Selexipag (NS-304) is an orally available and long-acting IP receptor agonist prodrug, and its active form, MRE-269, is highly selective for the IP receptor. Selexipag (NS-304) inhibits the binding of [3H]Iloprost to the human and rat IP receptors in a concentration-dependent manner. The Ki is 260 nM for the human IP receptor and 2100 nM for the rat IP receptor. The intracellular cAMP levels in hIP-CHO cells are increased in a concentration-dependent manner by treatment with Selexipag (NS-304) with EC50 of 177nM. Selexipag (NS-304) also inhibits platelet aggregation in humans and monkeys with IC50 values of 5.5 and 3.4 μM, respectively, but it shows no inhibition in dogs (IC50 of >100 μM)