Stereoselectivity of 8-OH-DPAT toward the serotonin 5-HT1A receptor: biochemical and molecular modeling study

The great majority of pharmacological investigations of 5-HT1A receptors' reactivity has been performed using racemic 8-OH-DPAT, therefore the biochemical as well as behavioral profiles of both 8-OH-DPAT enantiomers are not circumstantiated. In the biochemical study capability of racemic 8-OH-DPAT (0.05, 0.1 mg/kg s.c.) and its counterparts R-8-OH-DPAT (0.05, 0.1 mg/kg s.c.) and S-8-OH-DPAT (0.05, 0.1 mg/kg s.c.) to influence 5-HT synthesis rate in rats' prefrontal cortex, hypothalamus, hippocampus and brainstem was evaluated by HPLC/ED technique. Biochemical results are supported by the exhaustive computational study of possible differences between R- and S-enantiomer toward the 5-HT1A receptor. A reliable 3D model of the rat 5-HT1A receptor was constructed from the amino acid sequence using the crystal structure of bovine rhodopsin as a structural template. The structure of the receptor model was validated through docking studies and molecular dynamics simulations that gave results consistent with experimental data. Docking studies and the dynamics of ligand-receptor complexes emphasized different profiles of both enantiomers at the molecular level. The results of both biochemical and computational studies confirmed that R-enantiomer in contrast to S-8-OH-DPAT acts as full and potent agonist, whilst racemic form may display similar pharmacological profile to R-8-OH-DPAT.