Receptorphin: A conserved peptide derived from the sequence of the opioid receptor, with opioid displacement activity and potent antiproliferative actions in tumor cells

Marilena Kampa¹ , Spyros Loukas² , Andreas Tsapis³ and Elias Castanas¹

¹Laboratory of Experimental Endocrinology, University of Crete, School of Medicine, P.O. Box 1393, Heraklion, GR-71110, Greece

²Laboratory of Proteins and Bioactive Peptides, NCSR "Demokritos", Institute of Biology, Aghia Paraskevi 15310, Greece

³U131 INSERM, Clamart, France

author email corresponding author email

BMC Pharmacology 2001, 1:9doi:10.1186/1471-2210-1-9


Published:	27 November 2001

Abstract

Background

In addition to endogenous opioids, a number of peptide sequences, derived from endogenous (hemorphins, alphaS1-casomorphin), and exogenous proteins (casomorphins, exorphins) have been reported, possessing opioid activity. In the present work, we report the identification of a new peptide, receptorphin (Tyr-Ile-Phe-Asn-Leu), derived from the sequence of the second transmembrane loop of the opioid receptor. This sequence is unique for the opioid receptor, and conserved in all species and receptor-types.

Results and Discussion

Receptorphin competes for opioid binding, presenting a kappa-receptor interaction, while it binds equally to delta- and mu- opioid and somatostatin-binding sites, and inhibits the cell proliferation of a number of human cancer cell lines, in a dose-dependent and reversible manner, at the picomolar or the nanomolar range. Receptorphin shows a preferential action on prostate cancer cells.

Conclusion

Our work identifies, for the first time a peptide, in a receptor sequence, possessing ligand-agonistic activities. A hypothesis, based on receptorphin liberation after cell death, is presented, which could tentatively explain the time-lag observed during opioid antiproliferative action.