Synovitis in a murine model of human factor VIII deficiency

Recurrent joint bleeding is the most common musculoskeletal manifestation of haemophilia and leads to a target joint and synovitis. The pathobiology of haemophilic synovitis (HS) is not well understood. Here the histopathological changes that occur following haemarthrosis were examined in an animal model for human HS. After two haemarthrosis, there was soft tissue and joint swelling and histological changes of acute synovitis included infiltration of the sub-synovial layer by mononuclear cells and neutrophils, thickening of the synovial membrane with villus formation, and hyperplasia of blood vessels. Subacute changes were evident after three haemarthrosis; muscle atrophy was present and an intense mononuclear cell infiltrate filled the sub-synovial space. There was destruction of articular surfaces and loss of cartilage. Seventeen months after three haemarthrosis, chronic joint changes included gross deformity and loss of congruence due to dense fibrotic tissue filling the joint space. The mononuclear inflammatory cell infiltrate and thickened synovial membrane persisted. Pits and erosions of articular surfaces and sub-chondral cysts were present. There was fibro-cartilage and new bone formation. This model of human HS should be useful to fully evaluate the biochemical and molecular changes that occur following joint bleeding and to test novel therapeutics to prevent HS.     

Evaluation of the activated partial thromboplastin time assay for clinical monitoring of PEGylated recombinant factor VIII (BAY 94‐9027) for haemophilia A

Patients with haemophilia (PWH) are usually monitored by the one‐stage activated partial thromboplastin time (aPTT) factor VIII (FVIII) assay. Different aPTT activators may affect clotting time (CT) and FVIII:C levels in patients treated with PEGylated FVIII. To evaluate the characteristics of PEGylated FVIII (BAY 94‐9027) in various aPTT clotting assays, and to identify suitable aPTT reagents for monitoring BAY 94‐9027 during the treatment of PWH, BAY 94‐9027 and World Health Organization (WHO) 8th FVIII standards (WHO‐8) were spiked into pooled and individual severe haemophilia A plasma at 1.0, 0.25 and 0.05 IU mL^?1. Five commercial aPTT reagents widely used in clinical laboratories were compared and evaluated for BAY 94‐9027 activity in plasma from PWH. BAY 94‐9027 and WHO‐8 bestowed similar CT and excellent precision when ellagic acid (SynthAFax, Dade Actin, and Cephascreen) aPTT reagents were used. In contrast, BAY 94‐9027 showed significantly prolonged CT and poor precision compared with WHO‐8 using silica aPTT reagents (APTT‐SP and STA PTT 5). Furthermore, free 60‐kDa polyethylene glycol (PEG), used for the conjugation of FVIII, showed a dose‐dependent prolongation of CT in the APTT‐SP assay. There was no effect on the SynthAFax‐APTT, prothrombin time, or FXIa‐initiated thrombin generation assay, demonstrating that the PEG moiety on FVIII has no general effect on the coagulation cascade. In summary, ellagic aPTT reagents (SynthAFax, Dade Actin, and Cephascreen) are most suitable for evaluating potency of BAY 94‐9027 and should be the preferred aPTT reagents used in clinical laboratories for monitoring FVIII activity after infusion of BAY 94‐9027 to PWH.     

von Willebrand factor contributes to longer half‐life of PEGylated factor VIII in vivo

