Fixed doses of N8-GP prophylaxis maintain moderate-to-mild factor VIII levels in the majority of patients with severe hemophilia A

Noninterventional study assessing joint health in persons with hemophilia A after switching to turoctocog alfa pegol: design of pathfinderReal

Background

Joint damage affects the quality of life of persons with hemophilia A. The long-term safety and efficacy of turoctocog alfa pegol (N8-GP) prophylaxis in persons with hemophilia A has been investigated in pivotal phase 3 trials in children, adolescents, and adults (pathfinder program). However, there is a lack of data on joint health in adult persons with hemophilia A treated with N8-GP.

Objectives

To describe the design of the ongoing pathfinderReal study investigating the joint health status in adult persons with hemophilia A after switching to N8-GP.

Methods

pathfinderReal is a multicountry, noninterventional, single-arm study (NCT05621746) of joint health in adult (≥18 years) male persons with hemophilia A who have switched to N8-GP. Patients enrolled in other interventional studies and those who have previously terminated N8-GP treatment will be excluded. Approximately 124 adults with hemophilia A will be enrolled and followed up for a maximum of 24 months. Data from routine clinical assessments of patients' joint health will be collected. The primary endpoint is change in Hemophilia Joint Health Score (defined as a change in total score of ≤2) from initiation of N8-GP treatment until the end of the study. Secondary endpoints include number of bleeding episodes, number and resolution of target joints, patient-reported outcomes of problem joint score, pain score, and change in physical function levels. An exploratory endpoint is included to measure the number of patients achieving improved Hemophilia Joint Health Score from the initiation of N8-GP until the end of the study.

Conclusion

The pathfinderReal study will provide insights regarding the impact of N8-GP on joint health in persons with hemophilia A in a real-world setting.

Cases of less-than-expected FVIII activity in previously treated patients during post-marketing surveillance of N8-GP

INTRODUCTION

Turoctocog alfa pegol (N8-GP) is a glycoPEGylated, extended half-life (EHL), human recombinant factor VIII (FVIII) approved for the treatment and prevention of bleeding episodes in patients with haemophilia A. Since its launch in August 2019, > 800 patients have been treated worldwide.

AIM

To present data from identified post-marketing cases of less-than-expected FVIII activity in previously treated patients (PTPs) without inhibitors after switching to N8-GP.

METHODS

The post-marketing safety database was searched using keywords such as 'coagulation FVIII level decreased'. Identified cases reported prior to 13 October 2021 were included in this report. Cases in which patients had FVIII inhibitors were excluded.

RESULTS

Here we report 14 cases of less-than-expected FVIII activity. Details varied greatly amongst the cases. At presentation, FVIII activity ranged from 1% (15 min post-dose) to 51% (2 days post-dose). Seven patients experienced bleeding episodes after switching to N8-GP with heterogeneity in bleeding presentations. Six out of seven patients who were tested for anti-PEG IgG and/or IgM antibodies were positive. In all known cases, FVIII activity returned to the expected range when switched to an alternative FVIII replacement product.

CONCLUSION

In conclusion, the 14 reported cases of less-than-expected FVIII activity, without presence of detectable FVIII inhibitors, presented with heterogenous characteristics, and wide variations in FVIII activity and anti-PEG antibody titre. FVIII activity returned to the expected range after switching to alternative FVIII products. In line with WFH guidelines, monitoring of FVIII activity can ensure FVIII activity in the expected range. The safety surveillance of N8-GP continues.

The road to implementation of pharmacokinetic-guided dosing of factor replacement therapy in hemophilia and allied bleeding disorders. Identifying knowledge gaps by mapping barriers and facilitators

Clinical guidelines and expert groups recommend the use of pharmacokinetic (PK)-guided dosing of factor replacement therapy for the treatment of bleeding disorders, especially for patients with hemophilia. Although PK-guided dosing is increasingly applied, it is generally not considered standard clinical practice. The aim of this scoping review is to map barriers and facilitators for the implementation of PK-guided dosing in clinical practice and to identify knowledge gaps. A literature search was performed and 110 articles were included that describe PK-guided dosing in patients with bleeding disorders, mostly hemophilia A. We defined two overarching themes, efficacy and feasibility, and discuss five topics within each theme. For each topic, barriers, facilitators and knowledge gaps were described. Although consensus was found with regard to some topics, contradicting reports were found for others, especially with respect to the efficacy of PK-guided dosing. These contradictions highlight the need for future research to elucidate current ambiguities.

