In vitro and in vivo characterisation of [3H]ANSTO-14 binding to the sigma 1 binding sites.
N-(4-phenylbutyl)-3-hydroxy-4-azahexacyclo[5.4.1.0(2,6).0(3, 10).0(5,9) .0(8,11)]dodecane (ANSTO-14) showed the highest activity for the sigma 1 site (Ki = 9.4 nM) and 19-fold sigma 1/sigma 2 selectivity. The present study showed that [3H]ANSTO-14 binds to a single high-affinity site in guinea pig brain membranes with an equilibrium Ki of 8.0 +/- 0.3 nM, in good agreement with the kinetic studies (Kd = 13.3 +/- 5.4 nM, n = 4), and a Bmax of 3.199 +/- 105 fmol/mg protein (n = 4). The in vivo biodistribution of [3H]ANSTO-14 showed a high uptake in the diencephalon. Pretreatment of rats with sigma ligands including (+)-pentazocine (sigma 1), ANSTO-14 (sigma 1), and DTG (sigma 1 and sigma 2) did not significantly reduce radiotracer uptake in the brain, but did in the spleen. A labelled metabolite was found in the liver and brain. Due to its insensitivity to sigma ligands, the accumulation of [3H]ANSTO-14 in the brain indicates high nonspecific binding. Therefore, [3H]ANSTO-14 is a suitable ligand for labelling sigma 1 sites in vitro but is not suitable for brain imaging of sigma binding sites in vivo.
Nguyen
V H
VH
Department of Pharmacology, The University of Sydney, NSW, Australia. V.H.Nguyen@ansto.gov.au
Mardon
K
K
Kassiou
M
M
Christie
M D
MD
D000818:Animals; D001921:Brain / Q000378:metabolism*; D001952:Bridged-Ring Compounds / Q000378:metabolism*; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D015394:Molecular Structure; D009928:Organ Specificity; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017480:Receptors, sigma / Q000378:metabolism*; D014018:Tissue Distribution
D001952:Bridged-Ring Compounds; C119664:N-(4-phenylbutyl)-3-hydroxy-4-azahexahydro(5.4.1.0(2,6).0(3,10).0(5,9).0(8,11))dodecane; D017480:Receptors, sigma