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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.

Background: The TOPCAT trial (Treatment of Preserved Cardiac Function Heart Failure With an Aldosterone Antagonist Trial) suggested clinical benefits of spironolactone treatment among patients with heart failure with preserved ejection fraction enrolled in the Americas. However, a comprehensive assessment of biologic pathways impacted by spironolactone therapy in heart failure with preserved ejection fraction has not been performed. Methods: We conducted aptamer-based proteomic analysis utilizing 5284 modified aptamers to 4928 unique proteins on plasma samples from TOPCAT participants from the Americas (n=164 subjects with paired samples at baseline and 1 year) to identify proteins and pathways impacted by spironolactone therapy in heart failure with preserved ejection fraction. Mean percentage change from baseline was calculated for each protein. Additionally, we conducted pathway analysis of proteins altered by spironolactone. Results: Spironolactone therapy was associated with proteome-wide significant changes in 7 proteins. Among these, CARD18 (caspase recruitment domain-containing protein 18), PKD2 (polycystin 2), and PSG2 (pregnancy-specific glycoprotein 2) were upregulated, whereas HGF (hepatic growth factor), PLTP (phospholipid transfer protein), IGF2R (insulin growth factor 2 receptor), and SWP70 (switch-associated protein 70) were downregulated. CARD18, a caspase-1 inhibitor, was the most upregulated protein by spironolactone (−0.5% with placebo versus +66.5% with spironolactone, P Conclusions: Proteomic analysis in the TOPCAT trial revealed proteins and pathways altered by spironolactone, including the caspase inhibitor CARD18 and multiple pathways that involved collagens. In addition to effects on fibrosis, our studies suggest potential antiapoptotic effects of spironolactone in heart failure with preserved ejection fraction, a hypothesis that merits further exploration.

Objectives The primary objective was to identify well-tolerated doses of cimlanod in patients with acute heart failure (AHF). Secondary objectives were to identify signals of efficacy, including biomarkers, symptoms, and clinical events. Background Nitroxyl (HNO) donors have vasodilator, inotropic and lusitropic effects. Bristol-Myers Squibb-986231 (cimlanod) is an HNO donor being developed for acute heart failure (AHF). Methods This was a phase IIb, double-blind, randomized, placebo-controlled trial of 48-h treatment with cimlanod compared with placebo in patients with left ventricular ejection fraction ≤40% hospitalized for AHF. In part I, patients were randomized in a 1:1 ratio to escalating doses of cimlanod or matching placebo. In part II, patients were randomized in a 1:1:1 ratio to either of the 2 highest tolerated doses of cimlanod from part I or placebo. The primary endpoint was the rate of clinically relevant hypotension (systolic blood pressure Results In part I (n = 100), clinically relevant hypotension was more common with cimlanod than placebo (20% vs. 8%; relative risk [RR]: 2.45; 95% confidence interval [CI]: 0.83 to 14.53). In part II (n = 222), the incidence of clinically relevant hypotension was 18% for placebo, 21% for cimlanod 6 μg/kg/min (RR: 1.15; 95% CI: 0.58 to 2.43), and 35% for cimlanod 12 μg/kg/min (RR: 1.9; 95% CI: 1.04 to 3.59). N-terminal pro–B-type natriuretic peptide and bilirubin decreased during infusion of cimlanod treatment compared with placebo, but these differences did not persist after treatment discontinuation. Conclusions Cimlanod at a dose of 6 μg/kg/min was reasonably well-tolerated compared with placebo. Cimlanod reduced markers of congestion, but this did not persist beyond the treatment period. (Evaluate the Safety and Efficacy of 48-Hour Infusions of HNO (Nitroxyl) Donor in Hospitalized Patients With Heart Failure [STANDUP AHF]; NCT03016325 )

Oral factor XIa (FXIa) inhibitors may provide a promising new antithrombotic therapy with an improved benefit to bleeding risk profile over existing antithrombotic agents. Herein, we report application of a previously disclosed cyclic carbamate P1 linker which provided improved oral bioavailability in the imidazole-based 13-membered macrocycle to the 12-membered macrocycle. This resulted in identification of compound 4 with desired FXIa inhibitory potency and good oral bioavailability but high in vivo clearance. Further structure-activity relationship (SAR) studies of heterocyclic core modifications to replace the imidazole core as well as various linkers to the P1 group led to the discovery of compound 6f, a potent FXIa inhibitor with selectivity against most of the relevant serine proteases. Compound 6f also demonstrated excellent pharmacokinetics (PK) profile (high oral bioavailability and low clearance) in multiple preclinical species. Compound 6f achieved robust antithrombotic efficacy in a rabbit efficacy model at doses which preserved hemostasis.

Objectives This study sought to assess if clinical phenogroups differ in comprehensive biomarker profiles, cardiac and arterial structure/function, and responses to spironolactone therapy. Background Previous studies identified distinct subgroups (phenogroups) of patients with heart failure with preserved ejection fraction (HFpEF). Methods Among TOPCAT (Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist Trial) participants, we performed latent-class analysis to identify HFpEF phenogroups based on standard clinical features and assessed differences in multiple biomarkers measured from frozen plasma; cardiac and arterial structure/function measured with echocardiography and arterial tonometry; prognosis; and response to spironolactone. Results Three HFpEF phenogroups were identified. Phenogroup 1 (n = 1,214) exhibited younger age, higher prevalence of smoking, preserved functional class, and the least evidence of left ventricular (LV) hypertrophy and arterial stiffness. Phenogroup 2 (n = 1,329) was older, with normotrophic concentric LV remodeling, atrial fibrillation, left atrial enlargement, large-artery stiffening, and biomarkers of innate immunity and vascular calcification. Phenogroup 3 (n = 899) demonstrated more functional impairment, obesity, diabetes, chronic kidney disease, concentric LV hypertrophy, high renin, and biomarkers of tumor necrosis factor-alpha–mediated inflammation, liver fibrosis, and tissue remodeling. Compared with phenogroup 1, phenogroup 3 exhibited the highest risk of the primary endpoint of cardiovascular death, heart failure hospitalization, or aborted cardiac arrest (hazard ratio [HR]: 3.44; 95% confidence interval [CI]: 2.79 to 4.24); phenogroups 2 and 3 demonstrated similar all-cause mortality (phenotype 2 HR: 2.36; 95% CI: 1.89 to 2.95; phenotype 3 HR: 2.26, 95% CI: 1.77 to 2.87). Spironolactone randomized therapy was associated with a more pronounced reduction in the risk of the primary endpoint in phenogroup 3 (HR: 0.75; 95% CI: 0.59 to 0.95; p for interaction = 0.016). Results were similar after excluding participants from Eastern Europe. Conclusions We identified important differences in circulating biomarkers, cardiac/arterial characteristics, prognosis, and response to spironolactone across clinical HFpEF phenogroups. These findings suggest distinct underlying mechanisms across clinically identifiable phenogroups of HFpEF that may benefit from different targeted interventions.

