Superiority of CS585 as a selective prostacyclin receptor agonist in prevention of thrombosis

Abstract Background A major challenge with development of new targets for antithrombotic treatment is the sustained effect on the platelet and the target selectivity. While increasing cAMP in the platelet through activation of the prostacyclin (IP) receptor represents a viable antiplatelet target for prevention of thrombosis, current IP receptor agonists lack stability and selectivity. Development of a selective IP receptor agonist that is stable in the blood and selective for the IP receptor would represent a new approach for prevention of platelet activation and thrombosis in the blood and expand the utility of IP receptor agonists which are currently used for the treatment of pulmonary arterial hypertension (PAH). Purpose Develop an IV and oral IP receptor agonist, CS585, with sustained activity in vivo in the blood and eliminating the off-target effects observed with other IP agonists not having selective activation of the IP receptor. These characteristics would make CS585 an attractive new therapeutic approach for limiting platelet activation and thrombosis. Methods We assessed platelet activation and thrombosis in human blood ex vivo and mouse models in vivo. For mouse models, platelets and fibrin were labelled and accumulation at the site of injury was measured using intravital microscopy. Thrombosis in the vessel was assessed in the laser-induced cremaster thrombosis assay. Selectivity was assessed in human blood pharmacologically using prostaglandin receptor inhibitors and in mouse with an IP receptor knockout mouse. Flow cytometry, aggregometry, and western blot techniques were used to assess selectivity. Results IV and oral administration of CS585 resulted in sustained inhibited clot formation and fibrin formation at the site of injury in the laser-induced cremaster arteriole thrombosis assay in wild-type mice but was unable to alter platelet function in IP knockout mice. CS585 inhibition of platelet activation was fully prevented in platelets from IP knockout mice as assessed by flow cytometry (integrin activation and granule secretion) and by VASP phosphorylation. Inhibition of human platelet activation by CS585 was inhibited by pharmacological inhibition of the IP receptor, but not by inhibition of the DP1, EP2, or EP4 receptors as assessed by aggregation, flow cytometry, and VASP phosphorylation. Conclusions We have shown for the first time that CS585, a novel IP receptor agonist, not only inhibits platelet activation and clot formation, but gives sustained inhibition through multiple routes of administration in an in vivo mouse model of thrombosis. Importantly, the challenge in selectivity observed with other IP receptor agonists is not observed with CS585 supporting its development for a number of diseases in the cardiovascular system including thrombosis, VTE, secondary prevention after MI and stroke, and PAH.CS585 inhibition of thrombosis in vivoCS585 selectively signals through IP