Biochemical and Pharmacologic Profiling of a Novel Dual Acting Antithrombin Agent with Antiprotease and Antiplatelet Actions. Hematologic Implications.

Background: The pathogenesis of thrombosis involves both cellular and humoral processes. Most antithrombotic drugs exhibit either anti-protease or anti-platelet effects. A combination of anti-protease and anti-platelet drugs provides better efficacy in the management of thrombotic disorders. A series of synthetic low molecular weight serine protease inhibitors with varying anti-platelet effects (Medicure Inc.) are being assessed for antithrombotic properties.

Materials and Methods: This investigation reports on a compound with low antithrombin/high anti-platelet activity MC 45301 (A) and a compound with high antithrombin/low anti-platelet activity MC 45308 (B) activity in in-vitro and in-vivo settings used to profile antithrombotic drugs.

Results: A exhibited strong anti-platelet actions as measured using ADP as an agonist (IC₅₀=1.1 g/ml), whereas B had a higher IC₅₀ (9.4 g/ml). In the antithrombin titration assay A (>100 μg/ml) showed a relatively higher IC₅₀ than B (45 μg/ml). In the global anticoagulant assays, A exhibited somewhat weaker effects than B. In the Xa generation assay, both compounds exhibited similar effects. However, in the thrombin generation assays B exhibited stronger effects. In whole blood assays both compounds produced anticoagulant and anti-platelet effects. Intravenous administration of these compounds to rabbits over a dose range of 50–500 g/kg produced strong dose dependent antithrombotic actions. In comparison to direct antithrombin agents such as argatroban, at a comparable dose, B produced identical antithrombotic actions, which were disproportional to the systemic anticoagulant effects. A produced modest antithrombotic actions with minimal ex vivo clotting effects. This data is highly suggestive that compounds with dual targets are able to produce stronger antithrombotic actions relative to monotherapeutic agents. Additional studies in arterial thrombosis may provide newer insights into the antithrombotic actions of compounds with dual sites of action. Moreover, these agents may be more effective in thrombotic conditions where both platelets and the coagulation system are involved.