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Modification with Organometallic Compounds Improves Crossing of the Blood–Brain Barrier of [Leu 5 ]‐Enkephalin Derivatives in an In Vitro Model System
Author(s) -
Pinto Antonio,
Hoffmanns Ulrich,
Ott Melanie,
Fricker Gert,
MetzlerNolte Nils
Publication year - 2009
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200900157
Subject(s) - chemistry , lipophilicity , moiety , peptide , enkephalin , combinatorial chemistry , permeation , leu enkephalin , dendrimer , selectivity , stereochemistry , organic chemistry , membrane , receptor , biochemistry , opioid , catalysis
Enkephalin peptides are thought to be suitable vectors for the passage of the blood–brain barrier (BBB). Modifications that do not alter the amino acid sequence are often used to improve the permeation through living membrane systems. As a new type of modification we introduce organometallic compounds, in particular ferrocene carboxylic acid. Derivatives of [Leu 5 ]enkephalin were synthesised and labelled with organometallic compounds by using solid‐phase synthesis techniques. All new metal–peptide bioconjugates were comprehensively characterised by HPLC, NMR spectroscopy and mass spectrometry and found to be at least 95 % pure. For the first time, permeation coefficients in a BBB model for organometal–peptide derivatives were determined in this work. The uptake and localisation of fluorescein‐labelled enkephalins was monitored by fluorescence microscopy on three cancer cell lines. Octanol/H 2 O partition coefficients of the compounds were measured by HPLC. The introduction of the organometallic moiety enhances the uptake into cells and the permeation coefficient of [Leu 5 ]‐enkephalin. This could be due to an increase in lipophilicity caused by the organometallic label. The metal–peptide conjugates were found to be nontoxic up to m M concentrations. The low cytotoxicity encourages further experiments that could take advantage of the selectivity of enkephalin derivatives for opioid receptors.