BAX 855, a PEGylated rFVIII product with prolonged half-life

Shifting Paradigms and Arising Concerns in Severe Hemophilia A Treatment

The management of hemophilia A has undergone a remarkable revolution, in line with technological advancement. In the recent past, the primary concern associated with Factor VIII (FVIII) concentrates was the risk of infections, which is now almost resolved by advanced blood screening and viral inactivation methods. Improving patients' compliance with prophylaxis has become a key focus, as it can lead to improved health outcomes and reduced health care costs in the long term. Recent bioengineering research is directed toward prolonging the recombinant FVIII (rFVIII) coagulant activity and synthesising higher FVIII yields. As an outcome, B-domain deleted, polyethylene glycolated, single-chain, Fc-fused rFVIII, and rFVIIIFc-von Willebrand Factor-XTEN are available for patients. Moreover, emicizumab, a bispecific antibody, is commercially available, whereas fitusiran and tissue factor pathway inhibitor are in clinical trial stages as alternative strategies for patients with inhibitors. With these advancements, noninfectious complications, such as inhibitor development, allergic reactions, and thrombosis, are emerging concerns requiring careful management. In addition, the recent approval of gene therapy is a major milestone toward a permanent cure for hemophilia A. The vast array of treatment options at our disposal today empowers patients and providers alike, to tailor therapeutic regimens to the unique needs of each individual. Despite significant progress in modern treatment options, these highly effective therapies are markedly more expensive than conventional replacement therapy, limiting their access for patients in developing countries.

PEGylated therapeutics in the clinic

The covalent attachment of polyethylene glycol (PEG) to therapeutic agents, termed PEGylation, is a well-established and clinically proven drug delivery approach to improve the pharmacokinetics and pharmacodynamics of drugs. Specifically, PEGylation can improve the parent drug's solubility, extend its circulation time, and reduce its immunogenicity, with minimal undesirable properties. PEGylation technology has been applied to various therapeutic modalities including small molecules, aptamers, peptides, and proteins, leading to over 30 PEGylated drugs currently used in the clinic and many investigational PEGylated agents under clinical trials. Here, we summarize the diverse types of PEGylation strategies, the key advantages of PEGylated therapeutics over their parent drugs, and the broad applications and impacts of PEGylation in clinical settings. A particular focus has been given to the size, topology, and functionalities of PEG molecules utilized in clinically used PEGylated drugs, as well as those under clinical trials. An additional section has been dedicated to analyzing some representative PEGylated drugs that were discontinued at different stages of clinical studies. Finally, we critically discuss the current challenges faced in the development and clinical translation of PEGylated agents.

Factor VIII and Factor IX Activity Measurements for Hemophilia Diagnosis and Related Treatments

Accurate measurement of clotting factors VIII (FVIII) or IX (FIX) is vital for comprehensive diagnosis and management of patients with hemophilia A or B. The one-stage activated partial thromboplastin time (aPTT)-based clotting assay is the most commonly used method worldwide for testing FVIII or FIX activities. Alternatively, FVIII and FIX chromogenic substrate assays, which assess the activation of factor X, are available in some specialized laboratories. The choice of reagent or methodology can strongly influence the resulting activity. Variation between one-stage FVIII or FIX activities has been reported in the measurement of some standard and extended half-life factor replacement therapies and gene therapy for hemophilia B using different aPTT reagents. Discrepancy between one-stage and chromogenic reagents has been demonstrated in some patients with mild hemophilia A or B, the measurement of some standard and extended half-life factor replacement therapies, and the transgene expression of hemophilia A and B patients who have received gene therapy. Finally, the measurement of bispecific antibody therapy in patients with hemophilia A has highlighted differences between chromogenic assays. It is imperative that hemostasis laboratories evaluate how suitable their routine assays are for the accurate measurement of the various hemophilia treatment therapies.

