Gut hormones, growth and malignancy

There is now clear-cut evidence that polypeptide growth factors control the proliferation of the normal gastrointestinal mucosa. Epidermal growth factor (EGF) stimulates normal growth throughout the gastrointestinal tract, and accelerates the healing of ulcerated epithelium. While the effects of gastrin were at first thought to be similarly widespread, the gastrin target now appears to be restricted to the enterochromaffin-like cells in the stomach. Isolated reports suggest that several other hormones, including fibroblast growth factor and the insulin-like growth factors, have similar proliferative effects. In contrast, indirect evidence suggests that somatostatin and transforming growth factor-beta inhibit the growth of the gastrointestinal mucosa. The same growth factors profoundly affect the growth of some gastrointestinal carcinomas. Prolonged hypergastrinaemia increases the risk of development of gastric endocrine tumours, but has no effect on the incidence of gastric adenocarcinoma. Gastrin also stimulates the in vivo growth of 50% of gastric and colorectal carcinoma xenografts, but has no consistent effect on the growth of carcinoma cell lines in vitro. EGF, on the other hand, significantly stimulates proliferation of many gastrointestinal cell lines in culture. Interest has recently focused on autocrine stimulation of gastrointestinal carcinoma growth. Elevated levels of EGF receptor, and of EGF or related mRNAs, have been demonstrated in gastric carcinomas, and the growth of some gastrointestinal cell lines is inhibited by antibodies against EGF, and by antisense oligonucleotides based on EGF mRNA. Similarly gastrin/cholecystokinin antagonists inhibit the growth of several colon carcinoma cell lines, although the spectrum of antagonist potencies suggests that classical gastrin and cholecystokinin receptors are not necessarily involved. Continued research on antagonists may therefore lead to novel therapies for gastrointestinal cancers.