Half-life extension through albumin fusion technologies

Prolonging the circulatory half-life of C1 esterase inhibitor via albumin fusion

Hereditary Angioedema (HAE) is an autosomal dominant disease characterized by episodic swelling, arising from genetic deficiency in C1-esterase inhibitor (C1INH), a regulator of several proteases including activated Plasma kallikrein (Pka). Many existing C1INH treatments exhibit short circulatory half-lives, precluding prophylactic use. Hexahistidine-tagged truncated C1INH (trC1INH lacking residues 1-97) with Mutated N-linked Glycosylation Sites N216Q/N231Q/N330Q (H6-trC1INH(MGS)), its murine serum albumin (MSA) fusion variant (H6-trC1INH(MGS)-MSA), and H6-MSA were expressed in Pichia pastoris and purified via nickel-chelate chromatography. Following intravenous injection in mice, the mean terminal half-life of H6-trC1INH(MGS)-MSA was significantly increased versus that of H6-trC1INH(MGS), by 3-fold, while remaining ~35% less than that of H6-MSA. The extended half-life was achieved with minimal, but significant, reduction in the mean second order rate constant of Pka inhibition of H6-trC1INH(MGS)-MSA by 33% relative to that of H6-trC1INH(MGS). Our results validate albumin fusion as a viable strategy for half-life extension of a natural inhibitor and suggest that H6-trC1INH(MGS)-MSA is worthy of investigation in a murine model of HAE.

Characterization of recombinant factor IX fusion proteins enabling subcutaneous administration

BACKGROUND

The X-linked bleeding disorder hemophilia B, caused by mutation(s) in the coagulation factor (F)IX gene, leads to partial or total loss of its function, requiring lifelong FIX replacement therapy. Although new recombinant FIX (rIX) therapeutics like albumin fusion proteins (rIX-FP) enable longer plasma half-life and thus less frequent administration, the complexity of intravenous (i.v.) injection remains.

OBJECTIVES

The study aimed to characterize rIX-FP variants with anticipated enhanced specific activity, which would leverage rIX-FP's superior pharmacokinetic profile with beneficial characteristics for subcutaneous (s.c.) administration.

METHODS

Two rIX-FP variants, R338L ("Padua variant") and R338L/E410K, were characterized in vitro. Pharmacokinetic profiles of FIX antigen and activity levels were evaluated in FIX-deficient mice after i.v. and s.c. administration of these variants (dosing based on antigen levels). The efficacy of the most promising variant was tested after i.v. and s.c. administration (dosing based on activity) in a tail clip bleeding model. A marketed wild-type (WT) rIX-FP product served as the comparator.

RESULTS

Both rIX-FP variants showed a 4- to 5-fold increase in specific activity in vitro compared with rIX(WT)-FP, while FXIa-mediated activation was the fastest for rIX(WT)-FP and rIX(R338L)-FP. Compared with rIX(WT)-FP and rIX(R338L/E410K)-FP, rIX(R338L)-FP exhibited higher FIX activity exposure after i.v. and s.c. administration and demonstrated comparable efficacy with rIX(WT)-FP in reducing bleeding time and blood loss in FIX-deficient mice requiring ∼4 times lower protein amount.

CONCLUSION

rIX(R338L)-FP was shown to be a promising candidate for s.c. administration, exhibiting increased specific activity combined with higher activity-based exposure and indicating efficacy at a lower protein dose.

A cleavable chimeric peptide with targeting and killing domains enhances LPS neutralization and antibacterial properties against multi-drug resistant E. coli

Pathogenic Escherichia coli is one of the most common causes of diarrhea diseases and its characteristic component of the outer membrane-lipopolysaccharide (LPS) is a major inducer of sepsis. Few drugs have been proven to kill bacteria and simultaneously neutralize LPS toxicity. Here, the chimeric peptides-R7, A7 and G7 were generated by connecting LBP14 (LPS-targeting domain) with L7 (killing domain) via different linkers to improve antibacterial and anti-inflammatory activities. Compared to parent LBP14-RKRR and L7, the antibacterial activity of R7 with a cleavable "RKRR" linker and the "LBP14-RKRR + L7" cocktail against Escherichia coli, Salmonella typhimurium and Staphylococcus aureus was increased by 2 ~ 4-fold. Both A7 and G7 with non-cleavable linkers almost lost antibacterial activity. The ability of R7 to neutralize LPS was markedly higher than that of LBP14-RKRR and L7. In vivo, R7 could be cleaved by furin in a time-dependent manner, and release L7 and LBP14-RKRR in serum. In vivo, R7 can enhance mouse survival more effectively than L7 and alleviate lung injuries by selective inhibition of the NF-κB signaling pathways and promoting higher IAP activity. It suggests that R7 may be promising dual-function candidates as antibacterial and anti-endotoxin agents.

Chemical Conjugation to Less Targeted Proteinogenic Amino Acids

Protein bioconjugates are in high demand for applications in biomedicine, diagnostics, chemical biology and bionanotechnology. Proteins are large and sensitive molecules containing multiple different functional groups and in particular nucleophilic groups. In bioconjugation reactions it can therefore be challenging to obtain a homogeneous product in high yield. Numerous strategies for protein conjugation have been developed, of which a vast majority target lysine, cysteine and to a lesser extend tyrosine. Likewise, several methods that involve recombinantly engineered protein tags have been reported. In recent years a number of methods have emerged for chemical bioconjugation to other amino acids and in this review, we present the progress in this area.

Viral Prefusion Targeting Using Entry Inhibitor Peptides: The Case of SARS-CoV-2 and Influenza A virus

In this study, peptide entry inhibitors against the fusion processes of severe acute respiratory syndrome coronavirus-2 (SCV2) and influenza A virus (IAV) were designed and evaluated. Fusion inhibitor peptides targeting the conformational shift of the viral fusion protein were designed based on the relatively conserved sequence of HR2 from SCV2 spike protein and the conserved fusion peptide from hemagglutinin (HA) of IAV. Helical HR2 peptides bind more efficiently to HR1 trimer, while helical amphipathic anti-IAV peptides have higher cell penetration and endosomal uptake. The initial sequences were mutated by increasing the amphipathicity, using helix favoring residues, and residues likely to form salt- and disulfide-bridges. After docking against their targets, all anti-SCV2 designed peptides bonded with the HR1 3-helical bundle's hydrophobic crevice, while AntiSCV2P1, AntiSCV2P3, AntiSCV2P7, and AntiSCV2P8 expected to form coiled coils with at least one of the HR1 strands. Four of the designed anti-IAV peptides were cell-penetrating (AntiIAVP2, AntiIAVP3, AntiIAVP4, AntiIAVP7). All of them interacted with the fusion peptide of HA and some of the residues in the conserved hydrophobic pocket of HA2 in H1N1, H3N1, and H5N1 subtypes of IAV. AntiIAVP3 and AntiIAVP4 peptides had the best binding to HA2 conserved hydrophobic pocket, while, AntiIAVP2 and AntiIAVP6 showed the best binding to the fusion peptide region. According to analyses for in-vivo administration, AntiSCV2P1, AntiSCV2P7, AntiIAVP2, and AntiIAVP7 were the best candidates. AntiSCV2 and AntiIAV peptides were also conjugated using an in vivo cleavable linker sensitive to TMPRSS2 applicable as a single therapeutic in coinfections or uncertain diagnosis.

