PT  - JOURNAL ARTICLE
AU  - Robert J. Cassell
AU  - Krishna K. Sharma
AU  - Hongyu Su
AU  - Benjamin R. Cummins
AU  - Haoyue Cui
AU  - Kendall L. Mores
AU  - Ryan A. Altman
AU  - Richard M. van Rijn
TI  - The Meta-Position of Phe<sup>4</sup> in Leu-enkephalin Regulates Potency, Selectivity, Functional Activity, and Signaling Bias at the Delta and Mu Opioid Receptors
AID  - 10.1101/750794
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 750794
4099  - http://biorxiv.org/content/early/2019/09/01/750794.short
4100  - http://biorxiv.org/content/early/2019/09/01/750794.full
AB  - 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 Phe4 position of the endogenous δ-opioid receptor ligand, Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). Substitution of the meta-position of Phe4 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 lower-affinity ligands with good biases at both receptors. Further, Phe4 substitution also improves peptide stability relative to Leu-enkephalin. Overall, these favorable substitutions to the meta-position of Phe4 might be combined with other modifications to Leu-enkephalin to deliver improved ligands with finely tuned potency, selectivity, bias and drug-like properties.TOC FIGUREcAMP3′,5′-cyclic adenosine monophosphateCNScentral nervous systemDAMGO[D-Ala2, N-MePhe4, Gly-ol]-enkephalinδORDelta opioid receptorsDMFN,N-DimethylformamideDPDPE[D-Pen2,D-Pen5]-enkephalinGTPγSguanosine 5′-O-[gamma-thio]triphosphateμORMu opioid receptorsRP-HPLCReverse phase high performance liquid chromatographyt1/2half-lifeUPLCUltra performance liquid chromatography.