Antibodies raised against the extracellular tail of the CCKB/gastrin receptor inhibit gastrin-stimulated signalling

Selection of potential therapeutic human single-chain Fv antibodies against cholecystokinin-B/gastrin receptor by phage display technology

BACKGROUND AND OBJECTIVE

Gastric/gastrointestinal cancers are associated with high mortality worldwide. G-protein coupled receptor (GPCR) superfamily members such as gastrin/cholecystokinin-B receptor (CCK-BR) are involved in progression of gastric tumors, thus CCK-BR is considered as a potential target for immunotherapy. However, production of functional monoclonal antibodies (mAbs) against GPCR seems to be very challenging, in part due to its integration in cell membranes and inaccessibility for selection. To tackle this problem, we implemented phage display technology and a solution-phase biopanning (SPB) scheme for production of mAbs specific to the native conformation of CCK-BR.

METHODS

To perform the SPB process, we utilized a synthetic biotinylated peptide corresponding to the second extracellular loop (ECL2) of CCK-BR and a semi-synthetic phage antibody library. After enzyme-linked immunosorbent assay (ELISA) screening, the CCK-BR specificity of the selected single-chain variable fragments (scFvs) were further examined using immunoblotting, whole-cell ELISA, and flow cytometry assays.

RESULTS

After performing four rounds of selection, we identified nine antibody clones which showed positive reactivity with the CCK-BR peptide in an ELISA assay. Of these, eight clones were unique scFv antibodies and one was a V(L) single domain antibody. Specificity analysis of the selected scFvs revealed that five of the selected scFvs recognized a denatured form of CCK-BR, while the majority of the selected scFvs were able to recognize the native conformation of CCK-BR on the surface of human gastric adenocarcinoma cells and cervical carcinoma HeLa cells.

CONCLUSION

For the first time, we report on the establishment of a diverse panel of scFv antibody fragments that are specific to the native conformation of CCK-BR. Based on these results, we suggest the selected scFv antibody fragments as potential agents for diagnosis, imaging, targeting, and/or immunotherapy of cancers that overexpress CCK-BR.

Gastrin increases murine intestinal crypt regeneration following injury

BACKGROUND & AIMS

A number of growth factors affect the regeneration of intestinal epithelia following injury, but the effects of amidated gastrin have not previously been assessed. We therefore investigated the effects of gastrin on intestinal regeneration following a range of stimuli.

METHODS

Intestinal crypt regeneration was assessed in transgenic mice overexpressing amidated gastrin (INS-GAS) and mice in which hypergastrinemia was induced using omeprazole, following gamma-radiation, 5-fluorouracil, and dextran sulphate sodium (DSS). Abundance of the CCK-2 receptor was assessed in intestinal epithelia and IEC-6 intestinal epithelial cells following gamma-radiation.

RESULTS

Four days following 14 Gy gamma-radiation, or 2 injections of 400 mg/kg 5-fluorouracil, INS-GAS mice exhibited significantly increased small intestinal and colonic crypt survival compared with their wild-type counterparts (FVB/N). INS-GAS mice treated with 3% DSS for 5 days showed less weight loss and increased colonic crypt regeneration at 8 days compared with FVB/N. Increased small intestinal and colonic crypt survival was also demonstrated following gamma-radiation in FVB/N mice rendered hypergastrinemic using omeprazole. The increased crypt survival in INS-GAS mice following 14 Gy gamma-radiation was inhibited by administration of a CCK-2 receptor antagonist (YF476). Increased abundance of the CCK-2 receptor was demonstrated in intestinal epithelia following 14 Gy gamma-radiation by Western blotting and immunohistochemistry. Similarly, increased CCK-2 receptor mRNA abundance and increased 125I-gastrin binding was demonstrated in IEC-6 cells following 4 Gy gamma-radiation.

CONCLUSIONS

Hypergastrinemia increases regeneration of intestinal epithelia following diverse forms of injury. Induction of the CCK-2 receptor in damaged epithelium confers potential for protection against injury by administration of gastrin.

Potential role of endocrine gastrin in the colonic adenoma carcinoma sequence

The role of hyper-gastrinaemia in the incidence of colonic cancer remains to be clarified. The aim of this study was to determine whether cholecystokinin-2 (CCK-2) receptor expression predicts the sensitivity of human colonic adenomas to the proliferative effects of serum hyper-gastrinaemia. Gene expression of the classical (74 kDa) CCK-2 receptor in human colonic adenoma specimens and cell lines, was quantified by real-time PCR. Western blotting, using a CCK-2 receptor antiserum, confirmed protein expression. A transformed human colonic adenoma was grown in SCID mice, with hyper-gastrinaemia induced by proton pump inhibitors. CCK-2 receptor blockade was achieved by using neutralising antiserum. Both human colonic adenoma cell lines and biopsies expressed CCK-2 receptor mRNA at levels comparable with CCK-2 receptor transfected fibroblasts and oxyntic mucosa. Western blotting confirmed immunoreactive CCK-2 receptor bands localised to 45, 74 and 82.5 kDa. Omeprazole and lansoprazole-induced hyper-gastrinaemia (resulting in serum gastrin levels of 34.0 and 153.0 pM, respectively) significantly increased the weight of the human adenoma grafts (43% (P=0.016) and 70% (P=0.014), respectively). The effect of hypergastrinaemia on tumour growth was reversed by use of antiserum directed against the CCK-2 receptor. Hyper-gastrinaemia may promote proliferation of human colonic adenomas that express CCK-2 receptor isoforms.

Gastrin, somatostatin, G and D cells of gastric ulcer in rats

AIM: To investigate the relationship among gastrin, somatostatin, G and D cells in gastric ulcer and in its healing process in rats.

METHODS: Fourty-nine Wistar rats were divided into 7 groups. The gastric ulcer model was induced by acetic acid successfully. The gastrin and the somatostatin in rat plasma, gastric fluid and antral tissue were measured by radioimmunoassay (RIA). G and D cells in antral mucosa were analyzed with polyclonal antibody of gastrin and somatostatin by immunohistochemical method and Quantimet 500 image analysis system.

RESULTS: In gastric ulcer, the level of gastrin in plasma, gastric fluid, and antral tissue increased, that of somatostatin declined, and the disorder gradually recovered to the normal level in the healing process. Immunohistochemical technique of G and D cells in antral mucosa demonstrated that the number of G cells increased and that of D cells decreased, both areas of G and D cells declined, the ratio of number and area of G/D increased in gastric ulcer, and the disorder gradually recovered in the healing process.

CONCLUSION: In gastric ulcer, the increased gastrin secreted by G cells, the declined somatostatin secreted by D cells, and the disordered G/D cell ratio can lead to gastrointestinal dysfunction.