Development of Functionally Selective, Small Molecule Agonists at Kappa Opioid Receptors

Jeffrey Aubé,Franck Madoux,Edward Stahl,Laura M. Bohn,Kevin J. Frankowski,Cullen L. Schmid,John M. Streicher,Stephen R. Slauson,Peter Hodder,Lei Zhou,Michael D. Cameron,Angela M. Phillips,Thomas E. Prisinzano,Kimberly M. Lovell

doi:10.1074/jbc.m113.504381

Abstract

The kappa opioid receptor (KOR) is widely expressed in the CNS and can serve as a means to modulate pain perception, stress responses, and affective reward states. Therefore, the KOR has become a prominent drug discovery target toward treating pain, depression, and drug addiction. Agonists at KOR can promote G protein coupling and βarrestin2 recruitment as well as multiple downstream signaling pathways, including ERK1/2 MAPK activation. It has been suggested that the physiological effects of KOR activation result from different signaling cascades, with analgesia being G protein-mediated and dysphoria being mediated through βarrestin2 recruitment. Dysphoria associated with KOR activation limits the therapeutic potential in the use of KOR agonists as analgesics; therefore, it may be beneficial to develop KOR agonists that are biased toward G protein coupling and away from βarrestin2 recruitment. Here, we describe two classes of biased KOR agonists that potently activate G protein coupling but weakly recruit βarrestin2. These potent and functionally selective small molecule compounds may prove to be useful tools for refining the therapeutic potential of KOR-directed signaling in vivo.

Highlights

Kappa opioid receptor (KOR) signaling may produce antinociception through G protein or dysphoria through ␤arrestin pathways
It has been suggested that the physiological effects of kappa opioid receptor (KOR) activation result from different signaling cascades, with analgesia being G protein-mediated and dysphoria being mediated through ␤arrestin2 recruitment
Dysphoria associated with KOR activation limits the therapeutic potential in the use of KOR agonists as analgesics; it may be beneficial to develop KOR agonists that are biased toward G protein coupling and away from ␤arrestin2 recruitment

Summary

Background

Kappa opioid receptor (KOR) signaling may produce antinociception through G protein or dysphoria through ␤arrestin pathways. We describe two classes of biased KOR agonists that potently activate G protein coupling but weakly recruit ␤arrestin2 These potent and functionally selective small molecule compounds may prove to be useful tools for refining the therapeutic potential of KOR-directed signaling in vivo. The isoquinolinone compounds are interesting in that they lack the basic nitrogen center common in small molecule KOR ligands (10, 39 – 41); the best known ligand lacking this feature is salvinorin A, a natural neoclerdane diterpene found to be a highly selective, potent KOR agonist [19] Following their initial disclosure, these scaffolds were subjected to iterative rounds of medicinal chemistry and structureactivity relationship studies with the goal of developing KOR agonists that are biased toward G protein coupling. We report five triazole analogues and two isoquinolinone analogues (Fig. 1) that activate KOR in a manner that is preferentially biased toward G protein signaling with minimal effects on ␤arrestin recruitment and downstream ERK1/2 activation

EXPERIMENTAL PROCEDURES

RESULTS

Whole Cell G Protein Signaling

Cellular Impedance- sample traces

62 Ϯ 12 31 Ϯ 11 77 Ϯ 13 68 Ϯ 10 60 Ϯ 15 33 Ϯ 11 80 Ϯ 8 20 Ϯ 11

DISCUSSION