Safety, pharmacokinetics, and immunogenicity of single-dose rFXIII administration to healthy volunteers

Factor XIII and surgical bleeding. A narrative review

FXIII is the final factor in the coagulation cascade. It converts soluble fibrin monomers into a stable fibrin clot, prevents premature degradation of fibrin, participates in wound healing, and helps prevent the loss of the endothelial barrier function. FXIII deficiency is believed to be rare, and this may explain why clinicians do not routinely take it into consideration. Congenital FXIII deficiency is a rare disease with a reported prevalence of 1 per million. However, the prevalence of acquired FXIII deficiency is much higher. Acquired forms have been described in patients with decreased hepatic or bone marrow synthesis, hyperconsumption and increased degradation by autoantibodies. This review offers guidance on how to suspect and diagnose FXIII deficiency in both the preoperative consultation and different surgical settings. We also analyze current scientific evidence in order to clarify when and why this clinical situation should be suspected, and how it may be treated.

Long-term prophylaxis in patients with severe congenital factor XIII deficiency is not complicated by inhibitor formation

: Congenital factor XIII (FXIII) deficiency is a rare bleeding disorder accompanied by a variety of bleeding events. Severely deficient patients require regular replacement therapy. With development of FXIII concentrate, the risk of viral infections transmitted by fresh frozen plasma and cryoprecipitate is diminished, but the possibility of inhibitor development remains a challenging issue in the management of these patients. The aim of this study was to assess FXIII inhibitor development in Iranian patients with FXIII deficiency (FXIIID). This study enrolled 50 (30 women and 20 men) patients with severe congenital FXIIID from southeast Iran who underwent long-term (more than 4 years or more than 50 injections) prophylaxis with FXIII concentrate (Fibrogammin P, Dade Behring, Marburg, Germany). We evaluated plasma FXIII activity and FXIII inhibitor on day 28 after the last prophylaxis administration. The method for investigation of FXIII inhibitor was based on Bethesda assay. The mean age of the study population was 13.8 ± 8.3 years. The minimum and maximum FXIII activity levels were less than 1-4.5% (mean ± SD, 2.6 ± 0.7%). Our investigations showed that all patients with severe form of FXIIID were treated without inciting inhibitor development. Despite long-term prophylaxis in the studied patients, none was found to have developed FXIII inhibitors.

Safety of Recombinant Human Factor XIII in a Cynomolgus Monkey Model of Extracorporeal Blood Circulation

Factor XIII (FXIII) is a thrombin-activated plasma coagulation factor critical for blood clot stabilization and longevity. Administration of exogenous FXIII to replenish depleted stores after major surgery, including cardiopulmonary bypass, may reduce bleeding complications and transfusion requirements. Thus, a model of extracorporeal circulation (ECC) was developed in adult male cynomolgus monkeys ( Macaca fascicularis) to evaluate the nonclinical safety of recombinant human FXIII (rFXIII). The hematological and coagulation profile in study animals during and after 2 h of ECC was similar to that reported for humans during and after cardiopulmonary bypass, including observations of anemia, thrombocytopenia, and activation of coagulation and platelets. Intravenous slow bolus injection of 300 U/kg (2.1 mg/kg) or 1000 U/kg (7 mg/kg) rFXIII after 2 h of ECC was well tolerated in study animals, and was associated with a dose-dependent increase in FXIII activity. No clinically significant effects in respiration, ECG, heart rate, blood pressure, body temperature, clinical chemistry, hematology (including platelet counts), or indicators of thrombosis (thrombin:antithrombin complex and D-Dimer) or platelet activation (platelet factor 4 and beta-thromboglobulin) were related to rFXIII administration. Specific examination of brain, heart, lung, liver, and kidney from rFXIII-treated animals provided no evidence of histopathological alterations suggestive of subclinical hemorrhage or thrombosis. Taken as a whole, the results demonstrate the ECC model suitably replicated the clinical presentation reported for humans during and after cardiopulmonary bypass surgery, and do not suggest significant concerns regarding use of rFXIII in replacement therapy after extracorporeal circulation.

