Mechanism of Inhibition of the GluA2 AMPA Receptor Channel Opening: The Role of 4-Methyl versus 4-Carbonyl Group on the Diazepine Ring of 2,3-Benzodiazepine Derivatives

2,3-Benzodiazepine derivatives are synthesized as drug candidates for the potential treatment of various neurodegenerative diseases involving the excessive activity of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Here, we describe a rapid kinetic investigation of the mechanism of inhibition of the GluA2Q_flip AMPA receptor channel opening by two 2,3-benzodiazepine derivatives, that is, the prototypic 2,3-benzodiazepine compound GYKI 52466 [(1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine)] and 1-(4-aminophenyl)-3,5-dihydro-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-one (BDZ-2). GYKI 52466 and BDZ-2 are structurally similar in that the 4-methyl group in the diazepine ring of GYKI 52466 is replaced by a carbonyl group, yielding BDZ-2. Using a laser-pulse photolysis technique with ∼60 μs time resolution, we characterize the effect of the two compounds individually on the channel-opening process of the GluA2Q_flip receptor expressed in HEK-293 cells. We find that BDZ-2 preferentially inhibits the open-channel state, whereas GYKI 52466 is more selective for the closed-channel state of the GluA2Q_flip receptors. Each inhibitor binds independently to its own noncompetitive site, and the two sites do not interact allosterically. The significance of these results in the context of both the structure–activity relationship and the properties of the GluA2Q_flip receptor channels is presented.