Background Better risk stratification strategies are needed to enhance clinical care and trial design in heart failure with preserved ejection fraction (HFpEF). Objectives The purpose of this study was to assess the value of a targeted plasma multi-marker approach to enhance our phenotypic characterization and risk prediction in HFpEF. Methods In this study, the authors measured 49 plasma biomarkers from TOPCAT (Treatment of Preserved Cardiac Function Heart Failure With an Aldosterone Antagonist) trial participants (n = 379) using a Multiplex assay. The relationship between biomarkers and the risk of all-cause death or heart failure-related hospital admission (DHFA) was assessed. A tree-based pipeline optimizer platform was used to generate a multimarker predictive model for DHFA. We validated the model in an independent cohort of HFpEF patients enrolled in the PHFS (Penn Heart Failure Study) (n = 156). Results Two large, tightly related dominant biomarker clusters were found, which included biomarkers of fibrosis/tissue remodeling, inflammation, renal injury/dysfunction, and liver fibrosis. Other clusters were composed of neurohormonal regulators of mineral metabolism, intermediary metabolism, and biomarkers of myocardial injury. Multiple biomarkers predicted incident DHFA, including 2 biomarkers related to mineral metabolism/calcification (fibroblast growth factor-23 and OPG [osteoprotegerin]), 3 inflammatory biomarkers (tumor necrosis factor-alpha, sTNFRI [soluble tumor necrosis factor-receptor I], and interleukin-6), YKL-40 (related to liver injury and inflammation), 2 biomarkers related to intermediary metabolism and adipocyte biology (fatty acid binding protein-4 and growth differentiation factor-15), angiopoietin-2 (related to angiogenesis), matrix metalloproteinase-7 (related to extracellular matrix turnover), ST-2, and N-terminal pro–B-type natriuretic peptide. A machine-learning–derived model using a combination of biomarkers was strongly predictive of the risk of DHFA (standardized hazard ratio: 2.85; 95% confidence interval: 2.03 to 4.02; p Conclusions Various novel circulating biomarkers in key pathophysiological domains are predictive of outcomes in HFpEF, and a multimarker approach coupled with machine-learning represents a promising strategy for enhancing risk stratification in HFpEF.

Little data are available regarding the determinants and prognostic significance of serum albumin in Heart Failure with Preserved Ejection Fraction (HFpEF). We sought to examine the phenotypic correlates of albumin and its independent prognostic implications in HFpEF. We analyzed data from 3,254 subjects enrolled the TOPCAT trial. We stratified subjects according to tertiles of albumin and examined differences in various phenotypic traits between these strata, including 8 protein biomarkers selected ad hoc and measured from frozen samples available in a subset of participants (n = 372). We also assessed the relationship between albumin and the trial primary endpoint. Lower albumin was associated with older age, black race, and greater prevalence of NYHA class III-IV, peripheral arterial disease, atrial fibrillation and diabetes mellitus. Lower albumin was also associated with increased levels of several inflammatory biomarkers, markers of liver fibrosis, albuminuria, and greater arterial stiffness, diastolic dysfunction and pulmonary hypertension. Albumin was a strong predictor of the primary trial endpoint, even after adjustment for the MAGGIC risk score (hazard ratio [HR] 0.72, confidence interval [CI] 0.67 to 0.78; p0.0001) and prespecified traditional risk factors (HR 0.78, CI 0.71 to 0.85; p0.0001). Lower albumin was strongly associated with a worse prognosis even well within normal ranges (3.5 g/dL), with a sharp increase in risk between 4.6 and 3.6 g/dL. In conclusion, albumin is an integrated marker of various adverse processes in HFpEF, including inflammation, subclinical liver disease, arterial stiffness, and renal disease. Albumin is a powerful risk predictor independent of traditional risk prediction models, even within normal ranges.

Hospitalisation for acute heart failure remains a major public health problem with high prevalence, morbidity, mortality, and cost. Prior attempts to develop new therapies for this condition have not been successful. Nitroxyl (HNO) plays a unique role in cardiovascular physiology by direct post-translational modification of thiol residues on target proteins, specifically SERCA2a, phospholamban, the ryanodine receptor and myofilament proteins in cardiomyocytes. In animal models, these biological effects lead to vasodilatation, increased inotropy and lusitropy, but without tachyphylaxis, pro-arrhythmia or evidence of increased myocardial oxygen demand. BMS-986231 is an HNO donor being developed as a therapy for heart failure, and initial studies in patients with heart failure support the potential clinical value of these physiological effects. In this manuscript, we describe the ongoing phase II development programme for BMS-986231, which consists of three related randomised placebo-controlled clinical trials, StandUP-AHF, StandUP-Imaging and StandUP-Kidney, which are designed to provide evidence of tolerability and efficacy as well as confirm the anticipated physiological effects in patients with heart failure with reduced ejection fraction. These studies will set the stage for the further study of BMS-986231 in future phase III clinical trials.