Preclinical Safety and Pharmacokinetics of Recombinant Human Factor XIII

Factor XIII (FXIII) is a thrombin-activated protransglutaminase responsible for fibrin clot stabilization and longevity. Deficiency in FXIII is associated with diffuse bleeding and wound-healing disorders in humans. This report summarizes results from several studies conducted in adult cynomolgus monkeys ( M. fascicularis) to evaluate the safety and pharmacokinetics of recombinant human factor XIII A2 dimer (rFXIII). Intravenous slow bolus injection of rFXIII resulted in the expected formation of the heterotetramer rA2cnB2, prolonged circulating half-life (5–7 days), and increased plasma transglutaminase activity. Recombinant FXIII was well tolerated as a single dose up to 20 mg/kg rFXIII (2840 U/kg), as repeated daily doses up to 6 mg/kg (852 U/kg) for 14 days, and as 3 repeated doses of 8 mg/kg (1136 U/kg) separated by 14 days. Overt toxicity occurred after a single intravenous injection of ≥ 22.5 mg/kg rFXIII (3150 U/kg), or with 2 doses of =12.5 mg/kg (1775 U/kg) administered within 72 hours. The rFXIII-mediated toxicity was expressed as an acute systemic occlusive coagulopathy. Evaluation of plasma samples from dosed animals demonstrated formation of cross-linked fibrin/fibrinogen oligomers and higher-order protein aggregates, which are hypothesized to be responsible for the observed vessel occlusion and associated embolic sequelae. These results demonstrate that rFXIII-mediated toxicity results from exaggerated pharmacological activity of the molecule at supraphysiological concentrations. The absence of observed toxicological effect with repeated intravenous doses up to 8 mg/kg (1136 U/kg) was used to support an initial clinical dose range of 0.014 to 0.35 mg/kg (2–50 U/kg).

Pharmacokinetics of recombinant factor XIII at steady state in patients with congenital factor XIII A-subunit deficiency

BACKGROUND

The use of monthly recombinant factor XIII (rFXIII) recently demonstrated favorable safety and efficacy for congenital FXIII A-subunit deficiency patients aged ≥ 6 years (mentor(™) 1 trial), although the pharmacokinetics (PK) were not fully evaluated.

OBJECTIVES

To comprehensively evaluate the steady-state PK of rFXIII in patients aged ≥ 6 years with congenital FXIII A-subunit deficiency.

PATIENTS/METHODS

mentor(™) 2 is an ongoing, multinational safety and efficacy trial in which patients are receiving monthly rFXIII (35 IU kg(-1) ) for ≥ 52 weeks. For this 28-day PK analysis, blood samples were collected immediately predosing, and 1 h, 2 h, 3, 7, 14, 21, and 28 days postdosing. FXIII activity was measured and PK parameters were calculated using non-compartmental analysis, without prior baseline adjustment. Information regarding adverse events and bleeding was collected at each visit. Antibody assessments were performed predosing and at day 28.

RESULTS

PK analysis in 23 patients revealed first-order elimination of rFXIII with a geometric mean half-life of 13.6 days. Mean FXIII activity was > 0.1 IU mL(-1) throughout the 28-day period, with a geometric mean peak activity of 0.87 IU mL(-1) and trough of 0.16 IU mL(-1) . The geometric mean clearance was 0.15 mL h(-1) kg(-1) . No bleeding episodes occurred during the PK session, and no anti-rFXIII antibodies were detected. Peak and trough FXIII activities were constant over time, compared with previous activities (≥ 10 rFXIII doses) in the same patients.

CONCLUSIONS

Clearance of rFXIII is unaffected over time, and monthly prophylaxis with 35 IU kg(-1) rFXIII provides FXIII activity > 0.1 IU mL(-1) throughout the dosing interval in patients with congenital FXIII A-subunit deficiency.

