Phase 2 Trials Demonstrating Antithrombotic Effect of Two Novel Regeneron Factor XI Antibodies Presented at American Heart Association Scientific Sessions and Published in The Lancet

Core Insights - Regeneron Pharmaceuticals has reported positive Phase 2 trial results for two investigational factor XI antibodies, REGN7508 and REGN9933, aimed at preventing blood clotting in patients undergoing total knee replacement surgery [2][3][5] - The antibodies are designed to have distinct profiles, with REGN7508 providing stronger anticoagulation and REGN9933 offering a lower risk of bleeding, allowing for tailored anticoagulant therapy based on patient risk profiles [2][3][12] Trial Results - The trials included two open-label, active-controlled Phase 2 studies: ROXI-VTE-I and ROXI-VTE-II, evaluating the efficacy of a single intravenous dose of REGN7508 and REGN9933 for preventing venous thromboembolism (VTE) after knee arthroplasty [4][11] - REGN7508 reduced VTE rates to 7.1%, superior to apixaban's rate of 12.4%, while REGN9933 decreased VTE rates to 17.2%, superior to enoxaparin's rate of 20.6% [5][7] Safety Profile - Both antibodies demonstrated robust anti-clotting effects with no clinically relevant bleeding reported in any treatment arm, indicating a favorable safety profile [5][8][13] - The only treatment-related adverse event was minimal bleeding in the enoxaparin arm, with overall adverse event rates being similar across treatment groups [7][8] Future Development - Regeneron is advancing its factor XI program with ongoing Phase 3 trials for REGN7508, including ROXI-APEX and ROXI-ASPEN, and plans to initiate additional trials for various indications in 2026 [14][12] - The company aims to explore the use of these antibodies in other clinical settings, including atrial fibrillation and cancer-associated thrombosis [14][12]