Visual Abstract, Highlights • DM is a significant risk factor for major adverse cardiovascular events in patients with HFpEF. • Patients with diabetes with HFpEF have a distinct proteome compared with patients without diabetes with HFpEF. • Proteomics analysis identified higher levels of alpha-1-microglobulin/bikunin precursor protein in patients with diabetes with HFpEF and lower levels of CILP2 and Apo M. • Lower Apo M levels mediate most of the association between diabetes and major adverse cardiovascular events in HFpEF., Summary Diabetes mellitus (DM) is associated with a higher risk of heart failure hospitalization and mortality in patients with heart failure with preserved ejection fraction (HFpEF). Using SomaScan assays and proteomics analysis of plasma from participants in the TOPCAT (Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist) trial and the Penn Heart Failure Study, this study identified 10 proteins with significantly different expression in patients with HFpEF and DM. Of these, apolipoprotein M was found to mediate 72% (95% CI: 36% to 100%; p

Background Inhibition of Factor XIa (FXIa) may provide a novel mechanism for systemic anticoagulation without increasing the risk of clinically significant bleeding in many conditions predisposing to a high risk of thrombotic or bleeding events. BMS-986177/JNJ-70033093 (BMS-177/JNJ-3093) is a small molecule that inhibits FXIa with high affinity and selectivity. Depending on the indication, BMS-177/JNJ-3093 may provide benefit to patients as add-on therapy to current standard of care (SOC) antithrombotic agents or potentially as a replacement for current SOC. Purpose To assess the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of single and multiple oral doses of BMS-177/JNJ-3093 in healthy subjects. Methods This was a 2-part, randomized, double-blind, placebo-controlled, sequential single- (Part A) and multiple- (Part B) ascending dose study to assess the safety, tolerability, PK, and PD of BMS-177/JNJ-3093 in healthy subjects. In Part A (SAD) of the study, 48 subjects were treated in 6 panels (8 subjects per panel). The 200 mg and 500 mg dose panels investigated the impact of a high fat diet on PK. In Part B (MAD), 56 subjects were treated in 7 panels (8 subjects per panel) on a once daily (QD) or twice daily (BID) regimen for a 14-day period. Within each panel in Parts A and B, subjects were randomized to receive either BMS-177/JNJ-3093 or matched placebo (3:1). Results Administration of single ascending doses of BMS-177/JNJ-3093 up to 500 mg and multiple ascending doses of BMS-177/JNJ-3093 up to 200 mg BID or 500 mg QD for 14 days were safe and well tolerated. No subjects had a clinically significant bleeding event. All treatment-emergent adverse events were mild in severity. After single doses of BMS-177/JNJ-3093 ranging from 4 to 500 mg in fasted status, BMS-177/JNJ-3093 plasma concentration reached Cmax at 3 h postdose in all panels, indicating a similar rate of absorption. The terminal half-life ranged from 8.26 to 13.8 h across SAD panels. Over 20 to 200 mg, a dose proportional increase was observed; however, saturable absorption was seen at higher doses of 300 and 500 mg. Food also increased the bioavailability of BMS-177/JNJ-3093. In the MAD portion of the study, based on visual inspection of trough plasma concentration profiles, BMS-177/JNJ-3093 plasma concentration steady state was reached between 1–3 dosing days (ie, Days 2–4) for the QD panels and 6 dosing days (ie, Day 7) for the 200 mg BID panel. Renal excretion was relatively low, ranging from 8–20%. After single oral dose or multiple oral doses, there is a clear trend that aPTT was prolonged and the magnitude of change was related to drug exposure. Conclusion BMS-177/JNJ-3093 was safe and well tolerated in healthy volunteers. The PK and PD profile demonstrates suitable dosing properties for further clinical studies. Currently, two Phase II studies are ongoing. Funding Acknowledgement Type of funding source: Private company. Main funding source(s): This work was sponsored by Bristol-Myers Squibb and Janssen Research & Development, LLC

ACE2 (angiotensin-converting enzyme 2) is a key component of the renin-angiotensin-aldosterone system. Yet, little is known about the clinical and biologic correlates of circulating ACE2 levels in humans. We assessed the clinical and proteomic correlates of plasma (soluble) ACE2 protein levels in human heart failure. We measured plasma ACE2 using a modified aptamer assay among PHFS (Penn Heart Failure Study) participants (n=2248). We performed an association study of ACE2 against ≈5000 other plasma proteins measured with the SomaScan platform. Plasma ACE2 was not associated with ACE inhibitor and angiotensin-receptor blocker use. Plasma ACE2 was associated with older age, male sex, diabetes mellitus, a lower estimated glomerular filtration rate, worse New York Heart Association class, a history of coronary artery bypass surgery, and higher pro-BNP (pro-B-type natriuretic peptide) levels. Plasma ACE2 exhibited associations with 1011 other plasma proteins. In pathway overrepresentation analyses, top canonical pathways associated with plasma ACE2 included clathrin-mediated endocytosis signaling, actin cytoskeleton signaling, mechanisms of viral exit from host cells, EIF2 (eukaryotic initiation factor 2) signaling, and the protein ubiquitination pathway. In conclusion, in humans with heart failure, plasma ACE2 is associated with various clinical factors known to be associated with severe coronavirus disease 2019 (COVID-19), including older age, male sex, and diabetes mellitus, but is not associated with ACE inhibitor and angiotensin-receptor blocker use. Plasma ACE2 protein levels are prominently associated with multiple cellular pathways involved in cellular endocytosis, exocytosis, and intracellular protein trafficking. Whether these have a causal relationship with ACE2 or are relevant to novel coronavirus-2 infection remains to be assessed in future studies.

Background: Apo (apolipoprotein) M mediates the physical interaction between high-density lipoprotein (HDL) particles and sphingosine-1-phosphate (S1P). Apo M exerts anti-inflammatory and cardioprotective effects in animal models. Methods: In a subset of PHFS (Penn Heart Failure Study) participants (n=297), we measured apo M by Enzyme-Linked ImmunoSorbent Assay (ELISA). We also measured total S1P by liquid chromatography–mass spectrometry and isolated HDL particles to test the association between apo M and HDL-associated S1P. We confirmed the relationship between apo M and outcomes using modified aptamer-based apo M measurements among 2170 adults in the PHFS and 2 independent cohorts: the Washington University Heart Failure Registry (n=173) and a subset of TOPCAT (Treatment of Preserved Cardiac Function Heart Failure With an Aldosterone Antagonist Trial; n=218). Last, we examined the relationship between apo M and ≈5000 other proteins (SomaScan assay) to identify biological pathways associated with apo M in heart failure. Results: In the PHFS, apo M was inversely associated with the risk of death (standardized hazard ratio, 0.56 [95% CI, 0.51–0.61]; P P P P =0.001) in models that adjusted for multiple confounders. This association was present in both heart failure with reduced and preserved ejection fraction and was replicated in the Washington University cohort and a cohort with heart failure with preserved ejection fraction only (TOPCAT). The S1P and apo M content of isolated HDL particles strongly correlated ( R =0.81, P Conclusions: Reduced circulating apo M is independently associated with adverse outcomes across the spectrum of human heart failure. Further research is needed to assess whether the apo M/S1P axis is a suitable therapeutic target in heart failure.

