prostaglandin-e3 and Carcinoma--Non-Small-Cell-Lung

The beneficial effects of omega-3 fatty acids are believed to be due in part to selective alteration of arachidonate metabolism that involves cyclooxygenase (COX) enzymes. Here we investigated the effect of eicosapentaenoic acid (EPA) on the proliferation of human non-small cell lung cancer A549 (COX-2 over-expressing) and H1299 (COX-2 null) cells as well as their xenograft models. While EPA inhibited 50% of proliferation of A549 cells at 6.05 µM, almost 80 µM of EPA was needed to reach similar levels of inhibition of H1299 cells. The formation of prostaglandin (PG)E3 in A549 cells was almost threefold higher than that of H1299 cells when these cells were treated with EPA (25 µM). Intriguingly, when COX-2 expression was reduced by siRNA or shRNA in A549 cells, the antiproliferative activity of EPA was reduced substantially compared to that of control siRNA or shRNA transfected A549 cells. In line with this, dietary menhaden oil significantly inhibited the growth of A549 tumors by reducing tumor weight by 58.8 ± 7.4%. In contrast, a similar diet did not suppress the development of H1299 xenograft. Interestingly, the ratio of PGE3 to PGE2 in A549 was about 0.16 versus only 0.06 in H1299 xenograft tissues. Furthermore, PGE2 up-regulated expression of pAkt, whereas PGE3 downregulated expression of pAkt in A549 cells. Taken together, the results of our study suggest that the ability of EPA to generate PGE3 through the COX-2 enzyme might be critical for EPA-mediated tumor growth inhibition which is at least partly due to down-regulation of Akt phosphorylation by PGE3.

Topics: Alprostadil; Animals; Antineoplastic Agents; Arachidonic Acid; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Proliferation; Cyclooxygenase 2; Diet; Dinoprostone; Eicosapentaenoic Acid; Gene Expression Regulation, Neoplastic; Humans; Lung Neoplasms; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; RNA Interference; RNA, Small Interfering; Xenograft Model Antitumor Assays

Biomarker discovery using mass spectrometry (MS) has recently seen a significant increase in applications, mainly driven by the rapidly advancing field of metabolomics. Instrumental and data handling advancements have allowed for untargeted metabolite analyses which simultaneously interrogate multiple biochemical pathways to elucidate disease phenotypes and therapeutic mechanisms. Although most MS-based metabolomic approaches are coupled with liquid chromatography, a few recently published studies used matrix-assisted laser desorption (MALDI), allowing for rapid and direct sample analysis with minimal sample preparation. We and others have reported that prostaglandin E3 (PGE3), derived from COX-2 metabolism of the omega-3 fatty acid eicosapentaenoic acid (EPA), inhibited the proliferation of human lung, colon and pancreatic cancer cells. However, how PGE3 metabolism is regulated in cancer cells, particularly human non-small cell lung cancer (NSCLC) cells, is not fully understood. Here, we successfully used MALDI to identify differences in lipid metabolism between two human non-small-cell lung cancer (NSCLC) cell lines, A549 and H596, which could contribute to their differential response to EPA treatment. Analysis by MALDI-MS showed that the level of EPA incorporated into phospholipids in H596 cells was 4-fold higher than A549 cells. Intriguingly, H596 cells produced much less PGE3 than A549 cells even though the expression of COX-2 was similar in these two cell lines. This appears to be due to the relatively lower expression of cytosolic phospholipase A2 (cPLA2) in H596 cells than that of A549 cells. Additionally, the MALDI-MS approach was successfully used on tumor tissue extracts from a K-ras transgenic mouse model of lung cancer to enhance our understanding of the mechanism of action of EPA in the in vivo model. These results highlight the utility of combining a metabolomics workflow with MALDI-MS to identify the biomarkers that may regulate the metabolism of omega-3 fatty acids and ultimately affect their therapeutic potentials.

Topics: Alprostadil; Animals; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cyclooxygenase 2; Eicosapentaenoic Acid; Gene Expression Regulation, Neoplastic; Humans; Lipid Metabolism; Lung Neoplasms; Metabolomics; Mice; Mice, Transgenic; Organ Specificity; Phospholipases A2; Proto-Oncogene Proteins p21(ras); Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization