Discovery of Potent Protease-Activated Receptor 4 Antagonists with in Vivo Antithrombotic Efficacy.

In an effort to identify novel antithrombotics, we have investigated protease-activated receptor 4 (PAR4) antagonism by developing and evaluating a tool compound, UDM-001651, in a monkey thrombosis model. Beginning with a high-throughput screening hit, we identified an imidazothiadiazole-based PAR4 antagonist chemotype. Detailed structure-activity relationship studies enabled optimization to a potent, selective, and orally bioavailable PAR4 antagonist, UDM-001651. UDM-001651 was evaluated in a monkey thrombosis model and shown to have robust antithrombotic efficacy and no prolongation of kidney bleeding time. This combination of excellent efficacy and safety margin strongly validates PAR4 antagonism as a promising antithrombotic mechanism.

Blockade of protease-activated receptor-4 (PAR4) provides robust antithrombotic activity with low bleeding.

Antiplatelet agents are proven efficacious treatments for cardiovascular and cerebrovascular diseases. However, the existing drugs are compromised by unwanted and sometimes life-threatening bleeding that limits drug usage or dosage. There is a substantial unmet medical need for an antiplatelet drug with strong efficacy and low bleeding risk. Thrombin is a potent platelet agonist that directly induces platelet activation via the G protein (heterotrimeric guanine nucleotide-binding protein)-coupled protease-activated receptors PAR1 and PAR4. A PAR1 antagonist is approved for clinical use, but its use is limited by a substantial bleeding risk. Conversely, the potential of PAR4 as an antiplatelet target has not been well characterized. Using anti-PAR4 antibodies, we demonstrated a low bleeding risk and an effective antithrombotic profile with PAR4 inhibition in guinea pigs. Subsequently, high-throughput screening and an extensive medicinal chemistry effort resulted in the discovery of BMS-986120, an orally active, selective, and reversible PAR4 antagonist. In a cynomolgus monkey arterial thrombosis model, BMS-986120 demonstrated potent and highly efficacious antithrombotic activity. BMS-986120 also exhibited a low bleeding liability and a markedly wider therapeutic window compared to the standard antiplatelet agent clopidogrel tested in the same nonhuman primate model. These preclinical findings define the biological role of PAR4 in mediating platelet aggregation. In addition, they indicate that targeting PAR4 is an attractive antiplatelet strategy with the potential to treat patients at a high risk of atherothrombosis with superior safety compared with the current standard of care.

Prediction of the therapeutic index of marketed anti-coagulants and anti-platelet agents by guinea pig models of thrombosis and hemostasis.

INTRODUCTION: Animal models of thrombosis and hemostasis are critical for target validation in pharmaceutical research. Guinea pig haemostatic mechanisms, such as the platelet thrombin receptor repertoire, resemble those of humans. Measuring the performance characteristics of marketed antithrombotic drugs in guinea pig models is a key to predicting therapeutic indices of new agents. The goal of the current study was to benchmark representative marketed drugs in thrombosis and hemostasis models in guinea pigs. METHODS: Effects of the cyclooxygenase inhibitor, aspirin, the P2Y(12) antagonist, clopidogrel, the glycoprotein IIb/IIIa inhibitor, tirofiban, and the direct thrombin inhibitors, argatroban and hirudin, were evaluated in this study. Antithrombotic agents were tested in FeCl(3)-induced carotid artery thrombosis and arterio-venous shunt thrombosis models. Haemostatic effects of drugs were evaluated in cuticle and renal bleeding models. Ex vivo measurements of platelet function and coagulation inhibition were performed to benchmark preclinical doses of each agent to those used clinically. RESULTS: The overall rank-order of potency in thrombosis models based on per cent of vessels occluded, average carotid blood flow, and thrombus weight was aspirin=argatroban=tirofiban