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Binding to the serotonin 5-HT2 receptor by the enantiomers of 125I-DOI
M P Johnson1, A J Hoffman, D E Nichols
1Department of Medicinal Chemistry and Pharmacognosy, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana 47907.
Abstract:
Preliminary receptor binding experiments with the stereoisomers of 125I-DOI, a new putative 5-HT2 agonist ligand, were conducted. The results indicated specific binding for both enantiomers, with a two-site model giving the best fit to the binding data. R-125I-DOI showed a high affinity dissociation constant of 1.26 nanoMolar, while the less active S-enantiomer had a two-fold lower affinity. Competition experiments with several 5-HT2 agonists also indicated a two site model, with high affinity inhibition constants less than 10 nanoMolar. These results show a stereoselective effect of ligand binding to the 5-HT2 receptor. The use of this ligand to investigate agonist-receptor interactions could be instrumental in the elucidation of the role of serotonergic systems in the mechanism of action of hallucinogens.