Abstract 2900: COX-2 modulates murine lung adenocarcinoma cell survival by activating Akt and NF-κB pathways and inhibiting p38MAPK

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Cyclooxygenase-2 (COX-2) expression is increased in a number of tumors along with elevated prostaglandin (PG) production. The treatment with COX-2 inhibitors was found to have antitumor properties in different types of cancers, although the dependency of COX-2 inhibition remains controversial. We aimed to study the role of COX-2 in the progression of a murine lung adenocarcinoma. COX-2-specific inhibitor celecoxib delayed tumor growth (p < 0.001 by day 30 after subcutaneous tumor inoculation) and the metastatic outcome of LP07 cells. The treatment with celecoxib reduced LP07 cell motility, invasiveness and the activity of secreted matrix metalloproteinase-2 (MMP-2). Celecoxib (25 μM) also increased the susceptibility of LP07 cells to serum deprivation (p < 0.001) and exogenously added PGE2 (10 μM) counteracted this effect. The reduced viability of tumor cells by specific COX-2 inhibition correlated with decreased levels (2.25 fold) of phosphorylated Akt in serum-stimulated LP07 cells and a reduced activity of NF-κB (p < 0.001), a transcription factor with survival/anti-apoptotic properties. We also found increased levels of phosphorylated p38 MAPK in serum-starved LP07 cells treated with celecoxib. The effect of COX-2 inhibition on cell viability was partially abolished by infecting LP07 cells with a retroviral vector coding for a constitutively active form of Akt or by transfection with a dominant negative p38. The activation of the Akt pathway partially reverted the inhibition of NF-κB activity. To further study the role of COX-2 in LP07 tumor biology, we inhibited COX-2 expression by infection with a retroviral vector with specific shRNAs. Clones with the lowest COX-2 expression were selected. Controls expressed a shRNA for GFP or carried an empty vector. The inhibition of COX-2 expression resulted in reduced tumor growth in mice (p < 0.001 in all cases compared to the shGFP control). Homogenates from these tumors showed a low level of phosphorylated Akt, in line with in vitro experiments where LP07 cells were less responsive to serum pulses in phosphorylating Akt if COX-2 expression was blocked. The inhibition of COX-2 expression reduced the viability of tumor cells after serum depletion (p < 0.01), and this effect was completely abolished by PGE2 and partially by the expression of a constitutively active form of Akt and PI3K, or a dominant negative p38. NF-κB activity was also reduced by the inhibition of COX-2 expression (p < 0.01). Taken together, we found that COX-2 is a key player for the malignant behavior of the LP07 lung tumor. COX-2 and PGE2 had an important role for LP07 cell survival by modulating the Akt and p38 MAPK and NF-κB pathways Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2900. doi:10.1158/1538-7445.AM2011-2900