Department of Pharmacology and Therapeutics (H.X., K.W.A., F.S., A.R., S.C.J., Z.L., Y.-H.C., S.H., P.C., W.R.K.) and AMRIS, McKnight Brain Institute (J.R.R.), College of Medicine, University of Florida, Gainesville, Florida; National Center for Toxicological Research, US Food and Drug Administration, Jefferson, Arkansas (S.S.); Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania (J.M.L.); and Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (R.J.L.).
Department of Pharmacology and Therapeutics (H.X., K.W.A., F.S., A.R., S.C.J., Z.L., Y.-H.C., S.H., P.C., W.R.K.) and AMRIS, McKnight Brain Institute (J.R.R.), College of Medicine, University of Florida, Gainesville, Florida; National Center for Toxicological Research, US Food and Drug Administration, Jefferson, Arkansas (S.S.); Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania (J.M.L.); and Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (R.J.L.)
Mol Pharmacol. 2020 Aug;98(2):168-180. doi: 10.1124/mol.119.118786. Epub 2020 May 30.
The two major nicotinic acetylcholine receptors (nAChRs) in the brain are the 42 and 7 subtypes. A "methyl scan" of the pyrrolidinium ring was used to detect differences in nicotine's interactions with these two receptors. Each methylnicotine was investigated using voltage-clamp and radioligand binding techniques. Methylation at each ring carbon elicited unique changes in nicotine's receptor interactions. Replacing the 1'--methyl with an ethyl group or adding a second 1'--methyl group significantly reduced interaction with 42 but not 7 receptors. The 2'-methylation uniquely enhanced binding and agonist potency at 7 receptors. Although 3'- and 5'--methylations were much better tolerated by 7 receptors than 42 receptors, 4'-methylation decreased potency and efficacy at 7 receptors much more than at 42 receptors. Whereas -5'-methylnicotine lacked agonist activity and displayed a low affinity at both receptors, -5'-methylnicotine retained considerable 7 receptor activity. Differences between the two 5'-methylated analogs of the potent pyridyl oxymethylene-bridged nicotine analog A84543 were consistent with what was found for the 5'-methylnicotines. Computer docking of the methylnicotines to the acetylcholine binding protein crystal structure containing two persistent waters predicted most of the changes in receptor affinity that were observed with methylation, particularly the lower affinities of the -methylnicotines. The much smaller effects of 1'-, 3'-, and 5'-methylations and the greater effects of 2'- and 4'-methylations on nicotine 7 nAChR interaction might be exploited for the design of new drugs based on the nicotine scaffold. SIGNIFICANCE STATEMENT: Using a comprehensive "methyl scan" approach, we show that the orthosteric binding sites for acetylcholine and nicotine in the two major brain nicotinic acetylcholine receptors interact differently with the pyrrolidinium ring of nicotine, and we suggest reasons for the higher affinity of nicotine for the heteromeric receptor. Potential sites for nicotine structure modification were identified that may be useful in the design of new drugs targeting these receptors.
脑内两种主要的烟碱型乙酰胆碱受体（nAChR）是 42 和 7 亚型。采用“吡咯烷鎓环的甲基扫描”方法来检测尼古丁与这两种受体相互作用的差异。使用电压钳和放射性配体结合技术研究了每种甲基烟碱。环上每个碳原子的甲基化引起尼古丁与受体相互作用的独特变化。用乙基取代 1'-位甲基或在 1'-位添加第二个甲基基团，会显著降低与 42 受体的相互作用，但不影响 7 受体。2'-位甲基化可独特增强与 7 受体的结合和激动剂效力。虽然 3'-和 5'-位甲基化比 42 受体更能耐受 7 受体，但 4'-位甲基化对 7 受体的效力和效能的降低比 42 受体更为显著。尽管-5'-位甲基烟碱在两种受体上缺乏激动活性且显示低亲和力，但它在 7 受体上仍保留相当的活性。强效吡啶氧基亚甲基桥接尼古丁类似物 A84543 的两种 5'-甲基化类似物之间的差异与 5'-甲基烟碱的发现一致。将甲基烟碱对接至包含两个持久水的乙酰胆碱结合蛋白晶体结构的计算机预测，预测了大多数与甲基化相关的受体亲和力变化，特别是-甲基烟碱的低亲和力。1'-、3'-和 5'-位甲基化的影响较小，而 2'-和 4'-位甲基化对尼古丁 7 nAChR 相互作用的影响较大，这可能会被利用来设计基于尼古丁骨架的新型药物。意义：我们采用全面的“甲基扫描”方法，证明了两种主要脑烟碱型乙酰胆碱受体中乙酰胆碱和尼古丁的正位结合位点与尼古丁吡咯烷鎓环的相互作用不同，并提出了尼古丁对异源受体亲和力更高的原因。鉴定出尼古丁结构修饰的潜在部位，这可能有助于设计针对这些受体的新型药物。
