In vitro and in vivo characterisation of [H-3]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 ( K-i = 9.4 nM) and 19-fold sigma(1)/sigma(2) selectivity. The present study showed that [H-3]ANSTO-14 binds to a single high-affinity site in guinea pi g brain membranes with an equilibrium K-d of 8.0 +/- 0.3 nM, in good agreem ent with the kinetic studies (K-d = 13.3 +/- 5.4 nM, n = 4), and a B-max of 3,199 +/- 105 fmol/mg protein (n = 4). The in vivo biodistribution of [H-3 ]ANSTO-14 showed a high uptake in the diencephalon. Pretreatment of rats wi th sigma ligands including (+)-pentazocine (sigma(1)), ANSTO-14 (sigma(1)), and DTG (sigma(1) and sigma(2)) did not significantly reduce radiotracer u ptake in the brain, but did in the spleen. A labelled metabolite was found in the liver and brain. Due to its insensitivity to a ligands, the accumula tion of [H-3]ANSTO-14 in the brain indicates high nonspecific binding. Ther efore, [H-3]ANSTO-14 is a suitable ligand for labelling sigma(1) sites in v itro but is not suitable for brain imaging of sigma binding sites In vivo. NUCL MED BIOL 26;2:209-215, 1999. (C) 1999 Elsevier Science Inc. All rights reserved.