Abstract 5859: Enhanced therapy for MYC-driven medulloblastoma by targeting protein translation pathway

Abstract

Abstract Medulloblastoma is the most frequent pediatric brain tumor of neuroectodermal cerebellar origin. High-risk MB patients with MYC overexpression and amplification usually show an extremely poor clinical outcome responding poorly to current therapies. Recent preclinical studies have revealed that the aberrant activation and interactions of PI3K/AKT/mTOR signaling is frequently associated with MYC-driven MB therapy-resistance. In addition, it is evident that both MYC and mTOR components of the PI3K/AKT/mTOR signaling axis can directly control and share a common translation pathway in increasing protein synthesis by regulating the expression of multiple components of the protein synthesis machinery, including ribosomal proteins and initiation factors of translation. Thus, inhibiting enhanced protein synthesis may represent a highly relevant strategy for the treatment of MYC-driven MB. Therefore, in this study, we investigated the single agents and combined anti-MB efficacies of a recently well-established BRD4 (bromodomain-containing protein 4)/MYC inhibitor JQ1 and PI3K-mTOR dual inhibitor BEZ235. Using four MB cell lines including three MYC amplified cell lines, the in vitro efficacy of this combined approach on cell growth/apoptosis and cell cycle along with associated molecular mechanism(s) were investigated. We used an MTT assay to measure survival and proliferation, flow-cytometric-based propidium-iodide staining to determine the effects of these inhibitors on cell-cycle, Annexin-V analyses to examine the cells undergoing apoptosis following treatments and western blot analyses to determine the expression levels of target molecules. Our results showed that both inhibitors as single agents, significantly decreased MB cell growth and induced apoptosis by targeting the key molecules of the associated pathways. Combined treatment of JQ1 and BEZ235 significantly decreased MB cell growth/survival in a dose-dependent fashion compared to single agent activity. Moreover, JQ1 and BEZ235 alone or combined significantly induced G1 cell-cycle arrest which coincided with decreased expression of cyclin-D1 and increased expression of p21 proteins in MYC-driven MB cells. Mechanistically, the co-treatment of JQ1 and BEZ235 significantly downregulated the expression levels of phosphorylated 4EBP1/p70-S6K (mTOR components) and BRD4/MYC proteins. Together, our findings demonstrate that the combination of JQ1 and BEZ235 showed significant synergistic efficacy against MYC-driven MB, by enhancing the inhibition of protein synthesis (translation) pathway. Initial evidence from this targeted approach, suggests that additional preclinical evaluation is warranted to determine likely clinical utility of targeted therapy for high-risk MB patients. Citation Format: Nagendra K. Chaturvedi, Don W. Coulter, Matthew J. Kling, Sutapa Ray, Timothy R. McGuire, Shantaram S. Joshi, J. Graham Sharp. Enhanced therapy for MYC-driven medulloblastoma by targeting protein translation pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5859.