Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, Intramural Research Program, National Institutes of Health, 35 Convent Drive, MSC-3723, Bethesda, Maryland 20892-3723, United States.
Medicinal Chemistry Section, Molecular Targets and Medication Discovery Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, 333 Cassell Drive, Baltimore, Maryland 21224, United States.
ACS Chem Neurosci. 2020 Oct 21;11(20):3309-3320. doi: 10.1021/acschemneuro.0c00425. Epub 2020 Oct 5.
The D3 dopamine receptor (D3R) has been suggested as a drug target for the treatment of a number of neuropsychiatric disorders, including substance use disorders (SUD). Many D3R-selective antagonists are bivalent in nature in that they engage two distinct sites on the receptor-a primary pharmacophore binds to the orthosteric site, where dopamine binds, whereas a secondary pharmacophore interacts with a unique secondary binding pocket (SBP). When engagement of the secondary pocket exerts allosteric activity, the compound is said to be bitopic. We recently reported the synthesis and characterization of two bitopic antagonists of the D3R, (±)-VK04-87 and (±)-VK05-95, which incorporated a racemic -cyclopropylmethyl linking chain. To gain a better understanding of the role of chirality in determining the pharmacology of such compounds, we resolved the enantiomers of (±)-VK04-87. We found that the (+)-isomer displays higher affinity for the D3R and exhibits greater selectivity versus the D2R than the (-)-isomer. Strikingly, using functional assays, we found that (+)-VK04-87 inhibits the D3R in a noncompetitive manner, while (-)-VK04-87 behaves as a purely competitive antagonist, indicating that the apparent allosteric activity of the racemate is due to the (+)-isomer. Molecular dynamic simulations of (+)-VK04-87 and (-)-VK04-87 binding to the D3R suggest that the (+)-isomer is able to interact with the SBP of the receptor whereas the (-)-isomer bends away from this pocket, thus potentially explaining their differing pharmacology. These results emphasize the importance of the linker, and its isomeric conformations, within extended-length molecules for their positioning and engagement within GPCR binding pockets.
D3 多巴胺受体 (D3R) 被认为是治疗多种神经精神疾病的药物靶点，包括物质使用障碍 (SUD)。许多 D3R 选择性拮抗剂在性质上是双价的，因为它们与受体上的两个不同位点结合 - 主要药效基团与多巴胺结合的正构位点结合，而次要药效基团与独特的次级结合口袋 (SBP) 相互作用。当结合次级口袋发挥变构活性时，该化合物被称为双位点。我们最近报道了两种 D3R 双位点拮抗剂 (+)-VK04-87 和 (+)-VK05-95 的合成和表征，它们包含一个外消旋 -环丙基甲基连接链。为了更好地了解手性在确定此类化合物药理学中的作用，我们拆分了 (+)-VK04-87 的对映异构体。我们发现 (+)-异构体对 D3R 的亲和力更高，与 D2R 的选择性比 (-)-异构体更高。引人注目的是，使用功能测定，我们发现 (+)-VK04-87 以非竞争性方式抑制 D3R，而 (-)-VK04-87 表现为纯竞争性拮抗剂，表明外消旋体的表观变构活性是由于 (+)-异构体。(+)-VK04-87 和 (-)-VK04-87 与 D3R 结合的分子动力学模拟表明，(+)-异构体能够与受体的 SBP 相互作用，而 (-)-异构体则从该口袋弯曲，从而可能解释它们不同的药理学。这些结果强调了在扩展长度分子中连接子及其异构体构象的重要性，它们在 GPCR 结合口袋中的定位和结合。
