Search

SummaryBackground Acquired thrombotic thrombocytopenic purpura (TTP) is caused by an autoantibody-mediated deficiency of the von Willebrand factor-cleaving protease ADAMTS-13. Acute episodes of the disease are treated with a combination of immunosuppression and repeated cycles of plasma exchange to remove anti-ADAMTS-13 autoantibodies and, at the same time, replenish functional ADAMTS-13. Although this is often effective, the mortality rate has remained between 10% and 20%, highlighting the need for safer treatment options. Objectives We previously showed that, in vitro, human recombinant ADAMTS-13 (rADAMTS-13) is able to override neutralizing antibodies and restore ADAMTS-13 activity in plasma from patients with acquired TTP. In the present study, we assessed the in vivo feasibility of this strategy by using a rat model. Methods Wild-type rats were adjusted to an ADAMTS-13 inhibitor (inhibitor) titer of ~ 10 BU mL−1 with goat anti-ADAMTS-13 IgG, and treated with increasing doses of rADAMTS-13. Blood samples were drawn and analyzed for ADAMTS-13-specific parameters, including FRETS-VWF73 activity, inhibitor, and ADAMTS-13-specific immune complexes (ICs). The pharmacokinetics of ADAMTS-13 activity and inhibitors were evaluated. Results Administration of inhibitor titer-adjusted doses of rADAMTS-13 to inhibitor-treated rats predictably restored activity. Inhibitors were readily neutralized through formation of ADAMTS-13-specific ICs, which were cleared at a higher rate than the free inhibitor. Surplus protease was enzymatically active in plasma, and showed similar pharmacokinetics to ADAMTS-13 in not inhibitor-treated rats. Conclusions Defined doses of rADAMTS-13 neutralized circulating anti-ADAMTS-13 antibodies and enabled reconstitution of ADAMTS-13 activity in plasma in our model, indicating that the protease may be a promising candidate for further exploration in treating acute episodes of acquired TTP.

Objective— The metalloprotease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) regulates the size of von Willebrand factor multimers. A deficiency in ADAMTS13 activity is associated with the life-threatening disease thrombotic thrombocytopenic purpura (TTP). The vast majority of patients have acquired TTP, where circulating anti-ADAMTS13 autoantibodies are causative for the decreased ADAMTS13 activity. Current treatment consists of plasma exchange, but improved therapies are highly warranted. Approach and Results— We have developed a new rat model mimicking various aspects of acquired TTP to investigate the therapeutic efficacy of human recombinant ADAMTS13. A polyclonal antibody against ADAMTS13 completely blocked endogenous rat ADAMTS13 activity in Sprague–Dawley rats. When TTP was triggered using recombinant von Willebrand factor, the animals displayed severe TTP-like symptoms, such as thrombocytopenia, hemolytic anemia, and von Willebrand factor–rich thrombi in the kidneys and brain. Subsequent injection of 400, 800, or 1600 U/kg recombinant ADAMTS13 prevented full development of these symptoms. Analysis of plasma samples confirmed that recombinant ADAMTS13 was able to override circulating anti-ADAMTS13 inhibitory antibodies, resulting in restoration of ADAMTS13 activity and degradation of ultralarge von Willebrand factor multimers. Conclusions— Recombinant ADAMTS13 was shown to be effective in averting severe acquired TTP-like symptoms in rats and holds promising value for the treatment of this severe and life-threatening disease in humans.

Introduction Acquired haemophilia A (AHA) is a rare, often severe, auto-immune bleeding disorder caused by the development of inhibitory antibodies (inhibitors) to factor VIII (FVIII). Bypassing agents, recombinant activated FVII or activated prothrombin complex concentrate, are currently recommended as first-line treatments to control bleeding events in patients with AHA. Aim A plasma-derived porcine FVIII (Hyate:C, Ipsen, UK) was used as a first-line treatment for AHA but was discontinued in 2004 due to viral safety concerns. A recombinant pFVIII (rpFVIII), Obizur (OBI-1; BAX801), which is expected to have a similar efficacy profile to Hyate:C but with a superior safety profile was developed and recently approved by the US Food and Drug Administration for the treatment of AHA. Methods Obizur manufacturing begins with the expression of B domain deleted rpFVIII by genetically modified baby hamster kidney-derived cells. The final purified and lyophilized drug product has a negligible risk of viral contamination and contains no animal-derived plasma proteins. Obizur was evaluated for immunogenicity, tolerability, pharmacokinetics and bleeding times in preclinical models including in haemophiliac dogs, cynomolgus monkeys and FVIII-knockout mice. Results Preclinical animal studies show that the efficacy and immunogenicity of Obizur are similar to that of Hyate:C and that Obizur has a more favourable safety profile. Conclusions Obizur is a highly purified recombinant porcine FVIII drug product that has been demonstrated to have a favourable safety and efficacy profile when compared with Hyate:C and can be a valuable treatment option for control of bleeding in AHA patients.

Nonacog gamma is a new recombinant factor IX to treat factor IX deficiency. It is indicated for control of bleeding episodes, perioperative management and routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and children with hemophilia B. Nonacog gamma was first approved in the USA in June 2013 under the trade name RIXUBIS followed by market approvals in Australia and the EU in 2014, and marketing authorization decision is pending in Japan. Nonacog gamma is derived from a recombinant Chinese hamster ovary cell line using a state of the art biotechnological manufacturing process. Recombinant factor IX is produced by Baxter's protein-free fermentation technology, which was first developed for ADVATE. The product is purified and formulated in the absence of any human or animal-derived protein. Nonacog gamma was characterized both in comprehensive in vitro and in vivo non-clinical studies as well as in an extensive clinical trial program.

