n-3 PUFAs reduce VEGF expression in human colon cancer cells modulating the COX-2/PGE ₂ induced ERK-1 and -2 and HIF-1α induction pathway

Abstract

n-3 Polyunsaturated fatty acids (PUFAs) inhibit the development of microvessels in mammary tumors growing in mice. Human colorectal tumors produce vascular endothelial growth factor (VEGF) whose expression is up-regulated in tumor cells by both cyclooxygenase-2 (COX-2) and PGE ₂ and directly correlated to neoangiogenesis and clinical outcome. The goal of this study was to examine the capability of n-3 PUFAs to regulate VEGF expression in HT-29 human colorectal cells in vitro and in vivo . Constitutive VEGF expression was augmented in cultured HT-29 cells by serum starvation and the effects of eicosapentaenoic (EPA) or docosahexaenoic acid (DHA) on VEGF, COX-2, phosphorylated extracellular signal-regulated kinase (ERK)-1 and -2 and hypoxia-inducible-factor 1-α (HIF-1α) expression and PGE ₂ levels were assessed. Tumor growth, VEGF, COX and PGE ₂ analysis were carried out in tumors derived from HT-29 cells transplanted in nude mice fed with either EPA or DHA. Both EPA and DHA reduced VEGF and COX-2 expression and PGE ₂ levels in HT-29 cells cultured in vitro . Moreover, they inhibited ERK-1 and -2 phosphorylation and HIF-1α protein over-expression, critical steps in the PGE ₂ -induced signaling pathway leading to the augmented expression of VEGF in colon cancer cells. EPA always showed higher efficacy than DHA in vitro . Both fatty acids decreased the growth of the tumors obtained by inoculating HT-29 cells in nude mice, microvessel formation and the levels of VEGF, COX-2 and PGE ₂ in tumors. The data provide evidence that these n-3 PUFAs are able to inhibit VEGF expression in colon cancer cells and suggest that one possible mechanism involved may be the negative regulation of the COX-2/PGE ₂ pathway. Their potential clinical application as anti-angiogenic compounds in colon cancer therapy is proposed.

COX-2, cyclooxygenase-2, DHA, docosahexaenoic acid, EPA, eicosapentaenoic, ERK, extracellular signal-regulated kinase, HIF1-α, hypoxia-inducible factor 1-α, LI %, Labeling Index, PUFAs, polyunsaturated fatty acids, RIA, radioimmunoassay, VEGF, vascular endothelial growth factor