Pharmacological characterization of a novel factor Xa inhibitor, FXV673

Synergistic inhibition of SARS-CoV-2 cell entry by otamixaban and covalent protease inhibitors: pre-clinical assessment of pharmacological and molecular properties

SARS-CoV-2, the cause of the COVID-19 pandemic, exploits host cell proteins for viral entry into human lung cells. One of them, the protease TMPRSS2, is required to activate the viral spike protein (S). Even though two inhibitors, camostat and nafamostat, are known to inhibit TMPRSS2 and block cell entry of SARS-CoV-2, finding further potent therapeutic options is still an important task. In this study, we report that a late-stage drug candidate, otamixaban, inhibits SARS-CoV-2 cell entry. We show that otamixaban suppresses TMPRSS2 activity and SARS-CoV-2 infection of a human lung cell line, although with lower potency than camostat or nafamostat. In contrast, otamixaban inhibits SARS-CoV-2 infection of precision cut lung slices with the same potency as camostat. Furthermore, we report that otamixaban's potency can be significantly enhanced by (sub-) nanomolar nafamostat or camostat supplementation. Dominant molecular TMPRSS2-otamixaban interactions are assessed by extensive 109 μs of atomistic molecular dynamics simulations. Our findings suggest that combinations of otamixaban with supplemental camostat or nafamostat are a promising option for the treatment of COVID-19.

Interspecies comparison of simultaneous thrombin and plasmin generation

Animal models of hemostasis are often extrapolated to humans; however, only a few studies have compared coagulation and fibrinolysis across species. Simultaneous thrombin (TG) and plasmin (PG) generation is useful to assessing coagulation and fibrinolysis within the same sample. In this study, we performed simultaneous TG and PG analysis in blood plasma samples from humans and 6 species commonly evaluated in pre-clinical research. TG and PG were investigated in male and female donor platelet-poor plasmas (PPP) obtained from 28 healthy humans, 10 baboons, 12 rhesus monkeys, 20 Yorkshire pigs, 20 Sprague-Dawley rats, 10 New Zealand White rabbits and 14 Hartley guinea pigs. The continuous generation of the 7-amino-4-methylcoumarin (AMC) from substrates specific to thrombin or plasmin was monitored. The thrombin and plasmin concentration peak heights (PH) and production rates (PR) were calculated. TG and PG parameters from baboon and rhesus macaque plasma approximated that of humans. The other species differed significantly from both human and non-human primates. For example, swine and rat plasmas demonstrated similar TG, but swine plasmas did not generate plasmin. TG and PG parameters from Guinea pig samples were extremely low, while rabbit plasmas showed variable PG curves demonstrating one or two peaks with low and high PR values, respectively. Correlations between PH and PR values were significant with the exceptions of human PG, baboon TG, rat TG and Guinea pig PG. These findings are informative to pre-clinical animal species selection and optimization of coagulation and fibrinolysis translational research.

Pharmacokinetics of Otamixaban, a Direct Factor Xa Inhibitor, in Healthy Male Subjects: Pharmacokinetic Model Development for Phase 2/3 Simulation of Exposure

The pharmacokinetics of otamixaban was investigated in healthy male subjects over a wide range of intravenous doses, with duration of administration varying between 1-minute infusions (bolus dose) and 24-hour infusions, using noncompartmental and multicompartmental methods. A global compartmental analysis (2 and 3 compartments) generated a single set of pharmacokinetic parameters, regardless of infusion rate and duration, and took into account the 30% decrease in clearance and volume of distribution observed over the dose range. The 2-compartment model was retained to predict bolus plus 3-hour-infusion doses of otamixaban for future phase (2/3) studies. Otamixaban exhibited in healthy subjects several interesting pharmacokinetic features in view of its potential therapeutic use in coronary thrombosis: a rapid plasma distribution and elimination, a well-described dose-exposure relationship, a low intersubject variability in plasma exposure, and a mixed renal and biliary excretion with constant renal clearance.

