DiscoveryProbe™ Inhibitor Library In conclusion our work led
In conclusion, our work led to the characterization of some signalling events of the CysLT1 receptor variants, at several levels, and showed that a punctual serine mutation could alter the response of receptors to cysLTs. Although atopy is a complex phenotype implicating different cell types, mediators and pathways, the variant CysLT1-G300S of the CysLT1 receptor may, at some point, play a role in this association, through its higher signal transduction capabilities.
This work was supported by a grant (MOP-82716) from the Canadian Institutes of Health Research (to J.S. and M.R.-P.) and a Canada Research Chair in Inflammation (to M.R.-P); the work was performed at the Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke, funded by the Fonds de la Recherche du Québec en Santé, of which M.R.-P. and J.S. are members.
Introduction Persistent inflammation in the lungs is linked to higher risk for lung cancer; thus, mitigation of inflammation may be a preventive or therapeutic approach [1,2]. Leukotriene (LT) C4 and its metabolites LTD4 and LTE4 (together referred to as Cysteinyl LTs, CysLTs) are inflammatory mediators derived from arachidonic DiscoveryProbe™ Inhibitor Library in the 5-lipoxygenase (5-LO) pathway. They exert many of their functions through the CysLT1 receptor, which is expressed in pulmonary smooth muscle and interstitial macrophages. CysLTs contribute to cancer progression  and several observations support a pro-tumorigenic effect of LTD4 via CysLT1 in colorectal cancer . Montelukast is a CysLT1 receptor antagonist already used in asthma treatment. Interestingly, asthma patients treated with montelukast have a considerably lower risk to develop cancer . In animal studies, montelukast increased survival rates in a spontaneous metastasis model of Lewis lung carcinoma (LLC)  and delayed tumor growth . Abrogation of ALOX5, the gene encoding 5-LO, reduced pro-tumorigenic effects of neutrophils in lung metastasis in a mouse breast cancer model, an effect sustained by LTB4 and CysLTs . On the other hand, deletion of 5-LO could also promote LLC primary tumor and metastasis  probably reflecting different effects of distinct macrophage populations in different stages of cancer progression . Cancer cells promote low-grade inflammatory conditions in the surrounding milieu to support tumorigenesis . The tumor micro-environment is influenced also via exosomes, nanovesicles which can be released by all cell types including cancer cells and immune cells, and carry RNA, proteins and other signaling molecules . For example, myeloid derived suppressor cells release pro-angiogenic exosomes supporting lung metastasis . Also, tumor derived exosomes could prepare the pre-metastatic niche via MET  and were found to activate TLR3 in alveolar epithelium to recruit neutrophils and promote lung metastasis . We recently demonstrated that LTC4 produced by monocytic cells was efficiently transformed to LTD4 by γ-glutamyl transpeptidase-1 (GGT-1) in the lung cancer cell line A549 and their exosomes, suggesting that cancer cell-derived exosomes contribute to inflammation by amplifying the biosynthesis of this most potent CysLT1 agonist . In this study, we extended these investigations to authentic exosomes and primary cells from cancer patients. Exosomes and cells were prepared from pleural exudates of 14 patients with lung cancer. We demonstrate that both cells and exosomes avidly transform LTC4 to LTD4, and furthermore that the pleural exudate derived exosomes promote migration and survival of primary cancer cells ‘ex vivo’. This highlights a role for exosomes in supporting tumor growth via leukotrienes, but also opens for investigations on reducing tumor burden by interfering with exosomes and/or leukotriene pathways.
Materials and methods For detailed methods, see supplement.
Discussion The pleural cavity is a metastatic niche in lung cancer , and a fundamental step in metastasis is invasion of malignant cells. Exosomes promote migration of granulocytes  and chemotaxis of cancer cells . Here we demonstrate a new mechanism for exosome mediated cancer cell migration. We show that exosomes prepared from lung cancer pleural exudates promoted migration of both A549 and primary cancer cells (Fig. 6), via cysLTs, as montelukast abolished this migration. Importantly, MTT assay revealed no increase in proliferation by exosomes, thus the effects seen in the scratch assay were due to migration and not to proliferation, specifically LTD4, formed effectively via GGT-1.