A variant of recombinant factor VIIa with enhanced procoagulant and antifibrinolytic activities in an in vitro model of hemophilia

Investigation of thrombin concentration at the time of clot formation in simultaneous thrombin and fibrin generation assays

Thrombin generation (TG) and fibrin clot formation represent the central process of blood coagulation. Up to 95% of thrombin is considered to be generated after the clot is formed. However, this was not investigated in depth. In this study, we conducted a quantitative analysis of the Thrombin at Clot Time (TCT) parameter in 5758 simultaneously recorded TG and clot formation assays using frozen plasma samples from commercial sources under various conditions of activation. These samples were supplemented with clotting factor concentrates, procoagulant lipid vesicles and a fluorogenic substrate and triggered with tissue factor (TF). We found that TCT is often close to a 10% of thrombin peak height (TPH) yet it can be larger or smaller depending on whether the sample has low or high TPH value. In general, the samples with high TPH are associated with elevated TCT. TCT appeared more sensitive to some procoagulant phenotypes than other commonly used parameters such as clotting time, TPH or Thrombin Production Rate (TPR). In a minority of cases, TCT were not predicted from TG parameters. For example, elevated TCT (above 15% of TPH) was associated with either very low or very high TPR values. We conclude that clotting and TG assays may provide complementary information about the plasma sample, and that the TCT parameter may serve as an additional marker for the procoagulant potential in plasma sample.

Clot formation and fibrinolysis assays reveal functional differences among hemostatic agents in hemophilia A plasma

Background

Measuring the activity of hemostatic agents used to treat hemophilia A often requires drug-specific assays. In vitro assays show hemophilic clots have abnormal characteristics, including prolonged clotting time and decreased resistance to fibrinolysis. The ability of certain agents to correct these parameters in vitro is associated with hemostatic efficacy in vivo.

Objectives

To compare effects of established and emerging hemostatic agents on clot formation and fibrinolysis in hemophilia A plasma.

Methods

Pooled and individual hemophilia A platelet-poor plasmas were spiked with replacement (recombinant factor VIII [rFVIII], PEGylated rFVIII, polysialylated rFVIII, and porcine rFVIII) or bypassing (emicizumab, rFVIIa, and activated prothrombin complex concentrate) products. Effects on tissue factor-initiated clot formation and fibrinolysis were measured by turbidity.

Results

Compared to normal pooled plasma, hemophilia-pooled plasma showed reduced clot formation and increased fibrinolysis, and all replacement agents improved these characteristics. rFVIII and PEGylated rFVIII produced similar effects at similar concentrations, whereas polysialylated rFVIII produced slightly higher and porcine rFVIII slightly lower effects at these concentrations. Bypassing agents enhanced clot formation and stability, but patterns differed from replacement agents. The clotting rate showed a concentration-response relationship for all agents. High concentrations of all products produced effects that exceeded the normal range in at least some parameters. Responses of individual donors varied, but all agents improved clot formation and stability in all donors tested.

Conclusion

Clotting and fibrinolysis assays reveal hemostatic effects of replacement and bypassing therapies at clinically relevant concentrations. These assays may help characterize hemostatic agents and optimize dosing.

Phage-assisted evolution of botulinum neurotoxin proteases with reprogrammed specificity

Although bespoke, sequence-specific proteases have the potential to advance biotechnology and medicine, generation of proteases with tailor-made cleavage specificities remains a major challenge. We developed a phage-assisted protease evolution system with simultaneous positive and negative selection and applied it to three botulinum neurotoxin (BoNT) light-chain proteases. We evolved BoNT/X protease into separate variants that preferentially cleave vesicle-associated membrane protein 4 (VAMP4) and Ykt6, evolved BoNT/F protease to selectively cleave the non-native substrate VAMP7, and evolved BoNT/E protease to cleave phosphatase and tensin homolog (PTEN) but not any natural BoNT protease substrate in neurons. The evolved proteases display large changes in specificity (218- to >11,000,000-fold) and can retain their ability to form holotoxins that self-deliver into primary neurons. These findings establish a versatile platform for reprogramming proteases to selectively cleave new targets of therapeutic interest.

Human platelets express endothelial protein C receptor, which can be utilized to enhance localization of factor VIIa activity

Essentials Factor VIIa binds activated platelets to promote hemostasis in hemophilia patients with inhibitors. The interactions and sites responsible for platelet-FVIIa binding are not fully understood. Endothelial cell protein C receptor (EPCR) is expressed on activated human platelets. EPCR binding enhances the efficacy of a FVIIa variant and could impact design of new therapeutics.

SUMMARY

Background High-dose factor VIIa (FVIIa) is routinely used as an effective bypassing agent to treat hemophilia patients with inhibitory antibodies that compromise factor replacement. However, the mechanism by which FVIIa binds activated platelets to promote hemostasis is not fully understood. FVIIa-DVQ is an analog of FVIIa with enhanced tissue factor (TF)-independent activity and hemostatic efficacy relative to FVIIa. Our previous studies have shown that FVIIa-DVQ exhibits greater platelet binding, thereby suggesting that features in addition to lipid composition contribute to platelet-FVIIa interactions. Objectives Endothelial cell protein C receptor (EPCR) also functions as a receptor for FVIIa on endothelial cells. We therefore hypothesized that an interaction with EPCR might play a role in platelet-FVIIa binding. Methods/results In the present study, we used flow cytometric analyses to show that platelet binding of both FVIIa and FVIIa-DVQ is partially inhibited in the presence of excess protein C or an anti-EPCR antibody. This decreased binding results in a corresponding decrease in the activity of both molecules in FXa and thrombin generation assays. Enhanced binding to EPCR was sufficient to account for the increased platelet binding of FVIIa-DVQ compared with wild-type FVIIa. As EPCR protein expression has not previously been shown in platelets, we confirmed the presence of EPCR in platelets using immunofluorescence, flow cytometry, immunoprecipitation, and mass spectrometry. Conclusions This work represents the first demonstration that human platelets express EPCR and suggests that modulation of EPCR binding could be utilized to enhance the hemostatic efficacy of rationally designed FVIIa analogs.