The purpose of this study was to determine the relationship between body composition, N-terminal B-type natriuretic peptide (NT-proBNP) levels, and heart failure (HF) phenotypes and outcomes.Abnormalities in body composition can influence metabolic dysfunction and HF severity; however, data assessing fat distribution and skeletal muscle (SM) size in HF with reduced (HFrEF) and preserved EF (HFpEF) are limited. Further, whether NPs relate more closely to axial muscle mass than measures of adiposity is not well studied.We studied 572 adults without HF (n = 367), with HFrEF (n = 113), or with HFpEF (n = 92). Cardiac magnetic resonance was used to assess subcutaneous and visceral abdominal fat, paracardial fat, and axial SM size. We measured NT-proBNP in 334 participants. We used Cox regression to analyze the relationship between body composition and mortality.Compared with controls, pericardial and subcutaneous fat thickness were significantly increased in HFpEF, whereas patients with HFrEF had reduced axial SM size after adjusting for age, sex, race, and body height (p 0.05 for comparisons). Lower axial SM size, but not fat, was significantly predictive of death in unadjusted (standardized hazard ratio: 0.63; p 0.0001) and multivariable-adjusted analyses (standardized hazard ratio = 0.72; p = 0.0007). NT-proBNP levels more closely related to lower axial SM rather than fat distribution or body mass index (BMI) in network analysis, and when simultaneously assessed, only SM (p = 0.0002) but not BMI (p = 0.18) was associated with NT-proBNP. However, both NT-proBNP and axial SM mass were independently predictive of death (p 0.05).HFpEF and HFrEF have distinct abnormalities in body composition. Reduced axial SM, but not fat, independently predicts mortality. Greater axial SM more closely associates with lower NT-proBNP rather than adiposity. Lower NT-proBNP levels in HFpEF compared with HFrEF relate more closely to muscle mass rather than obesity.

Aims The aims of the present study were to assess the safety, pharmacokinetics (PK) and pharmacodynamics (PD) of BMS-962212, a first-in-class factor XIa inhibitor, in Japanese and non-Japanese healthy subjects. Methods This was a randomized, placebo-controlled, double-blind, sequential, ascending-dose study of 2-h (part A) and 5-day (part B) intravenous (IV) infusions of BMS-962212. Part A used four doses (1.5, 4, 10 and 25 mg h-1 ) of BMS-962212 or placebo in a 6:2 ratio per dose. Part B used four doses (1, 3, 9 and 20 mg h-1 ) enrolling Japanese (n = 4 active, n = 1 placebo) and non-Japanese (n = 4 active, n = 1 placebo) subjects per dose. The PK, PD, safety and tolerability were assessed throughout the study. Results BMS-962212 was well tolerated; there were no signs of bleeding, and adverse events were mild. In parts A and B, BMS-962212 demonstrated dose proportionality. The mean half-life in parts A and B ranged from 2.04 to 4.94 h and 6.22 to 8.65 h, respectively. Exposure-dependent changes were observed in the PD parameters, activated partial thromboplastin time (aPTT) and factor XI clotting activity (FXI:C). The maximum mean aPTT and FXI:C change from baseline at 20 mg h-1 in part B was 92% and 90%, respectively. No difference was observed in weight-corrected steady-state concentrations, aPTT or FXI:C between Japanese and non-Japanese subjects (P > 0.05). Conclusion BMS-962212 has tolerability, PK and PD properties suitable for investigational use as an acute antithrombotic agent in Japanese or non-Japanese subjects.

Optimization of macrocyclic inhibitors of FXIa is described which focused on modifications to both the macrocyclic linker and the P1 group. Increases in potency were discovered through interactions with a key hydrophobic region near the S1 prime pocket by substitution of the macrocyclic linker with small alkyl groups. Both the position of substitution and the absolute stereochemistry of the alkyl groups on the macrocyclic linker which led to improved potency varied depending on the ring size of the macrocycle. Replacement of the chlorophenyltetrazole cinnamide P1 in these optimized macrocycles reduced the polar surface area and improved the oral bioavailability for the series, albeit at the cost of a decrease in potency.

Factor XIa (FXIa) inhibitors are promising novel anticoagulants, which show excellent efficacy in preclinical thrombosis models with minimal effects on hemostasis. The discovery of potent and selective FXIa inhibitors which are also orally bioavailable has been a challenge. Here, we describe optimization of the imidazole-based macrocyclic series and our initial progress toward meeting this challenge. A two-pronged strategy, which focused on replacement of the imidazole scaffold and the design of new P1 groups, led to the discovery of potent, orally bioavailable pyridine-based macrocyclic FXIa inhibitors. Moreover, pyridine-based macrocycle

This study sought to assess if clinical phenogroups differ in comprehensive biomarker profiles, cardiac and arterial structure/function, and responses to spironolactone therapy.Previous studies identified distinct subgroups (phenogroups) of patients with heart failure with preserved ejection fraction (HFpEF).Among TOPCAT (Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist Trial) participants, we performed latent-class analysis to identify HFpEF phenogroups based on standard clinical features and assessed differences in multiple biomarkers measured from frozen plasma; cardiac and arterial structure/function measured with echocardiography and arterial tonometry; prognosis; and response to spironolactone.Three HFpEF phenogroups were identified. Phenogroup 1 (n = 1,214) exhibited younger age, higher prevalence of smoking, preserved functional class, and the least evidence of left ventricular (LV) hypertrophy and arterial stiffness. Phenogroup 2 (n = 1,329) was older, with normotrophic concentric LV remodeling, atrial fibrillation, left atrial enlargement, large-artery stiffening, and biomarkers of innate immunity and vascular calcification. Phenogroup 3 (n = 899) demonstrated more functional impairment, obesity, diabetes, chronic kidney disease, concentric LV hypertrophy, high renin, and biomarkers of tumor necrosis factor-alpha-mediated inflammation, liver fibrosis, and tissue remodeling. Compared with phenogroup 1, phenogroup 3 exhibited the highest risk of the primary endpoint of cardiovascular death, heart failure hospitalization, or aborted cardiac arrest (hazard ratio [HR]: 3.44; 95% confidence interval [CI]: 2.79 to 4.24); phenogroups 2 and 3 demonstrated similar all-cause mortality (phenotype 2 HR: 2.36; 95% CI: 1.89 to 2.95; phenotype 3 HR: 2.26, 95% CI: 1.77 to 2.87). Spironolactone randomized therapy was associated with a more pronounced reduction in the risk of the primary endpoint in phenogroup 3 (HR: 0.75; 95% CI: 0.59 to 0.95; p for interaction = 0.016). Results were similar after excluding participants from Eastern Europe.We identified important differences in circulating biomarkers, cardiac/arterial characteristics, prognosis, and response to spironolactone across clinical HFpEF phenogroups. These findings suggest distinct underlying mechanisms across clinically identifiable phenogroups of HFpEF that may benefit from different targeted interventions.