The More Recent History of Hemophilia Treatment

The availability first in the 1970s of plasma-derived and then in the 1990s of recombinant clotting factor concentrates represented a milestone in hemophilia care, enabling not only treatment of episodic bleeding events but also implementation of prophylactic regimens. The treatment of hemophilia has recently reached new landmarks. The traditional clotting factor replacement therapy for hemophilia has been substituted over the last 10 years by novel treatments such as bioengineered factor VIII and IX molecules with extended half-life and non-factor treatments including the bispecific antibody emicizumab. This narrative review is dedicated to these newer therapies, which are contributing significantly to improving the long-term management of prophylaxis in hemophilia patients. Another section is focused on the current state of gene therapy, which is a promising definitive cure for severe hemophilia A and B.

Immunogenicity of Current and New Therapies for Hemophilia A

Anti-drug antibody (ADA) development is a significant complication in the treatment of several conditions. For decades, the mainstay of hemophilia A treatment was the replacement of deficient coagulation factor VIII (FVIII) to restore hemostasis, control, and prevent bleeding events. Recently, new products have emerged for hemophilia A replacement therapy, including bioengineered FVIII molecules with enhanced pharmacokinetic profiles: the extended half-life (EHL) recombinant FVIII products. However, the main complication resulting from replacement treatment in hemophilia A is the development of anti-FVIII neutralizing alloantibodies, known as inhibitors, affecting approximately 25–30% of severe hemophilia A patients. Therefore, the immunogenicity of each FVIII product and the mechanisms that could help increase the tolerance to these products have become important research topics in hemophilia A. Furthermore, patients with inhibitors continue to require effective treatment for breakthrough bleedings and procedures, despite the availability of non-replacement therapy, such as emicizumab. Herein, we discuss the currently licensed treatments available for hemophilia A and the immunogenicity of new therapies, such as EHL-rFVIII products, compared to other products available.

The safety and efficacy of N8-GP (turoctocog alfa pegol) in previously untreated pediatric patients with hemophilia A

N8-GP (turoctocog alfa pegol) is a recombinant, glycoPEGylated, extended half-life, factor VIII replacement product. Here, we examined the immunogenicity, safety, and efficacy of N8-GP in previously untreated patients (PUPs). pathfinder6 is an ongoing, open-label, phase 3 trial that enrolled PUPs with severe hemophilia A and were aged <6 years. The primary end point was the incidence of factor VIII inhibitors (≥0.6 Bethesda units [BU]). Eighty patients received ≥1 N8-GP dose and were included in this analysis; ≥50 patients had ≥50 exposure days to N8-GP. The inhibitor incidence was 29.9% (14.9% high-titer [>5 BU]). Sixty-five patients received N8-GP prophylaxis for an average of 2.17 years with a median annualized bleeding rate (interquartile range) of 1.42 (0.76; 3.13) and a 90.5% hemostatic success rate. Temporarily decreased incremental recovery (IR), defined as ≥2 consecutive measurements of IR <0.6 (IU/dL)/(IU/kg) but no inhibitors, was observed in 17 patients within 5 exposure days to N8-GP and had a strong temporal correlation with anti-polyethylene glycol immunoglobulin G antibody titers. IR returned within the expected range with continued N8-GP dosing. During the period of decreased IR, hemostatic response was similar to that of the overall trial population, and no hypersensitivity related to N8-GP or unexpected new adverse events were reported. N8-GP prophylaxis was efficacious for the prevention and treatment of bleeding episodes in PUPs with severe hemophilia A. The inhibitor incidence was 29.9%. All patients with temporarily decreased IR continuing on N8-GP dosing returned within the expected range and had no evident lack of efficacy. This trial was registered at www.clinicaltrials.gov as #NCT02137850.

