Regeneron Reports Promising Phase 2 Results For Novel Factor XI Antibodies In Knee Surgery Patients

(RTTNews) - Regeneron Pharmaceuticals Inc. (REGN) announced encouraging results from two Phase 2 clinical trials evaluating its investigational factor XI antibodies—REGN7508Cat and REGN9933A2—for the prevention of blood clots in patients undergoing total knee replacement surgery. These antibodies were specifically engineered to target different domains of factor XI: REGN7508Cat targets the catalytic domain, while REGN9933A2 targets the A2 domain.

The two therapies were designed with distinct mechanisms of action to offer tailored anticoagulation strategies. REGN7508Cat aims to deliver stronger anticoagulation, whereas REGN9933A2 is intended to minimize bleeding risk. Both antibodies demonstrated robust anti-clotting effects aligned with their design goals, and importantly, neither was associated with clinically significant bleeding.

The data come from two open-label, active-controlled Phase 2 trials. ROXI-VTE-I evaluated a single 300 mg IV dose of REGN9933A2 against daily enoxaparin or twice-daily apixaban. ROXI-VTE-II assessed a single 250 mg IV dose of REGN7508Cat compared to daily enoxaparin. The trials focused on preventing both symptomatic and asymptomatic deep venous thromboembolism (VTE) following unilateral total knee arthroplasty.

Results showed that both antibodies significantly reduced VTE rates compared to historical placebo data, where 48% of patients developed VTE. REGN7508Cat lowered the VTE rate to 7.1%, outperforming apixaban's 12.4% rate. REGN9933A2 achieved a VTE rate of 17.2%, also better than enoxaparin's 20.6%. These findings support the hypothesis that factor XI activation by factor XIIa plays a key role in postoperative VTE, even when other activation pathways remain functional.

These promising results suggest that Regeneron's factor XI antibodies could offer a new, customizable approach to thromboprophylaxis in orthopedic surgery patients.

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