PT  - JOURNAL ARTICLE
AU  - Setola, Vincent
AU  - Dukat, Malgorzata
AU  - Glennon, Richard A.
AU  - Roth, Bryan L.
TI  - Molecular Determinants for the Interaction of the Valvulopathic Anorexigen Norfenfluramine with the 5-HT<sub>2B</sub> Receptor
AID  - 10.1124/mol.104.009266
DP  - 2005 Jul 01
TA  - Molecular Pharmacology
PG  - 20--33
VI  - 68
IP  - 1
4099  - http://molpharm.aspetjournals.org/content/68/1/20.short
4100  - http://molpharm.aspetjournals.org/content/68/1/20.full
SO  - Mol Pharmacol2005 Jul 01; 68
AB  - S-(+)-Norfenfluramine (SNF)—an active metabolite of the now-banned anorexigen fenfluramine—has been implicated in the drug's appetite-suppressing actions and its life-threatening cardiovascular side effects. SNF reduces appetite through serotonin 5-HT2C receptor activation; it causes cardiopulmonary side effects through 5-HT2B receptor activation. Thus, we attempted to identify molecular determinants of SNF binding to 5-HT2B receptors distinct from those underlying SNF-5-HT2C/2A receptor interactions. Mutagenesis implicated Val2.53 in SNF binding to 5-HT2B receptors. Ligand docking simulations suggested both Val2.53 γ-methyl groups form stabilizing van der Waals' (vdW) interactions with the α-methyl group of SNF. A V2.53L mutation induced a 17-fold decrease in affinity; molecular dynamics (MD) simulations suggested that this decrease resulted from the loss of one 2.53-α-methyl group vdW interaction. Supporting this, 1) the binding of norfenfluramine (NF) analogs lacking an S-(+) α-methyl group (RNF and α-desmethyl-NF) was less sensitive to the V2.53L mutation, and 2) a V2.53A mutation decreased SNF affinity 190-fold, but decreased RNF and α-desmethyl-NF affinities only 16- and 45-fold, respectively. We next addressed whether the α-methyl group of SNF contributes to 5-HT2C/2A receptor affinity. Removal of the α-methyl group (RNF and α-desmethyl-NF), which reduced 5-HT2B receptor binding 3-fold, did not affect 5-HT2C/2A receptor binding. An α-ethyl substituent (α-ethyl-NF), which decreased 5-HT2B receptor affinity 46-fold, reduced 5-HT2C and 5-HT2A receptor binding by 14- and 5-fold, respectively. Finally, we determined that residue 2.53 affects SNF potency and efficacy at 5-HT2B receptors but not at 5-HT2C and 5-HT2A receptors. In conclusion, vdW interactions between residue 2.53 and the α-methyl group of SNF contribute to the ligand's 5-HT2 receptor subtype-selective pharmacology.