gastrin-17 and Colorectal-Neoplasms

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 orph

Topics: Animals; Cancer Vaccines; Clinical Trials as Topic; Colorectal Neoplasms; Gastrins; Humans; Orphan Drug Production; Pancreatic Neoplasms; Peptic Ulcer; Rats; Stomach Neoplasms; Vaccines

The interaction of gastrin with the cholecystokinin 2 (CCK2)/gastrin receptor has been studied extensively in relation to gastric acid secretion. However, not much is known about the contribution of individual amino acids of gastrin interacting with the CCK2 receptor, when gastrin is acting as a tumor growth factor. The purpose of the present study was to determine the significance of each individual amino acid residue of human gastrin-17 with respect to CCK2 receptor-mediated cell proliferation. Activation of this receptor was assessed using an in vitro bioassay based on gastrin-induced expression of a c-fos-luciferase reporter, transfected in AR42JB13 and Colo 320 cells, a rat pancreatic and human colorectal cell line respectively. Gastrin-17 dose dependently increased c-fos induction in both cancer cell lines. L365,260, a known CCK2 receptor antagonist, completely blocked the gastrin signal, demonstrating the specificity of this assay. We demonstrated for the first time that four carboxy-terminal amino acids of gastrin-17 are essential for activation of the CCK2 receptor with respect to c-fos induction. Also other residues of gastrin-17, notably glycine-2 for the rat CCK2 receptor and glutamic acid 8-10 and tyrosine-12 for the human receptor, were found to be important, although to a lesser extent. Alanine-substitution variants of each of the four carboxy-terminal amino acids of gastrin-17 showed strongly reduced receptor activation but did not act as competitive inhibitors of gastrin-17. Identification of the essential role of the carboxy-terminal tetrapeptide of gastrin-17 in CCK2 receptor-mediated c-fos induction indicates that gastrin inhibitory therapeutic strategies should mainly be targeted toward this region of gastrin.

Topics: Alanine; Amino Acid Substitution; Animals; Cell Proliferation; Colorectal Neoplasms; DNA Primers; Gastrins; Genes, fos; Humans; Luciferases; Pancreatic Neoplasms; Pentagastrin; Promoter Regions, Genetic; Protein Precursors; Rats; Receptor, Cholecystokinin B; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured

As gastrin may play a role in the pathophysiology of gastrointestinal (GI) malignancies, the elucidation of the mechanisms governing gastrin-induced proliferation has recently gained considerable interest. Several studies have reported that a large percentage of colorectal tumours overexpress or stabilise the beta-catenin oncoprotein. We thus sought to determine whether gastrin might regulate beta-catenin expression in colorectal tumour cells. Amidated gastrin-17 (G-17), one of the major circulating forms of gastrin, not only enhanced beta-catenin protein expression, but also one of its target genes, cyclin D1. Furthermore, activation of beta-catenin-dependent transcription by gastrin was confirmed by an increase in LEF-1 reporter activity, as well as enhanced cyclin D1 promoter activity. Finally, G-17 prolonged the tau(1/2) of beta-catenin protein, demonstrating that gastrin appears to exert its mitogenic effects on colorectal tumour cells, at least in part, by stabilising beta-catenin.

Topics: Animals; beta Catenin; Blotting, Northern; Blotting, Western; Cell Line, Tumor; Colorectal Neoplasms; Cyclin D1; Cytoskeletal Proteins; Gastrins; Mice; Promoter Regions, Genetic; Trans-Activators; Transcription, Genetic

