Vol. 53, Issue 3, 590-596, March 1998

Antagonist Properties of a Phosphono Isoxazole Amino Acid at Glutamate R1-4 (R,S)-2-Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic Acid Receptor Subtypes

Philip Wahl, Charlotte Anker, Stephen F. Traynelis, Jan Egebjerg, Jesper S. Rasmussen, Povl Krogsgaard-Larsen, and Ulf Madsen

Department of Molecular Pharmacology, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Maaloev, Denmark (P.W., C.A.), Department of Pharmacology, Emory University, Atlanta, GA 30322-3090, USA (S.F.T.), Department of Molecular Genetics, Novo Nordisk A/S, DK-2880 Bagsværd, Denmark (J.E., J.S.R.) and Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, DK-2100 Copenhagen, Denmark (P.K.-L., U.M.)

The activity of the (R,S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor antagonist, (R,S)-2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl]propionic acid (ATPO), at recombinant ionotropic glutamate receptors (GluRs) was evaluated using electrophysiological techniques. Responses at homo- or heterooligomeric AMPA-preferring GluRs expressed in human embryonic kidney (HEK) 293 cells (GluR1-flip) or Xenopus laevis oocytes (GluR1-4-flop or GluR1-flop + GluR2) were potently inhibited by ATPO with apparent dissociation constants (K_b values) ranging from 3.9 to 26 µM. A Schild analysis for kainate (KA)-activated GluR1 receptors showed ATPO to have a K_B of 8.2 µM and a slope of unity, indicating competitive inhibition. The antagonism by ATPO at GluR1 was of similar magnitude at holding potentials between 100 mV and +20 mV. In contrast, ATPO (<300 µM), does not inhibit responses to kainate at homomeric GluR6 or heterooligomeric GluR6/KA2 expressed in HEK 293 cells but activated GluR5 and GluR5/KA2 expressed in X. laevis oocytes. ATPO produced <15% inhibition at the maximal concentration (300 µM) of current responses through NR1A + NR2B receptors expressed in X. laevis oocytes. Thus, ATPO shows a unique pharmacological profile, being an antagonist at GluR1-4 and a weak partial agonist at GluR5 and GluR5/KA2.