Impact of novel hemophilia therapies around the world

Hemophilia A and B are hereditary bleeding disorders, characterized by factor VIII or IX deficiencies, respectively. For many decades, prophylaxis with coagulation factor concentrates (replacement therapy) was the standard‐of‐care approach in hemophilia. Since the 1950s, when prophylaxis started, factor concentrates have been improved with virus inactivation and molecule modification to extend its half‐life. The past years have brought an intense revolution in hemophilia care, with the development of nonfactor therapy and gene therapy. Emicizumab is the first and only nonreplacement agent to be licensed for prophylaxis in people with hemophilia A, and real‐world data show similar efficacy and safety from the pivotal studies. Other nonreplacement agents and gene therapy have ongoing studies with promising results. Innovative approaches, like subcutaneous factor VIII and lipid nanoparticles, are in the preclinical phase. These novel agents, such as extended half‐life concentrates and emicizumab, have been available in resource‐constrained countries through the constant efforts of the World Federation of Haemophilia Humanitarian Aid Program. Despite the wide range of new approaches and therapies, the main challenge remains the same: to guarantee treatment for all. In this article, we discuss the evolution of hemophilia care, global access to hemophilia treatment, and the current and future strategies that are now under development. Finally, we summarize relevant new data on this topic presented at the ISTH 2021 virtual congress.

Predictive Modeling Identifies Total Bleeds at 12-Weeks Postswitch to N8-GP Prophylaxis as a Predictor of Treatment Response

Background  Predicting annualized bleeding rate (ABR) during factor VIII (FVIII) prophylaxis for severe hemophilia A (SHA) is important for long-term outcomes. This study used supervised machine learning-based predictive modeling to identify predictors of long-term ABR during prophylaxis with an extended half-life FVIII.

Methods  Data were from 166 SHA patients who received N8-GP prophylaxis (50 IU/kg every 4 days) in the pathfinder 2 study. Predictive models were developed to identify variables associated with an ABR of ≤1 versus >1 during the trial's main phase (median follow-up of 469 days). Model performance was assessed using area under the receiver operator characteristic curve (AUROC). Pre-N8-GP prophylaxis models learned from data collected at baseline; post-N8-GP prophylaxis models learned from data collected up to 12-weeks postswitch to N8-GP, and predicted ABR at the end of the outcome period (final year of treatment in the main phase).

Results  The predictive model using baseline variables had moderate performance (AUROC = 0.64) for predicting observed ABR. The most performant model used data collected at 12-weeks postswitch (AUROC = 0.79) with cumulative bleed count up to 12 weeks as the most informative variable, followed by baseline von Willebrand factor and mean FVIII at 30 minutes postdose. Univariate cumulative bleed count at 12 weeks performed equally well to the 12-weeks postswitch model (AUROC = 0.75). Pharmacokinetic measures were indicative, but not essential, to predict ABR.

Conclusion  Cumulative bleed count up to 12-weeks postswitch was as informative as the 12-week post-switch predictive model for predicting long-term ABR, supporting alterations in prophylaxis based on treatment response.

Illustrative Cases from the Pathfinder Clinical Trials of Patients with Hemophilia A Treated with Turoctocog Alfa Pegol (N8-GP)

PURPOSE

To illustrate the benefits of the extended half-life (EHL) recombinant factor VIII product N8-GP (Esperoct^®, turoctocog alfa pegol) by describing individual cases of patients with severe hemophilia A treated with N8-GP in the pathfinder clinical trial program.

