Pharmacodynamic and Pharmacokinetic Characterization of Poly(Ethylene glycol) Conjugation to Met-Enkephalin Analog [d-Pen2,d-Pen5]-enkephalin (DPDPE)

  1. Ken A. Witt1,
  2. Jason D. Huber1,
  3. Richard D. Egleton1,
  4. Michael J. Roberts2,
  5. Michael D. Bentley2,
  6. Lihong Guo2,
  7. Hongbing Wei1,
  8. Henry I. Yamamura1 and
  9. Thomas P. Davis1
  1. 1Department of Pharmacology, University of Arizona, College of Medicine, Tucson, Arizona (K.A.W., J.D.H., R.D.E., H.W., H.I.Y., T.P.D.); and 2Shearwater Corporation, Huntsville, Alabama (M.J.R., M.D.B., L.G.)
  1. Dr. Thomas P. Davis, Department of Pharmacology, College of Medicine, University of Arizona, P.O. Box 245050, Tucson, AZ 85712. E-mail:davistp{at}u.arizona.edu

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 δ-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 [125I]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 [125I]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 μM 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.

Footnotes

  • This research was supported by National Institute on Drug Abuse Grants DA 11271 and DA 06284 and a gift from the Shearwater Corporation.

  • Abbreviations:
    PEG
    poly(ethylene glycol)
    DPDPE
    [d-Pen2,d-Pen5]-enkephalin
    GI
    gastrointestinal
    BBB
    blood-brain barrier
    P-gp
    P-glycoprotein
    CNS
    central nervous system
    DAMGO
    [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin
    RP-HPLC
    reverse phase-high pressure liquid chromatography
    TFA
    trifluoroacetic acid
    %MPE
    percent maximal possible effect
    CSF
    cerebrospinal fluid
    BBMEC
    bovine brain microvascular endothelial cell
    ANOVA
    analysis of variance
    CL
    clearance rate
    Vd
    volume of distribution
    fu
    unbound fraction
    AUC
    area under the curve
    Rcell%
    percent ratio of cellular uptake
    • Received March 9, 2001.
    • Accepted April 2, 2001.
« Previous | Next Article »Table of Contents

This Article

  1. JPET August 1, 2001 vol. 298 no. 2 848-856
  1. » Abstract
  2. Full Text
  3. Full Text (PDF)

Responses

  1. Submit a response
  2. No responses published

Current Issue

  1. November 2009, 331 (2)
  1. Current Issue
  1. Alert me to new issues of JPET