title: Antinociceptive structure-activity studies with enkephalin-based opioid glycopeptides.
abstract: Development of opioid peptides as therapeutic agents has historically been limited due to pharmacokinetic issues including stability and blood-brain barrier (BBB) permeability. Glycosylation of opioid peptides can increase peptide serum stability and BBB penetration. To further define the requirements for optimizing in vivo antinociceptive potency following intravenous administration, we synthesized a series of enkephalin-based glycopeptides using solid phase 9-fluorenylmethyloxy carbamate methods. The compounds differed in the sixth and subsequent amino acid residues (Ser or Thr) and in the attached carbohydrate moiety. In vitro binding and functional smooth muscle bioassays indicated that the addition of mono- or disaccharides did not significantly affect the opioid receptor affinity or agonist activity of the glycopeptides compared with their unglycosylated parent peptides. All of the glycopeptides tested produced potent antinociceptive effects in male ICR mice following intracerebroventricular injection in the 55 degrees C tail-flick test. The calculated A(50) values for the Ser/Thr and monosaccharide combinations were all very similar with values ranging from 0.02 to 0.09 nmol. Selected compounds were administered to mice intravenously and tested for antinociception to indirectly assess serum stability and BBB penetration. All compounds tested produced full antinociceptive effects with calculated A (50) values ranging from 2.2 to 46.4 micromol/kg with the disaccharides having potencies that equaled or exceeded that of morphine on a micromoles per kilogram basis. Substitution of a trisaccharide or bis- and tris-monosaccharides resulted in a decrease in antinociceptive potency. These results provide additional support for the utility of glycosylation to increase central nervous system bioavailability of small peptides and compliment our ongoing stability and blood-brain barrier penetration studies.
authors.affiliation: Department of Biological Sciences, University of Northern Colorado, Greely, USA.
authors.forename: Nura O
authors.initials: NO
authors.lastname: Elmagbari
authors.forename: Richard D
authors.initials: RD
authors.lastname: Egleton
authors.forename: Michael M
authors.initials: MM
authors.lastname: Palian
authors.forename: John J
authors.initials: JJ
authors.lastname: Lowery
authors.forename: Wendi R
authors.initials: WR
authors.lastname: Schmid
authors.forename: Peg
authors.initials: P
authors.lastname: Davis
authors.forename: Edita
authors.initials: E
authors.lastname: Navratilova
authors.forename: Muthu
authors.initials: M
authors.lastname: Dhanasekaran
authors.forename: Charles M
authors.initials: CM
authors.lastname: Keyari
authors.forename: Henry I
authors.initials: HI
authors.lastname: Yamamura
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Hruby
authors.forename: Robin
authors.initials: R
authors.lastname: Polt
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Bilsky
mesh_terms: D000700:Analgesics / Q000737:chemistry / Q000627:therapeutic use*; D000818:Animals; D004195:Disease Models, Animal; D004745:Enkephalins / Q000737:chemistry / Q000627:therapeutic use*; D006020:Glycopeptides / Q000737:chemistry / Q000627:therapeutic use*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D018847:Opioid Peptides / Q000737:chemistry / Q000627:therapeutic use; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects; D013329:Structure-Activity Relationship
chemical_list: D000700:Analgesics; D004745:Enkephalins; D006020:Glycopeptides; D018847:Opioid Peptides