Minimal interference of concizumab with standard clinical coagulation laboratory assays - An in vitro study.

INTRODUCTION: Non-factor replacement therapies are emerging as prophylactic treatment options in haemophilia A or B (HA/HB) with and without inhibitors. Concizumab is an anti-tissue factor pathway inhibitor (TFPI) monoclonal antibody preventing factor (F)Xa inhibition and enhancing thrombin generation. Based on experience with other non-factor therapies and extended half-life products, there is a focus on potential interference with common clinical coagulation assays used to monitor patients treated with concizumab. AIM: To evaluate the impact of concizumab on standard clinical coagulation assays. METHODS: Plasma samples (normal, HA/HB with/without inhibitors) in the presence/absence of added concizumab (250-16,000 ng/mL) were analysed in clinical assays including activated partial thromboplastin time (aPTT), prothrombin time (PT), FVIII and FIX one-stage clot and chromogenic substrate assay, assays for detecting FVIII or FIX inhibitors and other assays for coagulation factors. RESULTS: Concizumab did not impact PT assays, but resulted in a small shortening of aPTT (up to 5 s in haemophilia plasma and 0.4 s in normal plasma). Concizumab had no, or only a minor impact on FVIII and FIX activity assays or Bethesda inhibitor assays. FXI and FXII activity in normal plasma, as measured by single factor aPTT-based assay, was significantly increased in the presence of concizumab (+11% each). This was also the case for FVII and FX measured by PT-based assays using plasma with 25% of FVII or FX (+64% and +22%, respectively). CONCLUSION: The presence of concizumab did not, or only slightly, influence the outcome of standard clinical coagulation assays relevant for HA and HB.

Managing invasive procedures in haemophilia patients with limited resources, extended half-life concentrates or non-replacement therapies in 2022.

New treatment possibilities and modalities are now available globally for patients with haemophilia requiring surgery or invasive procedures. The first is the appropriate application of low-dose protocols of clotting factor concentrates (CFC) achieving adequate perioperative haemostasis in resources constraint environments. The increasing availability of CFC through humanitarian aid programs allows more invasive surgeries to be performed for which efficacy and safety data should be more widely collected and reported. Second, extended half-life CFC that are increasingly available in many countries represent valuable alternatives to standard half-life products in surgical patients allowing reduced number of infusions and lower consumption, in particular for extended half-life factor IX. Third, in the era of recently introduced nonfactor prophylaxis, some minor surgical procedures can now be performed without additional haemostatic treatment, others with few low-dose administrations of CFC or bypassing agents. Additional factor VIII/IX or recombinant activated factor VII has proven to be safe and effective in association with emicizumab for major surgeries and it was effectively given at low doses in association with fitusiran (including activated prothrombin complex concentrate). No thrombotic complications have been reported in the surgical setting so far. A multidisciplinary team/facility remains crucial to manage major surgery in patients on prophylaxis with these new agents.

Advances in the management of haemophilia: emerging treatments and their mechanisms.

Mainstay haemophilia treatment, namely intravenous factor replacement, poses several clinical challenges including frequent injections due to the short half-life of recombinant factors, intravenous administration (which is particularly challenging in those with difficult venous access), and the risk of inhibitor development. These impact negatively upon quality of life and treatment compliance, highlighting the need for improved therapies. Several novel pharmacological therapies developed for haemophilia aim to rebalance the clotting cascade and potentially circumvent the aforementioned challenges. These therapies utilise a range of different mechanisms, namely: the extension of the circulating half-life of standard recombinant factors; the mimicking of factor VIII cofactor activity; rebalancing of coagulation through targeting of natural anticoagulants such as antithrombin and tissue factor pathway inhibitor; and inducing the production of endogenous factors with gene therapy. These therapies carry the potential of revolutionising haemophilia treatment by alleviating the current challenges presented by mainstay factor replacement. This review will provide an overview of the key trial findings related to novel therapies based on the mechanisms described above.

