Selective κ receptor partial agonist HS666 produces potent antinociception without inducing aversion after i.c.v. administration in mice

Br J Pharmacol. 2017 Aug;174(15):2444-2456. doi: 10.1111/bph.13854. Epub 2017 Jun 27.


Background and purpose: The κ receptor has a central role in modulating neurotransmission in central and peripheral neuronal circuits that subserve pain and other behavioural responses. Although κ receptor agonists do not produce euphoria or lead to respiratory suppression, they induce dysphoria and sedation. We hypothesized that brain-penetrant κ receptor ligands possessing biased agonism towards G protein signalling over β-arrestin2 recruitment would produce robust antinociception with fewer associated liabilities.

Experimental approach: Two new diphenethylamines with high κ receptor selectivity, HS665 and HS666, were assessed following i.c.v. administration in mouse assays of antinociception with the 55°C warm-water tail withdrawal test, locomotor activity in the rotorod and conditioned place preference. The [35 S]-GTPγS binding and β-arrestin2 recruitment in vitro assays were used to characterize biased agonism.

Key results: HS665 (κ receptor agonist) and HS666 (κ receptor partial agonist) demonstrated dose-dependent antinociception after i.c.v. administration mediated by the κ receptor. These highly selective κ receptor ligands displayed varying biased signalling towards G protein coupling in vitro, consistent with a reduced liability profile, reflected by reduced sedation and absence of conditioned place aversion for HS666.

Conclusions and implications: HS665 and HS666 activate central κ receptors to produce potent antinociception, with HS666 displaying pharmacological characteristics of a κ receptor analgesic with reduced liability for aversive effects correlating with its low efficacy in the β-arrestin2 signalling pathway. Our data provide further understanding of the contribution of central κ receptors in pain suppression, and the prospect of dissociating the antinociceptive effects of HS665 and HS666 from κ receptor-mediated adverse effects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics / administration & dosage
  • Analgesics / chemistry
  • Analgesics / pharmacology*
  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / chemistry
  • Analgesics, Opioid / pharmacology*
  • Animals
  • CHO Cells
  • Cells, Cultured
  • Cricetulus
  • Dose-Response Relationship, Drug
  • Locomotion / drug effects
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Molecular Structure
  • Phenethylamines / administration & dosage
  • Phenethylamines / chemistry
  • Phenethylamines / pharmacology*
  • Receptors, Opioid, kappa / agonists*
  • Structure-Activity Relationship
  • Tail / drug effects


  • 3-(2-((cyclobutylmethyl)(phenethyl)amino)ethyl)phenol
  • Analgesics
  • Analgesics, Opioid
  • Phenethylamines
  • Receptors, Opioid, kappa