Background: Thrombin activates platelets by hydrolysis of the protease-activated receptors (PAR) PAR1 and PAR4. Small molecule antagonists of PAR1 and PAR4 have demonstrated antithrombotic activity in nonhuman primate models of thrombosis.

Aims: To characterize the pharmacology of BMS-986141, a potent and selective PAR4 antagonist, in platelet calcium mobilization assays and in a microfluidics model of thrombosis.

Methods: Human blood from healthy donors was spiked with BMS-986141. Platelet calcium mobilization assays were performed with agonists including ADP, convulxin, U46619, thrombin, PAR1 and PAR4 agonist peptides. Arterial plaque rupture thrombosis was simulated by flowing blood through microfluidics channels patterned with von Willebrand Factor (vWF) to allow platelet adhesion and lipidated tissue factor (TF) to trigger thrombin generation.

Results: BMS-986141 specifically blocked calcium mobilization by PAR4 agonist peptide (AYPGKF, IC₅₀ ~1.3 nM). The PAR4 antagonist reduced the secondary phase of calcium mobilization in platelets challenged with 200 nM thrombin, without affecting the initial peak calcium, as expected for slower more sustained PAR4 signaling compared to the rapid, short lived signaling of PAR1. For corn trypsin inhibitor (CTI)-treated whole blood perfused over vWF/TF surface under high shear rate (800 s^-1) in Figure 1, BMS-986141 reduced platelet deposition by ~20 %, but not fibrin deposition (N=7 donors, 27 clots; p < 0.03).

Figure 1. PAR4 antagonist, BMS-986141, reduces platelet deposition on a vWF/TF surface at 800 s-1. (F.I. fluorescence intensity)
Figure 1. PAR4 antagonist, BMS-986141, reduces platelet deposition on a vWF/TF surface at 800 s^-1. (F.I. fluorescence intensity)

Conclusions: BMS-986141 is a highly specific antagonist of PAR4. This small molecule reduced platelet deposition in a microfluidic assay of perfused CTI-treated whole blood over patterned surfaces of vWF/TF, which simulate conditions of arterial thrombosis.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/bms-986141-a-selective-par4-antagonist-reduces-platelet-deposition-in-a-microfluidic-thrombosis-assay/