Phase 1 dose-escalating study to evaluate the safety, pharmacokinetics, and pharmacodynamics of a recombinant factor Xa variant (FXaI16L )

Latest advances in the reversal strategies for direct oral anticoagulants

BACKGROUND

Since the late 2000s, Europe has granted approval for various thrombotic risk-related uses of direct oral anticoagulants (DOACs). Unlike traditional anticoagulants, DOACs do not necessitate routine coagulation monitoring. Nevertheless, clinical practice often encounters bleeding events associated with these medications, making the need for effective reversal strategies evident.

OBJECTIVES

The study aims to take stock of current reversal strategies for DOACs, with a particular emphasis on the latest compounds that have been developed or are currently under development.

METHODS

For obtaining information regarding the ongoing reversal strategies and the compounds under development, we referred to ClinicalTrials website, PubMed, and Google Scholar.

RESULTS

In 2024, two specific antidotes to DOACs have already received approval when reversal of anticoagulation is needed owing to life-threatening or uncontrolled bleeding: idarucizumab that reverses the effects of dabigatran, and andexanet alfa, designed to counteract activated factor X inhibitors such as apixaban and rivaroxaban. Furthermore, ciraparantag, a potential universal reversal agent, is currently in advanced stages of clinical development. Concerns remain regarding the safety of specific reversal agents, especially concerning the risk of thrombosis. Additionally, the cost of these antidotes remains high. Consequently, nonspecific strategies to counteract anticoagulant medications, including activated charcoal, hemodialysis, and concentrates of coagulation factors, still have utility.

CONCLUSION

With the validation of specific and nonspecific antidotes, DOACs could supplant traditional oral anticoagulants. This progress represents a significant advancement in anticoagulation therapy. However, ongoing research is crucial to address remaining safety concerns of the specific reversion agents of DOACs in clinical practice.

Ultra-Early Hemostatic Therapy for Acute Intracerebral Hemorrhage: An Updated Review

Intracerebral hemorrhage (ICH) is the second most common type of stroke, accounting for approximately 10-20% of all strokes, and is linked to severe neurological disability and death. Since the most accurate predictor of outcome in patients with ICH is hematoma volume, there is a great need for pharmacologic therapy that can reduce hematoma expansion and resultant mass effect and edema. This is especially critical within the ultra-early window of 3-4 hours after the presentation. Hemostatic therapies are exceptionally important for those patients taking antiplatelet or anticoagulant medications to reverse the effects of these medications and therefore prevent hematoma expansion. Furthermore, the recent publication of the 2023 Guideline for the Management of Patients with Aneurysmal Subarachnoid Hemorrhage by the American Heart Association/American Stroke Association, the first update to the guidelines since 2012, underscores the importance of optimizing anticoagulation reversal for this population. The purpose of this selective, nonsystematic review is to examine current literature regarding the use of hemostatic therapies in ICH, with particular attention paid to antiplatelet, anticoagulation, and antifibrinolytic therapies.

Novel strategies in antithrombotic therapy: targeting thrombosis while preserving hemostasis

Antithrombotic therapy is a delicate balance between the benefits of preventing a thrombotic event and the risks of inducing a major bleed. Traditional approaches have included antiplatelet and anticoagulant medications, require careful dosing and monitoring, and all carry some risk of bleeding. In recent years, several new targets have been identified, both in the platelet and coagulation systems, which may mitigate this bleeding risk. In this review, we briefly describe the current state of antithrombotic therapy, and then present a detailed discussion of the new generation of drugs that are being developed to target more safely existing or newly identified pathways, alongside the strategies to reverse direct oral anticoagulants, showcasing the breadth of approaches. Combined, these exciting advances in antithrombotic therapy bring us closer than we have ever been to the "holy grail" of the field, a treatment that separates the hemostatic and thrombotic systems, preventing clots without any concurrent bleeding risk.

Preclinical studies of a factor X activator and a phase 1 trial for hemophilia patients with inhibitors

BACKGROUND

Bleeding episodes in hemophiliacs with inhibitors are difficult to control. Staidson protein-0601 (STSP-0601), a specific factor (F)X activator purified from the venom of Daboia russelii siamensis, has been developed.

OBJECTIVES

We aimed to investigate the efficacy and safety of STSP-0601 in preclinical and clinical studies.