Coagulation factor XIII deficiency. Diagnosis, prevalence and management of inherited and acquired forms

The plasma circulating zymogenic coagulation factor XIII (FXIII) is a protransglutaminase, which upon activation by thrombin and calcium cross-links preformed fibrin clots/fibrinolytic inhibitors making them mechanically stable and less susceptible to fibrinolysis. The zymogenic plasma FXIII molecule is a heterotetramer composed of two catalytic FXIII-A and two protective FXIII-B subunits. Factor XIII deficiency resulting from inherited or acquired causes can result in pathological bleeding episodes. A diverse spectrum of mutations have been reported in the F13A1 and F13B genes which cause inherited severe FXIII deficiency. The inherited severe FXIII deficiency, which is a rare coagulation disorder with a prevalence of 1 in 4 million has been the prime focus of clinical and genetic investigations owing to the severity of the bleeding phenotype associated with it. Recently however, with a growing understanding into the pleiotropic roles of FXIII, the fairly frequent milder form of FXIII deficiency caused by heterozygous mutations has become one of the subjects of investigative research. The acquired form of FXIII deficiency is usually caused by generation of autoantibodies or hyperconsumption in other disease states such as disseminated intravascular coagulation. Here, we update the knowledge about the pathophysiology of factor XIII deficiency and its therapeutic options.

Pharmacokinetics of recombinant factor XIII in young children with congenital FXIII deficiency and comparison with older patients

Congenital factor XIII (FXIII) deficiency is a rare bleeding disorder, which in its severe form is associated with a significant bleeding phenotype, requiring regular prophylactic therapy. A recently developed recombinant FXIII (rFXIII) has demonstrated safety and efficacy in children aged ≥6 years and adults (mentor1 trial). This article describes the mentor4 trial, which has assessed the pharmacokinetics (PK) and safety of rFXIII in younger children (1 to <6 years) with congenital FXIII deficiency, and compares extrapolated PK parameters with the mentor1 trial. Six children with congenital FXIII A-subunit deficiency received a single, 35 IU kg(-1) rFXIII dose. PK properties were similar in all the children, with a mean area under the concentration vs. 30-day time curve of 248.6 IU h(-1) mL(-1) , maximal FXIII activity (30 min) of 0.67 IU mL(-1) , and mean 30-day trough of 0.21 IU mL(-1) . All patients maintained FXIII activity above the lower target level (0.1 IU mL(-1) ). rFXIII half-life was 15.1 days (range, 10-25). No safety findings of clinical concern were observed. PK properties of rFXIII were similar in patients from both trials. The study demonstrated that a single dose of 35 IU kg(-1) rFXIII maintained plasma FXIII levels above 0.1 IU mL(-1) over a 30-day period in young children with congenital FXIII deficiency, and is, therefore, likely to provide adequate prophylaxis in this age group. The study extends the previous findings of the mentor1 trial and confirms that no dose adjustment is required for different age groups with congenital FXIII deficiency.

Treatment of refractory hemorrhage with Factor XIII in a patient with hemophilia A with inhibitor

An 11-year-old male with hemophilia A and a known high-titer Factor VIII inhibitor was admitted with retroperitoneal hemorrhage. The patient was receiving infusions of recombinant activated Factor VII (rFVIIa) for a recent elbow hemorrhage when retroperitoneal bleeding commenced. Despite increased dosing of rFVIIa and a dose of activated prothrombin complex concentrate (aPCC), he continued to hemorrhage and required several blood transfusions. Factor XIII was administered 1 hour after rFVIIa and the patient demonstrated cessation of bleeding and normalization of clot strength. Factor XIII may act as an adjuvant in effective clot stabilization in patients with hemophilia and inhibitory antibodies.