Expert opinion paper on the treatment of hemophilia B with albutrepenonacog alfa

Introduction: Current guidelines recommend prophylactic treatment of hemophilia B with the missing coagulation factor IX, either with standard half-life or extended half-life products. Extended half-life products have half-lives three to six times longer than the former, allowing a reduction in the number of weekly injections and therefore, potentially impacting on treatment adherence and quality of life. Albutrepenonacog alfa is an extended half-life fusion protein of coagulation factor IX with recombinant human albumin, indicated for both on-demand and prophylactic treatment for bleeding in patients with hemophilia B of all ages.Areas covered: The authors review the clinical and pharmacokinetic characteristics of albutrepenonacog alfa, as well as the available information regarding trough levels and real-world evidence. Given the availability of other factor IX products in the market, indirect comparisons of clinical and pharmacokinetic characteristics are presented.Expert opinion: The authors exhibit their expert opinion on which patient profiles are candidates for prophylactic treatment with albutrepenonacog alfa, and on the management of patients in terms of dosing, regimens of administration and protocols for switching the treatment.

Fusion of engineered albumin with factor IX Padua extends half-life and improves coagulant activity

The short half‐life of coagulation factor IX (FIX) for haemophilia B (HB) therapy has been prolonged through fusion with human serum albumin (HSA), which drives the neonatal Fc receptor (FcRn)‐mediated recycling of the chimera. However, patients would greatly benefit from further FIX‐HSA half‐life extension. In the present study, we designed a FIX‐HSA variant through the engineering of both fusion partners. First, we developed a novel cleavable linker combining the two FIX activation sites, which resulted in improved HSA release. Second, insertion of the FIX R338L (Padua) substitution conferred hyperactive features (sevenfold higher specific activity) as for FIX Padua alone. Furthermore, we exploited an engineered HSA (QMP), which conferred enhanced human (h)FcRn binding [dissociation constant (K_D) 0·5 nM] over wild‐type FIX‐HSA (K_D 164·4 nM). In hFcRn transgenic mice, Padua‐QMP displayed a significantly prolonged half‐life (2·7 days, P < 0·0001) versus FIX‐HSA (1 day). Overall, we developed a novel FIX‐HSA protein with improved activity and extended half‐life. These combined properties may result in a prolonged functional profile above the therapeutic threshold, and thus in a potentially widened therapeutic window able to improve HB therapy. This rational engineering of both partners may pave the way for new fusion strategies for the design of engineered biotherapeutics.

A supramolecular nanocarrier for efficient cancer imaging and therapy by targeting at matriptase

Human serum albumin (HSA), a versatile protein carrier for endogenous and exogenous compounds, is a proven macromolecule to form nanoparticles for drug delivery. To render HSA carrier specificity toward tumors, we designed a recombinant HSA protein fused with Kunitz domain 1 (KD1) of hepatocyte growth factor activator inhibitor type 1, which targets to matriptase, a type II transmembrane serine protease overexpressed on tumor cell surface. The carrier was thus named matriptase targeting carrier (MTC). In this study, we showed that MTC displayed the same inhibitory potency as the KD1 againast matriptase, demonstrating the HSA fusion did not affect the KD1 targeting potency. For tumor optical imaging and ablation, MTC was prepared as nanoparticle drug carrier by a novel method via denaturation and refolding to incorporate photosensitizer, CPZ. This matriptase targeting nanoparticles, CPZ:MTC@NPs, showed high specificity and cytotoxicity for matriptase-overexpressing cancer cells in vitro. In tumor-bearing mice, CPZ:MTC@NPs demonstrated selective accumulation and high retention in matriptase-overexpressing tumor. Under illumination, the nanoparticles significantly reduced tumor volumes (79.6%) as compared to saline control. These findings showed that this supramolecular nanocarrier, a new type of tumor targeting self-assembly nanoparticle, had potential as a highly efficient tumor targeting drug carrier for imaging and therapy.

Safety, pharmacokinetics, and pharmacodynamics of a next-generation subcutaneously administered coagulation factor IX variant, dalcinonacog alfa, in previously treated hemophilia B patients

BACKGROUND

Dalcinonacog alfa (DalcA), a next-generation, recombinant human factor IX (FIX) variant, was developed using a rational design approach for increased procoagulant activity and longer duration of action to be administered subcutaneously (SC) for prophylaxis of hemophilia B bleeding episodes.

OBJECTIVES

To investigate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of DalcA.

METHODS

This multicenter, phase 1/2a study (NCT03186677) was conducted in 11 males aged 12 to 65 years with severe hemophilia B. In cohort 1, subjects received intravenous (IV) 75 IU/kg BeneFIX and DalcA. Cohorts 2 and 3 had DalcA IV 75 IU/kg and SC 75 IU/kg or 150 IU/kg. Cohort 4 was omitted. Cohort 5 received daily SC 150 IU/kg DalcA for 6 days and cohort 6 received IV 75 IU/kg and daily SC 150 IU/kg DalcA for 9 days. Blood sampling was performed for chemistry, hematology, PK, PD, and anti-drug antibody measurement. Subjects were monitored for safety endpoints for 30 days postdosing.

RESULTS

DalcA demonstrated a 24-fold greater potency over BeneFIX and longer mean residence time (33.8 h). SC bioavailability 8.2% to 20.3%, beta half-life 53.9 to 106.9 h and Tmax 24 to 48 h. A median 15.7% FIX activity level (interquartile range, 14.9%-16.6%) was reached after 6 daily doses. Neutralizing antibodies to ISU304, but not wild-type FIX, occurred in two cousins.

