A novel B-domain O-glycoPEGylated FVIII (N8-GP) demonstrates full efficacy and prolonged effect in hemophilic mice models.

Frequent infusions of intravenous factor VIII (FVIII) are required to prevent bleeding associated with hemophilia A. To reduce the treatment burden, recombinant FVIII with a longer half-life was developed without changing the protein structure. FVIII-polyethylene glycol (PEG) conjugates were prepared using an enzymatic process coupling PEG (ranging from 10 to 80 kDa) selectively to a unique O-linked glycan in the FVIII B-domain. Binding to von Willebrand factor (VWF) was maintained for all conjugates. Upon cleavage by thrombin, the B-domain and the associated PEG were released, generating activated FVIII (FVIIIa) with the same primary structure and specific activity as native FVIIIa. In both FVIII- and VWF-deficient mice, the half-life was found to increase with the size of PEG. In vivo potency and efficacy of FVIII conjugated with a 40-kDa PEG (N8-GP) and unmodified FVIII were not different. N8-GP had a longer duration of effect in FVIII-deficient mouse models, approximately a twofold prolonged half-life in mice, rabbits, and cynomolgus monkeys; however, the prolongation was less pronounced in rats. Binding capacity of N8-GP on human monocyte-derived dendritic cells was reduced compared with unmodified FVIII, resulting in several-fold reduced cellular uptake. In conclusion, N8-GP has the potential to offer efficacious prevention and treatment of bleeds in hemophilia A at reduced dosing frequency.

Prolonged half-life and preserved enzymatic properties of factor IX selectively PEGylated on native N-glycans in the activation peptide.

Current management of hemophilia B entails multiple weekly infusions of factor IX (FIX) to prevent bleeding episodes. In an attempt to make a longer acting recombinant FIX (rFIX), we have explored a new releasable protraction concept using the native N-glycans in the activation peptide as sites for attachment of polyethylene glycol (PEG). Release of the activation peptide by physiologic activators converted glycoPEGylated rFIX (N9-GP) to native rFIXa and proceeded with normal kinetics for FXIa, while the K(m) for activation by FVIIa-tissue factor (TF) was increased by 2-fold. Consistent with minimal perturbation of rFIX by the attached PEG, N9-GP retained 73%-100% specific activity in plasma and whole-blood-based assays and showed efficacy comparable with rFIX in stopping acute bleeds in hemophilia B mice. In animal models N9-GP exhibited up to 2-fold increased in vivo recovery and a markedly prolonged half-life in mini-pig (76 hours) and hemophilia B dog (113 hours) compared with rFIX (16 hours). The extended circulation time of N9-GP was reflected in prolonged correction of coagulation parameters in hemophilia B dog and duration of effect in hemophilia B mice. Collectively, these results suggest that N9-GP has the potential to offer efficacious prophylactic and acute treatment of hemophilia B patients at a reduced dosing frequency.

Vatreptacog alfa from conception to clinical proof of concept.

Vatreptacog alfa is a genetically engineered variant of recombinant factor VIIa (rFVIIa) containing three amino acid changes. Aspartic acid, valine, and glutamine residues replace valine, glutamic acid, and methionine at positions 158, 296, and 298, respectively. These substitutions result in considerable enhancement of the intrinsic (tissue factor-independent) capability to activate factor X and the downstream hemostatic events are consequently augmented. The beneficial effects of vatreptacog alfa have been demonstrated in numerous in vitro systems attempting to mimic hemophilia and corroborated in in vivo models. Vatreptacog alfa has successfully passed through phase 1 and 2 clinical trials and the molecule is currently being explored in phase 3 clinical trial for the treatment of bleedings in hemophilia patients with inhibitors. This article describes the proposed mechanism behind the increased activity and action of vatreptacog alfa and reviews available data, which suggest that vatreptacog alfa could be a valuable addition to the existing portfolio of treatment options for hemophilia patients with inhibitors.

Generation and biochemical characterization of glycoPEGylated factor VIIa derivatives.