PEGylation of B‐domain deleted factor VIII (PEG‐FVIII‐BDD) prolongs the half‐life of the molecule by approximately twofold in animals (Mei et al., Blood 2010; 116 : 270). To investigate the role of von Willebrand factor (vWF) in the catabolism of PEG‐FVIII‐BDD in vivo, a FVIII‐BDD mutant (F8V), which is incapable of binding vWF, was generated by deleting the vWF‐binding region in the a3 domain of FVIIII‐BDD. F8V was expressed, purified and PEGylated by site‐specific conjugation. The biochemical and biological properties of F8V and PEGylated F8V (PEG‐F8V) were evaluated in vitro and in vivo. The specific activity of purified F8V by a chromogenic assay was similar to FVIII‐BDD and PEGylation had minimal impact on the specific activity of F8V in this assay. Analysis by Biacore indicated that both F8V and PEG‐F8V display greatly reduced vWF binding in vitro. Pharmacokinetic studies in FVIII knockout (HaemA) mice showed that the terminal half‐life (T_1/2) of F8V was dramatically reduced relative to FVIII‐BDD (0.6 h vs. 6.03 h). PEGylation of F8V promoted a significant increase in T_1/2, although PEGylation did not fully compensate for the loss in vWF binding. PEG‐F8V showed a shorter T_1/2 than PEG‐FVIII‐BDD both in HaemA mice (7.7 h vs. 14.3 h) and in Sprague‐Dawley male rats (2.0 ± 0.3 h vs. 6.0 ± 0.5 h). These data demonstrated that vWF contributes to the longer T_1/2 of PEG‐FVIII‐BDD. Furthermore, this suggests that the clearance of the FVIII:vWF complex, through vWF receptors, is not the sole factor which places an upper limit on the duration of PEG‐FVIII circulation in plasma.     

Improved joint health in subjects with severe haemophilia A treated prophylactically with recombinant factor VIII Fc fusion protein

Introduction

Joint arthropathy is the long‐term consequence of joint bleeding in people with severe haemophilia.

Aim

This study assessed change in joint health over time in subjects receiving recombinant factor VIII Fc fusion protein (rFVIIIFc) prophylaxis.

Methods

ALONG is the phase 3 pivotal study in which the benefit of rFVIIIFc as a prophylactic treatment for bleeding control was shown in previously treated severe haemophilia patients ≥12 years of age (arm 1: 25‐65 IU/kg every 3‐5 days, arm 2: 65 IU/kg weekly and arm 3: episodic). After completing ALONG, subjects had the option to enrol into the extension study (ASPIRE). This interim, post hoc analysis assessed changes in joint health over ~2.8 years in these patients.

Results

Forty‐seven subjects had modified Haemophilia Joint Health Score (mHJHS) data at A‐LONG baseline, ASPIRE baseline and ASPIRE Year 1 and Year 2. Compared with A‐LONG baseline (23.4), mean improvement at ASPIRE Year 2 was ?4.1 (95% confidence interval [CI], ?6.5, ?1.8; P = .001). Regardless of prestudy treatment regimen, subjects showed continuous improvement in mHJHS from A‐LONG baseline through ASPIRE Year 2 (prestudy prophylaxis: ?2.4, P = .09; prestudy episodic treatment: ?7.2, P = .003). Benefits were seen in subjects with target joints (?5.6, P = .005) as well as those with severe arthropathy (?8.8, P = .02). The mHJHS components with the greatest improvement at ASPIRE Year 2 were swelling (?1.4, P = .008), range of motion (?1.1, P = .03) and strength (?0.8, P = .04).

Conclusions

Prophylaxis with rFVIIIFc may improve joint health over time regardless of prestudy prophylaxis or episodic treatment regimens.     

Experimental haemophilic synovitis: rationale and development of a murine model of human factor VIII deficiency

Haemophilia is a genetic disease as a result of the deficiency of blood coagulation factor VIII or IX. Bleeding is common, especially into joints where an inflammatory, proliferative synovitis develops resulting in a debilitating arthritis, haemophilic arthropathy. The pathogenesis of blood-induced haemophilic synovitis (HS) is poorly understood. The gross, microscopic and ultrastructural changes that occur in the synovial membrane following human and experimental hemarthrosis have been described. Repeated episodes of bleeding induce synoviocyte hypertrophy and hyperplasia, an intense neovascular response and inflammation of the synovial membrane. The component(s) in blood that initiates these changes is(are) not known, although iron is often proposed as one possibility. Here, we describe a novel murine model of human haemophilia A, which facilitates the examination of large number of animals and tissue specimens. The effects of hemarthrosis on the physical, gross and microscopic changes evoked following joint bleeding are described. Controlled, blunt trauma to the knee joint consistently resulted in joint swelling because of a combination of bleeding and inflammation. Hemosiderin was found in the synovial membrane. Similar to hemarthrosis in human haemophilia, joint bleeding resulted in acute morbidity evidenced by inactivity, weight loss and immobility. With time the animals recovered. The model of experimental murine HS described here has utility in the study of the pathogenesis of HS. This is the first of a series of articles, which will discuss the pathophysiology and characterize the model, with comparison of his model to others which have been published previously. It should provide a useful model to test potential therapeutic interventions.     