Blood loss during hepatic surgery leads to poor patient outcomes. This study investigates the hemostatic efficacy of a novel sealing hemostatic pad (polyethylene glycol-coated collagen, PCC) and a fibrin sealant pad (fibrin-thrombin coated collagen, FTC) in a leporine hepatic segmentectomy and a porcine hepatic abrasion model. A segmentectomy was used to compare hemostatic success and hematoma incidence in 20 rabbits (10/group). Hepatic abrasions were used to compare hemostatic success up to 10 min after application in six pigs (42 lesions/group). In the segmentectomy model, PCC achieved 100% hemostatic success within 2 min (95% CI: 72.3% to 100%) and FTC achieved 80% hemostatic success within 3 min (49.0% to 94.3%). PCC had lower hematoma incidence at 15 min (0.0 versus 11.1%) and 24 h (20.0 versus 66.7%). In the abrasion model, PCC provided superior hemostatic success at 3 (odds ratio: 24.8, 95% CI: 8.86 to 69.2, P<0.001), 5 (66.3, 28.5 to 153.9, P<0.001), 7 (177.5, 64.4 to 489.1, P<0.001), and 10 min (777.6, 148.2 to 4078, P<0.001) leading to statistically significant less blood loss. The novel sealing hemostat provides faster and more sustained hemostasis than a fibrin sealant pad in a leporine hepatic segmentectomy and a porcine hepatic abrasion model of hepatic surgery.

Deficiency of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), a VWF-cleaving protease, is the key factor in the pathogenesis of thrombotic thrombocytopenic purpura (TTP), a life-threatening thrombotic microangiopathy. It is well established that ADAMTS13 deficiency results in elevated plasma levels of ultra-large VWF multimers (ULVWF), which are prone to induce platelet aggregation; however, the actual trigger of TTP development remains uncertain. Here we describe a new animal model in which some TTP-like symptoms can be triggered in ADAMTS13 knockout mice by challenge with 2000 units/kg body weight of recombinant human VWF containing ULVWF multimers. Animals rapidly showed clinical symptoms and developed severe thrombocytopenia. Schistocytosis, a decrease in hematocrit, and elevated serum lactate dehydrogenase levels were observed. The heart was identified as the most sensitive target organ with rapid onset of extensive platelet aggregation in the ventricles and myocardial necrosis. Prophylactic administration of 200 units/kg recombinant human ADAMTS13 protected ADAMTS13 knockout mice from developing TTP. Therapeutic administration of 320 units/kg rhADAMTS13 reduced the incidence and severity of TTP findings in a treatment interval-dependent manner. We therefore consider this newly established mouse model of thrombotic microangiopathy highly predictive for investigating the efficacy of new treatments for TTP.

The tail cut bleeding model (CUT) is routinely used in factor VIII-deficient mice to assess pharmacodynamic effects of therapeutic strategies for haemophilia A. Results from this model are highly variable, many modifications to the model are reported and at times the animals’ wellbeing may be compromised by recording survival as an endpoint. We therefore investigated if the ferric chloride carotid occlusion model (COM) used for thrombosis research can be applied to enhance data quality and animal welfare in haemophilia A research. Relative dose effects and relative dose variations were calculated for the CUT and COM. The requisite sample sizes were estimated and the importance of survival rates to assess rebleeds during recovery was evaluated by correlating initial blood loss to mortality. Relative dose effects increased with higher doses in both models. The COM was more sensitive at lower doses than the CUT, had up to 82% less variation across doses and clearly showed superior accuracy. Only 5% of the sample size required for the CUT would be needed to establish non-inferiority between a specific therapeutic dose in haemophilia A mice and healthy wild-type animals. A strong statistically significant correlation was found between initial blood loss and mortality within 24 h. Our findings clearly suggest that the COM is a valid tool for assessing haemophilia A treatment in vivo. The highly reproducible data means that significantly fewer animals are required and a more humane endpoint can be used by directly assessing clot stability instead of survival rate.

This study addresses the correlation of retinal topography with factors such as the visual environment, life style, and behavior for a major mammalian group, the artiodactyls. To provide a broader basis for semiquantitative comparison, short-wavelength-sensitive (S)- and middle-to-long-wavelength-sensitive (M)-opsin cone receptor populations from 25 species from five artiodactyl families and of the African elephant were labeled and sampled. The resulting topographic maps were analyzed with respect to the position and extension of high-density regions. For better parameter differentiation, systematic relationships were statistically normalized. In all species examined, two classes of cones have been detected. In most species, the S-cone maxima were located in the temporodorsal retina, but there are exceptions such as the roe deer with accumulation in the ventral retina. For M-cones, as a consequence of their role in terrain/food assessment and predator detection, the standard topography is L-shaped: a horizontal visual streak including a temporal area centralis is extended by a temporal rim. Its extension is correlated with the animal's body height (P = 0.0017): small species (pudu, mouse deer) tend to have a visual streak only, whereas the giraffe shows a complete dorsal arch of elevated densities. Furthermore, a size-independent habitat correlation was revealed for a similar M-cone pattern (P < 0.0001): mountainous species show a striking specialization around the dorsal retina, pointing to the importance of the inferior visual field in precipitous terrain.

*Departments of Pharmacology and Pediatrics, The University of Pennsylvania School of Medicine and the Division of Pediatrics,The Childrens Hospital of Philadelphia, Philadelphia, PA, USA; and Department of Experimental Pharmacology, TA Bio Therapeutics,Baxter BioScience, Vienna, AustriaTo cite this article: Greene TK, Schiviz A, Hoellriegl W, Poncz M, Muchitsch E-M, on behalf of the Animal Models Subcommittee of the Scientificand Standardization Committee of the ISTH. Towards a standardization of the murine tail bleeding model. J Thromb Haemost 2010; 8: 2820–2.