Concizumab restores thrombin generation potential in patients with haemophilia: Pharmacokinetic/pharmacodynamic modelling results of concizumab phase 1/1b data.

INTRODUCTION: Concizumab enhances thrombin generation (TG) potential in haemophilia patients by inhibiting tissue factor pathway inhibitor (TFPI). In EXPLORER3 (phase 1b), a dose-dependent pharmacokinetic/pharmacodynamic (PK/PD) relationship was confirmed between concizumab dose, free TFPI and TG potential. AIM: Determine the association between concizumab exposure, PD markers (free TFPI; peak TG) and bleeding episodes to establish the minimum concizumab concentration for achieving sufficient efficacy. METHODS: Free TFPI predictions were generated using an estimated concizumab-free TFPI exposure-response (Emax ) model based on concizumab phase 1/1b data for which simultaneously collected concizumab and free TFPI samples were available. Concizumab concentration at the time of a bleed was predicted using a PK model, based on available data for concizumab doses >50 µg/kg to ≤9 mg/kg. Peak TG vs concizumab concentration analyses and an Emax model were constructed based on EXPLORER3 observations. RESULTS: The Emax model showed a tight PK/PD relationship between concizumab exposure and free TFPI; free TFPI decreased with increasing concizumab concentration. A strong correlation between concizumab concentration and peak TG was observed; concizumab >100 ng/mL re-established TG potential to within the normal reference range. Estimated EC50 values for the identified concizumab-free TFPI and concizumab-TG potential models were very similar, supporting free TFPI as an important biomarker. A correlation between bleeding episode frequency and concizumab concentration was indicated; patients with a concizumab concentration >100 ng/mL experienced less frequent bleeding. The PK model predicted that once-daily dosing would minimize within-patient concizumab PK variability. CONCLUSION: Concizumab phase 2 trials will target an exposure ≥100 ng/mL, with a once-daily regimen.

Treatment and prevention of bleeding in congenital hemophilia A patients with inhibitors.

The treatment of bleeding in hemophilia A patients with persistent inhibitory antibodies to factor VIII is problematic. The current standard hemostatic agents for inhibitor patients are recombinant activated factor VII (rFVIIa) and activated prothrombin complex concentrate (APCC). These "inhibitor bypassing agents" are less reliably effective than are replacement therapies for patients without inhibitors, and there are no validated laboratory assays to monitor their efficacy. Furthermore, only single rFVIIa and APCC products are available worldwide, and their use can be complicated, albeit rarely, by thrombotic events. For all these reasons, new approaches to treat bleeding in inhibitor patients are eagerly awaited. These new approaches include replacement therapy with porcine factor VIII concentrate (currently approved for use in acquired hemophilia patients), bispecific antibodies to simulate the biologic function of factor VIII (already in use in some jurisdictions), pegylated forms of activated factor VII, and strategies targeting the natural anticoagulants TFPI and antithrombin, which create a hypercoagulable phenotype to counterbalance the hypocoagulability imposed by hemophilia.

The Potential Close Future of Hemophilia Treatment - Gene Therapy, TFPI Inhibition, Antithrombin Silencing, and Mimicking Factor VIII with an Engineered Antibody.

Summary Hemophilia is one of the best researched monogenic diseases. Hemophilia A will affect approximately 1:5,000 male live births. In recent decades, great progress has been made with the introduction of recombinant proteins in the 1990s for therapy and prophylaxis, securing adequate availability and, with the introduction of the prophylaxis concept, reducing the negative impact of hemophilia on morbidity (especially arthropathy). Despite this progress, there are still challenges to overcome to secure adequate prophylaxis and treatment: for the time being, causal pharmacological hemophilia prophylaxis and therapy requires repeated i.v. application on a regular basis. Although this approach leads to a reduced comorbidity, it does not yet represent an optimized approach with continuous reversal of the hemophilic defect, which would be the ideal solution. This review summarizes the very new treatment strategies for the treatment of hemophilia A and B.

