Abstract
Two novel N-methyl-d-aspartate (NMDA) antagonists with unique chemical structures, EAA-090 (2-[8,9-dioxo-2, 6-diazabicyclo[5.2.0]non-1(7)-en2-yl]ethylphosphonic acid) and EAB-318 (R-α-amino-5-chloro-1-(phosphonomethyl)-1H-benzimidazole-2-propanoic acid hydrochloride), were compared with CGS-19755 (Selfotel) in ligand binding, electrophysiology, and neuroprotection assays. CGS-19755, EAA-090 and EAB-318 inhibited [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding to NMDA receptors with IC50 values of 55, 28, and 7.9 nM, respectively. All three compounds decreased the duration of spontaneous synaptic currents and inhibited NMDA-activated currents in rat hippocampal neurons. IC50 values for inhibition of current induced by 10 μM NMDA were 795, 477, and 69 nM for CGS-19755, EAA-090, and EAB-318, respectively. The NMDA antagonists protected chick embryo retina slices and cultured rat hippocampal and cortical neurons from glutamate- and NMDA-induced neurotoxicity. In experiments in which different NMDA receptor splice variants and subtypes were expressed in Xenopus oocytes, all three antagonists preferentially blocked NMDA-elicited currents mediated by N-methyl-d-aspartate receptor (NR)1 splice variants containing the N-terminal insertion. They also favored NR2A-versus NR2B- or NR2C-containing NMDA receptors, with EAA-090 showing the greatest selectivity. EAA-090 was 10 times more potent at blocking NR2A-versus NR2B- or NR2C-containing NMDA receptors. In addition to being the most potent NMDA antagonist, EAB-318 inhibited α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors. The combination of NMDA and AMPA/kainate block enabled EAB-318 to protect neurons against ischemia induced cell death.
Footnotes
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DOI: 10.1124/jpet.104.066092.
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ABBREVIATIONS: AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; NMDA, N-methyl-d-aspartate; PCP, phencyclidine; NR, N-methyl-d-aspartate receptor; EAA-090, 2-[8,9-dioxo-2,6-diazabicyclo [5.2.0]non-1(7)-en2-yl]ethylphosphonic acid; EAB-318, R-α-amino-5-chloro-1-(phosphonomethyl)-1H-benzimidazole-2-propanoic acid hydrochloride; CPP, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid; TCP, [1-(2-thienyl)cyclohexy-l]piperidine; MK-801, (–)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate; HBSS, Hanks' balanced salt solution; LDH, lactate dehydrogenase; O.D., optical density; YM90K, 6-(1H-imidazol-11-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione hydrochloride; Ro 25-6981, R-(R*,S*)-α-(4-hydroxyphenyl)-β-methyl-4-(phenylmethyl)-1-peperidine propanol; Ro 63-1908, 1-[2-(4-hydroxy-phenoxy)-ethyl]-4-(4-methyl-benzyl)-piperidin-4-ol.
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↵1 Current address: Discovery Toxicology, Pharmaceutical Research Institute, Bristol-Myers Squibb Co., Princeton, NJ 08543.
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↵2 Current address: St. Jude Children's Research Hospital, Developmental Neurobiology, Memphis, TN 38105.
- Received January 26, 2004.
- Accepted April 6, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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