The multifunctional peptide DN-9 produced peripherally acting antinociception in inflammatory and neuropathic pain via mu and kappa opioid receptors.

Considerable effort has recently been directed at developing multifunctional opioid drugs to minimize the unwanted side-effects of opioid analgesics. We developed a novel multifunctional agonist named DN-9. Here, we studied the analgesic profiles and related side-effects of peripheral DN-9 in various pain models.Antinociceptive effects of DN-9 were investigated in nociceptive, inflammatory and neuropathic pain. Whole-cell patch-clamp and calcium imaging assays were used to evaluate the inhibitory effects of DN-9 to calcium current and high-K -induced intracellular calcium ([Ca ] ) on dorsal root ganglion (DRG) neurons, respectively. Furthermore, the side-effects of DN-9 were evaluated in antinociceptive tolerance, abuse, gastrointestinal transit and rotarod tests.Our study showed that subcutaneous DN-9 dose-dependently produced antinociception via peripheral opioid receptors in different pain models without sex difference. In addition, DN-9 exhibited more potent ability than morphine to inhibit calcium current and high-K -induced [Ca ] in DRG neurons. Repeated treatment with DN-9 produced equivalent antinociception for 8 days in multiple pain models, and DN-9 also maintained potent analgesia in morphine-tolerant mice. Furthermore, chronic DN-9 administration had no apparent effect on the microglial activation of spinal cord. DN-9 exhibited less abuse potential compared with morphine after subcutaneous injection, as was gastroparesis and effects on motor coordination.DN-9 produces potent analgesia with minimal side-effects, which strengthen the candidacy of peripherally acting opioids with multifunctional agonistic properties to enter human studies to alleviate the current highly problematic mis-use of classic opioid on a large scale.