Design and rationale of the treatment of acute coronary syndromes with otamixaban trial: a double-blind triple-dummy 2-stage randomized trial comparing otamixaban to unfractionated heparin and eptifibatide in non-ST-segment elevation acute coronary syndromes with a planned early invasive strategy

BACKGROUND

Otamixaban is a synthetic intravenous direct factor Xa inhibitor, with rapid onset/offset, linear kinetics, and no significant renal elimination. A phase II trial in acute coronary syndromes (ACS) showed a marked reduction in the combined end point of death or myocardial infarction (MI) and similar bleeding rates with otamixaban at midrange doses, compared with unfractionated heparin (UFH) and eptifibatide.

DESIGN

The TAO trial is a phase III, randomized, double-blind, triple-dummy controlled trial testing the efficacy of otamixaban over UFH plus eptifibatide in patients with non-ST-segment elevation ACS to be treated with dual oral antiplatelet therapy and an invasive strategy. Approximately 13,220 patients in 55 countries will be randomized (1:1:1 ratio) to receive UFH plus downstream eptifibatide (started pre-percutaneous coronary intervention and continued per label) or otamixaban (0.08 mg/kg intravenous bolus at randomization then 0.100 or 0.140 mg/kg per hour intravenous infusion). An interim analysis was performed after ≥1,969 patients per arm completed 7 days of follow-up and the Data Monitoring Committee selected 1 otamixaban dose (blinded to investigators) to be carried forward using a prespecified algorithm. The primary efficacy outcome is the composite of all-cause mortality or new MI through day 7. The primary safety outcome is thrombolysis in MI major or minor bleeding through day 7. Secondary outcomes include all-cause mortality, recurrent ischemia/infarction resulting in prolonged/recurrent hospitalization, periprocedural angiographic complications, and pharmacokinetic data in 6,000 patients.

CONCLUSIONS

The TAO trial will assess the clinical efficacy and safety of otamixaban in non-ST-segment elevation ACS with planned invasive strategy.

Large inter-individual variation of the pharmacodynamic effect of anticoagulant drugs on thrombin generation

Anticoagulation by a standard dosage of an inhibitor of thrombin generation presupposes predictable pharmacokinetics and pharmacodynamics of the anticoagulant. We determined the inter-individual variation of the effect on thrombin generation of a fixed concentration of direct and antithrombin-mediated inhibitors of thrombin and factor Xa. Thrombin generation was determined by calibrated automated thrombinography in platelet-poor plasma from 44 apparently healthy subjects which was spiked with fixed concentrations of otamixaban, melagatran, unfractionated heparin, dermatan sulfate and pentasaccharide. The variability of the inhibitory effect of the different anticoagulants within the population was determined using the coefficient of variation, i.e. the standard deviation expressed as a percentage of the mean. The inter-individual coefficients of variation of the endogenous thrombin potential and peak height before inhibition were 18% and 16%, respectively and became 20%-24% and 24%-43% after inhibition. The average inhibition of endogenous thrombin potential and peak height (ETP, peak) brought about by the anticoagulants was respectively: otamixaban (27%, 83%), melagatran (56%, 63%), unfractionated heparin (43%, 58%), dermatan sulfate (68%, 57%) and pentasaccharide (25%, 67%). This study demonstrates that the addition of a fixed concentration of any type of anticoagulant tested causes an inhibition that is highly variable from one individual to another. In this respect there is no difference between direct inhibitors of thrombin and factor Xa and heparin(-like) inhibitors acting on the same factors.

