The Therapeutic Potential of Dual NMR (NOP/MOP) Agonism in Pain Management

Addressing pain effectively remains a major global challenge for healthcare systems and public health initiatives. While this issue is pervasive worldwide, it is particularly pressing in the United States, where pain management using opioid analgesics has led to significant concerns due to widespread misuse, drug dependence, and overdose fatalities. A central dilemma for clinicians in pain management lies in balancing the delivery of sufficient pain relief while minimizing potential risks. Although preferential μ-opioid receptor (MOP) agonists, such as morphine and oxycodone, often remain a necessary therapeutic choice, particularly for individuals experiencing moderate to severe pain, their safety profiles present a clinical dilemma, as there are limited other options available to clinicians. A promising area of research focus is on the development of dual NOP/MOP receptor (NMR) agonists , compounds that co-activate the nociceptin/orphanin FQ (NOP) receptor and the MOP receptor. Despite sharing some structural homology with opioid receptors, the NOP receptor exhibits a distinct pharmacological profile. Activating the NOP receptor induces pain relief and, more importantly, counteracts important adverse effects associated with MOP activation including reduction in euphoria by inhibiting opioid-induced activation of dopaminergic neuron activity in the ventral tegmental area (VTA), which in turn reduces the likelihood of misuse. Preclinical data have shown a potential role of NOP activation in reducing the occurrence of opioid withdrawal symptoms and, perhaps most importantly, respiratory depression. Investigations in nonhuman primates support the NOP receptor's modulatory role, demonstrating that NOP agonism not only produced analgesia across various pain models (nociceptive, neuropathic, and inflammatory) but also lessened MOP-related negative outcomes, such as opioid reward-seeking behavior, the development of tolerance, and withdrawal symptoms. Preclinical studies using dual NMR agonists showed that administration of a NOP antagonist increased the side effects similar to those caused by a preferential MOP agonist, underscoring the role of NOP receptor activation in counteracting these adverse events. Altogether these findings suggest that dual NMR (NOP/MOP receptor) agonists represent a promising novel class of medications with the potential to achieve strong analgesia while lessening the side effects of opioid agonists.