In an effort to identify novel antithrombotics, we have investigated protease-activated receptor 4 (PAR4) antagonism by developing and evaluating a tool compound, UDM-001651, in a monkey thrombosis model. Beginning with a high-throughput screening hit, we identified an imidazothiadiazole-based PAR4 antagonist chemotype. Detailed structure-activity relationship studies enabled optimization to a potent, selective, and orally bioavailable PAR4 antagonist, UDM-001651. UDM-001651 was evaluated in a monkey thrombosis model and shown to have robust antithrombotic efficacy and no prolongation of kidney bleeding time. This combination of excellent efficacy and safety margin strongly validates PAR4 antagonism as a promising antithrombotic mechanism.

Selective tissue factor-factor VIIa complex (TF-FVIIa) inhibitors are viewed as promising compounds for treating thrombotic disease. In this contribution, we describe multifaceted exploratory SAR studies of S1′-binding moieties within a macrocyclic chemotype aimed at replacing cyclopropyl sulfone P1′ group. Over the course of the optimization efforts, the 1-(1H-tetrazol-5-yl)cyclopropane P1′ substituent emerged as an improved alternative, offering increased metabolic stability and lower clearance, while maintaining excellent potency and selectivity.

Inhibitors of the tissue factor (TF)/factor VIIa complex (TF-FVIIa) are promising novel anticoagulants which show excellent efficacy and minimal bleeding in preclinical models. Starting with an aminoisoquinoline P1-based macrocyclic inhibitor, optimization of the P' groups led to a series of highly potent and selective TF-FVIIa inhibitors which displayed poor permeability. Fluorination of the aminoisoquinoline reduced the basicity of the P1 group and significantly improved permeability. The resulting lead compound was highly potent, selective, and achieved good pharmacokinetics in dogs with oral dosing. Moreover, it demonstrated robust antithrombotic activity in a rabbit model of arterial thrombosis.

Nitroxyl (HNO) causes post-translational modification of thiol proteins. In animal models, the HNO donor BMS-986231 causes vasodilation and has inotropic and lusitropic actions. We compared the effects of BMS-986231 to nitroglycerin (NTG) or placebo on cardiac performance in patients with chronic

The discovery of orally bioavailable FXIa inhibitors has been a challenge. Herein, we describe our efforts to address this challenge by optimization of our imidazole-based macrocyclic series. Our optimization strategy focused on modifications to the P2 prime, macrocyclic amide linker, and the imidazole scaffold. Replacing the amide of the macrocyclic linker with amide isosteres led to the discovery of substituted amine linkers which not only maintained FXIa binding affinity but also improved oral exposure in rats. Combining the optimized macrocyclic amine linker with a pyridine scaffold afforded compounds 23 and 24 that were orally bioavailable, single-digit nanomolar FXIa inhibitors with excellent selectivity against relevant blood coagulation enzymes.

With the introduction of thrombin and factor Xa inhibitors to the oral anticoagulant market, significant improvements in both efficacy and safety have been achieved. Early clinical and preclinical data suggest that inhibitors of factor XIa can provide a still safer alternative, with expanded efficacy for arterial indications. This Perspective provides an overview of target rationale and details of the discovery and development of inhibitors of factor XIa as next generation antithrombotic agents.

Compound 2 was previously identified as a potent inhibitor of factor XIa lacking oral bioavailability. A structure-based approach was used to design analogs of 2 with novel P1 moieties with good selectivity profiles and oral bioavailability. Further optimization of the P1 group led to the identification of a 4-chlorophenyltetrazole P1 analog, which when combined with further modifications to the linker and P2' group provided compound 32 with FXIa Ki=6.7 nM and modest oral exposure in dogs.

The structure-activity relationships (SAR) of six-membered ring replacements for the imidazole ring scaffold is described. This work led to the discovery of the potent and selective pyridine (S)-23 and pyridinone (±)-24 factor XIa inhibitors. SAR and X-ray crystal structure data highlight the key differences between imidazole and six-membered ring analogs.

Pyridazine and pyridazinone derivatives were designed and synthesized as coagulation factor XIa inhibitors. Potent and selective inhibitors with single digit nanomolar affinity for factor XIa were discovered. Selected inhibitors demonstrated moderate oral bioavailability.

Factor XIa (FXIa) is a blood coagulation enzyme that is involved in the amplification of thrombin generation. Mounting evidence suggests that direct inhibition of FXIa can block pathologic thrombus formation while preserving normal hemostasis. Preclinical studies using a variety of approaches to reduce FXIa activity, including direct inhibitors of FXIa, have demonstrated good antithrombotic efficacy without increasing bleeding. On the basis of this potential, we targeted our efforts at identifying potent inhibitors of FXIa with a focus on discovering an acute antithrombotic agent for use in a hospital setting. Herein we describe the discovery of a potent FXIa clinical candidate, 55 (FXIa Ki = 0.7 nM), with excellent preclinical efficacy in thrombosis models and aqueous solubility suitable for intravenous administration. BMS-962212 is a reversible, direct, and highly selective small molecule inhibitor of FXIa.

A series of macrocyclic factor XIa (FXIa) inhibitors was designed based on an analysis of the crystal structures of the acyclic phenylimidazole compounds. Further optimization using structure-based design led to inhibitors with pM affinity for FXIa, excellent selectivity against a panel of relevant serine proteases, and good potency in the activated partial thromboplastin time (aPTT) clotting assay.

