Osocimab: A Novel Agent in Preventing Venous Thromboembolism

Factor XIa inhibition as a therapeutic strategy for atherothrombosis

When selecting an anticoagulant, clinicians consider individual patient characteristic, the treatment indication, drug pharmacology, and safety and efficacy as demonstrated in randomized trials. An ideal anticoagulant prevents thrombosis with little or no increase in bleeding. Direct oral anticoagulants represent a major advance over traditional anticoagulants (e.g., unfractionated heparin, warfarin) but still cause bleeding, particularly from the gastrointestinal tract which can limit their use. Epidemiological studies indicate that patients with congenital factor XI (FXI) deficiency have a lower risk of venous thromboembolism (VTE) and ischemic stroke (IS) than non-deficient individuals, and do not have an increased risk of spontaneous bleeding, even with severe deficiency. These observations provide the rationale for targeting FXI as a new class of anticoagulant. Multiple FXI inhibitors have been introduced and several are being evaluated in Phase III trials. In this review, we explain why drugs that target FXI may be associated with a lower risk of bleeding than currently available anticoagulants and summarize the completed and ongoing trials.

Dual Inhibition of Factor XIIa and Factor XIa Produces a Synergistic Anticoagulant Effect

ABSTRACT

Clinical practice shows that a critical unmet need in the field of thrombosis prevention is the availability of anticoagulant therapy without bleeding risk. Inhibitors against FXIa or FXIIa have been extensively studied because of their low bleeding risk. However, whether these compounds produce synergistic effects has not yet been explored. In this study, analyses of activated partial thromboplastin time in combination with the FXIa inhibitor PN2KPI and the FXIIa inhibitor Infestin4 at different proportions were performed using the SynergyFinder tool identifying synergistic anticoagulation effects. Both an FeCl 3 -induced carotid artery thrombosis mouse model and a transient occlusion of the middle cerebral artery mouse model showed that the combination of PN2KPI and Infestin4, which are 28.57% and 6.25% of the effective dose, respectively, significantly prevents coagulation, and furthermore, dual inhibition does not cause bleeding risk.

Current Gaps in the Provision of Safe and Effective Anticoagulation in Atrial Fibrillation and the Potential for Factor XI-Directed Therapeutics

The global prevalence of atrial fibrillation is rapidly increasing, in large part due to the aging of the population. Atrial fibrillation is known to increase the risk of thromboembolic stroke by 5 times, but it has been evident for decades that well-managed anticoagulation therapy can greatly attenuate this risk. Despite advances in pharmacology (such as the shift from vitamin K antagonists to direct oral anticoagulants) that have increased the safety and convenience of chronic oral anticoagulation in atrial fibrillation, a preponderance of recent observational data indicates that protection from stroke is poorly achieved on a population basis. This outcomes deficit is multifactorial in origin, stemming from a combination of underprescribing of anticoagulants (often as a result of bleeding concerns by prescribers), limitations of the drugs themselves (drug-drug interactions, bioaccumulation in renal insufficiency, short half-lives that result in lapses in therapeutic effect, etc), and suboptimal patient adherence that results from lack of understanding/education, polypharmacy, fear of bleeding, forgetfulness, and socioeconomic barriers, among other obstacles. Often this adherence is not reported to treating clinicians, further subverting efforts to optimize care. A multidisciplinary, interprofessional panel of clinicians met during the 2023 International Society of Thrombosis and Haemostasis Congress to discuss these gaps in therapy, how they can be more readily recognized, and the potential for factor XI-directed anticoagulants to improve the safety and efficacy of stroke prevention. A full appreciation of this potential requires a reevaluation of traditional teaching about the "coagulation cascade" and decoupling the processes that result in (physiologic) hemostasis and (pathologic) thrombosis. The panel discussion is summarized and presented here.

