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NEUROPHARMACOLOGY
Discovery Biology Research (A.M., H.O., T.O., K.T., Y.M., J.T.), Pharmacokinetics, Dynamics, and Metabolism (M.M.), and Discovery Chemistry Research (K.N., T.K., Y.O.), Pfizer Global Research and Development, Aichi, Japan
The prostaglandin (PG) EP4 receptor subtype is expressed by peripheral sensory neurons. Although a potential role of EP4 receptor in pain has been suggested, a limited number of selective ligands have made it difficult to explore the physiological functions of EP4 or its potential as a new analgesic target. Here, we describe the in vitro and in vivo pharmacology of a novel EP4 receptor antagonist, N-[({2-[4-(2-ethyl-4,6-dimethyl-1H-imidazo [4,5-c] pyridin-1-yl) phenyl]ethyl}amino) carbonyl]-4-methylbenzenesulfonamide (CJ-023,423). In vitro, CJ-023,423 inhibits [3H]PGE2 binding to both human and rat EP4 receptors with Ki of 13 ± 4 and 20 ± 1 nM, respectively. CJ-023,423 is highly selective for the human EP4 receptor over other human prostanoid receptor subtypes. It also inhibits PGE2-evoked elevation in intracellular cAMP at the human and rat EP4 receptors with pA2 of 8.3 ± 0.03 and 8.2 ± 0.2 nM, respectively. In vivo, oral administration of CJ-023,423 significantly reduces thermal hyperalgesia induced by intraplantar injection of PGE2 (ED50 = 12.8 mg/kg). CJ-023,423 is also effective in models of acute and chronic inflammatory pain. CJ-023,423 significantly reduces mechanical hyperalgesia in the carrageenan model. Furthermore, CJ-023,423 significantly reverses complete Freund's adjuvant-induced chronic inflammatory pain response. Taken together, the present data indicate that CJ-023,423, a highly potent and selective antagonist of both human and rat EP4 receptors, produces antihyperalgesic effects in animal models of inflammatory pain. Thus, specific blockade of the EP4 receptor signaling may represent a novel therapeutic approach for the treatment of inflammatory pain.
Address correspondence to: Dr. Junji Takada, Discovery Biology Research, Nagoya Laboratories, Pfizer Global Research and Development, Pfizer Inc., 5-2 Taketoyo, Aichi, 470-2393, Japan. E-mail: junji.takada{at}pfizer.com
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