Acquired factor XIII deficiency: a therapeutic challenge

Less than 60 cases of acquired factor (F)XIII deficiencies have been reported, most having distinct clinical features. To illustrate the therapeutic challenges of acquired FXIII inhibitors, we report a case of a 65-year-old patient with no previous bleeding history who suddenly developed massive haemorrhages associated to a strong and isolated FXIII inhibitor. No underlying disorder has been detected till now after three years of follow-up. Despite aggressive treatment with prednisone, rituximab, cyclophosphamide, immunoglobulin, immunoadsorption and immune tolerance his inhibitor is still present, although at low titre and with a clinical benefit since the patient has no more bleed since more than one year. Moreover the patient had a venous thromboembolic complication. After a review of the management of acquired FXIII deficiency patients and based on the management of acquired haemophilia we discuss a possible strategy for such difficult cases.

Impaired dimer assembly and decreased stability of naturally recurring R260C mutant A subunit for coagulation factor XIII

Factor XIII (FXIII) consists of catalytic A subunits (FXIII-A) and carrier B subunits. Congenital FXIII deficiency is a severe bleeding disorder. We previously identified an R260C missense mutation and an exon-IV deletion in Japanese patients' F13A genes. To characterize the molecular basis of this disease, we expressed a wild-type and the mutant FXIII-A in yeast cells for detailed investigation, by taking advantage of yeast's ability for mass protein production. The mutant proteins were expressed less efficiently than the wild-type and considerably aggregated; even their non-aggregated forms became aggregated with time. Ultra-centrifugation and gel-filtration analyses revealed that the mutants were of extremely high-molecular weight, and that the wild-type formed a dimer. Notably, a part of the R260C mutant was found in monomer form. This was consistent with the prediction by molecular modelling that the mutant molecule would lose the electrostatic interaction between the two monomers, leading to their inability to form a dimer. The mutants lost enzymatic activity. The mutants were only partially converted by thrombin to the cleaved form. The wild-type was fully converted and activated. These mutants might have significantly altered conformations, resulting in their aggregation in vitro, and may ultimately lead to FXIII deficiency in vivo as well.

Recombinant factor XIII diminishes multiple organ dysfunction in rats caused by gut ischemia-reperfusion injury

Plasma factor XIII (FXIII) is responsible for stabilization of fibrin clot at the final stage of blood coagulation. Because FXIII has also been shown to modulate inflammation and endothelial permeability, we hypothesized that FXIII diminishes multiple organ dysfunction caused by gut I/R injury. A model of superior mesenteric artery occlusion (SMAO) was used to induce gut I/R injury. Rats were subjected to 45-min SMAO or sham SMAO and treated with recombinant human FXIII A2 subunit (rFXIII) or placebo at the beginning of the reperfusion period. Lung permeability, lung and gut myeloperoxidase activity, gut histology, neutrophil respiratory burst, and microvascular blood flow in the liver and muscles were measured after a 3-h reperfusion period. The effect of activated rFXIII on transendothelial resistance of human umbilical vein endothelial cells was tested in vitro. Superior mesenteric artery occlusion-induced lung permeability as well as lung and gut myeloperoxidase activity was significantly lower in rFXIII-treated versus untreated animals. Similarly, rFXIII-treated rats had lower neutrophil respiratory burst activity and ileal mucosal injury. Rats treated with rFXIII also had higher liver microvascular blood flow compared with the placebo group. Superior mesenteric artery occlusion did not cause FXIII consumption during the study period. In vitro, activated rFXIII caused a dose-dependent increase in human umbilical vein endothelial cell monolayer resistance to thrombin-induced injury. Thus, administration of rFXIII diminishes SMAO-induced multiple organ dysfunction in rats, presumably by preservation of endothelial barrier function and the limitation of polymorphonuclear leukocyte activation.

