In view of the ubiquitous distribution of the arachidonate S
In view of the ubiquitous distribution of the arachidonate 12S-lipoxygenase isoforms and the variety of cellular reactions influenced by the resulting arachidonate metabolites, these products widely play important roles in many biological systems. The development of new type-specific inhibitors of the 12/15-lipoxygenases is of biological significance and useful for the elucidation of their functional relevance to clinical diseases , . There may be therapeutic benefits of 12S-lipoxygenase inhibitors especially in reducing the risk of atherosclerosis, epilepsy, and proliferation and metastasis of cancer.
Introduction Metastasis is the leading cause of cancer-related death. Metastasis is a very complex cascade of events such as tumour growth, invasion and angiogenesis. The metastatic process is dependent on cross-talk between tumour cells and the adjacent microenvironment. Cell adhesion plays an important role in all stages of cancer metastasis. Arachidonic Nalidixic acid sale (AA) is a polyunsaturated fatty acid that is present in the phospholipids. Free arachidonic acid can be metabolised by two key enzymes: cyclooxygenase (COX) and lipoxygenase (LOX). Numerous clinical and pharmacologic studies have shown that COX-2 expression and its downstream products, such as prostaglandins are attributed to inflammation-associated cancers such as lung, colon, bladder and prostate cancer. On the other hand, LOXs are a group of closely related non-haeme iron-containing dioxygenases and are classified depending on their site of oxygen insertion on AA into 5-, 8-, 12- and 15-LOXs. Recent studies show a functional role of LOXs and their metabolite derivatives in carcinogenesis. However, the role of LOX isoforms in the pathology of human cancers remains unknown. The major product of AA via the 12/15-LOX (encoded by the ALOX15 gene) is hydroxyeicosatetraenoic acid (HETE). HETEs can stimulate various signalling molecules such as Src, lipid kinase phosphoinositide 3-kinase (PI3K), Akt, extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) and c-Jun N-terminal protein kinase-1 (JNK1), leading to the activation of transcriptional factors including activating transcriptional factor 2 (ATF2), activator protein 1 (AP1), early growth response factor (Egr1) and signal transducer and transcription factors (STATs).9, 10, 11, 12, 13 Furthermore, 12(S)-HETE has been shown to promote melanoma cell spreading on the matrix protein fibronectin and the increase of tyrosine phosphorylation of focal adhesion kinase (FAK) is involved in the enhancement of focal adhesion. 12(S)-HETE has been reported to play a key role in mediating several steps of the process of hematogenous metastasis and tumour cell adhesion. 12(S)-HETE induces the expression of integrins and other cell adhesion molecules.16, 17, 18 Moreover, high concentrations of 12(S)-HETE have been found in highly metastatic murine melanoma cell lines as compared with low metastatic potential cell lines.19, 20 We are the first to examine the role of host 12/15-LOX on the lung metastasis of melanoma cells.
Materials and methods
Discussion Many studies investigate the role of 12/15-LOX in cancer cell,23, 24, 25 however we here first found that host 12/15-LOX also plays an important role in metastasis progression. We have demonstrated that 12(S)-HETE increased melanoma cell adhesion to the host epithelial cells and various ECM substrates in vitro and lung metastasis in vivo. Lung is one of the most common sites for melanoma cell dissemination. Here we found that tumour growth was reduced in 12/15-LOX null mice when the B16F10 melanoma cells were subcutaneously injected. Furthermore, the lung nodule formation was decreased in 12/15-LOX null mice when the melanoma cells were intravenously injected. Co-treatment of 12(S)-HETE with melanoma cells also increased lung metastasis. It has been reported that angiogenesis inhibition can decrease lung metastasis and 15(S)-HETE, a 12/15-LOX metabolite, is a well-known angiogenic factor. 15(S)-HETE increased vessel density in chick CAM, induced sprouting in rat aortic rings and increased endothelial cell–cell contact and the formation of tubular network-like structures in human umbilical vein endothelial cells (HUVECs). Similarly, 12-HETE has been shown to contribute to tumour angiogenesis via a vascular endothelial growth factor (VEGF)-dependent pathway and to stimulate endothelial cell mitogenesis.29, 30 Although there are several emerging experimental studies indicated that 12/15-LOX enhanced cancer cell growth via angiogenesis, we here found that 12(S)-HETE and 15(S)-HETE but not LXA4 or LXB4 could directly increase the absorbance of MTT reaction of B16F10 melanoma cells in vitro.