Introduction: Acute stroke intervention with antithrombotic agents is limited due to an increased risk of bleeding and a frequent inability to swallow existing oral agents. Preclinical and early clinical data with an antisense oligonucleotide suggest inhibition of Factor XI (FXI) as a means to achieve antithrombotic efficacy with a reduced risk of bleeding. Here we report a preclinical characterization and results from first-in-human studies of BMS-962212, a first in class, direct, reversible, and highly selective IV small molecule inhibitor of FXIa (FXIa K i = 0.7 nM). Methods: BMS-962212 at 0.001+0.0063 to 0.46+3.1 mg/kg+mg/kg/h or its vehicle were administered IV in anesthetized rabbit models of electrically-induced carotid artery thrombosis and cuticle bleeding time. To evaluate the pharmacokinetics, pharmacodynamics, safety, and tolerability of BMS-962212 in humans, 6 healthy subjects per dose panel received BMS-962212 at 1.5, 4, 10, and 25 mg/h as 2 hour IV infusions and, respectively, 1, 3, 9, and 20 mg/h as 5 day IV infusions, randomized with placebo. Additionally, 12 healthy subjects received BMS-962212 at 15 mg/h co-administered with 325 mg ASA for 5 days. Results: In rabbits, BMS-962212 reduced thrombus weight with an EC 50 of 80 nM. At a dose that produced 80% antithrombotic efficacy, BMS-962212 did not increase bleeding time. BMS-962212 increased ex vivo activated partial thromboplastin time (aPTT) dose-dependently without changing prothrombin time and thrombin time. In humans, IV administration of BMS-962212 was well tolerated with no serious adverse events observed. Within 30 minutes of BMS-962212 administration, >90% of the mean maximal aPTT within each dose group was achieved. Following completion of the infusion, BMS-962212 demonstrated rapid drug elimination with a direct relationship observed with aPTT decreasing by more than 50% within 4 hours. Template bleeding times were not increased by BMS-962212 alone or when co-administered with ASA. Conclusion: BMS-962212 exhibits properties suited for investigational use as an acute care antithrombotic agent including robust antithrombotic activity with a low potential to increase bleeding risk in preclinical models, and a rapid onset and offset of aPTT activity in humans.

This manuscript describes the discovery of a series of macrocyclic inhibitors of FXIa with oral bioavailability. Assisted by structure based drug design and ligand bound X-ray crystal structures, the group linking the P1 moiety to the macrocyclic core was modified with the goal of reducing H-bond donors to improve pharmacokinetic performance versus 9. This effort resulted in the discovery of several cyclic P1 linkers, exemplified by 10, that are constrained mimics of the bioactive conformation displayed by the acrylamide linker of 9. These cyclic P1 linkers demonstrated enhanced bioavailability and improved potency.

Antithrombotic agents that are inhibitors of factor XIa (FXIa) have the potential to demonstrate robust efficacy with a low bleeding risk profile. Herein, we describe a series of tetrahydroquinoline (THQ) derivatives as FXIa inhibitors. Compound 1 was identified as a potent and selective tool compound for proof of concept studies. It exhibited excellent antithrombotic efficacy in rabbit thrombosis models and did not prolong bleeding times. This demonstrates proof of concept for the FXIa mechanism in animal models with a reversible, small molecule inhibitor.

Preclinical data suggests that P2Y1 antagonists, such as diarylurea compound 1, may provide antithrombotic efficacy similar to P2Y12 antagonists and may have the potential of providing reduced bleeding liabilities. This manuscript describes a series of diarylureas bearing solublizing amine side chains as potent P2Y1 antagonists. Among them, compounds 2l and 3h had improved aqueous solubility and maintained antiplatelet activity compared with compound 1. Compound 2l was moderately efficacious in both rat and rabbit thrombosis models and had a moderate prolongation of bleeding time in rats similar to that of compound 1.

A novel series of macrocyclic FXIa inhibitors was designed based on our lead acyclic phenyl imidazole chemotype. Our initial macrocycles, which were double-digit nanomolar FXIa inhibitors, were further optimized with assistance from utilization of structure-based drug design and ligand bound X-ray crystal structures. This effort resulted in the discovery of a macrocyclic amide linker which was found to form a key hydrogen bond with the carbonyl of Leu41 in the FXIa active site, resulting in potent FXIa inhibitors. The macrocyclic FXIa series, exemplified by compound 16, had a FXIa Ki = 0.16 nM with potent anticoagulant activity in an in vitro clotting assay (aPTT EC1.5x = 0.27 μM) and excellent selectivity against the relevant blood coagulation enzymes.

Factor VIIa (FVIIa) inhibitors have shown strong antithrombotic efficacy in preclinical thrombosis models with limited bleeding liabilities. Discovery of potent, orally active FVIIa inhibitors has been largely unsuccessful due to the requirement of a basic P1 group to interact with Asp189 in the S1 binding pocket, limiting their membrane permeability. We have combined recently reported neutral P1 binding substituents with a highly optimized macrocyclic chemotype to produce FVIIa inhibitors with low nanomolar potency and enhanced permeability.

Two novel series of meta-linked phenylglycine-based macrocyclic FVIIa inhibitors have been designed to improve the rodent metabolic stability and PK observed with the precursor para-linked phenylglycine macrocycles. Through iterative structure-based design and optimization, the TF/FVIIa Ki was improved to subnanomolar levels with good clotting activity, metabolic stability, and permeability.

Inhibitors of Factor VIIa (FVIIa), a serine protease in the clotting cascade, have shown strong antithrombotic efficacy in preclinical thrombosis models with minimal bleeding liabilities. Discovery of potent, orally active FVIIa inhibitors has been largely unsuccessful because known chemotypes have required a highly basic group in the S1 binding pocket for high affinity. A recently reported fragment screening effort resulted in the discovery of a neutral heterocycle, 7-chloro-3,4-dihydroisoquinolin-1(2H)-one, that binds in the S1 pocket of FVIIa and can be incorporated into a phenylglycine FVIIa inhibitor. Optimization of this P1 binding group led to the first series of neutral, permeable FVIIa inhibitors with low nanomolar potency.