CONCLUSIONS

The data demonstrated that DalcA achieved protective FIX activity levels between 11% and 18%, corresponding to a reduced chance of spontaneous bleeds. Based on the results, a phase 2b trial to assess the safety and efficacy of 28 daily SC doses of DalcA was performed.

Tissue distribution of rIX-FP after intravenous application to rodents

BACKGROUND

Hemophilia B is caused by coagulation factor IX (FIX) deficiency. Recombinant fusion protein linking coagulation FIX with recombinant albumin (rIX-FP; Idelvion® ) is used for replacement therapy with an extended half-life. A previous quantitative whole-body autoradiography (QWBA) study investigating the biodistribution of rIX-FP indicated equal biodistribution, but more prolonged tissue retention compared with a marketed recombinant FIX product.

OBJECTIVES

To complete and confirm the QWBA study data by directly measuring rIX-FP protein and activity levels in tissues following intravenous (i.v.) administration to normal rats and FIX-deficient (hemophilia B) mice.

METHODS

After i.v. administration of rIX-FP at a dose of 2000 IU/kg, animals were euthanized at specific time points up to 72 hours postdosing. Subsequently, plasma and various tissues, which were selected based on the previous QWBA results, were harvested and analyzed for FIX antigen levels using an ELISA (both species) or an immunohistochemistry method (mice only), as well as for FIX activity levels (mice only) using a chromogenic assay.

RESULTS

In rats, rIX-FP distributed extravascularly into all tissues analyzed (ie, liver, kidney, skin and knee) with peak antigen levels reached between 1 and 7 hours postdosing. In hemophilia B mice, rIX-FP tissue distribution was comparable to rats. FIX antigen levels correlated well with FIX activity readouts.

CONCLUSIONS

Our results confirm QWBA data showing that rIX-FP distributes into relevant target tissues. Importantly, it was demonstrated that rIX-FP available in tissues retains its functional activity and can thus facilitate its therapeutic activity at sites of potential injury.

Preclinical evaluation of a next-generation, subcutaneously administered, coagulation factor IX variant, dalcinonacog alfa

Introduction

The rapid clearance of factor IX necessitates frequent intravenous administrations to achieve effective prophylaxis for patients with hemophilia B. Subcutaneous administration has historically been limited by low bioavailability and potency. Dalcinonacog alfa was developed using a rational design approach to be a subcutaneously administered, next-generation coagulation prophylactic factor IX therapy.

Aim

This study aimed to investigate the pharmacokinetic, pharmacodynamic, and safety profile of dalcinonacog alfa administered subcutaneously in hemophilia B dogs.

Methods

Two hemophilia B dogs received single-dose daily subcutaneous dalcinonacog alfa injections for six days. Factor IX antigen and activity, whole blood clotting time, and activated partial thromboplastin time were measured at various time points. Additionally, safety assessments for clinical adverse events and evaluations of laboratory test results were conducted.

Results

There was an increase in plasma factor IX antigen with daily subcutaneous dalcinonacog alfa. Bioavailability of subcutaneous dalcinonacog alfa was 10.3% in hemophilia B dogs. Daily subcutaneous dosing of dalcinonacog alfa demonstrated the effects of bioavailability, time to maximal concentration, and half-life by reaching a steady-state activity sufficient to correct severe hemophilia to normal, after four days.

Conclusion

The increased potency of dalcinonacog alfa facilitated the initiation and completion of the Phase 1/2 subcutaneous dosing study in individuals with hemophilia B.

A mutated factor X activatable by thrombin corrects bleedings in vivo in a rabbit model of antibody-induced hemophilia A

Rendering coagulation factor X sensitive to thrombin was proposed as a strategy that can bypass the need for factor VIII. In this paper, this non-replacement strategy was evaluated in vitro and in vivo in its ability to correct factor VIII but also factor IX, X and XI deficiencies. A novel modified factor X, named Actiten, was generated and produced in the HEK293F cell line. The molecule possesses the required post-translational modifications, partially keeps its ability to be activated by RVV-X, factor VIIa/tissue factor, factor VIIIa/factor IXa and acquires the ability to be activated by thrombin. The potency of the molecule was evaluated in respective deficient plasmas or hemophilia A plasmas, for some with inhibitors. Actiten corrects dose dependently all the assayed deficient plasmas. It is able to normalize the thrombin generation at 20 μg/mL showing however an increased lagtime. It was then assayed in a rabbit antibody-induced model of hemophilia A where, in contrast to recombinant factor X wild-type, it normalized the bleeding time and the loss of hemoglobin. No sign of thrombogenicity was observed and the generation of activated factor X was controlled by the anticoagulation pathway in all performed coagulation assays. This data indicates that Actiten may be considered as a possible non replacement factor to treat hemophilia's with the advantage of being a zymogen correcting bleedings only when needed.

Targeting drug delivery in the vascular system: Focus on endothelium

The bloodstream is the main transporting pathway for drug delivery systems (DDS) from the site of administration to the intended site of action. In many cases, components of the vascular system represent therapeutic targets. Endothelial cells, which line the luminal surface of the vasculature, play a tripartite role of the key target, barrier, or victim of nanomedicines in the bloodstream. Circulating DDS may accumulate in the vascular areas of interest and in off-target areas via mechanisms bypassing specific molecular recognition, but using ligands of specific vascular determinant molecules enables a degree of precision, efficacy, and specificity of delivery unattainable by non-affinity DDS. Three decades of research efforts have focused on specific vascular targeting, which have yielded a multitude of DDS, many of which are currently undergoing a translational phase of development for biomedical applications, including interventions in the cardiovascular, pulmonary, and central nervous systems, regulation of endothelial functions, host defense, and permeation of vascular barriers. We discuss the design of endothelial-targeted nanocarriers, factors underlying their interactions with cells and tissues, and describe examples of their investigational use in models of acute vascular inflammation with an eye on translational challenges.

Switching patients in the age of long-acting recombinant products?

Introduction: Prophylaxis with factor replacement therapy is the gold standard for the treatment of hemophilia, but this often requires frequent infusions. A number of long-acting factor products have been developed to reduce the burden on patients. Areas covered: This is an overview of information presented at two symposia held at the World Federation of Hemophilia and International Society on Thrombosis and Haemostasis - Scientific and Standardization Committee annual meetings. The pharmacokinetic, safety and efficacy data for long-acting recombinant products are reviewed, with a focus on recombinant factor IX albumin fusion protein (rIX-FP) and rVIII-SingleChain. This overview also provides a guide for managing a patient's switch to long-acting products. Expert opinion: Long-acting products may allow patients to maintain or decrease bleeding rates whilst increasing their dosing interval, which may in turn reduce the burden on patients and caregivers. When switching patients to long-acting products health-care professionals should provide balanced and thorough education to the patient, whilst supporting their emotional well-being. Regimens should address patients' needs and goals but should also be guided by clinical phenotype and pharmacokinetic assessment. Follow-up should assess safety concerns, bleeding rates, joint health and the impact of the regimen on patients' lifestyle.

