¹²⁵I-(Thr₃₄, Nle₃₇)- CCK_31–39 A Non Oxidizable Tracer for the Characterization of CCK Receptor on Pancreatic Acini and Radio-Immunoassay of C-Terminal CCK Peptides

Abstract

A derivative of the C-terminal nonapeptide of CCK, namely (Thr₃₄, Nle₃₇) - CCK_31–39 was radio-iodinated by conjugation with ¹²⁵I-Bolton-Hunter reagent. The labelled peptide was purified by RP-HPLC on a C-18 column. Validation of the iodinated peptide was performed by measuring its biological integrity and by studying its binding characteristics on pancreatic acini. ¹²⁵I-(Thr, Nle)-CCK-9 present the same ability to stimulates amylase release than (Thr, Nle)- CCK-9 and CCK-8. Binding of the radio-ligand to CCK receptors is specific, reversible, saturable. Inhibition of the binding by CCK-related peptides correlates well their biological potencies. ¹²⁵I-(Thr, Nle)-CCK-9 is able to interact with high affinity CCK receptors. Furthermore, ¹²⁵I-(Thr, Nle)-CCK-9 is recognized by C-terminal CCK directed antibodies. This reliable tracer could be used as a replacement of CCK-8 since it is protected from risks of oxidation.