Abstract 1872: Targeting MYC-driven medulloblastoma using inhibitors of glutamine metabolism.

Medulloblastoma is the most common malignant brain tumor in children. Currently, treatment consists of surgical resection, chemotherapy, and whole brain and spine radiation, and is associated with high morbidity. Medulloblastoma is divided into four subgroups with different associated mutations and clinical prognoses. Group 3 medulloblastoma tumors are associated with elevated MYC levels and have the worst clinical prognosis of all four subtypes. Because MYC over-expression can lead to increased glutamine metabolism and glutamine addiction in other cancer types, we hypothesized that MYC-driven medulloblastoma would exhibit increased glutamine metabolism and be sensitive to inhibitors of glutamine metabolism. In medulloblastoma cell lines, MYC expression positively correlates with increased expression of enzymes involved in glutamine metabolism as measured by western blot and qPCR. Also, forced MYC expression in the non-MYC driven medulloblastoma cell lines UW228 and DAOY leads to corresponding increases in glutaminase expression as measured by western blot. To investigate the hypothesis that inhibition of glutamine metabolism would preferentially target MYC driven medulloblastoma, we tested the effects of two glutamine analogs—acivicin and 6-diazo-5-L-norleucine (DON)—that inhibit enzymes in the glutamine metabolism pathway. Acivicin decreased the growth of the high-MYC medulloblastoma cell lines D425 and D283 by 50% and 75% respectively compared to vehicle treated cells, but did not significantly affect UW228, a MYC-negative cell line. Acivicin treatment caused a 36% decrease in growth in UW228 cells forced to express MYC compared to a 5% decrease in growth in parental UW228 cells (p=.00029). We next tested the effect of acivicin on cell proliferation as measured by BrdU incorporation in neurosphere models of MYC and non-MYC driven medulloblastoma. MYC-expressing cells had a 30% decrease in proliferation following acivicin treatment, while MYC negative cells only showed a 7% decrease in proliferation (p=0.02). Treatment of MYC expressing cells with acivicin lead to increased apoptosis as measured by flow cytometry. MYC positive neurospheres treated with acivicin had a 65% increase in the percentage of cells in the sub2N population, while MYC-negative neurospheres did not show an increase in the sub2N population. Our laboratory is currently investigating the in vivo efficacy of glutamine metabolism inhibitors in orthotopic xenograft experiments using MYC-driven medulloblastoma cell lines. Taken together, our data suggests that glutamine metabolism may be a therapeutic target in MYC-driven medulloblastoma and that glutamine analogs may be useful therapeutic agents. Citation Format: Allison R. Hanaford, Charles G. Eberhart, Eric H. Raabe. Targeting MYC-driven medulloblastoma using inhibitors of glutamine metabolism. [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 1872. doi:10.1158/1538-7445.AM2013-1872