title: Blockade of non-opioid excitatory effects of spinal dynorphin A at bradykinin receptors.
abstract: Dynorphin A (Dyn A) is an endogenous opioid ligand that possesses neuroinhibitory (antinociceptive) effects via μ, δ, and κ opioid receptors. However, under chronic pain conditions, up-regulated spinal Dyn A can also interact with bradykinin receptors (BRs) to promote hyperalgesia through a neuroexcitatory(pronociceptive) effect. These excitatory effects cannot be blocked by an opioid antagonist, and thus are non-opioid in nature. On the basis of the structural dissimilarity between Dyn A and endogenous BR ligands, bradykinin(BK) and kallidin (KD), Dyn A's interaction with BRs could not be predicted, and provided an opportunity to identify a novel potential neuroexcitatory target. Systematic structure-activity relationship (SAR) studies discovered a minimum pharmacophore of Dyn A, [des-Arg7]-Dyn A-(4-11) LYS1044 for antagonist activity at the BRs, along with insights into the key structural features for BRs recognition, i.e., amphipathicity. The des-Tyr fragment of dynorphin does not bind to opioid receptors. Intrathecal administration of des-Tyr dynorphin produces hyperalgesia reminiscent of behaviors seen in peripheral n europathic pain models and at higher doses, neurotoxicity. Our lead ligand LYS1044 negatively modulated Dyn A-(2-13)-induced neuroexcitatory effects in naïve animals and blocked mechanical hypersensitivity and thermal hyperalgesia in a dose-dependent manner in animals with experimental neuropathic pain. Based on these results, ligand LYS1044 might prevent abnormal pain states by blocking the neuroexcitatory effects of increased levels of Dyn A that are seen in experimental models of neuropathic pain and that likely promote excitation mediated by BRs in the spinal cord.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Yeon Sun
authors.initials: YS
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Sara M
authors.initials: SM
authors.lastname: Hall
authors.affiliation: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Cyf
authors.initials: C
authors.lastname: Ramos-Colon
authors.affiliation: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Remesic
authors.affiliation: Department of Pharmacology, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: David
authors.initials: D
authors.lastname: Rankin
authors.affiliation: Department of Pharmacology, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Todd W
authors.initials: TW
authors.lastname: Vanderah
authors.affiliation: Department of Pharmacology, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
authors.affiliation: Department of Pharmacology, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Josephine
authors.initials: J
authors.lastname: Lai
authors.affiliation: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Hruby