Antagonism of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane stimulus with a newly identified 5-HT2- versus 5-HT(1C)-selective antagonist

Article abstract of DOI:10.1021/jm00069a010

DOM [i.e., 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane] is a 5- HT(1C/2) serotonin agonist that exerts stimulus control of behavior in animals. In order to determine if the discriminative stimulus effect of DOM is 5-HT(1C)- or 5-HT₂-mediated, it would be informative to conduct tests of stimulus antagonism with a 5-HT(1C)- or 5-HT₂-selective antagonist. To date, no such agents exist. Although the neuroleptic agent spiperone binds at D2 dopamine receptors and 5-HT(1A) serotonin receptors, (a) it displays about a 1000-fold selectivity for 5-HT₂ versus 5-HT(1C) sites and (b) it has been used as a '5-HT₂-selective' antagonist. Because spiperone is a behaviorally disruptive agent, it is not suitable for use in drug-discrimination studies. Using the spiperone molecule as a starting point, a limited structure- affinity investigation was conducted in order to identify a suitable antagonist with high affinity and selectivity for 5-HT₂ receptors, and yet an antagonist that might lack the disruptive actions of spiperone. Various modifications of the spiperone molecule were examined, but most resulted in decreased 5-HT₂ affinity or in loss of selectivity. One compound, 8-[3-(4- fluorophenoxy)propyl]-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (26), was shown to bind at 5-HT₂ sites with high affinity (K(i) = 2 nM) and >2,000- fold selectivity versus 5-HT(1C) sites. In tests of stimulus antagonism using rats trained to discriminate 1 mg/kg of DOM from saline vehicle, 26 behaved as a potent antagonist (ED₅₀ = 0.003 mg/kg) and lacked the disruptive effects associated with spiperone. As such, (a) it would appear that the DOM stimulus is primarily a 5-HT₂-mediated, and not 5-HT(1C)-mediated, phenomenon, and (b) compound 26 may find application in other pharmacologic investigations where spiperone may not be a suitable antagonist.