Abstract 3668: Chemopreventive effect of omega-3 fatty acid, EPA, in non-small cell lung cancer through formation of PGE3 and inhibition of PI3kinase/mTOR pathways.
Authors: Pan Yong , Pirman David , Efuet Ekem , Rhea Patrea , Cartwright Carrie , Ravoori Murali , Kundra Vikas , Fischer Susan , Yang Peiying 
Published: August 2014

Abstract
The beneficial effects of eicosapentaenoic acid (EPA) are due, in part, to selective alteration of arachidonic acid metabolism that involves cyclooxygenase enzymes. We previously reported that the anti-proliferative effect of EPA in human non-small cell lung cancer (NSCLC) A549 cells was associated with formation of PGE3, a COX-2 metabolite of the fish oil derived EPA (J. Lipid Res. 45: 1030-1039, 2004). Here we report that EPA differentially regulated the in vitro anti-proliferative effect in non-small cell lung cancer A549 and H596 cells and the in vivo chemopreventive effect in K-ras transgenic murine lung carcinoma. When both A549 and H596 cells were treated with EPA (1 to 100 μM) for 72 hrs, EPA inhibited proliferation of A549 cells (IC50 &lt; 6.25 μM) more effectively than H596 cells (IC50 &gt; 50 μM), although both expressed similar level of COX-2. Analysis by MALDI MS showed that the level of EPA incorporated into phospholipids in H596 cells was 4-fold higher than A549 cells. Unexpectedly, H596 cells produced much less PGE3 than A549 cells. This is likely due to the relatively lower expression and activity of cytosolic phospholipase A2 (cPLA2) in H596 cells than in A549 cells. Use of siRNA to knock down cPLA2 in A549 cells markedly reduced the anti-proliferative activity of EPA compare to the control siRNA transfected cells. Intriguingly, PGE3 exhibited a dose dependent inhibition of proliferation, invasion and migration in A549 cells, possibly through down regulation of phosphorylation of Akt and S6 proteins. To assess the chemopreventive effect of EPA in lung cancer development, FVB/Kras (LA2) mouse were fed either a soybean oil diet (control) or one containing 1% or 2% EPA for 20 weeks. There was a 54% reduction in the number of tumor nodules in the 2% EPA diet group compared to control (P &lt; 0.05). In addition, average tumor volume was dramatically reduced by 67% in the 2% EPA diet fed animals compared with the control group (P &lt; 0.05). These results were confirmed by micro-CT and histopathology examinations. Interestingly, the endogenous levels of PGE2 in mouse lung tumor tissues were significantly reduced from control level of 489.1 ± 125.5 ng/mg to 171.9 ± 57.3 ng/mg protein in EPA (2%) treated mice, whereas PGE3 levels were significantly increased to 76.2 ± 33.3 ng/mg protein in EPA (2%) diet group compared to control group (5.1 ± 2.0 ng/mg protein). Furthermore, EPA (2%) markedly inhibited expression of both pAkt and pS6 in lung tumor tissues compared to the control. Taken together, the data suggest that EPA has the ability to inhibit the proliferation of NSCLC cells and prevent the development of mouse lung carcinoma. The anti-proliferative effect of EPA might be mediated through increased production of PGE3, which is regulated by cPLA2 and COX-2 enzymes, and inhibition of mTOR and PI3kinase pathways. This study is supported by NCI Grant 1R01CA144053-01.
Citation Format: Yong Pan, David Pirman, Ekem Efuet, Patrea Rhea, Carrie Cartwright, Murali Ravoori, Vikas Kundra, Susan Fischer, Peiying Yang. Chemopreventive effect of omega-3 fatty acid, EPA, in non-small cell lung cancer through formation of PGE3 and inhibition of PI3kinase/mTOR pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3668. doi:10.1158/1538-7445.AM2013-3668