Hemophilia A and B are X-linked disorders caused by deficient or defective clotting factor VIII (FVIII) or IX factor (FIX) proteins, and characterized by spontaneous or traumatic bleeding into joints ...and muscles. Previous use of plasma and plasma-derived clotting factors that lacked appropriate viral inactivation steps in manufacturing led to significant morbidity associated with transfusion-transmitted HIV and hepatitis C virus (HCV). The development of recombinant proteins revolutionized their treatment, and, with no new HIV or HCV infection via clotting proteins for nearly 30 years, greatly improved their lifespan, which now approaches that of the general population, and with the same risks for aging complications. Novel long-acting factor proteins are being licensed to extend FVIII and FIX half-life, thereby reducing infusion frequency and potentially bleed frequency and associated morbidity. Further, novel therapeutics which take advantage of new technologies, including siRNA, monoclonal antibody, and small peptide inhibition technologies, have the potential to simplify treatment and improve outcomes for those with inhibitors.
Given the shortcomings of current factor-, nonfactor-, and adeno-associated virus gene-based therapies, the recent advent of RNA-based therapeutics for hemophilia is changing the fundamental approach ...to hemophilia management. From small interfering RNA therapeutics that knockdown clot regulators antithrombin, protein S, and heparin cofactor II, to CRISPR/Cas9 gene editing that may personalize treatment, improved technologies have the potential to reduce bleeds and factor use and avoid inhibitor formation. These novel agents, some in preclinical studies and others in early phase trials, have the potential to simplify treatment and improve hemostasis and quality of life. Furthermore, because these therapies arise from manipulation of the coagulation cascade and thrombin generation and its regulation, they will enhance our understanding of hemostasis and thrombosis and ultimately lead to better therapies for children and adults with inherited bleeding disorders. What does the future hold? With the development of novel preclinical technologies at the bench, there will be fewer joint bleeds, debilitating joint disease, orthopedic surgery, and improved physical and mental health, which were not previously possible. In this review, we identify current limitations of treatment and progress in the development of novel RNA therapeutics, including messenger RNA nanoparticle delivery and gene editing for the treatment of hemophilia.
Fitusiran is an RNA interference therapeutic that targets antithrombin (AT) in the liver and interferes with AT translation by binding and degrading messenger RNA-AT, thereby silencing AT gene ...expression and preventing AT synthesis. In both preclinical and clinical studies, AT knockdown results in dose-dependent AT lowering when fitusiran is given weekly or monthly subcutaneously. In clinical trials, fitusiran dose escalation has resulted in improved thrombin generation and clinical hemostasis as measured by reduction in annualized bleed rate. Unlike currently licensed drugs, this improvement was not only in patients with hemophilia A but in also those with hemophilia B, with or without inhibitors. In dental and surgical procedures, fitusiran also provided perioperative hemostasis in association with AT lowering. Fitusiran is well tolerated, with minor local injection site reactions, but in one subject with severe hemophilia A, the concomitant use of daily high-dose factor VIII, inconsistent with trial guidance to avoid high, repeat doses of clotting factor, was associated with fatal thrombosis, suggesting the need for caution when using hemostatic agents in conjunction with fitusiran. Preclinical in vitro and in silico studies indicate improvement in thrombin generation in rare bleeding disorder plasmas, including in plasmas from patients with severe factors V, VII, and X deficiency, suggesting potential therapeutic benefit.
This phase 3 pivotal study evaluated the safety, efficacy, and pharmacokinetics of a recombinant FVIII Fc fusion protein (rFVIIIFc) for prophylaxis, treatment of acute bleeding, and perioperative ...hemostatic control in 165 previously treated males aged ≥12 years with severe hemophilia A. The study had 3 treatment arms: arm 1, individualized prophylaxis (25-65 IU/kg every 3-5 days, n = 118); arm 2, weekly prophylaxis (65 IU/kg, n = 24); and arm 3, episodic treatment (10-50 IU/kg, n = 23). A subgroup compared recombinant FVIII (rFVIII) and rFVIIIFc pharmacokinetics. End points included annualized bleeding rate (ABR), inhibitor development, and adverse events. The terminal half-life of rFVIIIFc (19.0 hours) was extended 1.5-fold vs rFVIII (12.4 hours; P < .001). Median ABRs observed in arms 1, 2, and 3 were 1.6, 3.6, and 33.6, respectively. In arm 1, the median weekly dose was 77.9 IU/kg; approximately 30% of subjects achieved a 5-day dosing interval (last 3 months on study). Across arms, 87.3% of bleeding episodes resolved with 1 injection. Adverse events were consistent with those expected in this population; no subjects developed inhibitors. rFVIIIFc was well-tolerated, had a prolonged half-life compared with rFVIII, and resulted in low ABRs when dosed prophylactically 1 to 2 times per week. This trial was registered at www.clinicaltrials.gov as #NCT01181128.