METHODS

In vitro and in vivo preclinical studies were performed. A phase 1, first-in-human, multicenter, and open-label trial was conducted. The clinical study was divided into parts A and B. Hemophiliacs with inhibitors were eligible for this study. Patients received a single intravenous injection of STSP-0601 (0.01 U/kg, 0.04 U/kg, 0.08 U/kg, 0.16 U/kg, 0.32 U/kg, or 0.48 U/kg) in part A or a maximum of 6 4-hourly injections (0.16 U/kg) in part B. The primary endpoint for each part was the number of adverse events (AEs) from baseline to 168 hours after administration. This study was registered at clinicaltrials.gov (NCT-04747964 and NCT-05027230).

RESULTS

Preclinical studies showed that STSP-0601 could specifically activate FX in a dose-dependent manner. In the clinical study, 16 patients in part A and 7 patients in part B were enrolled. Eight (22.2%) AEs in part A and 18 (75.0%) AEs in part B were reported to be related to STSP-0601. Neither severe AEs nor dose-limiting toxicity events were reported. There were no thromboembolic event. The antidrug antibody of STSP-0601 was not detected.

CONCLUSION

Preclinical and clinical studies showed that STSP-0601 had a good ability to activate FX and had a good safety profile. STSP-0601 could be used as a hemostatic treatment in hemophiliacs with inhibitors.

Adeno-associated virus-mediated expression of activated factor V (FVa) for hemophilia phenotypic correction

Adeno-associated virus (AAV) gene therapy has been successfully applied in hemophilia patients excluding patients with inhibitors. During the coagulation pathway, activated factor V (FVa) functions downstream as a cofactor of activated factor X (FXa) to amplify thrombin generation. We hypothesize that the expression of FVa via gene therapy can improve hemostasis of both factor IX and FVIII deficiencies, regardless of clotting factor inhibitor. A human FVa (hFVa) expression cassette was constructed, and AAV8 vectors encoding hFVa (AAV8/TTR-hFVa) were intravenously administrated into mice with hemophilia A and B with or without FVIII inhibitors. Hemostasis, including hFVa level, activated partial thromboplastin time (aPTT), tail clip, and the saphenous vein bleeding assay (SVBA), was evaluated. In hemophilia B mice, a dose of 4 × 1013 vg/kg AAV8/TTR-hFVa vectors achieved a complete phenotypic correction over 28 weeks. In hemophilia A mice, hemostasis improvement was also achieved, regardless of FVIII inhibitor development. In vivo hemostasis efficacy was confirmed by tail clip and SVBA. Interestingly, while minimal shortening of aPTT was observed at a lower dose of AAV8 vectors, hemostasis improvement was still achieved via in vivo bleeding assays. Collectively, FVa-based AAV gene therapy shows promise for hemostasis correction in hemophilia, regardless of inhibitor development and no potential risk for thrombosis.

Molecular therapeutics of Hemophilia A and B

INTRODUCTION

Hemophilia A (HA) or B (HB) is an X-linked recessive disorder caused by a defect in the factor VIII (FVIII) or factor IX (FIX) gene which leads to the dysfunction of blood coagulation. Protein replacement therapy (PRT) uses recombinant proteins and plasma-derived products, which incurs high cost and inconvenience requiring routine intravenous infusions and life-time treatment. Understanding of detailed molecular mechanisms on FVIII gene function could provide innovative solutions to amend this disorder. In recent decades, gene therapeutics have advanced rapidly and a one-time cure solution has been proposed.

AREAS COVERED

This review summarizes current understanding of molecular pathways involved in blood coagulation, with emphasis on FVIII's functional role. The existing knowledge and challenges on FVIII gene expression, from transcription, translation, post-translational modification including glycosylation to protein processing and secretion, and co-factor interactions are deciphered and potential molecular interventions discussed.

EXPERT OPINION

This article reviews the potential treatment targets for HA and HB, including antibodies, small molecules and gene therapeutics, based on molecular mechanisms of FVIII biosynthesis, and further, assessing the pros and cons of these various treatment strategies. Understanding detailed FVIII protein synthesis and secretory pathways could provide exciting opportunities in identifying novel therapeutics to ameliorate hemophilia state.