Factor VIII activation by factor VIIa analog (V158D/E296V/M298Q) in tissue factor-independent mechanisms

Factor (F)VIIa with tissue factor (TF) is a primary trigger of blood coagulation. The recombinant (r)FVIIa analog, NN1731 (V158D/E296V/ M298Q) containing a thrombin/FIXa-mimicking catalytic domain, is ~30-fold more effective on activated platelets without TF, but ~1.2-fold with TF, than rFVIIa for FX activation. We have recently demonstrated the FVIIa/TF-dependent FVIII activation in the early coagulation phase. We assessed the action of NN1731 on FVIII activation. NN1731/TF increased FVIII activity ~2.9-fold within 30 seconds, followed by rapid inactivation, and was slightly more active than rFVIIa/TF. NN1731-catalysed activation, however, was enhanced ~6-fold at 5 minutes (min), and its peak level persisted for ~30 min. NN1731/TF proteolysed FVIII at Arg740, Arg372, and Arg336, similar to rFVIIa/TF, but cleavage by NN1731 alone was much slower at Arg336 than at Arg740 and Arg372. The Km and Vmax for NN1731/TF-catalysed activation were ~1.8-fold lower and ~2.3-fold greater than rFVIIa/TF. The Km for NN1731 alone was ~1.3-fold lower than rFVIIa, whilst the Vmax was ~7.9-fold greater, indicating that the efficiency of FVIII activation by NN1731 and NN1731/TF was ~11- and ~4-fold greater, respectively, than equivalent reactions with rFVIIa. In SPR-based assays, NN1731 bound to FVIII and the heavy chain (Kd; 0.62 and 1.9 nM) with ~1.4- and ~3.1-fold higher affinity than rFVIIa, and the A2 domain contributed to this increase. Von Willebrand factor moderated NN1731-catalysed activation more significantly than NN1731/TF. In conclusion, NN1731 was a greater potential than rFVIIa in up-regulating FVIII activity, and the TF-independent FVIII activation might represent a potential extra mode of its enhanced haemostatic effect.

A highly sensitive thrombin generation assay for assessment of recombinant activated factor VII therapy in haemophilia patients with an inhibitor

Bypass agents are the common treatment for haemophilia patients who develop inhibitory antibodies. Laboratory assessment of the efficacy of bypassing agent therapy is a challenge. In the present work we modified the conditions triggering thrombin generation (TG) assay in order to find the most sensitive assay for detection of rFVIIa and its analogue NN1731 in haemophilic plasma. TG was measured in samples of normal plasma, plasma of haemophilia patient with inhibitors, as well as haemophilia induced plasma. Recalcification-induced TG was compared to tissue factor (TF) -induced TG in the presence and absence of rFVIIa and NN1731. Recalcification-induced TG (without TF) in haemophilic plasma yielded baseline flat curves, with increased TG as a consequence of spiking the plasma rFVIIa. Using our system, we observed both dose-dependence and time-dependence of rFVIIa effect on TG. Elevated concentrations of TF mask the difference between rFVIIa-treated and non-treated haemophilic plasma. NN1731 yielded normal-isation of recalcification-induced TG curves (without TF) which may reflect high potency. In conclusion, we suggest that triggering TG by recalcification-only may be the most sensitive assay for determining the impact of bypassing agents in haemophilic plasma, and may serve as a caution surrogate safety marker in future studies.

Phage-assisted continuous evolution of proteases with altered substrate specificity

Here we perform phage-assisted continuous evolution (PACE) of TEV protease, which canonically cleaves ENLYFQS, to cleave a very different target sequence, HPLVGHM, that is present in human IL-23. A protease emerging from ∼2500 generations of PACE contains 20 non-silent mutations, cleaves human IL-23 at the target peptide bond, and when pre-mixed with IL-23 in primary cultures of murine splenocytes inhibits IL-23-mediated immune signaling. We characterize the substrate specificity of this evolved enzyme, revealing shifted and broadened specificity changes at the six positions in which the target amino acid sequence differed. Mutational dissection and additional protease specificity profiling reveal the molecular basis of some of these changes. This work establishes the capability of changing the substrate specificity of a protease at many positions in a practical time scale and provides a foundation for the development of custom proteases that catalytically alter or destroy target proteins for biotechnological and therapeutic applications.Proteases are promising therapeutics to treat diseases such as hemophilia which are due to endogenous protease deficiency. Here the authors use phage-assisted continuous evolution to evolve a variant TEV protease with altered target peptide sequence specificities.

An activated factor VII variant with enhanced tissue factor-independent activity speeds wound healing in a mouse hemophilia B model

Essentials Disorders of hemostasis can lead to delayed and defective wound healing. In hemophilia B (HB) mice, 7 days of Factor (F)IX or VIIa are needed to normalize wound healing. One dose of a highly active FVIIa variant (DVQ) restored normal wound closure time in HB mice. Coagulation factors with enhanced activity may acquire biological effects not due to hemostasis.

SUMMARY

Introduction We have previously reported that hemophilia B (HB) mice have delayed healing of cutaneous wounds and alterations in wound histology. Administration of a single dose of either factor IX or recombinant activated FVII (rFVIIa) (NovoSeven) prior to wounding did not improve wound closure time or histology. The FVIIa analog DVQ (V158D, E296V and M298Q mutations) was designed to have higher tissue factor-independent activity than rVIIa. We hypothesized that a single dose of DVQ would be more effective in restoring wound healing in HB mice. Methods Cutaneous punch wounds were made on the backs of HB and wild-type mice, and the time to wound closure was monitored. HB mice were treated with a dose of rFVIIa (10 mg kg(-1) ) or DVQ (1 mg kg(-1) ) that corrected the tail bleeding time. Skin samples were taken at various time points after wounding, fixed, and stained, and the histology was examined. Results As previously reported, wound closure times in HB mice given one dose of rFVIIa were not improved over those in untreated HB mice. Surprisingly, healing times in HB mice treated with an equally hemostatic dose of DVQ were normalized to that in wild-type mice. However, DVQ did not correct all histologic abnormalities in HB mice. Conclusions As the doses of DVQ and rFVIIa were chosen to support comparable levels of hemostasis, our data suggest that the improved healing seen with DVQ is not solely attributable to its hemostatic activity. It is possible that the improved wound healing arises through the effect of DVQ on cell signaling mechanisms.

Modeling thrombin generation: plasma composition based approach

Thrombin has multiple functions in blood coagulation and its regulation is central to maintaining the balance between hemorrhage and thrombosis. Empirical and computational methods that capture thrombin generation can provide advancements to current clinical screening of the hemostatic balance at the level of the individual. In any individual, procoagulant and anticoagulant factor levels together act to generate a unique coagulation phenotype (net balance) that is reflective of the sum of its developmental, environmental, genetic, nutritional and pharmacological influences. Defining such thrombin phenotypes may provide a means to track disease progression pre-crisis. In this review we briefly describe thrombin function, methods for assessing thrombin dynamics as a phenotypic marker, computationally derived thrombin phenotypes versus determined clinical phenotypes, the boundaries of normal range thrombin generation using plasma composition based approaches and the feasibility of these approaches for predicting risk.

Predicting dosing advantages of factor VIIa variants with altered tissue factor-dependent and lipid-dependent activities

BACKGROUND

Recombinant factor VIIa (rFVIIa) is an FX-cleaving coagulation enzyme licensed for the treatment of bleeding episodes in hemophiliacs with inhibitory antibodies. Even though the optimal dosing and comparative dose efficacy of rFVIIa remain poorly understood, genetic or chemical modifications of rFVIIa have been proposed, with the goal of achieving faster and longer hemostatic action. No ongoing trial is currently comparing rFVIIa variants with each other.

OBJECTIVES AND METHODS

We used mathematical modeling to compare the pharmacokinetics, dose-response (pharmacodynamics) and dose-effect duration (pharmacokinetics/pharmacodynamics) of rFVIIa variants to predict their optimal doses. The pharmacodynamic (PD) model of FXa generation by FVIIa in complexes with tissue factor (TF) and procoagulant lipids (PLs) was validated against published ex vivo and in vitro thrombin generation (TG) experiments. To compare variants' safety profiles, the highest non-thrombogenic doses were estimated from the clinical evidence reported for the licensed rFVIIa product.

