IDENTIFICATION AND CHARACTERIZATION OF CCK-B GASTRIN RECEPTORS IN HUMAN PANCREATIC-CANCER CELL-LINES/

The gastrointestinal peptide cholecystokinin (CCK) is known to stimula te growth of human pancreatic cancer in a receptor-mediated fashion. T he purpose of this study was to characterize the receptor responsible for the trophic effects of CCK in cancer cells. With the use of homoge nates of PANC-1 human pancreatic cancer cells grown in vitro, the bind ing characteristics and optimal conditions of radiolabeled selective C CK-receptor antagonists ([H-3]L-365,260 and [H-3]L-364,718) were exami ned. Specific and saturable binding was detected with [H-3]L-365,260, and Scatchard analysis revealed that the data were consistent for a si ngle site of binding with a binding affinity of 4.3 +/- 0.6 nM and a b inding capacity (B-MAX) of 283 +/- 68 fmol/mg protein in log phase cel ls. Binding was dependent on protein concentration, time, temperature, and pH and was sensitive to Na+, K+, Mg2+, and ethylene and glycol-bi s(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. In contrast to lo g phase cells, B-MAX decreased by 80 and 92% in confluent and postconf luent cultures, respectively. Subcellular fractionation studied reveal ed 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 [H-3]L-364,718. Assays performed with [H-3]L-365,260 on five additional human pancreatic cancer cell lines in vitro and tu mor tissue from xenografts in nude mice also revealed specific and sat urable binding. These results provide the first identification of a CC K-B/gastrin receptor in human pancreatic cancer cells and tumors and e xplain the effects of CCK on the growth of this malignancy.