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To develop safer and potent analgesics, we designed, synthesized, and evaluated a new series of benzylaminofentanyl derivates as bifunctional μ opioid receptor (MOR) and σ 1 receptor (σ 1 R) ligands. Compound 68 (Tao-191) showed desirable MOR agonism (K i  = 6.5 nΜ; EC 50  = 48.5 nΜ, E max  = 66.3%) and σ 1 R antagonism (K i  = 35.7 nM) in vitro, and exerted powerful analgesic effects in the abdominal constriction test (ED 50  = 0.32 mg/kg, in mice), formalin-induced pain test (phase II, ED 50  = 2.26 mg/kg, in rats), and paclitaxel-induced neuropathic pain model (ED 50  = 0.30 mg/kg, in mice). The contributions of MOR and σ 1 R to its antinociceptive effect were verified by combined administration with the MOR antagonist naloxone and the σ 1 R agonist PRE-084, respectively. At equianalgesic doses, compound 68 induced fewer MOR-related side effects-including physical and psychological dependence, respiratory depression, constipation, and acute hyperlocomotion-than fentanyl. The results provide a rationale for further exploration of the action and safety of dual MOR/σ 1 R ligands as a promising avenue for the development of potent and safe analgesics., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

The synthesis and sigma-1 receptor (σ1R) antagonist activity of a new series of 3,4-dihydro-2(1H)-quinolinone derivatives are reported. The new compounds were evaluated in vitro in sigma-1 and sigma-2 receptor-binding assays in guinea pig brain membranes. The structure-activity relationship led us to the promising derivative 7-(3-(piperidin-1-yl)propoxy)-1-(4-fluorobenzyl)-3,4-dihydro-2(1H)-quinolinone (35). The compounds with highest affinity and greatest selectivity were further profiled, and compound 35 had a high binding constant for sigma-1 receptor (Kiσ1 = 1.22 nM) and high sigma-1/2 selectivity (1066-fold). Thus, compound 35, which proved to be an antagonist of sigma-1 receptor, emerged as the most interesting candidate. In addition, compound 35 exerted dose-dependent anti-nociceptive effects in the formalin test. These characteristics suggested that the potent and selective compound 35 could be a potent candidate for pain treatment., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Opioid analgesics are highly effective painkillers for the treatment of moderate or severe pain, but they are associated with a number of undesirable adverse effects, including the development of tolerance, addiction, constipation and life-threatening respiratory depression. The development of new and safer analgesics with innovative mechanisms of action, which can enhance the efficacy in comparison to available treatments and reduce their side effects, is urgently needed. The sigma-1 receptor (σ 1 R), a unique Ca2+-sensing chaperone protein, is expressed throughout pain-modulating tissues and affects neurotransmission by interacting with different protein partners, including molecular targets that participate in nociceptive signalling, such as the μ-opioid receptor (MOR), N -methyl- d - aspartate receptor (NMDAR) and cannabinoid 1 receptor (CB 1 R). Overwhelming pharmacological and genetic evidence indicates that σ 1 R antagonists induce anti-hypersensitive effects in sensitising pain conditions (e.g. chemically induced, inflammatory and neuropathic pain) and enhance opioid analgesia but not opioid-mediated detrimental effects. It has been suggested that balanced modulation of MORs and σ 1 Rs may improve both the therapeutic efficacy and safety of opioids. This review summarises the functional profiles of ligands with mixed MOR agonist and σ 1 R antagonist activities and highlights their therapeutic potentials for pain management. Dual MOR agonism/σ 1 R antagonism represents a promising avenue for the development of potent and safer analgesics. [Display omitted] • σ 1 R antagonists exhibit anti-hypersensitive effects in sensitising pain conditions. • σ 1 R antagonists enhance opioid analgesia but not opioid-mediated unwanted effects. • Bifunctional MOR and σ 1 R ligands possess wider therapeutic window with fewer adverse effects. • Representative ligands with MOR agonist and σ 1 R antagonist activities were summarised. • Dual MOR-agonism/σ 1 R-antagonism represents a promising avenue for the development of potent and safer analgesics. [ABSTRACT FROM AUTHOR]