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C-terminal heptapeptide of gastrin inhibits astrocytomas motility by interacting with a new gastrin binding site.

It is well known that the amidated C-terminal part of gastrin is crucial for its interaction with the classical seven transmembrane domain receptors CCK-1 or CCK-2. Nevertheless, over the past 10 years, several groups have characterized new binding sites using peptides related to gastrin (particularly glycine-extended forms of gastrin) on various tumoral and nontumoral cell lines. In the present study, we focused on the human astrocytic tumoral cell line U373. Although it has been described that gastrin was able to inhibit the motility of these cells, we were unable to detect any classical CCK/gastrin receptor. On the other hand, by using the radiolabeled C-terminal heptapeptide of gastrin ((125)I-G-7), we evidenced a new binding site that possessed a pharmacological profile different from the classical CCK/gastrin receptors. This new gastrin binding site seemed to be coupled to G proteins and be implicated in c-Fos transcription gene. Moreover, we showed that G-7 was able to induce a strong inhibition of U373 cell migration, a crucial biological effect when we know that astrocytoma cells' migration in brain parenchyma constitutes a major feature of malignancy in astrocytic tumors.

Amino Acid Sequence↗

Serum gastrin levels in hypertrophic pyloric stenosis of infancy. Response to a gastrin secretion test.

The aim of this study was to look for a difference in fasting serum gastrin levels or in serum gastrin response to oral feeding between infants with hypertrophic pyloric stenosis and normal controls. Fasting serum gastrin levels were measured by radioimmunoassay in 10 patients with pyloric stenosis, before pyloromyotomy and 7 and 15 days after it, and in 11 controls. In addition, the serum gastrin responses to a casein hydrolysate meal were studied in both groups (in the patients, 7 days after operation). The fasting serum gastrin levels in the patients did not differ from those in the controls before operation, but they did so after it. The serum gastrin response to feeding in patients after pyloromyotomy was no greater than in controls.

Caseins↗

Effects of amidated gastrin and glycine-extended gastrin on cell proliferation and crypt fission in parenterally and orally fed rats.

BACKGROUND/AIMS: It has been suggested that processing variants of gastrin, such as glycine-extended gastrin (G17-Gly), are enterotrophic to the colon. METHODS: Cell proliferation and crypt branching were studied in total parenteral nutrition (TPN) and orally fed rats after infusion of G17-Gly or gastrin-17. RESULTS: Gastrin produced an increase in the weight of the stomach and small intestine and a marked proliferative action on the proximal small intestine, which diminished distally. No proliferative effects of gastrin were seen in the colon. G17-Gly was associated with a small, but significant, increase in colonic weight but had little effect on cell proliferation, except in the gastric fundus. In the distal colon, G17-Gly was associated with a significant decrease in proliferation. Neither agent affected crypt branching in the small intestine or colon, but both proliferation and branching were significantly decreased by TPN. CONCLUSION: Gastrin was trophic to the stomach and the proximal small intestine but not the colon. G17-Gly had only modest proliferative actions on the intestinal epithelium in this study.

Animals↗

The interrelations of gastrin release, antral gastrin concentration and acid secretion rate.

The interrelations of meal stimulated gastrin release, antral gastrin concentration (AGC) and acid secretion rate were examined in a heterogenous group of 72 patients, Gastrin release calculated as the integrated gastrin output was directly related to AGC, r = 0.50 (p less than 0.001) and inversely related to maximum acid output (MAO), r = -0.31 (p less than 0.01). The relation between integrated gastrin output and AGC was significant in 21 patients with low acid secretion rates (MAO: less than 10 mEq/h), r = 0.66 (p less than 0.01) and in 27 patients with normal acid secretion rates (MAO: 10-25 mEq/h), r = 0.56 (p less than 0.05), but not in 24 patients with high acid secretion rates (MAO: greater than 25 mEq/h), r= 0.35 (p greater than 0.05). A weak inverse relation between AGC and MAO may exist in patients with low acid secretion rates, r = -0.40 (p less than 0.10). Considered together using multiple regression procedures AGC and MAO explained less than one-half of the variability in meal stimulated gastrin release.

Food↗

Gastrin 17 vaccine--Aphton: Anti-gastrin 17 immunogen, G17DT.