Concizumab, an anti-tissue factor pathway inhibitor antibody, induces increased thrombin generation in plasma from haemophilia patients and healthy subjects measured by the thrombin generation assay.

AIMS: Concizumab, a humanized monoclonal antibody against tissue factor pathway inhibitor (TFPI), is being developed as a subcutaneously (s.c.) administered treatment for haemophilia. It demonstrated a concentration-dependent procoagulant effect in functional TFPI assays; however, global haemostatic assays, such as the thrombin generation assay (TGA), offer a more complete picture of coagulation. We investigated how concizumab affects thrombin generation following ex vivo spiking in plasma from haemophilia patients using the TGA, and if the assay can detect the effect of multiple s.c. concizumab doses in healthy subjects. METHODS: For the ex vivo spiking study, platelet-poor plasma (PPP) from 18 patients with severe haemophilia was spiked with 0.001-500 nm concizumab. For the multiple-dosing study, four healthy males received concizumab 250 µg kg-1 s.c. every other day for eight doses; blood was collected before and after dosing and processed into PPP. In both studies, thrombin generation was measured using a Calibrated Automated Thrombogram® system with 1 pm tissue factor. RESULTS: In spiked samples from haemophilia patients, peak thrombin and endogenous thrombin potential (ETP) increased concentration dependently, reaching near-normal levels at concizumab concentrations >10 nm. Repeated s.c. doses of concizumab in healthy subjects increased both peak thrombin and ETP; these effects were sustained throughout the dosing interval. CONCLUSIONS: Thrombin generation assay demonstrated increased thrombin generation with concizumab after ex vivo spiking of haemophilia plasma and multiple s.c. doses in healthy subjects, supporting both the utility of the TGA in evaluating concizumab treatment and the potential of s.c. concizumab as a novel haemophilia therapy.

Emerging drugs for the treatment of hemophilia A and B.

INTRODUCTION: Replacement therapy with clotting factor concentrates is the most appropriate and effective way to treat bleedings of Hemophilia A&B to prevent chronic arthropathy. Unfortunately, the short half-life (HL) of FVIII/IX concentrates obliges the patients to receive frequent infusions, a big concern for children. The development of inhibitors in about 30-45% of hemophilia A and in 3-5% of hemophilia B patient is the major adverse event of replacement therapy. AREAS COVERED: In the last few years, new rFIX have been developed with HL. New rFVIII concentrates are displaying small increase of PK characteristics. The new bio-engineering methods allowed the production of molecules fused with Fc fragment of IgG or Albumin or linked to PEG. A new approach to improve hemostasis is represented by Mab against TFPI and small RNA interfering with Antithrombin synthesis. Another innovative drug seems to be the new bi-specific antibody which mimics FVIII function in linking FXa and FX to tenase production. EXPERT OPINION: The emerging drugs for hemophilia treatment seem to be very promising. The extended half-life will improve the adherence of patients to therapy. Accurate post-marketing surveillance studies will be necessary to check the efficacy, safety and immunogenicity of these new molecules.

Targeting tissue factor pathway inhibitor with concizumab to improve hemostasis in patients with Glanzmann thrombasthenia: an in vitro study.

BACKGROUND: Glanzmann thrombasthenia (GT) is caused by an inherited defect of platelet αIIbß3 integrin. Concizumab, a monoclonal antibody specific for tissue factor pathway inhibitor, abolishes its anticoagulant effect. OBJECTIVES: To evaluate the in vitro ability of concizumab to improve hemostasis in GT. METHODS: The effects of concizumab were evaluated in whole blood or platelet-rich plasma from GT patients (n = 5-9) using a thrombin generation assay, rotational thromboelastometry (ROTEM), a global fibrinolytic capacity assay, and a flow chamber assay (Total Thrombus formation Analysis System). Washed platelets (WPs) and 20 nM recombinant activated factor VII (rFVIIa) were included for comparison. RESULTS: The lag time in the thrombin generation assay was significantly longer (+85%; P < .0001) in GT patients than in controls. WPs, rFVIIa, and concizumab each significantly improved thrombin generation profiles. The ROTEM clotting time (CT) was significantly longer in GT patients than in controls (677 seconds vs 523 seconds; P = .03). However, CT improved after adding WPs, rFVIIa, or concizumab. Under flow, occlusive thrombi were present in all healthy controls after 10 minutes, whereas platelet-fibrin depositions were not seen in GT patients. Subocclusive or occlusive thrombi formed when GT blood was mixed with WPs, rFVIIa, or concizumab. Clots in GT platelet-rich plasma were more susceptible to fibrinolysis and were improved by WPs, rFVIIa, or concizumab. CONCLUSION: Concizumab enhanced thrombin generation, decreased the ROTEM CT, improved thrombus formation under flow, and reduced clot lysis. Our results demonstrate the potential of concizumab for subcutaneous prophylaxis in GT patients.