PATIENTS AND METHODS

This manuscript presents selected patient cases from the pivotal pathfinder clinical trial program, which included a number of clinical studies in adults (pathfinder 2 and 3) and children (pathfinder 5); overall results published previously. Clinical data and outcomes described in this manuscript are more detailed and derived from several interesting patient cases (five adults from pathfinder 2 and two children from pathfinder 5), who received N8-GP as prophylaxis (PPX) for their severe hemophilia A. Three of the five adults described here also underwent multiple major surgeries (for which they moved from pathfinder 2 into pathfinder 3 and later returned to pathfinder 2). New analyses on pediatric joint health from pathfinder 5 are also summarized here. Outcomes assessed included bleeding complications, improvements in quality of life, intraoperative hemostatic response, blood loss during surgery, number of blood transfusions, and annualized bleeding rates. For the pediatric patients, target joint resolution, adverse events, and annualized joint bleeding rate were also assessed, all by the treating physician.

RESULTS

Considerable improvements in treatment adherence, bleeding rates, and overall physical activity levels were demonstrated in two adult cases from the pathfinder 2 trial. N8-GP demonstrated good or excellent hemostatic coverage in three adult patients undergoing multiple major surgeries. The benefits of N8-GP for joint health and in support of children and adolescents with evolving active lifestyles were reported for several pediatric cases.

CONCLUSION

These patient cases highlight the benefits of EHL products, such as N8-GP, for patients with severe hemophilia A. They include more challenging scenarios relating to improvements in previously poor adherence to PPX, children with active sporting lifestyles, and patients requiring multiple major surgeries.

Measuring factor VIII activity in samples from patients treated with N8-GP (Esperoct® ; turoctocog alfa pegol) during the pathfinder clinical trials programme

FVIII activity in samples taken at various time points from 21 patients treated with N8-GP (Esperoct^® ; turoctocog alfa pegol) during the pathfinder clinical trial programme was assessed and compared using different assay methods. FVIII activity measurements in samples from patients treated with N8-GP were similar using chromogenic assays, regardless of calibration method or kit/analyser combination. FVIII activity measurements using one-stage aPTT-based assays were slightly lower when calibrated using normal human plasma (NHP) compared with a product-specific standard; this difference may be partially attributable to differences in the aPTT reagent/analyser combinations used to perform the measurements. Overall, these results confirm the accuracy of FVIII activity measurements using N8-GP-treated patient samples and routine clinical laboratory methods with NHP calibration.

An overview of the pathfinder clinical trials program: Long-term efficacy and safety of N8-GP in patients with hemophilia A

N8-GP (turoctocog alfa pegol, Esperoct® ; Novo Nordisk A/S, Bagsvaerd, Denmark) is a state-of-the-art, extended half-life factor VIII (FVIII) molecule used for prophylactic and on-demand treatment of patients with hemophilia A. The pathfinder clinical trial program, which began with the pathfinder1 trial in 2010, was developed to assess the long-term efficacy and safety of N8-GP in children, adolescents, and adults. The pivotal pathfinder2 (adolescents and adults) and pathfinder5 (children) trials were completed in late 2018, and comprehensive analyses of the end-of-trial results are published together with this article as part of an N8-GP Supplement. Furthermore, results from the pathfinder3 trial, which was designed to evaluate the safety and efficacy of N8-GP during major surgery, have also recently been finalized. Here, we provide an overview of the pathfinder clinical development program and summarize key data from the completed pathfinder trials. We also provide perspectives on the future of extended half-life FVIII molecules in the treatment of patients with hemophilia A and describe currently ongoing pathfinder trials.

Long-term safety and efficacy of N8-GP in previously treated pediatric patients with hemophilia A: Final results from pathfinder5

BACKGROUND

N8-GP (turoctocog alfa pegol; Esperoct® , Novo Nordisk A/S, Bagsvaerd, Denmark) is a glycoPEGylated, extended half-life human recombinant factor VIII (FVIII).

OBJECTIVE

Here, we report end-of-trial safety and efficacy results from the completed N8-GP pathfinder5 trial.