Aphton is developing an anti-gastrin vaccine [Anti-gastrin 17 immunogen, G17DT, Gastrimmune], which neutralises the gastrin 17 hormone and the Gly-G17 hormone. Gastrin 17 is a growth factor for pancreatic, stomach and colorectal cancers, and a potent stimulator of gastric acid secretion.The anti-gastrin immunogen, G17DT, consists of a large carrier protein, called Diptheria Toxoid (DT). A synthetic peptide, which is similar to a portion of the gastrin 17 hormone (GT), is attached to the carrier protein. These are then contained in a liquid suspension vehicle. When administered to patients, G17DT induces an immune response producing antibodies, which cross-react and neutralise the target hormone thus preventing its interaction with disease-causing or -participating cells. Aphton has entered into an agreement with Aventis Pasteur for the marketing of G17DT in all human cancer indications in North America and Europe. Under the terms of the agreement, Aphton is responsible for product development, clinical trials and regulatory agency approvals. The agreement was originally with Pasteur Mérieux Connaught, a subsidiary of Rhône-Poulenc. However, in December 1999, Rhône-Poulenc merged with Hoechst to form Aventis. As a result of the merger, Pasteur Mérieux Connaught underwent a name change to Aventis Pasteur. In July 2002, Aphton announced that it would negotiate with companies wanting to licence the vaccine in territories other than North America and Europe. In February 2003, Aphton announced it had received fast track designation for G17DT in combination with cisplatin and fluorouracil for use in stage IV gastric cancer to improve overall survival. In July 2002, the US FDA granted G17DT orphan drug status for the treatment of gastric cancer, an indication that was broader than the indication Aphton originally sought. The vaccine was also granted orphan drug status in Australia for gastric cancer in December 2002. In July 2002, Aphton announced that the US FDA had granted G17DT orphan drug status for the treatment of adenocarcinoma of the pancreas. In September 2002, the US FDA also granted G17DT, used in combination with gemcitabine, fast track status for the treatment of pancreatic cancer patients. In addition, the vaccine was also granted orphan drug status in Australia for pancreatic cancer in December 2002. In March 2003, Aphton announced that the Committee for Orphan Medicinal Products had recommended to the European Commission that G17DT be granted orphan drug status for both pancreatic and gastric cancer in the EU. Aphton expects this will be approved and ratified within a few weeks. In August 2002, Aphton filed an IND with the US FDA, as well as the European equivalent, to conduct clinical trials for patients suffering from gastro-esophophageal reflux disease (GERD). The trials will assess, among other endpoints, the efficacy of G17DT in providing symptomatic relief to patients with GERD. In November 2002, Aphton announced that it had received approval to initiate a clinical trial in Europe. Additionally, Aphton has agreed with the FDA to conduct toxicology and other preclinical studies prior to initiation of a trial in the US. Patient recruitment for the European study was scheduled to begin in January 2003.

Animals↗

Gastrin in the human fetus. Distribution and molecular forms of gastrin in the antro-pyloric gland area, duodenum and pancreas.

The ontogeny of human fetal gastrin has been investigated by immunocytochemistry and radioimmunochemistry. Gastrin and gastrin cells are shown to appear later in the antral than in the duodenal mucosa. At the ages studied (11--22 weeks of gestation) pancreatic gastrin could not be detected. Gastrin component III was found to predominate in the antrum, whereas component II was quantitatively very important in the duodenum. Circumstantial evidence suggests that fetal gastrin is delivered to the blood, and that it may exert trophic functions in the fetus.

Duodenum↗

Inhibition of pentagastrin-stimulated up-regulation of gastrin receptors and growth of mouse colon tumor in vivo by proglumide, a gastrin receptor antagonist.

We have recently demonstrated that gastrin stimulates growth of mouse colon cancer (MC-26) in vivo by regulation of gastrin receptors (GR). In the present study, we have tested the effect of proglumide (PGL), a GR antagonist, on the trophic and GR-regulatory effects of gastrin on MC-26 tumors. Four groups of 12 mice each were inoculated with 5 X 10(4) MC-26 cells and given injections of either normal saline (control), pentagastrin (PG), PGL, or both PG + PGL for 21 days. At the end of the treatment period, body, tumor, fundic, and colon weights were noted and GR measured. Two types of specific gastrin-binding sites were found on tumor cell membranes of control mice, one with high binding affinity (Kd = less than 1.0 nM) and low capacity (GR), and the other with a very high capacity and a low affinity (Kd = greater than 0.1 microM) (type 2 gastrin-binding sites). Only the type 1 GR were observed on the fundic mucosal and colon membranes. PG treatment resulted in a significant weight increase of the tumors with an up-regulation of only type 1 GR. On the other hand, PG had no significant effect on fundic mucosal and colonic GR levels, but caused a significant increase in fundic mucosal weights. PGL completely inhibited both the trophic and GR up-regulatory effects of PG on tumors, but incompletely reduced the PG-stimulated fundic mucosal weight gain, indicating differential sensitivity of tumor and normal tissues to PGL. PGL, in the absence of PG, was slightly trophic for normal fundic mucosa, but had no effect on MC-26 tumors and normal colon. The one striking effect of PGL, in the presence of PG, was the significant lowering of the binding affinity of type 1 GR for gastrin on both the tumor and normal gastrointestinal tissues. This effect may be another mechanism by which PGL interferes with the actions of PG on MC-26 tumors and fundic mucosa of mice.