Prophylaxis with 2-4 times weekly dosing of factor (F)VIII or FIX is established as an efficacious and safe treatment in haemophilia. Although prophylaxis is not readily available for the inhibitor patient, recent studies have demonstrated a reduction in bleeding episodes in inhibitor patients treated with daily infusions of FVIIa. In order to develop a treatment option comparable to prophylaxis with FVIII or FIX we looked to PEGylation which is an established method for prolonging the circulatory half-life of proteins. However, due to the numerous interactions of FVIIa with the cell surface, TF, FIX and FX there are limited options for unspecific chemical modification of FVIIa without loss of activity. Consequently, we explored the GlycoPEGylationtrade mark technology for selective PEGylation of the two N-glycans in the FVIIa light chain and protease domain to generate seven specifically modified derivatives with PEG groups ranging from 2 to 40 kDa. These derivatives were evaluated in vitro for their ability to interact with small synthetic substrates as well as key molecules relevant to function in the coagulation pathway. The results demonstrate that modification of FVIIa using glycoPEGylation has only a very limited effect on the hydrolysis S-2288 and FX activation. However, the modification does to some extend alter the ability of FVIIa to interact with TF and more importantly, reduces the rate of ATIII inhibition by up to 50% which could allow for an extended active half-life in circulation.

High-dose erythropoietin alters platelet reactivity and bleeding time in rodents in contrast to the neuroprotective variant carbamyl-erythropoietin (CEPO).

The haematopoietic hormone erythropoietin (EPO) has neuroprotective properties and is currently being explored for treatment of stroke and other neurological disorders. Short-term, high-dose treatment with EPO seems to improve neurological function of stroke patients but may be associated with increased thrombotic risk, whereas alternative non-erythropoietic neuroprotective derivatives of EPO, such as carbamylated EPO (CEPO), may be devoid of such side-effects. We investigated the effects of short-term, high-dose treatment with EPO and CEPO on platelet function and haemostasis in healthy mice and rats. Animals received three daily doses of EPO or CEPO (50 microg/kg), and blood was compared with respect to alterations in haematology and platelet reactivity. In rats, treatment with EPO increased the haematocrit to >50% and the mean platelet volume by 37%, while CEPO had no effect on these parameters. Platelets from EPO-treated rats showed an increased sensitivity to thrombin receptor agonist peptides and elevated plasma levels of soluble P-selectin (sP-selectin) were found in treated mice. Further indicators of platelet hyperreactivity in EPO, but not CEPO-treated animals, were significantly increased aggregatory responses to collagen in whole blood and platelet-rich plasma (PRP). The increased platelet reactivity was paralleled by a decreased bleeding time after tail transection in rats. Samples from EPO-treated rats showed an attenuated response to ADP in whole blood aggregometry and thrombelastography (TEG) platelet mapping but not in apyrase-treated PRP, suggesting involvement of ADP receptor desensitization. These findings suggest that while EPO affects various aspects of platelet function, CEPO is devoid of such effects.

Characterization of recombinant murine factor VIIa and recombinant murine tissue factor: a human-murine species compatibility study.

Tissue factor (TF) is believed to play an important role in coagulation, inflammation, angiogenesis and wound healing as well as in tumor growth and metastasis. To facilitate in vivo studies in experimental murine models, we have produced recombinant murine factor VII (FVII) and the ectodomain of murine TF, TF(1-223). Murine FVII was activated to FVIIa with human factor Xa and upon reaction with FFR-chloromethyl ketone converted into an active site-blocked TF antagonist, FFR-FVIIa. The activity of murine FVIIa was characterized in factor X activation assays as well as in clot assays with murine and human thromboplastin in murine and human plasma. In these assays murine FVIIa exhibited a specific activity equivalent to or higher than human FVIIa. Further analysis showed that murine FVIIa binds with high affinity to both murine and human TF, whereas the association of human FVIIa to murine TF is about three orders of magnitude weaker than the association to human TF. This difference was further emphasized by the effect of murine-and human FFR-FVIIa on bleeding in an in vivo mouse model. Intra-peritoneal administration of 1 mg/kg murine FFR-FVIIa significantly prolonged the tail-bleeding time, whereas no effect on bleeding was observed with a 25-times higher dose of the human FFR-FVIIa. Together, these data confirms the notion of poor species compatibility between human FVII and murine TF and emphasizes the requirement for autologous FVIIa in studies on the role of the TF in experimental in vivo pharmacology.

