Abstract 3179: TORC1/2 inhibition sensitizes MYC-driven medulloblastoma cells to carboplatin chemotherapy

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Abstract Medulloblastoma is the most common malignant pediatric brain tumor. Tumors having high levels of c-MYC have the worst clinical prognosis, with only a minority of patients surviving. To address this unmet clinical need, we generated a human neural stem cell model of high medulloblastoma that recapitulated the most aggressive subtype phenotypically and by mRNA expression profiling. We performed an in silico analysis of these cells, which predicted that mTOR inhibitors would be potential therapeutic agents. The dual TORC1/2 inhibitor TAK228 (also known as MLN128 and INK128) is orally bioavailable and penetrates the brain. TAK228 is currently in early clinical trials for adults with glioblastoma. We hypothesized that TAK228 would have activity against MYC-driven medulloblastoma. We tested this hypothesis using the MYC amplified medulloblastoma cell lines D425 and D283 as well as our human neural stem cell models. We determined that TAK228 was effective in inhibiting both mTORC1/2 as measured by western blots showing decreased p-S6 and p-AKT473 expression. P-S6 expression is decreased by 90% and p-AKT expression is decreased by 70% in D425 cell lines treated with 20nM TAK228. We found that treatment with TAK228 decreases cell growth in D425 and D283 high-MYC medulloblatoma cell lines at concentrations of 20nM (D425 p<0.005 vs vehicle, D283 p<0.0005 vs vehicle). We also found that TAK228 induces apoptosis as measured by cleaved caspase 3 staining and an increased expression of cleaved PARP (D425 p<0.05 vs vehicle, D283 p<0.0005 vs vehicle). Because mTOR inhibition can suppress glutathione production, and glutathione is required to detoxify platinum containing chemotherapy, we hypothesized that TAK228 would cooperate with carboplatin, which is part of the current standard treatment for high-risk medulloblastoma. TAK228 in combination with carboplatin inhibits cell growth as measured by MTS assay (D425 p<0.05 vs vehicle, D283 p<0.05 vs vehicle) and induces apoptosis as measured by cleaved PARP expression. Combination therapy of TAK228 and carboplatin treatment leads to a 7-fold increase in cleaved PARP compared to cells treated with the vehicle. In vivo testing in orthotopic xenografts is currently underway to determine the survival benefit of TAK228 in combination with carboplatin. TAK228 is effective at inhibiting growth and inducing apoptosis in high-MYC medulloblastoma cell lines and shows strong combinatorial efficacy with carboplatin. Citation Format: Rachael E. Maynard. TORC1/2 inhibition sensitizes MYC-driven medulloblastoma cells to carboplatin chemotherapy [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 3179.