RESULTS

The PD model correctly described the biphasic TF-dependent and PL-dependent dose response observed in TG experiments in vitro. The pharmacokinetic/PD simulations agreed with published ex vivo TG data for rFVIIa and the BAY 86-6150 variant, and explained the similar efficacies of a single dose of 270 μg kg(-1) (as reported in the literature) and repeated doses of 90 μg kg(-1) of unmodified rFVIIa. The duration of the simulated hemostatic effect after a single optimal dose was prolonged for rFVIIa variants with increased TF affinity or extended half-lives, but not for those with modulated PL activity.

CONCLUSIONS

Some modifications of the rFVIIa molecule may not translate into a prolonged hemostatic effect.

Abnormal plasma clot structure and stability distinguish bleeding risk in patients with severe factor XI deficiency

BACKGROUND

Factor XI (FXI) deficiency is a rare autosomal recessive disorder. Many patients with even very low FXI levels (< 20 IU dL(-1) ) are asymptomatic or exhibit only mild bleeding, whereas others experience severe bleeding, usually following trauma. Neither FXI antigen nor activity predicts the risk of bleeding in FXI-deficient patients.

OBJECTIVES

(i) Characterize the formation, structure and stability of plasma clots from patients with severe FXI deficiency and (ii) determine whether these assays can distinguish asymptomatic patients ('non-bleeders') from those with a history of bleeding ('bleeders').

METHODS

Platelet-poor plasmas were prepared from 16 severe FXI-deficient patients who were divided into bleeders or non-bleeders, based on bleeding associated with at least two tooth extractions without prophylaxis. Clot formation was triggered by recalcification and addition of tissue factor and phospholipids in the absence or presence of tissue plasminogen activator and/or thrombomodulin. Clot formation and fibrinolysis were measured by turbidity and fibrin network structure by laser scanning confocal microscopy.

RESULTS

Non-bleeders and bleeders had similarly low FXI levels, normal prothrombin times, normal levels of fibrinogen, factor VIII, von Willebrand factor and factor XIII, and normal platelet number and function. Compared with non-bleeders, bleeders exhibited lower fibrin network density and lower clot stability in the presence of tissue plasminogen activator. In the presence of thrombomodulin, seven of eight bleeders failed to form a clot, whereas only three of eight non-bleeders did not clot.

CONCLUSIONS

Plasma clot structure and stability assays distinguished non-bleeders from bleeders. These assays may reveal hemostatic mechanisms in FXI-deficient patients and have clinical utility for assessing the risk of bleeding.

New treatments in hemophilia: insights for the clinician

Hemophilia has evolved from an often fatal hereditary bleeding disorder to a disorder for which safe and effective treatment is available. However, there are several challenges remaining in the treatment of hemophilia. Prophylaxis to prevent bleeding is costly and requires frequent intravenous injections, which are cumbersome for patients. Venous access is often difficult to achieve, especially in small children where central venous lines may need to be implanted. Development of inhibitory antibodies makes treatment of acute bleeds difficult and prophylaxis in patients with inhibitors must also be better addressed. In order to improve treatment, new products are being developed, some of which are already in clinical trials. There are several approaches to prolonging half-lives such as PEGylation, Fc fusion and albumin fusion. Increased activity has been demonstrated in preclinical trials for factor IX and in a human trial with factor VII where the activity of the molecules has been increased by manipulation of the molecular composition. Additional approaches, including blockage of inhibitors of clotting, are also under investigation. Factor VIII and factor IX gene therapy have become a tangible possibility since phase I data recently have been published. Results are promising and there is hope that in the near future substantial progress will be made, perhaps making hemophilia the first genetic condition to be cured.

Pharmacokinetics and pharmacodynamics of rFVIIa and new improved bypassing agents for the treatment of haemophilia

Animal models have played a critical role in developing our understanding of haemophilia and its treatment. For example, studies in mice and dogs have provided insights into the pharmacokinetics and pharmacodynamics of recombinant activated factor VII (rFVIIa). Such studies have shown that antithrombin has a significant impact on clearance of rFVIIa, which explains discrepancies between the antigen and activity half-lives of rFVIIa. Animal studies have also shown that the major clearance organs for rFVIIa are the liver and the kidneys, whereas distribution studies suggest that FVII and rFVIIa leave the circulation and enter the tissues, before returning to the circulation through the lymph. One agent that has benefited greatly from the use of animal models in its development is vatreptacog alfa, a new analogue of rFVIIa. Promising in vitro results, including increased generation of FXa, shortened clotting times and increased clot stability, were subsequently confirmed in animal models. In a severe tail-bleed model in FVIII knock-out mice, reduction in maximal blood loss was substantially greater with vatreptacog alfa than with rFVIIa, FVIII or plasma-derived activated prothrombin complex concentrate. In a mouse model of joint bleeding, rFVIIa and vatreptacog alfa significantly reduced bleeding compared with vehicle-treated haemophilic controls. More recently, a model of endothelial injury based on mouse cremaster muscle has been developed. Overall, animal models are a valuable tool in elucidating the haemostatic process and the effects of therapeutic agents, although direct extrapolation to the clinical setting should be done with caution.

Unifying the mechanism of recombinant FVIIa action: dose dependence is regulated differently by tissue factor and phospholipids

Recombinant factor VIIa (rFVIIa) is used for treatment of hemophilia patients with inhibitors, as well for off-label treatment of severe bleeding in trauma and surgery. Effective bleeding control requires supraphysiological doses of rFVIIa, posing both high expense and uncertain thrombotic risk. Two major competing theories offer different explanations for the supraphysiological rFVIIa dosing requirement: (1) the need to overcome competition between FVIIa and FVII zymogen for tissue factor (TF) binding, and (2) a high-dose-requiring phospholipid-related pathway of FVIIa action. In the present study, we found experimental conditions in which both mechanisms contribute simultaneously and independently to rFVIIa-driven thrombin generation in FVII-deficient human plasma. From mathematical simulations of our model of FX activation, which were confirmed by thrombin-generation experiments, we conclude that the action of rFVIIa at pharmacologic doses is dominated by the TF-dependent pathway with a minor contribution from a phospholipid-dependent mechanism. We established a dose-response curve for rFVIIa that is useful to explain dosing strategies. In the present study, we present a pathway to reconcile the 2 major mechanisms of rFVIIa action, a necessary step to understanding future dose optimization and evaluation of new rFVIIa analogs currently under development.

Phase I, randomized, double-blind, placebo-controlled, single-dose escalation study of the recombinant factor VIIa variant BAY 86-6150 in hemophilia

BACKGROUND

BAY 86-6150 is a new human recombinant factor VIIa variant developed for high procoagulant activity and longer action in people with hemophilia with inhibitors.

OBJECTIVES

To investigate the safety, tolerability, pharmacodynamics, pharmacokinetics and immunogenicity of BAY 86-6150 in non-bleeding hemophilia subjects.