Relevance of the Materno-Fetal Interface for the Induction of Antigen-Specific Immune Tolerance

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

Albumin nanoscience: homing nanotechnology enabling targeted drug delivery and therapy

Albumin is a biocompatible, non-immunogenic and versatile drug carrier system. It has been widely used to extend the half-life, enhance stability, provide protection from degradation and allow specific targeting of therapeutic agents to various disease states. Understanding the role of albumin as a drug delivery and distribution system has increased remarkably in the recent years from the development of albumin-binding prodrugs to albumin as a drug carrier system. The extraordinary surface property of albumin makes it possible to bind various endogenous and exogenous molecules. This review succinctly deals with several albumin-drug conjugates and nanoparticles along with their preparation techniques and focuses on surface-modified albumin and targeting of albumin formulation to specific organs and tissues. It also summarizes research efforts on albumin nanoparticles used for delivering drugs to tumor cells and describes their role in permeation through tumor vasculature and in receptor mediated endocytosis, which is also described in this review. The versatility of albumin and ease of preparation makes it a suitable drug carrier system, swhich is the major objective of this review.

Extended Half-Life Coagulation Factors: A New Era in the Management of Hemophilia Patients

Despite effective factor replacement and various treatment schedules, there remain several challenges and unmet needs in the prophylactic treatment of hemophilia limiting its adoption and thereby posing an increased risk of spontaneous bleeding. In this regard, extended half-life (EHL) recombinant factor VIII (rFVIII) and factor IX (rFIX) products promise optimal prophylaxis by decreasing the dose frequency, increasing the compliance, and improving the quality of life without compromising safety and efficacy. EHL products might lead to higher trough levels without increasing infusion frequency, or could facilitate the ability to maintain trough levels while reducing infusion frequency. This paper aims to provide a comprehensive review of the rationale for developing EHL coagulation factors and their utility in the management of hemophilia, with special emphasis on optimal techniques for half-life extension and criteria for defining EHL coagulation factors, as well as indications, efficacy, and safety issues of the currently available EHL-rFVIII and EHL-rFIX products. Potential impacts of these factors on quality of life, health economics, and immune tolerance treatment will also be discussed alongside the challenges in pharmacokinetic-driven prophylaxis and difficulties in monitoring the EHL products with laboratory assays.

Performance of a recombinant fusion protein linking coagulation factor IX with recombinant albumin in one-stage clotting assays

Essentials Performance of the one-stage clotting (OSC) assay varies with the clotting activator used. Recombinant FIX-albumin fusion protein (rIX-FP) was reliably monitored with most OSC reagents. rIX-FP shows comparable reagent-dependent variability to other rFIX products in the OSC assay. Actin® FS and kaolin-based reagents underestimated rIX-FP activity by around 50% in the OSC assay. SUMMARY: Background Measuring factor IX activity (FIX:C) with one-stage clotting (OSC) assays, based on the activated partial thromboplastin time (APTT), is the current mainstay of diagnostic techniques for hemophilia B. Assessing the performance of new recombinant FIX (rFIX) products in OSC assays is essential, as APTT reagents from different manufacturers yield different potency estimates for rFIX. Objectives To evaluate the extent to which choice of reagent composition influences rFIX potency measurements of recombinant FIX-albumin fusion protein (rIX-FP, IDELVION) activity in OSC assays. Methods rIX-FP was added to FIX-deficient plasma, and FIX:C was assessed centrally and locally in a multicenter international field study with a variety of commercial OSC APTT reagents. Paired sample analysis of clinical samples was performed to compare values of FIX:C from local and central laboratories. In-house bioanalytical investigations with spiked samples were conducted to compare the APTT-reagent dependent variability of rIX-FP with unmodified rFIX and rFIX Fc fusion protein (rFIXFc). Results Central and local assessments of FIX:C from 10 countries and 21 participating centers showed comparable results to those from the central laboratory across the majority of 18 different APTT reagents from both clinical and spiked samples. There was a consistent underestimation of rIX-FP activity of ≈ 50% with OSC assays using Actin FS or kaolin-based APTT reagents. In the bioanalytical study, rIX-FP showed comparable variability in OSC assays to unmodified rFIX and rFIXFc. Conclusions rIX-FP activity can be accurately measured by the use of OSC assays with the majority of commercial reagents. Actin FS or kaolin-based reagents will probably lead to a 50% underestimation of activity.

The carboxyl-terminal region of human coagulation factor X as a natural linker for fusion strategies

Fusion with human serum albumin (HSA), which represents a well-established technique to extend half-life of therapeutic proteins, commonly exploits intervening peptide linkers as key components. Here, we explored the human coagulation factor X (FX) carboxyl-terminal region, previously demonstrated by us to be dispensable for secretion and coagulant activity, as a natural linker for fusion purposes. To test our hypothesis, we compared direct FX-HSA fusion with the designed FX-HSA fusion proteins mimicking the recombinant activated factor VII (rFVIIa)-HSA or factor IX (FIX)-HSA chimeras, both strongly dependent from artificial linkers. Three constructs were produced by direct tandem fusion (FX-HSA) and through flexible (glycine/serine; FX-GS-HSA, mimicking rFVIIa-HSA) or cleavable (incorporating the FX activation site; FX-CL-HSA, mimicking FIX-HSA) linkers. The FX-HSA was efficiently secreted and displayed prolonged plasma persistence in mice. All chimeras possessed remarkable pro-coagulant activity, comparable to FX for FX-HSA (88.7 ± 6.0%) and FX-CL-HSA (98.0 ± 16.4%) or reduced for FX-GS-HSA (55.8 ± 5.4%). Upon incubation with activators, FX-HSA and FX-CL-HSA displayed a correct activation profile while the FX-GS-HSA activation was slightly defective. In fluorogenic-based assays, FX-HSA showed normal activity over time and a specific amidolytic activity (1.0 ± 0.12) comparable to that of FX. Overall, the FX-HSA features indicate that the FX carboxyl-terminal region represents an intrinsic sequence allowing direct tandem fusion. Our results provide the first experimental evidence for i) a coagulation factor fusion protein with biological properties independent from artificial linkers, ii) the suitability of FX carboxyl-terminal region as a natural linker for fusion purposes.

