CYCLIC CHOLECYSTOKININ ANALOGUES EXHIBIT HIGH BLOOD STABILITY AND BINDING AFFINITY WITH CHOLECYSTOKININ RECEPTOR

Recently, incidence of Cholecystokinin (CCK) receptor is recognized as a factor that determines the aggressive phenotype of pancreatic cancer. In this study, a novel Cholecystokinin (CCK) analogues; DOTA-Nle-cyclo (Glu-Trp-Met-Asp-Phe-Lys-NH2) (DOTA-cCCK) and DOTA-Nle-cyclo (Glu-Trp-Nle-Asp-Phe-Lys-NH2) (DOTA-[Nle]-cCCK) were synthesized and radiolabeled and the targeting abilities on the CCK receptor were evaluated for new CCK receptor targeting agents searching. Peptides were prepared through a solid phase synthesis method and their purity was over 98%. DOTA is the chelating agent for 68Ga-labelling, which the peptides were radiolabeled with 68Ga by a high radiolabeling yield (>98%). Peptides were stable over 98% by incubation in mouse blood at 37°C for 2 h. A competitive displacement of 125I-CCK8 on the AR42J human pancreatic carcinoma cells revealed that 50% inhibitory concentration value (IC50) were 12.31 nM of DOTA-cCCK and 1.69 nM of DOTA-[Nle]-cCCK. Stable in the blood of both DOTA-cCCK and DOTA-[Nle]-cCCK, but the binding rate with the CCK receptor on AR42J cells, DOTA-[Nle]-cCCK confirmed better than DOTA-cCCK. Therefore, it is concluded that 68Ga-DOTA-[Nle]-cCCK can be potential candidate as a targeting modality for the CCK receptor over-expressing tumors and further studies to evaluate their biological characteristics are needed.