Abstract TMP98: A New Class of Precision Oral Anticoagulants (proacs) That Mostly Preserves Platelet Activity in vitro and in vivo

Abstract

Introduction: Anticoagulants, while an effective prophylactic for ischemic stroke increase a patient’s risk of major bleeding. There is currently an unmet need for new anticoagulants with the ideal combination of efficacy and low bleeding risk. Here we describe the in vitro and in vivo pharmacology of two development candidates VE-01902 and VE-02851, expected to enter phase I clinical trials in 2018 and 2019 respectively. These compounds belong to a new class of anti-coagulants, the PRecision Oral AntiCoagulants (PROACs), which inhibit fibrinogen cleavage at potencies comparable to the known Direct Thrombin Inhibitors (DTIs) while only weakly inhibiting thrombin induced platelet activation in plasma and whole blood. Methods: Enzyme activity assays by optical methods. Platelet status by expression of CD62P by flow cytometry. In vitro coagulation by Thrombin Generation Assay (TGA). In vivo efficacy and bleeding risk evaluated by rodent models of thrombosis and bleeding time tests. Results and Conclusions: The PROACs are a class of compounds that share a unique mechanism of action: reversible covalent inhibitors of thrombin with slow enzyme kinetics. We examined Thrombin Generation in platelet Poor Plasma (PPP) and Platelet Rich Plasma (PRP) of VE-01902 and VE-02851 and compared it to the known DTIs argatroban and dabigatran. In both plasma samples the PROACs potently inhibit the propagation phase (Endogenous Thrombin Potential (ETP)) while, unlike the known DTIs, only weakly affect the initiation phase of thrombin generation (10 to 20-fold weaker). In the PRP samples the PROACs do not significantly affect platelet activation even while suppressing ETP. To better understand the unique in vitro properties of the PROACs we studied the activity of multiple key factors of the coagulation cascade. Like argatroban and dabigatran, the PROACs protect mice from the effects of thrombin-induced pulmonary embolism and inhibit clot formation in the arteriovenous shunt rat model. However unlike these DTIs, they do not significantly inhibit platelet activation in either of these rodent models. Despite its strong anticoagulant properties, the PROACs show significantly lower bleeding than comparators.