Animals↗

[Gastrin and gastrin receptor].

Gastrin is a well known endogenous stimulator of gastric acid. In addition, recent studies have revealed that gastrin has a growth promoting effect on gastric ECL cells. Indeed, development of ECL carcinoid tumor occurs almost exclusively in patients with hypergastrinemia such as autoimmune gastritis and Zollinger-Ellison syndrome with MEN type I. We have recently cloned human gastrin receptor gene, and by using it, we found that both gastric carcinoid tumor and endocrine cell carcinoma of the stomach express significant amount of gastrin receptor gene whereas none of gastric cancer tissue shows gastrin receptor gene expression. Thus, it is clear that gastrin plays important roles in the development of gastric carcinoid tumor as well as endocrine cell carcinoma of the stomach.

Animals↗

Closing the gastrin loop in pancreatic carcinoma: coexpression of gastrin and its receptor in solid human pancreatic adenocarcinoma.

BACKGROUND: Alpha-amidated gastrin promotes the growth of nontransfected pancreatic cell lines expressing the gastrin/cholecystokinin (CCK)-B receptor. Gastrin/CCK-B and CCK-A receptors recently were demonstrated in human pancreatic adenocarcinomas, but to the authors' knowledge expression of their ligands to date have not been adequately investigated. As a prerequisite for making suggestions regarding local growth stimulation, the authors examined whether gastrin and the homologous CCK peptides as well as their specific receptors were expressed in consecutively collected solid human pancreatic adenocarcinomas. METHODS: Using a library of radioimmunoassays specific for different epitopes on proCCK, progastrin, their processing intermediates, and bioactive end products, CCK and gastrin gene expression was measured in extracts of solid human pancreatic adenocarcinomas (n = 19), resection margins (n = 15), and normal pancreatic tissue (n = 8). Moreover, CCK, CCK-A receptor, and gastrin/CCK-B receptor mRNA were measured by reverse transcriptase-polymerase chain reaction. RESULTS: Amidated gastrins were synthetized in 14 of 19 carcinomas (median, 0.4 pmol/g; range, < 0.1-84.0 pmol/g) and in 12 of 15 resection margin samples (median, 0.3 pmol/g; range, < 0.1-6.1 pmol/g). In contrast, normal human pancreatic tissue expressed only traces of poorly processed progastrin. Gastrin/CCK-B receptor mRNA was present in all carcinomas, resection margins, and normal pancreatic tissue. CCK-A receptor mRNA was detected in most tumors, but neither the mature ligands (alpha-amidated and O-sulfated CCK peptides) nor their precursors were expressed in carcinoma and normal pancreatic tissue. CONCLUSIONS: The results of the current study demonstrate that alpha-amidated gastrin peptides and their receptor invariably are coexpressed in pancreatic adenocarcinoma. Therefore these findings support the contention of a role for local gastrin regulatory mechanisms, but no CCK mechanisms, in pancreatic carcinoma.

Adenocarcinoma↗

Gastrin and gastrin receptor ligands - a review of recent patent literature.

The peptide hormone gastrin is involved in the regulation of acid secretion in the stomach and acts as a growth hormone in the stomach. Although gastrin receptors are expressed in many tumors throughout the body, the clinical significance of this is still unknown. Despite considerable efforts from many pharmaceutical organizations for over a decade, there is as yet no commercially available gastrin ligand. This review covers the patent literature relating both to novel gastrin ligands and to new applications of gastrin and its ligands, including gastrin antibodies, between April 1998 and April 2002.

Journal Article↗

Insulinotropic and gastrin-releasing action of gastrin-releasing peptide (GRP).

The effect of intravenous administration of gastrin-releasing peptide ( GRP ) on serum gastrin and insulin levels was studied in ad libitum fed and 24-h fasted rats. Administration of GRP (55 micrograms/kg body weight) caused a significant (P less than 0.05) elevation in serum gastrin levels at 10, 30, 60, and 120 min in the rats fed ad libitum, whereas in the fasted rats, gastrin levels rose significantly only at 10 min. GRP did not cause insulin release in fasted rats, but in the fed rats, it led to a significant elevation in serum insulin levels at 10 and 30 min, in comparison to controls. GRP appears to have an insulinotropic action in addition to a gastrin-releasing effect.

