Molecular functions and applications of peptide agonists acting on mouse neuromedin U receptor 1

Neuromedin U (NMU), a neuropeptide, activates two types of NMU receptors (NMUR1 and NMUR2). The anti-obesity drug development focused on appetite suppression among physiological actions of NMU have been attempted worldwide; however, several reports have pointed out the possibility of tachyphylaxis induction by the repeated treatment of agonistic molecules, including our NMUR1 agonist CPN-267. Recently, NMUR1-mediated activation of type 2 inflammation has received considerable attention, although its tachyphylaxis induction has not yet been examined. In addition, through the acquisition of CPN-267, we were interested in the molecular functions affecting the in vitro efficacy (E_max) of mouse NMUR1. In this study, CPN-267-inspired derivatives of mouse NMU (mNMU) and palmitoylated analogs were designed and synthesized to reveal the structural factors modulating efficacy and evaluate the tachyphylaxis induction ability in mice. A calcium-mobilization assay using HEK293 cells transiently expressing receptors clarified that amino acid substitutions at positions 17-19 of mNMU to obtain NMUR1 selectivity led to a decrease in efficacy, and position 18 on palmitoylated analogs was the residue involving in the efficacy modulation. Using the most potent palmitoylated NMUR1 agonist 1, we confirmed that repeated subcutaneous injection for 3 consecutive days in mice rapidly induced tachyphylaxis of the appetite-suppressive effect. Moreover, we successfully demonstrated that the marked elevation in serum IL-5 levels by a single injection of peptide 1 was abolished by a similar repeated treatment, proposing that palmitoylated analogs acting on NMUR1 have the potential to develop as a suppressive agent against type 2 inflammation in future.