Mechanistic Insights into G Protein-Biased κ-Opioid Receptor Signaling Using Dual-Charged Naltrexamine Amides

Opioids remain a cornerstone of pain management, but currently used therapeutics are associated with serious side effects. While κ-opioid receptor (KOR) agonists offer an alternative to classical μ-opioid receptor (MOR) agonists, their clinical potential is limited by severe adverse effects. G protein-biased KOR agonists are a promising strategy for developing safer analgesics. In this study, we used virtual screening to develop novel dual-charged naltrexamine amide derivatives as tool compounds for investigating biased agonism at the KOR. All of the predicted ligands demonstrate low-nanomolar activity and G protein bias at both the KOR and MOR. Molecular dynamics simulations revealed a key allosteric communication involving TM4, TM5, and ICL2. These compounds achieve their effects through interactions with residues E209^ECL2, D223^5.35, E297^6.58, and K227^5.39. These findings provide insight into the structural mechanisms of KOR signaling bias and inform the rational design of improved KOR therapeutics.