METHODS

The study included non-bleeding men (18-65 years of age) with moderate or severe hemophilia A or B with or without inhibitors. Sixteen subjects were randomized 3 : 1 to four cohorts of escalating doses of BAY 86-6150 (6.5, 20, 50 or 90 μg kg(-1) [n = 3 per cohort]) or placebo (n = 1 per cohort); an independent data-monitoring committee reviewed previous cohort data before the next dose escalation. Blood sampling was performed predose and postdose; subjects were monitored for 50 days postdose.

RESULTS

At the tested doses, BAY 86-6150 was not associated with clinically significant adverse events or dose-limiting toxicities. BAY 86-6150 pharmacokinetics exhibited a linear dose response, with a half-life of 5-7 h. Subjects demonstrated consistent, dose-dependent thrombin generation ex vivo in platelet-poor plasma (PPP) (mean peak effect, 26-237 nm thrombin from 6.5 to 90 μg kg(-1)). Peak thrombin levels over time paralleled BAY 86-6150, with thrombin kinetics appearing to be slightly shorter; thus, circulating BAY 86-6150 retained activity. There were corresponding decreases in activated partial thromboplastin and prothrombin times. No subject developed de novo anti-BAY 86-6150 neutralizing antibodies during the 50-day follow-up.

CONCLUSIONS

In this first-in-human, multicenter, randomized, double-blind, placebo-controlled, single-dose escalation study, BAY 86-6150 was tolerated at the highest dose (90 μg kg(-1)), with no safety concerns. Safety and efficacy will be further evaluated in phase II/III studies.

Hemostatic properties of the FVIIa analog NN1731

Recombinant activated coagulation factor VII (rFVIIa) has proven to be a useful prohemostatic agent in patients with hemophilia and antibody inhibitors. It has also been used off-label in other settings. A major mechanism of its hemostatic efficacy is its ability to activate factor X on the surface of activated platelets in a tissue factor (TF)-independent manner. Novel analogs of FVIIa have been designed to have greater platelet-surface activity in the hope that these will be more active and reliable hemostatic agents. The analog NN1731 (vatreptacog alfa) was designed to have greater activity in the absence of TF, with the same substrate specificity as FVIIa. Surprisingly, it also binds to a greater number of sites on activated platelets by an, as yet, unknown mechanism. This molecule exhibits greater potency than FVIIa in biochemical assays, in vitro and animal models, and in early phase clinical trials.

Recombinant factor VIIa analog (vatreptacog alfa [activated]) for treatment of joint bleeds in hemophilia patients with inhibitors: a randomized controlled trial

BACKGROUND

A recombinant factor VIIa analog (NN1731; vatreptacog alfa [activated]) was developed to provide safe, rapid and sustained resolution of bleeds in patients with hemophilia and inhibitors.

PATIENTS/METHODS

This global, prospective, randomized, double-blinded, active-controlled, dose-escalation trial evaluated and compared one to three doses of vatreptacog alfa at 5, 10, 20, 40, and 80 lg kg(-1) with one to three doses of recombinant FVIIa (rFVIIa) at 90 lg kg(-1) in the treatment of acute joint bleeds in hemophilia patients with inhibitors. The primary endpoint comprised adverse events; secondary endpoints were evaluations of immunogenicity, pharmacokinetics, and efficacy.

RESULTS AND CONCLUSIONS

Overall, 96 joint bleeds in 51 patients (> 12 years of age) were dosed. Vatreptacog alfa was well tolerated, with a low frequency of adverse events. No immunogenic or thrombotic events related to vatreptacog alfa were reported. A high efficacy rate of vatreptacog alfa in controlling acute joint bleeds was observed; 98% of bleeds were controlled within 9 h of the initial dose in a combined evaluation of 20–80 lg kg(-1) vatreptacog alfa. The efficacy rate observed for rFVIIa (90%) is consistent with data from published clinical trials. The trial was not powered to compare efficacy, and further trials are needed to investigate the efficacy of vatreptacog alfa as compared with that of rFVIIa. The trial was registered at ClinicalTrials.gov (

REGISTRATION NUMBER

NCT00486278).

Recombinant factor VIIa analog NN1731 (V158D/E296V/M298Q-FVIIa) enhances fibrin formation, structure and stability in lipidated hemophilic plasma

INTRODUCTION

The bypassing agent recombinant factor VIIa (rFVIIa) is efficacious in treating bleeding in hemophilia patients with inhibitors. Efforts have focused on the rational engineering of rFVIIa variants with increased hemostatic potential. One rFVIIa analog (V158D/E296V/M298Q-FVIIa, NN1731) improves thrombin generation and clotting in purified systems, whole blood from hemophilic patients and factor VIII-deficient mice.

METHODS

We used calibrated automated thrombography and plasma clotting assays to compare effects of bypassing agents (rFVIIa, NN1731) on hemophilic clot formation, structure, and ability to resist fibrinolysis.

RESULTS

Both rFVIIa and NN1731 shortened the clotting onset and increased the maximum rate of fibrin formation and fibrin network density in hemophilic plasma clots. In the presence of tissue plasminogen activator, both rFVIIa and NN1731 shortened the time to peak turbidity (TTPeak(tPA)) and increased the area under the clot formation curve (AUC(tPA)). Phospholipids increased both rFVIIa and NN1731 activity in a lipid concentration-dependent manner. Estimated geometric mean concentrations of rFVIIa and NN1731 producing similar onset, rate, TTPeak(tPA), and AUC(tPA) as seen with 100% factors VIII and IX were: 24.5, 74.3, 29.7, and 37.1 nM rFVIIa, and 8.6, 31.2, 9.0, and 11.3 nM NN1731, respectively. In each case, the NN1731 concentration was significantly lower than rFVIIa.

CONCLUSIONS

These findings suggest that like rFVIIa, NN1731 improves the formation, structure, and stability of hemophilic clots. Higher lipid concentrations may facilitate assessment of both rFVIIa and NN1731 activity. NN1731 appears likely to support rapid clot formation in tissues with high endogenous fibrinolytic activity.

Procoagulant activity in hemostasis and thrombosis: Virchow's triad revisited

Virchow's triad is traditionally invoked to explain pathophysiologic mechanisms leading to thrombosis, alleging concerted roles for abnormalities in blood composition, vessel wall components, and blood flow in the development of arterial and venous thrombosis. Given the tissue-specific bleeding observed in hemophilia patients, it may be instructive to consider the principles of Virchow's triad when investigating mechanisms operant in hemostatic disorders as well. Blood composition (the function of circulating blood cells and plasma proteins) is the most well studied component of the triad. For example, increased levels of plasma procoagulant proteins such as prothrombin and fibrinogen are established risk factors for thrombosis, whereas deficiencies in plasma factors VIII and IX result in bleeding (hemophilia A and B, respectively). Vessel wall (cellular) components contribute adhesion molecules that recruit circulating leukocytes and platelets to sites of vascular damage, tissue factor, which provides a procoagulant signal of vascular breach, and a surface upon which coagulation complexes are assembled. Blood flow is often characterized by 2 key variables: shear rate and shear stress. Shear rate affects several aspects of coagulation, including transport rates of platelets and plasma proteins to and from the injury site, platelet activation, and the kinetics of fibrin monomer formation and polymerization. Shear stress modulates adhesion rates of platelets and expression of adhesion molecules and procoagulant activity on endothelial cells lining the blood vessels. That no one abnormality in any component of Virchow's triad fully predicts coagulopathy a priori suggests coagulopathies are complex, multifactorial, and interactive. In this review, we focus on contributions of blood composition, vascular cells, and blood flow to hemostasis and thrombosis, and suggest that cross-talk among the 3 components of Virchow's triad is necessary for hemostasis and determines propensity for thrombosis or bleeding. Investigative models that permit interplay among these components are necessary to understand the operant pathophysiology, and effectively treat and prevent thrombotic and bleeding disorders.