Antiplatelet agents are proven efficacious treatments for cardiovascular and cerebrovascular diseases. However, the existing drugs are compromised by unwanted and sometimes life-threatening bleeding that limits drug usage or dosage. There is a substantial unmet medical need for an antiplatelet drug with strong efficacy and low bleeding risk. Thrombin is a potent platelet agonist that directly induces platelet activation via the G protein (heterotrimeric guanine nucleotide-binding protein)-coupled protease-activated receptors PAR1 and PAR4. A PAR1 antagonist is approved for clinical use, but its use is limited by a substantial bleeding risk. Conversely, the potential of PAR4 as an antiplatelet target has not been well characterized. Using anti-PAR4 antibodies, we demonstrated a low bleeding risk and an effective antithrombotic profile with PAR4 inhibition in guinea pigs. Subsequently, high-throughput screening and an extensive medicinal chemistry effort resulted in the discovery of BMS-986120, an orally active, selective, and reversible PAR4 antagonist. In a cynomolgus monkey arterial thrombosis model, BMS-986120 demonstrated potent and highly efficacious antithrombotic activity. BMS-986120 also exhibited a low bleeding liability and a markedly wider therapeutic window compared to the standard antiplatelet agent clopidogrel tested in the same nonhuman primate model. These preclinical findings define the biological role of PAR4 in mediating platelet aggregation. In addition, they indicate that targeting PAR4 is an attractive antiplatelet strategy with the potential to treat patients at a high risk of atherothrombosis with superior safety compared with the current standard of care.

SummaryPlasma kallikrein is a multifunctional serine protease involved in contact activation of coagulation. Deficiency in humans is characterised by prolonged activated partial thromboplastin time (aPTT); however, the balance between thrombosis and haemostasis is not fully understood. A study of plasma kallikrein-deficient mice revealed increased aPTT, without prolonged bleeding time. Prekallikrein antisense oligonucleotide (ASO) treatment in mice suggested potential for a positive therapeutic index. The current goal was to further define the role of plasma kallikrein in coagulation. Blood pressure and heart rate were normal in plasma kallikrein-deficient mice, and mice were completely protected from occlusion (100 ± 1.3% control flow) in 3.5% FeCl3 -induced arterial thrombosis versus heterozygotes (20 ± 11.4%) and wild-type littermates (8 ± 0%). Vessels occluded in 8/8 wild-type, 7/8 heterozygotes, and 0/8 knockouts. Anti-thrombotic protection was less pronounced in 5% FeCl3-induced arterial injury. Integrated blood flow was 8 ± 0% control in wild-type and heterozygotes, and significantly (p

The amyloid-beta (Abeta) peptide, which likely plays a key role in Alzheimer disease, is derived from the amyloid-beta precursor protein (APP) through consecutive proteolytic cleavages by beta-site APP-cleaving enzyme and gamma-secretase. Unexpectedly gamma-secretase inhibitors can increase the secretion of Abeta peptides under some circumstances. This "Abeta rise" phenomenon, the same inhibitor causing an increase in Abeta at low concentrations but inhibition at higher concentrations, has been widely observed. Here we show that the Abeta rise depends on the beta-secretase-derived C-terminal fragment of APP (betaCTF) or C99 levels with low levels causing rises. In contrast, the N-terminally truncated form of Abeta, known as "p3," formed by alpha-secretase cleavage, did not exhibit a rise. In addition to the Abeta rise, low betaCTF or C99 expression decreased gamma-secretase inhibitor potency. This "potency shift" may be explained by the relatively high enzyme to substrate ratio under conditions of low substrate because increased concentrations of inhibitor would be necessary to affect substrate turnover. Consistent with this hypothesis, gamma-secretase inhibitor radioligand occupancy studies showed that a high level of occupancy was correlated with inhibition of Abeta under conditions of low substrate expression. The Abeta rise was also observed in rat brain after dosing with the gamma-secretase inhibitor BMS-299897. The Abeta rise and potency shift are therefore relevant factors in the development of gamma-secretase inhibitors and can be evaluated using appropriate choices of animal and cell culture models. Hypothetical mechanisms for the Abeta rise, including the "incomplete processing" and endocytic models, are discussed.

Pyridine-based Factor XIa (FXIa) inhibitor (S)-2 was optimized by modifying the P2 prime, P1, and scaffold regions. This work resulted in the discovery of the methyl N-phenyl carbamate P2 prime group which maintained FXIa activity, reduced the number of H-bond donors, and improved the physicochemical properties compared to the amino indazole P2 prime moiety. Compound (S)-17 was identified as a potent and selective FXIa inhibitor that was orally bioavailable. Replacement of the basic cyclohexyl methyl amine P1 in (S)-17 with the neutral p-chlorophenyltetrazole P1 resulted in the discovery of (S)-24 which showed a significant improvement in oral bioavailability compared to the previously reported imidazole (S)-23. Additional improvements in FXIa binding affinity, while maintaining oral bioavailability, was achieved by replacing the pyridine scaffold with either a regioisomeric pyridine or pyrimidine ring system.

Thrombocytopenia exposes patients to increased bleeding risk. This serious adverse event was observed with a frequency of approximately 2% in early clinical trials with the potent, orally bioavailable glycoprotein (GP) IIb/IIIa receptor antagonist roxifiban. We previously reported that drug-dependent antibodies (DDAbs) to GP IIb/IIIa are the main cause of thrombocytopenia with roxifiban. Two ELISA assays for detection of free DDAbs (in citrate plasma) and total DDAbs (in EDTA plasma to elute platelet bound DDAbs) were developed and analytically validated. These tests served two purposes during the clinical development program, to pre-screen patients for pre-existing antibodies and monitor patients for increasing antibody titers as a surrogate for eminent thrombocytopenia. The free DDAb assay showed inter and intra-assay precision of 5-12 and 12-14% CV, respectively. The total DDAb assay showed a precision of 5-10 and 4-12% CV, respectively. Three cycles of freeze-thaw did not significantly alter DDAb values in citrate plasma, EDTA plasma or extraction solution. The clinical qualifications of the two assays were conducted in two phase II clinical trials in coronary arterial disease (CAD) patients dosed with roxifiban. Both assays have demonstrated clinical sensitivity of nearly 99-100% and clinical specificity of nearly 95%.