Plasma Clearance of Coagulation Factor VIII and Extension of Its Half-Life for the Therapy of Hemophilia A: A Critical Review of the Current State of Research and Practice

Factor VIII (FVIII) is an important component of blood coagulation as its congenital deficiency results in life-threatening bleeding. Current prophylactic therapy of the disease (hemophilia A) is based on 3-4 intravenous infusions of therapeutic FVIII per week. This poses a burden on patients, demanding reduction of infusion frequency by using FVIII with extended plasma half-life (EHL). Development of these products requires understanding FVIII plasma clearance mechanisms. This paper overviews (i) an up-to-date state of the research in this field and (ii) current EHL FVIII products, including recently approved efanesoctocog alfa, for which the plasma half-life exceeds a biochemical barrier posed by von Willebrand factor, complexed with FVIII in plasma, which results in ~1 per week infusion frequency. We focus on the EHL FVIII products' structure and function, in particular related to the known discrepancy in results of one-stage clotting (OC) and chromogenic substrate (CS) assays used to assign the products' potency, dosing, and for clinical monitoring in plasma. We suggest a possible root cause of these assays' discrepancy that is also pertinent to EHL factor IX variants used to treat hemophilia B. Finally, we discuss approaches in designing future EHL FVIII variants, including those to be used for hemophilia A gene therapy.

Selective human factor VIII activity measurement after analytical in-line purification

Background

It is essential to measure the activity of factor VIII (FVIII) throughout the life cycle of a coagulation FVIII concentrate. Such measurement in nonclinical pharmacokinetic studies is potentially biased by the presence of endogenous nonhuman FVIII, and certain manufacturing process-related additives can also impact the assay performance. Finally, the presence of FVIII activity-mimicking antibodies poses challenges when measuring FVIII in samples. Therefore, we developed an antibody-based chromogenic FVIII assay, which facilitates the selective and sensitive activity measurement of human FVIII in the presence of animal plasma and interfering agents.

Methods

Plate-bound monoclonal anti-FVIII antibody specifically captured human FVIII, which was then measured with a chromogenic activity assay. A human reference plasma preparation was used to construct the calibration curve. Spike recovery was carried out in a citrated cynomolgus monkey plasma-solvent/detergent mixture and in the presence of the bispecific antibody emicizumab.

Results

The calibration curve ranged from 3.03 to 97.0 mIU FVIII/ml and was obtained repeatedly with good accuracy. B domain-deleted and full-length FVIII did not differ in their responses. Recovery of spiked human FVIII in citrated cynomolgus monkey plasma was 102.7%, while neither native monkey plasma nor the other animal specimen tested showed any activity. Solvent/detergent solution and the bispecific antibody emicizumab had no influence on the assay.

Conclusion

Combining antibody-mediated specific capture of human FVIII and a chromogenic activity assay resulted in a selective and sensitive measurement of human FVIII with no interference by endogenous, nonhuman FVIII, manufacturing process additives, or an FVIII activity-mimicking antibody.

Rational Control of Protein-Protein Interactions with Protein-ATRP-Generated Protease-Sensitive Polymer Cages

Protease-protease interactions lie at the heart of the biological cascades that provide rapid molecular responses to living systems. Blood clotting cascades, apoptosis signaling networks, bacterial infection, and virus trafficking have all evolved to be activated and sustained by protease-protease interactions. Biomimetic strategies designed to target drugs to specific locations have generated proprotein drugs that can be activated by proteolytic cleavage to release native protein. We have previously demonstrated that the modification of enzymes with a custom-designed comb-shaped polymer nanoarmor can shield the enzyme surface and eliminate almost all protein-protein interactions. We now describe the synthesis and characterization of protease-sensitive comb-shaped nanoarmor cages using poly(ethylene glycol) [Sundy, J. S. Arthritis Rheum. 2008, 58(9), 2882-2891]methacrylate macromonomers where the PEG tines of the comb are connected to the backbone of the growing polymer chain by peptide linkers. Protease-induced cleavage of the tines of the comb releases a polymer-modified protein that can once again participate in protein-protein interactions. Atom transfer radical polymerization (ATRP) was used to copolymerize the macromonomer and carboxybetaine methacrylate from initiator-labeled chymotrypsin and trypsin enzymes, yielding proprotease conjugates that retained activity toward small peptide substrates but prevented activity against proteins. Native proteases triggered the release of the PEG side chains from the polymer backbone within 20 min, thereby increasing the activity of the conjugate toward larger protein substrates by 100%. Biomimetic cascade initiation of nanoarmored protease-sensitive protein-polymer conjugates may open the door to a new class of responsive targeted therapies.