The relationship between plasma gastrin levels and colorectal cancer is controversial. When confounding factors which increase plasma gastrin levels are taken into account, it has been shown that gastrin levels are not elevated in patients with colorectal cancer. However, these studies only measured amidated gastrin. Total gastrin (which includes unprocessed, partially processed, and mature forms of gastrin) has been shown to be elevated in patients with colorectal cancer.. The aim of this study was to determine whether fasting plasma levels of progastrin, amidated gastrin, or glycine extended gastrin are elevated in patients with colorectal cancer or colorectal polyps compared with controls.. Progastrin, amidated gastrin, and glycine extended gastrin were estimated by radioimmunoassay using the following antibodies: L289, 109-21, and L2. Blood samples were analysed for Helicobacter pylori by an enzyme linked immunosorbent assay.. Median progastrin levels were significantly higher in the cancer group (27.5 pmol/l) than in the polyp (< or =15 pmol/l) or control (< or =15 pmol/l) group (p=0.0001 There was no difference in median levels of amidated gastrin between groups. Median levels of amidated gastrin were significantly higher in H pylori positive patients (19 pmol/l) than in H pylori negative patients (8 pmol/l) (p=0.0022). Median plasma progastrin levels were significantly higher for moderately dysplastic polyps (38 pmol/l) compared with mildly dysplastic (15 pmol/l) and severely dysplastic (15 pmol/l) polyps (p=0.05).. Plasma levels of progastrin, but not amidated gastrin or glycine extended gastrin, are significantly elevated in patients with colorectal cancer compared with those with colorectal polyps or controls, irrespective of their H pylori status. We conclude that measuring plasma progastrin levels in patients with colorectal cancer is warranted.

Topics: Adult; Aged; Aged, 80 and over; Antibodies, Bacterial; Biomarkers, Tumor; Carcinoma; Case-Control Studies; Colonic Polyps; Colorectal Neoplasms; Female; Gastrins; Helicobacter Infections; Helicobacter pylori; Humans; Male; Middle Aged; Protein Precursors

Mature amidated gastrin (G17 amide) mediates its effects in the gastrointestinal tract by activating G protein-coupled CCK-B/gastrin receptors. Although trophic actions of gastrin on the gastric mucosa have been well-established, the effect of G17 amide, progastrin and intermediates to colon neoplasia in humans is controversial. While epidemiological evidence from patients with elevated serum gastrin levels related to pernicious anaemia does not support an increased risk for colon cancer, a recent study suggests that prolonged hypergastrinaemia is associated with an increased risk for colon cancer. The extent to which trophic actions of gastrin in colorectal cancer are mediated by functional gastrin receptors remains to be defined. The aim of the present study was to determine CCK-B/gastrin receptor expression, structure, and function in 79 patients with colon cancer.. CCK-B/gastrin receptor cDNAs were isolated from 79 human colorectal cancer specimens and 15 control tissues, subcloned into the eukaryotic expression vector pCR3.1 and subjected to DNA sequence analysis. Wild-type and mutant cDNAs were transiently expressed in COS-7 cells to determine ligand affinities by 125I-labelled CCK-8S competition binding. Activation of the MAP kinase signalling cascade by G17 amide was determined in transfected Colo 320 cells expressing the wild-type or mutant CCK-B/gastrin receptors. Clonal expansion of single cells was quantified in transfected Colo 320 cells.. Gastrin mRNA is expressed in 44% of colorectal cancers and in 13% of control tissues. CCK-B/gastrin receptor mRNA is expressed in 38% of colorectal cancers and 13% of normal colonic tissue. Co-expression of gastrin and CCK-B/gastrin receptor message is significantly increased in colorectal cancer specimens (32% vs. 0%). There is no correlation between CCK-B/gastrin receptor expression and disease stage or histological grading. DNA sequence analysis revealed one spontaneous CCK-B/gastrin receptor mutation within the third intracellular loop with an exchange of valine-287 for phenylalanine. Pharmacological characterisation of the 287V --> F CCK-B/gastrin receptor reveals wild-type affinities for G17 amide, glycine-extended gastrin, CCK-8S and L-365,260. Mutation 287V --> F is associated with a loss of gastrin-induced MAPK p44/p42 signalling in Colo 320 cells while clonal expansion from single cells is increased by 53.1 +/- 15.9% when compared to Colo 320 cells expressing wild-type CCK-B/gastrin receptors.. Structural alterations of CCK-B/gastrin receptors may account for increased growth-promoting effects of amidated gastrins in colorectal cancer.

