– MF-766 (MF766) is a highly potent and selective EP(4) antagonist with binding Ki of 0.23 nM, displays no significant affinity (>7000-fold selectivity) against other PG receptors (IC50>1500 nM); behaved as a full antagonist with an IC50 of 1.4 nM (shifted to 1.8 nM in the presence of 10% HS) in the functional assay; exhibits blockade of inhibition of TNFa-induced IP10 release by the specific EP4 agonist L-000902688 (IC50=9.5 nM); demonstrates potency and efficacy of in the rat AIA model measuring inhibition of paw swelling.