Key Points
Current hemophilia treatment involves frequent intravenous infusions of clotting factors, which is associated with variable hemostatic protection, a high treatment burden, and a risk of the ...development of inhibitory alloantibodies. Fitusiran, an investigational RNA interference (RNAi) therapy that targets antithrombin (encoded by SERPINC1), is in development to address these and other limitations.
In this phase 1 dose-escalation study, we enrolled 4 healthy volunteers and 25 participants with moderate or severe hemophilia A or B who did not have inhibitory alloantibodies. Healthy volunteers received a single subcutaneous injection of fitusiran (at a dose of 0.03 mg per kilogram of body weight) or placebo. The participants with hemophilia received three injections of fitusiran administered either once weekly (at a dose of 0.015, 0.045, or 0.075 mg per kilogram) or once monthly (at a dose of 0.225, 0.45, 0.9, or 1.8 mg per kilogram or a fixed dose of 80 mg). The study objectives were to assess the pharmacokinetic and pharmacodynamic characteristics and safety of fitusiran.
No thromboembolic events were observed during the study. The most common adverse events were mild injection-site reactions. Plasma levels of fitusiran increased in a dose-dependent manner and showed no accumulation with repeated administration. The monthly regimen induced a dose-dependent mean maximum antithrombin reduction of 70 to 89% from baseline. A reduction in the antithrombin level of more than 75% from baseline resulted in median peak thrombin values at the lower end of the range observed in healthy participants.
Once-monthly subcutaneous administration of fitusiran resulted in dose-dependent lowering of the antithrombin level and increased thrombin generation in participants with hemophilia A or B who did not have inhibitory alloantibodies. (Funded by Alnylam Pharmaceuticals; ClinicalTrials.gov number, NCT02035605 .).
In the childbearing years, hormonal therapy or hormonal changes in the menstrual cycle or the puerperium may be complicated by bleeding or thrombosis; however, among women with congenital disorders ...of hemostasis and thrombosis, the risk of bleeding or thrombosis may be increased. In women with congenital bleeding disorders, heavy menstrual bleeding is the most common bleeding symptom, and postpartum hemorrhage occurs despite treatment. Given the limitations of current therapy and the associated medical and psychological burden in women with bleeding disorders, better treatment approaches are needed to improve health outcomes and quality of life. In women with congenital thrombotic disorders, thromboembolism may complicate exogenous hormonal therapy and endogenous hormonal change during pregnancy and procedures, but risk differs by type of thrombophilia, procedure, time at risk, and thrombosis risk factors, all of which affect management. In this article, I shall consider a case-based discussion of current issues in women with congenital bleeding and clotting disorders, including heavy menstrual bleeding in a woman with VWD, postpartum hemorrhage risk in VWD, and thrombosis risk with oocyte retrieval in a woman with factor V Leiden and past thromboembolism. The goals are to review bleeding or thrombosis risk in these cases, current data, limitations of current treatment guidelines, and areas for future study.
The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies ...directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.
Introduction
Emicizumab is a bispecific monoclonal antibody that mimics factor VIII (FVIII) by binding to factors IXa and X to promote hemostasis in haemophilia A (HA) and HA with inhibitors (HA‐I). ...As emicizumab differs biochemically from FVIII, there is interest in its real‐world haemostatic efficacy.
Aim
To describe real‐world patient experience with emicizumab by retrospective chart review.
Methods
We reviewed medical records of patients cared for at the Hemophilia Center of Western PA, who initiated emicizumab following its licensure, and on whom bleeding events and factor use were available. Comparisons between groups were done by Student's t test for continuous data and by chi‐square or Fisher's exact test for discrete data.
Results
A total of 42 patients whose charts were reviewed included 18 (42.9%) with HA and 24 (52.1%) with HA‐I. Groups were similar in age, 17 (40.5%) <18 years, race, and haemophilia severity, and initiated weekly subcutaneous emicizumab 1.5 mg/kg, following 4‐week induction. Fourteen (33.3%) experienced at least one breakthrough bleed, of which 11 (44.0%) were joint bleeds, with an annualized bleed rate (ABR), 0.9 ± 0.3, not different between groups, P = .251. Surgical procedures were performed in 10 (23.8%), of whom 4 (40.0%) had postoperative bleeding and one developed postoperative thrombosis in association with FEIBA despite emicizumab discontinuation 1 month preoperatively. Local skin reactions occurred in three and headache in one. Overall, 85.0% of those who rated their health indicated it was improved.
Discussion
Despite breakthrough bleeds and postoperative thrombosis associated with emicizumab, most HA and HA‐I experienced improved health.
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