An Update on Laboratory Diagnostics in Haemophilia A and B

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

Purification of Modified Therapeutic Proteins Available on the Market: An Analysis of Chromatography-Based Strategies

Proteins, which have inherent biorecognition properties, have long been used as therapeutic agents for the treatment of a wide variety of clinical indications. Protein modification through covalent attachment to different moieties improves the therapeutic's pharmacokinetic properties, affinity, stability, confers protection against proteolytic degradation, and increases circulation half-life. Nowadays, several modified therapeutic proteins, including PEGylated, Fc-fused, lipidated, albumin-fused, and glycosylated proteins have obtained regulatory approval for commercialization. During its manufacturing, the purification steps of the therapeutic agent are decisive to ensure the quality, effectiveness, potency, and safety of the final product. Due to the robustness, selectivity, and high resolution of chromatographic methods, these are recognized as the gold standard in the downstream processing of therapeutic proteins. Moreover, depending on the modification strategy, the protein will suffer different physicochemical changes, which must be considered to define a purification approach. This review aims to deeply analyze the purification methods employed for modified therapeutic proteins that are currently available on the market, to understand why the selected strategies were successful. Emphasis is placed on chromatographic methods since they govern the purification processes within the pharmaceutical industry. Furthermore, to discuss how the modification type strongly influences the purification strategy, the purification processes of three different modified versions of coagulation factor IX are contrasted.

Development and Validation of a Population-Pharmacokinetic Model for Rurioctacog Alfa Pegol (Adynovate®): A Report on Behalf of the WAPPS-Hemo Investigators Ad Hoc Subgroup

BACKGROUND AND OBJECTIVE

Rurioctacog alfa pegol (Adynovate) is a modified recombinant factor VIII concentrate used for treating hemophilia A. Aiming to improve treatment tailoring on the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) platform for patients of all ages treated with Adynovate, we have developed and evaluated a population pharmacokinetic (PopPK) model. On the platform, PopPK models are used as priors for Bayesian forecasting that derive individual PK of hemophilia patients and are subsequently used for personalized dose regimen design.

METHODS

Factor activity measurements and demographic covariate data from patients infused with Adynovate were extracted from the WAPPS-Hemo database. Evaluations testing the appropriateness of Bayesian forecasting included 10-fold cross validation, a limited sampling analysis (LSA), and an external evaluation using additional independent data extracted from the WAPPS-Hemo database at a later date.

RESULTS

The model was constructed using 650 plasma factor activity observations (555 one stage assay and 95 chromogenic assay - 4.6% below limit of quantification) measured in 154 patients from 36 hemophilia centres. A two-compartment model including between subject variability on clearance and central volume was selected as the base model. Covariates were fat free mass on clearance and central volume, age on clearance and assay type on activity. The final model was well-suited to predict PK parameters of new individuals (n = 26) from sparse observations.

CONCLUSIONS

The development of a PopPK model for Adynovate using real-world data increases the covariate space (e.g. age) beyond what is possible from clinical trial data. This model is available on the WAPPS-Hemo platform for tailoring treatment in hemophilia A patients.

Enhanced Half-Life Recombinant Factor VIII Concentrates for Hemophilia A: Insights from Pivotal and Extension Studies

The development of enhanced half-life recombinant factor VIII (EHL-rFVIII) concentrates has improved the management of hemophilia. Furthermore, the chance of maintaining higher trough levels has allowed higher protection from bleeding and, in turn, improved safely performance for certain types of physical activity. The first technology used to improve the pharmacokinetic profile of factor VIII (FVIII) was fusion with the Fc domain of immunoglobulin G. More recently, conjugation to hydrophilic polymers of polyethylene glycol (PEG) has been demonstrated to prolong plasma half-life of FVIII by means of a reduction in clearance of the molecule due to steric hindrance by PEG covering the protein. Here we report results of a systematic review of pivotal studies on EHL-rFVIII concentrates. Significant heterogeneity is observed among different studies on EHL-rFVIII concentrates, and direct comparisons should be avoided. The annualized bleeding rate has ranged between 1.2 and 1.9 in different EHL-rFVIII concentrates, with a progressive further decrease during extension phases of pivotal studies. Zero bleeding was reported by 40 to 45% of patients. Overall, the emerging treatment options seem to be highly effective and safe, associated with a decreased dosing interval to twice weekly or less, which reduces, but does not entirely eliminate, the burden of treatment. Overall, further information is needed from real-life settings to permit differentiation between EHL-FVIII concentrates and for individualizing treatment.