Concizumab as a Subcutaneous Prophylactic Treatment Option for Patients with Hemophilia A or B: A Review of the Evidence and Patient's Perspectives.

Concizumab is a monoclonal, humanized IgG4 antibody specific for the Kunitz-2 domain of Tissue Factor Pathway Inhibitor (TFPI). Preclinical studies in vitro or on animal models and in vivo have demonstrated the ability of concizumab to restore thrombin generation, promoting the establishment of a procoagulant action; all these results were subsequently confirmed in the studies of EXPLORER program. Concizumab may represent a new opportunity for the treatment of persons with hemophilia, so there is much anticipation for the results of the ongoing trials still. This review retraces all the studies on concizumab published to date, with a brief discussion about the patient' perspectives.

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.

[Progress of Non-Factor Products in Hemophilia Treatment--Review].

Traditional replacement therapy is the main treatment method of hemophilia, while inhibitor generation makes replacement therapy ineffective. The emergence of non-factor therapy brings new hope for the treatment of patients with inhibitor. Non-factor products mainly achieve therapeutic purpose by imitating the function of coagulation factor Ⅷ, inhibiting the function of anti-tissue factor pathway inhibitors, the expression of antithrombin mRNA, and the function of activated protein C. This paper reviews the latest research progress of non-factor products in the treatment of hemophilia.

Non-factor therapies for bleeding disorders: A primer for the general haematologist.

Management of patients with severe bleeding disorders, particularly haemophilia A and B, and to a lesser extent, von Willebrand disease, has come on leaps and bounds over the past decade. Until recently, patients relied upon the administration of factor concentrates to prevent or treat bleeding episodes. Factor administration requires intravenous access and, in up to one-third of patients, leads to the development of neutralising antibodies, or inhibitors, which are associated with more frequent bleeding episodes and higher morbidity. Novel non-factor therapies may offer a solution to these unmet needs. In this review, we discuss the factor mimetics, particularly emicizumab, and the rebalancing agents, which inhibit antithrombin, tissue factor pathway inhibitor and activated protein C, and novel treatments to enhance von Willebrand factor levels. We review the available trial data, unanswered questions and challenges associated with these new treatment modalities. Finally, we provide practical management algorithms to aid the general haematologist when faced with a patient receiving emicizumab who requires surgery or may develop bleeding.

Post-authorization pharmacovigilance for hemophilia in Europe and the USA: Independence and transparency are keys.

The regulatory process is currently designed to ensure drug safety during the pre-marketing process. Due to limitations of the pivotal studies owing to their short duration and small number of highly selected cases, some adverse drug reactions (ADRs) are not detected, particularly the rarest and those which appear a long time after exposure. Thus it is essential to foster pharmacovigilance run totally independently from marketing authorization holders in order to attain transparent surveillance. This challenge is relevant for hemophilia drugs, after recent advances offered innovative replacement and non-replacement medicines that warrant monitoring due to the occurrence of predicted but also unexpected and rare ADRs. This article contains an overview of pharmacovigilance systems in the European Union and USA, describing the main ADRs related to traditional and recently available hemophilia medications and suggests how to involve stakeholders other than marketing authorization holders for an independent and transparent pharmacovigilance targeted to detect not only early ADRs but also those emerging post-marketing.

