title: Pharmacodynamic and pharmacokinetic characterization of poly(ethylene glycol) conjugation to met-enkephalin analog [D-Pen2, D-Pen5]-enkephalin (DPDPE).
abstract: Poly(ethylene glycol), or PEG, conjugation to proteins and peptides is a growing technology used to enhance efficacy of therapeutics. This investigation assesses pharmacodynamic and pharmacokinetic characteristics of PEG-conjugated [D-Pen2,D-Pen5]-enkephalin (DPDPE), a met-enkephalin analog, in rodent (in vivo, in situ) and bovine (in vitro) systems. PEG-DPDPE showed increased analgesia (i.v.) compared with nonconjugated form (p < 0.01), despite a 172-fold lower binding affinity for the delta-opioid receptor. [125I]PEG-DPDPE had a 36-fold greater hydrophilicity (p < 0.01) and 12% increase in the unbound plasma protein fraction (p < 0.01), compared with [(125)I]DPDPE. [125I]PEG-DPDPE had a 2.5-fold increase in elimination half-life (p < 0.01), 2.7-fold decrease in volume of distribution (p < 0.01), and a 7-fold decrease in plasma clearance rate (p < 0.01) to [125I]DPDPE. Time course distribution showed significant concentration differences (p < 0.01) in plasma, whole blood, liver, gallbladder, gastrointestinal (GI) content, GI tract, kidneys, spleen, urine, and brain (brain, p < 0.05), between the conjugated and nonconjugated forms. Increased brain uptake of [(125)I]PEG-DPDPE corresponded to analgesia data. [125I]PEG-DPDPE in brain was shown to be 58.9% intact, with 41.1% existing as [125I]DPDPE (metabolite), whereas [125I]DPDPE was 25.7% intact in the brain (at 30 min). In vitro P-glycoprotein affinity was shown for [125I]DPDPE (p < 0.01) but not shown for [125I]PEG-DPDPE. In vitro saturable uptake, with 100 microM DPDPE, was shown for [125I]PEG-DPDPE (p < 0.05). In this study, PEG-conjugated DPDPE seems to act as a prodrug, enhancing peripheral pharmacokinetics, while undergoing hydrolysis in the brain and allowing nonconjugated DPDPE to act at the receptor.
authors.affiliation: Department of Pharmacology, University of Arizona, College of Medicine, Tucson, Arizona 85712, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Witt
authors.forename: J D
authors.initials: JD
authors.lastname: Huber
authors.forename: R D
authors.initials: RD
authors.lastname: Egleton
authors.forename: M J
authors.initials: MJ
authors.lastname: Roberts
authors.forename: M D
authors.initials: MD
authors.lastname: Bentley
authors.forename: L
authors.initials: L
authors.lastname: Guo
authors.forename: H
authors.initials: H
authors.lastname: Wei
authors.forename: H I
authors.initials: HI
authors.lastname: Yamamura
authors.forename: T P
authors.initials: TP
authors.lastname: Davis
mesh_terms: D000701:Analgesics, Opioid / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D002199:Capillary Permeability / Q000187:drug effects; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000737:chemistry / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D007455:Iodine / Q000737:chemistry; D051379:Mice; D008813:Mice, Inbred ICR; D010147:Pain Measurement / Q000187:drug effects; D011092:Polyethylene Glycols / Q000737:chemistry*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D000701:Analgesics, Opioid; D011092:Polyethylene Glycols; D020881:Enkephalin, D-Penicillamine (2,5)-; D007455:Iodine