Functional Selectivity and Antinociceptive Effects of a Novel KOPr Agonist

Abstract

Kappa opioid receptor (KOPr) agonists represent alternative analgesics for their low abuse potential, although relevant adverse effects have limited their clinical use. Functionally selective KOPr agonists may activate, in a pathway-specific manner, G protein-mediated signaling, that produces antinociception, over b-arrestin 2-dependent induction of p38MAPK, which preferentially contributes to adverse effects. Thus, functionally selective KOPr agonists biased toward G protein-coupled intracellular signaling over barrestin-2-mediated pathways may be considered candidate therapeutics possibly devoid of many of the typical adverse effects elicited by classic KOPr agonists. Nonetheless, the potential utility of functionally selective agonists at opioid receptors is still highly debated; therefore, further studies are necessary to fully understand whether it will be possible to develop more effective and safer analgesics by exploiting functional selectivity at KOPr. In the present study we investigated in vitro functional selectivity and in vivo antinociceptive effects of LOR17, a novel KOPr selective peptidic agonist that we synthesized. LOR17mediated effects on adenylyl cyclase inhibition, ERK1/2, p38MAPK phosphorylation, and astrocyte cell proliferation were studied in HEK-293 cells expressing hKOPr, U87-MG glioblastoma cells, and primary human astrocytes; biased agonism was investigated via cAMP ELISA and b-arrestin 2 recruitment assays. Antinociception and antihypersensitivity were assessed in mice via warm-water tail-withdrawal test, intraperitoneal acid-induced writhing, and a model of oxaliplatin-induced neuropathic cold hypersensitivity. Effects of LOR17 on locomotor activity, exploratory activity, and forced-swim behavior were also assayed. We found that LOR17 is a selective, G protein biased KOPr agonist that inhibits adenylyl cyclase and activates early-phase ERK1/2 phosphorylation. Conversely to classic KOPr agonists as U50,488, LOR17 neither induces p38MAPK phosphorylation nor increases KOPr-dependent, p38MAPK-mediated cell proliferation in astrocytes. Moreover, LOR17 counteracts, in a concentration-dependent manner, U50,488induced p38MAPK phosphorylation and astrocyte cell proliferation. Both U50,488 and LOR17 display potent antinociception in models of acute nociception, whereas LOR17 counteracts oxaliplatin-induced thermal hypersensitivity better than U50,488, and it is effective after single or repeated s.c. administration. LOR17 administered at a dose that fully alleviated oxaliplatin-induced thermal hypersensitivity did not alter motor coordination, locomotor and exploratory activities nor induced pro-depressant-like behavior. LOR17, therefore, may emerge as a novel KOPr agonist displaying functional selectivity toward G protein signaling and eliciting antinociceptive/antihypersensitivity effects in different animal models, including oxaliplatin-induced neuropathy.

G protein-coupled receptors: structure- and function-based drug discovery

“…140 Another µ-OR-biased ligand, oliceridine (TRV130, Olinvo TM ), passed phase III clinical trial but did not get the FDA approval for safety concerns. 141 The NDA for oliceridine was resubmitted and a new counterpart, TRV734, is not only suitable for oral administration but also safer due to reduced dependency. 142 A fourth µ-OR-biased ligand, PZM21, cross-reacts with κ-OR and failed to reduce respiratory depression in C57BL and CD-1 mice.…”

“…Similar situation occurred with κ-OR as well whose agonists possess analgesic property and have a low risk of dependence and abuse but with adverse effects such as sedation, motor dysfunction, hallucination, and dysphoria. 145 G protein-biased agonists of κ-OR, 146 including RB-64, 145 mesyl salvinorin B, triazole 1.1, diphenethylamines and LOR17, 141 were reported to minimize the adverse effects in preclinical settings. One of such, nalfurafine, was approved in Japan (2015) as an anti-pruritic agent for patients with chronic liver diseases.…”

Pharmacological Characterization of µ-Opioid Receptor Agonists with Biased G Protein or β-Arrestin Signaling, and Computational Study of Conformational Changes during Receptor Activation

“…Experiments conducted with β-arrestin 2 knockout animals indicated that MOP activation produced analgesia, but significantly fewer side effects [9]. Therefore, significant efforts have been placed on designing ligands biased toward G-protein activation [17][18][19][20][21][22][23][24][25][26][27][28], a requirement for analgesic efficacy, while avoiding interaction with β-arrestin. Biased ligands are believed to stabilize specific receptor conformations distinct from those of unbiased agonists [15,16].…”

“…A glycosylated analog of bilorphin was orally active, with similar in vivo potency to morphine but improved safety [26]. Very recently, the cyclotetrapeptide LOR17, c[Phe-Gly-β-Ala-D-Trp] (Figure 1), lacking a protonable amino group [27], emerged as a novel KOP-selective partial agonist displaying functional selectivity toward G protein signaling and eliciting antinociceptive/antihypersensitivity effects in different animal models, without altering motor coordination, locomotor, and exploratory activities or inducing pro-depressant-like behavior [28]. Finally, the naturally occurring alkaloids corydine and corydaline were identified by virtual screening protocols (Figure 1).…”

Strategies for DevelopingκOpioid Receptor Agonists for the Treatment of Pain with Fewer Side Effects

“…LOR17 is a novel peptidic KOPr agonist displaying extreme G-protein bias with U50,488 as the reference ligand (Bedini et al, 2020). In male CD-1 mice, LOR17 had similar antinociceptive effects to U50,488 in the warm-water tail-withdrawal and acetic acid-induced writhing test, whereas, LOR17 was more effective at reducing thermal hypersensitivity in the oxaliplatin-induced neuropathic pain model (Bedini et al, 2020). LOR17 did not affect motor coordination in the rotarod test, exploratory behaviour in the hole-board test, and did not have pro-depressant effects in the forced swim test (Bedini et al, 2020).…”