Pharmacokinetics,efficacy and safety of BAX326, a novel recombinant factor IX: a prospective,controlled, multicentre phase I/III study in previously treated patients with severe (FIX level <1%) or moderately severe (FIX level ≤2%) haemophilia B

BAX326 is a recombinant factor IX (rFIX; nonacog gamma) manufactured without the addition of any materials of human or animal origin, and with two viral inactivation steps (solvent/detergent treatment and 15 nm nanofiltration). The aim of this prospective trial was to investigate the pharmacokinetics, haemostatic efficacy and safety of BAX326 in previously treated patients aged 12–65 years with severe or moderately severe haemophilia B. BAX326 was safe and well tolerated in all 73 treated subjects; adverse events considered related to treatment (2.7% incidence, all non‐serious) were transient and mild, and no hypersensitivity reactions, inhibitor formation or thrombotic events were observed. Pharmacokinetic (PK) equivalence (n = 28) between BAX326 and a licensed rFIX was confirmed in terms of the ratio of geometric mean AUC_0–72 h per dose. Twice‐weekly prophylaxis [mean duration 6.2 (±0.7) months; 1.8 (±0.1) infusions per week, 49.5 (±4.8) IU kg^?1 per infusion] was effective in preventing bleeding episodes, with a significantly lower (79%, P < 0.001) annualized bleed rate (4.2) compared to an on‐demand treatment in a historical control group (20.0); 24 of 56 subjects on prophylaxis (43%) did not bleed throughout the study observation period. Of 249 total acute bleeds, 211 (84.7%) were controlled with one to two infusions of BAX326. Haemostatic efficacy at resolution of bleed was rated excellent or good in 96.0% of all treated bleeding episodes. The results of this study indicate that BAX326 is safe and efficacious in treating bleeds and routine prophylaxis in patients aged 12 years and older with haemophilia B.     

The safety and efficacy of B-domain deleted recombinant factor VIII concentrate in patients with severe haemophilia A

BACKGROUND: B-domain-deleted recombinant factor VIII (BDDrFVIII) was developed when the B-domain was found to be redundant for maintaining haemostasis. This allows formulation of the final product without albumin added as a stabilizer. METHODS: Three multicentre clinical studies and one pharmacokinetic study were conducted in 218 patients to evaluate the safety and haemostatic efficacy of BDDrFVIII. RESULTS: Previously treated patients (n = 113; median duration, 1711 days; median exposure days, 385; total 98,096,287 IU infused) rated 97-99% of all infusions as good or excellent efficacy. FVIII inhibitor was noted in one patient in the previously treated patient cohort after 113 exposure days. Among 101 previously untreated patients, responses to BDDrFVIII were rated as excellent or good in 92-95% of infusions (median duration, 1413 days; median exposure days, 148; total 12,636,458 IU infused). Thirty-two previously untreated patients developed inhibitors after a median duration of 12 exposure days (range, 3-49). Sixteen of 32 (50%) patients had low levels (< or = 5 Bethesda units) and 16 had high levels of inhibitors. Inhibitors disappeared in six of 14 (43%) of the high-level and six of eight (75%) of the low-level patients who underwent immune tolerance induction therapy. A total of 42 patients underwent surgery and the overall efficacy of BDDrFVIII was rated as excellent or good for 99.6% of infusions. CONCLUSIONS: The results of these clinical studies indicate that BBDrFVIII is safe and effective and has haemostatic activity similar to that of full-length FVIII concentrates.     

