Binding characterization of N-(2-chloro-5-thiomethylphenyl)-N'-(3-[³ H]₃ methoxy phenyl)-N'-methylguanidine ([³ H]GMOM), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist.

ABSTRACT: Labeled with carbon-11, N-(2-chloro-5-thiomethylphenyl)-N'-(3-methoxyphenyl)-N'-methylguanidine ([¹¹ C]GMOM) is currently the only positron emission tomography (PET) tracer that has shown selectivity for the ion-channel site of N-methyl-D-aspartate (NMDA) receptors in human imaging studies. The present study reports on the selectivity profile and in vitro binding properties of GMOM. The compound was screened on a panel of 80 targets, and labeled with tritium ([³ H]GMOM). The binding properties of [³ H]GMOM were compared to those of the reference ion-channel ligand [³ H](+)-dizocilpine maleate ([³ H]MK-801), in a set of concentration-response, homologous and heterologous inhibition, and association kinetics assays, performed with repeatedly washed rat forebrain preparations. GMOM was at least 70-fold more selective for NMDA receptors compared to all other targets examined. In homologous inhibition and concentration-response assays, the binding of [³ H]GMOM was regulated by NMDA receptor agonists, albeit in a less prominent manner compared to [³ H]MK-801. Scatchard transformation of homologous inhibition data produced concave upward curves for [³ H]GMOM and [³ H]MK-801. The radioligands showed bi-exponential association kinetics in the presence of 100 ?mol L^-1 l-glutamate/30 ?mol L^-1 glycine. [³ H]GMOM (3 nmol L^-1 and 10 nmol L^-1 ) was inhibited with dual affinity by (+)-MK-801, (R,S)-ketamine and memantine, in both presence and absence of agonists. [³ H]MK-801 (2 nmol L^-1 ) was inhibited in a monophasic manner by GMOM under baseline and combined agonist conditions, with an IC₅₀ value of ~19 nmol L^-1 . The non-linear Scatchard plots, biphasic inhibition by open channel blockers, and bi-exponential kinetics of [³ H]GMOM indicate a complex mechanism of interaction with the NMDA receptor ionophore. The implications for quantifying the PET signal of [¹¹ C]GMOM are discussed.

SUBMITTER: Metaxas A 

PROVIDER: S-EPMC6381215 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature