Abstract 1280: The intersection of the PI3K/mTOR and HIPPO pathways: a potential therapeutic target for medulloblastoma

Abstract

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor; it is genetically defined into 4 subgroups which defines the clinical course of the disease. Despite current treatment modalities such as surgical resection, radiation, and chemotherapy, there are still significant morbidities and adverse side-effects. Recently defined genetic pathways could possibly offer a better management and treatment of patients with MB. The HIPPO signaling pathway has recently been shown to intersect with PI3K and Sonic Hedgehog (SHH) pathways to modulate mechanistic target of rapamycin (mTOR), an important regulator in cell growth and migration. The aim of this study is to elucidate the interaction of Hippo and Akt/mTOR signaling pathways with SHH pathways in MB, and define the potential downstream targets of therapy by using combined inhibitors. In order to achieve our goals, we evaluated the expression of activated AKT/mTOR in MB tumors using immunohistochemistry (IHC), along with the expression of transcriptional co-activators yes-associated protein (YAP), a down-stream effector of the HIPPO pathway. Scratch and chemotactic migration were used to assess the motility of MB cells following treatment with inhibitors of the aforementioned pathways. Cell cycle analysis and proliferation were measured using EdU and MTT techniques, respectively. YAP-SiRNA treatment was used to inhibit HIPPO pathway. MicroRNA-29, which mediates the mTOR pathway by modulating PTEN levels, was investigated. Results demonstrated: 1. A significant number of MBs expressed activated pAKTSer473 and pmTORSer2448, along with YAP, the downstream effector of the HIPPO pathway; 2. Treatment with inhibitors of PI3K/AKT (LY294002) and mTOR (rapamycin), given with EGF, significantly reduced cellular motility; 3. SHH inhibitor cyclopamine given with LY294002 or rapamycin significantly reduced cellular motility; 4. Cell proliferation was suppressed by inhibition of the HIPPO pathway using 3 unique 27mer duplexes of YAP1 siRNA treatments; 5. Combined treatment of cyclopamine with either LY294002 or rapamycin caused maximum suppression of cellular growth. In conclusion, these results demonstrate that the Hippo and PI3K/Akt/mTOR pathways are over-expressed in MB, and that the combined targeting of mTOR/HIPPO pathway with SHH inhibitor may provide alternative strategies for the treatment of MB, and offers a targeted therapy for improved prognosis. Citation Format: Jennifer S. Ronecker, Paul Lee, Sudeepta Sridhara, Michael LaBagnara, Raj Murali, Meena Jhanwar-Uniyal. The intersection of the PI3K/mTOR and HIPPO pathways: a potential therapeutic target for medulloblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1280.