Clinical evaluation of moroctocog alfa (AF-CC), a new generation of B-domain deleted recombinant factor VIII (BDDrFVIII) for treatment of haemophilia A: demonstration of safety, efficacy, and pharmacokinetic equivalence to full-length recombinant factor VIII

Summary.  BDDrFVIII is a B-domain deleted recombinant factor VIII (rFVIII) product for haemophilia A. Manufacture uniquely includes purification chromatography by synthetic-affinity ligand rather than murine-based monoclonal antibody, as well as an albumin-free cell culture process. BDDrFVIII was studied in 204 patients, including 62 subjects <16 years old, in two studies. A double-blind, randomized, pharmacokinetic (PK) crossover study, utilizing a central laboratory assay (one-stage (OS)) for both drug potency assignment and plasma FVIII-activity measurements, demonstrated that BDDrFVIII was PK-equivalent to a full-length rFVIII. Favourable efficacy and safety were observed: during defined routine prophylaxis in a patient population significant for preexisting target joints, nearly half (45.7%) of patients had no bleeding, and a low-annualized bleed rate (ABR) was achieved (median 1.9); 92.5% of haemorrhages ( n  = 187) required ≤2 infusions. Three subjects (1.5%, across both studies) developed de novo inhibitors (low-titre, transient), and the primary safety endpoint, based on a prospective Bayesian analysis, demonstrated the absence of neoantigenicity for BDDrFVIII. The PK-equivalence, based on central testing to align test and reference articles, and the novel Bayesian analysis of inhibitor safety in these investigations reflect robust experimental designs with relevance to future studies. This extensive dataset demonstrates the safety and efficacy of BDDrFVIII for haemophilia A.     

Defining ''full-length'' recombinant factor VIII: a comparative structural analysis

Coagulation factor VIII (FVIII) is an important glycoprotein co-factor involved in haemostasis, functioning to accelerate activation of factor X by activated factor IX. Insertion of expression vectors containing the full-length cDNA sequence of human FVIII into mammalian cell lines results in the production of recombinant factor VIII (rFVIII), typically referred to as 'full-length' rFVIII (FLrFVIII). Both FLrFVIII and plasma-derived FVIII exist primarily as heterodimeric proteins, consisting of a heterogenous light and heavy chain. The objectives of this study were to compare the structural heterogeneity of high-purity FVIII preparations and further define the term 'full length' as it refers to rFVIII protein structure. Five commercially available FVIII concentrates were characterized based on SDS-PAGE, N-terminal sequencing, and peptide and domain mapping coupled to mass spectrometry. The major heavy chain species identified in FLrFVIII included various B-domain-truncated forms of FVIII, with the predominant species terminating at Arg(1313). This study demonstrates that the use of full-sequence FVIII cDNA for the production of rFVIII does not result in a homogeneous FLrFVIII protein product. Rather, commercially available FLrFVIII represents a heterogenous mixture of various B-domain-truncated forms of the molecule, with no evidence of a contiguous, intact B-domain.     

B-domain deleted recombinant factor VIII preparations are bioequivalent to a monoclonal antibody purified plasma-derived factor VIII concentrate: a randomized, three-way crossover study

BACKGROUND: Deletion of the B-domain of recombinant blood coagulation factor VIII (BDDrFVIII) increases the manufacturing yield of the product but does not impair in vitro or in vivo functionality. BDDrFVIII (ReFacto) has been developed with the additional benefit of being formulated without human albumin. OBJECTIVE: The primary objective of this three-way crossover-design study was to compare the pharmacokinetic (PK) parameters of two BDDrFVIII formulations (one reconstituted with 5 mL of sterile water, the other reconstituted with 4 mL sodium chloride 0.9% USP) with those of a plasma-derived, full-length FVIII preparation (Hemofil M) in patients with haemophilia A to determine bioequivalence. METHODS: A series of blood samples were collected over a period of 48 h after i.v. administration of each of the FVIII preparations. Plasma FVIII activity was determined using a validated chromogenic substrate assay. Plasma FVIII activity vs. time curves was characterized for a standard set of PK parameter estimates. Two parameter estimates, the maximum plasma concentration (Cmax) and the area under plasma concentration vs. time curves (AUCs), were used to evaluate bioequivalence. The two preparations were considered bioequivalent if the 90% confidence intervals for the ratio of geometric means for Cmax and AUCs fell within the bioequivalence window of 80% to 125%. RESULTS/CONCLUSION: Results show that each BDDrFVIII formulation is bioequivalent to Hemofil M and the two formulations of BDDrFVIII are bioequivalent to each other.