Abstract：
BACKGROUND: Novel synthetic opioids (NSOs) are emerging in recreational drug markets worldwide. In particular, 2-benzylbenzimidazole \'nitazene\' compounds are problematic NSOs associated with serious clinical consequences, including fatal respiratory depression. Evidence from in vitro studies shows that alkoxy chain length can influence the potency of nitazenes at the mu-opioid receptor (MOR). However, structure-activity relationships (SARs) of nitazenes for inducing opioid-like effects in animal models are not well understood compared to relevant opioids contributing to the ongoing opioid crisis (e.g., fentanyl).
OBJECTIVE: Here, we examined the in vitro and in vivo effects of nitazene analogues with varying alkoxy chain lengths (i.e., metonitazene, etonitazene, isotonitazene, protonitazene, and butonitazene) as compared to reference opioids (i.e., morphine and fentanyl).
RESULTS: Nitazene analogues displayed nanomolar affinities for MOR in rat brain membranes and picomolar potencies to activate MOR in transfected cells. All compounds induced opioid-like effects on locomotor activity, hot plate latency, and body temperature in male mice, and alkoxy chain length markedly influenced potency. Etonitazene, with an ethoxy chain, was the most potent analogue in MOR functional assays (EC50 = 30 pM, Emax = 103%) and across all in vivo endpoints (ED50 = 3-12 μg/kg). In vivo SARs revealed that ethoxy, isopropoxy, and propoxy chains engendered higher potencies than fentanyl, whereas methoxy and butoxy analogues were less potent. MOR functional potencies, but not MOR affinities, were positively correlated with in vivo potencies to induce opioid effects.
CONCLUSIONS: Overall, our data show that certain nitazene NSOs are more potent than fentanyl as MOR agonists in mice, highlighting concerns regarding the high potential for overdose in humans who are exposed to these compounds.
OBJECTIVE: Here, we examined the in vitro and in vivo effects of nitazene analogues with varying alkoxy chain lengths (i.e., metonitazene, etonitazene, isotonitazene, protonitazene, and butonitazene) as compared to reference opioids (i.e., morphine and fentanyl).
RESULTS: Nitazene analogues displayed nanomolar affinities for MOR in rat brain membranes and picomolar potencies to activate MOR in transfected cells. All compounds induced opioid-like effects on locomotor activity, hot plate latency, and body temperature in male mice, and alkoxy chain length markedly influenced potency. Etonitazene, with an ethoxy chain, was the most potent analogue in MOR functional assays (EC50 = 30 pM, Emax = 103%) and across all in vivo endpoints (ED50 = 3-12 μg/kg). In vivo SARs revealed that ethoxy, isopropoxy, and propoxy chains engendered higher potencies than fentanyl, whereas methoxy and butoxy analogues were less potent. MOR functional potencies, but not MOR affinities, were positively correlated with in vivo potencies to induce opioid effects.
CONCLUSIONS: Overall, our data show that certain nitazene NSOs are more potent than fentanyl as MOR agonists in mice, highlighting concerns regarding the high potential for overdose in humans who are exposed to these compounds.
摘要：
背景：新型合成阿片类药物（NSOs）正在全球休闲药物市场中出现。特别是,2-苄基苯并咪唑''硝基苯'化合物是与严重临床后果相关的有问题的NSO，包括致命的呼吸抑制.来自体外研究的证据表明，烷氧基链长度可以影响硝基苯在μ阿片受体（MOR）上的效力。然而,与导致持续阿片类药物危机的相关阿片类药物相比，在动物模型中诱导阿片类药物样作用的硝唑烯的结构-活性关系（SARs）尚未得到很好的理解（例如，芬太尼）。
目标：这里，我们检查了具有不同烷氧基链长度的硝唑烯类似物的体外和体内作用(即，甲硝唑,依托氮嗪,异硝基苯,质子三氮烯,和butonitazene)与参考阿片类药物(即，吗啡和芬太尼）。
结果：硝唑烯类似物在大鼠脑膜中显示出对MOR的纳摩尔亲和力和在转染细胞中激活MOR的皮摩尔效力。所有化合物都会对运动活动产生类阿片样作用，热板延迟，和雄性小鼠的体温，和烷氧基链长度显着影响效力。Etonitazene,带有乙氧基链，是MOR功能测定中最有效的类似物(EC50=30pM，Emax=103%）和所有体内终点（ED50=3-12μg/kg）。体内SAR揭示了乙氧基，异丙氧基,丙氧基链产生比芬太尼更高的效力，而甲氧基和丁氧基类似物效力较低。MOR功能效力，但不是MOR亲和力，与体内诱导阿片类药物作用的效力呈正相关。
结论：总体而言，我们的数据显示，某些硝基苯NSO作为小鼠MOR激动剂比芬太尼更有效，强调了对暴露于这些化合物的人类服用过量的高可能性的担忧。
目标：这里，我们检查了具有不同烷氧基链长度的硝唑烯类似物的体外和体内作用(即，甲硝唑,依托氮嗪,异硝基苯,质子三氮烯,和butonitazene)与参考阿片类药物(即，吗啡和芬太尼）。
结果：硝唑烯类似物在大鼠脑膜中显示出对MOR的纳摩尔亲和力和在转染细胞中激活MOR的皮摩尔效力。所有化合物都会对运动活动产生类阿片样作用，热板延迟，和雄性小鼠的体温，和烷氧基链长度显着影响效力。Etonitazene,带有乙氧基链，是MOR功能测定中最有效的类似物(EC50=30pM，Emax=103%）和所有体内终点（ED50=3-12μg/kg）。体内SAR揭示了乙氧基，异丙氧基,丙氧基链产生比芬太尼更高的效力，而甲氧基和丁氧基类似物效力较低。MOR功能效力，但不是MOR亲和力，与体内诱导阿片类药物作用的效力呈正相关。
结论：总体而言，我们的数据显示，某些硝基苯NSO作为小鼠MOR激动剂比芬太尼更有效，强调了对暴露于这些化合物的人类服用过量的高可能性的担忧。
