title: Dual inhibition of 5-LOX and COX-2 suppresses colon cancer formation promoted by cigarette smoke.
abstract: Previous studies indicate that the arachidonic acid-metabolizing enzymes COX-2 and 5-LOX are overexpressed during the process of colonic adenoma formation promoted by cigarette smoke. The aims of the present study were to investigate whether there exists a relationship between COX-2 and 5-LOX, and whether dual inhibition of COX-2 and 5-LOX has an anticarcinogenic effect in the colonic tumorigenesis promoted by cigarette smoke. Results showed that pretreating colon cancer cells with cigarette smoke extract (CSE) promoted colon cancer growth in the nude mouse xenograft model. Inhibition of COX-2 or 5-LOX reduced the tumor size. In the group treated with COX-2-inhibitor, the PGE2 level decreased while the LTB4 level increased. In contrast, in the 5-LOX-inhibitor treated group, the LTB4 level was reduced and the PGE2 level was unchanged. However, combined treatment with both COX-2 and 5-LOX inhibitors further inhibited the tumor growth promoted by CSE over treatment with either COX-2-inhibitor or 5-LOX-inhibitor alone. This was accompanied by the downregulation of PGE2 and LTB4. In an in vitro study, we found that the action of CSE on colon cancer cells was mediated by 5-LOX DNA demethylation. In summary, these results indicate that inhibition of COX-2 may lead to a shunt of arachidonic acid metabolism towards the leukotriene pathway during colonic tumorigenesis promoted by CSE. Suppression of 5-LOX did not induce such a shunt and produced a better response. Therefore, 5-LOX inhibitor is more effective than COX-2 inhibitor, and blocker of both COX-2 and 5-LOX may present a superior anticancer profile in cigarette smokers.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Zhejiang University, Hangzhou, Republic of China.
authors.forename: Y N
authors.initials: YN
authors.lastname: Ye
authors.forename: W K K
authors.initials: WK
authors.lastname: Wu
authors.forename: V Y
authors.initials: VY
authors.lastname: Shin
authors.forename: I C
authors.initials: IC
authors.lastname: Bruce
authors.forename: B C Y
authors.initials: BC
authors.lastname: Wong
authors.forename: C H
authors.initials: CH
authors.lastname: Cho
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology / Q000209:etiology / Q000517:prevention & control*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001094:Arachidonate 5-Lipoxygenase / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000201:enzymology / Q000209:etiology / Q000517:prevention & control*; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000627:therapeutic use*; D019175:DNA Methylation; D015232:Dinoprostone / Q000378:metabolism; D005260:Female; D007975:Leukotriene B4 / Q000378:metabolism; D016859:Lipoxygenase Inhibitors / Q000627:therapeutic use*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000517:prevention & control; D011451:Prostaglandin-Endoperoxide Synthases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012906:Smoke / Q000009:adverse effects; D014026:Nicotiana; D014407:Tumor Cells, Cultured
chemical_list: D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D016859:Lipoxygenase Inhibitors; D012333:RNA, Messenger; D012906:Smoke; D007975:Leukotriene B4; D001094:Arachidonate 5-Lipoxygenase; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone