Abstract 570: Aptamers Against Factor Xa or Thrombin Synergize With Catalytic Site Inhibitors of FXa or Thrombin, Respectively, to Effectively Anticoagulate Blood in an Ex Vivo Oxygenator Circuit

Introduction: The RNA aptamers 11F7t and R9D-14T, which inhibit Factor (F)Xa and thrombin respectively, function as reversible anticoagulants but achieve less intense anticoagulation than unfractionated heparin (UFH). Neither aptamer inhibits the catalytic site of its target; 11F7t binds a FXa exosite in a manner that impedes FVa binding, while R9D-14T binds thrombin exosite I, thereby obstructing fibrinogen binding. However, 11F7t synergizes with a FXa catalytic site inhibitor and R9D-14T synergizes with a thrombin catalytic site inhibitor; each combination prevents clot formation for >180 minutes (min) in a whole blood thromboelastography (TEG) assay, thereby replicating the effect of UFH (5U/mL). Aims: To determine whether 11F7t plus a FXa catalytic site inhibitor, or R9D-14T plus a thrombin catalytic site inhibitor, can also maintain the fluidity of blood circulated continuously for 120 min within an ex vivo membrane oxygenator circuit. Methods: Human whole blood anticoagulated with (A) 11F7t (2μM) + edoxaban (2μM), (B) 11F7t (2μM) + apixaban (2μM), (C) 11F7t (2μM) + fondaparinux (2μM), (D) R9D-14T (10μM) + argatroban (10μM), or (E) UFH (5U/ml) was circulated continuously within the oxygenator circuit at 33°C for 120 min at a flow rate of 50 mL/min. Activated Clotting Time (ACT) was assessed at 0, 5, 60, and 120 min after circulation was initiated, and post-circulation scanning electron microscopy (SEM) images of the oxygenator membranes were obtained. Results: 11F7t (2μM) or R9D-14T (10μM) alone failed to prevent visible clot formation in the circuit. In contrast, strategies (A) through (E) each prevented visible clot formation for 120 min. At 120 min, ACTs (mean ± SE) were, respectively, 565.8 ± 34.7, 446.5 ± 7.4, 387.6 ± 1.6, 903.4 ± 19.0, and 411.4 ± 16.5 seconds. Post-circulation SEM images of oxygenator membranes were similar for all five strategies and revealed minimal fibrinous and cellular debris. Conclusion: The anticoagulant synergy achieved by combining aptamer 11F7t or aptamer R9D-14T with a FXa or thrombin catalytic site inhibitor, respectively, can maintain the fluidity of blood circulated continuously within an ex vivo oxygenator circuit. Such synergy may prove useful in clinical settings that require intense anticoagulation.