Inhibition of 5-lipoxygenase by MK886 augments the antitumor activity of celecoxib in human colon cancer cells

Abstract

Cyclooxygenase (COX)-2 and 5-lipoxygenase (5-LOX) are key enzymes involved in arachidonic acid metabolism. Their products, prostaglandins and leukotrienes, are involved in colorectal tumor development. We aimed at evaluating whether combined blocking of the COX-2 and 5-LOX pathways might have additive antitumor effects in colorectal cancer. The expression/activity of COX-2 and 5-LOX were assessed in 24 human colorectal cancer specimens. The effects of the COX-2 inhibitor celecoxib and the 5-LOX inhibitor MK886 on prostaglandin E 2 and cysteinyl leukotriene production, tumor cell proliferation, cell apoptosis, and Bcl-2/Bax expression were evaluated in the Caco-2 and HT29 colon cancer cells. We also investigated the effect of the enzymatic inhibition on mitochondrial membrane depolarization, one of the most important mechanisms involved in ceramide-induced apoptosis. Up-regulation of the COX-2 and 5-LOX pathways was found in the tumor tissue in comparison with normal colon mucosa. Inhibition of either COX-2 or 5-LOX alone resulted in activation of the other pathway in colon cancer cells. Combined treatment with 10 Mmol/L celecoxib and MK886 could prevent this activation and had additive effects on inhibiting tumor cell proliferation, inducing cell apoptosis, decreasing Bcl-2 expression, increasing Bax expression, and determining mitochondrial depolarization in comparison with treatment with either inhibitor alone. The administration of the ceramide synthase inhibitor fumonisin B1 could prevent some of these antineoplastic effects. In conclusion, our study showed that inhibition of 5-LOX by MK886 could augment the antitumor activity of celecoxib in human colorectal cancer. [Mol Cancer Ther 2006;5(11):2716 -26]

Role of histamine H 4 receptor ligands in bleomycin-induced pulmonary fibrosis

“…The total protein for the lung samples were obtained as described previously [31]. Lung tissues were lysed with buffer containing 0.9% NaCl, 20 mmol/L Tris-HCl (pH 7.6), 0.1% Triton X-100, 1 mmol/L phenylmethylsulfonyl fluoride, and 0.01% leupeptin, and homogenized.…”

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

“…Furthermore, omega-3 supplementation was reported to significantly reduce synthesis of pro-inflammatory 5-LOX metabolites LTA 4 and lipid peroxides, thereby inhibiting IL-1β and TNF-α release [156]. shown to have additive effects in colon cancer cells [157].…”

Role of eicosanoids on intestinal epithelial homeostasis

“…Cianchi et al [53] reported that the two major metabolic pathways of the AA cascade, COX and 5-LOX, are simultaneously up-regulated in human colorectal cancer.…”