Topics: Aged; Amino Acid Sequence; Animals; Antibodies; Colorectal Neoplasms; COS Cells; Female; Gastrins; Gene Expression Regulation, Neoplastic; Humans; Iodine Radioisotopes; Male; Middle Aged; Mitogen-Activated Protein Kinases; Molecular Sequence Data; Phosphorylation; Point Mutation; Rabbits; Radioligand Assay; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; RNA, Messenger; Transfection; Tumor Cells, Cultured

Although ectopic expression of the cholecystokinin B/gastrin receptor (CCK-BR) is widely reported in human colorectal cancers, its role in mediating the proliferative effects of gastrin1-17 (G-17) on these cancers is unknown. Here we report the isolation of a novel splice variant of CCK-BR that exhibits constitutive (ligand-independent) activation of pathways regulating intracellular free Ca(2+) ([Ca(2+)](i)) and cell growth. The splice variant (designated CCK-BRi4sv for intron 4-containing splice variant) is expressed in colorectal cancers but not in normal colonic mucosa adjacent to the cancer. Balb3T3 cells expressing CCK-BRi4sv exhibited spontaneous, ligand-independent, oscillatory increases in [Ca(2+)](i), whereas cells expressing wild-type CCK-BR did not. Primary cultures of cells isolated from resected colorectal cancers also exhibited a similar pattern of spontaneous [Ca(2+)](i) oscillations. For both Balb3T3 and primary tumor cells, application of G-17 (10 and 200 nm, respectively) caused an increase in [Ca(2+)](i). Selective CCK-BR antagonists blocked the G-17-stimulated Ca(2+) responses but not the spontaneous [Ca(2+)](i) oscillations. Cells expressing CCK-BRi4sv exhibited an increased growth rate ( approximately 2.5-fold), in the absence of G-17, compared with cells expressing wild-type CCK-BR. The selective pattern of expression, constitutive activity, and trophic action associated with CCK-BRi4sv suggest that this variant may regulate colorectal cancer cell proliferation though a gastrin-independent mechanism.

Topics: 3T3 Cells; Alternative Splicing; Amino Acid Sequence; Animals; Base Sequence; Binding, Competitive; Calcium; Calcium Signaling; Cell Division; Cloning, Molecular; Colorectal Neoplasms; Female; Gastrins; Gene Expression Regulation, Neoplastic; Humans; Introns; Male; Mice; Molecular Sequence Data; Neoplasm Staging; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Tumor Cells, Cultured

The neutralising ability of rabbit anti-gastrin-17 (G17) antiserum raised by Gastrimmune, an immunogen constructed of the N-terminal portion of human G17 conjugated to diptheria toxoid (DT), was evaluated. The anti-serum (denoted anti-G17: DT) was shown to displace 125[I] G17 from the gastrin receptors on AR42J cells. The therapeutic effect of the rabbit anti-G17:DT anti-serum was evaluated on a freshly derived human colorectal cancer cell line, AP5, which was shown to express both gastrin receptors and gastrin immunoreactivity as assessed by immunocytochemistry. Rabbit anti-G17:DT anti-serum was shown to block basal in vitro growth of AP5 cells when used at an antigen binding capacity of 3.75 x 10(-9) M. The same dilution of anti-serum completely reversed growth stimulated by human G17 at concentrations of 1 x 10(-10) and 1 x 10(-9) M but did not inhibit growth at 1 x 10(-8) M G17. When AP5 was grown as a xenograft in nude mice, the sensitivity to the proliferative effect of human G17 was maintained. In addition, the basal growth of AP5 xenografts was significantly reduced by i.v. infusion of rabbit anti-G17:DT anti-serum when compared to treatment with rabbit anti:DT control anti-serum. Thus anti-G17:DT antibodies raised by Gastrimmune may be of clinical value in gastrin-sensitive tumours.

