Effects of the novel selective κ-opioid receptor agonist NP-5497-KA on morphine-induced reward-related behaviors.

Opioid addiction and the opioid overdose epidemic are becoming more serious, and the development of therapeutic agents is essential for the pharmacological treatment of substance use disorders. The κ-opioid receptor (KOP) is a member of the opioid receptor system that has been gaining attention as a promising molecular target for the treatment of numerous human disorders, including pain, depression, anxiety, and drug addiction. Here, we biologically and pharmacologically evaluated a novel azepane-derived ligand, NP-5497-KA, as a selective KOP agonist. NP-5497-KA had 1000-fold higher selectivity for the KOP over the µ-opioid receptor (MOP), which was higher than nalfurafine (KOP/MOP: 65-fold), and acted as a selective KOP full agonist in the 3',5'-cyclic adenosine monophosphate assay. The oral administration of NP-5497-KA (1-10 mg/kg) dose-dependently suppressed morphine-induced conditioned place preference in C57BL/6 J mice, and its effects were comparable to an intraperitoneal injection of nalfurafine (1-10 µg/kg). Nalfurafine (10 µg/kg) significantly inhibited rotarod performance, whereas NP-5497-KA (10 mg/kg) exerted no effect on rotarod performance. These results indicate that NP-5497-KA may be a novel option for the treatment of opioid use disorder with fewer side effects.