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.

Aim: NN1731 is a recombinant activated factor VII (rFVIIa) analogue with enhanced activity. The objective of the present study was to evaluate the clearance mechanisms of rFVIIa and NN1731 after intravenous administration to Beagle dogs.Methods: The study was performed in Beagle dogs administered with a single dose of 5.4 nmol/kg rFVIIa or NN1731 intravenously. Plasma samples collected up to 12-h post-administration were analysed using three different assays to determine FVIIa clot activity (FVIIa:C), total FVIIa antigen, and levels of FVIIa-antithrombin (AT) complexes. Pharmacokinetic parameters were determined by use of standard non-compartmental and non-linear mixed effects methods.Results: For both compounds, complex formation with AT accounted for the observed difference between the activity and the antigen curves and constituted 60-70% of the total clearance. The clearance of rFVIIa and NN1731 was estimated to be 73 and 214 mL/h/kg, respectively, accordingly, AT complex formation occurred around three times faster for NN1731. The difference in activity observed in the initial phase, resulting in distribution half-lives of 0.71 and 0.22 h for rFVIIa and NN1731, was mainly caused by the 3-fold difference in clearance. The terminal half-life of rFVIIa and NN1731 was estimated to be 2.1 and 2.5 h, respectively. The non-compartmental analysis resulted in almost identical parameters.Conclusion: The present study demonstrates that the difference between the activity and the antigen profiles of rFVIIa and NN1731 in Beagle dogs is the result of complex formation with AT which constitutes a major pathway for the clearance of rFVIIa activity. (C) 2011 Elsevier B.V. All rights reserved.

Abstract Abstract 1182 VWF protects FVIII from clearance in the circulation and is believed to ensure location of platelets to the site of injury. However, it is unknown if binding of FVIII to VWF has a role in localizing and thereby also facilitating the effect of FVIII in vivo. In the present study, a FVIII variant, FVIII-Y1680F, lacking the high affinity binding to VWF (Leyet et al. JCB 1991; 15; 740) was used to evaluate the binding of FVIII to VWF in clot formation hemophilia A mice in vivo. Binding of the FVIII variant to immobilized VWF was evaluated by surface plasmon resonance showing a 50–25 fold reduction in the Kd for FVIII-Y1680F compared to wt FVIII. Furthermore, pharmacokinetic studies in hemophilia A mice indicated that FVIII-Y1680F is basically devoid of VWF binding in vivo. The circulating half-life decreased from 7–8 hours for wt FVIII to 0.5 hours for FVIII-Y1680F (see figure) which is comparable to the half-life of wt FVIII in VWF knockout mice (0.5 hours). Using a chromogenic assay the specific activity of FVIII-Y1680F was 9200 IU/mg similar to that of wt FVIII confirming normal activity FVIII-Y1680F after cleavage with thrombin and removal of VWF. As the short half-life may influence the haemostatic effect of FVIII-Y1680F in vivo, a 40 kDa PEG moiety was attached to the O-glycan in the B-domain of the FVIII variant. This re-establishes the circulating half-life (6.1 hours) to that of wt FVIII without affecting the specific activity in vitro. The haemostatic effect of 40K-O-PEG FVIII-Y1680F was subsequently used to investigate if high affinity VWF binding of FVIII influences its haemostatic effect in vivo. The acute haemostatic effect of 40K-O-PEG-FVIII-Y1680F was compared to wt FVIII (Advate®) in the tail bleeding model in hemophilia A mice at doses equivalent to the 50% of the maximal effect and at maximal efficacy (20 and 280 IU/kg; Elm et al., Hemophilia 2011 epub). The blood loss was significantly reduced at both doses with comparable effect of 40K-O-PEG-FVIII-Y1680F and wt FVIII (see see figure, * indicates significant differences compared to vehicle treated hemophilia A mice). This indicates that the lack of VWF binding does not interfere with the haemostatic properties of FVIII in this particular model. To further support these data, the haemostatic effect of 40K-O-PEG-FVIII-Y1680F was tested in the FeCl3 injury model (2.5, 5 and 10 IU/kg) in hemophilia A mice. No clot formation was observed in vehicle mice and 40K-O-PEG-FVIII-Y1680F normalized dose dependently the clot formation time comparable to wt FVIII. In conclusion, the current data suggest that the haemostatic effect of FVIII in vivo is not dependent on high affinity binding of FVIII to VWF. Disclosures: Holmberg: Novo Nordisk A/S: Employment. Kjalke:Novo Nordisk A/S: Employment. Karpf:Novo NOrdisk A/S: Employment. Hilden:Novo Nordisk A/S: Employment. Pelzer:Novo Nordisk A/S: Employment. Koefoed-Hansen:Novo Nordisk A/S: Employment. Johnsen:Novo Nordisk A/S: Employment. Thim:Novo Nordisk A/S: Employment. Karlsson:Novo Nordisk A/S: Employment. Jespersgaard:Novo Nordisk A/S: Employment. Bolt:Novo Nordisk: Employment. Stennicke:Novo Nordisk A/S: Employment.

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.

