Abstract 5048: mTORC1/mTORC2 signaling in pediatric low grade glioma and pilocytic astrocytoma.

Abstract

Abstract Pilocytic astrocytoma is the most frequent low grade glioma in children and young adults. Previous studies support a role for MAPK pathway signaling, and more recently AKT/mTOR, in its biology. mTOR operates as part of two different multiprotein signaling complexes, mTORC1 and mTORC2. In the current study we evaluated mTORC1/mTORC2 pathway activity in pediatric low grade astrocytoma. We used formalin-fixed paraffin embedded human pilocytic astrocytomas for immunohistochemical studies in tissue microarrays. Moderate (2+) to strong (3+) immunostaining was observed for pS6 in 66/114(58%), p4EBP1 in 35/116(30%), pElF4G in 66/113 (58%), and mTOR (total) in 52/114 (46%), supporting mTOR pathway activation in a subset of pediatric astrocytomas. Specifically, there was increased immunoreactivity in pilocytic astrocytomas of the optic nerve proper (pS6 39/54(72%), p4EBP1 22/54 (41%), 4IF4G 41/53 (77%), and mTOR 28/54 (52%)), a difference that was statistically significant for pS6, p4E-BP1 and pEIF4G (p<0.05, Chi Square). Next, we studied total levels of Raptor (mTORC1 component) and Rictor (mTORC2 component). We observed moderate to strong Raptor reactivity in 81/142 (57%) and Rictor in 69/141(49%) pilocytic astrocytomas. By contrast, we observed increased Rictor immunostaining in 90/144 (63%) diffuse gliomas grade II-IV and Raptor in 28/147 (19%), a difference that was statistically significant between the two groups (p<0.001, Chi Square). Next we studied in vitro the effect of mTORC1 blockade in pediatric low grade glioma cell lines Res 186 and Res 259 with a TORC1 inhibitor. Using the MTT assay, Res 186 cell growth was inhibited with 1nM and 10nM drug concentrations, compared with DMSO (p<0.005, t-test), but the effect was less pronounced in Res 259. Additionally, pS6 levels were decreased by Western Blot in Res 186 cells, but not in Res 259, consistent with mTORC1 inhibition of Res 186 cells. The findings suggest that the mTOR pathway is active in a subset of pediatric low grade gliomas, that it varies by clinicopathologic subtype, and that it is primarily mediated by mTORC1 compared with other glioma subtypes. Furthermore, mTOR may represent a therapeutic target in pediatric low grade glioma that merits further investigation. Citation Format: Smit Shah, Marianne Hutt, Matthias A. Karajannis, Eric Raabe, Charles G. Eberhart, Fausto J. Rodriguez. mTORC1/mTORC2 signaling in pediatric low grade glioma and pilocytic astrocytoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5048. doi:10.1158/1538-7445.AM2013-5048