Topics: 3T3 Cells; Animals; Antibody Formation; Cell Division; Cell Line; Colorectal Neoplasms; Diphtheria Toxoid; Fasting; Gastrins; Humans; Immunotherapy; Immunotoxins; Iodine Radioisotopes; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Neoplasm Transplantation; Pancreas; Rabbits; Rats; Transplantation, Heterologous; Tumor Cells, Cultured

The purpose of this study was to determine the effect of the gastrin receptor antagonist, CR2093, on basal and gastrin-stimulated growth of primary human colorectal adenocarcinomas and to relate this to gastrin receptor expression. Tumour cells, derived from surgical specimens by enzymatic disaggregation, were grown on matrices of type I collagen and irradiated fibroblasts. Gastrin receptor expression was measured by using a mouse monoclonal antibody directed against the gastrin receptor and an avidin-biotin immunocytochemical method. Increased growth in the presence of gastrin-17 (used at physiological concentrations and as assessed by [3H] thymidine uptake) was shown in 16/34 (47%) tumours. CR2093 significantly reversed this stimulated growth (P < 0.05, one way analysis of variance) in 9/16 (56.3%) of the tumours and inhibited the basal growth of 11/34 (32.4%). Basal growth inhibition was reversed by gastrin-17 in 82% (9/11) of tumours. Gastrin receptor expression was widespread, but was not related to the degree of growth response to gastrin, and there was no significant correlation between intensity of receptor expression and inhibition of basal growth by CR2093. In conclusion, both gastrin-stimulated and basal growth of primary human colorectal can be inhibited by gastrin receptor antagonism, but gastrin receptor expression does not predict the sensitivity of tumours to (i) the proliferative effects of gastrin or (ii) the inhibitory effects of a gastrin receptor antagonist on basal growth. Antigastrin agents may have clinical value in the treatment of gastrin-sensitive colorectal tumours, and gastrin receptor expression may be related to endogenous gastrin production by colorectal tumour cells.

Topics: Amino Acids; Cell Division; Colorectal Neoplasms; Gastrins; Hormone Antagonists; Hormones; Humans; Immunoenzyme Techniques; Receptors, Cholecystokinin; Thymidine; Tumor Cells, Cultured

Two colorectal (HT29, LoVo) and one gastric (MKN45) human tumour cell lines were examined for their in vitro trophic response to human gastrin-17. MKN45 and HT29 responded by increased 75Se selenomethionine uptake to exogenous gastrin (139 +/- 5.5% and 123 +/- 3% of control values respectively) whereas LoVo showed no significant response to this hormone. When these same cell lines were grown as xenografts in nude mice, similar responses were seen to exogenously administered human gastrin-17 (10 micrograms mouse-1 day-1, subcutaneous injection). MKN45 xenografts showed a greater response to continuously administered gastrin (osmotic mini-pumps, (10 micrograms mouse-1 day-1) when compared to the same dose given via a subcutaneous bolus injection. The hormone-treated xenografts had a two-fold increase in tumour cross-sectional area and growth rate when compared to saline-treated controls. Dose-response studies revealed that 0.4 micrograms gastrin mouse-1 day-1 appeared to be the minimally effective dose. As gastric and colorectal tumour cells show a trophic response to gastrin, antagonists of the gastrin receptor may prevent this effect causing tumour stasis. The gastric tumour cell line, MKN45, is gastrin-responsive and would be an ideal model for screening potent receptor antagonists.

Topics: Adenocarcinoma; Animals; Cell Division; Cell Line; Colorectal Neoplasms; Gastrins; Hormones; Humans; Mice; Mice, Nude; Neoplasm Transplantation; Stomach Neoplasms; Tumor Cells, Cultured