Regular articleIn vivo evaluation of [11C]N-(2-chloro-5-thiomethylphenyl)-N′- (3-methoxy-phenyl)-N′-methylguanidine ([11C]GMOM) as a potential PET radiotracer for the PCP/NMDA receptor
Introduction
The N-methyl-D-aspartate (NMDA) ion channel is a major site of action for glutamate involved in neuroprotection, neurodegeneration, long-term potentiation, memory, and cognition [1], [2], [3], [4], [5], [6], [7], [8], [9]. Alterations in normal NMDA channel composition and function have been implicated in the pathophysiology of certain neurological and neuropsychiatric disorders such as Parkinson's Disease, Huntington's Chorea, schizophrenia, alcoholism and stroke [10], [11], [12], [13], [14]. Each NMDA ion channel is formed by one subunit called NR-1, along with select combinations of the four distinct NR-2 subunits, termed NR-2A, -2B, -2C, and -2D) [2], [15], [16], [17], [18]. In addition, NR3 subunits have been recently described [19]. Several distinct functional receptors and modulatory sites exist on each channel. The best characterized of these are the receptors for the agonist L-glutamate and the co-agonists glycine and D-serine. There are also specific binding sites within the channel for Mg2+ and phencyclidine (called the PCP site); both of these mediate ion flux through the channel. Additional modulatory sites rest on the outside of the channel, including distinct binding sites for polyamines and Zn(II).
Our ultimate goal is to use positron emission tomography (PET) imaging methods to explore the possible etiological role and therapeutic potential of the NMDA ion channel in neurodegenerative and psychiatric disorders. Imaging the PCP site in particular would allow the opportunity for quantification of active NMDA channels, including assessments of the effect of drug action and the active state of the channel [20]. It is well established that the in vitro and in vivo binding of the selective PCP site ligand [3H]MK801 is affected by the state of activation of NMDA receptors [21], [22]. Agonists at NMDA associated glutamate or glycine receptors increase [3H]MK801 binding, while competitive antagonists at these sites reduce [3H]MK801 binding. Therefore, in theory the in vivo binding of a PET PCP site PET ligand could be used to assess the regional activation state of NMDA ion channels in normal subjects and in patients before and after treatment.
To date, about two dozen candidate PCP site tracers have been reported, and a recent review on NMDA/PCP site tracer development has been published [20]. Examples published tracers include [11C]ketamine [23], [24], [25], fluorine-18, iodine-123, and carbon-11 labeled MK801 derivatives [26], [27], [28], fluorine-18 and carbon-11 labeled derivatives of phencyclidine (PCP) such as [18F]fluorothienylcyclohexylpiperidine ([18F]FETCP [29], [30], [31], novel adamantane derivatives including [18F]1-amino-3-fluoromethyl-5-methyl-adamantane ([18F]AFA) [32], [33], and the benzomorphan based tracer [11C]methyl BCLIII277CL [34]. Another approach involves a group of selective non-competitive NMDA/PCP site ligands consisting of trisubstituted N-(phenyl)-N′-(phenyl)-N′-methylguanidines [35], [36], [37]. Compounds of this series comprise some of the highest affinity PCP site ligands reported to date, moderate lipophilicity, and several exhibit specificity for the PCP site versus sigma receptors and therefore should produce a variety of potential NMDA radioligands. Herein, we report the in vivo evaluation of the first novel PET tracer of this series, [11C]N-(2-chloro-3-thiomethylphenyl)-N′-(3-methoxyphenyl)-N′-methylguanidine ([11C]GMOM) [38]. A preliminary report of this work has been published [39].
