Thrombin generation in haemophilia A patients with factor VIII inhibitors after infusion of recombinant factor VIIa

Thrombin generation assays to personalize treatment in bleeding and thrombotic diseases

Treatment of bleeding and thrombotic disorders is highly standardized and based on evidence-based medicine guidelines. These evidence-based treatment schemes are well accepted but may lead to either insufficient treatment or over-dosing, because the individuals' hemostatic properties are not taken into account. This can potentially introduce bleeding or thrombotic complications in individual patients. With the incorporation of pharmacokinetic (PK) and pharmacodynamic (PK-PD) parameters, based on global assays such as thrombin generation assays (TGAs), a more personalized approach can be applied to treat either bleeding or thrombotic disorders. In this review, we will discuss the recent literature about the technical aspects of TGAs and the relation to diagnosis and management of bleeding and thrombotic disorders. In patients with bleeding disorders, such as hemophilia A or factor VII deficiency, TGAs can be used to identify patients with a more severe bleeding phenotype and also in the management with non-replacement therapy and/or bypassing therapy. These assays have also a role in patients with venous thrombo-embolism, but the usage of TGAs in patients with arterial thrombosis is less clear. However, there is a potential role for TGAs in the monitoring of (long-term) antithrombotic therapy, for example with the use of direct oral anticoagulants. Finally this review will discuss controversies, limitations and knowledge gaps in relation to the introduction of TGAs to personalize medicine in daily medical practice.

Thrombin generation for monitoring hemostatic therapy in hemophilia A: A narrative review

Patients with severe hemophilia A (HA) have an increased risk of spontaneous and trauma-related bleeding because of a congenital absence of factor VIII (FVIII). Most severe HA patients use prophylactic FVIII concentrate, the effect of which can be monitored with FVIII activity level measurement. However, FVIII activity level is less valuable in predicting the potential clinical bleeding risk. Some patients still experience breakthrough bleeds despite adequate FVIII trough levels, whereas others do not bleed with trough levels below threshold. This difference may be caused by inter-individual differences in pro- and anticoagulant factors, the so-called hemostatic balance. Thrombin generation assays (TGAs) measure the hemostatic balance as a whole. Thereby, the TGAs may be a better tool in the guidance and monitoring of treatment in HA patients. In addition, TGAs offer the opportunity to determine the response to bypassing agents and treatment with non-factor replacement therapy, in which FVIII activity assays are not suitable for monitoring. This review summarizes the current knowledge about monitoring different HA treatment modalities by TGA, as a single treatment option and when used in a concomitant fashion.

Targeting of antithrombin in hemophilia A or B with investigational siRNA therapeutic fitusiran-Results of the phase 1 inhibitor cohort

BACKGROUND

Fitusiran, an investigational small interfering RNA therapy, reduces antithrombin production to rebalance hemostasis in people with hemophilia A or B, with or without inhibitors.

OBJECTIVES

To evaluate the safety and efficacy of fitusiran treatment for people with moderate/severe hemophilia A or B with inhibitors.

PATIENTS/METHODS

In this open-label phase 1, part D study, 17 males with hemophilia A or B with inhibitors received three once-monthly subcutaneous injections of fitusiran 50 mg (n = 6) or 80 mg (n = 11); followed for up to 112 days. Endpoints included safety (primary), pharmacokinetics/pharmacodynamics (secondary), annualized bleeding rate, and patient-reported outcomes (exploratory).

RESULTS

The most common adverse event was injection site erythema (n = 8). No thrombotic events were reported. At nadir, mean (standard error of the mean [SEM]) antithrombin activity decreased from baseline by 82.0% (2.2) and 87.4% (0.7) in the 50 mg and 80 mg groups, respectively. Antithrombin reduction was associated with increased thrombin generation. 11/17 (64.7%) participants had no bleeds during the observation period (mean [standard deviation] 69.4 [16.3] days). Mean (SEM) changes from baseline in Haemophilia Quality of Life Questionnaire for Adults total (-9.2 [2.9]) and physical health (-12.3 [3.9]) domain scores suggested clinically meaningful improvement.

CONCLUSIONS

Monthly fitusiran was generally well tolerated, lowered antithrombin levels from baseline, and resulted in improved thrombin generation. These preliminary results suggest that monthly fitusiran treatment may reduce bleeding episodes and improve quality of life in participants with hemophilia A or B with inhibitors.

Kaolin, used to trigger coagulation in thrombin generation test, increases sensitivity of the method in hemophilia patients

