title: (-)-Stepholidine is a potent pan-dopamine receptor antagonist of both G protein- and β-arrestin-mediated signaling.
abstract: BACKGROUND
  (-)-Stepholidine is a tetrahydroberberine alkaloid that is known to interact with dopamine receptors and has also been proposed as a novel antipsychotic agent. Its suggested novelty lies in the fact that it has been proposed to have D1-like receptor agonist and D2-like receptor antagonist properties. Thus, it might be effective in treating both positive and negative (cognition) symptoms of schizophrenia. However, its activity on specific dopamine receptor subtypes has not been clarified, especially with respect to its ability to activate D1-like receptors.
  
  
  OBJECTIVE
  We wished to examine the affinity and functional activity of (-)-stepholidine at each of the human dopamine receptor subtypes expressed in a defined cellular environment.
  
  
  METHODS
  D1-D5 dopamine receptors were stably expressed in cell lines and their interactions with (-)-stepholidine were examined using radioligand binding and various functional signaling assays. Radioligand binding assays were also performed using bovine striatal membranes.
  
  
  RESULTS
  (-)-Stepholidine exhibited high (nM) affinity for D1 and D5 receptors, somewhat lower (two- to four-fold) affinity for D2 and D3 receptors, and low micromolar affinity for D4 receptors. Functionally, (-)-stepholidine was ineffective in activating G protein-mediated signaling of D1-like and D2 receptors and was also ineffective in stimulating β-arrestin recruitment to any dopamine receptor subtype. It did, however, antagonize all of these responses. It also antagonized D1-D2 heteromer-mediated Ca(2+) mobilization. Radioligand binding assays of D1-like receptors in brain membranes also indicated that (-)-stepholidine binds to the D1 receptor with antagonist-like properties.
  
  
  CONCLUSIONS
  (-)-Stepholidine is a pan-dopamine receptor antagonist and its in vivo effects are largely mediated through dopamine receptor blockade with potential cross-talk to other receptors or signaling proteins.
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 5625 Fishers Lane, Room 4S-04, Bethesda, MD, 20892-9405, USA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Meade
authors.forename: R Benjamin
authors.initials: RB
authors.lastname: Free
authors.forename: Nicole R
authors.initials: NR
authors.lastname: Miller
authors.forename: Lani S
authors.initials: LS
authors.lastname: Chun
authors.forename: Trevor B
authors.initials: TB
authors.lastname: Doyle
authors.forename: Amy E
authors.initials: AE
authors.lastname: Moritz
authors.forename: Jennie L
authors.initials: JL
authors.lastname: Conroy
authors.forename: Val J
authors.initials: VJ
authors.lastname: Watts
authors.forename: David R
authors.initials: DR
authors.lastname: Sibley
mesh_terms: D000818:Animals; D019390:Arrestins / Q000378:metabolism*; D001599:Berberine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D016466:CHO Cells; D003412:Cricetulus; D018492:Dopamine Antagonists / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D011954:Receptors, Dopamine / Q000378:metabolism*; D050641:Receptors, Dopamine D5 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D018492:Dopamine Antagonists; D011954:Receptors, Dopamine; D000071557:beta-Arrestins; D001599:Berberine; C010513:stepholidine; D050641:Receptors, Dopamine D5; D019204:GTP-Binding Proteins