Section snippets
General
N-(2-Chloro-5-thiomethylphenyl)-N′-(3-methoxyphenyl)-N′-methylguanidine (GMOM) and the corresponding phenol precursor were synthesized as previously reported [38]. All other chemicals, reagents and solvents were obtained from commercial sources and were used without further purification. [11C]Methyl iodide is prepared routinely at Columbia University Radioligand Laboratory using established methods. HPLC purification and quality control analysis of the radioligand was performed using a Waters
Results and discussion
[11C]GMOM was synthesized in good yield and high specific activity using our previously reported method [39] (Scheme 1). Radiochemical yield ranged from 5.8 to 13.0% (EOS) and high radiochemical purity (96.7±1.5%) and specific activity (1.25±0.45 Ci/μmol EOS) were obtained. The tracer was utilized for in vivo studies between 20 and 30 min after synthesis. The regional brain distribution and specific binding of [11C]GMOM was examined through distribution studies in male rats ([11C]GMOM dose: 6–8
Acknowledgements
Funding for this work was provided for by grants from the National Institutes of Health (NIAAA IP50AA-12870-01 and NIMH MH59342-01).
References (49)
- et al.
NMDA-receptor trafficking and targetingimplications for synaptic transmission and plasticity
Trends Neurosci
(2002) Glutamate as a neurotransmitter in the brainreview of physiology and pathology
J Nutrit
(2000)Modulation of NMDA receptor responsiveness by neurotransmitters, drugs and chemical modification
Life Sci
(1990)- et al.
The role of N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission in the pathophysiology and therapeutics of psychiatric syndromes
Eur Neuropsychopharmacol
(1998) - et al.
Ligand affinities at recombinant N-methyl-D-aspartate receptors depend on subunit composition
Eur J Pharm
(1994) - et al.
Subunit- and site-specific pharmacology of the NMDA receptor channel
Prog Neurobiol
(1999) Imaging the PCP Site of the NMDA Ion Channel
Nucl Med Biol
(2003)- et al.
Brain kinetics of (R)- and (S)-[N-methyl-11C]ketamine in the rhesus monkey studied by positron emission tomography (PET)
Nucl Med Biol
(1994) - et al.
Carbon-11 labelled ketamine-synthesis, distribution in mice and PET studies in baboons
Nucl Med Biol
(1997) - et al.
PET studies of [18F]methyl-MK-801, a potential NMDA receptor complex radioligand
Neurosci Lett
(1991)
(+)-3-[123I]lodo-MK-801synthesis and characterization of binding to the N-methyl-D-aspartate receptor complex
Life Sci
In vivo study of NMDA-sensitive glutamate receptor by fluorothienylcyclohexylpiperidine [correction of fluorothienylcycloexylpiperidine], a possible ligand for positron emission tomography
Neuropharmacology
Synthesis and evaluation of 1-(1-[5-(2′-[18F]fluoroethyl)-2-thienyl]-cyclohexyl)piperidine as a potential in vivo radioligand for the NMDA receptor-channel complex
Nucl Med Biol
[125I]thienylphencyclidine, a novel ligand for the NMDA receptor
Eur J Pharm
Electrophysiological study, biodistribution in mice, and preliminary PET evaluation in a rhesus monkey of 1-amino-3-[18F]fluoromethyl-5-methyl-adamantane (18F-MEM)a potential radioligand for mapping the NMDA-receptor complex
Nucl Med Biol
Synthesis and in vitro evaluation of N,N′-diphenyl and N-naphthyl-N′-phenylguanidines as N-methyl-D-aspartate receptor ion-channel ligands
Bioorg Med Chem Lett
Modulation of [3H]MK-801 binding to NMDA receptors in vivo and in vitro
Eur J Parm
Intrathecal administration of N-methyl-D-aspartate receptor antagonist reduces the minimum alveolar anaesthetic concentration of isoflurane in rats
Brit J Anaesth
Volatile anesthetics and glutamate activation of N-methyl-D-aspartate receptors
Biochem Pharm
Molecular biology of mammalian amino acid receptors
Faseb J
Amantadine and memantine are NMDA receptor antagonists with neuroprotective properties
J Neural Transmission
Stress and hippocampal plasticity
Annu Rev Neurosci
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