Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.
RTI International, Research Triangle Park, North Carolina, USA.
Pharmacol Res Perspect. 2022 Feb;10(1):e00901. doi: 10.1002/prp2.901.
Neutral antagonists of GPCRs remain relatively rare-indeed, a large majority of GPCR antagonists are actually inverse agonists. The synthetic cannabinoid receptor agonist (SCRA) EG-018 was recently reported as a low efficacy cannabinoid receptor agonist. Here we report a comparative characterization of EG-018 and 13 analogues along with extant putative neutral antagonists of CB . In HEK cells stably expressing human CB , assays for inhibition of cAMP were performed by real-time BRET biosensor (CAMYEL), G protein cycling was quantified by [ S]GTPγS binding, and stimulation of pERK was characterized by AlphaLISA (PerkinElmer). Signaling outcomes for the EG-018 analogues were highly variable, ranging from moderate efficacy agonism with high potency, to marginal agonism at lower potency. As predicted by differing pathway sensitivities to differences in ligand efficacy, most EG-018-based compounds were completely inactive in pERK alone. The lowest efficacy analogue in cAMP assays, 157, had utility in antagonism assay paradigms. Developing neutral antagonists of the CB receptor has been a long-standing research goal, and such compounds would have utility both as research tools and in therapeutics. Although these results emphasize again the importance of system factors in determining signaling outcomes, some compounds characterized in this study appear among the lowest efficacy agonists described to date and therefore suggest that development of neutral antagonists is an achievable goal for CB .
G 蛋白偶联受体的中性拮抗剂仍然相对较少——事实上，大多数 G 蛋白偶联受体拮抗剂实际上都是反向激动剂。合成大麻素受体激动剂（SCRA）EG-018 最近被报道为一种低效能大麻素受体激动剂。在这里，我们报告了对 EG-018 及其 13 种类似物以及现有的潜在中性 CB 拮抗剂的比较特征。在稳定表达人 CB 的 HEK 细胞中，通过实时 BRET 生物传感器（CAMYEL）进行抑制 cAMP 的测定，通过 [ S]GTPγS 结合来量化 G 蛋白循环，通过 AlphaLISA（PerkinElmer）来描述 pERK 的刺激。EG-018 类似物的信号转导结果高度可变，从具有高效力的中等效能激动作用，到较低效力的边缘激动作用。正如不同配体效力差异对不同途径的敏感性所预测的那样，大多数基于 EG-018 的化合物在单独的 pERK 中完全没有活性。在 cAMP 测定中效力最低的类似物 157，在拮抗测定方案中具有实用性。开发 CB 受体的中性拮抗剂一直是一个长期的研究目标，此类化合物将作为研究工具和治疗药物都具有实用性。尽管这些结果再次强调了系统因素在确定信号转导结果方面的重要性，但本研究中描述的一些化合物似乎是迄今为止描述的最低效能激动剂之一，因此表明开发中性拮抗剂是 CB 的一个可实现的目标。