Differential clot stabilising effects of rFVIIa and rFXIII-A2 in whole blood from thrombocytopenic patients and healthy volunteers

The haemostatic effect of recombinant activated factor VII (rFVIIa;NovoSeven) in thrombocytopenic patients has been a matter of controversy. Haemostasis by rFVIIa occurs via FVIIa-mediated thrombin generation in a platelet-dependent manner and may therefore be suboptimal in patients without functional platelets. Under such conditions, a clot-stabilizing agent, such as factor XIII (FXIII), may supplement the effect ofrFVIIa and improve haemostasis. Recombinant factor XIII (rFXIII-A2) is produced as an A2 homodimer of the FXIII A subunit and is equivalent to cellular FXIII normally found in platelets. The combined effects of rFVIIa andrFXIII-A2 were evaluated in clot lysis assays using factor XIII-deficient plasma and by whole blood thrombelastography (TEG) analysis from normal donors and thrombocytopenic stem cell transplantation patients. Clotting time was shortened by rFVIIa (0.6-10 microg/ml). rFVIIa only modestly improved anti-fibrinolysis,whereas rFXIII-A2 (0-20 microg/ml) enhanced anti-fibrinolysis without effect on clotting time. TEG analysis showed rFVIIa shortened the clotting time, and enhanced clot development, maximal mechanical strength and resistance to fibrinolysis, whereas, rFXIII-A2 enhanced clot development,maximal mechanical strength and markedly enhanced resistance to fibrinolysis. These data illustrate that rFVIIa and rFXIII-A2 contribute to clot formation and stability by different mechanisms suggesting enhanced haemostatic efficacy by combining these agents.

Preclinical toxicity biomarkers for combination treatment with clotting factors rFXIII and rFVIIa

Combination treatment with the clotting factors recombinant activated factor VII (rFVIIa), serine protease, and recombinant factor XIII (rFXIII), protransglutaminase, is being explored for haemostatic therapy. We performed a single-dose toxicology study in the cynomolgus monkey, with four dose groups receiving 0.1 + 0.34 mg kg(-1) (group 1), 0.33 + 1.12 mg kg(-1) (group 2), 1.67 + 5.60 mg kg(-1) (group 3) and 5.00 + 16.80 mg kg(-1) (group 4) of a rFVIIa + rFXIII combination. In the three lower dose groups, no clinical, histopathological or blood chemistry changes were observed. In group 4, the animals died at 4 h post-dosing, with histopathology revealing a systemic coagulopathy resembling, but distinct from, disseminated intravascular coagulation. Due to the absence of toxicity warning signs, toxicity biomarkers were identified by a Western blot-based screening of approximately 20 plasma proteins known to be involved in the clotting cascade. Three of the examined proteins were specifically affected by rFVIIa + rFXIII treatment. Fibronectin and fibrinogen exhibited dose-dependent reductions from less than 10% reduction (group 2) to more than 90% reduction (group 4). These reductions were reversible, and specific. For vitronectin, a dose-dependent conversion to the 65-kDa form was found to occur in groups 3 and 4. Thus, fibrinogen, fibronectin and vitronectin represent the first biomarkers for clotting factor toxicity.

Characterization of high molecular weight plasma protein complexes induced by clotting factor rFXIII-treatment in the cynomolgus monkey

BACKGROUND

In cynomolgus monkeys, suprapharmacological doses of clotting recombinant factor XIII (rFXIII) cause a generalized coagulopathy, associated with formation of circulating high molecular weight protein complexes (HMEX). HMEX consist of plasma protein substrates cross-linked by FXIII transglutaminase activity.

OBJECTIVE

To characterize HMEX, with a view to develop safety biomarker assays.

METHODS

Cynomolgus monkeys received single i.v. injections with vehicle or rFXIII at 1, 3 and 10 mg kg(-1). Plasma HMEX were analyzed by sodium dodecylsulfate-polyacrylmide gel electrophoresis, silver staining, Western blotting and quantitative dissociation-enhanced lanthanide fluoroimmunoassay. Plasma FXIII antigen was analyzed by quantitative ELISA. Human HMEX were made in vitro, by spiking plasma with thrombin-activated rFXIII.

