Anthos to stop factor XI trial in atrial fibrillation early after ‘overwhelming benefit’

Anthos Therapeutics announced Monday morning that it is stopping a Phase II study of its next-generation anticoagulant abelacimab in atrial fibrillation as a result of “overwhelming benefit.”

The decision came after an independent data monitoring committee recommended the company and its academic collaborator — the TIMI Study Group from Brigham and Women’s Hospital and Harvard — to stop the study early since patients in the treatment arm saw a substantial reduction in bleeding events compared to those in the control arm, who received Johnson & Johnson’s Xarelto.

Anthos spun out of Novartis with abelacimab, a factor XI and XIa antibody, in 2019 with $250 million from Blackstone. It is part of a class of up-and-coming anticoagulants that the industry hopes to capitalize on. The idea behind factor XI inhibitors is to reduce the risk of stroke and blood clots — as current anticoagulants do — but without increasing risk of bleeding.

Bayer, as well as Bristol Myers Squibb partnered with J&J, are both developing factor XIa inhibitor pills, which are currently in massive Phase III studies for reducing stroke and bleeding risk in people with atrial fibrillation and after a first stroke or stroke-like symptoms.

Dan Bloomfield

In an interview Friday afternoon, Anthos executives told Endpoints News they had learned of the decision on Thursday. According to Dan Bloomfield, Anthos’ CMO, the independent data monitoring committee recommended that the company stop the trial after it accumulated just over half of the 166 events the trial initially set out to reach.

“They tell me I’m understated. So I’ll start with that,” said Bloomfield, who was previously CEO of Cardurion and led the cardiometabolic program at Merck. “But this is a remarkable result — it’s the single most exciting result in my 20-year career.”

Time to the first “major or clinically relevant non-major (CRNM) bleeding event” is the primary metric of the Phase II AZALEA-TIMI 71 study, which enrolled around 1,200 patients. But Anthos did not share the specific details of results in its press release, adding that data would be presented at an upcoming medical meeting.

Anthos is currently studying abelacimab in two Phase III studies for blood clots in cancer patients. In January, it also began enrolling a Phase III study for the antibody in people with atrial fibrillation who have been deemed unsuitable for current blood thinner pills.

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