The Potential Close Future of Hemophilia Treatment - Gene Therapy, TFPI Inhibition, Antithrombin Silencing, and Mimicking Factor VIII with an Engineered Antibody

Recent Advances in Gene Therapy for Hemophilia: Projecting the Perspectives

One of the well-known X-linked genetic disorders is hemophilia, which could be hemophilia A as a result of a mutation in the F8 (factor VIII) gene or hemophilia B as a result of a mutation in the F9 (factor IX) gene, leading to insufficient levels of the proteins essential for blood coagulation cascade. In patients with severe hemophilia, factor VIII or factor IX activities in the blood plasma are considerably low, estimated to be less than 1%. This is responsible for spontaneous or post-traumatic bleeding episodes, or both, leading to disease complications and death. Current treatment of hemophilia relies on the prevention of bleeding, which consists of expensive lifelong replacement infusion therapy of blood plasma clotting factors, their recombinant versions, or therapy with recombinant monoclonal antibodies. Recently emerged gene therapy approaches may be a potential game changer that could reshape the therapeutic outcomes of hemophilia A or B using a one-off vector in vivo delivery and aim to achieve long-term endogenous expression of factor VIII or IX. This review examines both traditional approaches to the treatment of hemophilia and modern methods, primarily focusing on gene therapy, to update knowledge in this area. Recent technological advances and gene therapeutics in the pipeline are critically reviewed and summarized. We consider gene therapy to be the most promising method as it may overcome the problems associated with more traditional treatments, such as the need for constant and expensive infusions and the presence of an immune response to the antibody drugs used to treat hemophilia.

Updates on Novel Non-Replacement Drugs for Hemophilia

Over the last decade, the world of hemophilia has experienced an unprecedented therapeutic advance, thanks to the progress in bioengineering technologies, leading to the introduction of drugs with novel mechanisms of action based on restoring thrombin generation or coagulation factor VIII mimicking. Apart from the bispecific monoclonal antibody emicizumab, already approved for patients with severe hemophilia A with and without inhibitors, novel non-replacement drugs designed to reduce the treatment burden of patients with hemophilia A or B with or without inhibitors are undergoing evaluation in clinical trials. Thanks to their innovative mechanism of action and subcutaneous administration, these drugs promise to provide effective bleeding protection together with improved adherence and improve health-related quality of life for patients with hemophilia. On the other hand, rare thromboembolic events have been reported with some of these drugs and warrant continuous post-marketing surveillance and investigation of predisposing factors, although the overall safety profile of most of these drugs is good. Finally, new challenges need to be faced in the clinical and laboratory monitoring of the hemostatic status in patients treated with these innovative therapies. In this review, we provide an update on the available data on novel non-replacement drugs currently undergoing evaluation in clinical trials for patients with hemophilia.

Tailoring the effect of antithrombin-targeting therapy in haemophilia A using in silico thrombin generation

Factor (F) VIII deficiency causes bleeding in haemophilia A patients because of the reduced formation of procoagulant enzyme thrombin, which is needed to make the blood clot. We measured the dynamics of coagulation in haemophilia A patients by measuring thrombin generation (TG). Additionally, we quantified the procoagulant process of prothrombin conversion and anticoagulant process of thrombin inhibitor complex formation. In haemophilia A, prothrombin conversion is severely reduced, causing TG to be low. Nevertheless, the thrombin inactivation capacity of these patients is comparable to that in healthy subjects, leading to a severe imbalance between procoagulant and anticoagulant processes and a subsequent increased bleeding risk. A novel therapy in haemophilia A is the targeting of anticoagulant pathway, e.g. thrombin inhibitor antithrombin (AT), to restore the haemostatic balance. We simulated the effect of AT reduction on TG in silico. Lowering AT levels restored TG dose-dependently and an AT reduction of 90-95% led to almost normal TG in most patients . However, the variation in response to AT reduction was large between patients, indicating that this approach should be tailored to each individual patients. Ideally, TG and thrombin dynamics simulation could in the future contribute to the management of patients undergoing AT targeting therapy.

Practical considerations for nonfactor-replacement therapies in the treatment of haemophilia with inhibitors

New therapeutic agents for haemophilia with inhibitors that are in development or already licensed are expected to provide transformative treatment options. Many of these new therapies are not based on simply replacing the missing factor; new strategies include bispecific antibody technology that mimics factor VIII coagulation function (emicizumab), and inhibition of anticoagulant proteins such as tissue factor pathway inhibitor (eg PF-06741086) and antithrombin (eg fitusiran). These agents are administered subcutaneously and should significantly reduce treatment burden and increase the ability to deliver prophylaxis for patients. Limited real-world data and validated practical guidance on these recently licensed/upcoming treatments resulted in the authors convening to discuss recommendations on their use. Emicizumab is currently the only licenced nonfactor therapy; thus, our recommendations focus on this product. Target candidates for emicizumab prophylaxis are difficult-to-treat patients with haemophilia A and inhibitors and/or venous access issues, frequent bleeds and target joints. In case of breakthrough bleeding while receiving emicizumab, patients still require treatment with bypassing agents; the adjunct treatment of choice is recombinant activated factor VII. This treatment is also recommended to prevent bleeds in patients with inhibitors undergoing surgery. Our recommendations on suitable laboratory assays and monitoring new products, as well as the benefit of patient-reported outcomes (such as pain and physical activity levels), are included. We also briefly discuss future treatment options for patients with haemophilia B and inhibitors. Although these nonfactor treatments offer great promise, further data and real-world evidence are needed.