Direct oral anticoagulant reversal: An update

ABSTRACT

The rise in direct oral anticoagulant (DOAC) use means nurses must understand the reversal of these agents in case of bleeding. Depending on bleed severity, as well as other criteria, pharmacologic reversal can be considered in place of supportive care alone. Knowledge of literature surrounding DOAC reversal is crucial.

Blood coagulation factor X: molecular biology, inherited disease, and engineered therapeutics

Blood coagulation factor X/Xa sits at a pivotal point in the coagulation cascade and has a role in each of the three major pathways (intrinsic, extrinsic and the common pathway). Due to this central position, it is an attractive therapeutic target to either enhance or dampen thrombin generation. In this brief review, I will summarize key developments in the molecular understanding of this critical clotting factor and discuss the molecular basis of FX deficiency, highlight difficulties in expressing recombinant factor X, and detail two factor X variants evaluated clinically.

Pharmacology-Guided Rule-Based Adaptive Dose Escalation in First-in-Human Studies

First-in-human (FIH) studies typically progress through cohorts of fixed, standard size throughout the escalation scheme. This work presents and tests a pharmacology-guided rule-based adaptive dose escalation design that aims at making "best use" of participants in early clinical drug evaluation; it is paper based, not requiring real-time access to computational methods. The design minimizes the number of participants exposed to dose levels with low likelihood of being therapeutically relevant. Using criteria based on dose-limiting adverse event rate and on target exposure or target pharmacodynamics, the design increases the sample size when approaching the dose range of potential clinical relevance. The adaptive escalation design was retrospectively tested on actual data from a sample of 40 recently executed FIH studies with novel small and large molecules, and it was evaluated by simulating trials with three compounds with different therapeutic windows, i.e., representing a promising, unacceptable, and dubious profile. In retrospective evaluation of the adaptive escalation design, none of the cases overshot the actually reported top dose; one case resulted in a top dose that was within 20% under the estimated maximum tolerated dose in the original study. The median reduction of total number of participants per study was 38%. Trial simulations confirmed the retrospective evaluation, showing a similar performance of the adaptive escalation design compared with the conventional 6 + 2 design, at a reduced study size for compounds with a presumed acceptable therapeutic window. The adaptive escalation design was shown to make "best use" of participants in FIH studies without compromising safety.

Reversal Agents for the Direct Factor Xa Inhibitors: Biochemical Mechanisms of Current and Newly Emerging Therapies

The direct oral anticoagulants targeting coagulation factor Xa or thrombin are widely used as alternatives to vitamin K antagonists in the management of venous thromboembolism and nonvalvular atrial fibrillation. In case of bleeding or emergency surgery, reversal agents are helpful to counteract the anticoagulant therapy and restore hemostasis. While idarucizumab has been established as an antidote for the direct thrombin inhibitor dabigatran, reversal strategies for the direct factor Xa inhibitors have been a focal point in clinical care over the past years. In the absence of specific reversal agents, the off-label use of (activated) prothrombin complex concentrate and recombinant factor VIIa have been suggested as effective treatment options during inhibitor-induced bleeding complications. Meanwhile, several specific reversal agents have been developed. In this review, an overview of the current state of nonspecific and specific reversal agents for the direct factor Xa inhibitors is provided, focusing on the biochemistry and mechanism of action and the preclinical assessment of newly emerging therapies.

Evaluation of biomarkers for monitoring thrombogenic potential of FXaI16L

: A zymogen-like activated factor X variant (FXa) is being developed for treating acute bleeding conditions. Activated factor V is an essential cofactor to FXa for activating prothrombin to thrombin. Thrombi/emboli formation was observed microscopically in FXa toxicity studies in animals. The objective of this research was to evaluate candidate biomarkers for FXa-induced thrombi/emboli formation to inform safety monitoring and dose-escalation decisions in FXa clinical trials. Effects of intravenous FXa administration on platelets, fibrinogen, activated partial thromboplastin time (aPTT), prothrombin time (PT), D-dimer, tissue factor pathway inhibitor, thrombin : antithrombin complex, antithrombin, and factor V, and protein C (PC) activities were evaluated in mice, rats, and monkeys. Mice had endogenous factor V activity 10× that of monkeys and were overly sensitive to FXa-induced thrombi/emboli formation. In monkeys, decreases in fibrinogen and prolongation in aPTT and PT emerged as potential biomarkers for impending FXa-induced thrombi/emboli formation, based on association of changes with microscopically observable thrombi/emboli (0-97 thrombi/emboli per monkey). PC decreases, measured by a clot-based assay, were also observed. A similar reduction in PC activity, when measured by clot-based assay, was observed in a phase 1 clinical trial. However, an in-vitro experiment with human plasma spiked with increasing concentrations of FXa indicated dose-dependent FXa-induced interference with clot-based assays and no depletion of PC or S by FXa in non-clot-based assays. Nonclinical biomarker studies identified fibrinogen, aPTT and PT as potential biomarkers for monitoring the clinical safety of FXa. Results of clot-based assays with FXa treatment should be interpreted with caution.