Updates in clinical trial data of extended half-life recombinant factor IX products for the treatment of haemophilia B

Whilst the global prevalence of haemophilia B is less than that of haemophilia A, rapid and remarkable innovations have been made in the development of haemophilia B therapies in the last decade. The most recent developments are the evolution of extended half-life haemophilia B replacement therapies which are designed to reduce the treatment burden associated with prophylactic infusion of factor IX (FIX) to prevent bleeding in haemophilia B participants. Clinical development programmes have culminated in the completion of three phase III studies on extended half-life (EHL) recombinant FIX (rFIX) products and subsequent approval and registration of these in many countries around the world. Current data from the three EHL rFIX clinical studies indicate that these products have acceptable safety profiles with no allergic reactions, thromboembolic phenomena or neutralizing antibodies when given to previously treated adolescent and adults for the prevention of bleeds, for the treatment of bleeds and in the perisurgical haemostasis use. Studies in previously untreated paediatric participants are currently ongoing. The EHL rFIX products have the potential impact to reduce the treatment burden associated with prophylactic infusion of replacement FIX, to treat and prevent bleeds in participants with haemophilia B and to improve the participant's health-related quality of life. The impact of EHL rFIX is likely to be modified by current development of other haemophilia B therapy such as antitissue factor pathway inhibitors and haemophilia B gene therapy. In this review, we aim to provide an update on the safety and efficacy data from the three EHL rFIX clinical studies and to consider their roles in the face of novel haemophilia B therapy currently evolving.

Pharmacokinetic-based prediction of real-life dosing of extended half-life clotting factor concentrates on hemophilia

The improvement of clotting factor concentrates (CFCs) has undergone an impressive boost during the last six years. Since 2010, several new recombinant factor (rF)VIII/IX concentrates entered phase I/II/III clinical trials. The improvements are related to the culture of human embryonic kidney (HEK) cells, post-translational glycosylation, PEGylation, and co-expression of the fragment crystallizable (Fc) region of immunoglobulin (Ig)G1 or albumin genes in the manufacturing procedures. The extended half-life (EHL) CFCs allow an increase of the interval between bolus administrations during prophylaxis, a very important advantage for patients with difficulties in venous access. Although the inhibitor risk has not been fully established, phase III studies have provided standard prophylaxis protocols, which, compared with on-demand treatment, have achieved very low annualized bleeding rates (ABRs). The key pharmacokinetics (PK) parameter to tailor patient therapy is clearance, which is more reliable than the half-life of CFCs; the clearance considers the decay rate of the drug concentration-time profile, while the half-life considers only the half concentration of the drug at a given time. To tailor the prophylaxis of hemophilia patients in real-life, we propose two formulae (expressed in terms of the clearance, trough and dose interval between prophylaxis), respectively based on the one- and two-compartmental models (CMs), for the prediction of the optimal single dose of EHL CFCs. Once the data from the time decay of the CFCs are fitted by the one- or two-CMs after an individual PK analysis, such formulae provide to the treater the optimal trade-off among trough and time-intervals between boluses. In this way, a sufficiently long time-interval between bolus administration could be guaranteed for a wider class of patients, with a preassigned level of the trough. Finally, a PK approach using repeated dosing is discussed, and some examples with new EHL CFCs are shown.

Half-life-extended recombinant coagulation factor IX-albumin fusion protein is recycled via the FcRn-mediated pathway

The neonatal Fc receptor (FcRn) has a pivotal role in albumin and IgG homeostasis. Internalized IgG captured by FcRn under acidic endosomal conditions is recycled to the cell surface where exocytosis and a shift to neutral pH promote extracellular IgG release. Although a similar mechanism is proposed for FcRn-mediated albumin intracellular trafficking and recycling, this pathway is less well defined but is relevant to the development of therapeutics exploiting FcRn to extend the half-life of short-lived plasma proteins. Recently, a long-acting recombinant coagulation factor IX–albumin fusion protein (rIX-FP) has been approved for the management of hemophilia B. Fusion to albumin potentially enables internalized proteins to engage FcRn and escape lysosomal degradation. In this study, we present for the first time a detailed investigation of the FcRn-mediated recycling of albumin and the albumin fusion protein rIX-FP. We demonstrate that following internalization via FcRn at low pH, rIX-FP, like albumin, is detectable within the early endosome and rapidly (within 10–15 min) traffics into the Rab11+ recycling endosomes, from where it is exported from the cell. Similarly, rIX-FP and albumin taken up by fluid-phase endocytosis at physiological pH traffics into the Rab11+ recycling compartment in FcRn-positive cells but into the lysosomal compartment in FcRn-negative cells. As expected, recombinant factor IX (without albumin fusion) and an FcRn interaction–defective albumin variant localized to the lysosomal compartments of both FcRn-expressing and nonexpressing cells. These results indicate that FcRn-mediated recycling via the albumin moiety is a mechanism for the half-life extension of rIX-FP observed in clinical studies.

Haemophilia B: impact on patients and economic burden of disease

Worldwide, haemophilia is the most common hereditary bleeding disorder. The incidence of haemophilia B, however, is considerably less than haemophilia A and consequently appears to have received less attention in the research literature. This article aims to summarise the available evidence documenting the patient and economic burden associated with haemophilia B and current methods of disease management. Both the immediate and long-term clinical consequences of haemophilia B can have significant implications for patients in terms of functional limitations and diminished health-related quality of life (HRQOL). Evidence demonstrates that primary prophylaxis is the optimal strategy for replacing missing clotting factor IX (FIX) and managing haemophilia B. Use of recombinant FIX (rFIX) over plasma-derived FIX (pd-FIX) is also generally preferred for safety reasons. Prophylaxis using currently available rFIX products, however, requires a demanding regimen of intravenous infusions 2–3 times a week which may have significant implications for adherence and ultimately the long-term efficacy of such regimens. Only limited assessments of the cost-effectiveness of prophylactic versus on-demand FIX treatment regimens have been conducted to date. Prophylaxis, however, is generally more costly as greater quantities of FIX are consumed. Any reduction in FIX replacement dosing frequency is expected to improve patient adherence and contribute to improved clinical outcomes, further supporting the costeffectiveness of such interventions. Although a rare disease, as economic constraints for healthcare increase, generating further information regarding the key clinical, patient and economic outcomes associated with haemophilia B will be essential for supporting improvements in care for people with haemophilia B.

