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Cheng KT.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2006 Oct 21 [updated 2008 May 21].


1-([4-methoxy-11C]-3,4-Dimethoxyphenethyl)-4-[3-(4-fluorophenyl)propyl]piperazine ([11C]SA5845) is a radioligand developed for positron emission tomography (PET) imaging of the sigma (σ) receptors. [11C]SA5845 is a potent σ receptor agonist labeled with 11C, a positron emitter with a physical half-life (t½) of 20.4 min (1). σ receptors are functional, membrane-bound proteins distributed in the central nervous system (CNS) and peripheral organs such as the gastrointestinal tract and immune systems (2). The CNS σ receptors are unique binding sites related to higher brain functions (3). They are distinct from opiate and phencyclidine binding sites. There are at least two subtypes of σ receptors σ1 and σ2 receptors. The precise mechanism of the functional response of these receptors is not entirely known. These receptors appear to be involved in numerous pharmacological and physiologic functions, and they also modulate a number of central neurotransmitter systems, including noradrenergic, glutamatergic, and dopaminergic systems. phencyclidine and derivatives, cocaine and derivatives, some neuroleptics, atypical antipsychotic agents, and other chemically unrelated compounds can bind to the σ receptor sites. Studies have shown that these receptors may play a role in pathogenesis of psychiatric disorders (4, 5). These receptors are also expressed on a number of human and murine tumors (6). The σ1 receptor subtypes have a molecular weight of ≈25 kDa, and through the process of cloning they have shown a 30% sequence homology with the yeast C89-C7 sterol isomerase (2, 7, 8) The σ2 receptor subtypes have a molecular weight of ≈21.5 kDa and have not been cloned. The σ1 receptors are thought to be involved in certain neuropsychiatric disorders, and the σ2 receptors are also implicated in malignant neoplastic diseases. Because of these effects, σ receptor ligands may be useful for detection and treatment in neurology and oncology. Matsuno et al. (9) developed a potent σ1 agonist, 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)-piperazine dihydrochloride (SA4503), which is highly selective for σ1 receptors versus σ2 receptors. Small modifications in the SA4503 structure appear to have profound effects on the σ12 receptor affinity and selectivity (10). Fujimura et al. (11) prepared its fluorinated analog, SA5845, and reported that this compound had a high affinity for σ receptors. Kawamura et al. (12, 13) radiolabeled SA5845 with 11C and evaluated its potential for PET studies of σ receptors in CNS and tumors.

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