METHODS

pathfinder5 (NCT01731600) was a multi-national, open-label, single-arm, non-randomized, non-controlled trial in previously treated male patients aged <12 years old with severe hemophilia A that comprised a main and an extension phase. During the main phase, patients received twice-weekly N8-GP 60 IU/kg for 50 exposure days (~26 weeks). During the extension phase, patients received the same regimen until the end of trial (first patient in main phase, 20 February 2013; trial end, 28 September 2018).

RESULTS

Sixty-eight patients were exposed to N8-GP for a median time of ~4.9 years on regimen. Of the 63 patients who started in the extension phase, 62 completed the trial. No FVIII inhibitors (≥0.6 BU) or other safety concerns were detected. The overall estimated annualized bleeding rate was 1.08 (median 0.81), and nearly 20% of patients had no bleeds during the entire trial. The proportion of patients with no annual bleeds increased with time, with 56% of patients experiencing no bleeds and 86% experiencing no spontaneous bleeds during the fourth year of exposure. All baseline target joints of patients who participated in both phases of this trial were resolved in slightly over 2 years.

CONCLUSION

Overall, data from the completed pathfinder5 trial show that long-term (median 4.9 years) N8-GP treatment was efficacious and well tolerated in previously treated pediatric patients with severe hemophilia A.

Clinical Evidence and Safety Profile of Emicizumab for the Management of Children with Hemophilia A

Emicizumab is a bispecific, humanized, monoclonal antibody mimicking the factor (F) VIII cofactor activity in mediating the generation of FXa by FIXa in patients with hemophilia A (HA). This subcutaneous non-factor agent has been recently extensively approved for the prophylaxis of patients of HA patients with and without FVIII-inhibitors of all ages, although few data are currently available in children. In Phase 3 clinical trials and case series, emicizumab prophylaxis significantly reduced bleeding rates compared to previous treatment in HA adolescents and children with or without FVIII-inhibitors and was generally well tolerated. In addition, subcutaneous administration of emicizumab provided beneficial effects on health-related quality of life, and lessened the burden of the disease in HA patients as well as in their caregivers. However, additional prospective studies are required to evaluate the long-term safety of emicizumab prophylaxis in very young patients, including previously untreated patients. The aim of this paper was to review the limited data available on the use of emicizumab prophylaxis in children and to highlight the need for further studies to address remaining concerns.

Pharmacokinetic-tailored approach to hemophilia prophylaxis: Medical decision making and outcomes

BACKGROUND

Clinical application of population pharmacokinetics (popPK) is of increasing interest to patients with hemophilia, providers, and payers. Routine use of popPK profiles in factor replacement prophylaxis decision making has the potential to maintain or improve efficacy and reduce product consumption.

AIM

To investigate the feasibility of implementation and longitudinal assessment of pharmacokinetic (PK)-tailored prophylaxis in routine clinical practice for hemophilia A and to describe factors that influence decision making for prescribed hemophilia prophylaxis.

METHODS

This longitudinal, multicenter, prospective feasibility study of children and adults with hemophilia A without inhibitors used the Web Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) to generate PK profiles. Assessments over 12 weeks captured data on prescribed prophylaxis, popPK tool use, provider decision making, and patient-reported outcomes.

RESULTS

Eighteen participants aged 6 to 39 years enrolled; half used extended half-life concentrates. Patient interest in their PK centered on general curiosity followed by a desire for participation in physical activity and decrease in infusion frequency. Providers used the WAPPS clinical calculator feature to simulate prophylaxis regimens under different dose, infusion, and trough conditions. Most targeted troughs were 1 to 3 IU/dL. The feasibility assessment demonstrated challenges with patient recruitment; however, the majority of participants successfully completed study assessments meeting feasibility targets.

CONCLUSION

A larger-scale study powered to evaluate the impact of PK-tailored prophylaxis on clinical and patient-reported outcomes is feasible with study design modifications to support increased recruitment rate. Shared decision making incorporating patient and provider goals is important and facilitated by regimen simulations with the clinical calculator.

Corrigendum

[This corrects the article DOI: 10.1002/rth2.12220.].