Improved kinetics of rIX-FP, a recombinant fusion protein linking factor IX with albumin, in cynomolgus monkeys and hemophilia B dogs

Engineering a New IFN-ApoA-I Fusion Protein with Low Toxicity and Prolonged Action

Recombinant human interferon alpha-2b (rIFN) is widely used in antiviral and anticancer immunotherapy. However, the high efficiency of interferon therapy is accompanied by a number of side effects; this problem requires the design of a new class of interferon molecules with reduced cytotoxicity. In this work, IFN was modified via genetic engineering methods by merging it with the blood plasma protein apolipoprotein A-I in order to reduce acute toxicity and improve the pharmacokinetics of IFN. The chimeric protein was obtained via biosynthesis in the yeast P. pastoris. The yield of ryIFN-ApoA-I protein when cultivated on a shaker in flasks was 30 mg/L; protein purification was carried out using reverse-phase chromatography to a purity of 95-97%. The chimeric protein demonstrated complete preservation of the biological activity of IFN in the model of vesicular stomatitis virus and SARS-CoV-2. In addition, the chimeric form had reduced cytotoxicity towards Vero cells and increased cell viability under viral load conditions compared with commercial IFN-a2b preparations. Analysis of the pharmacokinetic profile of ryIFN-ApoA-I after a single subcutaneous injection in mice showed a 1.8-fold increased half-life of the chimeric protein compared with ryIFN.

IDELVION: A Comprehensive Review of Clinical Trial and Real-World Data

Hemophilia B is a bleeding disorder caused by a deficiency of coagulation factor IX (FIX). Treatment with FIX replacement products can increase FIX activity levels to minimize or prevent bleeding events. However, frequent dosing with standard-acting FIX products can create a high treatment burden. Long-acting products have been developed to maintain bleed protection with extended dosing intervals. Recombinant factor IX–albumin fusion protein (rIX-FP) is a long-acting product indicated for the treatment and prophylaxis of bleeding events and perioperative management in adult and pediatric patients. This review outlines data from all previously treated patients in the Prophylaxis and On-Demand Treatment using Longer Half-Life rIX-FP (PROLONG-9FP) clinical trial program and summarizes real-world data evaluating the use of rIX-FP in routine clinical practice. In the PROLONG-9FP program, rIX-FP demonstrated effective hemostasis in all patients at dose regimens of up to 21 days in patients aged ≥ 18 years and up to 14 days in patients aged < 12 years. rIX-FP has a favorable pharmacokinetic profile and an excellent safety and tolerability profile. Extended dosing intervals with rIX-FP led to high levels of adherence and reduced consumption compared with other FIX therapies. Data from real-world practice are encouraging and reflect the results of the clinical trials.

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.

The availability of new drugs for hemophilia treatment

INTRODUCTION

A number of new FVIII/IX concentrates enriched the portfolio of products available for the treatment of hemophilia A/B patients. Due to the large inter-patient variability, accurate tailoring of the therapy became essential to improve patients' adherence, clinical outcomes, and cost/effectiveness ratio. Recently, non-replacement therapies have taken the limelight and succeeded in decreasing the bleedings of patients.

AREAS COVERED

The PK characteristics, efficacy, and safety of the new rFVIII and rFIX concentrates and of non-replacement therapy, are reported in detail in the published clinical trials.

EXPERT OPINION

Outstanding improvements of rFIX concentrates' pharmacokinetics and pharmacodynamics have allowed to reduce the bleedings in hemophilia B patients, in order to increase their adherence to prophylaxis and quality of life. Less significant are the effects of pegylation or Fc fusion on the pharmacokinetics of the new rFVIII concentrates. The new non-replacement therapy is achieving the favor of many treaters and patients, in particular those with Factor VIII inhibitors. Great attention must be paid to the dangerous synergy of APCC and emicizumab, responsible for some fatal events during the clinical trials and compassionate use of this drug. So far, replacement therapy should be the standard of care for hemophilia patients without inhibitors or difficulties in venous access.

Potential limits of AAV-based gene therapy with the use of new transgenes expressing factor IX fusion proteins

INTRODUCTION

The variety of treatment for haemophilia B (HB) has recently improved with the emergence of both AAV-based gene therapy and bioengineered human factor IX (hFIX) molecules with prolonged half-life due to fusion to either albumin (Alb) or immunoglobulin Fc fragment (Fc).

