Abstract 5874: Targeting DDX3 in medulloblastoma by RK-33

Abstract

Abstract Introduction: Medulloblastoma is the most common form of pediatric brain cancer. Current treatments of surgical resection, craniospinal irradiation, and chemotherapy increase survival but around 40% of patients experience disease recurrence. Classically, four molecular subgroups of medulloblastoma have been identified: Wnt; Sonic hedgehog (SHH); Group 3; and Group 4. More recent work has subtyped up to seven molecular subgroups. The RNA helicase DDX3 is involved in many biological activities such as transcription, mRNA translation, splicing, and nuclear export. About 8% of medulloblastoma cases involve mutations in DDX3, of which 11% involve the pediatric Wnt and SHH subtypes. In addition, coinciding DDX3 and CTNNB1 mutations associated with dysregulated Wnt /β-catenin signaling in Wnt-type medulloblastomas have also been reported. Aims and Methods: The goal of this work was to study whether RK-33, a small molecule inhibitor of DDX3, would be effective against medulloblastoma as a single agent and in combination with radiotherapy. We studied DDX3 expression in medulloblastoma cell lines DAOY and UW228 and human tissue microarrays by immunohistochemistry, western blotting, and qRT-PCR. We targeted DDX3 by siRNA and by RK-33 and observed proliferation and viability changes by MTS assays. Flow cytometric analysis was used to determine effect of RK-33 on cell cycle and apoptosis. TOP/FOP promoter assay was utilized to study effect on TCF promoter activity. We used colony formation assays to study effect of combining radiation and RK-33 treatment on cells. DAOY tumors were generated in nude mice and treated with combination therapy to study effects in vivo. Results: High DDX3 expression was observed in 55% of pediatric and 66% of adult medulloblastomas. DDX3 knockdown resulted in reduced cellular proliferation. Both the medulloblastoma cell lines were sensitive to RK-33, with IC50 values of 2.5 µM and 3.5 µM, respectively and resulted in decreased levels of DDX3 expression, with no observable toxicity. RK-33 resulted in a G1 phase cell cycle arrest before the onset of apoptosis. DDX3 knockdown resulted in a significant decrease of TCF activity and reduced transcription of Axin2, CCND1, MYC, and Survivin. A combination of RK-33 and radiation resulted in a significantly higher inhibitory effect than using single treatment of either RK-33 or radiation. We conclude that inhibiting DDX3 via the small molecule inhibitor RK-33 is effective in reducing medulloblastoma tumors and that the effect is synergistic with radiation treatment. Citation Format: Saritha Tantravedi, Farhad Vesuna, Allison Martin, Michael Lim, Charles G. Eberhart G. Eberhart, Paul J. van Diest, Venu Raman. Targeting DDX3 in medulloblastoma by RK-33 [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 5874.