Animals↗

Somatostatin, gastrin-releasing peptide and gastrin in the stomach of rats with streptozotocin-induced diabetes and insulinoma.

Somatostatin, gastrin-releasing peptide (GRP) and gastrin were measured in the stomach of rats with streptozotocin-induced diabetes, insulinoma-bearing rats and their respective controls. Rats injected with streptozotocin exhibited hyperphagia, insulinopenia and severe hyperglycemia. Stomach weights, and the concentrations and total amounts of GRP and gastrin in the stomach, were similar to nondiabetic control rats. The concentration of somatostatin in the stomach of diabetic rats was 25% greater, but the total stomach content of somatostatin was similar to that of control rats. Insulinoma-bearing rats exhibited hyperphagia, hyperinsulinemia and hypoglycemia. Concentrations of GRP and gastrin in the stomach were 72% and 19% lower, respectively, than in control rats. Despite 45% greater stomach weight, the total stomach content of GRP was 61% lower. Stomach concentrations of somatostatin, and total stomach contents of somatostatin and gastrin, were similar in insulinoma-bearing and control rats. The results demonstrate abnormalities in the stomach concentrations of regulatory peptides in rats with diabetes and insulinoma. These abnormalities are not attributable to changes in food intake alone, suggesting specific effects of these metabolic diseases on gastric regulatory peptides and gastric function.

Animals↗

Effects of cholecystokinin and gastrin antagonists on pancreatic exocrine secretion stimulated by gastrin-releasing peptide.

The effects of a specific cholecystokinin (CCK) receptor antagonist (L364,718) and a gastrin receptor antagonist (L365,260) on gastrin-releasing peptide-10 (GRP-10)-stimulated pancreatic secretion were investigated in the anesthetized rat. GRP-10 stimulated pancreatic exocrine secretion in a dose-dependent manner. A dose of 1.0 nmol/kg/h elicited a significant increase in pancreatic protein output. L364,718 (2.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous CCK-8 (3.0 nmol/kg/h) on pancreatic secretion, did not suppress the excitatory effect of GRP-10. L365,260 (5.0 mg/kg/h), at a dose that completely inhibited the stimulatory effect of exogenous gastrin (20 micrograms/kg/h) on gastric acid secretion, did not suppress the excitatory effect of GRP-10 either. We concluded that CCK or gastrin do not mediate the excitatory mechanism of bombesin/GRP on pancreatic secretion. Since CCK and gastrin are the most probable candidates for excitatory mediator of bombesin/GRP, these results support the hypothesis that bombesin/GRP directly stimulates the exocrine pancreas in the rat.

Animals↗

Stimulation of gastrin release by bombesin and canine gastrin-releasing peptides. Studies with isolated canine G cells in primary culture.

Bombesin, a polypeptide derived from frog skin, has been shown to stimulate gastrin release from the gastric antrum in vivo and in vitro. To elucidate the mechanisms of this effect, we developed a method to culture isolated and enriched G cells from canine stomach. After digestion of antral mucosa with collagenase and EDTA, dispersed cells were fractionated by counterflow elutriation then cultured on a collagen support. Bombesin and three molecular forms of canine gastrin-releasing peptides all stimulated gastrin release from G cells in a dose-dependent manner. The effect of bombesin was suppressed by somatostatin and potentiated by dibutyryl cyclic AMP (10(-3) M) but not by carbachol (10(-6) M). Extracellular calcium depletion attenuated the stimulation of gastrin release by bombesin but not by forskolin. These findings suggest that the bombesin family peptides directly activate G cells through calcium-dependent mechanisms to cause gastrin release.

Animals↗

[Co-existence and co-release of gastrin 34 N-terminal fragment with gastrin 17 in rat stomach].

