Polyamines are essential in various biological systems such as cellular proliferation including tumor growth, differentiation and neoplastic transformation including carcinogenesis. alpha-Difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine decarboxylase, a key enzyme in polyamine biosynthesis, and has been used for clinical chemotherapy and chemoprevention trials against several tumors with various effects. The cellular mechanisms of DFMO action are unclear. Because our hypothesis with regard to polyamine-directed chemoprevention includes anti-angiogenesis and apoptosis as essential parts of the cellular mechanism of action of DFMO, we examined these effects in our human gastric cancer model. In our initial experiments, DFMO inhibited the growth of both human umbilical vein endothelial cells (HUVEC), angio-endothelial cells in vitro, and KKLS, a gastric cancer cell line, in culture, and also the growth of KKLS cells transplanted into nude mice. DFMO also inhibited liver metastasis of KKLS orthotransplanted in the stomach of nude mice. The vessel density of DFMO-treated tumors was significantly lower than that of non-treated tumors. The apoptotic index was significantly greater in DFMO-treated tumors than in non-treated tumors. These results suggest that anti-angiogenesis and apoptosis play significant roles in the DFMO inhibition of the growth and metastasis in this human gastric cancer model and provide evidence that DFMO induces apoptosis.
Copyright 2000 Wiley-Liss, Inc.