Evaluation of Factor VIII Polysialylation: Identification of a Longer-Acting Experimental Therapy in Mice and Monkeys

Extended half-life (EHL) factor therapies are needed to reduce the burden of prophylaxis and improve treatment adherence in patients with hemophilia. BAX 826 is a novel polysialylated full-length recombinant factor VIII [polysialyic acid (PSA) rFVIII] with improved pharmacokinetics (PK), prolonged pharmacology, and maintained safety attributes to enable longer-acting rFVIII therapy. In factor VIII (FVIII)-deficient hemophilic mice, PSArFVIII showed a substantially higher mean residence time (>2-fold) and exposure (>3-fold), and prolonged efficacy in tail-bleeding experiments (48 vs. 30 hours) compared with unmodified recombinant FVIII (rFVIII), as well as a potentially favorable immunogenicity profile. Reduced binding to a scavenger receptor (low-density lipoprotein receptor-related protein 1) and von Willebrand factor (VWF) as well as a largely VWF-independent circulation time in mice provide a rationale for prolonged BAX 826 activity. The significantly improved PK profile versus rFVIII was confirmed in cynomolgus monkeys [mean residence time: 23.4 vs. 10.1 hours; exposure (area under the curve from time 0 to infinity): 206 vs. 48.2 IU/ml⋅h] and is in line with results from rodent studies. Finally, safety and toxicity evaluations did not indicate increased thrombogenic potential, and repeated administration of BAX 826 to monkeys and rats was well tolerated. The favorable profile and mechanism of this novel experimental therapeutic demonstrated all of the requirements for an EHL-rFVIII candidate, and thus BAX 826 was entered into clinical assessment for the treatment of hemophilia A. SIGNIFICANCE STATEMENT: Prolongation of FVIII half-life aims to reduce the burden of prophylaxis and improve treatment outcomes in patients with hemophilia. This study shows that polysialylation of PSArFVIII resulted in prolongations of rFVIII circulation time and procoagulant activity, together with a favorable nonclinical safety profile of the experimental therapeutic.

Shifting Landscape of Hemophilia Therapy: Implications for Current Clinical Laboratory Coagulation Assays

Clinical coagulation assays are an integral part of diagnosing and managing patients with hemophilia; however, in this new era of bioengineered factor products and non-factor therapeutics, problems have arisen with use of traditional coagulation tests for the quantification of several of these new products. Discussion over the use of one-stage clotting assays versus chromogenic substrate assays for clinical decision making and potency labeling has been ongoing for many years. Emerging factor concentrates have heightened concern over assay selection and availability. Emicizumab interferes with all aPTT based assays, rendering them unreliable and potentially falsely reassuring to the unaware provider. This review explores considerations for coagulation assays in the clinical setting and highlights how awareness of institutional coagulation assays and potential limitations have never been more critical for providers caring for patients with bleeding disorders. This article is protected by copyright. All rights reserved.

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.

Novel therapies and current clinical progress in hemophilia A

The evolution of hemophilia treatment and care is a fascinating one but has been fraught with many challenges at every turn. Over the last 50 years or so patients with hemophilia and providers have witnessed great advances in the treatment of this disease. With these advances, there has been a dramatic decrease in the mortality and morbidity associated with hemophilia. Even with the remarkable advancements in treatment, however, new and old challenges continue to plague the hemophilia community. The cost of factor replacement and the frequency of infusions, especially in patients with severe hemophilia on prophylaxis, remains a significant challenge for this population. Other challenges include obtaining reliable venous access, especially in younger patients, and the development of neutralizing alloantibodies (inhibitors). The development of extended half-life products, a bispecific antibody which mimics the coagulation function of factor VIII (FVIII) and inhibition of anticoagulation proteins such as antithrombin with antibodies, aptamers or RNA interference technology have offered novel therapeutic approaches to overcome some of these existing challenges. Additionally, ongoing gene therapy research offers a way to possibly cure hemophilia. These novel treatment tools in conjunction with the establishment of an increasing number of comprehensive hemophilia centers and worldwide advocacy efforts have continued to push the progress of hemophilia care to new frontiers. This review highlights and summarizes these novel therapeutic approaches and the current clinical progress of hemophilia A.

