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Abstract
Receptors for prostanoids on platelets include the EP3 receptor for which the natural agonist is the inflammatory mediator prostaglandin E2 (PGE2) produced in atherosclerotic plaques. EP3 is implicated in atherothrombosis and an EP3 antagonist might provide atherosclerotic lesion-specific antithrombotic therapy. DG-041 (2,3-dichlorothiophene-5-sulfonic acid, 3-[1-(2,4-dichlorobenzyl)-5-fluoro-3-methyl-1H-indol-7-yl]acryloylamide) is a direct-acting EP3 antagonist currently being evaluated in Phase 2 clinical trials. We have examined the contributions of EP3 to platelet function using the selective EP3 agonist sulprostone and also PGE2, and determined the effects of DG-041 on these. Studies were in human platelet-rich plasma or whole blood and included aggregometry and flow cytometry. Sulprostone enhanced aggregation induced by primary agonists including collagen, TRAP, platelet activating factor, U46619, serotonin and adenosine diphosphate, and enhanced P-selectin expression and platelet–leukocyte conjugate formation. It inhibited adenylate cyclase (measured by vasodilator-stimulated phosphoprotein phosphorylation) and enhanced Ca2+ mobilization. It potentiated platelet function even in the presence of aspirin and/or AR-C69931 (a P2Y12 antagonist). DG-041 antagonized the effects of sulprostone on platelet function. The effect of PGE2 on platelet aggregation depended on the nature of the agonist and the concentration of PGE2 used as a consequence of both pro-aggregatory effects via EP3 and anti-aggregatory effects via other receptors. DG-041 potentiated the protective effects of PGE2 on platelet aggregation by inhibiting the pro-aggregatory effect via EP3 stimulation. DG-041 remained effective in the presence of a P2Y12 antagonist and aspirin. DG-041 warrants continued investigation as a potential agent for the treatment of atherothrombosis without inducing unwanted bleeding risk.