Fluorescent-labeled bioconjugates of the opioid peptides biphalin and DPDPE incorporating fluorescein-maleimide linkers

  • Future Med Chem. 2017 Jun;9(9):859-869. doi: 10.4155/fmc-2016-0232.
Azzurra Stefanucci  1 ,  Wei Lei  2 ,  Victor J Hruby  3 ,  Giorgia Macedonio  1 ,  Grazia Luisi  1 ,  Simone Carradori  1 ,  John M Streicher  2 ,  Adriano Mollica  1
Affiliations
  • 1. Dipartimento di Farmacia, Università di Chieti-Pescara "G. d'Annunzio", Via dei Vestini 31, 66100 Chieti, Italy.
  • 2. Department of Pharmacology, College of Medicine, University of Arizona, 85721 AZ, USA.
  • 3. Department of Chemistry & Biochemistry, College of Science, University of Arizona, 85721 AZ, USA.
PMID: 28635314 DOI: 10.4155/fmc-2016-0232
Abstract

Aim: The conjugation of fluorescent labels to opioid peptides is an extremely challenging task, which needs to be overcome to create new classes of probes for biological assays.

Materials & methods: Three opioid peptide analogs of biphalin and [D-Pen2,5]-Enkephalin (DPDPE) containing a fluorescein-maleimide motif were synthesized.

Results & discussion: The biphalin analog 17 binds to opioid receptors with Kiμ = 530 ± 90 nM and Kiδ = 69.8 ± 16.4 nM. We then tested the ability of the compounds to stimulate G-protein-coupling, 17 activated μ-receptor expressing cells (EC50 = 16.7 ± 6.7 nM, EMax = 76 ± 4%) as well as δ-receptor expressing cells (EC50 = 42 ± 10 nM, EMax = 34 ± 8%). However, 17 was not able to fluorescently label receptor in live or fixed cells.

Conclusion: Our data suggest that the biphalin scaffold could be employed to develop fluorescent ligands with the appropriate fluorescent motif, and suggest a means for further probe development.

Keywords
DPDPE; GPCRs; biphalin; fluorescein; fluorescent probes; opioid peptides.
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