AIM

Adeno-associated viral vectors (AAV) mediating expression of hFIX-Alb and hFIX-Fc fusion proteins was investigated for gene therapy of HB to explore if their extended half-life translates to higher plasma levels of FIX.

METHODS

Single-stranded cross-packaged AAV2/8 vectors expressing hFIX-Alb, hFIX-Fc and hFIX were evaluated in vitro, and in mice.

RESULTS

Both hFIX-Alb and hFIX-Fc fusion proteins were synthesized and expressed as single chains of expected size following AAV-mediated gene transfer in vitro and in vivo. The procoagulant properties of these hFIX-fusion proteins were comparable to wild-type hFIX. However, their expression levels were threefold lower than wild-type hFIX in vivo most likely due to inefficient secretion.

CONCLUSION

This, the first, evaluation of hFIX-fusion proteins in the context of AAV gene transfer suggests that the hFIX-fusion proteins are secreted inefficiently from the liver, thus preventing their optimal use in gene therapy approaches.

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.

Albumin-based drug delivery using cysteine 34 chemical conjugates – important considerations and requirements

The long blood circulation time of albumin has been clinically utilized as a half-life extension technology for improved drug performance. The availability of one free thiol for site-selective chemical conjugation offers an alternative approach to current genetic fusion and association-based products. This special report highlights important factors for successful conjugation that allows the reader to design and evaluate next-generation albumin conjugates. Albumin type, available conjugation chemistries, linker length, animal models and influence of conjugation on albumin pharmacokinetics and drug activity are discussed.

Long-acting recombinant coagulation factor IX albumin fusion protein (rIX-FP) in hemophilia B: results of a phase 3 trial

A global phase 3 study evaluated the pharmacokinetics, efficacy, and safety of recombinant fusion protein linking coagulation factor IX with albumin (rIX-FP) in 63 previously treated male patients (12-61 years) with severe hemophilia B (factor IX [FIX] activity ≤2%). The study included 2 groups: group 1 patients received routine prophylaxis once every 7 days for 26 weeks, followed by either 7-, 10-, or 14-day prophylaxis regimen for a mean of 50, 38, or 51 weeks, respectively; group 2 patients received on-demand treatment of bleeding episodes for 26 weeks and then switched to a 7-day prophylaxis regimen for a mean of 45 weeks. The mean terminal half-life of rIX-FP was 102 hours, 4.3-fold longer than previous FIX treatment. Patients maintained a mean trough of 20 and 12 IU/dL FIX activity on prophylaxis with rIX-FP 40 IU/kg weekly and 75 IU/kg every 2 weeks, respectively. There was 100% reduction in median annualized spontaneous bleeding rate (AsBR) and 100% resolution of target joints when subjects switched from on-demand to prophylaxis treatment with rIX-FP (P< .0001). The median AsBR was 0.00 for all prophylaxis regimens. Overall, 98.6% of bleeding episodes were treated successfully, including 93.6% that were treated with a single injection. No patient developed an inhibitor, and no safety concerns were identified. These results indicate rIX-FP is safe and effective for preventing and treating bleeding episodes in patients with hemophilia B at dosing regimens of 40 IU/kg weekly and 75 IU/kg every 2 weeks. This trial was registered at www.clinicaltrials.gov as #NCT0101496274.

New developments in the management of moderate-to-severe hemophilia B

Hemophilia B is an X-linked genetic deficiency of coagulation factor IX (FIX) activity associated with recurrent deep tissue and joint bleeding that may lead to long-term disability. FIX replacement therapy using plasma-derived protein or recombinant protein has significantly reduced bleeding and disability from hemophilia B, particularly when used in a prophylactic fashion. Although modern factor replacement has excellent efficacy and safety, barriers to the broader use of prophylaxis remain, including the need for intravenous (IV) access, frequent dosing, variability in individual pharmacokinetics, and cost. To overcome the requirement for frequent factor dosing, novel forms of recombinant FIX have been developed that possess extended terminal half-lives. Two of these products (FIXFc and rIX-FP) represent fusion proteins with the immunoglobulin G1 (IgG1) Fc domain and albumin, respectively, resulting in proteins that are recycled in vivo by the neonatal Fc receptor. The third product has undergone site-specific PEGylation on the activation peptide of FIX, similarly resulting in a long-lived FIX form. Clinical trials in previously treated hemophilia B patients have demonstrated excellent efficacy and confirmed less-frequent dosing requirements for the extended half-life forms. However, gaps in knowledge remain with regard to the risk of inhibitor formation and allergic reactions in previously untreated patient populations, safety in elderly patients with hemophilia, effects on in vivo FIX distribution, and cost-effectiveness. Additional strategies designed to rebalance hemostasis in hemophilia patients include monoclonal-antibody-mediated inhibition of tissue factor pathway inhibitor activity and siRNA-mediated reduction in antithrombin expression by the liver. Both of these approaches are long acting and potentially involve subcutaneous administration of the drug. In this review, we will discuss the biology of FIX, the evolution of FIX replacement therapy, the emerging FIX products possessing extended half-lives, and novel “rebalancing” approaches to hemophilia therapy.

