Engineered KOR peptide agonist beta01 reduces sedation and anxiety while retaining antinociception

The κ-opioid receptor (KOR) is a promising target for pain and pruritus, but current agonists like difelikefalin (FDA-approved for chronic pruritus) activate both G protein and β-arrestin pathways. This 'balanced' signaling leads to undesirable side effects such as sedation and anxiety-like behaviors, primarily linked to β-arrestin recruitment. Developing KOR agonists that selectively activate G protein signaling (G protein-biased) could offer superior therapeutic profiles by mitigating these adverse effects, addressing a critical gap in opioid pharmacology.

Researchers employed a rational design approach, beginning with cryo-electron microscopy (cryo-EM) to determine the structure of the difelikefalin-KOR-Gi complex. This structural analysis identified Y3207.43 as a key residue influencing signaling bias. Guided by this insight, they engineered beta01, a β-amino acid-substituted analog. The team then evaluated beta01 in mouse models for its antinociceptive and antipruritic efficacy, comparing it to existing KOR agonists. Further molecular dynamics simulations and 2D 13C-Met NMR analyses were conducted to elucidate the conformational changes induced by beta01 binding to KOR.

Structural analysis of the difelikefalin-KOR-Gi complex revealed Y3207.43 as a critical residue for signaling bias. The engineered peptide, beta01, demonstrated potent G protein activation while exhibiting minimal β-arrestin recruitment, indicating successful bias. In mouse models, beta01 maintained robust antinociceptive and antipruritic efficacy, comparable to balanced agonists. Crucially, beta01 significantly reduced sedation and anxiety-like behaviors compared to difelikefalin, suggesting a favorable side-effect profile. Molecular dynamics simulations and NMR analyses provided further mechanistic insight:

beta01 stabilizes a unique KOR conformation characterized by an expanded intracellular cavity, which physically disfavors β-arrestin binding. This structural alteration underpins the observed G protein bias.