Factor XI: structure, function and therapeutic inhibition

Arterial and venous thromboembolism is a major medical concern that requires therapeutic anticoagulation in various medical fields to prevent its drastic consequences. Despite significant advances in anticoagulant therapy, thrombosis remains a leading cause of morbidity and mortality worldwide. Traditional anticoagulants like heparin and vitamin K antagonists (VKAs) have shown efficacy in preventing and treating thrombosis but come with an inherent risk of bleeding due to their non-specific inhibition of multiple coagulation factors. Subsequent direct oral anticoagulants (DOACs), targeting specific factors such as Xa or thrombin, demonstrated improved safety profiles compared to VKAs, yet bleeding remains a concern. Accordingly, research is focused on developing anticoagulants with improved safety profiles. A safer class of anticoagulants would have broad appeal. The intrinsic pathway of coagulation, involving factor XI (FXI), has attracted attention as a potential target for safer anticoagulants. Preclinical studies and epidemiological data indicate that FXI deficiency or inhibition protects against thrombosis with minimal bleeding. Current research involves evaluating various FXI-directed strategies, and phase 2 studies have shown promising results in orthopedic surgery, atrial fibrillation, end-stage renal disease (ESRD), myocardial infarction, and ischemic stroke. Several agents, such as antisense oligonucleotides, monoclonal antibodies, small synthetic molecules, natural peptides, and aptamers, have been developed to inhibit FXI at different stages, offering potentially safer alternatives to traditional anticoagulants. However, the optimal balance between preventing thrombosis and the risk of bleeding associated with FXI inhibitors requires validation through extensive phase 3 clinical trials using definite clinical endpoints. Several of such trials are currently underway or planned to define the role of FXI inhibitors in clinical practice and determine the most suitable FXI inhibitor for each specific indication. The current review highlights the rationale behind developing FXI inhibitors, presenting the most advanced agents in development, summarizing completed clinical trials, and discussing ongoing research efforts.

Anticoagulants for atrial fibrillation: from warfarin and DOACs to the promise of factor XI inhibitors

Anticoagulation is the mainstay of stroke prevention in appropriate patients with atrial fibrillation. Due to advances in pharmacotherapy the anticoagulants used for this purpose have evolved significantly over the past decades with the aim of optimizing effectiveness while minimizing bleeding risks. Though significant improvements have been made toward this goal, bleeding risk remains the major concern with these therapies. An investigational class of agents which inhibit Factor XI have shown promise in pre-clinical and early clinical trials to significantly minimize bleeding while maintaining efficacy against stroke and systemic embolism. This mini-review will discuss anticoagulants currently used for stroke prevention in patients with atrial fibrillation including warfarin and direct oral anticoagulants. We will also review the mechanism of action and data from early clinical trials for Factor XI inhibitors and discuss their potential advantages and shortcomings.

Anticoagulation with osocimab in patients with kidney failure undergoing hemodialysis: a randomized phase 2 trial

Individuals with kidney failure undergoing hemodialysis are at elevated risk for thromboembolic events. Factor (F) XI, which is in the intrinsic pathway of coagulation, is emerging as an attractive target for new anticoagulants that may be safer than existing agents. Osocimab-an inhibitory FXIa antibody-is a potential treatment option for such patients. We conducted a phase 2b, double-blind, placebo-controlled trial, in which 704 participants (448 male, 256 female) with kidney failure undergoing hemodialysis were randomized to receive lower- or higher-dose osocimab or placebo. In total, 686 participants (436 male, 250 female) received treatment for ≤18 months (planned minimal treatment period of 6 months). The co-primary outcomes were clinically relevant bleeding (a composite of major and clinically relevant nonmajor bleeding) and a composite of the incidence of moderate, severe or serious adverse events. Clinically relevant bleeding occurred in 16/232 (6.9%) and 11/224 (4.9%) participants who received lower- and higher-dose osocimab, respectively, and in 18/230 participants (7.8%) who received a placebo. For the composite adverse event endpoint, incidences were 51%, 47% and 43% in the lower-dose osocimab, higher-dose osocimab and placebo groups, respectively. These results suggest that osocimab is associated with a low risk of bleeding and is generally well tolerated in this population; findings that require confirmation in larger trials. ClinicalTrials.gov identifier, NCT04523220 .

Investigation of the anticoagulant activity of cyclic sulfated glycosaminoglycan mimetics

Thrombotic disorders are among the leading causes of deaths worldwide. Anticoagulants are frequently prescribed for their prevention and/or treatment. Current anticoagulants, which target either thrombin or factor Xa, are plagued with a number of drawbacks, the most important of which is the increased risk of internal bleeding. To develop better antithrombotic agents, the anticoagulant activity of cyclic glycosaminoglycan mimetics was evaluated. Human plasma clotting assays and enzyme inhibition assays were exploited to evaluate the anticoagulant activity of sulfated β-cyclodextrin (SBCD) and its three analogs: sulfated α-cyclodextrin, β-cyclodextrin, and methylated β-cyclodextrin. In normal human plasma, SBCD selectively doubled the activated partial thromboplastin time (APTT) at ∼9 μg/mL, with no effect on prothrombin time (PT) at the same concentration. Likewise, SBCD doubled APTT at ∼9 μg/mL and at ∼8 μg/mL in antithrombin-deficient plasma and heparin cofactor II-deficient plasma, respectively. Interestingly, the three SBCD derivatives were inactive at the highest concentrations tested which highlighted the importance of the sulfate groups and the size of the molecule. Enzyme assays revealed that SBCD inhibits factor XIa (FXIa) with an IC50 value of ∼20 μg/mL and efficacy of near 100%. SBCD did not inhibit other related proteins including thrombin, factor IXa, factor Xa, factor XIIa, factor XIIIa, plasmin, chymotrypsin, or trypsin at the highest concentrations tested demonstrating a significant selectivity. In Michaelis-Menten kinetics, SBCD decreased the VMAX and increased the KM of FXIa hydrolysis of a tripeptide chromogenic substrate indicating a mixed inhibition mechanism. Together, it appears that SBCD is a potent and selective inhibitor of human FXIa with substantial anticoagulant activity in human plasma. Overall, this study introduces SBCD as a promising lead for further development as a safer anticoagulant.