Clinical pharmacology of direct and indirect factor Xa inhibitors

The limitations of conventional anticoagulants have stimulated the development of new anticoagulants. The central position of factor Xa (FXa) at the junction of the intrinsic and extrinsic pathways in the coagulation cascade means that direct and indirect FXa inhibitors have increasingly changed antithrombotic strategies. FXa inhibitors potently and selectively inhibit thrombin formation rather than thrombin activity. Direct FXa inhibitors may directly bind to FXa, whereas indirect inhibitors are dependent on antithrombin. Direct inhibitors may bind free FXa and, in contrast to indirect inhibitors, FXa within the prothrombinase complex or within clots as well. Fondaparinux is the prototype indirect FXa inhibitor and has been extensively studied in the prevention and treatment of thromboembolic diseases, including acute coronary syndromes. Due to a favourable efficacy and safety profile and convenient once-daily dosing without the need for monitoring, fondaparinux is preferentially recommended in recent guidelines dealing with antithrombotic treatment. A number of small-molecule direct FXa inhibitors are currently at different stages of clinical development. After an extensive clinical trial programme demonstrating superior efficacy without a significant increase in major bleeds compared with enoxaparin, rivaroxaban is now available for the prevention of thromboembolic events in patients undergoing orthopaedic surgery. Rivaroxaban also offers the convenience of oral once-daily dosing without the need for monitoring. Whereas most direct FXa inhibitors are orally active, otamixaban is administered intravenously, offering rapid on-off anticoagulant activity. Other compounds under development may offer additional options for tailored antithrombotic strategies according to differing indications, clinical situations and patient variables.

Novel oral anticoagulants for prophylaxis and treatment of venous thromboembolism: part I (Factor Xa inhibitors)

The quest for an ideal anticoagulant is ongoing. Oral agents that do not require blood level monitoring are presently undergoing taut scrutiny for efficacies and potential side effects, and would potentially soon revolutionize coagulation medicine. The first part of this article reviews oral Factor Xa inhibitors, such as rivaroxaban, apixaban, eribaxaban, edoxaban and YM150--exploring the outcomes of major clinical trials for prophylaxis and treatment of venous thromboembolism--and also briefly outlining their pharmacological properties. The second part of the article (in a separate issue) will cover oral Factor IIa (thrombin), such as dabigatran and AZD0837 and oral Factor IX inhibitors, such as TTP889.

Synergistic effect of a factor Xa inhibitor, TAK-442, and antiplatelet agents on whole blood coagulation and arterial thrombosis in rats

INTRODUCTION

Activated platelets facilitate blood coagulation by providing factor V and a procoagulant surface for prothrombinase. Here, we investigated the potential synergy of a potent factor Xa/prothrombinase inhibitor, TAK-442, plus aspirin or clopidogrel in preventing arterial thrombosis and whole blood coagulation.

METHODS

Thrombus formation was initiated by FeCl(3)-induced rat carotid injury. Bleeding time was evaluated with the rat tail transection model. Whole blood coagulation was assessed by thromboelastographic examination (TEG) for which blood obtained from control, aspirin-, or clopidogrel-treated rats was transferred to a TEG analyzer containing, collagen or adenosine diphosphate (ADP), and TAK-442 or vehicle.

RESULTS

TAK-442 (3mg/kg, po), aspirin (100mg/kg, po) or clopidogrel (3mg/kg, po) alone had no significant effect on thrombus formation, whereas the combination of TAK-442 with aspirin and clopidogrel remarkably prolonged the time to thrombus formation without additional significant prolongation of bleeding time. TEG demonstrated that the onset of collagen-induced blood coagulation were slightly longer in aspirin-treated rats than control; however, when the blood from aspirin-treated rats was subsequently treated in vitro with 100 nM TAK-442, the onset of clotting was significantly prolonged. In contrast, only marginal prolongation was observed with TAK-442 treatment of blood from control animals. The onset time of ADP-induced blood coagulation was slightly longer in clopidogrel-treated rats compared with control, and it was further extended by TAK-442 treatment.

CONCLUSION

These results demonstrate that blood coagulation can be markedly delayed by the addition of TAK-442 to antiplatelets treatment which could contribute to synergistic antithrombotic efficacy in these settings.

Otamixaban for the treatment of patients with non-ST-elevation acute coronary syndromes (SEPIA-ACS1 TIMI 42): a randomised, double-blind, active-controlled, phase 2 trial

BACKGROUND

Otamixaban is an intravenous direct factor Xa inhibitor. We aimed to assess its efficacy and safety in non-ST-elevation acute coronary syndromes and to identify the optimum dose range for further assessment in a phase 3 study.