Progress in the Development of Anti-tissue Factor Pathway Inhibitors for Haemophilia Management.

The unprecedented progress in addressing unmet needs in haemophilia care to date includes developing several novel therapies that rebalance haemostasis by restoring thrombin generation in patients with haemophilia A or B with and without inhibitors. These novel therapies are FVIII mimetics, antithrombin interference RNA therapy and several monoclonal antibodies directed against the tissue factor pathway inhibitor (anti-TFPI). In this review, we provide an update on the progress made in developing anti-TFPI therapie. Phase 1 data from the three anti-TFPI studies showed acceptable safety profiles, and currently, available phase 2 data are encouraging. While these data support these molecules' further development progression, there is uncertainty on several aspects of their evolution. Two of the three anti-TFPIs have shown drug-related thrombosis, with one study consequently terminated. None of the thrombotic events is predictable with current monitoring tools, and none correlate with known coagulation parameters. All three anti-TFPIs undergo target mediated drug disposition, which impacts the formulation of dosing regimen fo these therapies. They would require more frequent dosing than some of the extended half-life clotting factor products and antithrombin RNAi therapy. There is no assay to measure the TFPI as the physiological levels are very low, which makes monitoring the impact of the anti-TFPI a challenge. The anti-TFPIs have several advantages, including their bioavailability when administered subcutaneously, their stable pharmacokinetics and their ability to prevent bleeds in haemophilia A or B patients with and without inhibitors. Whether these advantages can be realized will depend on the outcome of the currently ongoing studies.

The availability of new drugs for hemophilia treatment.

INTRODUCTION: A number of new FVIII/IX concentrates enriched the portfolio of products available for the treatment of hemophilia A/B patients. Due to the large inter-patient variability, accurate tailoring of the therapy became essential to improve patients' adherence, clinical outcomes, and cost/effectiveness ratio. Recently, non-replacement therapies have taken the limelight and succeeded in decreasing the bleedings of patients. AREAS COVERED: The PK characteristics, efficacy, and safety of the new rFVIII and rFIX concentrates and of non-replacement therapy, are reported in detail in the published clinical trials. EXPERT OPINION: Outstanding improvements of rFIX concentrates' pharmacokinetics and pharmacodynamics have allowed to reduce the bleedings in hemophilia B patients, in order to increase their adherence to prophylaxis and quality of life. Less significant are the effects of pegylation or Fc fusion on the pharmacokinetics of the new rFVIII concentrates. The new non-replacement therapy is achieving the favor of many treaters and patients, in particular those with Factor VIII inhibitors. Great attention must be paid to the dangerous synergy of APCC and emicizumab, responsible for some fatal events during the clinical trials and compassionate use of this drug. So far, replacement therapy should be the standard of care for hemophilia patients without inhibitors or difficulties in venous access.

Investigational drugs to treat hemophilia.

Introduction: Hemophilia A and B are congenital bleeding disorders. The current standard management of patients with severe hemophilia is prophylaxis which is given intravenously two or three times weekly; however, this is associated with a significant burden on the quality of life of the patient. The main attempts to improve the management of hemophilia is hence through the development of a new generation of products with properties facilitating prophylaxis and/or a better control of bleeding.Areas covered: This review describes the preclinical and phase 1/2 studies investigating the innovative products for the management of hemophilia patients with or without coagulation factor inhibitors.Expert opinion: Numerous innovative therapeutics, including factor concentrates and non-clotting factor-based therapies with extended half-life, are under clinical investigation. Among replacement therapies for hemophilia A, the results from phase 1/2 studies indicate that the most interesting products are those bioengineered using XTEN fusion technology. The anti-tissue factor pathway inhibitor antibody concizumab is the most innovative and interesting agent among non-clotting factor products. If the results of ongoing trials confirm the preliminary positive results, these promising agents will provide further improvements in the management and quality of life of patients with hemophilia.

