bombesin--tyr(4)- and Carcinoma--Small-Cell

The ability of reduced peptide bond analogues of gastrin releasing peptide (GRP) to antagonize small cell lung cancer (SCLC) GRP receptors was investigated. BW462U89, BW1023U90, BW2123U89 and BW2258U89 inhibited binding of (125I-Tyr4) BN to NCI-H345 cells with IC50 values of 5, 6, 140 and 10 nM respectively. The GRP analogues had no effect on basal cytosolic Ca2+ but inhibited the increase caused by 10 nM BN. BW462U89 reversibly blocked the increase in cytosolic Ca2+ caused by BN. The GRP analogues (1 microM) inhibited NCI-H345 colony formation in the absence or presence of 10 nM BN. Also, BW2258U89 (0.4 mg/kg, s.c. daily) inhibited xenograft growth in nude mice. These data indicate that BW2258U89 inhibits SCLC growth in vitro and in vivo.

Topics: Amino Acid Sequence; Animals; Bombesin; Calcium; Carcinoma, Small Cell; Humans; Lung Neoplasms; Mice; Mice, Nude; Molecular Sequence Data; Neoplasm Transplantation; Oligopeptides; Receptors, Bombesin; Structure-Activity Relationship; Tumor Cells, Cultured

To examine the biochemical basis for growth factor-induced responses in human lung cancer cells, we used the quin2 technique to study the effect of the amphibian peptide bombesin and its congeners including mammalian gastrin-releasing peptide (GRP) on the intracellular free calcium level [Ca2+]i in small cell lung cancer cell lines. In five of eleven cell lines tested, Tyr4-bombesin or GRP elicited a rapid and transient increase in [Ca2+]i. The response was seen with as little as 1 nM ligand, was not affected by membrane depolarization, and derived in part from internal calcium stores. Desensitization to a second addition of active bombesin congeners occurs subsequent to initial addition of Tyr4-bombesin. Structure-activity analysis showed the carboxyl-terminal octapeptide was the active portion of the peptide. Analogs in which the carboxyl terminus was oxidized or deamidated were inactive. Ranatensin, litorin, alytesin, and GRP, but not physalaemin, were as active as Tyr4-bombesin. A monoclonal antibody to the carboxyl terminus of bombesin selectively blocked the increased [Ca2+]i elicited by Tyr4-bombesin. These studies suggest that bombesin congeners can act on some small cell lung cancer cell lines by a pathway utilizing increased [Ca2+]i.

Topics: Amino Acid Sequence; Bombesin; Calcium; Carcinoma, Small Cell; Cell Line; Dose-Response Relationship, Drug; Gastrin-Releasing Peptide; Humans; Kinetics; Lung Neoplasms; Oligopeptides; Peptides; Pyrrolidonecarboxylic Acid; Structure-Activity Relationship

The binding of a radiolabeled bombesin analogue to human small cell lung cancer (SCLC) cell lines was investigated. (125I-Tyr4)bombesin bound with high affinity (Kd = 0.5 nM) to a single class of sites (2,000/cell) using SCLC line NCI-H446. Binding was reversible, saturable and specific. The pharmacology of binding was investigated using NCI-H466 and SCLC line NCI-H345. Bombesin and structurally related peptides, such as gastrin releasing peptide (GRP), but not other peptides, such as substance P or vasopressin, inhibited high affinity (125I-Tyr4)BN binding activity. Finally, the putative receptor, a 78,000 dalton polypeptide, was identified by purifying radiolabeled cell lysates on bombesin or GRP affinity resins and then displaying the bound polypeptides on sodium dodecylsulfate polyacrylamide gels. Because SCLC both produces bombesin/GRP-like peptides and contains high affinity receptors for these peptides, they may function as important autocrine regulatory factors for human SCLC.

Topics: Bombesin; Carcinoma, Small Cell; Cell Line; Chromatography, Affinity; Gastrin-Releasing Peptide; Humans; Kinetics; Lung Neoplasms; Peptides; Receptors, Bombesin; Receptors, Cell Surface; Substance P; Vasopressins