Overcoming delayed in-vitro response to rFVIIa: effects of rFVIIa and rFVIIa analogue (vatreptacog alfa) concentration escalation in whole blood assays

In a previous pharmacokinetic/pharmacodynamic study in nonbleeding hemophilia patients, variability in laboratory response to recombinant factor VIIa (rFVIIa) 90 μg/kg was noted, and the patients were described as delayed or rapid laboratory responders based on time to clot formation. The current study determined whether in-vitro experiments could reproduce previous in-vivo findings; whether the delayed laboratory response to rFVIIa 90 μg/kg is improved by spiking with high-dose rFVIIa or rFVIIa analogue (vatreptacog alfa); whether a dose-response is observed with our method. In-vitro experiments were conducted in our previous patient cohort using rFVIIa 1.28 and 3.84 μg/ml and vatreptacog alfa 0.28 and 0.56 μg/ml. Whole blood studies were conducted using the Hemodyne Hemostasis Analysis System (platelet contractile force, clot elastic modulus, force onset time) and rotational thromboelastometry (clotting time, maximum clot firmness). Spiking with rFVIIa 1.28 μg/ml showed the same distribution of delayed and rapid laboratory response as observed previously. Increasing in-vitro rFVIIa concentrations improved the coagulation parameters; however, there remained delayed and rapid responders. Vatreptacog alfa improved the coagulation parameters at all concentrations tested, and the 0.56 μg/ml concentration normalized the force onset time, platelet contractile force, clot elastic modulus and clotting time parameters. A dose-response was observed with both assays. There was good agreement between the laboratory responses obtained after intravenous administration of rFVIIa 90 μg/kg and in-vitro spiking studies. Escalating rFVIIa and vatreptacog alfa concentrations improved coagulation parameters in all patients compared to rFVIIa 1.28 μg/ml. Vatreptacog alfa produced more pronounced coagulation effects at lower concentrations than rFVIIa; and the 0.56 μg/ml concentration completely normalized responses in all patients.

Proteases as therapeutics

Proteases are an expanding class of drugs that hold great promise. The U.S. FDA (Food and Drug Administration) has approved 12 protease therapies, and a number of next generation or completely new proteases are in clinical development. Although they are a well-recognized class of targets for inhibitors, proteases themselves have not typically been considered as a drug class despite their application in the clinic over the last several decades; initially as plasma fractions and later as purified products. Although the predominant use of proteases has been in treating cardiovascular disease, they are also emerging as useful agents in the treatment of sepsis, digestive disorders, inflammation, cystic fibrosis, retinal disorders, psoriasis and other diseases. In the present review, we outline the history of proteases as therapeutics, provide an overview of their current clinical application, and describe several approaches to improve and expand their clinical application. Undoubtedly, our ability to harness proteolysis for disease treatment will increase with our understanding of protease biology and the molecular mechanisms responsible. New technologies for rationally engineering proteases, as well as improved delivery options, will expand greatly the potential applications of these enzymes. The recognition that proteases are, in fact, an established class of safe and efficacious drugs will stimulate investigation of additional therapeutic applications for these enzymes. Proteases therefore have a bright future as a distinct therapeutic class with diverse clinical applications.

Platelet binding and activity of a factor VIIa variant with enhanced tissue factor independent activity

BACKGROUND AND OBJECTIVES

Platelet binding and activity play important roles in the efficacy of factor VIIa (FVIIa) as a bypassing agent for hemophilia treatment. An analog of FVIIa with increased tissue factor (TF)-independent activity, NN1731, has been produced by introducing three amino acid changes in the protease domain. NN1731 has a conformation similar to TF-bound FVIIa, even in the absence of TF. This results in much greater intrinsic proteolytic activity, but similar activity in the presence of TF.

OBJECTIVES

We hypothesized that these changes would not alter binding to platelets or phospholipid, a characteristic thought to be localized to the Gla domain. The goal of the current work was to compare platelet binding and activity of NN1731 and wild-type FVIIa.

METHODS/RESULTS

FVIIa and NN1731 bound identically to phospholipid vesicles as assessed by both activity assays and electrophoretic quasielastic light scattering techniques. However, NN1731 bound to a greater number of sites on activated platelets than FVIIa, as assessed by flow cytometry. Removal of the Gla domain abolished binding of both FVIIa and NN1731. Inhibition of the active site did not reduce NN1731 binding to the level of FVIIa. When corrected for the amount of protein bound, NN1731 had greater activity than FVIIa on platelet surfaces.

CONCLUSIONS

While the Gla domain is essential for FVIIa binding to platelets, changes in the protease domain in NN1731 enhanced platelet binding as well as proteolytic activity. Features in addition to lipid composition appear to contribute to binding of rFVIIa and, especially, NN1731 to platelets.

Recent advances in the development of coagulation factors and procoagulants for the treatment of hemophilia

Hemophilia is a family of rare bleeding disorders. The two primary types, hemophilia A and hemophilia B, are caused by recessive X-chromosome linked mutations that result in deficiency of coagulation factor VIII (FVIII) or factor IX (FIX), respectively. Clinically, hemophilia is manifested by spontaneous bleeding, particularly into the joints (haemarthrosis) and soft tissue, and excessive bleeding following trauma or surgery. The total overall number of hemophilia patients worldwide is approximately 400,000, however only about 100,000 of these individuals are treated. The first treatment of hemophilia was initiated when it was determined that the clotting deficiency could be corrected by a plasma fraction taken from normal blood. The discovery of factor VIII enrichment by cryoprecipitation of plasma opened a new era of therapy which eventually led to the production of factor concentrates and the subsequent development of highly purified forms of plasma factors. The most significant improvements have been the availability of recombinant forms of factors VIII and IX. Unfortunately, recombinant factors still retain some of the limitations of plasma concentrates. These limitations include development of antibody responses in patients and the relatively short half-life of the molecules requiring frequent injection to maintain effective concentration. Treatment beyond replacement of native factors has been tried. They include the development of modified factor VIII and IX molecules with improved potency, stability and circulating half-life and enhancement of a prothrombotic responses and/or stabilization of coagulation factors via inhibition of key negative regulatory pathways. These approaches will be reviewed in this commentary.

