Modification with Organometallic Compounds Improves Crossing of the Blood–Brain Barrier of [Leu5]‐Enkephalin Derivatives in an In Vitro Model System |
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Authors: | Antonio Pinto Ulrich Hoffmanns Dr. Melanie Ott Gert Fricker Prof. Dr. Nils Metzler‐Nolte Prof. Dr. |
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Affiliation: | 1. Faculty of Chemistry and Biochemistry, Ruhr‐Universit?t Bochum, Universit?tsstrasse 150, 44801 Bochum (Germany), Fax: (+49)?234‐32‐14378;2. Institut für Pharmazie und Molekulare Biotechnologie, Universit?t Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg (Germany) |
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Abstract: | 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 [Leu5]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/H2O 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 [Leu5]‐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 mM concentrations. The low cytotoxicity encourages further experiments that could take advantage of the selectivity of enkephalin derivatives for opioid receptors. |
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Keywords: | bioorganometallic chemistry blood– brain barrier neuropeptides peptides solid‐phase synthesis |
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