AXIOMATIC-SSP: Cautious Optimism on Factor XI Inhibitor in Stroke

August 28, 2022

The new factor XI inhibitor antithrombotic, milvexian (BMS/Janssen), has shown promising results in a dose-finding phase 2 trial in patients with acute ischemic stroke or transient ischemic attack (TIA), when given in addition to dual antiplatelet therapy.

Although there was no significant reduction in the primary composite endpoint of ischemic stroke or incident infarct on brain MRI at 90 days with milvexian vs placebo in the AXIOMATIC-SSP study, with no apparent dose response, the drug numerically reduced the risk for symptomatic ischemic stroke at most doses. And doses from 25 mg to 100 mg twice daily showed an approximately 30% relative risk reduction in symptomatic ischemic stroke vs placebo.

Milvexian at 25 once and twice daily was associated with a low incidence of major bleeding, similar to that seen with; a moderate increase in bleeding was seen with higher doses.

There was no increase in severe bleeding compared with placebo, and no fatal bleeding occurred any study group.

"Based on the observed efficacy signal for ischemic stroke, the bleeding profile, and the overall safety and tolerability, milvexian will be further studied in a phase 3 trial in a similar stroke population," concluded lead investigator, Mukul Sharma, MD, associate professor of medicine at McMaster University, Hamilton, Ontario, Canada.

Sharma presented the AXIOMATIC-SSP study results today at the European Society of Cardiology (ESC) Congress 2022, being held in Barcelona, Spain.

New Generation

Sharma explained that factor XI inhibitors represent the latest hope for a new generation of antithrombotic drugs with a low bleeding risk.

This has come about after observations that individuals born with factor XI deficiency have lower rates of ischemic stroke and thromboembolism than matched controls, without an offsetting increase in cerebral hemorrhage. In addition, spontaneous bleeding in these individuals is uncommon, and it is thought that factor XI is a strong driver of thrombus growth but plays a less important role in hemostasis, he noted.

"I think there is a tremendous niche for these drugs in stroke prevention," Sharma told | Medscape Cardiology. "There is a huge unmet need in stroke patients for something other than aspirin over the long term which is effective but doesn't cause hemorrhage," he said.

Sharma reported that antithrombotic efficacy of milvexian has already been demonstrated in a study of patients undergoing knee replacement in which the drug showed similar or increased efficacy in reducing thromboembolism compared with enoxaparin, 40 mg, without an increase in major bleeding.

The aim of the current AXIOMATIC-SSP study was to find a dose suitable for use in the treatment of patients with acute stroke or TIA.

Patients with an acute ischemic stroke or TIA are at a high risk for another stroke in the first few months. Although antiplatelet drugs have reduced this event rate, there is still a significant residual risk for ischemic stroke, and the potential for major bleeding with additional antithrombotic therapies has limited the effectiveness of these options, Sharma explained. Currently, no anticoagulants are approved for noncardioembolic ischemic stroke prevention in the early phase.

The AXIOMATIC-SSP study included 2366 patients within 48 hours of onset of a mild-to-moderate acute nonlacunar ischemic stroke. All patients had visible atherosclerotic plaque in a vessel supplying the affected brain region, and they all received background treatment with open-label aspirin and clopidogrel for 21 days, followed by open-label aspirin alone from days 22 to 90.

They were randomly assigned to one of five doses of milvexian (25, 50, 100, or 200 mg twice daily or 25 mg once daily) or placebo daily for 90 days.

The primary efficacy endpoint (symptomatic ischemic stroke or incident infarct on brain MRI) was numerically lower at the 50-mg and 100-mg twice-daily doses, and there was no apparent dose response (placebo, 16.6%; 25 mg once daily, 16.2%; 25 mg twice daily, 18.5%; 50 mg twice daily, 14.1%; 100 mg twice daily, 14.7%; 200 mg twice daily, 16.4%).

However, milvexian was associated with a numerically lower risk for clinical ischemic stroke at all doses except 200 mg twice daily, with doses from 25 to 100 mg twice daily showing an approximately 30% relative risk reduction vs placebo (placebo, 5.5%; 25 mg once daily, 4.6%; 25 mg twice daily, 3.8%; 50 mg twice daily, 4.0%; 100 mg twice daily, 3.5%; 200 mg twice daily, 7.7%).

The main safety endpoint was major bleeding, defined as Bleeding Academic Research Consortium (BARC) type 3 or 5 bleeding. This was similar to placebo for milvexian 25 mg once daily and twice daily (all 0.6%) but was moderately increased in the 50 mg twice daily (1.5%), 100 mg twice daily (1.6%), and 200 mg twice daily (1.5%) groups.

Most major bleeding episodes were gastrointestinal. There was no increase in severe bleeding or symptomatic intracranial hemorrhage vs placebo, and no fatal bleeding occurred in any arm of the study.

Incremental Improvement

On the hope for a class of drugs that reduce ischemic events without increasing bleeding, Sharma said, "We keep hoping for a home run where there is no increase in bleeding with a new generation of antithrombotic, but what we seem to get is an incremental improvement with each new class.

"Factor Xa inhibitors have a lower rate of bleeding compared to warfarin. I think we will see another incremental improvement in bleeding with these new factor XI inhibitors and hopefully less of the more serious bleeding," he told | Medscape Cardiology.

He pointed out that in this study, milvexian was given on top of dual antiplatelet therapy. "In stroke neurology that sounds very risky as we know that going from a single antiplatelet to two antiplatelet agents increases the risk of bleeding and now we are adding in a third antithrombotic, but we feel comfortable doing it because of what has been observed in patients who have a genetic deficiency of factor XI — very low rates of spontaneous bleeding and they don't bleed intracranially largely," he added.

In addition to milvexian, another oral factor XI inhibitor, asundexian (Bayer), is also in development, and similar results were reported in a phase 2 stroke trial (PACIFIC-STROKE) at the same ESC session.

Both drugs are now believed to be going forward into phase 3 trials.

Discussant of the study at the ESC Hotline session, Giovanna Liuzzo, MD, Catholic University of Rome, Italy, highlighted the large unmet need for stroke therapies, noting that patients with acute stroke or TIA have a stroke recurrence rate of 5% at 30 days and 17% at 2 years. Although antiplatelet agents are recommended, the use of anticoagulants has been limited by concerns over bleeding risk, and the factor XI inhibitors are promising in that they have the potential for a lower bleeding risk, she said.

She suggested that results from the AXIOMATIC-SSP could point to a dose of milvexian of 25 mg twice daily as a balance between efficacy and bleeding to be taken into larger phase 3 trials

"The jury is still out on the safety and efficacy of milvexian as an adjunct to dual antiplatelet therapy for the prevention of recurrent noncardioembolic stroke," Liuzzo concluded. "Only largescale phase 3 trials will establish the safety and efficacy of factor XI inhibitors in the prevention of venous and arterial thrombosis."

The AXIOMATIC-SSP study was funded by the BMS/Janssen alliance. Sharma reports research contracts with BMS, Bayer, and Astra Zeneca, and consulting fees from Janssen, Bayer, HLS Therapeutics and Alexion.

European Society of Cardiology (ESC) Congress 2022. Presented August 28, 2022.

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