Concizumab (Novo Nordisk), a subcutaneous monoclonal antibody administered once daily, shows significant reductions in annualized bleeding rates in patients with hemophilia A or B with inhibitors, potentially representing the first subcutaneous treatment option for patients with hemophilia B with inhibitors.
“These results demonstrate the potential of concizumab as an efficacious treatment option for people living with hemophilia A or B with inhibitors – the latter a population with severely limited treatment options,” first author Tadashi Matsushita, MD, PhD, of the department of transfusion medicine, Nagoya (Japan) University Hospital, said in an interview regarding the study, published in the New England Journal of Medicine.
The results are from the prospective, multicenter, phase 3 explorer7 trial, involving 133 patients, including 80 with hemophilia A and 53 had hemophilia B, all with inhibitors, a complication of hemophilia therapy in which antibodies ‘inhibit’ clot formation and complicate standard treatment.
The patients, aged 12 or older and all receiving on-demand treatment with bypassing agents, were randomized to receive no prophylaxis for at least 24 weeks (n = 19) or concizumab prophylaxis for at least 32 weeks (n = 33), with the remaining patients nonrandomly assigned to two groups receiving concizumab prophylaxis for at least 24 weeks (n = 81).
For the primary endpoint of the estimated mean annualized bleeding rate, the rate in the no-prophylaxis group was 11.8 episodes versus just 1.7 episodes in the concizumab prophylaxis 32-week group (rate ratio, 0.14; P < .001).
The overall median annualized bleeding rate for patients in all three groups receiving concizumab was zero episodes.
Annualized rates of treated spontaneous, joint, and target joint bleeding episodes were also lower in the concizumab groups versus the no-prophylaxis group, with annualized rate ratios that were similar to the annualized rate ratio for the primary endpoint.
While similar annualized bleeding rates were observed in hemophilia subtypes, the study wasn’t powered to show superiority according the hemophilia A or B, the authors noted.
Plasma concentrations of concizumab remained stable over the course of the study.
There were no significant differences in terms of key secondary endpoints of change in bodily pain and physical functioning scores from the start of treatment to week 24.
Pause for safety
Treatment in the study was paused for 6 months from March 2020 to August 2020 following nonfatal thromboembolic events occurring in three patients receiving concizumab, including one in the explorer7 trial and two in the concurrent explorer8 trial, evaluating the drug in patients with hemophilia without inhibitors.
The authors wrote that the three patients had all received concomitant treatment for bleeding and had thrombotic risk factors including obesity and other comorbidities.
The trial resumed following mitigation measures that included revising the dosing regimen to include a 1–mg/kg concizumab loading dose, followed by a subcutaneous once-daily dose of 0.2 mg/kg concizumab. No further thromboembolic events were reported after the pause. Otherwise, adverse events were mainly low grade, with serious events being rare.
Option for hemophilia B important
Of the two disease types, hemophilia A is much more common, with an estimated prevalence in the United States of 12 cases per 100,000 males versus hemophilia B, which has a rate of only 3.7 cases per 100,000, according to the Centers for Disease Control and Prevention. Women make up only about 1% of cases with moderate to severe hemophilia.
A standard treatment of hemophilia A or B is prophylaxis with factor replacement therapies allow for improved clotting and reduced bleeding. However, one caveat is the need for intravenous injections, as often as once daily in some cases.
The development of inhibitors in response to replacement therapy may further necessitate the need for treatment with bypassing agents for breakthrough bleeding.
As an alternative, non–factor replacement therapies can promote coagulation, notably the factor VIII mimetic emicizumab, given by subcutaneous injection, and approved by the Food and Drug Administration in 2018 for patients with and without inhibitors.
Emicizumab is recommended by the World Federation on Hemophilia over bypassing agents as prophylaxis for patients with hemophilia A and persistent inhibitors.
Importantly, however, there are no effective prophylactic treatments or easily administered subcutaneous therapies available for hemophilia B with inhibitors, underscoring the potential importance of concizumab, which targets the tissue factor pathway inhibitor protein, linked to coagulation.
“Concizumab has the potential to become the first subcutaneous and first-in-class treatment for hemophilia B with inhibitors,” Dr. Matsushita said. “There are other therapies investigated for hemophilia B with and without inhibitors still in clinical development,” he noted.
FDA resubmission planned
In May, Novo Nordisk announced that the FDA had rejected its application for concizumab, requesting more information on the drug’s manufacturing process and its system for the monitoring and dosing of patients to ensure proper drug administration. In a statement, Novo Nordisk reported its plans to move ahead.
“Novo Nordisk has begun addressing the FDA’s feedback and is working closely with the FDA as plans for resubmission continue,” the company reported. “We are confident in the potential of concizumab to address a significant unmet need, particularly for people with hemophilia B with inhibitors who currently have limited prophylactic options and are committed to bringing this important treatment to people with hemophilia with inhibitors living in the U.S.A.”
Meanwhile in Canada, concizumab was approved in March 2023 for the treatment of adolescent and adult patients with hemophilia B with inhibitors and who require routine prophylaxis to prevent or reduce the frequency of bleeding episodes.
The authors wrote that concizumab continues to be investigated across all hemophilia subtypes, including in the explorer10 study, which is evaluating the drug in children living with hemophilia A or B, with and without inhibitors.
The study was supported by Novo Nordisk. Dr. Matsushita reported speaking for and participating on a scientific advisory board of Novo Nordisk.