Abstract

The effects of cholecystokinin (CCK) antagonists on small cell lung cancer (SCLC) cells were investigated. CI-988, L-365,260, and L-364,718 inhibited specific ¹²⁵I-CCK-8 binding to NCI-H209 cells with IC₅₀ values of 5, 2, and 200 nM. ([R-(R*,R*)]-4[[2-[[3-(1H-Indole-3-yl)-2-methyl-1-oxo-2-[[tricyclo[3.3.1.1^3,7]- dec-2-yloxy)carbonyl[amino]propyl]amino]-1-phenylethyl]amino]-4-oxobutanoic acid) (CI-988; 100 nM) inhibited the ability of 10 nM CCK-8 to elevate cytosolic Ca²⁺ in 1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2′-amino-5′-methylphenoxy)-ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl ester-loaded NCI-H209 cells. By Western blot, CI-988 inhibited tyrosine phosphorylation of focal adhesion kinase and paxillin stimulated by CCK-8. Also, CI-988 inhibited tyrosine phosphorylation of mitogen-activated protein kinase stimulated by CCK-8. By Northern blot, CI-988 antagonized the ability of 10 nM CCK-8 to increase c-fos mRNA in NCI-H209 cells. Also, CI-988 inhibited the ability of CCK-8 to increase vascular endothelial cell growth factor mRNA. Using a [3-(4,5 dimethylthiazol-2-yl)-2.5-diphenyl-2H-tetrazolium bromide] and clonogenic assay, CI-988 inhibited the proliferation of NCI-H209 cells in vitro. Using nude mice, CI-988 inhibited the proliferation of NCI-H209 xenografts. These results suggest that CI-988 is a CCK₂ receptor antagonist that inhibits the proliferation of SCLC cells.