Molecular Determinants for the Interaction of the Valvulopathic Anorexigen Norfenfluramine with the 5-HT<sub>2B</sub> Receptor
作者:Vincent Setola、Malgorzata Dukat、Richard A. Glennon、Bryan L. Roth
DOI:10.1124/mol.104.009266
日期:2005.7
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.
S -(+)-诺芬氟拉明(SNF)是现已被禁用的厌食素芬氟拉明的一种活性代谢物,它与该药物抑制食欲的作用及其危及生命的心血管副作用有关。SNF通过激活5-羟色胺5-HT2C受体降低食欲;通过激活5-HT2B受体导致心肺副作用。因此,我们试图找出 SNF 与 5-HT2B 受体结合的分子决定因素,这些因素与 SNF-5-HT2C/2A 受体相互作用的分子决定因素不同。突变研究表明,Val2.53 与 SNF 与 5-HT2B 受体的结合有关。配体对接模拟表明,Val2.53的两个γ-甲基与SNF的α-甲基形成稳定的范德华(vdW)相互作用。V2.53L 突变导致亲和力下降 17 倍;分子动力学(MD)模拟表明,亲和力下降是由于失去了一个 2.53-α- 甲基 vdW 相互作用。与此相印证的是:1)缺乏 S -(+) α-甲基的诺芬氟拉明(NF)类似物(RNF 和 α-去甲基-NF)的结合对 V2.53L 突变不那么敏感;2)V2.53A 突变使 SNF 亲和力下降了 190 倍,但 RNF 和 α-去甲基-NF 的亲和力分别只下降了 16 倍和 45 倍。我们接下来研究了 SNF 的 α-甲基是否对 5-HT2C/2A 受体亲和力有影响。去除α-甲基(RNF 和 α-去甲基-NF)会使 5-HT2B 受体的结合力降低 3 倍,但不会影响 5-HT2C/2A 受体的结合力。α-乙基取代基(α-乙基-NF)会使 5-HT2B 受体的亲和力降低 46 倍,但会使 5-HT2C 和 5-HT2A 受体的结合力分别降低 14 倍和 5 倍。最后,我们确定残基 2.53 会影响 SNF 在 5-HT2B 受体上的效力和功效,但不会影响 SNF 在 5-HT2C 和 5-HT2A 受体上的效力和功效。总之,SNF 的残基 2.53 和 α-甲基之间的 vdW 相互作用促成了配体的 5-HT2 受体亚型选择性药理作用。