title: In vitro characterization of novel NR2B selective NMDA receptor antagonists.
abstract: N-Methyl-D-aspartate (NMDA) subunit specific receptor antagonism has potential therapeutic application for multiple CNS pathologies. MERCK 1, MERCK 2, and MERCK 3 are novel NR2B subtype selective NMDA receptor antagonists. The affinity and the kinetic mechanism of inhibition by these antagonists and ifenprodil were investigated using the whole-cell configuration of the patch clamp technique, calcium flux, and radioligand binding on a mouse cell line L(tk-) expressing recombinant human heteromeric NMDA receptors consisting of NR1a/NR2B subunit combinations. The rank order of potency, as determined by electrophysiology, was ifenprodil<MERCK 2<MERCK 1<MERCK 3 with K(D)'s 79+/-8, 2.4+/-1.1, 1.3+/-0.9, and approximately 0.16+/-0.02 nM, respectively. The apparent dissociation rate constants among these compounds differed by as much as 394-fold whereas the apparent association constants varied less than 3-fold. Higher affinities were a result of slower drug dissociation kinetics of receptor unbinding. Maximal inhibition was not voltage-dependent and was not statistically different at saturating concentrations by these compounds. These results provide the first detailed functional analysis of the kinetic mechanism of MERCK 1, MERCK 2, and MERCK 3 inhibition of NMDA receptors.
authors.affiliation: Neuroscience Drug Discovery, Merck Research Laboratories, West Point, PA 19486, USA. laszlo_kiss@merk.com
authors.forename: Laszlo
authors.initials: L
authors.lastname: Kiss
authors.forename: Gong
authors.initials: G
authors.lastname: Cheng
authors.forename: Bohumil
authors.initials: B
authors.lastname: Bednar
authors.forename: Rodney A
authors.initials: RA
authors.lastname: Bednar
authors.forename: Paul B
authors.initials: PB
authors.lastname: Bennett
authors.forename: Stefanie A
authors.initials: SA
authors.lastname: Kane
authors.forename: Charles J
authors.initials: CJ
authors.lastname: McIntyre
authors.forename: John A
authors.initials: JA
authors.lastname: McCauley
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Koblan
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry* / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D015394:Molecular Structure; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D011869:Radioligand Assay; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
chemical_list: D002352:Carrier Proteins; D018691:Excitatory Amino Acid Antagonists; C485668:GRIN1 protein, human; C121001:NR2B NMDA receptor; D009419:Nerve Tissue Proteins; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; C010739:ifenprodil