Altered expression of prostaglandin synthases in NSCLC: Therapeutic strategies and targets for intervention

Abstract

18083 Background: Prostacyclin Synthase (PGIS) and Thromboxane synthase (TXS) metabolize PGH(2) into prostacyclin and thromboxane respectively. PGIS over-expression inhibits cancer growth in a mouse model, while over-expression of TXS caused opposite effects. TXS is expressed in a variety of tumours, associated with poor prognosis and increased metastasis. The aim of this study was to examine the expression of PGIS and TXS in NSCLC, the effect of targeted TXS inhibition, and the mechanisms regulating these effects. Methods: A panel of resected human lung tumours were stained for PGIS and TXS expression by IHC and by western analysis. A 170- core tissue microarray was stained for TXS and intensity correlated with tumour grade. Cell survival was examined by BrdU assay in A-549 (adenocarcinoma) and SKMES-1 (squamous cell carcinoma) cells following 24h selective TXS inhibition with Ozagrel (500nM) alone, or in combination with chemotherapy. Multi-parameter apoptosis signalling was examined after TXS inhibition using In Cell Analyser and confirmed by DNA laddering and cell death ELISA. PCR arrays were used to examine genes involved in tumourigenesis following TXS inhibition. Results: PGIS was absent in lung cancer sections. TXS was over-expressed in lung cancer relative to matched normal, with significantly increased expression in lower grade tumours. PGIS was down-regulated or absent, while TXS expression was up-regulated in tumours v’s normal tissue. Ozagrel significantly reduced cell survival and induced apoptosis, determined by both DNA laddering and Cell Death ELISA. Multi-parameter apoptosis analysis revealed enlarged nuclei, decreased f-actin staining and decreased mitochondrial mass potential, while PCR arrays confirmed upregulation of the pro-apoptotic gene BAX following TXS inhibition. Ozagrel in combination with Doxorubicin (10nM) showed greatest efficacy compared to a number of other chemotherapy drugs. Conclusions: Expression of PGIS and TXS are altered in NSCLC. Overexpression of TXS may regulate tumour survival as its inhibition induces apoptosis, potentially through upregulation of pro- apoptotic proteins. Targeting TXS, alone or in combination with chemotherapy is a potential therapeutic strategy for the treatment of NSCLC. No significant financial relationships to disclose.