Surfing the Blood Coagulation Cascade: Insight into the Vital Factor Xa

Factor Xa (FXa) plays a key role in haemostasis, it is a central part of the blood coagulation cascade which catalyzes the production of thrombin and leads to clot formation and wound closure. Therefore, FXa is an attractive target for the development of new anticoagulant agents. In this review, we will first describe the molecular features of this fundamental protein in order to understand its mechanism of action, an essential background for the design of novel inhibitors by means of synthetic organic chemistry or using peptides obtained from recombinant methodologies. Then, we will review the current state of the synthesis of novel direct FXa inhibitors along with their mechanisms of action. Finally, approved reversal agents that aid in maintaining blood haemostasis by using these commercial drugs will also be discussed.

Induction and Impact of Anti-Drug Responses Elicited by a Human Recombinant Coagulation Factor FXaI16L in Preclinical Species

This paper presents a systemic investigation of ADA development and ADA impact of a human coagulation factor in nonclinical species during drug development and provides insights into potential implications in human if a similar ADA occurs. FXa^I16L-induced ADA response was characterized in monkey, mouse, rat, and dog in different studies, and ADA effects on pharmacokinetic and/or pharmacodynamics of FXa^I16L were further examined in ADA-negative and ADA-positive animals. After repeated administrations, FXa^I16L elicited a dose and exposure day-dependent ADA response which ranged from no response to a transient or persistent response. Increase in exposure day and increase in dose generally enhanced ADA incidence except for a decrease in ADA incidence was observed in monkeys after repeated high-dose administrations. The observable ADA impact on pharmacokinetics was only found in some ADA+ animals and included decrease in clearance and increase in systemic exposure but no increase in half-life. In addition, no or limited effect on pharmacodynamics by ADA was observed. The earliest ADA response was observed after three exposure days, marked elevation of drug exposure was observed in some animals at log titer > 2.0, and the highest antibody titer excited was about 4 (Log10) in all species. A correlation between ADA induction and accumulative exposure after various repeat treatments in different species was found for FXa^I16L. In addition, potential immunogenicity risk and mitigation of ADA in clinics are discussed.

Reversal of Anticoagulants in Critical Care

There has seen an increase in anticoagulant consumption worldwide over the past few decades. With this widespread utilization of anticoagulants, clinicians are increasingly likely to encounter situations where anticoagulants would need to be withheld. This includes emergency and elective procedures or surgeries as well as major or minor bleeding as a direct result of over anticoagulation or consequent to other intercurrent illnesses such as sepsis or trauma with multiorgan failure, where the anticoagulant may contribute to coagulation abnormalities. Clinicians are required to have a thorough understanding of the indications for anticoagulant prescription, drug interactions and monitoring, indications and options of reversal of anticoagulation and management of bleeding in the situations described above. Once the acute process is managed, the ongoing need and timing of reinitiation of anticoagulation is also crucial. This article provides an overview on the indications for reversal of anticoagulation, the agents used for reversal and the timing of reinitiation of anticoagulants.