Baxter has developed a new recombinant factor IX (rFIX) drug product (BAX326) for treating patients with hemophilia B, or congenital FIX deficiency. An extensive preclinical program evaluated the pharmacokinetics, efficacy, and safety of BAX326 in different species. The efficacy of BAX326 was tested in three mouse models of primary pharmacodynamics: tail-tip bleeding, carotid occlusion, and thrombelastography. The pharmacokinetics was evaluated after a single intravenous bolus injection in mice, rats, and macaques. Toxicity was assessed in rats and macaques, safety pharmacology in rabbits and macaques, and immunogenicity in mice. BAX326 was shown to be efficacious in all three primary pharmacodynamic studies (P ≤ 0.0076). Hemostatic efficacy was dose related and similar for the three lots tested. Pharmacokinetic results showed that rFIX activity and rFIX antigen concentrations declined in a bi-phasic manner, similar to a previously licensed rFIX product. BAX326 was well tolerated in rabbits and macaques at all dose levels; no thrombogenic events and no adverse clinical, respiratory, or cardiovascular effects occurred. BAX326 was also shown to have a similar immunogenicity profile to the comparator rFIX product in mice. These results demonstrate that BAX326 has a favorable preclinical safety and efficacy profile, predictive of a comparable effect to that of the previously licensed rFIX in humans. Electronic supplementary material The online version of this article (doi:10.1007/s12185-013-1448-z) contains supplementary material, which is available to authorized users.

Coronary heart disease is a major cause of death in the western world. Although essential for successful recovery, reperfusion of ischemic myocardium is inevitably associated with reperfusion injury. To investigate a potential protective role of ADAMTS13, a protease cleaving von Willebrand factor multimers, during myocardial ischemia/reperfusion, we used a mouse model of acute myocardial infarction. We found that Adamts13−/− mice developed larger myocardial infarctions than wild-type control mice, whereas treatment of wild-type mice with recombinant human ADAMTS13 (rhADAMTS13) led to smaller infarctions. The protective effect of ADAMTS13 was further confirmed by a significant reduction of cardiac troponin-I release and less myocardial apoptosis in mice that received rhADAMTS13 compared with controls. Platelets adherent to the blood vessel wall were observed in few areas in the heart samples from mice treated with vehicle and were not detected in samples from mice treated with rhADAMTS13. However, we observed a 9-fold reduction in number of neutrophils infiltrating ischemic myocardium in mice that were treated with rhADAMTS13, suggesting a potent anti-inflammatory effect of ADAMTS13 during heart injury. Our data show that ADAMTS13 reduces myocardial ischemia/reperfusion injury in mice and indicate that rhADAMTS13 could be of therapeutic value to limit myocardial ischemia/reperfusion injury.

Memory B cells are involved in long-term maintenance of antibody-dependent immunologic disorders. Therefore, it is essential to understand how the restimulation of FVIII-specific memory B cells in hemophilia A with FVIII inhibitors is regulated. We asked whether concurrent activation of the innate immune system by an agonist for toll-like receptor (TLR) 7 is able to facilitate the differentiation of FVIII-specific memory B cells in the absence of T-cell help. TLR7 recognizes single-stranded RNA as contained in RNA viruses such as influenza, Sendai, and Coxsackie B viruses. Our results indicate that highly purified murine memory B cells do not differentiate into FVIII-specific antibody-secreting cells in the presence of FVIII and the TLR7 agonist when cultured in the absence of CD4+ T cells. However, CD11c+ dendritic cells facilitate the T cell–independent differentiation of FVIII-specific memory B cells but only in the presence of FVIII and the TLR7 agonist. In contrast to T cell–dependent restimulation, the antibody response after T cell–independent restimulation of FVIII-specific memory B cells is skewed toward IgG2a, an antibody subclass that is efficient in activating the complement system and in inducing Fc-receptor–mediated effector functions, both are required for effective immune responses against pathogens.

Replacement of the missing factor VIII (FVIII) is the current standard of care for patients with hemophilia A. However, the short half-life of FVIII makes frequent treatment necessary. Current efforts focus on the development of longer-acting FVIII concentrates by introducing chemical and genetic modifications to the protein. Any modification of the FVIII protein, however, risks increasing its immunogenic potential to induce neutralizing antibodies (FVIII inhibitors), and this is one of the major complications in current therapy. It would be highly desirable to identify candidates with a high risk for increased immunogenicity before entering clinical development to minimize the risk of exposing patients to such altered FVIII proteins. In the present study, we describe a transgenic mouse line that expresses a human F8 cDNA. This mouse is immunologically tolerant to therapeutic doses of native human FVIII but is able to mount an antibody response when challenged with a modified FVIII protein that possesses altered immunogenic properties. In this situation, immunologic tolerance breaks down and antibodies develop that recognize both the modified and the native human FVIII. The applicability of this new model for preclinical immunogenicity assessment of new FVIII molecules and its potential use for basic research are discussed.