Current and emerging factor VIII replacement products for hemophilia A

Hemophilia A is a congenital X-linked bleeding disorder caused by coagulation factor VIII (FVIII) deficiency. Routine infusion of factor replacement products is the current standard of care; however, the development of alloantibodies against FVIII remains a challenge. The treatment of hemophilia has undergone major advances over the past century to improve safety, effectiveness, manufacturing, and convenience of factor products. Major recent advances in the treatment of hemophilia A include the emergence of extended half-life products, factor VIII orthologs, and gene therapy products. Extended half-life products were designed to decrease the frequency of infusions, but only modest half-life extension is achieved. Factor VIII orthologs featuring lower cross-reactivity with anti-FVIII antibodies may be less susceptible to inactivation by inhibitors. Meanwhile, gene therapy may potentially provide a cure for hemophilia A, thus abrogating the need for protein-based factor replacement. This review aims to discuss current and emerging FVIII replacement products for hemophilia A.

Outcome of Clinical Trials with New Extended Half-Life FVIII/IX Concentrates

The development of a new generation of coagulation factors with improved pharmacokinetic profile will change the paradigm of treatment of persons with hemophilia (PWH). The standard treatment in PWH is represented by regular long-term prophylaxis that, given intravenously twice or thrice weekly, is associated with a not-negligible burden on patients' quality of life. The availability of drugs with improved pharmacokinetic profile may improve prophylaxis feasibility and protection against bleeding episodes. This article summarizes the main results obtained from clinical trials with modified factor VIII (FVIII) and factor IX (FIX) molecules. Published literature on new molecules for replacement treatment in hemophilia A and B was retrieved using PubMed search, and all ongoing clinical trials have been researched via www.clinicaltrials.gov. Such new molecules are usually engineered to have a longer plasma half-life than that which has been obtained by chemical modification (i.e., conjugation with polyethylene glycol, PEG) or by creating recombinant fusion proteins. Results from phase I/III studies in previously treated adults and children are now available for the vast majority of new products, including the results of their use in a surgical setting. On the contrary, trials involving previously untreated patients are still ongoing for all and results not yet available.

2017 Clinical trials update: Innovations in hemophilia therapy

A surge in therapeutic clinical trials over recent years is paving the way for transformative treatment options for patients with hemophilia. The introduction of recombinant factor concentrates in the early 1990s facilitated the use of prophylactic replacement as standard care for hemophilia rather than on-demand treatment. This has revolutionized health outcomes for hemophilia patients, enabling participation in physical activities and reducing debilitating, chronic joint damage. Challenges of prophylactic factor infusion include the frequency of infusions needed to maintain factor levels greater than 1%, patient adherence, reliable intravenous access, and development of neutralizing alloantibodies ("inhibitors"). Novel therapeutics seek to improve upon current factor concentrates by several different mechanisms: (1) extending the half-life of circulating exogenous factor protein, (2) replacing the gene necessary for production of endogenous factor protein, (3) employing bispecific antibody technology to mimic the coagulation function of factor VIII, (4) disrupting anticoagulant proteins, such as tissue factor pathway inhibitor (TFPI) or antithrombin (AT3) with antibodies, aptamers, or RNA interference technology. Emerging treatment options may reduce the frequency of (extended half-life products) or eliminate (gene therapy) the need for scheduled factor concentrate infusions, or provide a subcutaneous administration option (bispecific antibody, AT3, and TFPI targeting therapies). In addition, the nonfactor replacement strategies provide a promising treatment option for patients with inhibitors, presently the greatest unmet medical need in hemophilia. This review highlights current and recently completed clinical trials that are driving a paradigm shift in our approach to hemophilia care for patients with and without inhibitors. Am. J. Hematol. 91:1252-1260, 2016. © 2016 Wiley Periodicals, Inc.

