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

Abstract

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.

PAR4 (Protease-Activated Receptor 4)

“…BMS-986120 blocked human platelet activation in platelet-rich plasma stimulated by γ-thrombin or a PAR4 activation peptide with an IC 50 <10 nmol/L. 12 The most compelling findings in this study resulted from a direct comparison of BMS-986120 to clopidogrel in a nonhuman primate thrombosis model. BMS-986120 administered orally at 1 mg/kg decreased thrombus weight by 80% with limited bleeding risk.…”

“…In contrast, the dose of clopidogrel that achieved >80% reduction in thrombus weight (1 mg/kg) led to >8-fold increase in bleeding. 12 This comprehensive study showed BMS-986120 to be an effective PAR4 antagonist with a lower bleeding risk and a wider therapeutic window compared with clopidogrel.…”

“…12 This compound was identified in a high-throughput screen of 1.1 million compounds from the Bristol-Myers-Squibb (BMS) library. Compounds that blocked calcium signaling induced by an optimized PAR4 activation peptide were further characterized for their ability to inhibit γ-thrombin-induced platelet aggregation.…”

“…BMS-986120 did not inhibit platelet response to other agonists (SFLLRN [PAR1 activation peptide], ADP, or arachidonic acid), which is consistent with the previous report that demonstrated that BMS-986120 specifically blocks PAR4 signaling when added to platelets ex vivo. 12 The authors demonstrated that BMS-986120 reduces thrombus growth to a similar degree as the combined treatment of aspirin and clopidogrel, signifying a potential major therapeutic advance. However, these treatments were not directly compared with statistical analysis (Figure 3B and 3C).…”

Drugs targeting protease-activated receptor-4 improve the anti-thrombotic therapeutic window

“…The recent preclinical study by Wong et al (5) details the development and preclinical evaluation of the first PAR4 antagonist to enter a clinical trial and represents a potentially important breakthrough in the treatment of arterial thrombosis. While further insights are still to be gained regarding the utility of PAR4 antagonism in clinical settings, this study has contributed an important reagent to help study this previously under-appreciated platelet activation mechanism, and has identified a potentially useful approach for the safe and effective prevention of arterial thrombosis.…”