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Synthesis and evaluation of potential affinity labels derived from endomorphin-2
H Choi1, T F Murray, J V Aldrich
1Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, USA.
Summary
Researchers modified endomorphin-2 to create peptide-based affinity labels for mu-opioid receptors. The best analog, [Phe(p-NH2)4]endomorphin-2, showed high mu-receptor affinity, aiding in opioid receptor research.
Area of Science:
- Medicinal Chemistry
- Neuroscience
- Pharmacology
Background:
- Endomorphin-2 is a potent and selective endogenous ligand for mu-opioid receptors.
- Developing peptide-based affinity labels is crucial for studying opioid receptor interactions.
Purpose of the Study:
- To synthesize and evaluate endomorphin-2 analogs as potential peptide-based affinity labels for opioid receptors.
- To identify modifications that enhance binding affinity and selectivity for mu-opioid receptors.
Main Methods:
- Standard Fmoc-solid phase peptide synthesis was employed to create tetrapeptide analogs.
- Electrophilic groups (isothiocyanate, bromoacetamide) were introduced at the para position of Phe3 or Phe4.
- Radioligand-binding assays using Chinese hamster ovary (CHO) cells expressing mu- and delta-opioid receptors were performed.
Main Results:
- Modification at Phe4 was better tolerated for mu-receptor binding compared to Phe3.
- [Phe(p-NH2)4]endomorphin-2 exhibited the highest affinity (IC50 = 37 nm) for mu-receptors.
- The Phe(p-NHCOCH2Br)4 analog showed the highest mu-receptor affinity (IC50 = 158 nm) among labeled peptides, with negligible delta-receptor binding.
Conclusions:
- Peptide modifications on endomorphin-2 can yield potent affinity labels for mu-opioid receptors.
- The Phe(p-NH2)4 analog represents a promising tool for investigating mu-opioid receptor pharmacology.
- These findings contribute to the development of novel probes for opioid receptor research.