Discovery of a Highly Selective and Potent κ Opioid Receptor Agonist from N-Cyclopropylmethyl-7α-phenyl-6,14-endoethanotetrahydronorthebaines with Reduced Central Nervous System (CNS) Side Effects Navigated by the Message-Address Concept.

Effective and safe analgesics represent an unmet medical need for the treatment of acute and chronic pain. A series of N-cyclopropylmethyl-7α-phenyl-6,14-endoethanotetrahydronorthebaines were designed, synthesized, and assayed, leading to the discovery of a benzylamine derivative (compound 4, SLL-039) as a highly selective and potent κ opioid agonist (κ, Ki = 0.47 nM, κ/µ = 682, κ/δ = 283), which was confirmed by functional assays in vitro and antinociceptive assays in vivo. The in vivo effect could be blocked by pretreatment with the selective κ antagonist nor-BNI. Moreover, this compound did not induce sedation, a common dose limiting effect of κ opioid receptor agonists, at its analgesic dose compared to U50,488H. The dissociation of sedation/antinociception found in SLL-039 was assumed to be correlated with the occupation of its benzamide motif in a unique subsite involving V1182.63, W124EL1, and E209EL2.

Pharmacological Characterization of Dezocine, a Potent Analgesic Acting as a κ Partial Agonist and µ Partial Agonist.

Dezocine is becoming dominated in China market for relieving moderate to severe pain. It is believed that Dezocine's clinical efficacy and little chance to provoke adverse events during the therapeutic process are mainly attributed to its partial agonist activity at the µ opioid receptor. In the present work, we comprehensively studied the pharmacological characterization of Dezocine and identified that the analgesic effect of Dezocine was a result of action at both the κ and µ opioid receptors. We firstly found that Dezocine displayed preferential binding to µ opioid receptor over κ and δ opioid receptors. Dezocine, on its own, weakly stimulated G protein activation in cells expressing κ and µ receptors, but in the presence of full κ agonist U50,488 H and µ agonist DAMGO, Dezocine inhibited U50,488H- and DAMGO-mediated G protein activation, indicating that Dezocine was a κ partial agonist and µ partial agonist. Then the in intro results were verified by in vivo studies in mice. We observed that Dezocine-produced antinociception was significantly inhibited by κ antagonist nor-BNI and µ antagonist ß-FNA pretreatment, indicating that Dezocine-mediated antinociception was via both the κ and µ opioid receptors. When co-administrating of Dezocine with U50,488 H or morphine, Dezocine was capable of inhibiting U50,488H- or morphine-induced antinociception. Finally, κ receptor activation-associated side effect sedation was investigated. We found that Dezocine displayed limited sedative effect with a ceiling effecting at a moderate dose. Thus, our work led to a better understanding of the analgesic mechanism of action of Dezocine in vivo.