Coagulation factors VII (FVII), IX (FIX), X (FX), and protein C share the same domain organization but display very different plasma half-lives. It is plausible that the half-life is influenced by the activation peptide, differing in length and glycosylation and missing in FVII. To test this hypothesis, the influence of activation peptides on the plasma half-life of human FVII was studied by administering human FVII variants containing activation peptide motifs to mice. Insertion of the activation peptide from FX gave 4-fold longer terminal half-life (5.5 hours vs 1.4 hours for FVII), whereas the activation peptide from FIX and protein C resulted in half-lives of 4.3 and 1.7 hours, respectively. Using FX's activation peptide we identified the N-linked glycans as structural features important for the half-life. The peptide location within the FVII molecule appeared not to be critical because similar prolongation was obtained with the activation peptide inserted immediately before the normal site of activation and at the C-terminus. However, only the latter variant was activatable, yielding full amidolytic activity and reduced proteolytic activity with preserved long half-life. Our data support that activation peptides function as plasma retention signals and constitute a new manner to extend the half-life of FVII(a).

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.

Summary The mechanism for the elimination of factor VII (FVII) from the circulation is unknown, just as it is unclear how activation of FVII to FVIIa and subsequent complex formation with antithrombin III (AT) or α2-macroglobulin (α2M) affects clearance. The possibility that the clearance mechanism involves activation and inhibitor complex formation as obligatory intermediate reactions is examined in this study. Human and murine sera were spiked with human FVIIa in the absence and presence of heparin and analysed for complex formation. Complex formation in vivo was studied after intravenous injection of 125I-VIIa in mice; and the pharmacokinetics (PK) of human and murine FVIIa was studied in normal mice. Furthermore, comparative PK studies were performed with FVII, FVIIa, active site blocked FVIIa and a preformed FVIIa-AT complex in normal and α2M-deficient mice. The data demonstrated that FVIIa-AT complexes and to a much lesser extent FVIIa-α2M-complexes accumulated in vivo after FVIIa administration. FVIIa-AT accounted for about 50% of total FVIIa antigen left in the circulation after 3 hours. All FVII derivatives studied including FVII, FVIIa and FVIIa-AT were cleared with similar rates suggesting an elimination kinetics which is unaffected by FVII activation and subsequent inactivation by plasma inhibitors.

The practical advantages of using the mouse in pharmacokinetic (PK) studies of human recombinant proteins are many and obvious. However, the relevance of studying human proteins in a mouse model is always questionable. The aims of the present study were i) to investigate if the mouse can be used as a model for PK studies of human FVIIa and FVIIa analogues by comparing the clearance of human recombinant FVIIa (hFVIIa) and murine recombinant FVIIa (mFVIIa), and ii) to study the roles of tissue factor (TF) in clearance of FVIIa. Eighteen NMRI mice were given a single intravenous 1 mg/kg dose of FVIIa or derivative containing trace amounts of iodinated FVIIa or derivative. Eye blood was sampled from anaesthetized mice in the interval of 0–8 h post administration. A sparse sampling schedule was employed in that three blood samples were taken pr. time point and three samples were drawn pr. mouse. The FVIIa plasma concentration was determined from the radioactivity measured by a γ-counter. The PK parameters were calculated by a 2-compartmental method using the WinNonlin software (Pharsight Corporation, USA), and the data was analyzed in one-way ANOVA test. The pharmacokinetic profile for both proteins was best determined by a 2-compartment analysis. The PK parameters obtained for the two proteins were statistically indistinguishable and showed a rapid distribution phase followed by a slower terminal half-life. The following values were obtained for hFVIIa and mFVIIa: T½ (distribution) was 0.38 h for hFVIIa and 0.71 h for mFVIIa, while a T½ (elimination) of 4.85 h was found for hFVIIa and 5.53 h for mFVIIa. Total clearance values of 34.7 ml/kg/h and 32.8 ml/kg/h were obtained for hFVIIa for mFVIIa, respectively. The volumes of distribution for the two proteins were also statistically indistinguishable, being 220.1 ml/kg for hFVIIa and 203.9 ml/kg for mFVIIa. No significant difference was thus observed between hFVIIa and mFVIIa in terms of the PK parameters including the terminal half-lives. These data might indicate that human FVIIa and murine FVIIa are cleared by the same mechanism(s) in mice, suggesting that the mouse is a valid model for PK studies of human FVIIa and derivatives thereof. The similar PK profiles for hFVIIa and mFVIIa observed further indicated a TF-independent clearance mechanism of FVIIa. Relative to mFVIIa the affinity of hFVIIa for mTF is known to be markedly decreased (Petersen LC et. al. Thromb Res.2005;116:75–85). Involvement of TF binding in clearance was therefore expected to result in different PK profiles for the two proteins; hence in a mouse model one would expect hFVIIa to be cleared at a much slower rate than mFVIIa. Since this was not the case, this study suggests a TF-independent mechanism of FVIIa clearance in mice. Our studies suggest that the mice can be used as a model to evaluate the PK profile of human FVIIa, and that TF is not involved in the clearance mechanisms of FVIIa.