The Possible Non-Mutational Causes of FVIII Deficiency: Non-Coding RNAs and Acquired Hemophilia A

Hemophilia type A (HA) is the most common type of blood coagulation disorder. While the vast majority of cases are inherited and caused by mutations in the F8 gene, recent data raises new questions regarding the non-heritability of this disease, as well as how other molecular mechanisms might lead to the development of HA or increase the severity of the disease. Some data suggest that miRNAs may affect the severity of HA, but for some patients, miRNA-based interference might cause HA, in the absence of an F8 mutation. A mechanism in HA installation that is also worth investigating and which could be identified in the future is the epigenetic silencing of the F8 gene that might be only temporarily. Acquired HA is increasingly reported and as more cases are identified, the description of the disease might become challenging, as cases without FVIII autoantibodies might be identified.

Post-authorization pharmacovigilance for hemophilia in Europe and the USA: Independence and transparency are keys

The regulatory process is currently designed to ensure drug safety during the pre-marketing process. Due to limitations of the pivotal studies owing to their short duration and small number of highly selected cases, some adverse drug reactions (ADRs) are not detected, particularly the rarest and those which appear a long time after exposure. Thus it is essential to foster pharmacovigilance run totally independently from marketing authorization holders in order to attain transparent surveillance. This challenge is relevant for hemophilia drugs, after recent advances offered innovative replacement and non-replacement medicines that warrant monitoring due to the occurrence of predicted but also unexpected and rare ADRs. This article contains an overview of pharmacovigilance systems in the European Union and USA, describing the main ADRs related to traditional and recently available hemophilia medications and suggests how to involve stakeholders other than marketing authorization holders for an independent and transparent pharmacovigilance targeted to detect not only early ADRs but also those emerging post-marketing.

Pharmacokinetics, immunogenicity, safety, and preliminary efficacy of subcutaneous turoctocog alfa pegol in previously treated patients with severe hemophilia A (alleviate 1)

BACKGROUND

The current standard of care for patients with hemophilia A is regular prophylaxis with factor VIII (FVIII) administered intravenously. Interest in subcutaneous (s.c.) administration, to potentially increase convenience, reduce the treatment burden and improve compliance, is increasing.

OBJECTIVES

Evaluate the pharmacokinetics (PK), immunogenicity, safety, and preliminary efficacy of s.c. administration of turoctocog alfa pegol (s.c. N8-GP) in adult or adolescent previously treated patients (PTPs) with severe hemophilia A (alleviate 1; NCT02994407).

PATIENTS/METHODS

In part A, 24 PTPs received a single dose of s.c. N8-GP (12.5, 25, 50, or 100 IU/kg) with 6 patients per cohort. PK modelling of data from part A supported a suitable dose for part B. Part B comprised a multiple dose trial in 26 PTPs; patients <60 kg received 2000 IU and patients ≥60 kg received 4000 IU s.c. N8-GP daily for 3 months.

RESULTS

Single-dose s.c. N8-GP supported dose linearity. Daily prophylaxis with s.c. N8-GP appeared well tolerated and efficacious, achieving a mean trough FVIII activity close to 10% at steady state. Five patients developed anti-N8-GP binding antibodies after 42 to 91 exposure days, one of whom developed an inhibitor to FVIII. Anti-N8-GP antibody appearance was associated with a decline in FVIII plasma activity in four of the five patients. Five patients reported a total of nine treatment-requiring bleeding episodes during prophylaxis.

CONCLUSIONS

Subcutaneous administration of N8-GP is associated with a high incidence of antibodies in PTPs with severe hemophilia A. Further clinical development of s.c. N8-GP has been suspended.

Attempting to remedy sub-optimal medication adherence in haemophilia: The rationale for repeated ultrasound visualisations of the patient's joint status

Haemophilia is marked by joint bleeding (haemarthrosis) leading to cartilage damage (arthropathy). Lifelong prophylaxis-initiated after the first bleeding episode-leads to a dramatic decrease in arthropathy in haemophilia patients. However, adherence to continuous intravenous administrations of factor VIII (FVIII) or FIX products is challenging, and patients potentially suffer from breakthrough bleedings while on prophylaxis. Newer FVIII/FIX products with enhanced convenience attributes and/or easier infusion procedures are intended to improve adherence. However, pharmacokinetic data should be harmonised with information from individual attitudes and treatment needs, to tailor intravenous dosing and scheduling in patients who receive extended half-life products. Nor is there sound evidence as to how subcutaneous non-FVIII/FIX replacement approaches (concizumab; emicizumab; fitusiran) or single intravenous injections of adeno-associated viral vectors (when employing gene therapy) will revolutionize adherence in haemophilia. In rheumatoid arthritis, repeated ultrasound examination of a patient's major joints is a valuable tool to educate patients and parents to understand the disease and provide an objective framework for clinicians to acknowledge patient's adherence. Joint ultrasound examination in haemophilia significantly correlates with cartilage damage, effusion, and synovial hypertrophy evaluated by magnetic resonance imaging. Furthermore, in patients with haemophilia undergoing prophylaxis with an extended half-life product for a ≈ 2.8 year period, a significant continued improvement in joint health is detected at the physical examination. This provides the rationale for studies on repeated ultrasound examinations of joint status to attempt to remedy sub-optimal medication adherence and help identify which approach is most suited on which occasion and for which patient.