Big gastrin comprising 34 amino acid residues (G34) consists of an N-terminal pentadecapeptide linked via two lysine residues to a C-terminal heptadecapeptide identical with little gastrin (G17). Both G17 and G34 have now been established as the principal active forms of gastrin. In this study, release of G34 N-terminal peptide fragment of methacholine and porcine gastrin releasing peptide (pGRP) stimulation in isolated rat stomach perfusion system was investigated by radioimmunoassay with use of an antiserum specific to the N-terminal portion of G34. G34 N-terminal immunoreactivity (IR-G34-N) was detected in rat stomach and proximal duodenum, and the highest concentration was found in extract of the antral mucosa. The concentration of IR-G34-N was constantly lower than that of IR-G17. By gel-filtration study, IR-G34-N in antral mucosa extract was attributed mostly to the G34 N-terminal pentadecapeptide-like component, and the concentration of G34 was about one tenth of G17. Methacholine 10(-8)-10(-3) M produced a biphasic dose-dependent release of IR-G34-N from the vascularly perfused isolated rat stomach. The maximal release was shown by 10(-5) M of methacholine. The release was concomitant with that of IR-G17 during methacholine stimulation. Stimulation of pGRP (14-27) (10(-7) M) produced a monophasic release of IR-G34-N from the vascularly perfused isolated rat stomach. The release was concomitant with that of G17 during the stimulation. The integrated IR-G34-N release was not stoichiometric with that of IR-G17, and IR-G34-N was constantly low. Gel-filtration of the perfusate from rat stomach revealed the presence of the G34 N-terminal pentadecapeptide-like component as a sole major component. The present results demonstrate that post-translational processing of the gastrin precursor in the rat antrum did not necessarily produce G34, which is further converted in the tissue to G17-related peptide(s) and that the G34 N-terminal fragment formed in the G34 conversion is stored and released concomitantly with G17-related peptide(s).

Animals↗

Serum gastrin and gastrin-like immunoreactivity of gastrointestinal mucosa in fetal, neonatal and adult rats.

Serum gastrin concentration became became detectable in rats at one week after birth (56 pg/ml), and a rapid rise to 198 pg/ml was seen at two weeks after birth. Gradual decreases were seen again at three weeks and four weeks, and thereafter it attained the adult level of 132 +/- 17.6 pg/ml. In regards to the gastrin-like immunoreactivity (GLI) in the gastrointestinal mucosa during the fetal period, the values were extremely low even in the antral mucosa. However, the GLI showed an increase during the neonatal suckling period, and was accompanied by a remarkable increase at the commencement of feeding. This GLI coincided with so-called little gastrin, and while an increase accompanied by the development of growth was seen, no qualitative changes were evident. GLI values were high in the duodenal mucosa followed by the antrum, and positive evidence was also seen in the corpus of the stomach and jejunum. High values of GLI in the mucosae were gradually seen at two weeks after birth coinciding with the rise in serum gastrin levels, and the significance of the increases was discussed from the anlge of the trophic effect of gastrin.

Age Factors↗

Neither glycine-extended gastrin nor the 1-13 fragment of gastrin 17 influences gastric acid secretion in humans.

The effect on gastric acid secretion of two gastrin 17-related peptides without the carboxyamide, i.e., the glycine-extended 5-17 fragment and the 1-13 fragment of human gastrin 17, was examined in normal subjects. Acid secretion was stimulated by an intravenous infusion of 21 pmol/kg.h of gastrin 17 or by intragastric instillation of peptone; gastric acid output during simultaneous infusion of 325 pmol/kg.h of the glycine-extended 5-17 fragment or 319 pmol/kg.h of the 1-13 fragment was then compared with acid output during infusion of saline. Neither the glycine-extended 5-17 fragment nor the 1-13 fragment of gastrin 17 influenced gastric acid secretion. By gel and ion-exchange chromatography of serum drawn during infusion, the infused peptide was recovered at the position of the intact synthetic peptide. The disappearance curve of circulating glycine-extended gastrin could be described by two components with half-lives of 3.6 and 48 min. As the glycine-extended fragment was stable in serum or plasma in vitro for 1 h at 37 degrees C, the rapid elimination observed in vivo cannot be ascribed to circulating plasma enzymes.

Adult↗

Synthesis and biological activity of new peptide segments of gastrin exhibiting gastrin antagonist property.

A series of C-terminal peptide segments of gastrin, i.e., (tert-butyloxycarbonyl)-L-tryptophyl-L-methionyl-L-aspartic acid amide, (tert-butyloxycarbonyl)-glycyl-L-tryptophyl-L-methionyl-L-aspartic acid amide, (tert-butyloxy-carbonyl)-L-tyrosyl-glycyl-L-tryptophyl-L-methionyl-L-asp artic acid amide, and (benzyloxycarbonyl)-L-glutamyl-L-alanyl-L-tyrosyl-glycyl-L-tryptophyl-L -methionyl-L-aspartic acid amide were prepared and were shown to competitively inhibit the binding of labeled human gastrin to its receptors in an isolated gastric mucosal cell preparation and to antagonize the action of gastrin on gastric acid secretion (ED50 from 1.5 to 7 mg/kg) in vivo in the reperfused rat stomach, determined according to the method of Ghosh and Schild. From these studies, it could be concluded that the C-terminal phenylalanine residue, which is of primary importance for intrinsic biological gastrin-like activity, is not essential for binding to gastrin receptors.

Amino Acid Sequence↗