Factor VIII (FVIII) is a critical component of the intrinsic coagulation pathway. Plasma-derived or recombinant (r) FVIII concentrates are used in patients with hemophilia A to provide a FVIII level sufficient to treat and prevent bleeding episodes. Prophylactic FVIII levels can only be maintained by administering several infusions per week. Extended FVIII circulation times would reduce the frequency of infusions, increase patient compliance, reduce the number of bleeds, and offer the possibility to achieve higher trough levels of FVIII. Prolonged circulation can be achieved by modifying the FVIII molecule with hydrophilic polymers, for example with polysialic acid (PSA). BAX 826, Baxalta's polysialylated FVIII is based on ADVATE, a full length recombinant FVIII molecule with an established extensive safety and efficacy profile. The aim of the presented studies was to assess the pharmacokinetic profile of BAX 826 in hemophilia A mice, wild-type rats, and cynomolgus monkeys. Unmodified rFVIII (ADVATE) was used as the reference compound. Test and reference compounds were administered at the same dose. Hemophilia A mice and Sprague Dawley rats were intravenously injected with BAX 826 at a target dose of 200 IU/kg rFVIII, and blood was sampled pre-dose and 5 min to 48 h after administration. Cynomolgus monkeys received a target dose of 350 IU/kg rFVIII and blood sampled 5 min to 120 h after administration. Citrated plasma was prepared and analyzed for FVIII activity (chromogenic), FVIII antigen (ELISA), and PSA-rFVIII concentration. The primary endpoint was area under the curve from administration time to the last quantifiable time point (AUC0-tlast). Mean residence time (MRT) and systemic clearance (CLs) were also assessed. Unless stated otherwise, results for FVIII activity (mice, monkeys) and FVIII antigen (rats) are presented. In mice, the AUC0-tlast for BAX 826 was 20.6 h*IU/mL, which was 2.4 times larger than for ADVATE (8.71 h*IU/mL); MRT was 10.6 h for BAX 826 and 5.8 h for ADVATE. Clearance was lower for BAX 826 (9.4 vs. 22.3 mL/h/kg). In rats, the AUC0-tlast for BAX 826 was 18.0 h*IU/mL, which was 1.8 times larger than for ADVATE (9.9 h*IU/mL). MRT was 12.5 h for BAX 826 and 4.0 h for ADVATE, and CLs was 5.3 and 28.1 mL/h/kg. In monkeys, the geometric mean of AUC0-tlast was 189.0 h*IU/mL for BAX 826 and 39.6 h*IU/mL for ADVATE. MRT was 23.4 and 10.1 h, and CLs was 2.25 and 6.72 mL/h/kg for BAX 826 and ADVATE, respectively. In monkeys, a baseline FVIII activity level was detected and adequately taken into account in calculating pharmacokinetic parameters. Nevertheless, to better follow the pharmacokinetic profile of BAX 826, the polysialylated rFVIII concentration was also assessed using a PSA specific assay. PSA-FVIII was measured in all animals after administration of BAX 826. In summary, pharmacokinetics studies in three animal species provided evidence that modification of ADVATE with PSA increases circulation time and exposure compared with the unmodified protein. Disclosures Schiviz: Baxalta Innovations GmbH: Employment. Hoebarth:Baxalta Innovations GmbH: Employment. Wolfsegger:Baxalta Innovations GmbH: Employment. Rossato:Baxalta Innovations GmbH: Employment. Weber:Baxalta Innovations GmbH: Employment. Gritsch:Baxalta Innovations GmbH: Employment. Rottensteiner:Baxalta Innovations GmbH: Employment. Turecek:Baxalta Innovations GmbH: Employment. Scheiflinger:Baxalta Innovations GmbH: Employment. Hoellriegl:Baxalta Innovations GmbH: Employment. Putz:Baxalta Innovations GmbH: Employment.

Introduction Tissue factor pathway inhibitor (TFPI) is an important inhibitor of the extrinsic coagulation pathway as it inhibits factor Xa (FXa) and the tissue factor (TF) – FVIIa complex. Inhibition of TFPI with blocking antibodies, aptamers, or peptide inhibitors improves hemostasis and may become an option to treat patients with hemophilia including those with inhibitors. We developed a TFPI-antagonistic fusion peptide (FP) consisting of a linear and a cyclic peptide connected by a linker. The two peptide entities bind to different epitopes on TFPI and together synergistically inhibit TFPI. The FP was further improved by half-life extending (HL) non-covalent albumin binding. HL-FP was characterized for in vitroinhibition of TFPI, pharmacokinetics, and improvement of coagulation in animal models of hemophilia. Methods HL-FP was characterized in a set of in vitro assays for binding to and inhibition of TFPI. Interaction with immobilized TFPI was studied by BiaCore. Functional inhibition was analyzed in model assay systems such as inhibition of FXa and FX activation by TF/FVIIa and plasma assays according to the calibrated automated thrombography (CAT) protocol at low TF in hemophilia plasma. Addition of TFPI simulated conditions of potentially elevated TFPI plasma concentrations. In a single dose PK study, mice (n=6 per time point) received 400 nmol/kg of the HL-FP intravenously (i.v.) or subcutaneously (s.c.). Plasma was sampled up to 38 h after dosing and HL-FP level quantified by a compound specific LC-MS protocol. To provide an ex vivo activity measure, FVIII inhibitory antibodies were added to mouse plasma to mimic a hemophilic condition and then analyzed by calibrated automated thrombography (CAT). A 2-week repeated i.v. dose study in mice investigated TFPI accumulation due to HL-FP. HL-FP was dosed at 40, 400, and 2000 nmol/kg and mouse plasma TFPI levels determined by ELISA. The efficacy of the HL-FP was studied in a hemophilia A mouse tail cut model and in a marmoset monkey model of ex vivoimprovement of coagulation. FVIII knockout mice (n=16 per group) were dosed i.v. with 12-400 nmol/kg HL-FP in the presence of a sub-therapeutic level of recombinant FVIII (10 U/kg) and blood loss (mg) was assessed. Marmoset monkeys (N=4) received 400 nmol/kg HL-FP i.v. and plasma samples obtained 1 h after dosing were analyzed by CAT in the presence of FVIII inhibitory antibodies. Results HL-FP bound to and efficiently inhibited TFPI as demonstrated in several in vitro test systems. Binding affinity of < 1nM correlated well with functional inhibition of TFPI in model assays, resulting in IC50s of ~0.7nM. The HL-fusion peptide (HL-FP) efficiently inhibited plasma TFPI, which resulted in an improvement of all thrombin generation parameters in plasma of hemophilia A and B patients, with EC50s ranging from 6 to 20nM. HL-FP increased peak thrombin levels of hemophilia plasma to or slightly above a range established for individual normal plasma. Non-covalent binding to albumin substantially increased the half-life to ~4 h with ~ 50% s.c. bioavailability in mice. The ex vivo procoagulant activity determined by CAT correlated well with HL-FP plasma concentrations. In the repeated dose study, the HL-FP was well tolerated and did not accumulate TFPI, which strongly indicates that HL-FP did not interfere with TFPI clearance receptor interactions. HL-FP significantly reduced bleeding in the hemophilia mouse tail cut bleeding model at a dose as low as 40 nmol/kg. In marmoset monkeys, HL-FP efficiently improved ex vivo plasma thrombin generation, even at low peptide plasma concentrations (25- 55 nM). Summary We developed a TFPI inhibitor composed of two TFPI antagonistic peptides that completely inhibits TFPI. Introduction of an entity non-covalently bound to albumin provides intermediate half-life extension and s.c. bioavailability. This HL-FP improved coagulation and hemostasis in animal models of hemophilia and did not interfere with TFPI clearance receptor interactions. TFPI-antagonistic peptides with a prolonged half-life, resistance to elevated TFPI, and minimal interference with TFPI clearance. Our HL-FP appears to be useful in preventing bleeding in hemophilia and provides a FVIII and FIX independent approach for non-i.v. treatment. Disclosures Dockal: Baxter Innovations GmbH, Vienna, Austria: Employment. Hartmann:Baxter Innovations GmbH, Vienna, Austria: Employment. Polakowski:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Panholzer:Baxter Innovations GmbH, Vienna, Austria: Employment. Kammlander:Baxter Innovations GmbH, Vienna, Austria: Employment. Osterkamp:3B Pharmaceuticals, Berlin, Germany: Employment. Reineke:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Schiviz:Baxter Innovations GmbH, Vienna, Austria: Employment. Hoellriegl:Baxter Innovations GmbH, Vienna, Austria: Employment. Scheiflinger:Baxter Innovations GmbH, Vienna, Austria: Employment.