METHODS

In this double-blind, phase 2 trial undertaken in 196 sites in 36 countries, 3241 patients with non-ST-elevation acute coronary syndromes were randomly assigned via a central, telephone-based interactive voice response system to one of five doses of otamixaban (0.08 mg/kg bolus followed by infusions of 0.035 [n=125], 0.070 [676], 0.105 [662], 0.140 [658], or 0.175 [671] mg/kg/h) or to a control of unfractionated heparin (60 IU/kg intravenous bolus followed by an infusion of 12 IU/kg/h) plus eptifibatide (180 microg/kg intravenous bolus followed by an infusion of 1.0-2.0 microg/kg/min [n=449]). Both investigators and patients were unaware of treatment allocation. Enrolment into the lowest dose group was stopped early at the recommendation of the Data Monitoring Committee. The primary efficacy endpoint was a composite of death, myocardial infarction, urgent revascularisation, or bailout glycoprotein IIb/IIIa inhibitor use up to 7 days. The primary safety endpoint was TIMI major or minor bleeding not related to coronary-artery bypass grafting. Efficacy analyses were by intention to treat; safety analyses were in treated patients. This study is registered with ClinicalTrials.gov, number NCT00317395.

FINDINGS

Rates of the primary efficacy endpoint in the five otamixaban doses were 7.2% (nine of 125) with 0.035 mg/kg/h, 4.6% (31/676) with 0.070 mg/kg/h, 3.8% (25/662) with 0.105 mg/kg/h, 3.6% (24/658) with 0.140 mg/kg/h, and 4.3% (29/671) with 0.175 mg/kg/h (p=0.34 for trend). In the control group, the rate was 6.2% (28/449), yielding relative risks for the five otamixaban doses of 1.16 (95% CI 0.56-2.38), 0.74 (0.45-1.21), 0.61 (0.36-1.02), 0.58 (0.34-1.00), and 0.69 (0.42-1.15), respectively. Rates of the primary safety endpoint in the five otamixaban doses were 1.6% (two of 122), 1.6% (11/669), 3.1% (20/651), 3.4% (22/651), and 5.4% (36/664), respectively (p=0.0001 for trend); the rate in the control group was 2.7% (12/448).

INTERPRETATION

In patients with non-ST-elevation acute coronary syndromes, otamixaban infusions of 0.100-0.140 mg/kg/h might reduce ischaemic events and have a safety profile similar to unfractionated heparin plus eptifibatide. Further testing in a phase 3 trial is warranted.

FUNDING

Sanofi-Aventis.

The discovery of glycine and related amino acid-based factor Xa inhibitors

Herein, we report on the identification of three potent glycine and related amino acid-based series of FXa inhibitors containing a neutral P1 chlorophenyl pharmacophore. A X-ray crystal structure has shown that constrained glycine derivatives with optimized N-substitution can greatly increase hydrophobic interactions in the FXa active site. Also, the substitution of a pyridone ring for a phenylsulfone ring in the P4 sidechain resulted in an inhibitor with enhanced oral bioavailability.

Pharmacokinetic/pharmacodynamic relationships for otamixaban, a direct factor Xa inhibitor, in healthy subjects

Direct pharmacokinetic/pharmacodynamic relationships for otamixaban were investigated after rising doses in healthy subjects using mixed-effect modeling. Activated partial thromboplastin time, prothrombin time, dilute prothrombin time, and Russell's viper venom-induced clotting time (RVVT) related linearly, whereas Heptest clotting time (HCT) followed a sigmoidal E(max) model. The pharmacokinetic/pharmacodynamic response (slope) and their corresponding interindividual variability (seconds per ng/mL, [% coefficient of variation]) were 0.263 (29%) for Russell's viper venom-induced clotting time, 0.117 (10%) for dilute prothrombin time, 0.058 (19%) for activated partial thromboplastin time, and 0.021 (11%) for prothrombin time. For Heptest clotting time, the parameter estimates with their corresponding interindividual variability (% coefficient of variation) were 71 ng/mL (30%) for EC(50), 186 seconds (64%) for E(max), and 17 seconds (16%) for E(0). The model predicted otamixaban plasma concentrations to double the clotting times that were close to those observed. These pharmacokinetic/pharmacodynamic relationships, together with the predictable pharmacokinetics, allowed the anticoagulant effect at given doses of otamixaban to be foreseen in healthy subjects.

