A Cyclic Tetrapeptide ("Cyclodal") and Its Mirror-Image Isomer Are Both High-Affinity μ Opioid Receptor Antagonists.

ABSTRACT: Head-to-tail cyclization of the μ opioid receptor (MOR) agonist [Dmt¹]DALDA (H-Dmt-d-Arg-Phe-Lys-NH₂ (9; Dmt = 2',6'-dimethyltyrosine) resulted in a highly active, selective MOR antagonist, c[-d-Arg-Phe-Lys-Dmt-] (1) ("cyclodal"), with subnanomolar binding affinity. A docking study of cyclodal using the crystal structure of MOR in the inactive form showed a unique binding mode with the two basic residues of the ligand forming salt bridges with the Asp¹²⁷ and Glu²²⁹ receptor residues. Cyclodal showed high plasma stability and was able to cross the blood-brain barrier to reverse morphine-induced, centrally mediated analgesia when given intravenously. Surprisingly, the mirror-image isomer (optical antipode) of cyclodal, c[-Arg-d-Phe-d-Lys-d-Dmt-] (2

SUBMITTER: Weltrowska G 

PROVIDER: S-EPMC5222732 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature