Binding of the novel radioligand [3H]UFP-101 to recombinant human and native rat nociceptin/orphanin FQ receptors

Massimo Ibba, Masato Kitayama, John McDonald, Girolamo Calo, Remo Guerrini, Judit Farkas, Geza Toth, David G. Lambert

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16 Citations (Scopus)


Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide receptor (NOP). Binding studies have relied on [leucyl- 3H]N/OFQ, but as this is an agonist G-protein coupling will affect affinity. In this paper, we describe a new [3H]labeled NOP antagonist, [Nphe1,4'-3H-Phe4,Arg 14,Lys15]N/OFQ-NH2 ([3H]UFP-101). We have characterized [3H]UFP-101 at recombinant human NOP expressed in Chinese hamster ovary cells (CHOhNOP) and native rat NOP in cerebrocortex. Radioligand saturation and competition studies were performed on membranes, and [3H]UFP-101 (antagonist) was compared with [ 3H]N/OFQ (agonist). The effects of GTPγS (10 μM) and Na + were investigated alone and in combination in competition experiments with both radioligands. In CHOhNOP, B max, and pK D, values were 561 and 580 fmol mg protein-1 and 9.97 and 10.19 for [3H]UFP-101 and [leucyl-3H]N/OFQ, respectively. In rat cerebrocortex B max and pK D, values were 65 and 88 fmol mg protein-1 and 10.12 and 10.34 for [ 3H]UFP-101 and [leucyl-3H]N/OFQ. The binding of both radioligands was displaced by a range of peptide and non-peptide NOP ligands at both isoforms with good correlation (r 2 0.92 in Rat and 0.97 in CHOhNOP). Naloxone was inactive. The binding of both radioligands was Na+-dependent with [3H]UFP-101 being more sensitive (IC50 ~20 mM). Unlike the agonist [leucyl-3H]N/OFQ, the antagonist [3H]UFP-101 was unaffected by GTPγS. [ 3H]UFP-101 binds to human and rat NOP with high affinity and good agreement with standard [leucyl-3H]N/OFQ in competition experiments. In addition, the binding of [3H]UFP-101 is unaffected by GTPγS. This radioligand will be useful to further characterize NOP in a range of binding paradigms.

Original languageEnglish
Pages (from-to)553-561
Number of pages9
JournalNaunyn-Schmiedeberg's Archives of Pharmacology
Issue number6
Publication statusPublished - Dec 1 2008


  • Guanine nucleotides
  • NOP receptor
  • Nociceptin/Orphanin FQ
  • Radiolabeled Nociceptin/Orphanin FQ receptor antagonist [H]UFP-101
  • Radioligand binding

ASJC Scopus subject areas

  • Pharmacology

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