Abstract 2216 Baxter is currently developing a recombinant ADAMTS13 (rADAMTS13, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) product for potential prophylaxis and treatment of thrombotic thrombocytopenic purpura (TTP). We established a disease model in ADAMTS13 ko mice (B6.129-ADAMTS13tm1Dgi), in which the animals simultaneously and consistently develop TTP-like symptoms by challenge with a high dose of human recombinant von Willebrand factor (rVWF) containing ultra-large VWF multimers. To test the prophylactic efficacy of Baxter's rADAMTS13, groups of 10 ADAMTS13 ko mice received single doses of rADAMTS13 (1, 5, 40, 80 or 200U/kg) before challenge with rVWF. Doses of 1 and 5mL/kg fresh frozen plasma corresponding to 1 and 5U/kg ADAMTS13 served as positive controls. In a second study, the prophylactic and therapeutic efficacy of Baxter's rADAMTS13 was tested over time. Groups of 10 ADAMTS13 ko mice received a single dose of 200 FRETS-U/kg rADAMTS13 5min-120h before, or 15–180min after challenge with rVWF. In both studies, buffer was used as a negative control. Efficacy was defined as the degree of prevention of platelet drop and LDH increase. Schistocytosis and organ damage were also assessed. Morbidity in negative controls was 100%: all animals receiving rVWF containing ultra-large VWF multimers were severely thrombocytopenic, showed increased LDH levels, schistocytosis and organ damage. Prophylactic treatment with rADAMTS13 prevented LDH increase (p Efficacy of rADAMTS13 was treatment interval-dependent in both studies. Platelet count at termination of all rADAMTS13-treated animals was statistically higher than that of buffer-treated controls (p≤0.0001). However, animals receiving prophylactic treatment 120h before administration of rVWF showed severe thrombocytopenia; clinically relevant protection was only seen with treatment intervals ≤72h. Therapeutic treatment with rADAMTS13 stabilized platelet count and prevented further thrombocytopenia. LDH, schistocytosis and organ damage confirmed the treatment interval-dependent improvement in platelet count. In summary, Baxter's rADAMTS13 was effective in an rVWF-induced animal model closely mimicking the situation in patients with hereditary TTP. Comparison with FFP, the current standard of treatment of TTP, showed Baxter's rADAMTS13 to have similar or slightly improved efficacy. Disclosures: Schiviz: Baxter Innovations GmbH: Employment. Resch:Baxter Innovations GmbH: Employment. Farnleitner:Baxter Innovations GmbH: Employment. Rottensteiner:Baxter Innovations GmbH: Employment. Schwarz:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Muchitsch:Baxter Innovations GmbH: Employment.

Abstract 2233 Baxter has developed a new recombinant factor IX (rFIX) product (BAX 326) for treating patients with hemophilia B. The aim of the presented studies was to evaluate the function, safety and efficacy of BAX 326 compared to a commercially available rFIX regarding differences in activated FIX (FIXa) content. The FIXa concentration of BAX 326 was about 10 fold less than that of a commercial rFIX product. To address the influence of FIXa on functional FIX in vitro assays, the FIXa concentration of BAX 326 was increased. Samples were analyzed by one-stage clotting assay, non-activated partial thromboplastin time assay and thrombin generation assay. In all three assays, FIXa affected the potency determination for FIX, indicating that rFIX products should preferentially contain a low FIXa content. The thrombogenic potential of BAX 326 was assessed in rabbits using a modified Wessler Test at 750 IU/kg (10-fold human clinical dose). No thrombogenic potential was observed with BAX 326 (individual scores of 0), whereas the mean score for the commercially available rFIX was 0.5. After increasing the FIXa concentration of BAX 326 to equalize it with the commercially available rFIX, a mean score of 0.42 (individual scores 0 – 0.5) was determined. These data strongly suggest that the differences in preclinical thrombogenicity were caused by the higher FIXa content of the commercially available rFIX, thereby confirming earlier findings [1]. Efficacy of the rFIX products was studied in hemophilia B (FIX ko) mice that received prophylactic treatment with 75 IU/kg of BAX 326 or the commercially available rFIX. Treated animals were analyzed in two primary pharmacodynamic models: a carotid occlusion model and one using thrombelastography. In both models, results for the two groups were similar, demonstrating that despite its lower FIXa content, BAX 326 was as efficacious as a commercially available rFIX at 75 IU/kg (p Disclosures: Auer: Baxter Innovations GmbH: Employment. Rottensteiner:Baxter Innovations GmbH: Employment. Schrenk:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Schiviz:Baxter Innovations GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment. Schwarz:Baxter Innovations GmbH: Employment. Turecek:Baxter Innovations GmbH: Employment. Muchitsch:Baxter Innovations GmbH: Employment.