Factor VIIa analog has marked effects on platelet function and clot kinetics in blood from patients with hemophilia A

To evaluate the hemostatic effects of NN1731 and rFVIIa, an ex-vivo study in hemophilia patients used the Hemodyne Hemostasis Analysis System (HAS) to measure platelet contractile force (PCF), clot elastic modulus (CEM), and force onset time (FOT), and the Haemoscope Thrombelastograph (TEG) to measure reaction time (R), kinetics time (K), and maximum amplitude (MA). Blood samples from 10 healthy volunteers and 10 Factor VIII-deficient patients of varying severity (mild, moderate, severe), were spiked with rFVIIa and NN1731 (both 0.64 and 1.28 microg/ml, respectively) and analyzed to characterize platelet function and clot kinetics. There was wide variability in the rFVIIa response. NN1731 had greater and more consistent effects on PCF, CEM, FOT, R, and K relative to rFVIIa, in all hemophilia groups. The lowest NN1731 concentration (0.64 microg/ml) shortened R and FOT, and increased CEM and PCF more than rFVIIa 1.28 microg/ml. NN1731 normalized clotting parameters equivalent to values obtained in healthy volunteers. FOT and R were highly correlated (r = 0.96). No correlation was observed between CEM and MA. NN1731 produced less variable, more pronounced and predictable ex-vivo hemostatic effects on PCF, CEM, FOT, R and K than rFVIIa in all hemophilia groups. HAS and TEG assays provided similar estimates of FOT and R, however CEM appeared to be more sensitive than MA to changes in clot firmness.

Safety, pharmacokinetics and efficacy of factor VIIa formulated with PEGylated liposomes in haemophilia A patients with inhibitors to factor VIII--an open label, exploratory, cross-over, phase I/II study

  Recombinant activated factor VIIa (FVIIa) is a bypassing agent used to treat bleeding episodes in haemophilia patients with inhibitors to factor VIII (FVIII) and factor IX. The pharmacological effect of FVIIa is short-lived and therefore with the recommended dose of 90 μg kg(-1), a bleeding episode is treated with multiple injections. A long-acting form of FVIIa that can ensure adequate haemostasis with a single infusion, without increasing the thrombotic risk, would therefore be beneficial. PEGylated liposomes (PEGLip) have been shown to bind FVIIa and to improve haemostatic efficacy in preclinical experiments. In the present phase I/II clinical trial, we assessed the safety and efficacy of PEGLip-formulated FVIIa in severe haemophilia A patients (FVIII≤1%) with inhibitors to FVIII. Each patient received one prophylactic infusion of standard FVIIa and one prophylactic infusion of PEGLip-formulated FVIIa. The order of the infusions was randomized and the two infusions were separated by a ten-day washout period. Efficacy assessed by thromboelastography revealed that PEGLip-FVIIa induced significantly shorter clotting times and produced higher clot firmnesses than standard FVIIa. Thrombin generation assays showed that PEGLip-FVIIa induced faster thrombin generation and higher peak levels of thrombin than standard FVIIa. These effects lasted up to 5 h postinfusion. Measurements of D-dimer, prothrombin fragment 1+2 and fibrinogen showed no significant differences between the PEGLip-FVIIa and standard FVIIa treatments. PEGLip-FVIIa therefore showed improved haemostatic efficacy without increased risk of thrombosis and may be further developed for the treatment for bleeding episodes in haemophilia patients with inhibitors.

Recombinant human factor VIIa (rFVIIa) cleared principally by antithrombin following intravenous administration in hemophilia patients

OBJECTIVE

The objective of the present study was to evaluate the pharmacokinetics and the clearance pathways of rFVIIa after intravenous administration to hemophilia patients.

METHODS

Ten severe hemophilia patients were included in the study; all patients were intravenously administered a clinically relevant dose of 90 μg kg(-1) (1.8 nmol kg(-1)) rFVIIa. Blood samples were collected consecutively to describe the pharmacokinetics of rFVIIa. All samples were analyzed using three different assays: a clot assay to measure the activity (FVIIa:C), an enzyme immunoassay (EIA) to measure the antigen levels (FVII:Ag), and an EIA (FVIIa-AT) to measure the FVIIa antithrombin III (AT) complex. Pharmacokinetic parameters were evaluated both by use of standard non-compartmental methods and by use of mixed effects methods. A population pharmacokinetic model was used to simultaneously model all three datasets. The total body clearance of rFVIIa:C was estimated to be 38 mL h(-1) kg(-1). The rFVII-AT complex formation was responsible for 65% of the total rFVIIa:C clearance. The initial and the terminal half-life of rFVIIa:C was estimated to be 0.6 and 2.6 h, respectively. The formation of rFVII-AT complex was able to explain the difference observed between the rFVIIa:C and the rFVII:Ag concentration. The non-compartmental analysis resulted in almost identical parameters.

Plasma and cellular contributions to fibrin network formation, structure and stability

Growing evidence suggests that fibrin network structure and stability are important determinants of haemostasis and thrombosis, with alterations in fibrin structure implicated as a causative mechanism in various haemostatic and thrombotic disorders. In haemophilia, for example, deficiency of factor VIII or IX reduces the rate and peak of thrombin generation and produces coarse fibrin clots that show increased susceptibility to fibrinolysis. More recently, studies have shown significant effects of cellular activity and integrin composition on fibrin network and stability. Platelets support the formation of a dense, stable fibrin network via interactions between the alphaIIbbeta3 integrin and the fibrin network, whereas tissue factor-bearing cells regulate fibrin structure and stability predominantly via procoagulant activity. Highly procoagulant extravascular cells (e.g. fibroblasts and smooth muscle cells) support the formation of dense fibrin networks that resist fibrinolysis, whereas unstimulated intravascular cells (e.g. endothelial cells) produce coarser networks that are susceptible to fibrinolysis. Moreover, cellular contributions produce heterogeneous clots in which fibrin network density and stability decrease with increasing distance from the cell surface. Together, these findings suggest that specific plasma and cellular mechanisms link thrombin generation, clot stability and haemostatic or thrombotic outcome. Understanding these mechanisms may provide new therapeutic targets in the management of bleeding and thrombotic disorders.

Hemophilia: New Protein Therapeutics

Therapeutic advances for patients with hemophilia have resulted in reduced mortality, improved joint outcomes, safety from blood-transmitted pathogens, improved quality of life, and a normalized life span in the developed world. The production of recombinant coagulation factors has increased the worldwide capacity for replacement therapy and facilitated aggressive prophylactic therapy. However, this has come at significant cost, and barriers remain to broad application of prophylaxis. Recombinant DNA technology remains a promising platform to develop novel hemophilia therapeutics with improved functional properties to try to overcome some of these remaining barriers. Bioengineering strategies have produced novel therapeutics with increased production efficiency, increased potency and resistance to inactivation, prolonged plasma half-lives, and reduced immunogenicity. Alternative nonbiologic therapies may lead to new treatment paradigms. The current pipeline of new technologies and products is promising and growing with several agents already advancing from preclinical to clinical trials.

