EFFECTS OF NEUROPEPTIDE ANALOGS ON CALCIUM FLUX AND PROLIFERATION IN LUNG-CANCER CELL-LINES

Small cell lung cancers (SCLC) and some non-small cell lung cancers (N SCLC) have neuroendocrine features which include production of a varie ty of neuropeptides, cell surface expression of the receptors for thes e peptides, and autocrine stimulation by the peptides. Previous studie s showed that some peptide antagonists and anti peptide antibodies inh ibited the growth of SCLC cell lines which expressed receptors for the specific peptide. We and others showed that the heterogeneity of pept ide receptor expression and responsiveness was a major potential obsta cle for developing therapeutic uses of peptide antagonists. In this ma nuscript we evaluated the effects of 11 peptide antagonists (3 bombesi n-specific, 2 cholecystokinin-specific, 1 arginine vasopressin (AVP)-s pecific, and 5 substance P derivatives with broad specificity) on pept ide-induced calcium mobilization and growth of SCLC and NSCLC cell lin es. For each antagonist, we determined the dose-response effects, spec ificity of peptide antagonism, and biological stability in serum using Indo-1AM-based flow cytometric assays. We found that the three bombes in antagonists, S30, SC196, and L336,175, varied in potency from 10 nM to 10 mu M, varied in serum stability from 6 h to more than 24 h, and had no effect on the calcium response elicited by other peptides. Non e of these compounds effectively inhibited the growth of SCLC cell lin es in [H-3]dThd and cell growth assays in vitro. Similarly, the three cholecystokinin and AVP antagonists were highly specific for cholecyst okinin and AVP, respectively, had widely varying potency, but had litt le inhibitory effect on SCLC growth in vitro. In contrast, the five su bstance P derivatives inhibited the calcium response to bombesin, AVP, bradykinin, and fetal bovine serum. None of these five antagonists we re as potent as the six specific antagonists described above, but they were more effective in inhibiting the growth of SCLC cell lines in vi tro. These substance P derivatives inhibited the growth of peptide-sen sitive SCLC cell lines more efficiently than their inhibition of pepti de-insensitive NSCLC or breast cancer cell lines. Relatively high conc entrations of these substance P derivatives were required to inhibit i n vitro growth, even in the absence of added peptide. It is likely tha t more potent broad spectrum antagonists, toxins, or radio-labeled sta ble antagonists will need to be developed for maximal clinical develop ment of this type of anti-growth factor therapy.