Abstract 4346 The pharmacokinetic profile of BAX 855, a longer acting PEGylated variant of Baxter’s recombinant FVIII based on the ADVATE™ manufacturing process, was assessed in comparison to ADVATE™ after a single intravenous bolus injection at a target dose of 200 IU/kg BW in mice and rats and 350 IU/kg BW in cynomolgus monkeys. Mean residence time (MRT), terminal half-life (HL), total clearance standardized per kg body mass (Cl), the AUC0-tlast (the area under the concentration vs. time curve from 0 to the last measured time point), the in vivo recovery (IVR) and volume of distribution at steady state (Vss) for FVIII activity (mice and cynomolgus monkey), FVIII antigen (rats) and FVIII-bound PEG were evaluated in all three models. Blood was sampled at baseline and each of the time points after a single intravenous bolus injection of BAX 855 or ADVATE™. A serial sacrifice design was used for the PK in mice. Sixteen FVIII ko mice (B6;129S4-F8tm2Kaz; m/f) for BAX 855 and eight FVIII ko mice for ADVATE™ per time point were bled by cardiac puncture under anesthesia for blood sampling 5 minutes – 48 hours after a single intravenous bolus injection. A single treatment design was used for the single dose PK in Sprague Dawley rats: 8m + 8f for BAX 855 and 4m + 4f for ADVATE™. A single treatment design was also used for the cynomolgus monkeys: 4m + 4f for BAX 855 and 2m + 2f for ADVATE™. Blood samples were drawn from rats and cynomolgus monkeys for citrated plasma (for analysis of baseline FVIII levels) before administration and 5 minutes - 48 hours (rats) and 5 minutes to 96 hours (cynomolgus monkeys) after administration. The citrated plasma samples were analyzed for FVIII activity (chromogenic assay) in mice and cynomolgus monkeys, for FVIII–bound PEG (using a PEG-FVIII ELISA) in all models and FVIII antigen (using a FVIII ELISA) in rats. In all three models a prolongation in MRT of Baxter’s and Nektar’s new BAX 855 compared with ADVATE™ could be demonstrated. FVIII activity analysis showed an increase of MRT in mice from 4.9 to 7.9 hours and in cynomlogus monkeys from 7.5 to 11.5 hours. This prolongation was also reflected in the terminal half-lives (4.3 to 5.9 hours in mice and 5.7 to 9.4 hours in cynomolgus monkeys). According to this prolongation a lower clearance [mL/h/kg] could be observed for BAX 855 than for ADVATE™ (22.1 to 12.2 in mice and 8.1 to 4.9 in monkeys). Similar levels in all PK parameters could be shown when measuring FVIII-bound PEG in all three preclinical models and FVIII antigen analysis in rats. These PK data provide evidence that PEGylation of human rFVIII increases the circulation time. Disclosures: Hoebarth: Baxter Innovations GmbH: Employment. Kubik:Baxter Innovations GmbH: Employment. Wolfsegger:Baxter Innovations GmbH: Employment. Lawo:Baxter Innovations GmbH: Employment. Weber:Baxter Innovations GmbH: Employment. Gritsch:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Schiviz:Baxter Innovations GmbH: Employment. Ehrlich:Baxter Innovations GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment. Turecek:Baxter Innovations GmbH: Employment. Schwarz:Baxter BioScience: Employment. Muchitsch:Baxter Innovations GmbH: Employment.

Abstract 24 Tissue factor pathway inhibitor (TFPI) is an activated (a) factor X (FXa)-dependent inhibitor of the extrinsic factor X (FX) activation complex and efficiently regulates the extrinsic pathway of coagulation. We are developing peptide inhibitors of TFPI with a view to improving hemostasis in hemophilia. The goal is to inhibit the interaction of TFPI with the factor Xa (FXa)-tissue factor (TF)-factor VIIa (FVIIa) complex, and thereby enhance thrombin formation to the extent that a stable clot is formed. Successful development of these peptides could allow treatment of hemophilia via a non-intravenous route of administration. By screening mRNA display libraries, we identified a de novo peptide which binds to and efficiently inhibit TFPI. The peptide was optimized by iterative amino acid substitution resulting in affinity-improved peptide with a well-characterized structure-activity relation. The affinity of the peptide was analyzed by Biacore and ELISA experiments. One of our optimized peptides bound to immobilized TFPI with an affinity below 1 nM. Kunitz domain 1 of TFPI was identified as the interaction site by NMR studies. We characterized the inhibitory activity of this TFPI binding peptide using in vitro model assay systems including inhibition of FXa and of the extrinsic tenase (TF-FVIIa-PL-Ca2+ complex). Inhibition of cell-associated TFPI was verified in a TF- and TFPI-dependent cell-based assay using TNFalpha-stimulated human umbilical vein endothelial cells (HUVECs) as a source of TF and TFPI. Inhibition of plasma TFPI was probed by thrombin generation experiments using FVIII-deficient patient plasma and ROTEM experiments using FVIII-inhibited whole blood. Furthermore, a cross-reactivity of the peptide to murine TFPI was demonstrated in thrombin generation experiments and in murine FXa inhibition model assays. Conjugation of a 40-kDa polyethyleneglycol (PEG) to the peptide base structure resulted in a peptide with significantly reduced renal clearance. The in vivo terminal half-life of this 40kD-PEG modified peptide was 21.5h and 19.8h after 1 mg/kg i.v and s.c. administration, respectively, with 73% bioavailability after s.c. administration. In a tail-tip bleeding model, administration of an anti-murine-TFPI antibody and 40kD-PEG-peptide in combination with sub-therapeutical doses of recombinant coagulation factors (10 IU/kg of rFVIII in FVIII ko mice and rFIX in FIX ko mice) led to a marked reduction of blood loss compared with buffer-treated or rFVIII/rFIX-treated mice. In addition, we established a murine nail-cut model using C57Bl6 wild-type mice for testing in vivo efficacy in a normal FVIII background as well. The TFPI sensitivity of the nail-cut model was verified by an anti-murine TFPI antibody. 40kD-PEG-peptide significantly reduced blood loss after i.v. and s.c. administration in all treatment groups compared with vehicle-treated animals. Furthermore, the i.v. administration of the peptide was well tolerated in all animals across all treatment groups without any signs of acute toxicity. In conclusion, we identified a low-molecular-weight peptide which efficiently inhibit all forms of naturally occurring TFPI proteins, including plasma TFPI and TFPI in vivo. Our results demonstrate that targeting TFPI efficiently improves hemostasis in hemophilia and provide an in vivo proof of concept for a non i.v. route of administration. Thus, the TFPI inhibitory peptides could be useful to prevent bleeding in hemophilia patients. Moreover, this new approach would probably allow treatment of inhibitor patients. Disclosures: Dockal: Baxter Innovations GmbH: Employment. Hartmann:Baxter Innovations GmbH: Employment. Polakowski:3B Pharmaceuticals GmbH: Employment. Frank:3B Pharmaceuticals GmbH: Employment. Ehrlich:Baxter Innovations GmbH: Employment. Schiviz:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Muchitsch:Baxter Innovations GmbH: Employment. Reinecke:3B Pharmaceuticals GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment.