Factor XIa Inhibitors as a Novel Anticoagulation Target: Recent Clinical Research Advances

BACKGROUND

While current clinically administered anticoagulant medications have demonstrated effectiveness, they have also precipitated significant risks: severe bleeding complications including, but not limited to, gastrointestinal hemorrhaging and intracranial and other life-threatening major bleedings. An ongoing effort is being made to identify the best targets for anticoagulant-targeted drugs. Coagulation factor XIa (FXIa) is emerging as an important target of current anticoagulant treatment.

OBJECTIVE

This review will summarize the development of anticoagulants and recent advances in clinical trials of experimental factor XI inhibitors from a clinical application perspective.

RESULTS

As of 1 January 2023, our search screening included 33 clinical trials. We summarized the research progress of FXIa inhibitors from seven clinical trials that evaluated their efficacy and safety. The results showed no statistically meaningful distinction in the primary efficacy between patients receiving FXIa inhibitors compared to controls (RR = 0.796; 95% CI: 0.606-1.046; I² = 68%). The outcomes did not indicate a statistical difference in the occurrence of any bleeding between patients receiving FXIa inhibitors compared to controls (RR = 0.717; 95% CI: 0.502-1.023; I² = 60%). A subgroup analysis found significant differences in severe bleeding and clinically relevant hemorrhaging in subjects receiving FXIa inhibitors compared to Enoxaparin (RR = 0.457; 95% CI: 0.256-0.816; I² = 0%).

CONCLUSIONS

Clinical trials to date have indicated that factor XIa is a potential anticoagulation target, and factor XIa inhibitors may play an important role in the development of anticoagulants.

Potential anticoagulant of traditional chinese medicine and novel targets for anticoagulant drugs

BACKGROUND

Anticoagulants are the main drugs used for the prevention and treatment of thrombosis. Currently, anticoagulant drugs are primarily multitarget heparin drugs, single-target FXa inhibitors and FIIa inhibitors. In addition, some traditional Chinese drugs also have anticoagulant effects, but they are not the main direction of treatment at present. But the anticoagulant drugs mentioned above, all have a common side effect is bleeding. Many other anticoagulation targets are under investigation. With further exploration of coagulation mechanism, how to further determine new anticoagulant targets and how to make traditional Chinese medicine play anticoagulant role have become a new field of exploration.

PURPOSE

The purpose of the study was to summarize the recent research progress on coagulation mechanisms, new anticoagulant targets and traditional Chinese medicine.

METHODS

A comprehensive literature search was conducted using four electronic databases, including PubMed, Embase, CNKI, Wanfang database and ClinicalTrials.gov, from the inception of the study to 28 Feb 2023. Key words used in the literature search were "anticoagulation", "anticoagulant targets", "new targets", "coagulation mechanisms", "potential anticoagulant", "herb medicine", "botanical medicine", "Chinese medicine", "traditional Chinese medicine", "blood coagulation factor", keywords are linked with AND/OR. Recent findings on coagulation mechanisms, potential anticoagulant targets and traditional Chinese medicine were studied.

RESULTS

The active components extracted from the Chinese medicinal herbs, Salvia miltiorrhiza, Chuanxiong rhizoma, safflower and Panax notoginseng have obvious anticoagulant effects and can be used as potential anticoagulant drugs, but the risk of bleeding is unclear. TF/FVIIa, FVIII, FIX, FXI, FXII, and FXIII have all been evaluated as targets in animal studies or clinical trials. FIX and FXI are the most studied anticoagulant targets, but FXI inhibitors have shown stronger advantages.