Intravascular inhibition of factor VIIa and the analogue NN1731 by antithrombin

NN1731 is a recombinant activated factor VII (rFVIIa) analogue with increased intrinsic activity. This also applies to its reactivity towards antithrombin (AT), the role of which was investigated in a pharmacokinetic (PK) study. NN1731 or rFVIIa was administered to normal and haemophilia A dogs and elimination was measured by FVIIa clot activity, FVIIa- and FVIIa-AT antigen. In vitro AT complex formation was studied in canine plasma spiked with NN1731 or rFVIIa. Based on FVIIa antigen concentrations, PK profiles in normal and haemophilia A dogs were similar for NN1731 and rFVIIa with antigen half lives, t(½) ≈1·8 h. In contrast, PK profiles based on activity measurements were distinctly different. NN1731 induced a strong, short lasting (t(½) ≈0·5 h) pro-coagulant response, whereas rFVIIa induced a lower, longer lasting (t(½) ≈1·1 h) response. Western Blot and FVIIa-AT antigen analysis demonstrated in vivo AT complex formation that accounted for these divergences. AT complex formation with FVIIa or NN1731 in vitro in canine plasma was considerably slower than the in vivo reaction. The results suggest that in vivo inhibition by AT contributes significantly to define drug duration in haemophilia treatment with rFVIIa and in particular with the NN1731 analogue.

Ensembles of uncertain mathematical models can identify network response to therapeutic interventions

The role of mechanistic modeling and systems biology in molecular medicine remains unclear. In this study, we explored whether uncertain models could be used to understand how a network responds to a therapeutic intervention. As a proof of concept, we modeled and analyzed the response of the human coagulation cascade to recombinant factor VIIa (rFVIIa) and prothrombin (fII) addition in normal and hemophilic plasma. An ensemble of parametrically uncertain human coagulation models was developed (N = 437). Each model described the time evolution of 193 proteins and protein complexes interconnected by 301 interactions under quiescent flow. The 467 unknown model parameters were estimated, using multiobjective optimization, from published in vitro coagulation studies. The model ensemble was validated using published in vitro thrombin measurements and thrombin measurements taken from coronary artery disease patients. Sensitivity analysis was then used to rank-order the importance of model parameters as a function of experimental or physiological conditions. A novel strategy for the systematic comparison of ranks identified a family of fX/FXa and fII/FIIa interactions that became more sensitive with decreasing fVIII/fIX. The fragility of these interactions was preserved following the addition of exogenous rFVIIa and fII. This suggested that exogenous rFVIIa did not alter the qualitative operation of the cascade. Rather, exogenous rFVIIa and fII took advantage of existing fluid and interfacial fX/FXa and fII/FIIa sensitivity to restore normal coagulation in low fVIII/fIX conditions. The proposed rFVIIa mechanism of action was consistent with experimental literature not used in model training. Thus, we demonstrated that an ensemble of uncertain models could unravel key facets of the mechanism of action of a focused intervention. Whereas the current study was limited to coagulation, perhaps the general strategy used could be extended to other molecular networks relevant to human health.

The use of PEGylated liposomes in the development of drug delivery applications for the treatment of hemophilia

Hemophilia A is a rare X-linked bleeding disorder caused by lack or dysfunction of coagulation factor VIII (FVIII). Hemophilia A is treated with replacement therapy, but frequent injections of the missing FVIII often lead to the formation of inhibitory antibodies. Patients who develop high levels of inhibitors must be treated with bypassing agents such as activated FVII (FVIIa). Both FVIII and FVIIa have short half-lives and require multiple injections. Long-acting forms of these proteins would therefore reduce the frequency of injections, improve patient compliance and reduce complications. In this article we present a new platform technology that produces long-acting forms of FVIII and FVIIa and improves the efficacy of hemophilia treatment. This technology is based on the binding of proteins/peptides to the outer surface of PEGylated liposomes (PEGLip). Binding is dependent on an amino acid consensus sequence within the proteins and is highly specific. At the same time, binding is non-covalent and does not require any modification of the therapeutic agent or its production process. Association of proteins with PEGLip results in substantial enhancements in their pharmacodynamic properties following administration. These improvements seem to arise from the association of formulated proteins with platelets prior to induction of coagulation.

Thrombin generation and fibrinolysis in anti-factor IX treated blood and plasma spiked with factor VIII inhibitor bypassing activity or recombinant factor VIIa

Activated prothrombin complex concentrates (aPCC) and recombinant activated factor VIIa (rFVIIa) are two important therapies in haemophilia patients with inhibitors and improve clot stability. We hypothesized that potential differences in procoagulant and fibrinolytic actions of aPCC and rFVIIa may lie in the clot stability against fibrinolytic activation. We used thrombin generation, fluorescence detection and thromboelastometry in anti-factor IXa (FIXa) aptamer-treated whole blood (WB) and plasma to evaluate: (i) generation of thrombin and activated factor X (FXa) and (ii) viscoelastic properties of blood clots in the presence of tissue plasminogen activator (tPA) after addition of aPCC (0.4 U mL(-1)) or rFVIIa (60 nm). Peak thrombin generation increased from 85 +/- 19 nm in aptamer-treated plasma to 276 +/- 83 nm and 119 +/- 22 nm after addition of aPCC and rFVIIa respectively (P < 0.001). FXa activity increased within 20 min by 87 +/- 6% and by 660 +/- 97% after addition of aPCC and rFVIIa respectively (P < 0.001). TPA-induced lysis time increased from 458 +/- 378 s in aptamer-treated WB to 1597 +/- 366 s (P = 0.001) and 1132 +/- 214 s (P = 0.075), after addition of aPCC and rFVIIa respectively. In this haemophilia model using the anti-FIXa aptamer, the larger amount of thrombin was generated with aPCC compared with rFVIIa, while FXa generation was more rapidly increased in the presence of rFVIIa. Furthermore, clot formation in anti-FIXa aptamer-treated WB was less susceptible to tPA-induced fibrinolysis after adding aPCC compared with rFVIIa.

rFVIIa and NN1731 reduce bleeding in hydroxyethyl starch hemodiluted rabbits

BACKGROUND

Colloid plasma expanders are used to maintain blood pressure and ensure tissue perfusion during hypovolemia, e.g., caused by traumatic bleeding. Although colloids stabilize the cardiovascular system, they can also potentially cause coagulopathy. Consequently, bleeding tendency may increase, as well as the associated risk of morbidity and mortality. Thus, there is a need for hemostatic treatment options for these patients. rFVIIa (NovoSeven, Novo Nordisk A/S, Bagsvaerd, Denmark) is a hemostatic agent that effectively controls bleedings in patients with inhibitor-complicated hemophilia. rFVIIa works by enhancing thrombin generation on the activated platelet surface at the site of injury, leading to the formation of a stable fibrin clot. NN1731 is an rFVIIa analog with increased hemostatic potential and is currently under clinical development.

METHODS

In this study, the effect of rFVIIa and NN1731 on cuticle bleeding in rabbits 50% hemodiluted with hydroxyethyl starch (molecular weight ∼ 200,000) was tested. Cuticle bleeding was induced after a two-stage hemodilution procedure. After 5 minutes, the animals were treated with rFVIIa (2, 5, or 10 mg/kg), NN1731 (1 or 2 mg/kg), or vehicle, followed by 30 minutes of observation.

