unexpected hemorrhages occurring spontaneously or after trauma or surgical procedures.

OBSERVATIONS

Few cases have been reported in the neurosurgical literature, all occurring spontaneously or after head trauma. Owing to its subtle features, the true incidence of the disease is probably underestimated. The authors report a case of a patient with previously undiagnosed factor XI deficiency who underwent uncomplicated resection of a fourth-ventricle papilloma and experienced delayed, severe hemorrhagic complications.

LESSONS

The known association between choroid plexus tumors and intracranial bleeding raised differential diagnosis issues. This report may serve to help to investigate delayed hemorrhages after cranial surgery.

WPK5, a Novel Kunitz-Type Peptide from the Leech Whitmania pigra Inhibiting Factor XIa, and Its Loop-Replaced Mutant to Improve Potency

Kunitz-type proteins or peptides have been found in many blood-sucking animals, but the identity of them in leeches remained elusive. In the present study, five Kunitz-type peptides named WPK1-WPK5 were identified from the leech Whitmania pigra. Recombinant WPK1-WPK5 were expressed in Pichia pastoris GS115, and their inhibitory activity against Factor XIa (FXIa) was tested. WPK5 showed inhibitory activity against FXIa with an IC₅₀ value of 978.20 nM. To improve its potency, the loop replacement strategy was used. The loop 1 (TGPCRSNLER) and loop 2 (QYGGC) in WPK5 were replaced by loop 1 (TGPCRAMISR) and loop 2 (FYGGC) in PN2KPI, respectively, and the resulting peptide named WPK5-Mut showed an IC₅₀ value of 8.34 nM to FXIa, which is about 100-fold the potency of FXIa compared to that of WPK5. WPK5-Mut was further evaluated for its extensive bioactivity in vitro and in vivo. It dose-dependently prolonged APTT on both murine plasma and human plasma, and potently inhibited FeCl₃-induced carotid artery thrombosis in mice at a dose of 1.5 mg/kg. Additionally, WPK5-Mut did not show significant bleeding risk at a dose of 6 mg/kg. Together, these results showed that WPK5-Mut is a promising candidate for the development of an antithrombotic drug.

Analysis of 272 Genetic Variants in the Upgraded Interactive FXI Web Database Reveals New Insights into FXI Deficiency

Coagulation Factor XI (FXI) is a plasma glycoprotein composed of four apple (Ap) domains and a serine protease (SP) domain. FXI circulates as a dimer and activates Factor IX (FIX), promoting thrombin production and preventing excess blood loss. Genetic variants that degrade FXI structure and function often lead to bleeding diatheses, commonly termed FXI deficiency. The first interactive FXI variant database underwent initial development in 2003 at https://www.factorxi.org . Here, based on a much improved FXI crystal structure, the upgraded FXI database contains information regarding 272 FXI variants (including 154 missense variants) found in 657 patients, this being a significant increase from the 183 variants identified in the 2009 update. Type I variants involve the simultaneous reduction of FXI coagulant activity (FXI:C) and FXI antigen levels (FXI:Ag), whereas Type II variants result in decreased FXI:C yet normal FXI:Ag. The database updates now highlight the predominance of Type I variants in FXI. Analysis in terms of a consensus Ap domain revealed the near-uniform distribution of 81 missense variants across the Ap domains. A further 66 missense variants were identified in the SP domain, showing that all regions of the FXI protein were important for function. The variants clarified the critical importance of changes in surface solvent accessibility, as well as those of cysteine residues and the dimer interface. Guidelines are provided below for clinicians who wish to use the database for diagnostic purposes. In conclusion, the updated database provides an easy-to-use web resource on FXI deficiency for clinicians.

An Oil Hyper-Accumulator Mutant Highlights Peroxisomal ATP Import as a Regulatory Step for Fatty Acid Metabolism in Aurantiochytrium limacinum

Thraustochytrids are marine protists that naturally accumulate triacylglycerol with long chains of polyunsaturated fatty acids, such as ω3-docosahexaenoic acid (DHA). They represent a sustainable response to the increasing demand for these "essential" fatty acids (FAs). Following an attempt to transform a strain of Aurantiochytrium limacinum, we serendipitously isolated a clone that did not incorporate any recombinant DNA but contained two to three times more DHA than the original strain. Metabolic analyses indicated a deficit in FA catabolism. However, whole transcriptome analysis did not show down-regulation of genes involved in FA catabolism. Genome sequencing revealed extensive DNA deletion in one allele encoding a putative peroxisomal adenylate transporter. Phylogenetic analyses and yeast complementation experiments confirmed the gene as a peroxisomal adenylate nucleotide transporter (AlANT1), homologous to yeast ScANT1 and plant peroxisomal adenylate nucleotide carrier AtPNC genes. In yeast and plants, a deletion of the peroxisomal adenylate transporter inhibits FA breakdown and induces FA accumulation, a phenotype similar to that described here. In response to this metabolic event, several compensatory mechanisms were observed. In particular, genes involved in FA biosynthesis were upregulated, also contributing to the high FA accumulation. These results support AlANT1 as a promising target for enhancing DHA production in Thraustochytrids.