RESULTS

Maximal circulating HMEX levels were reached within 1 h of rFXIII treatment, and remained stable over 24 h. HMEX above 250 kDa contained fibrinogen alpha-chains and fibronectin. Fibrinogen gamma-chain was detected only in HMEX below 250 kDa. The total plasma concentration of HMEX was in the low microg mL(-1) range, distributed on less than 20 main species. Human and cynomolgus HMEX were similar. HMEX formation increased with rFXIII dose in a disproportionate manner, with 3-fold and fortyfold increases in HMEX exposure associated with rFXIII dose increments from 1 to 3 and 3 to 10 mg kg(-1), respectively.

CONCLUSIONS

The disproportionate HMEX formation parallels the steep toxicity dose response previously reported for rFXIII in cynomolgus monkeys, supporting a mechanistical role for HMEX in the generalized coagulopathy seen in rFXIII toxicity. Our findings support that HMEX constitute candidate (potential) safety biomarkers in rFXIII treatment.

Safety and pharmacokinetics of recombinant factor XIII-A2 administration in patients with congenital factor XIII deficiency

Congenital factor XIII (FXIII) deficiency is associated with a tendency for severe bleeding, a risk for spontaneous abortion, and a high rate of spontaneous intracranial hemorrhage. This phase 1 escalating-dose study was developed to evaluate the safety and pharmacokinetics of a single administration of human recombinant FXIII-A2 (rFXIII-A2) homodimer in adults with congenital FXIII deficiency. Pharmacokinetics and activity of rXIII and changes in endogenous B subunit levels were assessed. Recombinant FXIII-A2 homodimer were complexed with endogenous FXIII-B subunits to form an FXIII-A2B2 heterotetramer with a half-life of 8.5 days, similar to that of endogenous FXIII. The median dose response was a 2.4% increase in FXIII activity based on unit per kilogram rFXIII administered. After the administration of rFXIII-A2, clot solubility normalized as measured by clot lysis in urea. Clot strength and resistance to fibrinolysis, as assessed by thromboelastography, also improved. Safety reviews were conducted before each dose escalation; no serious adverse events, including bleeding or thrombosis, were noted during the study. In addition, there was no evidence of the generation of specific antibodies to rFXIII or yeast proteins. Recombinant FXIII appears to be a safe and potentially effective alternative for FXIII replacement in patients with FXIII deficiency. (Blood. 2006;108:57-62)

Population pharmacokinetics of recombinant factor XIII in cynomolgus monkeys

Hemostasis in humans and other animals is a complex process that controls blood loss after a vascular injury. Factor XIII (FXIII) stabilizes clots primarily by cross-linking fibrin, thus protecting a newly formed clot from fibrinolysis by plasmin. Congenital deficiencies in humans involving FXIII are associated with delayed bleeding and wound healing and severe spontaneous hemorrhaging. These symptoms can be alleviated by intravenous administration of enriched FXIII plasma fractions. Circulating plasma FXIII is found as a heterotetramer that dissociates in the presence of calcium and thrombin into an active dimer and 2 inactive monomers. The recombinant FXIII under investigation is the active dimer alone. A 3-compartment, nonlinear population pharmacokinetic model was implemented in NONMEM V and then used to analyze data from preclinical studies in cynomolgus monkeys. The model simultaneously describes endogenous production of dimer (0.622 microg kg(-1) hr(-1)) and monomer (12.1 microg kg(-1) hr(-1)), and the administration of recombinant dimer. The model incorporates the rate and extent of complexation of recombinant dimer with available endogenous monomer (6.59 mg(-1) kg hr(-1)) to form the heterotetramer. Half-lives for dimer, heterotetramer, and monomer (3.33 hours, 2.83 days, and 3.94 hours for A(2), A(2)B(2), and B, respectively) were estimated, along with their variability in the population studied.