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

Abstract

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.

Discovery of Two Novel Antiplatelet Clinical Candidates (BMS-986120 and BMS-986141) That Antagonize Protease-Activated Receptor 4

“…These hits were optimized into a potent, selective, and orally bioavailable tool compound, UDM-001651 (1, Table 1), which showed antithrombotic efficacy and limited bleeding liability in monkey models. 23 Subsequently, this series of imidazothiadiazoles was elaborated into an initial clinical candidate, BMS-986120 (43, Table 5). We have also previously reported on the outstanding antithrombotic efficacy and low bleeding liability of BMS-986120 as a first-in-class PAR4 antagonist.…”

“…In a prior publication, we described initial structure−activity relationship (SAR) studies that resulted in the discovery of a benzyl substituted lead compound, 2, and a more potent bis-benzyloxy substituted tool compound, UDM-001651 (compound 1, Table 1). 23 Additionally, we provided detailed descriptions of the PAR4 FLIPR assay, which measures inhibition of intracellular calcium signaling induced by a PAR4 agonist peptide, and the γthrombin induced platelet-rich plasma aggregation assay (γ-Thr PRP), a platelet aggregation assay that incorporates a PAR4specific proteolyzed form of the biologically relevant platelet agonist thrombin and plasma protein binding. 23 Based on the 60-fold antagonist potency improvement in the PRP IC 50 from addition of a benzyloxy substituent at the meta position of the benzyl group in compound 2 to give 1 (Table 1), we continued to explore benzyl substitution, with a focus on hydrophobic substituents at the meta position.…”

Molecular basis for activation and biased signaling at the thrombin-activated GPCR proteinase activated receptor-4 (PAR4)

“…Given the liabilities seen with targeting PAR1 as a platelet thrombin receptor, there has been renewed interest in developing small molecule PAR4 antagonists (18 -20). Recently, small molecule antagonists of PAR4 have been described with efficacy in inhibiting injury-induced thrombosis in both nonhuman primates and humans (21)(22)(23). Despite these promising advances, there remains the question of whether a complete inhibition of PAR4 might also lead to bleeding liability.…”

Discovery and Optimization of a Novel Series of Competitive and Central Nervous System-Penetrant Protease-Activated Receptor 4 (PAR4) Inhibitors

“…Protease activated receptors (PARs) are family A G protein-coupled receptors (GPCRs) that signal in response to the serine protease cleavage of their N -terminal domains to reveal an encrypted tethered ligand (TL) that interacts with and activates the receptor. − Protease-activated receptor 4 (PAR4) is essential for the thrombin-induced procoagulant effect on platelets, and a recent noncompetitive antagonist (BMS-986120, 1 ) demonstrated clinical efficacy for antiplatelet therapy to treat thrombosis without bleeding. − However, the therapeutic potential of inhibiting PAR4 in the central nervous system (CNS) has only recently been recognized and appreciated. In the CNS, PAR4 is expressed on astrocytes, dendrites in the hippocampus, neurons, and glial cells; moreover, activation of PAR4 leads to a breakdown of the blood–brain barrier (BBB), suggesting that inhibition of PAR4 could be of benefit across a broad range and neurodegenerative and neuroinflammatory disorders, such as Alzheimer’s disease and Parkinson’s disease. , To support this, cerebral ischemia/reperfusion injury was attenuated in PAR4 KO mice, demonstrating a greater than 80% reduction of infarct volume with improved motor and neurologic functions as compared to wild-type mice.…”