The gastrointestinal peptide cholecystokinin (CCK) is known to stimulate growth of human pancreatic cancer in a receptor-mediated fashion. The purpose of this study was to characterize the receptor responsible for the trophic effects of CCK in cancer cells. With the use of homogenates of PANC-1 human pancreatic cancer cells grown in vitro, the binding characteristics and optimal conditions of radiolabeled selective CCK-receptor antagonists ([3H]L-365,260 and [3H]L-364,718) were examined. Specific and saturable binding was detected with [3H]L-365,260, and Scatchard analysis revealed that the data were consistent for a single site of binding with a binding affinity of 4.3 +/- 0.6 nM and a binding capacity (Bmax) of 283 +/- 68 fmol/mg protein in log phase cells. Binding was dependent on protein concentration, time, temperature, and pH and was sensitive to Na+, K+, Mg2+, and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. In contrast to log phase cells, Bmax decreased by 80 and 92% in confluent and postconfluent cultures, respectively. Subcellular fractionation studies revealed that binding was in the membrane fraction. Competition experiments indicated that L-365,260 and gastrin were more effective at displacing the radiolabeled L-365,260 than CCK. No binding was detected with the CCK-A antagonist [3H]L-364,718. Assays performed with [3H]L-365,260 on five additional human pancreatic cancer cell lines in vitro and tumor tissue from xenografts in nude mice also revealed specific and saturable binding. These results provide the first identification of a CCK-B/gastrin receptor in human pancreatic cancer cells and tumors and explain the effects of CCK on the growth of this malignancy.
Differential modulation of nicotine-induced gemcitabine resistance by GABA receptor agonists in pancreatic cancer cell xenografts and in vitro
