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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 medulloblastoma that recapitulated the most aggressive subtype phenotypically and by mRNA expression profiling. An in silico analysis of these cells identified mTOR inhibitors as potential therapeutic agents. We hypothesized that the orally bioavailable TORC1/2 kinase inhibitor TAK228 would have activity against MYC-driven medulloblastoma. TAK228 inhibited mTORC1/2, decreased cell growth and caused apoptosis in high-MYC medulloblastoma cell lines. Comprehensive metabolic profiling of medulloblastoma orthotopic xenografts showed upregulation of glutathione compared to matched normal brain. TAK228 suppressed glutathione production. Because glutathione is required to detoxify platinum-containing chemotherapy, we hypothesized that TAK228 would cooperate with carboplatin in medulloblastoma. TAK228 synergized with carboplatin to inhibit cell growth and induce apoptosis and extended survival in orthotopic xenografts of high-MYC medulloblastoma. Brain-penetrant TORC1/2 inhibitors and carboplatin may be an effective combination therapy for high-risk medulloblastoma.

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. We performed an in silico analysis of human stem cell model of medulloblastoma, which predicted mTOR inhibitors as a potential therapeutic agent. We hypothesized that the dual TORC1/1 inhibitor TAK228 would have activity against MYC-driven medulloblastoma. We tested this hypothesis using the MYC-amplified medulloblastoma cell lines D425 and D283. We determined that TAK228 was effective in inhibiting both mTORC1/2 in D425 at concentrations of 20nM as measured by western blots showing decreased p-S6 (90% decrease) and p-AKT473 (70% decrease) expression. We found that treatment with TAK228 decreases cell growth at concentrations of 20nM (D425 p

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 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.

Atypical teratoid rhabdoid tumor (AT/RT) is among the most fatal of all pediatric brain tumors. Aside from loss of function mutations in the SMARCB1 (BAF47/INI1/SNF5) chromatin remodeling gene, little is known of other molecular drivers of AT/RT. LIN28A and LIN28B are stem cell factors that regulate thousands of RNAs and are expressed in aggressive cancers. We identified high-levels of LIN28A and LIN28B in AT/RT primary tumors and cell lines, with corresponding low levels of the LIN28-regulated microRNAs of the let-7 family. Knockdown of LIN28A by lentiviral shRNA in the AT/RT cell lines CHLA-06-ATRT and BT37 inhibited growth, cell proliferation and colony formation and induced apoptosis. Suppression of LIN28A in orthotopic xenograft models led to a more than doubling of median survival compared to empty vector controls (48 vs 115 days). LIN28A knockdown led to increased expression of let-7b and let-7g microRNAs and a down-regulation of KRAS mRNA. AT/RT primary tumors expressed increased mitogen activated protein (MAP) kinase pathway activity, and the MEK inhibitor selumetinib (AZD6244) decreased AT/RT growth and increased apoptosis. These data implicate LIN28/RAS/MAP kinase as key drivers of AT/RT tumorigenesis and indicate that targeting this pathway may be a therapeutic option in this aggressive pediatric malignancy.