bombesin--tyr(4)- and Adenocarcinoma

Gut hormones that modulate the growth of normal pancreas may also modulate the growth of cancers originating from pancreas. This study visualized and compared the receptors for cholecystokinin (CCK), bombesin (BBS), secretin and vasoactive intestinal peptide (VIP) in tumour-free tissue sections of human pancreas (n = 10) and pancreatic ductal adenocarcinomas (n = 12) with storage phosphor autoradiography using radioligands. CCK-B receptors, present in control pancreata, were not detected in any of the pancreatic cancers. BBS receptors were visualized in control pancreata, but they were absent in 10 of 12 pancreatic cancers. In 5 of 12 pancreatic cancers, receptors for secretin were visualized, while binding for secretin was present in all tumour-free pancreata. Conversely, no specific binding of VIP was detected in control pancreata but was identified in 3 of 12 pancreatic cancer specimens. It is concluded that the expression of gut peptide receptors in pancreatic cancer differs from that in tumour-free pancreas. Receptors for these peptides are present in only a minority of pancreatic cancer specimens.

Topics: Adenocarcinoma; Adult; Aged; Autoradiography; Bombesin; Female; Humans; Iodine Radioisotopes; Kinetics; Male; Middle Aged; Pancreas; Pancreatic Neoplasms; Receptors, Bombesin; Receptors, Cholecystokinin; Receptors, G-Protein-Coupled; Receptors, Gastrointestinal Hormone; Receptors, Vasoactive Intestinal Peptide; Secretin; Sensitivity and Specificity; Sincalide; Succinimides

Binding of the radiolabeled bombesin analog [125I-Tyr4]bombesin to crude cell membranes of MKN45 human gastric cancer grown in nude mice was investigated in vitro. Scatchard analyses of multipoint binding data, performed by complete displacement method demonstrated the presence of two classes of [Tyr4]bombesin binding sites. The high-affinity binding sites had a mean dissociation constant (Kd1) of 2.75 nM with a mean maximal binding capacity (Bmax1) of 492 fmol/mg membrane protein, while the low-affinity binding sites showed a mean dissociation constant (Kd2) of 0.41 microM with a mean maximal binding capacity (Bmax2) of 41.4 pmol/mg membrane protein. Binding of [125(1)-Tyr4]bombesin was specific, reversible and linearly related to the protein concentration of tumor membrane. In displacement studies, the binding of radiolabeled [Tyr4]bombesin was inhibited in a dose-dependent manner by gastrin releasing peptide (GRP)(14-27) and two synthetic antagonists of bombesin/GRP, RC-3095 and RC-3950-II. Both antagonists exhibited high affinity in nearly the same concentration range as GRP(14-27). The presence of receptors for bombesin/GRP on human gastric cancer membranes suggests that bombesin-like peptides may play a role in growth of gastric cancer.

Topics: Adenocarcinoma; Animals; Binding Sites; Binding, Competitive; Bombesin; Cell Membrane; Female; Humans; Iodine Radioisotopes; Kinetics; Mice; Mice, Nude; Middle Aged; Neoplasm Transplantation; Receptors, Bombesin; Sensitivity and Specificity; Stomach Neoplasms; Transplantation, Heterologous; Tumor Cells, Cultured

The bombesin family of peptides elicit numerous biological responses in the gut, including stimulation of cell proliferation, and have been implicated as growth factors in a variety of gastrointestinal tumors. Even though these peptides and their receptors are distributed throughout the gastrointestinal tract, there are few cell lines available as model systems to study bombesin action in gastrointestinal cells. In this study, we have characterized functional bombesin receptors in a human duodenal cancer cell line, HuTu-80. The binding of [125I-Tyr4]bombesin to intact cells at 4 degrees C reached equilibrium by 6 h. Scatchard analysis of [125I-Tyr4]bombesin binding showed that HuTu-80 cells contained a single class of high affinity binding sites (5900 +/- 1960/cell; Kd = 80 +/- 20 pM). [125I-Tyr4]bombesin binding was inhibited by bombesin receptor agonists and antagonists with the following order of potencies: gastrin-releasing peptide (GRP) = GRP-(14-27) = bombesin > [DPhe6]bombesin(6-13)ethylamide > [Leu13 psi-(CH2NH)Leu14]bombesin > neuromedin B. Photoaffinity cross-linking studies, in which N-5-azido-2-nitrobenzoyloxysuccinimide was used to covalently couple [125I]GRP(14-27) to cells at 4 degrees C, resulted in the specific labeling of a broad band with an apparent molecular mass of 66,000 daltons. Consistent with the presence of high affinity receptors, bombesin increased the formation of inositol phosphates in HuTu-80 cells in a dose-dependent manner (concentration eliciting half-maximal effect, 290 +/- 70 pM). However, under conditions where both insulin and serum increased [3H]thymidine incorporation into DNA, 10 nM bombesin had no effect either alone or in the presence of insulin. Bombesin also had no effect on colony formation by HuTu-80 cells in soft agar. Furthermore, the bombesin receptor antagonist, [Leu13 psi(CH2NH)Leu14]bombesin, did not inhibit [3H]thymidine incorporation or clonal growth either in the absence or in the presence of serum. Together, these results show that HuTu-80 cells contain high affinity bombesin receptors of the GRP subtype. These receptors are functionally coupled to second messenger production but do not stimulate cell proliferation.

Topics: Adenocarcinoma; Affinity Labels; Amino Acid Sequence; Bombesin; Duodenal Neoplasms; Humans; Iodine Radioisotopes; Kinetics; Molecular Sequence Data; Receptors, Bombesin; Tumor Cells, Cultured