Protein-Engineered Coagulation Factors for Hemophilia Gene Therapy

Hemophilia A (HA) and hemophilia B (HB) are X-linked bleeding disorders due to inheritable deficiencies in either coagulation factor VIII (FVIII) or factor IX (FIX), respectively. Recently, gene therapy clinical trials with adeno-associated virus (AAV) vectors and protein-engineered transgenes, B-domain deleted (BDD) FVIII and FIX-Padua, have reported near-phenotypic cures in subjects with HA and HB, respectively. Here, we review the biology and the clinical development of FVIII-BDD and FIX-Padua as transgenes. We also examine alternative bioengineering strategies for FVIII and FIX, as well as the immunological challenges of these approaches. Other engineered proteins and their potential use in gene therapy for hemophilia with inhibitors are also discussed. Continued advancement of gene therapy for HA and HB using protein-engineered transgenes has the potential to alleviate the substantial medical and psychosocial burdens of the disease.

Novel therapeutics for hemophilia and other bleeding disorders

Hemophilia and von Willebrand disease are the most common congenital bleeding disorders. Treatment of these disorders has focused on replacement of the missing coagulation factor to prevent or treat bleeding. New technologies and insights into hemostasis have driven the development of many promising new therapies for hemophilia and von Willebrand disease. Emerging bypass agents including zymogen-like factor IXa and Xa molecules are in development and a bispecific antibody, emicizumab, demonstrated efficacy in a phase 3 trial in people with hemophilia A and inhibitors. Tissue factor pathway inhibitor, the protein C/S system, and antithrombin are targets of novel compounds in development to alter the hemostatic balance and new approaches using modified factor VIII molecules are being tested for prevention and eradication of inhibitor antibodies in hemophilia A. The first recombinant von Willebrand factor (VWF) product has been approved and has unique VWF multimer content and does not contain factor VIII. These new approaches may offer better routes of administration, improved dosing regimens, and better efficacy for prevention and treatment of bleeding in congenital bleeding disorders.

Management of Spontaneous Intracerebral Hemorrhage

Purpose of Review

We review the current evidence for medical and surgical treatments of spontaneous intracerebral hemorrhage (ICH).

Recent Findings

Therapy with hemostatic agents (e.g. factor VIIa and tranexamic acid) if started early after bleeding onset may reduce hematoma expansion, but their clinical effectiveness has not been shown. Rapid anticoagulation reversal with prothrombin concentrates (PCC) plus vitamin K is the first choice in vitamin K antagonist-related ICH. In ICH related to dabigatran, anticoagulation can be rapidly reversed with idarucizumab. PCC are recommended for ICH related to FXa inhibitors, whereas specific reversal agents are not yet approved. While awaiting ongoing trials studying minimally invasive approaches or hemicraniectomy, the role of surgery in ICH remains to be defined. Therapies targeting downstream molecular cascades in order to prevent secondary neuronal damage are promising, but the complexity and multi-phased nature of ICH pathophysiology is challenging. Finally, in addition to blood pressure control, antithrombotic prevention after ICH has to consider the risk of recurrent bleeding as well as the risk of ischemic events.

Summary

Treatment of acute ICH remains challenging, and many promising interventions for acute ICH await further evidence from trials.

Rendering factor Xa zymogen-like as a therapeutic strategy to treat bleeding

PURPOSE OF REVIEW

New therapies are needed to control bleeding in a range of clinical conditions. This review will discuss the biochemical properties of zymogen-like factor Xa, its preclinical assessment in different model systems, and future development prospects.

RECENT FINDINGS

Underlying many procoagulant therapeutic approaches is the rapid generation of thrombin to promote robust clot formation. Clinically tested prohemostatic agents (e.g., factor VIIa) can provide effective hemostasis to mitigate bleeding in hemophilia and other clinical situations. Over the past decade, we explored the possibility of using zymogen-like factor Xa variants to rapidly improve clot formation for the treatment of bleeding conditions. Compared to the wild-type enzyme, these variants adopt an altered, low activity, conformation which enables them to resist plasma protease inhibitors. However, zymogen-like factor Xa variants are conformationally dynamic and ligands such as its cofactor, factor Va, stabilize the molecule rescuing procoagulant activity. At the site of vascular injury, the variants in the presence of factor Va serve as effective prohemostatic agents. Preclinical data support their use to stop bleeding in a variety of clinical settings. Phase 1 studies suggest that zymogen-like factor Xa is safe and well tolerated, and a phase 1b is ongoing to assess safety in patients with intracerebral hemorrhage.

SUMMARY

Zymogen-like factor Xa is a unique prohemostatic agent for the treatment of a range of bleeding conditions.