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.

Quantifying vitamin K-dependent holoprotein compaction caused by differential γ-carboxylation using high-pressure size exclusion chromatography

This study uses high-pressure size exclusion chromatography (HPSEC) to quantify divalent metal ion (X(2+))-induced compaction found in vitamin K-dependent (VKD) proteins. Multiple X(2+) binding sites formed by the presence of up to 12 γ-carboxyglutamic acid (Gla) residues are present in plasma-derived FIX (pd-FIX) and recombinant FIX (r-FIX). Analytical ultracentrifugation (AUC) was used to calibrate the Stokes radius (R) measured by HPSEC. A compaction of pd-FIX caused by the filling of Ca(2+) and Mg(2+) binding sites resulted in a 5 to 6% decrease in radius of hydration as observed by HPSEC. The filling of Ca(2+) sites resulted in greater compaction than for Mg(2+) alone where this effect was additive or greater when both ions were present at physiological levels. Less X(2+)-induced compaction was observed in r-FIX with lower Gla content populations, which enabled the separation of biologically active r-FIX species from inactive ones by HPSEC. HPSEC was sensitive to R changes of approximately 0.01nm that enabled the detection of FIX compaction that was likely cooperative in nature between lower avidity X(2+) sites of the Gla domain and higher avidity X(2+) sites of the epidermal growth factor 1 (EGF1)-like domain.

The role of albumin receptors in regulation of albumin homeostasis: Implications for drug delivery

Albumin is the most abundant protein in blood and acts as a molecular taxi for a plethora of small insoluble substances such as nutrients, hormones, metals and toxins. In addition, it binds a range of medical drugs. It has an unusually long serum half-life of almost 3weeks, and although the structure and function of albumin has been studied for decades, a biological explanation for the long half-life has been lacking. Now, recent research has unravelled that albumin-binding cellular receptors play key roles in the homeostatic regulation of albumin. Here, we review our current understanding of albumin homeostasis with a particular focus on the impact of the cellular receptors, namely the neonatal Fc receptor (FcRn) and the cubilin-megalin complex, and we discuss their importance on uses of albumin in drug delivery.

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.

Role of enhanced half-life factor VIII and IX in the treatment of haemophilia

Treatment of congenital haemophilia with factor VIII and IX concentrates often requires frequent infusions. This has obvious implications in establishing effective administration strategies and, in turn, adherence. To overcome these issues, three main technologies--polyethylene-glycol, Fc-neonatal IgG1 and albumin fusion products--have emerged into various stages of clinical development. Published data indicates an approximately 1·5- and fivefold increase in half-life of factor VIII and IX, respectively, compared to standard recombinant concentrates. Studies into efficacy and safety are starting to be published. Monitoring and optimal use of these new concentrates remains unknown. Weekly factor IX prophylaxis appears to be a feasible prophylactic regimen in haemophilia B patients. Weekly longer-acting FVIII is unlikely to provide adequate prophylaxis in most patients with haemophilia A but may reduce the frequency of infusions. Ongoing clinical trials and real life experience will help shape how these products can be used in practice and their cost effectiveness. The drive for convenience however should not overshadow the ultimate goal of prophylaxis, namely, preventing bleeding and arthropathy.

Half-life extension technologies for haemostatic agents

The use of plasma-derived and recombinant coagulation factors for the treatment of haemophilia A and B is well established and permits patients to live a relatively normal life. In order to improve treatment options, several products are in development, which have a prolonged duration of action, thus enabling less frequent prophylactic dosing and aiming to reduce the burden of treatment. Several innovative approaches are being pursued to extend the half-life of factor VIIa, factor VIII and factor IX, utilising technologies such as Fc fusion, recombinant albumin fusion and addition of polyethyleneglycol (PEG) (PEGylation). These methods prolong the time in the circulation by reducing degradation and elimination. This review summarises the technologies and products in development and their stages of development, and also discusses their pros and cons.

