IDENTIFICATION, CHARACTERIZATION, AND BIOLOGICAL-ACTIVITY OF SOMATOSTATIN RECEPTORS IN HUMAN NEUROBLASTOMA CELL-LINES

To investigate the presence of biologically active somatostatin (SS) r eceptors in neural crest-derived tumors, radioligand binding studies, cyclic AMP accumulation, intracellular calcium, and growth assays were performed in eight human neuroblastoma (NB) cell lines. Mathematical modeling of binding experiments strongly indicates the presence of het erogeneity of sites. The first site (SS(R1)) is present in 40% of the NB cell lines and binds with low capacity (0.5 pmol/mg protein) and hi gh affinity (0.1-1 nM) SS14, SS28, and analogues. The second site (SS( R2)) is a high capacity site (200 pmol/mg protein), widely distributed in all of the cell lines investigated, that shows relative selectivit y vet low affinity (100 nM) for SS14, SS28, and [D-Trp8]SS14 without a ny apparent biological activity. SS(R1) is coupled to a pertussis toxi n-sensitive G protein, inhibits forskolin- or VIP-stimulated adenylate cyclase activity, decreases intracellular free calcium, and mediates inhibition (30%) of both DNA synthesis and cell growth. Analysis of ce ll cycle distribution in aphidicolin-synchronized SS(R1)-positive NB c ells indicated that this inhibitory effect is partially mediated by a transient accumulation in G0-G1. Our data indicate high affinity bindi ng sites for SS14, and analogues are present and biologically active i n a subset of NB cells.