Prostacyclin (PGI2) is a potent vasorelaxant and inhibitor of platelet aggregation. It mediates its actions by binding to a specific G protein-coupled receptor, the IP receptor, on the surface of endothelial cells, arterial smooth muscle, and platelets. The IP receptor also participates in signal transduction of the pain response, cardioprotection, and inflammation. MRE-269 is the active form of the prodrug NS-304. It is a potent and selective agonist for the human IP receptor with a Ki value of 20 nM. In contrast to PGI2, which has a half-life of 30 seconds to a few minutes in vivo, plasma concentrations of MRE-269 remain near peak levels for more than eight hours in rats and dogs. Unlike the PGI2 analogues, beraprost and iloprost, MRE-269 lacks high affinity for the EP3 receptor. As a result, MRE-269 induces vasodilation equally in large and small pulmonary arteries, whereas vasodilation of small arteries by beraprost and iloprost is reduced via EP3-mediated vasoconstriction.
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