Possible mechanism for improving the endogenous immune system through the blockade of peripheral μ-opioid receptors by treatment with naldemedine.

Background: It has been considered that activation of peripheral μ-opioid receptors (MORs) induces side effects of opioids. In this study, we investigated the possible improvement of the immune system in tumour-bearing mice by systemic administration of the peripheral MOR antagonist naldemedine.

Methods: The inhibitory effect of naldemedine on MOR-mediated signalling was tested by cAMP inhibition and β-arrestin recruitment assays using cultured cells.