CONCLUSION

This review of potential anticoagulants provides a comprehensive resource. Literature analysis suggests that FXI inhibitors can be used as potential anticoagulant candidates. In addition, we should not ignore the anticoagulant effect of traditional Chinese medicine, and look forward to more research and the emergence of new drugs.

Coming soon to a pharmacy near you? FXI and FXII inhibitors to prevent or treat thromboembolism

Anticoagulants have been in use for nearly a century for the treatment and prevention of venous and arterial thromboembolic disorders. The most dreaded complication of anticoagulant treatment is the occurrence of bleeding, which may be serious and even life-threatening. All available anticoagulants, which target either multiple coagulation factors or individual components of the tissue factor (TF) factor VIIa or the common pathways, have the potential to affect hemostasis and thus to increase bleeding risk in treated patients. While direct oral anticoagulants introduced an improvement in care for eligible patients in terms of safety, efficacy, and convenience of treatment, there remain unmet clinical needs for patients requiring anticoagulant drugs. Anticoagulant therapy is sometimes avoided for fear of hemorrhagic complications, and other patients are undertreated due to comorbidities and the perception of increased bleeding risk. Evidence suggests that the contact pathway of coagulation has a limited role in initiating physiologic in vivo coagulation and that it contributes to thrombosis more than it does to hemostasis. Because inhibition of the contact pathway is less likely to promote bleeding, it is an attractive target for the development of anticoagulants with improved safety. Preclinical and early clinical data indicate that novel agents that selectively target factor XI or factor XII can reduce venous and arterial thrombosis without an increase in bleeding complications.

Nanobodies against factor XI apple 3 domain inhibit binding of factor IX and reveal a novel binding site for high molecular weight kininogen

BACKGROUND

Factor XI (FXI) is a promising target for novel anticoagulants because it shows a strong relation to thromboembolic diseases, while fulfilling a mostly supportive role in hemostasis. Anticoagulants targeting FXI could therefore reduce the risk for thrombosis, without increasing the chance of bleeding side effects.

OBJECTIVES

To generate nanobodies that can interfere with FXIa mediated activation of factor IX (FIX).

METHODS

Nanobodies were selected for binding to the apple 3 domain of FXI and their effects on FXI and coagulation were measured in purified protein systems as well as in plasma-based coagulation assays. Additionally, the binding epitope of selected nanobodies was assessed by hydrogen-deuterium exchange mass spectrometry.

RESULTS

We have identified five nanobodies that inhibit FIX activation by FXI by competing with the FIX binding site on FXI. Interestingly, a sixth nanobody was found to target a different binding epitope in the apple 3 domain, resulting in competition with the FXI-high molecular weight kininogen (HK) interaction.

CONCLUSIONS

We have characterized a nanobody targeting the FXI apple 3 domain that elucidates the binding orientation of HK on FXI. Moreover, we have produced five nanobodies that can inhibit the FXI-FIX interaction.

Factor XI, a potential target for anticoagulation therapy for venous thromboembolism

Venous thromboembolism (VTE) is a common cause of mortality and disability in hospitalized patients, and anticoagulation is an essential therapeutic option. Despite the increasing use of direct oral anticoagulants, complications and adverse drug reactions still occur in patients with VTE. Within 5 years, 20% of patients with VTE experience recurrence, and 50% of patients with deep vein thrombosis develop post-thrombotic syndrome. Furthermore, bleeding due to anticoagulants is a side effect that must be addressed. Therefore, safer and more effective anticoagulant strategies with higher patient compliance are urgently needed. Available epidemiological evidence and animal studies have shown that factor XI (FXI) inhibitors can reduce thrombus size and loosen the thrombus structure with a relatively low risk of bleeding, suggesting that FXI has an important role in thrombus stabilization and is a safer target for anticoagulation. Recent clinical trial data have also shown that FXI inhibitors are as effective as enoxaparin and apixaban in preventing VTE, but with a significantly lower incidence of bleeding. Furthermore, FXI inhibitors can be administered daily or monthly; therefore, the monitoring interval can be longer. Additionally, FXI inhibitors can prolong the activated partial thromboplastin time without affecting prothrombin time, which is an easy and common test used in clinical testing, providing a cost-effective monitoring routine for patients. Consequently, the inhibition of FXI may be an effective strategy for the prevention and treatment of VTE. Enormous progress has been made in the research strategies for FXI inhibitors, with abelacimab already in phase III clinical trials and most other inhibitors in phase I or II trials. In this review, we discuss the challenges of VTE therapy, briefly describe the structure and function of FXI, summarize the latest FXI/activated FXI (FXIa) inhibitor strategies, and summarize the latest developments in clinical trials of FXI/FXIa inhibitors.