van de Wetering Ross, Alder Amy F, Biggerstaff Andrew, Sellen Katya, Luo Dan, Crowley Rachel S, Prisinzano Thomas E, Kivell Bronwyn M
School of Biological Sciences, Centre for Biodiscovery, Victoria University of Wellington, Wellington, 6012, New Zealand.
Department of Pharmaceutical Sciences, University of Kentucky, Lexington, Kentucky, 40506, USA.
Neuropsychopharmacology. 2025 Sep 3. doi: 10.1038/s41386-025-02214-z.
The development of safer mu opioid receptor (MOR) agonists with reduced side effects is a key focus of pain research. Some studies have suggested that MOR agonists with reduced β-arrestin 2 (βArr2) signaling (i.e. G-protein biased agonists) may have greater therapeutic windows. However, there have been a several conflicting reports, and it is not clear what role, if any, βArr2 signaling plays in MOR-mediated analgesia, tolerance, or side effects. Therefore, we used βArr2 knockout mice to systematically investigate the causal role of βArr2 signaling in antinociception, antinociceptive tolerance, respiratory depression, constipation, and reward induced by morphine and the two novel MOR agonists, kurkinorin and kurkinol. Kurkinorin and kurkinol exhibited potent antinociceptive effects that were reversed by MOR knockout. Unlike morphine or kurkinorin, our most G-protein biased agonist, kurkinol, showed no significant tolerance after seven days of ~2×ED dosing. However, in a chemotherapy-induced neuropathic pain model, all three compounds were ineffective after 20 days of ~ED dosing, indicative of tolerance. All compounds exhibited significant MOR-dependent side effects, though kurkinorin had reduced gastrointestinal and respiratory depressive effects compared to morphine despite exhibiting less G-protein bias. Knockout of βArr2 significantly increased antinociceptive potency for morphine and kurkinorin but not kurkinol, and otherwise had no significant impact on tolerance or any side effect tested. These results largely suggest that βArr2 signaling does not drive MOR-mediated antinociceptive tolerance, respiratory depression, constipation, or reward and do not support the development of G-protein biased compounds as a broadly effective strategy to reduce side effects.
开发副作用更小的更安全的μ阿片受体（MOR）激动剂是疼痛研究的一个关键重点。一些研究表明，具有降低的β-抑制蛋白2（βArr2）信号传导的MOR激动剂（即G蛋白偏向激动剂）可能具有更大的治疗窗口。然而，有几份相互矛盾的报告，尚不清楚βArr2信号传导在MOR介导的镇痛、耐受性或副作用中是否起作用（如果有作用的话）。因此，我们使用βArr2基因敲除小鼠系统地研究βArr2信号传导在吗啡以及两种新型MOR激动剂kurkinorin和kurkinol诱导的抗伤害感受、抗伤害感受耐受性、呼吸抑制、便秘和奖赏中的因果作用。Kurkinorin和kurkinol表现出强效的抗伤害感受作用，这种作用可被MOR基因敲除逆转。与吗啡或kurkinorin不同，我们最具G蛋白偏向性的激动剂kurkinol在约2倍有效剂量给药7天后未显示出明显的耐受性。然而，在化疗诱导的神经性疼痛模型中，在约有效剂量给药20天后，所有三种化合物均无效，表明出现了耐受性。所有化合物均表现出明显的MOR依赖性副作用，尽管kurkinorin与吗啡相比，胃肠道和呼吸抑制作用有所降低，尽管其G蛋白偏向性较小。敲除βArr2显著提高了吗啡和kurkinorin的抗伤害感受效力，但对kurkinol没有影响，并且在其他方面对耐受性或所测试的任何副作用均无显著影响。这些结果在很大程度上表明，βArr2信号传导不会驱动MOR介导的抗伤害感受耐受性、呼吸抑制、便秘或奖赏，并且不支持将G蛋白偏向性化合物作为一种广泛有效的减少副作用的策略来开发。
