title: Synthesis and characterization of bivalent peptide ligands targeted to G-protein-coupled receptors.
abstract: BACKGROUND
  Through the effects of avidity, multivalency can increase the apparent affinity of a ligand for its binding site. Low molecular weight, high affinity, multivalent ligands theoretically could be used to deliver a variety of agents to specific cell subtypes. In order to target specific G-protein-coupled receptors, a series of monospecific peptide dimers were synthesized that are designed to bind to two adjacent receptor sites.
  
  
  RESULTS
  Three dimers, consisting of a ligand region, a short, flexible, uncharged spacer, a longer, polylysine spacer and a single cysteine residue to permit dimerization, and the corresponding monomers were synthesized by solid-phase peptide synthesis. The ligand domain was either alpha-melanocyte stimulating hormone (alpha-MSH), an alpha-MSH receptor antagonist (alpha-MSH-ANT), or bombesin. These ligands were characterized in a functional melanocyte dispersion assay. In wild-type melanophores, the alpha-MSH dimer stimulated dispersion with an EC50 approximately seven-fold lower than that of the corresponding monomer. Similarly, in cells transfected with bombesin receptor cDNA, the bombesin dimer was approximately five-fold more potent than the monomer. The alpha-MSH-ANT monomer specifically inhibited alpha-MSH-mediated dispersion with no significant agonist activity, but the dimer acted predominantly as an agonist.
  
  
  CONCLUSIONS
  Peptide dimers can be synthesized easily and have enhanced functional activity; monospecific dimers have greater avidity and bispecific dimers are likely to have greater selectivity. They may therefore have practical potential as specific cell-targeting agents.
authors.affiliation: Department of Neurology, Yale University School of Medicine, New Haven, CT 06520-8024, USA. MRLERNER@aol.com
authors.forename: M D
authors.initials: MD
authors.lastname: Carrithers
authors.forename: M R
authors.initials: MR
authors.lastname: Lerner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001839:Bombesin / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D008024:Ligands; D008544:Melanocytes / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D018004:Receptors, Bombesin / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014162:Transfection; D014982:Xenopus laevis; D000521:alpha-MSH / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D008024:Ligands; D010455:Peptides; D018004:Receptors, Bombesin; D011956:Receptors, Cell Surface; D000521:alpha-MSH; D019204:GTP-Binding Proteins; D001839:Bombesin