New antithrombotic drugs on the horizon

Venous and arterial thromboembolism are a major cause for morbidity and mortality. The list of established drugs for the prevention of thrombus formation and embolisation includes heparins, hirudin and derivatives, aspirin, ADP and glycoprotein IIb/IIIa receptor antagonists, as well as vitamin K antagonists. Several limitations exist for these drugs that have stimulated the search for new and better anticoagulants. A series of selective clotting factor Xa inhibitors and direct factor IIa (thrombin) inhibitors are on the horizon, two of which are getting close to broad clinical application. Additional therapeutics that are still under preclinical and clinical investigation include inhibitors of the tissue factor pathway/factor VII complex, clotting factor VIII and XIII inhibitors and modulators of the protein C pathway or of endogenous fibrinolysis, as well as novel antiplatelet drugs. This review is focused on the current status of development of novel antithrombotics and their clinical potential. Even though only a few of a broad array of antithrombotic agents have reached clinical testing, some hold the potential for significant improvement in efficacy and safety of anticoagulant therapy.

Factor Xa inhibition in the prevention of venous thromboembolism and treatment of patients with venous thromboembolism

Venous thromboembolism (VTE) is a life-threatening complication following orthopedic surgery. Selective factor Xa inhibition is a new antithrombotic approach designed to avoid difficulties associated with heparins and other current anticoagulants. Several antifactor Xa compounds are in early investigation, but fondaparinux (Arixtra; NV Organon, Oss, The Netherlands; Sanofi-Synthelabo, Paris, France) is the first and most advanced compound in the development of a new class of synthetic antithrombotic agents--the selective factor Xa inhibitors. Fondaparinux has a highly favorable pharmacokinetic profile; four large phase 3 trials comparing subcutaneous fondaparinux 2.5 mg once daily with the low molecular weight heparin (LMWH) enoxaparin in doses approved by regulatory bodies showed that fondaparinux reduced the overall risk of VTE in major orthopedic surgery by > 50% without increasing clinically relevant bleeding. Fondaparinux also appears to be a very promising candidate for the treatment of patients with existing VTE.

Optimization of the beta-aminoester class of factor Xa inhibitors. Part 2: Identification of FXV673 as a potent and selective inhibitor with excellent In vivo anticoagulant activity

Further optimization of the beta-aminoester class of factor Xa (fXa) inhibitors is described culminating in the identification of 9c (FXV673), a potent and selective factor Xa inhibitor with excellent in vivo anticoagulant activity. An X-ray structure of FXV673 bound to human fXa is also presented. Based on its selectivity, potent in vivo activity and favorable pre-clinical safety profile, FXV673 was selected for further development and is currently undergoing clinical trials.

Molecular characterization of Ancylostoma inhibitors of coagulation factor Xa. Hookworm anticoagulant activity in vitro predicts parasite bloodfeeding in vivo

Bloodfeeding hookworms, which currently infect over a billion people in the developing world, are a leading cause of gastrointestinal hemorrhage and iron deficiency anemia. The major anticoagulant inhibitor of coagulation factor Xa has been identified from the hookworm parasite Ancylostoma ceylanicum using reverse transcription PCR and 3'-rapid amplification of cDNA ends. This is the first anticoagulant cloned from a hookworm species for which humans are recognized permissive hosts. Despite approximately 50% amino acid similarity, A. ceylanicum anticoagulant peptide 1 (AceAP1) is both immunologically and mechanistically distinct from AcAP5, its homologue isolated from the dog hookworm Ancylostoma caninum. Studies using plasma clotting times and single stage chromogenic assays of factor Xa activity have demonstrated that the recombinant AceAP1 protein is substantially less potent than AcAP5 and that soluble whole worm protein extracts of adult A. ceylanicum possess less anticoagulant activity than extracts of A. caninum. These values correlate with previously reported differences in bloodfeeding capabilities between these two species of hookworm, suggesting that factor Xa inhibitory activity is predictive of hookworm bloodfeeding capabilities in vivo. These fundamental differences in the mechanism of action and immunoreactivity of the major anticoagulant virulence factors from related Ancylostoma hookworm species may have significant implications for human vaccine development.