Lessons Learned from Animal Models of Inherited Bleeding Disorders

Advances in treatment of hemophilia and von Willebrand disease (VWD) depend heavily on the availability of well-characterized animal models. These animals faithfully recapitulate the severe bleeding phenotype that occurs in humans with these inherited bleeding disorders. Research in these animal models represents important early and intermediate steps of translational research aimed at addressing current limitations in treatment such as the development of inhibitory antibodies to coagulation factors VIII and IX (FVIII, FIX) or von Willebrand factor (VWF), the life-long need for frequent venous access, the expense of therapy, and the ongoing need for improved ex vivo coagulation assays and in vivo methods for assessing hemostasis. The primary strengths of research that utilizes these highly relevant animal models include the development of better and safer treatments for hemophilia and VWD. Careful consideration of the strengths and limitations of the specific models is essential for optimizing chances for successful translation of advances to clinical medicine that benefits humans and animals.

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.

Designing first-in-human dose of coagulation factors: application of pharmacokinetic allometric scaling

The objectives of this study were to (i) evaluate the predictive performance of pharmacokinetic interspecies scaling of coagulation factors to predict clearance (CL) and (ii) project first-in-human dose based on the predicted human CL. Human CL of nine coagulation factors was predicted using two or three animal species using two methods: (i) CL vs. body weight (simple allometry) and where applicable (ii) the product of CL and brain weight vs. body weight. Based on the predicted human CL, four methods were used to project the first-in-human dose. The predicted pharmacokinetic parameters and the estimated first-in-human dose of coagulation factors were compared with the observed human values obtained from clinical trials. The results of the study indicated that the CL of coagulation factors can be predicted with reasonable accuracy in humans and a good estimate of first-in-human dose can be obtained from the predicted human CL. The suggested methods in this study are not only time and cost-effective but also provide rational alternatives to the somewhat arbitrary dose selection process for coagulation factors often used.

Future of coagulation factor replacement therapy

Over a million patients worldwide currently suffer from hemophilia and other congenital clotting factor deficiencies. Patients affected with hemophilia A and B are treated by intravenous replacement therapy of factor VIII and factor IX, respectively. Current hemophilia treatments have favorably supported their efficacy, tolerability, and safety profiles. The onset of alloantibodies inactivating the infused coagulation factor is the main problem in hemophilia patients rendering replacement therapies ineffective; another disadvantage is the short half-life of the infused clotting factors with the need for multiple and frequent infusions to manage a bleeding episode. Now, the challenge in the management of hemophilia treatment is the prolongation of the half-life and reduction in the immunogenicity of recombinant clotting factors. The bioengineering strategies, previously applied successfully to other therapeutic proteins, encourage the current efforts to produce novel coagulation factors with more prolonged bioavailability, with increased potency and resistance to inactivation and potentially reduced immunogenicity.

Albumin as a versatile platform for drug half-life extension

BACKGROUND

Albumin is the most abundant plasma protein, is highly soluble, very stable and has an extraordinarily long circulatory half-life as a direct result of its size and interaction with the FcRn mediated recycling pathway. In contrast, many therapeutic molecules are smaller than the renal filtration threshold and are rapidly lost from the circulation thereby limiting their therapeutic potential. Albumin can be used in a variety of ways to increase the circulatory half-life of such molecules.

SCOPE OF REVIEW

This article will review the mechanisms which underpin albumin's extraordinarily long circulatory half-life and how the understanding of these processes are currently being employed to extend the circulatory half-life of drugs which can be engineered to bind to albumin, or are conjugated to, or genetically fused to, albumin.

MAJOR CONCLUSIONS

The recent and growing understanding of the pivotal role of FcRn in maintaining the extended circulatory half-life of albumin will necessitate a greater and more thorough investigation of suitable pre-clinical model systems for assessing the pharmacokinetic profiles of drugs associated, conjugated or fused to albumin.

GENERAL SIGNIFICANCE

Association, conjugation or fusion of therapeutic drugs to albumin is a well-accepted and established half-life extension technology. The manipulation of the albumin-FcRn interaction will facilitate the modulation of the circulatory half-life of albumin-enabled drugs, leading to superior pharmacokinetics tailored to the disease state and increased patient compliance. This article is part of a Special Issue entitled Serum Albumin.