AAT-008 is an orally bioavailable and potent antagonist of the prostaglandin E (PGE) receptor subtype 4 (EP; IC = 16.3 nM in a human EP functional assay). It is selective for EP with IC values of 2.4, 1,890, >20,000, and >20,000 nM for binding to human recombinant EP, EP, EP, and EP, respectively. AAT-008 has potent binding affinity for human, rat, and dog EP (Ks = 0.97, 6.1, and 38 nM, respectively) and suppresses PGE-induced elevation of intracellular cAMP with an antagonistic potency (pA) of 1.1 nM in vitro. Oral administration of AAT-008 reduces carrageenan-induced mechanical hyperalgesia in rats in a dose-dependent manner.