The synthesis, structural activity relationships (SAR), and selectivity profile of a potent series of phenylalanine diamide FXIa inhibitors will be discussed. Exploration of P1 prime and P2 prime groups led to the discovery of compounds with high FXIa affinity, good potency in our clotting assay (aPPT), and high selectivity against a panel of relevant serine proteases as exemplified by compound 21. Compound 21 demonstrated good in vivo efficacy (EC50=2.8μM) in the rabbit electrically induced carotid arterial thrombosis model (ECAT).

BMS-654457 ((+) 3′-(6-carbamimidoyl-4-methyl-4-phenyl-1,2,3,4-tetrahydro-quinolin-2-yl)-4-carbamoyl-5′-(3-methyl-butyrylamino)-biphenyl-2-carboxylic acid) is a small-molecule factor XIa (FXIa) inhibitor. We evaluated the in vitro properties of BMS-654457 and its in vivo activities in rabbit models of electrolytic-induced carotid arterial thrombosis and cuticle bleeding time (BT). Kinetic studies conducted in vitro with a chromogenic substrate demonstrated that BMS-654457 is a reversible and competitive inhibitor for FXIa. BMS-654457 increased activated partial thromboplastin time (aPTT) without changing prothrombin time. It was equipotent in prolonging the plasma aPTT in human and rabbit, and less potent in rat and dog. It did not alter platelet aggregation to ADP, arachidonic acid and collagen. In vivo, BMS-654457 or vehicle was given IV prior to initiation of thrombosis or cuticle transection. Preservation of integrated carotid blood flow over 90 min (iCBF, % control) was used as a marker of antithrombotic efficacy. BMS-654457 at 0.37 mg/kg + 0.27 mg/kg/h produced almost 90 % preservation of iCBF compared to its vehicle (87 ± 10 and 16 ± 3 %, respectively, n = 6 per group) and increased BT by 1.2 ± 0.04-fold (P

This report aims at exploring quantitatively the relationship between FXII inhibition and thromboprotection. FXII full and partial null in rats were established via zinc finger nuclease-mediated knockout and siRNA-mediated knockdown, respectively. The rats were subsequently characterized in thrombosis and hemostasis models. Knockout rats exhibited complete thromboprotection in both the arteriovenous shunt model (∼100% clot weight reduction) and the FeCl3-induced arterial thrombosis model (no reduction in blood flow), without any increase in cuticle bleeding time compared with wild-type control rats. Ex-vivo aPTT and the ellagic acid-triggered thrombin generation assay (TGA) exhibited anticoagulant changes. In contrast, ex-vivo PT or high tissue factor-triggered TGA was indistinguishable from control. Rats receiving single doses (0, 0.01, 0.03, 0.1, 0.3, 1 mg/kg) of FXII siRNA exhibited dose-dependent knockdown in liver FXII mRNA and plasma FXII protein (95 and 99%, respectively, at 1 mg/kg) at day 7 post dosing. FXII knockdown was associated with dose-dependent thromboprotection (maximal efficacy achieved with 1 mg/kg in both models) and negligible change in cuticle bleeding times. Ex-vivo TGA triggered with low-level (0.5 μmol/l) ellagic acid tracked best with the knockdown levels and efficacy. Our findings confirm and extend literature reports of an attractive benefit-to-risk profile of targeting FXII for antithrombotic therapies. Titrating of FXII is instructive for its pharmacological inhibition. The knockout rat is valuable for evaluating both mechanism-based safety concerns and off-target effects of FXII(a) inhibitors. Detailed TGA analyses will inform on optimal trigger conditions in studying pharmacodynamic effects of FXII(a) inhibition.

Structure-activity relationship optimization of phenylalanine P1' and P2' regions with a phenylimidazole core resulted in a series of potent FXIa inhibitors. Introducing 4-hydroxyquinolin-2-one as the P2' group enhanced FXIa affinity and metabolic stability. Incorporation of an N-methyl piperazine amide group to replace the phenylalanine improved both FXIa potency and aqueous solubility. Combination of the optimization led to the discovery of FXIa inhibitor 13 with a FXIa K i of 0.04 nM and an aPTT EC2x of 1.0 μM. Dose-dependent efficacy (EC50 of 0.53 μM) was achieved in the rabbit ECAT model with minimal bleeding time prolongation.

A multidisciplinary, fragment-based screening approach involving protein ensemble docking and biochemical and NMR assays is described. This approach led to the discovery of several structurally diverse, neutral surrogates for cationic factor VIIa P1 groups, which are generally associated with poor pharmacokinetic (PK) properties. Among the novel factor VIIa inhibitory fragments identified were aryl halides, lactams, and heterocycles. Crystallographic structures for several bound fragments were obtained, leading to the successful design of a potent factor VIIa inhibitor with a neutral lactam P1 and improved permeability.

Summary. Background: Increased plasma levels of coagulation factor (F) XI are a risk factor for venous thrombosis. Objective: To further explore the relationship between FXI and venous thrombosis, we evaluated FXI-deficient and wild-type mice in a ferric chloride (FeCl3)-induced vena cava thrombosis model. Methods and Results: Thrombosis was induced by 3-min topical application of filter papers containing increasing concentrations of FeCl3 and the thrombus was measured at 30 min. In contrast to wild-type mice, FXI-deficient mice failed to form a thrombus with 5% FeCl3, and were partially protected against 7.5% and 10% FeCl3, respectively. The protective effect was substantially stronger than a high dose of heparin (1000 units kg−1, i.v.), clopidogrel (30 mg kg−1, p.o.) or argatroban (30 mg kg−1, i.p.). These antithrombotic agents resulted in off-scale bleeding in a tail bleeding time assay, whereas the bleeding time of FXI-deficient mice was unchanged compared to wild-type mice. In addition to its known effect on the coagulation cascade, enhanced clot lysis was demonstrated in FXI-deficient mouse and human plasma compared to those supplemented with FXIa. Conclusion: Given the strong antithrombotic efficacy (possibly contributed by strong anticoagulant activity associated with increased fibrinolytic activity) and mild bleeding diathesis associated with FXI deficiency, therapeutic inhibition of FXI may be a reasonable therapeutic strategy to treat or prevent venous thrombosis.