[3H]N-[4-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)butyl]-2-methoxy-5-methylbenzamide: a novel sigma-2 receptor probe.
N-[4-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)butyl]-2-methoxy-5-methyl-benzamide (RHM-1) and N-[2-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)ethyl]-2-methoxy-5-methylbenzamide (RHM-2), two conformationally flexible benzamide analogues, were radiolabeled with tritium (specific activity=80 Ci/mmol) and the binding of [3H]RHM-1 and [3H]RHM-2 to sigma-2 (sigma2) receptors was evaluated in vitro. [3H]RHM-1 was found to have a higher affinity for sigma2 receptors compared to [3H]RHM-2 and [3H]1,3-di-o-tolylguanidine ([3H]DTG). [3H]RHM-1 had a dissociation constant (Kd) of 0.66+/-0.12 nM in rat liver membrane homogenates, which was 30-fold higher than that of [3H]RHM-2 (Kd=19.48+/-0.51 nM). The lower affinity of [3H]RHM-2 can be attributed to its faster K(off) rate since both radioligands have similar K(on) rates. Competitive binding assays were also conducted using a panel of compounds with known affinity for sigma2 receptors. The pharmacologic profile of [3H]RHM-1 was in agreement with that of [3H]DTG. The results of this study indicate that [3H]RHM-1 is a useful ligand for studying sigma2 receptors in vitro.
Xu
Jinbin
J
Department of Radiology, Washington University School of Medicine, 510 S. Kingshighway Blvd., St. Louis, MO 63110, USA.
Tu
Zhude
Z
Jones
Lynne A
LA
Vangveravong
Suwanna
S
Wheeler
Kenneth T
KT
Mach
Robert H
RH
D000818:Animals; D001549:Benzamides / Q000378:metabolism*; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D051381:Rats; D017207:Rats, Sprague-Dawley; D017480:Receptors, sigma / Q000378:metabolism*; D014183:Transplantation, Heterologous; D014316:Tritium
D001549:Benzamides; C507853:N-(2-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)ethyl)-2-methoxy-5-methylbenzamide; C507852:N-(4-(3,4-dihydro-6,7-dimethoxyisoquinolin-2(1H)-yl)butyl)-2-methoxy-5-methyl-benzamide; D017480:Receptors, sigma; C106107:sigma-2 receptor; D014316:Tritium