Received for publication October 7, 2004.
Revised November 17, 2004.
Accepted for publication November 23, 2004.

Structural determinants of arylacetic acid NSAIDs necessary for binding and activation of the PGD₂ receptor CRTH2

Abstract

The CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells) receptor, a G protein-coupled receptor that mediates chemotaxis of inflammatory cells in response to PGD₂, is hypothesized to play a role in Th2-mediated allergic disease. In addition to PGD₂, CRTH2 can be activated by indomethacin, a non-selective cyclooxygenase inhibitor and widely used nonsteroidal antiinflammatory drug (NSAID). To evaluate the structural features that confer CRTH2 binding selectivity, structure-activity relationship analysis of arylacetic acid-class NSAIDs as CRTH2 receptor ligands was performed. Indomethacin, sulindac sulfide and zomepirac displaced [³H]PGD₂ binding at the mouse CRTH2 receptor with comparable affinity (K_i = 1.5±0.1, 2.5±0.4 and 3.3±0.3 µM, respectively). The indomethacin metabolite 5'-O-desmethyl indomethacin (5'-DMI) possessed binding affinity similar to indomethacin, however elimination of the 2-methyl substituent on the indole ring resulted in a 10-fold decrease in binding affinity. No binding was detected for indole acetic acid and indole derivatives such as tryptophan, serotonin and 5-HIAA, demonstrating the importance of the N-acyl moiety of indomethacin. Neutral derivatives of indomethacin also failed to bind to mCRTH2, suggesting that the negatively-charged carboxylate moiety participates in a key ligand-receptor interaction. Despite similar binding affinities, NSAID-type mCRTH2 ligands exhibited variable potencies as mCRTH2 agonists. Sulindac sulfide and 5'-DMI inhibited [cAMP]_i generation and stimulated cell migration comparable to indomethacin. In contrast, zomepirac did not inhibit [cAMP]_i generation or stimulate cell migration but weakly antagonized the effects of indomethacin on [cAMP]_i. Taken together, these results reveal structural features of arylacetic acid NSAIDs that may be exploited for the development of selective CRTH2 ligands.

Key words: Prostanoid, Gi family, cAMP, Structure-activity relationships and modeling, Receptor binding studies, Cyclooxygenases, Eicosanoids

This article has been cited by other articles:

				I. M. Macias-Perez, R. Zent, M. Carmosino, M. D. Breyer, R. M. Breyer, and A. Pozzi Mouse EP3 {alpha}, {beta}, and {gamma} Receptor Variants Reduce Tumor Cell Proliferation and Tumorigenesis in Vivo J. Biol. Chem., May 2, 2008; 283(18): 12538 - 12545. [Abstract] [Full Text] [PDF]

				A. N. Hata, T. P. Lybrand, and R. M. Breyer Identification of Determinants of Ligand Binding Affinity and Selectivity in the Prostaglandin D2 Receptor CRTH2 J. Biol. Chem., September 16, 2005; 280(37): 32442 - 32451. [Abstract] [Full Text] [PDF]

				J. M. Mathiesen, T. Ulven, L. Martini, L. O. Gerlach, A. Heinemann, and E. Kostenis Identification of Indole Derivatives Exclusively Interfering with a G Protein-Independent Signaling Pathway of the Prostaglandin D2 Receptor CRTH2 Mol. Pharmacol., August 1, 2005; 68(2): 393 - 402. [Abstract] [Full Text] [PDF]