A novel peptide‐fentanyl conjugate with μ‐opioid and neuropeptide FF receptor agonism produces antinociception with limited side effects in male mice

Background and Purpose The opioid crisis caused by the proliferation of fentanyl‐related drugs has intensified concerns about the utilisation of opioid analgesics. Herein, a novel peptide‐drug conjugate FENPFF01, incorporating the neuropeptide FF (NPFF) and fentanyl pharmacophores, was synthesised and pharmacologically characterised. Experimental Approach The agonist activities of FENPFF01 at opioid and NPFF receptors were characterised in in vitro functional assays. Antinociceptive effects and underlying pharmacological mechanisms of FENPFF01 were assessed in multiple mouse pain models. The side effects of FENPFF01 were further investigated through antinociceptive tolerance, respiratory function, addiction potential and gastrointestinal transit tests. Key Results FENPFF01 functioned as a mixed partial agonist at the μ‐opioid and NPFF 2 receptors, and a full agonist at NPFF 1 receptor. Subcutaneous FENPFF01 produced potent antinociception in acute, inflammatory and post‐operative pain, which was mediated by the μ receptor. The in vivo pharmacological and pharmacokinetic data demonstrated that FENPFF01 could penetrate the blood–brain barrier (BBB) and activate the μ receptor in the brain to elicit antinociception. Importantly, chronic administration of FENPFF01 did not induce antinociceptive tolerance or observable effects on spinal microglial activation, which may be partly attributable to the activation of the NPFF 2 receptor. FENPFF01 also did not affect arterial gas parameters, respiratory rate, locomotor activity, conditioned place preference response, physical dependence and gastrointestinal transit. Conclusions and Implications The newly developed peptide‐drug conjugate FENPFF01 exhibited strong antinociception with reduced opioid‐like side effects. It represents an interesting candidate for developing novel analgesics with multi‐targeted agonist properties, aiming to address the widespread issues associated with opioid misuse.