title: Dermorphin-based potential affinity labels for mu-opioid receptors.
abstract: Dermorphin and [Lys7]dermorphin, selective micro -opioid receptor ligands originating from amphibian skin, have been modified with various electrophiles in either the 'message' or 'address' sequences as potential peptide-based affinity labels for micro -receptors. Introduction of the electrophilic isothiocyanate and bromoacetamide groups on the para position of Phe3 and Phe5 was accomplished by incorporating Fmoc-Phe(p-NHAlloc) into the peptide followed by selective deprotection and modification. The corresponding amine-containing peptides were also prepared. The pure peptides were evaluated in radioligand binding experiments using Chinese hamster ovary (CHO) cells expressing micro - and delta-opioid receptors. In dermorphin, introduction of the electrophilic groups in the 'message' domain lowered the binding affinity by > 1000-fold; only [Phe(p-NH2)3]dermorphin retained nanomolar affinity for micro -receptors. Modifications in the 'address' region of both dermorphin and [Lys7]dermorphin were relatively well tolerated. In particular, [Phe(p-NH2)5,Lys7]dermorphin showed similar affinity to dermorphin, with almost 2-fold higher selectivity for micro -receptors. [Phe(p-NHCOCH2Br)5]- and [Phe(p-NHCOCH2Br)5,Lys7]dermorphin exhibited relatively high affinity (IC50 = 27.7 and 15.1 nm, respectively) for micro -receptors. However, neither of these peptides inhibited [3H]DAMGO binding in a wash-resistant manner.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, USA.
authors.forename: H
authors.initials: H
authors.lastname: Choi
authors.forename: T F
authors.initials: TF
authors.lastname: Murray
authors.forename: J V
authors.initials: JV
authors.lastname: Aldrich
mesh_terms: D000345:Affinity Labels / Q000138:chemical synthesis* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D005260:Female; D020128:Inhibitory Concentration 50; D017879:Isothiocyanates / Q000737:chemistry; D008024:Ligands; D009842:Oligopeptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018847:Opioid Peptides; D010649:Phenylalanine / Q000737:chemistry; D011869:Radioligand Assay; D017465:Receptors, Opioid, delta / Q000737:chemistry / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D017879:Isothiocyanates; D008024:Ligands; D009842:Oligopeptides; D018847:Opioid Peptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; C030058:dermorphin; D010649:Phenylalanine