Abstract 4350 Factor VIII (FVIII) is a critical component of the intrinsic coagulation pathway. FVIII concentrates are used in patients with hemophilia A to provide a hemostatic FVIII level sufficient to treat and prevent bleeding episodes. Multiple prophylactic administrations per week are necessary to maintain a FVIII level of at least 1% of normal to effectively prevent or reduce spontaneous bleeding episodes. A longer acting FVIII concentrate would reduce the frequency of infusions. Baxter and Nektar have developed a longer-acting PEGylated variant (BAX 855) of Baxter’s recombinant FVIII (ADVATE process). The aim of the presented studies was to evaluate the efficacy of BAX 855 in two primary pharmacodynamics in hemophilia A mice: a tail-tip bleeding model (TTBM) and a carotid occlusion model (COM). BAX 855 was tested at a dose of 200 IU/kg rFVIII. ADVATE™ served as the active reference item, and formulation buffer as the negative control item. Mice received intravenous treatment with either BAX 855 or ADVATE™ 12–40h prior to the experiment. Buffer was administered 5–15min prior to the experiment. Animals were anesthetized using ketamine and xylazine. In the TTBM (n=16) the tip of the tail was cut off and total blood loss [mg] was assessed over 60 minutes. In the COM study (n=10) the left carotid artery was exposed and the endothelium was denuded by topical application of FeCl3. Time to occlusion [min] was assessed. Buffer-treated animals had a median blood loss of 951 mg in the TTBM and did not show vessel occlusion within 30 min in the COM. In the TTBM, a prophylactic effect of ADVATE™ could be observed for up to 18 h, leading to a reduction in blood loss to 121 mg after this treatment interval. Prophylactic efficacy after treatment with BAX 855 could be observed for up to 40 h with a median blood loss of 73 mg after 30 h and 436 mg after 40 h. In the COM, treatment with ADVATE™ 12 h before the experiment shortened the time to occlusion to 3.8 min. With BAX 855, a similar efficacy could be observed for up to 24 h after administration (5.2 min). In summary, the results of our studies show that BAX 855 is efficacious in these two mouse models of hemophilia A and that the efficacy of BAX 855 is prolonged compared with an unmodified rFVIII. Furthermore, the intravenous injection of BAX 855 was well tolerated in all animals across all treatment groups without any signs of acute toxicity. Disclosures: Schiviz: Baxter Innovations GmbH: Employment. Barbara:Baxter Innovations GmbH: Employment. Lawo:Baxter Innovations GmbH: Employment. Ehrlich:Baxter Innovations GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment. Turecek:Baxter Innovations GmbH: Employment. Schwarz:Baxter Innovations GmbH: Employment. Muchitsch:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment.

Abstract 2262 Fucoidans are sulfated polysaccharides extracted and purified from brown seaweeds. Described as non-anticoagulant polysaccharides (NASPs), they have been shown to improve clotting in FVIII- and FIX-deficient plasma (Liu et al. Thromb Haemost 2006;95:68), making them good candidates for hemophilia treatment. NASP orally administered to hemophilia A dogs over several weeks resulted in correction to normal ranges in thromboelastography (TEG) parameters and improvement of the cuticle bleeding time (Prasad et al. Blood 2008;111:672). We screened extracts of eleven brown algae species to select the most active, high-quality, homogeneous fucoidan. In-depth structural analysis and assessment of the pro-/anticoagulant and TFPI-inhibiting activities of a selected set of fucoidan preparations was performed. The effect of the best fucoidan candidate was studied in a novel guinea pig model by whole blood TEG monitoring supported by calibrated automated thrombographic (CAT) analysis. Comparative structural studies of fucoidans included monosaccharide composition and elemental analysis, molecular weight and overall structural determination by NMR. 13C-NMR spectroscopy gave a comprehensive picture of fucoidan structure including fucose and alginate content and the relative heterogeneity of the preparation distinguishing between fucoidans of different algae species. Heterogeneity of the materials was highest in U. pinnatifida and L. japonica and lowest in F. vesiculosus (F.v.) samples. Procoagualant activity was shown by CAT and rotation thromboelastometry. Clotting parameters of FVIII-inhibited human blood or plasma were corrected to normal levels at 1 and 3 μg/mL depending on the fucoidan. In addition, the fucoidans were analyzed by BiaCore and a modified dilute prothrombin time assay to show binding to TFPI and inhibition of full-length TFPI activity. The screening process supported the identification and optimization of new fucoidan-specific analytical methods. Furthermore, a CAT protocol optimized for guinea pig plasma was used to show the procoagulant effect of the overall best fucoidan candidate. We spiked F.v. fucoidan into FVIII-inhibited guinea pig plasma between 1 and 100μg/mL and triggered thrombin generation with low amounts of tissue factor. The FVIII-inhibited guinea pig plasma was corrected to normal CAT parameters at ∼30μg/mL NASP. Based on our findings in the CAT assay, we designed a dosage pattern for studying the procoagulant effect using TEG in FVIII-inhibited Dunkin Hartley guinea pigs (n=10) after intravenous administration of 0.1 to 1.6mg/kg NASP. The primary endpoint assessed was R-time (time to clotting). FVIII-inhibited guinea pigs showed a median R-time of ≥120min (no clotting), while R-time was reduced in a non-linear dose-dependent manner after administration of NASP down to 69min (0.4mg/kg NASP). Thus, the results generated in in vitro tests, were confirmed in vivo. This new animal model of induced hemophilia will support the development of alternative hemophilia therapeutics. Disclosures: Dockal: Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Zhang:Baxter Healthcare Corporation: Employment. Till:Baxter Innovations GmbH: Employment. Knappe:Baxter Innovations GmbH: Employment. Palige:Baxter Innovations GmbH: Employment. Schiviz:Baxter Innovations GmbH: Employment. Ehrlich:Baxter Innovations GmbH: Employment. Szabo:Baxter Healthcare Corporation: Employment. Muchitsch:Baxter Innovations GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment.

