PO72MGMT EXPRESSION, PROMOTER METHYLATION AND CIRCUMVENTION IN EPENDYMOMAS

Abstract

INTRODUCTION: Paediatric ependymomas are known to be aggressive drug-resistant tumours. Temozolomide(TMZ) is routinely employed to treat ependymomas. MGMT, an alkyltransferase repairs TMZ induced toxic O6-methylguanine lesions and is a key resistance mechanism. Proficient mismatch repair is essential for TMZ induced cytotoxicity. Studies looking at promoter hypermethylation, a common mechansim of MGMT loss have yielded conflicting results in ependymomas. Novel analogues of TMZ like N3-propargyl have shown to circumvent MGMT resistance in medulloblastomas. METHOD: MGMT immunohistochemistry(IHC) staining was performed on patient samples obtained from a chemotherapy-led infant trial (CNS9204) and a radiotherapy-led trial (CNS9904). Meta-analysis of ependymoma gene expression data available on r2 search engine was performed using SPSS. Protein expression of MGMT and MMR enzymes, MLH1 and MSH6 in ependymoma cell lines was assessed by western blotting. MTT assays were employed to investigate response to TMZ and its novel N3-propargyl analogue. RESULTS: MGMT expression correlated with poor overall survival(OS) in both cohorts (CNS9204-5yr OS 50% vs 80%, P = 0.013 and CNS9904-5yr OS 40% vs 75%, P = 0.001). On the basis of the meta-analysis, MGMT was overexpressed in younger patients and correlated with an aggressive tumour phenotype. MGMT promoter methylation was a marker of favourable prognosis in older children and adults. 2/3 ependymoma cell lines were MGMT positive. The MGMT expressing BXD1425 cell line was resistant to TMZ but sensitive to N3-propargyl analogue. CONCLUSION: MGMT expression correlates with poor survival in paediatric ependymoma patients and circumvention by novel analogues of TMZ could improve clinical outcome.