: Thrombin generation test (TGT) is well established tool to research blood coagulation in plasma of hemophilia patients. Traditionally coagulation in this test is triggered by a tissue factor (TF), an extrinsic coagulation pathway activator. However, it is known that disorders of the intrinsic pathway are most important for coagulation in hemophilia. In this study, we hypothesized that triggering coagulation via the intrinsic pathway could increase a sensitivity of the TGT to monitor hemophilia treatment. The aim of this study was to compare thrombin generation in hemophilia A patients with inhibitors to factor VIII before and after infusion of bypassing agent [recombinant-activated factor VIIa (rVIIa)] using standard activation of coagulation by TF or by kaolin, an activator of coagulation by intrinsic pathway. Endogenous thrombin potential (ETP) in nine patients was measured. ETP before (ETP0) and 60 min after rVIIa infusion (ETP60) were compared. It was shown that ETP0 and ETP60 were significantly different when using any coagulation activator (paired Student's t test, P = 0.017 and 3.7 × 10 for clotting activation by TF and kaolin, respectively). The ratios of ETP60/ETP0 were 1.2 ± 0.2 or 30.0 ± 22.4 (mean ± SD, n = 9) for coagulation activated by TF or kaolin, respectively, and were significantly different (paired Student's t test, P < 0.005). The TGT clearly distinguished between ETP0 and ETP60 in the case of any coagulation activator, but ETP increasing after rVIIa infusion was significantly higher when activated with kaolin. This provided increased sensitivity of this method for monitoring hemophilia therapy.

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.

A close insight to factor VIII inhibitor in the congenital hemophilia A

INTRODUCTION

Hemophilia A (HA) has an X-linked pattern of inheritance and is the most common of the hemorrhagic disorders. HA is caused by a decreased or deficiency of the functional clotting factor VIII (FVIII) and effects 1 in 5000-10,000 male births. The common treatment for hemophilia is replacement therapy by plasma-derived or recombinant FVIII. Approximately 20-30% of people with a severe type of HA develop an inhibitor and this phenomenon is the main challenge in the management of these patients. Genetic factors and environmental determinants contribute to inhibitor development. Here, the roles of various genetic and environmental factors such as the type of FVIII concentrate used, the number of exposure days, and peak treatment time will be discussed in detail. It seems this information is helpful for hematologists.

AREAS COVERED

A literature review was done in January 2016 on PubMed and Scopus using the following keywords:' h(a)emophilia A & factor VIII inhibitor', 'h(a)emophilia A & factor VIII alloantibody', 'h(a)emophilia A & inhibitor'. There was no time limitation; however, there was an English language limitation placed on the articles selected. Expert commentary: Influential genetic and environmental factors in developing inhibitors have been discussed. Most of the risk factors are related to previously untreated patients with hemophili.

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.

Global haemostasis assays, from bench to bedside

Bleeding and thrombosis are the ultimate clinical outcomes of aberrations in the haemostatic process. Haemostasis prevents excessive blood loss due to the effort of various compartments like the vasculature, blood cells, coagulation and fibrinolysis. The complexity of all processes involved makes the diagnosis of aberrations difficult, cumbersome and expensive. A single assay to detect any factor disturbing this haemostatic balance with high sensitivity and specificity would be of great value, especially if the outcome of this assay correlates well with clinical outcome. Despite years of research, such an assay is not yet available; however, some interesting candidates are under development and combine the effects of various compartments. This review describes the development of global haemostasis assays and summarizes the current state of the art of these haemostasis assays covering thrombin and plasmin generation, turbidity and thromboelastography/thromboelastometry. Finally, we discuss the applicability of global assays in clinical practice and we provide a future perspective on the ongoing development of automation and miniaturisation as it is our belief that these developments will benefit the standardization of global haemostasis assays.

The use of a single von Willebrand factor-containing, plasma-derived FVIII product in hemophilia A immune tolerance induction: the US experience

BACKGROUND

Inhibitors are a serious complication for patients with severe hemophilia A. Immune tolerance induction (ITI) is the primary method for eradicating these inhibitors. The role of type of concentrate and in particular the use of von Willebrand factor-containing, plasma-derived factor VIII (VWF/pd-FVIII) concentrate in primary or rescue ITI remains unclear.

OBJECTIVES

To report retrospective collection of data on the use of a single VWF/pd-FVIII concentrate in primary and rescue ITI.

METHODS

Retrospective chart review of hemophilia A inhibitor patients at 11 US institutions who received VWF/pd-FVIII concentrate in primary or rescue ITI.

RESULTS

Primary ITI was carried out in eight inhibitor patients with a 75% complete and partial success. Secondary ITI was carried out in 25 inhibitor patients, with 52% attaining complete or partial success.

CONCLUSIONS

This report represents the largest group of primarily pediatric, high-titer inhibitor patients treated with a single VWF/pd-FVIII concentrate. It adds retrospective data to the use of VWF-containing plasma-derived factor VIII concentrate in primary and rescue ITI, particularly in those patients with characteristics of poor response to ITI.

When should prophylaxis therapy in inhibitor patients be considered?

Currently, patients with severe haemophilia can expect to lead a relatively normal life including prevention of disabling arthropathy as a result of the development of factor replacement therapy and advances in the understanding of the use of such therapy given prophylactically. Unfortunately, a subset of patients develops neutralizing antibodies termed inhibitors rendering such therapy ineffective. These patients frequently develop recurrent joint bleeding resulting in arthropathy. Until recently, prophylactic therapy was not considered for patients with inhibitors because of the perceived lack of an effective therapeutic agent. However, an accumulation of case reports and a recent prospective study have suggested that prophylaxis with the currently available bypassing agents could be effective and appears to be safe in selected cases. This report will review the current data on prophylaxis with bypassing agents and suggest specific situations in which prophylaxis in inhibitor patients could be considered.