The Meta-Position of Phe⁴ in Leu-enkephalin Regulates Potency, Selectivity, Functional Activity, and Signaling Bias at the Delta and Mu Opioid Receptors

Abstract

Activation of an opioid receptor can trigger two distinct pathways (G protein coupling and arrestin recruitment) that differentially regulate a host of desired and undesired pharmacological effects. To explore the pharmacology of these pathways and to differentiate desired pharmacological effects from undesired side effects, "biased" ligands, those that selectively activate one pathway over the other, serve as useful tool compounds. Though an extensive array of biased ligands have been developed for exploring µ-opioid receptor pharmacology, few studies have explored biased ligands for the δ-opioid receptor, which is not associated with the detrimental side effects mediated by the µ-opioid receptor.Herein, we explore the Phe 4 position of the endogenous δ-opioid receptor ligand, Leuenkephalin (Tyr-Gly-Gly-Phe-Leu). Substitution of the meta-position of Phe 4 of Leu-enkephalin provides high-affinity ligands with varying levels of selectivity and bias at both the δ-opioid receptor and µ-opioid receptor, while substitution with picoline derivatives produced loweraffinity ligands with good biases at both receptors. Further, Phe 4 substitution also improves peptide stability relative to Leu-enkephalin. Overall, these favorable substitutions to the metaposition of Phe 4 might be combined with other modifications to Leu-enkephalin to deliver improved ligands with finely tuned potency, selectivity, bias and drug-like properties.

Engineering Quick- and Long-acting Naloxone Delivery Systems for Treating Opioid Overdose

“…The naloxone released from microparticles in this study could inhibit β-arrestin 2 recruitment induced by DAMGO, a μ-opioid receptor agonist. Thus, it is expected to prevent a signaling cascade potentially involved in opioidmediated respiratory depression (25,50). The cellular pharmacodynamics assay data support the therapeutic relevance of the prepared naloxone microparticles.…”

“…6-a). βarrestin 2 is critical for developing tolerance to opioids (25). Naloxone by itself does not recruit β-arrestin 2, but inhibits 1 μM (EC 80 ) DAMGO-induced β-arrestin 2 recruitment (pIC 50 = 8.8 ± 0.3, n = 7, Fig.…”

“…All cell lines were maintained in T75 flasks at 37°C and 5% CO 2 . βarrestin recruitment assays were performed using CHO-K1human μ-opioid receptor PathHunter β-arrestin 2 cells (DiscoverX) (25). Controls and samples were run at a minimum as biological triplicate using technical duplicates.…”