Simoctocog alfa for the treatment of hemophilia A

INTRODUCTION

Hemophilia A is the most frequent inherited bleeding disorder and most challenging coagulation disorder. To combat this, a number of new improved rFVIII/IX concentrates have recently been approved. Some of them are derived from protein fusion biotechnology or pegylation to extend their half-life (HL). However, prophylaxis has become a standard of care to prevent arthropathy in hemophiliacs though the need of frequent venipunctures is a major obstacle to primary prophylaxis. The new Extended Half-Life (EHL) rFIX concentrates allow increased intervals, while the improved HL of new rFVIII was moderate. rFVIII Simoctocog alfa is produced in Human Embryonic Kidney (HEK) cells and the post-translational modifications performed by HEK cells are very similar to those occurring in the native FVIII. Areas covered: Herein, the author provides a review of simoctocog alfa with its contents including information on simoctocog alfa's manufacturing, clinical trials, safety and tolerability. They also give their expert opinion and future perspectives on this therapy. Expert opinion: An important advantage of simoctocog alfa is the possibility to omit at least 30% of venipunctures with prophylaxis. Consequently, the standard three times weekly bolus administrations may be reduced to twice weekly, meaning approximately 50 fewer venipunctures per year. This may be particularly helpful to children.

Transforming the treatment for hemophilia B patients: update on the clinical development of recombinant fusion protein linking recombinant coagulation factor IX with recombinant albumin (rIX-FP)

Recombinant fusion protein linking recombinant coagulation factor IX with recombinant albumin (rIX-FP; Idelvion®(†)) is an innovative new treatment designed to extend the half-life of factor IX (FIX) and ease the burden of care for hemophilia B patients. The rIX-FP clinical development program - PROLONG-9FP - is in its advanced phases, with pivotal studies in previously treated adults, adolescents, and pediatrics now completed. Across all age groups studied, rIX-FP has demonstrated a markedly improved pharmacokinetic profile compared with plasma-derived and recombinant FIX treatments, with a 30-40% higher incremental recovery, an approximately 5-fold longer half-life, a lower clearance, and a greater area under the curve. rIX-FP has been very well tolerated with an excellent safety profile. In the pivotal studies, there have been no reports of FIX inhibitors or antidrug antibodies, and few treatment-related adverse events have been observed. Prophylactic regimens of rIX-FP administered once weekly to once every 14 days have been highly effective. When used for surgical prophylaxis, a single infusion of rIX-FP has been sufficient to maintain hemostasis, even during major orthopedic surgery. An ongoing study is now enrolling previously untreated patients and evaluating the possibility of extending the dosing interval to every 21 days. There is little doubt that rIX-FP will transform the treatment of hemophilia B.

Emerging drugs for the treatment of hemophilia A and B

INTRODUCTION

Replacement therapy with clotting factor concentrates is the most appropriate and effective way to treat bleedings of Hemophilia A&B to prevent chronic arthropathy. Unfortunately, the short half-life (HL) of FVIII/IX concentrates obliges the patients to receive frequent infusions, a big concern for children. The development of inhibitors in about 30-45% of hemophilia A and in 3-5% of hemophilia B patient is the major adverse event of replacement therapy.

AREAS COVERED

In the last few years, new rFIX have been developed with HL. New rFVIII concentrates are displaying small increase of PK characteristics. The new bio-engineering methods allowed the production of molecules fused with Fc fragment of IgG or Albumin or linked to PEG. A new approach to improve hemostasis is represented by Mab against TFPI and small RNA interfering with Antithrombin synthesis. Another innovative drug seems to be the new bi-specific antibody which mimics FVIII function in linking FXa and FX to tenase production.

EXPERT OPINION

The emerging drugs for hemophilia treatment seem to be very promising. The extended half-life will improve the adherence of patients to therapy. Accurate post-marketing surveillance studies will be necessary to check the efficacy, safety and immunogenicity of these new molecules.

Half-life extended biotherapeutics

INTRODUCTION

Many of the biotherapeutics approved or under development suffer from a short half-life necessitating frequent applications in order to maintain a therapeutic concentration over an extended period of time. The implementation of half-life extension strategies allows the generation of long-lasting therapeutics with improved pharmacokinetic and pharmacodynamic properties.

AREAS COVERED

This review gives an overview of the different half-life extension strategies developed over the past years and their application to generate next-generation biotherapeutics. It focuses on srategies already used in approved drugs and drugs that are in clinical development. These strategies include those aimed at increasing the hydrodynamic radius of the biotherapeutic and strategies which further implement recycling by the neonatal Fc receptor (FcRn).

EXPERT OPINION

Half-life extension strategies have become an integral part of development for many biotherapeutics. A diverse set of these strategies is available for the fine-tuning of half-life and adaption to the intended treatment modality and disease. Currently, half-life extension is dominated by strategies utilizing albumin binding or fusion, fusion to an immunoglobulin Fc region and PEGylation. However, a variety of alternative strategies, such as fusion of flexible polypeptide chains as PEG mimetic substitute, have reached advanced stages and offer further alternatives for half-life extension.

Fusion Proteins for Half-Life Extension of Biologics as a Strategy to Make Biobetters

The purpose of making a "biobetter" biologic is to improve on the salient characteristics of a known biologic for which there is, minimally, clinical proof of concept or, maximally, marketed product data. There already are several examples in which second-generation or biobetter biologics have been generated by improving the pharmacokinetic properties of an innovative drug, including Neulasta(®) [a PEGylated, longer-half-life version of Neupogen(®) (filgrastim)] and Aranesp(®) [a longer-half-life version of Epogen(®) (epoetin-α)]. This review describes the use of protein fusion technologies such as Fc fusion proteins, fusion to human serum albumin, fusion to carboxy-terminal peptide, and other polypeptide fusion approaches to make biobetter drugs with more desirable pharmacokinetic profiles.

Results of a phase I/II open-label, safety and efficacy trial of coagulation factor IX (recombinant), albumin fusion protein in haemophilia B patients

Introduction

rIX-FP is a coagulation factor IX (recombinant), albumin fusion protein with more than fivefold half-life prolongation over other standard factor IX (FIX) products available on the market.

Aim

This prospective phase II, open-label study evaluated the safety and efficacy of rIX-FP for the prevention of bleeding episodes during weekly prophylaxis and assessed the haemostatic efficacy for on-demand treatment of bleeding episodes in previously treated patients with haemophilia B.

Methods

The study consisted of a 10–14 day evaluation of rIX-FP pharmacokinetics (PK), and an 11 month safety and efficacy evaluation period with subjects receiving weekly prophylaxis treatment. Safety was evaluated by the occurrence of related adverse events, and immunogenic events, including development of inhibitors. Efficacy was evaluated by annualized spontaneous bleeding rate (AsBR), and the number of injections to achieve haemostasis.

Results

Seventeen subjects participated in the study, 13 received weekly prophylaxis and 4 received episodic treatment only. No inhibitors were detected in any subject. The mean and median AsBR were 1.25, and 1.13 respectively in the weekly prophylaxis arm. All bleeding episodes were treated with 1 or 2 injections of rIX-FP. Three prophylaxis subjects who were treated on demand prior to study entry had >85% reduction in AsBR compared to the bleeding rate prior to study entry.

Conclusion

This study demonstrated the efficacy for weekly routine prophylaxis of rIX-FP to prevent spontaneous bleeding episodes and for the treatment of bleeding episodes. In addition no safety issues were detected during the study and an improved PK profile was demonstrated.

Synthetic fusion protein design and applications

Synthetic fusion proteins can be designed to achieve improved properties or new functionality by synergistically incorporating multiple proteins into one complex. The fusion of two or more protein domains enhances bioactivities or generates novel functional combinations with a wide range of biotechnological and (bio)pharmaceutical applications. In this review, initially, we summarize the commonly used approaches for constructing fusion proteins. For each approach, the design strategy and desired properties are elaborated with examples of recent studies in the areas of biocatalysts, protein switches and bio-therapeutics. Subsequently, the progress in structural prediction of fusion proteins is presented, which can potentially facilitate the structure-based systematic design of fusion proteins toward identifying the best combinations of fusion partners. Finally, the current challenges and future directions in this field are discussed.

Fusion protein linkers: property, design and functionality

As an indispensable component of recombinant fusion proteins, linkers have shown increasing importance in the construction of stable, bioactive fusion proteins. This review covers the current knowledge of fusion protein linkers and summarizes examples for their design and application. The general properties of linkers derived from naturally-occurring multi-domain proteins can be considered as the foundation in linker design. Empirical linkers designed by researchers are generally classified into 3 categories according to their structures: flexible linkers, rigid linkers, and in vivo cleavable linkers. Besides the basic role in linking the functional domains together (as in flexible and rigid linkers) or releasing the free functional domain in vivo (as in in vivo cleavable linkers), linkers may offer many other advantages for the production of fusion proteins, such as improving biological activity, increasing expression yield, and achieving desirable pharmacokinetic profiles.

Innovative coagulation factors: albumin fusion technology and recombinant single-chain factor VIII

Albumin fusion technology has been used to enhance the pharmacokinetic properties of recombinant coagulation factors. The goal of linking albumin to coagulation factors is to extend the half-life of the coagulation factor, thereby allowing for less frequent dosing for patients with bleeding disorders, such as hemophilia. The novel recombinant fusion proteins linking coagulation factors VIIa and IX with albumin (rVIIa-FP and rIX-FP, respectively) have a longer half-life and similar hemostatic efficacy compared with available recombinant coagulation factor products. Clinical evaluation of these fusion proteins is underway, and preliminary results with rIX-FP in patients with hemophilia B are encouraging. Other advances in coagulation factor therapy include a unique recombinant single-chain factor VIII (FVIII) protein, which has improved intrinsic stability and a higher affinity for von Willebrand factor (VWF), relative to other recombinant FVIIIs, and a recombinant VWF-albumin fusion protein (rVWF-FP), which has a significant longer half-life compared to available VWF products. Evaluation of these novel recombinant proteins continues and will help determine their potential to enhance the management of patients with bleeding disorders.

Extending the pharmacokinetic half-life of coagulation factors by fusion to recombinant albumin

The prophylactic treatment of haemophilia B and the management of haemophilia A or B with inhibitors demand frequent administrations of coagulation factors due to the suboptimal half-lives of the products commercially available and currently in use, e.g. recombinant factor IX (rFIX) and recombinant factor VIIa (rFVIIa), respectively. The extension of the half-lives of rFIX and rFVIIa could allow for longer intervals between infusions and could thereby improve adherence and clinical outcomes and may improve quality of life. Albumin fusion is one of a number of different techniques currently being examined to prolong the half-life of rFIX and rFVIIa. Results from a phase I clinical trial demonstrated that the recombinant fusion protein linking FIX to albumin (rIX-FP) has a five-times longer half-life than rFIX, and preclinical studies with the recombinant fusion protein linking FVIIa to albumin (rVIIa-FP) suggest that rVIIa-FP possesses a significantly extended half-life versus rFVIIa. In this review, we describe albumin fusion technology and examine the recent progress in the development of rIX-FP and rVIIa-FP.

Site-specific fatty acid-conjugation to prolong protein half-life in vivo

Therapeutic proteins are indispensable in treating numerous human diseases. However, therapeutic proteins often suffer short serum half-life. In order to extend the serum half-life, a natural albumin ligand (a fatty acid) has been conjugated to small therapeutic peptides resulting in a prolonged serum half-life via binding to patients' serum albumin in vivo. However, fatty acid-conjugation has limited applicability due to lack of site-specificity resulting in the heterogeneity of conjugated proteins and a significant loss in pharmaceutical activity. In order to address these issues, we exploited the site-specific fatty acid-conjugation to a permissive site of a protein, using copper-catalyzed alkyne-azide cycloaddition, by linking a fatty acid derivative to p-ethynylphenylalanine incorporated into a protein using an engineered pair of yeast tRNA/aminoacyl tRNA synthetase. As a proof-of-concept, we show that single palmitic acid conjugated to superfolder green fluorescent protein (sfGFP) in a site-specific manner enhanced a protein's albumin-binding in vitro about 20 times and the serum half-life in vivo 5 times when compared to those of the unmodified sfGFP. Furthermore, the fatty acid conjugation did not cause a significant reduction in the fluorescence of sfGFP. Therefore, these results clearly indicate that the site-specific fatty acid-conjugation is a very promising strategy to prolong protein serum half-life in vivo without compromising its folded structure and activity.