Prolonged half-life of glycoPEGylated rFVIIa variants compared to native rFVIIa.

INTRODUCTION: Bleeding episodes in haemophilia patients with inhibitors are primarily treated with by-passing agents such as recombinant activated FVII (rFVIIa). Prophylactic treatment with rFVIIa has been shown to significantly reduce the number of bleeding episodes as compared to conventional on-demand haemostatic therapy, and a reduced dosing frequency could present an improved treatment option in inhibitor patients. MATERIALS AND METHODS: A series of glycoPEGylated rFVIIa derivatives (5-40K PEG) has been produced and their effect and pharmocokinetics have been investigated in several animal species. RESULTS: The glycoPEGylated rFVIIa derivatives exhibit significant prolongation of half-life in mice, dogs and pigs as measured by rFVIIa clot activity. The clearance of rFVIIa, rFVIIa-5K PEG, rFVIIa-10K PEG, rFVIIa-20K PEG and rFVIIa-40K PEG in minipigs were estimated to 59, 27, 22, 8.7 and 3.1 ml/h/kg, respectively. Across species a reduction in clearance as a function of the size of the attached PEG was observed. By allometric scaling, the compiled pharmacokinetics predicts a human half-life for rFVIIa-10K PEG and rFVIIa-40K PEG of approximately 7 and 12h, respectively. The rFVIIa-10K PEG and rFVIIa-40K PEG are efficacious in stopping a bleed in the haemophilia A mouse tail-bleeding model after intravenous administration. CONCLUSIONS: GlycoPEGylation of rFVIIa significantly increases the rFVIIa exposure in three animal models, glycoPEGylated rFVIIa compounds are effective in vivo and thus, represents a potential prophylactic treatment option for patients with inhibitors.

Prolonged effect of GlycoPEGylated rFVIIa (40k-PEG-rFVIIa) in rabbits correlates to activity in plasma.

The pharmacokinetics and pharmacodynamics of 40k-PEG-rFVIIa, a GlycoPEGylated derivative of recombinant wild-type FVIIa, were compared with rFVIIa in rabbits. The procoagulant effect was determined as the weight of the clot formed in a defined segment of a facial vein. A time course study was conducted where ligation was made 10 minutes, 12 or 24 hours after i.v. injection of equimolar doses of 40k-PEG-FVIIa or rFVIIa (2 mg/kg). This dose was selected based on a dose response study and a duration of effect study with rFVIIa. The clot weight increased with increasing doses of rFVIIa, and the duration of effect correlated with the plasma FVIIa clot activity. The plasma half-life of 40k-PEG-rFVIIa measured as FVIIa clot activity was found to be 25 hours, which was 5-6 times longer than rFVIIa. The aPTT and PT were reduced, and the measured increase in thrombin-antithrombin correlated to the effect on clot formation. Thus, the effect was similar at ligation 10 minutes after administration of 40k-PEG-rFVIIa or rFVIIa. At 12 hours, the effect of rFVIIa was absent while significant effect was seen 12 and 24 hours post dosing with 40k-PEG-rFVIIa. No consumption of platelets or fibrinogen was found and no thrombi formation was seen in histological examination of various organs. In conclusion, 40k-PEG-rFVIIa has shown prolonged duration of effect that correlated to various plasma markers and FVIIa clot activity. In perspective, the data support further clinical development of 40k-PEG-rFVIIa to potentially become a long-acting recombinant treatment option for prophylaxis in haemophilia patients with inhibitors.