Hemophilia in a Changing Treatment Landscape.

The mainstay of hemophilia management has been the regular, prophylactic infusion of missing coagulation factors VIII/IX. This approach is limited by the need for frequent intravenous infusions, high cost, limited availability, and the development of inhibitory antibodies to factors VIII/IX. Numerous recent breakthroughs are addressing many of these limitations. These include the development of extended half-life factors that require less frequent infusions and the development of various novel agents that can be given subcutaneously and infrequently, including FVIII-mimetic antibody and downregulators of natural anticoagulants. Finally, gene therapy is set to offer patients a possibility for a cure.

A systems pharmacokinetic/pharmacodynamic model for concizumab to explore the potential of anti-TFPI recycling antibodies.

Concizumab is a humanized monoclonal antibody in clinical investigation directed against membrane-bound and soluble tissue factor pathway inhibitor (mTFPI and sTFPI) for treatment of hemophilia. Concizumab displays a non-linear pharmacokinetic (PK) profile due to mTFPI-mediated endocytosis and necessitates a high dose and frequent dosing to suppress the abundant sTFPI, a negative regulator of coagulation. Recycling antibodies that can dissociate bound mTFPI/sTFPI in endosomes for degradation and rescue antibody from degradation have a potential in reducing the dose by extending antibody systemic persistence and sTFPI suppression. We developed a systems PK/pharmacodynamics (PD) model with nested endosome compartments to simulate the effect of decreased antibody binding to mTFPI/sTFPI in endosomes on antibody clearance and sTFPI suppression for exploring the potential of anti-TFPI recycling antibodies in reducing the dose. A dynamic model-building strategy was taken. A reduced PK/PD model without the endosome compartments was developed to optimize unknown target turnover parameters using concizumab PK data. The optimized parameters were then employed in the systems PK/PD model for simulations. The obtained systems PK/PD model adequately described the PK of concizumab in rabbits, monkeys, and humans and the PD in humans. The systems PK/PD model predicted that an anti-TFPI recycling antibody with a 100-fold higher mTFPI/sTFPI dissociation constant in endosomes than concizumab can extend sTFPI suppression from 12 days to 1 month. Thus, the systems PK/PD model provides a quantitative platform for guiding the engineering and translational development of anti-TFPI recycling antibodies.

Pharmacokinetics of an anti-TFPI monoclonal antibody (concizumab) blocking the TFPI interaction with the active site of FXa in Cynomolgus monkeys after iv and sc administration.

INTRODUCTION: Concizumab (mAb 2021) is a monoclonal IgG4 antibody (mAb) that binds to the Kunitz-type protease inhibitor (KPI) 2 domain of TFPI thereby blocking the interaction of this domain with the active site of FXa. The objective of the present study was to characterize the pharmacokinetics of concizumab in Cynomolgus monkeys after intravenous (iv) and subcutaneous (sc) administration. METHODS: Data from two studies were included in the modelling, all in all data from 52 monkeys distributed into 9 groups. Three groups received three escalating sc doses of concizumab with a one week dosing interval, two groups were administered a single dose, and four groups received multiple doses over 13 weeks of concizumab. The plasma concentration was measured using a standard ELISA, and pharmacokinetic data were analysed using NONMEM. RESULTS: The pharmacokinetics of concizumab were characterised by a high bioavailability (93%) after sc administration. The time course of the elimination of concizumab from the circulation was well described by the proposed target mediated drug disposition (TMDD) model. The clearance of concizumab was estimated to be 0.14 ml/h/kg, the target clearance was characterized by a 50% saturation level of 0.54 µg/ml (Km), and the clearance at target saturation was estimated to be 11 µg/h/kg. CONCLUSION: Concizumab displays a typical TMDD profile with important implications for a putative treatment regime in haemophilia patients. Compared to current standard haemophilia treatment, concizumab has a high bioavailability after sc administration and may provide a viable alternative to intravenous dosing for the treatment of haemophilia.