title: Investigation of the binding and functional properties of extended length D3 dopamine receptor-selective antagonists.
abstract: The D3 dopamine receptor represents an important target in drug addiction in that reducing receptor activity may attenuate the self-administration of drugs and/or disrupt drug or cue-induced relapse. Medicinal chemistry efforts have led to the development of D3 preferring antagonists and partial agonists that are >100-fold selective vs. the closely related D2 receptor, as best exemplified by extended-length 4-phenylpiperazine derivatives. Based on the D3 receptor crystal structure, these molecules are known to dock to two sites on the receptor where the 4-phenylpiperazine moiety binds to the orthosteric site and an extended aryl amide moiety docks to a secondary binding pocket. The bivalent nature of the receptor binding of these compounds is believed to contribute to their D3 selectivity. In this study, we examined if such compounds might also be "bitopic" such that their aryl amide moieties act as allosteric modulators to further enhance the affinities of the full-length molecules for the receptor. First, we deconstructed several extended-length D3-selective ligands into fragments, termed "synthons", representing either orthosteric or secondary aryl amide pharmacophores and investigated their effects on D3 receptor binding and function. The orthosteric synthons were found to inhibit radioligand binding and to antagonize dopamine activation of the D3 receptor, albeit with lower affinities than the full-length compounds. Notably, the aryl amide-based synthons had no effect on the affinities or potencies of the orthosteric synthons, nor did they have any effect on receptor activation by dopamine. Additionally, pharmacological investigation of the full-length D3-selective antagonists revealed that these compounds interacted with the D3 receptor in a purely competitive manner. Our data further support that the 4-phenylpiperazine D3-selective antagonists are bivalent and that their enhanced affinity for the D3 receptor is due to binding at both the orthosteric site as well as a secondary binding pocket. Importantly, however, their interactions at the secondary site do not allosterically modulate their binding to the orthosteric site.
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Cheryse A
authors.initials: CA
authors.lastname: Furman
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Roof
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Moritz
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Brittney N
authors.initials: BN
authors.lastname: Miller
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Trevor B
authors.initials: TB
authors.lastname: Doyle
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: R Benjamin
authors.initials: RB
authors.lastname: Free
authors.affiliation: Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA.
authors.forename: Ashwini K
authors.initials: AK
authors.lastname: Banala
authors.affiliation: Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA.
authors.forename: Noel M
authors.initials: NM
authors.lastname: Paul
authors.affiliation: Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Kumar
authors.affiliation: Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Sibley
authors.affiliation: Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA. Electronic address: anewman@intra.nida.nih.gov.
authors.forename: Amy Hauck
authors.initials: AH
authors.lastname: Newman
authors.affiliation: Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA. Electronic address: sibleyd@helix.nih.gov.
authors.forename: David R
authors.initials: DR
authors.lastname: Sibley
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D001667:Binding, Competitive; D016466:CHO Cells; D003412:Cricetulus; D018492:Dopamine Antagonists / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D004353:Drug Evaluation, Preclinical; D006801:Humans; D015394:Molecular Structure; D011869:Radioligand Assay; D050637:Receptors, Dopamine D3 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; C493593:DRD3 protein, human; D018492:Dopamine Antagonists; D050637:Receptors, Dopamine D3; D000071557:beta-Arrestins
keywords: Allosteric; Bitopic; Bivalent; D(3) receptor; Dopamine antagonists; Dopamine receptor