State-dependent NMDA receptor antagonism by Ro 8-4304, a novel NR2B selective, non-competitive, voltage-independent antagonist.
1. Subunit-selective blockade of N-methyl-D-aspartate (NMDA) receptors provides a potentially attractive strategy for neuroprotection in the absence of undesirable side effects. Here, we describe a novel NR2B-selective NMDA antagonist, 4-¿3-[4-(4-fluoro-phenyl)-3,6-dihydro-2H-pyridin-1-yl]-2-hydroxy-propoxy ¿-benzamide (Ro 8-4304), which exhibits >100 fold higher affinity for recombinant NR1(001)/NR2B than NR1(001)/NR2A receptors. 2. Ro 8-4304 is a voltage-independent, non-competitive antagonist of NMDA receptors in rat cultured cortical neurones and exhibits a state-dependent mode of action similar to that described for ifenprodil. 3. The apparent affinity of Ro 8-4304 for the NMDA receptor increased in an NMDA concentration-dependent manner so that Ro 8-4304 inhibited 10 and 100 microM NMDA responses with IC50s of 2.3 and 0.36 microM, respectively. Currents elicited by 1 microM NMDA were slightly potentiated in the presence of 10 microM Ro 8-4304, and Ro 8-4304 binding slowed the rate of glutamate dissociation from NMDA receptors. 4. These results were predicted by a reaction scheme in which Ro 8-4304 exhibits a 14 and 23 fold higher affinity for the activated and desensitized states of the NMDA receptor, respectively, relative to the agonist-unbound resting state. Additionally, Ro 8-4304 binding resulted in a 3 4 fold increase in receptor affinity for glutamate site agonists. 5. Surprisingly, whilst exhibiting a similar affinity for NR2B-containing NMDA receptors as ifenprodil, Ro 8-4304 exhibited markedly faster kinetics of binding and unbinding to the NMDA receptor. This spectrum of kinetic behaviour reveals a further important feature of this emerging class of NR2B-selective compounds.
Kew
J N
JN
Pharma Division, Preclinical CNS Research, F. Hoffmann-La Roche Ltd, Basel, Switzerland.
Trube
G
G
Kemp
J A
JA
D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D010880:Piperidines / Q000494:pharmacology; D011485:Protein Binding; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014982:Xenopus laevis
C111258:4-(3-(4-(4-fluoro-phenyl)-3,6-dihydro-2H-pyridin-1-yl)-2-hydroxy-propoxy)-benzamide; D001549:Benzamides; D018691:Excitatory Amino Acid Antagonists; D010880:Piperidines; D011725:Pyridines; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; C010739:ifenprodil