Abstract 763: A systematic screening identify new drugs impairing medulloblastoma tumorigenesis

Abstract Medulloblastoma (MB) is the most common Central nervous system (CNS) neoplasia accounting for 25% of all childhood brain tumors. The Wnt, Sonic and Notch developmental cascades all regulate CNS cell dynamics, and are mutationally activated in a subset of MBs. So far the main limitation of the current treatment of MB is the lack of drug specificity, we aim to identify new specific impairment pathway drugs to offer new therapeutic tools in order to improve the clinical management of this neoplasia. The Wnt signaling pathway ends in the regulation of the levels of β-catenin which accumulates in the nucleus and interacts with the LEF/TCF family of transcription factors; in the absence of Wnt stimulation, β-catenin is phosphorylated by several kinases, as a complex comprising GSK3-β, Axin and APC, and it is targeted for degradation in the cytoplasm via the ubiquitin-proteasome pathway. Wnt activation includes key regulators of proliferation, among which c-Myc and cyclin D1 play a crucial role. We screened a drug library including almost 1200 compounds which are not well characterized on their activity against cancer cells. The library contains a repository of Natural Products, that derive from marine and plant sources collected worldwide, and a Synthetic library Products. We tested the efficacy of the Natural Products to interfere with Wnt pathway, using the TOP/FOP luciferase assay. From this large screening, we focused our attention on three natural compounds (Cantharidin, Parthenolide, Homoharringotnine) which positively inhibit Wnt pathway in three independent MB cell lines: Daoy (a desmoplastic medulloblastoma), ONS-76 and UW288(classic medulloblastoma cell lines). We determined their ability to turn-off Wnt signaling by western blotting detecting β-catenin activated protein and by RT-PCR for controlling of mRNA levels of WNT target genes. Cantharidin (CTD) has an anticancer activity in leukemic cells and melanoma cells, but it is still to be identified which is the basis of its mechanism. CTD is a potent inhibitor of phosphatase PP1 and PP2A which play a positive role in regulating Wnt signalling since it dephosphorylates AXIN, by impairing APC complex. We screened CTD as the most effective drug to inhibit Wnt pathway in MB cells. By immunofluorescence, we observed that the nuclear amount of β-catenin was found reduced when the cells were exposed to CTD. We found its effectiveness in vitro and in vivo on tumor growth assays in nude and strengthen those with additional orthotopic cerebellum xenografs assays to further assign its molecular mechanism of action in MB thus suggesting its use for future therapeutic applications in mouse MB genetic models. Altogether these results are suggesting a new therapeutic strategy to treat MB to be further applied to other solid tumors which are mainly Wnt driven. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 763.