Longer-acting clotting factor concentrates for hemophilia

Hemophilia, when severe, leads to spontaneous life-threatening bleeding episodes. Current therapy requires frequent intravenous infusions. Most patients must limit their physical activities to avoid bleeding when the factor activity levels are below normal. In 2014, new therapeutic factor VIII and IX products were approved in Canada and the U.S. Over the next couple of years, other new factor products will likely be approved. These new factors have been engineered to have improved pharmacokinetic properties, including extended half-life in circulation, thus providing major therapeutic advances for patients with hemophilia. In the completed clinical trials, over 700 patients have successfully used these longer acting products regularly for more than one year. These promising new therapies should allow patients with hemophilia to use fewer infusions to prevent spontaneous bleeding or to treat bleeding episodes, and to provide appropriate clotting factor levels for different physical activities.

Lasting power of new clotting proteins

Hemophilia is a genetic disease caused by a deficiency of one of the coagulation proteins. The term usually refers to either hemophilia A, factor VIII (FVIII), with an incidence of ∼1 in 5000 male births, or hemophilia B, factor IX (FIX), with an incidence of ∼1 in 30 000 male births. When severe, the disease leads to spontaneous life-threatening bleeding episodes. Current therapy requires frequent intravenous infusions of therapeutic factor concentrates. Most patients administer the infusions at home every few days and must limit their physical activities to avoid bleeding when the factor activity levels are below normal. In March 2014, a new therapeutic FIX preparation was approved for clinical use in Canada and the United States and, in June 2014, a new FVIII preparation was approved for clinical use in the United States. Over the next couple of years, other new factor products for FIX, FVIIa, and FVIII, which are currently in late stages of clinical trials, will likely also be approved. These new factors have been engineered to extend their half-life in circulation, thus providing major therapeutic advances for patients with hemophilia primarily by allowing treatment with fewer infusions per month. In the clinical trials so far, >500 patients have successfully used these extended half-life products regularly for >1 year to prevent spontaneous bleeding, to treat successfully any bleeding episodes, and to provide effective coagulation for major surgery. Essentially all infusions were well tolerated and effective. These promising new therapies should allow patients to use fewer infusions to maintain appropriate clotting factor activity levels in all clinical settings.

A gene-specific method for predicting hemophilia-causing point mutations

A fundamental goal of medical genetics is the accurate prediction of genotype-phenotype correlations. As an approach to develop more accurate in silico tools for prediction of disease-causing mutations of structural proteins, we present a gene- and disease-specific prediction tool based on a large systematic analysis of missense mutations from hemophilia A (HA) patients. Our HA-specific prediction tool, HApredictor, showed disease prediction accuracy comparable to other publicly available prediction software. In contrast to those methods, its performance is not limited to non-synonymous mutations. Given the role of synonymous mutations in disease and drug codon optimization, we propose that utilizing a gene- and disease-specific method can be highly useful to make functional predictions possible even for synonymous mutations. Incorporating computational metrics at both nucleotide and amino acid levels along with multiple protein sequence/structure alignment significantly improved the predictive performance of our tool. HApredictor is freely available for download at http://www.ncbi.nlm.nih.gov/CBBresearch/Przytycka/HA_Predict/index.htm.

Molecular approaches for improved clotting factors for hemophilia

Hemophilia is caused by a functional deficiency of one of the coagulation proteins. Therapy for no other group of genetic diseases has seen the progress that has been made for hemophilia over the past 40 years, from a life expectancy in 1970 of ∼20 years for a boy born with severe hemophilia to essentially a normal life expectancy in 2013 with current prophylaxis therapy. However, these therapies are expensive and require IV infusions 3 to 4 times each week. These are exciting times for hemophilia because several new technologies that promise extended half-lives for factor products, with potential for improvements in quality of life for persons with hemophilia, are in late-phase clinical development.

Long-lasting recombinant factor VIII proteins for hemophilia A

In the past 50 years, the lifespan of an individual affected with severe hemophilia A has increased from a mere 20 years to near that of the general unaffected population. These advances are the result of and parallel advances in the development and manufacture of replacement therapies. We are now poised to witness further technologic leaps with the development of longer-lasting replacement therapies, some of which are likely to be approved for market shortly. Prophylactic therapy is currently the standard of care for young children with severe hemophilia A, yet requires frequent infusion to achieve optimal results. Longer-lasting products will transform our ability to deliver prophylaxis, especially in very young children. Longer-lasting replacement therapies will require changes to our current treatment plans including those for acute bleeding, prophylaxis, surgical interventions, and even perhaps immunotolerance induction. Ongoing observation will be required to determine the full clinical impact of this new class of products.