Department of Medicinal Chemistry, College of Pharmacy, Medical School, University of Minnesota, Minneapolis, MN 55455, USA.
Proc Natl Acad Sci U S A. 2011 Mar 22;108(12):5098-103. doi: 10.1073/pnas.1016277108. Epub 2011 Mar 8.
Numerous G protein-coupled receptors (GPCRs) have been shown to form heteromeric receptors in cell-based assays. Among the many heteromers reported in the opioid receptor family are μ/κ, κ/δ, and μ/δ. However, the in vivo physiological and behavioral relevance for the proposed heteromers have not yet been established. Here we report a unique example of a ligand, N-naphthoyl-β-naltrexamine (NNTA) that selectively activates heteromeric μ/κ-opioid receptors in HEK-293 cells and induces potent antinociception in mice. NNTA was an exceptionally potent agonist in cells expressing μ/κ-opioid receptors. Intriguingly, it was found to be a potent antagonist in cells expressing only μ-receptors. In the mouse tail-flick assay, intrathecal (i.t.) NNTA produced antinociception that was ~100-fold greater than by intracerebroventricular (i.c.v.) administration. The κ-antagonist, norBNI, decreased the i.t. potency, and the activity was virtually abolished in μ-opioid receptor knockout mice. No tolerance was induced i.t., but marginal tolerance (3-fold) was observed via the i.c.v. route. Moreover, NNTA produced neither significant physical dependence nor place preference in the ED50 dose range. Taken together, this work provides an important pharmacologic tool for investigating the in vivo functional relevance of heteromeric μ/κ-opioid receptors and suggests an approach to potent analgesics with fewer deleterious side effects.
大量 G 蛋白偶联受体 (GPCR) 在基于细胞的测定中已被证明能形成异源二聚体受体。在阿片受体家族中报告的许多异源二聚体中，有 μ/κ、κ/δ 和 μ/δ。然而，所提出的异源二聚体在体内的生理和行为相关性尚未确定。在这里，我们报告了一个独特的配体的例子，N-萘酰基-β-纳曲胺 (NNTA)，它在 HEK-293 细胞中选择性地激活μ/κ-阿片受体，并在小鼠中诱导强烈的镇痛作用。NNTA 在表达μ/κ-阿片受体的细胞中是一种非常有效的激动剂。有趣的是，它被发现是仅表达μ受体的细胞中的一种有效拮抗剂。在小鼠尾巴闪烁试验中，鞘内 (i.t.) NNTA 产生的镇痛作用比脑室内 (i.c.v.) 给药强约 100 倍。κ 拮抗剂 norBNI 降低了 i.t. 的效力，而在 μ-阿片受体敲除小鼠中，活性几乎被消除。鞘内给药不会引起耐受，但通过脑室内途径观察到轻微的耐受 (3 倍)。此外，NNTA 在 ED50 剂量范围内既没有引起明显的身体依赖，也没有引起位置偏好。总之，这项工作为研究异源二聚体 μ/κ-阿片受体的体内功能相关性提供了一个重要的药理工具，并提出了一种产生较少有害副作用的强效镇痛药的方法。
