PubMed · 14334175
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J H HUTTON. 1965. THE OVERWEIGHT PROBLEM.. https://pubmed.ncbi.nlm.nih.gov/14334175/
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Beginning with the passage of the Federal Food, Drug, and Cosmetic Act in 1938 and escalating with the 1962 Kefauver-Harris amendments, increasing pressure has been placed on pharmaceutical manufacturers to demonstrate that a drug's benefits outweigh its risks. Nowhere has the question of risk versus benefit come under greater scrutiny than with anorectics. After the approval in the 1940s and 1950s of a number of amphetamine and amphetamine-like compounds for the treatment of obesity, the U.S. Food and Drug Administration struggled to define the efficacy and safety of these agents. Labeling restrictions on duration of use and warnings about abuse and addiction ultimately contributed to the reduced use of anorectics. That trend continued until the mid-1990s, when the off-label use of fenfluramine plus phentermine (fen-phen) and the approval of dexfenfluramine gave rise to widespread, long-term use of anorectics to treat obesity. The adverse effects that came to be associated with fenfluramine and dexfenfluramine, leading to their eventual withdrawal from the market, gave pause to regulators, physicians, patients, and drug companies alike. Sibutramine, the latest anorectic to enter the market, is now the focus of a landmark trial that is examining, for the first time, whether drug-induced weight loss reduces the risk for fatal and nonfatal cardiovascular disease.
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-HT(2C) receptor activation; it causes cardiopulmonary side effects through 5-HT(2B) receptor activation. Thus, we attempted to identify molecular determinants of SNF binding to 5-HT(2B) receptors distinct from those underlying SNF-5-HT(2C/2A) receptor interactions. Mutagenesis implicated Val2.53 in SNF binding to 5-HT(2B) receptors. Ligand docking simulations suggested both Val2.53 gamma-methyl groups form stabilizing van der Waals' (vdW) interactions with the alpha-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-alpha-methyl group vdW interaction. Supporting this, 1) the binding of norfenfluramine (NF) analogs lacking an S-(+) alpha-methyl group (RNF and alpha-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 alpha-desmethyl-NF affinities only 16- and 45-fold, respectively. We next addressed whether the alpha-methyl group of SNF contributes to 5-HT(2C/2A) receptor affinity. Removal of the alpha-methyl group (RNF and alpha-desmethyl-NF), which reduced 5-HT(2B) receptor binding 3-fold, did not affect 5-HT(2C/2A) receptor binding. An alpha-ethyl substituent (alpha-ethyl-NF), which decreased 5-HT(2B) receptor affinity 46-fold, reduced 5-HT(2C) and 5-HT(2A) receptor binding by 14- and 5-fold, respectively. Finally, we determined that residue 2.53 affects SNF potency and efficacy at 5-HT(2B) receptors but not at 5-HT(2C) and 5-HT(2A) receptors. In conclusion, vdW interactions between residue 2.53 and the alpha-methyl group of SNF contribute to the ligand's 5-HT(2) receptor subtype-selective pharmacology.
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