Pharmacology of 5-chloro-7-trifluoromethyl-1,4-dihydro-2,3- quinoxalinedione: A novel systemically active ionotropic glutamate receptor antagonist

5-Chloro-7-trifluoromethyl-1,4-dihydro-2,3-quinoxalinedione (ACEA-1011) has analgesic properties in animal models of tonic pain. To investigate the mechanisms underlying this effect we used electrical recording techniques to characterize the in vitro pharmacology of ACEA-1011 at mammalian glutamate receptors. Two preparations were used: Xenopus oocytes expressing rat brain receptors and cultured rat cortical neurons. Results showed that ACEA-1011 is a competitive antagonist at NMDA receptor glycine sites. Apparent antagonist affinities (K(b) values) were 0.4 to 0.8 μM in oocytes and ~0.6 μM in neurons. IC₅₀ values for ACEA-1011 against four binary subunit combinations of cloned rat NMDA receptors (NR1A/NR2A, 2B, 2C or 2D) ranged from 0.4 to 8 μM (1 μM glycine). The 20-fold variation in sensitivity was due to a combination of subunit-dependent differences in glycine and antagonist affinities; EC₅₀ values for glycine ranged between 0.08 to 0.8 μM and K(b) values for ACEA-1011 between 0.2 to 0.8 μM. In addition, ACEA-1011 inhibited AMPA-preferring non-NMDA receptors by competitive antagonism at glutamate binding sites. K(b) values were 4 to 9 μM in oocytes and 9 to 10 μM in neurons. The ED₅₀ for ACEA-1011 in a mouse maximum electroshock-induced seizure model was ~12 mg/kg i.v.. Our results indicate that ACEA-1011 is a systemically active broad selectivity ionotropic glutamate receptor antagonist.