Abstract 4659 Baxter has developed a recombinant FVIIa (rFVIIa) product for the treatment of patients with hemophilia A and hemophilia B with inhibitors. The aim of the presented preclinical studies was to evaluate the efficacy of Baxter's rFVIIa. Four animal models that are considered to relevantly reflect the conditions in different patient populations were used: hemophilia A (FVIII ko) mice, hemophilia B (FIX ko) mice, factor VIII (FVIII)-inhibited rabbits and warfarin-pretreated rats. In all studies, Baxter's rFVIIa was tested at different doses to obtain dose-effect curves. A commercially available rFVIIa served as the active control item, buffer served as the negative control item. All test and control items were administered intravenously. Mice received prophylactic treatment 5 minutes prior to start of the experiment, rabbits and rats received therapeutic treatment after the injuries were inflicted. Twenty FVIII ko mice (B6;129S4-F8tm1Kaz; 10m/10f) and 20 FIX ko mice (B6;129P2-F9tm1Dws; 10m/10f) per group were used in a tail-tip bleeding model. Baxter's rFVIIa was tested at doses of 0.6, 1.2 and 2.7 mg/kg, the active control item was tested at a dose of 2.7 mg/kg. Ten FVIII ko mice (B6;129S4-F8tm1Kaz; 5m/5f) per group were used to assess the influence of rFVIIa on the thrombelastogram of hemophilic mice. Both items were tested at doses of 0.1, 0.6 and 1.2 mg/kg. Six rabbits (New Zealand White; 6m) per group were used in a nail-cut model. The animals were pretreated with a goat polyclonal FVIII-antibody (34,000 BU/kg i.v., 45 minutes prior to start of the experiment), leading to deficiency of endogenous FVIII. Baxter's new rFVIIa was tested at doses of 0.1, 1.0, 2.0, 2.5 and 3.0 mg/kg, the active control item at 2.0 mg/kg. Six rats (Sprague Dawley; 6m) per group were used in a tail-tip bleeding model. The animals were pretreated with warfarin (11 mg p.o., 1 day prior to start of the experiment), leading to a deficiency of vitamin K-dependent coagulation factors II, VII, IX and X, protein C and protein S. Baxter's new rFVIIa was tested at 0.25, 1.0 and 2.0 mg/kg, the active control item at 2.0 mg/kg. A dose-dependent hemostatic effect of Baxter's new rFVIIa could be shown in all primary pharmacodynamic studies performed. Furthermore, statistical evaluation of the efficacy of Baxter's new rFVIIa did not reveal any statistically significant differences from the commercially available rFVIIa product after treatment at the same doses. In summary, the results of our studies show that Baxter's new rFVIIa is prophylactically and therapeutically effective in animal models of efficacy closely reflecting the conditions in hemophiliacs with inhibitors and patients suffering from FVII-deficiency. Disclosures: Schiviz: Baxter Innovations GmbH: Employment. Lawo:Baxter Innovations GmbH: Employment. Resch:Baxter Innovations GmbH: Employment. Leidenmuehler:Baxter Innovations GmbH: Employment. Bischetsrieder:Baxter Innovations GmbH: Employment. Ehrlich:Baxter Innovations GmbH: Employment. Scheiflinger:Baxter Innovations GmbH: Employment. Schwarz:Baxter Innovations GmbH: Employment. Hoellriegl:Baxter Innovations GmbH: Employment. Muchitsch:Baxter Innovations GmbH: Employment.

Purpose: Currently available hemostatic pads are effective in treating oozing bleeds, but otherwise ineffective in more severe bleeding. This study investigates the hemostatic efficacy of a new hemostatic pad with advanced sealing properties using protein-reactive polyethylene glycol-coated collagen (PCC, Hemopatch) versus an oxidized regenerated cellulose (ORC, Tabotamp/Surgicel Original) in a leporine arterial bleeding model of vascular reconstruction and a porcine hepatic model of general surgery. Methods: In both models, paired lesions were created and treated according to a randomized scheme and evaluated up to 10 min after application (40 lesions/group/model). Arterial needle holes were created in the femoral arteries of anesthetized rabbits and hepatic lesions were created into hepatic parenchyma of anesthetized pigs. Both models were heparinized to mimic clinical comorbidity. Results: In the leporine vascular surgical model, PCC provided superior hemostatic success compared to ORC at 2 min (Odds Ratio of Success: 85, 95% CI: 25.8–282) and similar hemostatic success at 10 min. In the porcine hepatic model, PCC provided superior hemostatic success compared to ORC at 2 (98 vs 55%, P