Safety and pharmacokinetics of a novel recombinant fusion protein linking coagulation factor IX with albumin (rIX-FP) in hemophilia B patients

A recombinant fusion protein linking coagulation factor IX (FIX) with human albumin (rIX-FP) has been developed to facilitate hemophilia B treatment by less frequent FIX dosing. This first-in-human dose-escalation trial in 25 previously treated subjects with hemophilia B (FIX ≤ 2 IU/dL) examined the safety and pharmacokinetics of 25, 50, and 75 IU/kg rIX-FP. Patients in the 50-IU/kg cohort underwent a comparative pharmacokinetics assessment with their previous FIX product (plasma-derived or recombinant). No allergic reactions or inhibitors were observed. Four mild, possibly treatment-related adverse events were reported. In the 50-IU/kg cohort (13 subjects), the mean half-life of rIX-FP was 92 hours, more than 5 times longer than the subjects' previous FIX product. After 25 or 50 IU/kg rIX-FP administration, the baseline-corrected mean FIX activity remained elevated at day 7 (7.4 IU/dL and 13.4 IU/dL, respectively) and day 14 (2.5 IU/dL and 5.5 IU/dL, respectively). The incremental recovery of rIX-FP was higher than both recombinant and plasma-derived FIX (1.4 vs 0.95 and 1.1 IU/dL per IU/kg, respectively). These results demonstrated both the safety and improved pharmacokinetics of rIX-FP, thus indicating this new product with extended half-life as possibly able to control and prevent bleeding with less frequent injection.

Pharmacokinetics of recombinant bifunctional fusion proteins

INTRODUCTION

The development of biotechnology has enabled the creation of various recombinant fusion proteins as a new class of biotherapeutics. The uniqueness of fusion proteins lies in their ability to fuse two or more protein domains, providing vast opportunities to generate novel combinations of functions. Pharmacokinetic (PK) studies, which are critical components in preclinical and clinical drug development, have not been fully explored for fusion proteins. The lack of general PK models and study guidelines has become a bottleneck for translation of fusion proteins from basic research to the clinic.

AREAS COVERED

This article reviews the current status of PK studies for fusion proteins, covering the processes that affect PK. According to their PK properties, a classification of fusion proteins is suggested along with examples from the clinic or under development. Current limitations and future perspectives for PK of fusion proteins are also discussed.

EXPERT OPINION

A PK model for bifunctional fusion proteins is presented to highlight the importance of mechanistic studies for a thorough understanding of the PK properties of fusion proteins. The model suggests investigating the receptor binding and subsequent intracellular disposition of individual domains, which can have dramatic impact on the PK of fusion proteins.

Biophysical characterization and stabilization of the recombinant albumin fusion protein sEphB4-HSA

The use of albumin fusion proteins as therapeutic drug candidates is an attractive approach to design novel biopharmaceuticals with increased circulation time in vivo. The purpose of this work was to characterize and stabilize the fusion protein sEphB4-human serum albumin (HSA), a 120 kDa protein containing the extracellular domain of EphB4 and HSA, and to identify stabilizing excipients for storage. Comparative biophysical studies combined with empirical phase diagram analysis show that both structural integrity and conformational stability of sEphB4 and sEphB4-HSA are best maintained above pH 5 and below 50 °C, with different structural phases observed outside this range. A major physical degradation pathway for sEphB4-HSA is formation of soluble aggregates. Excipient studies using size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), and fluorescence spectroscopy identified disaccharide sugars (e.g., sucrose and trehalose) as effective stabilizers against protein aggregation, and NaCl as an effective stabilizer for protecting overall conformational stability. A combination of biophysical studies with sEphB4-HSA and its individual component proteins (sEphB4 and HSA), along with correlation analysis of SEC and DSC stability data in the presence of different excipients suggest that the aggregation pathway of the albumin fusion protein is primarily mediated by the sEphB4 rather than the HSA component.

Recombinant factor IX-Fc fusion protein (rFIXFc) demonstrates safety and prolonged activity in a phase 1/2a study in hemophilia B patients

Current factor IX (FIX) products display a half-life (t(1/2)) of ∼ 18 hours, requiring frequent intravenous infusions for prophylaxis and treatment in patients with hemophilia B. This open-label, dose-escalation trial in previously treated adult subjects with hemophilia B examined the safety and pharmacokinetics of rFIXFc. rFIXFc is a recombinant fusion protein composed of FIX and the Fc domain of human IgG(1), to extend circulating time. Fourteen subjects received a single dose of rFIXFc; 1 subject each received 1, 5, 12.5, or 25 IU/kg, and 5 subjects each received 50 or 100 IU/kg. rFIXFc was well tolerated, and most adverse events were mild or moderate in intensity. No inhibitors were detected in any subject. Dose-proportional increases in rFIXFc activity and Ag exposure were observed. With baseline subtraction, mean activity terminal t(1/2) and mean residence time for rFIXFc were 56.7 and 71.8 hours, respectively. This is ∼ 3-fold longer than that reported for current rFIX products. The incremental recovery of rFIXFc was 0.93 IU/dL per IU/kg, similar to plasma-derived FIX. These results show that rFIXFc may offer a viable therapeutic approach to achieve prolonged hemostatic protection and less frequent dosing in patients with hemophilia B. The trial was registered at www.clinicaltrials.gov as NCT00716716.

Strategies for extended serum half-life of protein therapeutics

With a growing number of protein therapeutics being developed, many of them exhibiting a short plasma half-life, half-life extension strategies find increasing attention by the biotech and pharmaceutical industry. Extension of the half-life can help to reduce the number of applications and to lower doses, thus are beneficial for therapeutic but also economic reasons. Here, a comprehensive overview of currently developed half-life extension strategies is provided including those aiming at increasing the hydrodynamic volume of a protein drug but also those implementing recycling processes mediated by the neonatal Fc receptor.

Biological rationale for new drugs in the bleeding disorders pipeline

Since the introduction of replacement coagulation factor infusions for the treatment of hemophilia in the 1970s and subsequent improvements in the safety profile of available factor VIII (FVIII) and factor IX (FIX) concentrates, mortality among patients with hemophilia has improved considerably and now parallels that of the noncoagulopathic population in developed countries. Substantial morbidity, however, continues from the development of inhibitory antibodies, a recognized complication of clotting factor replacement; from infections and thrombosis complicating placement of central venous catheters, which are required in children with hemophilia due to frequent prophylactic infusions of coagulation factors with defined half-lives; and from disabling joint disease in individuals without access to costly prophylaxis regimens. In response to the need for long-acting, more potent, less immunogenic, and more easily administered therapies, an impressive array of novel agents is nearly ready for use in the clinical setting. These therapeutics derive from rational bioengineering of recombinant coagulation factors or from the discovery of nonpeptide molecules that have the potential to support hemostasis through alternative pathways. The number of novel agents in clinical trials is increasing, and many of the initial results are promising. In addition to advancing treatment of bleeding episodes or enabling adherence to prophylactic infusions of clotting factor concentrate, newer therapeutics may also lead to improvements in joint health, quality of life, and tolerability of iatrogenic or comorbidity-associated bleeding challenges.