HG-16: THE ANTI-APOPTOTIC PROTEIN ARC IS OVER-EXPRESSED IN MALIGNANT GLIOMA AND CORRELATES WITH PATIENT OUTCOME

BACKGROUND: Glioblastoma multiforme (GBM) is among the most malignant of cancers with poor long term survival. ARC is an anti-apoptotic protein that we have previously examined published microarray data sets and found that ARC is overexpressed in malignant gliomas with higher mRNA levels correlating with poor survival. We hypothesised that ARC expression on immunohistochemistry may be a novel prognostic marker, that ARC may engender tumour resistance to conventional and targeted therapies. METHODS: We analysed a tissue bank of 94 grade 2-4 gliomas and performed immunohistochemistry (IHC) to assess ARC protein levels in high grade gliomas and correlation with patient outcomes. To assess the biological role of ARC in GBM we used siRNA and shRNA to suppress ARC expression and used an ARC plasmid to induce over-expression in U87 and U118 GBM cells. Following lenti-viral knock down, ARC expression was measured by western blot and PCR on the U87 VIII cells with non-silencing, empty vector and 2 shRNA variants. The biological effects of ARC silencing or overexpression, either alone or in combination with radiotherapy was measured using cell proliferation, clonogenic, caspase 3/7 activity and scratch assays. RESULTS: The IHC analysis of 94 glioma specimens showed that ARC protein levels in malignant gliomas specimens increased significantly with higher tumour grade. Increased protein levels of ARC in all high grade gliomas and separately in GBM, corresponded with reduced patient survival. Functional studies showed no impact on cell proliferation, colony formation, caspase 3/7 activity or sensitivity to radiation therapy or other cytotoxic therapies. CONCLUSION: Our findings indicate that ARC expression by IHC correlates with tumour grade and is a potential prognostic indicator and marker of higher grade malignant tumours. Functional studies showed no impact of ARC expression on tumour progression, apoptosis or treatment sensitivity indicating that increased ARC expression is likely a secondary phenomenon.