Abstract 1725: Activation of the p53 pathway by the MDM2 antagonist nutlin-3 downregulates the DNA repair protein hABH2 and sensitizes glioma cells to chemotherapy

Abstract

Abstract Glioblastoma is the most frequent and most malignant primary brain tumor in adults. Standard first line treatment for glioblastoma patients includes surgery followed by focal fractionated radiotherapy with concomitant and adjuvant administration of the alkylating agent temozolomide. During the course of therapy, however, radio- and chemoresistance typically become evident through local tumour recurrence, and median survival time for glioblastoma patients remains around 15 months. In order to improve this poor prognosis, there is a critical need to recognize the molecular basis for the low sensitivity of glioblastomas towards chemotherapeutic treatment. We have previously reported that elevated expression levels of the DNA repair protein hABH2 may provoke temozolomide resistance in glioma cells. In this work, we explored whether activation of the p53 (encoded by TP53) pathway by the MDM2 antagonist nutlin-3 would influence cellular levels of hABH2 and subsequently chemoresistance. Immunoblotting following nutlin-3 exposure for 24 hours showed increased protein levels of p53, MDM2, p21 and PUMA in glioma cell lines expressing wild type p53, but decreased hABH2 levels in a dose-dependent manner. Real-time quantitative PCR confirmed reduced hABH2 mRNA levels after nutlin-3 therapy, suggesting that hABH2 downregulation occurred at a transcriptional level. Combination therapy with nutlin-3 and temozolomide further enhanced activation of the p53 pathway, diminished levels of hABH2 protein and increased cellular cytotoxicity compared to either agent alone. Our results show that levels of hABH2 can be downregulated by activation of the p53 pathway in glioma cells. This suggests that p53 pathway activation may increase glioma sensitivity to chemotherapy not only by increased transcription of pro-apoptotic genes such as PUMA, but also by reducing levels of DNA repair proteins such as hABH2 that would otherwise promote drug resistance. 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 1725. doi:10.1158/1538-7445.AM2011-1725