RESULTS

Hemodilution caused a significant increase in bleeding time and blood loss. rFVIIa dose-dependently reduced bleeding time and blood loss, reaching statistical significance at 10 mg/kg. However, 2 mg/kg NN1731 reduced bleeding time and blood loss significantly and to a similar extent as 10 mg/kg rFVIIa. This increased hemostatic potential of NN1731 compared with rFVIIa and was confirmed by findings using thromboelastography on ex vivo hemodiluted whole blood.

CONCLUSION

In summary, rFVIIa and NN1731 significantly and dose-dependently reduced bleeding in extensively hemodiluted rabbits.

Faster onset of effect and greater efficacy of NN1731 compared with rFVIIa, aPCC and FVIII in tail bleeding in hemophilic mice

BACKGROUND

Recombinant factor VIIa (rFVIIa, Novoseven) is currently used to control bleeding in hemophiliacs with inhibitors. A new rFVIIa variant, NN1731, with increased activity on the surface of activated platelets, has demonstrated a more potent and faster onset of reactivity than rFVIIa in various in vitro models. The present study aimed to investigate whether this translates into greater efficacy and faster promotion of hemostasis in vivo.

METHOD AND RESULTS

In a severe tail-bleeding model in hemophilia A mice, NN1731 demonstrated significantly greater efficacy than rFVIIa, plasma-derived activated prothrombin complex concentrate (pd-aPCC, FEIBA or FVIII (Refacto). Assessment of the blood loss over time showed that NN1731 significantly and dose-dependently reduced the blood loss in the first 5-min observation period, whereas the effect of rFVIIa, FVIII and pd-aPCC first became evident 5-10 min after injury.

CONCLUSION

This study shows that NN1731 has a greater efficacy and faster resolution of bleeding in a severe bleeding model in hemophilia A mice compared with any of the other agents tested.

Thrombin generation and platelet activation induced by rFVIIa (NovoSeven) and NN1731 in a reconstituted cell-based model mimicking haemophilia conditions

Replacement therapy with factor VIII (FVIII) and factor IX (FIX) is routinely used in haemophilia patients with haemophilia A and B, respectively, while recombinant activated FVII (rFVIIa) has proven to induce haemostasis in haemophilia patients with inhibitors. To evaluate the effect of therapeutic intervention in patients with residual factor activities, the effects of increasing concentrations of rFVIIa or NN1731 on thrombin generation and platelet activation were measured in a cell-based model system mimicking severe, moderate and mild haemophilia A or B. Purified monocytes stimulated to express tissue factor and non-activated platelets from peripheral blood of healthy donors were incubated with a mixture of purified human coagulation factors in the absence or presence of increasing concentrations of FVIII or FIX. Sub-samples were analysed for thrombin activity and platelet activation measured as exposure of P-selectin by flow cytometry. Dose-dependent increases in thrombin generation and platelet activation were observed following increasing concentrations of rFVIIa or NN1731 in both haemophilia A- and B-like conditions. At 25 nm rFVIIa, which nears the peak levels in patient plasma after 90 microg kg(-1) intravenous dosing, the effects on maximum thrombin generation rate (maxTG) at 1-10% FVIII were comparable to those at 100% and 200% FVIII in the absence of rFVIIa. Normalization of maxTG required 500 nm rFVIIa and 25 nm NN1731 or 25-100 nm rFVIIa and 5 nm NN1731 in severe or moderate/mild haemophilia A and haemophilia B, respectively. This suggests that NN1731 holds its promise as a future bypassing agent for haemophilia patients with and without inhibitors.

rFVIIa and a new enhanced rFVIIa-analogue, NN1731, reduce bleeding in clopidogrel-treated and in thrombocytopenic rats

BACKGROUND

The pharmacological effect of rFVIIa occurs at the surface of activated platelets by enhancing thrombin generation at the site of vascular damage. It is therefore important to study the effects of rFVIIa in platelet-related bleeding situations. We examined the effect of rFVIIa and an rFVIIa-analogue, NN1731, on clopidogrel-induced and thrombocytopenic bleeding in rats.

METHODS AND RESULTS

Clopidogrel [10 mg kg(-1); per oral (p.o.)] severely inhibited platelet aggregation and increased blood loss after tail-transection four hours after administration. Treatment with rFVIIa (5, 10, 20 mg kg(-1)) or NN1731 (1, 5, 10 mg kg(-1)), administered five minutes after induction of bleeding, reduced blood loss significantly and dose-dependently. NN1731 had an increased hemostatic potential compared with rFVIIa, reducing blood loss to the control level, whereas this was not even achieved with the highest dose of rFVIIa. Antibody-induced thrombocytopenia reduced platelet numbers by more than 90% and increased the blood loss after tail-transection. Treatment with 10 and 20 mg kg(-1) rFVIIa significantly reduced blood loss, whereas 10 mg kg(-1) NN1731 reduced the bleeding to control levels.

CONCLUSIONS

The hemostatic effect of rFVIIa and NN1731 was demonstrated in thrombocytopenic and clopidogrel-treated rats, showing efficacy in situations with decreased platelet number or functionality. Our findings are consistent with the hypothesis that rFVIIa/NN1731 contribute to hemostasis by thrombin generation even in situations with platelet disorders. Furthermore, NN1731 demonstrated a higher hemostatic potential than rFVIIa.

Evaluation of the safety and pharmacokinetics of a fast-acting recombinant FVIIa analogue, NN1731, in healthy male subjects

BACKGROUND

NN1731 is a recombinant activated factor VII (rFVIIa) analog with enhanced activity.

OBJECTIVES

This clinical trial aimed to assess the safety and pharmacokinetics of single doses of NN1731 in healthy male subjects.

METHODS

This was a randomized, placebo-controlled dose-escalation trial with four dose tiers (NN1731 5-30 microg kg(-1)). Eight subjects were randomized to either NN1731 (n = 6) or placebo (n = 2) in each tier.

RESULTS

No thromboembolic or serious adverse events were reported and no antibody formation towards NN1731 was detected. NN1731 was demonstrated to be pharmacologically active based on coagulation-related parameters (prothrombin fragment 1+2, activated partial thromboplastin time and prothrombin time). There were five mild/moderate adverse events in three subjects. The FVIIa activity of NN1731 after ascending single-dose administration of NN1731 fits well with a two-compartment model, indicating a bi-exponential decline with a rapid initial distribution of approximately 73% FVIIa activity (half-life = 20 min), followed by a less rapid terminal elimination phase eliminating the remaining 27% (half-life = 3 h). Dose proportionality in healthy male subjects at the dose levels investigated (5-30 microg kg(-1)) was supported by the FVIIa activity data.

CONCLUSIONS

Based on the results of this trial, NN1731 appears safe and well tolerated in healthy subjects at doses up to 30 microg kg(-1). No immunogenic or thromboembolic events were reported. The pharmacokinetic profile of NN1731 as measured by FVIIa activity appears to follow two-compartment pharmacokinetics characterized by an initial rapid distribution phase followed by a less rapid elimination phase.