Abstract 5432: Transcriptional regulation of cyclooxygenase-2 by histone deacetylase inhibitors in non-small cell lung cancer cells

Cyclooxygenases (COXs), particularly inducible COX-2 catalyze the synthesis of pro-proliferative and pro-angiogenic prostaglandin E2 (PGE2) and NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is responsible for its metabolic inactivation. Down-regulation of 15-PGDH has been found in gastric, colorectal, breast and prostate cancers and is at least in part mediated by epigenetic silencing which we hypothesized also mediates 15-PGDH silencing observed in about half of all non-small cell lung cancers. Epigenetic strategies, in particular HDAC inhibitors have shown promise in combination with chemotherapy in the treatment of advanced non-small cell lung cancer. Therefore, we treated lung cancer cell lines with 5-aza-2′ deoxycytidine and/or the specific HDAC inhibitor, trichostatin A (TSA) in order to reverse epigenetic silencing and assess modulation of the Cox-2/15-PGDH axis. While 15-PGDH re-activation could be readily detected on the transcriptional level upon TSA but not DAC treatment, such changes could not be seen on the protein level questioning the functional significance of epigenetic regulation of 15-PGDH expression. However, TSA markedly induces COX-2 expression on both the transcriptional and translational level in all seven non-small cell lung cancer cell lines studied. The levels of COX-2 mRNA and protein were maximal at 24h after treatment with TSA and were also confirmed under hypoxic conditions better mimicking in vivo conditions. Five of these seven NSCLC cell lines indeed produced significantly more PGE2 than untreated cells did as determined by enzyme-linked immunosorbent assay under both normoxic and hypoxic conditions following TSA treatment, indicating that the induced COX-2 is functionally active. To confirm that PGE2 production was associated with the catalytic activity of COX-2, three NSCLC cell lines were selected and cultured in the presence of both TSA and indomethacin, a non-selective COX inhibitor and PGE2 levels were measured after 24 hours of co-treatment. Non-cytotoxic, 10uM concentration of indomethacin potently blocked PGE2 production induced by TSA, namely decreased PGE2 to the level of the control group in all three NSCLC cell lines examined. In conclusion, COX-2 is an inducible gene in NSCLC cells and appears to be transcriptionally regulated by a unique mechanism associated with histone acetylation. Histone deacetylase inhibitors (HDACi) are a new class of promising anti-tumor agents inhibiting cell proliferation and survival in tumor cells with very low toxicity toward normal cells. Induction of Cox-2 and as a result increased PGE2 production by HDAC inhibition could be an untoward side effect of clinical relevance. Our results suggest that combination therapy of TSA and indomethacin could be a potential strategy to overcome this undesirable effect of HDAC inhibitor therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5432.