Abstract 3090: Targeting glutamine metabolism as a therapeutic strategy in MYC-driven medulloblastoma

Abstract

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Currently, treatment consists of surgical resection, chemotherapy, craniospinal radiation, and is associated with high morbidity. Of the four molecular subgroups of MB, group 3 tumors are have the worst clinical prognosis and are associated with elevated c-MYC levels. Because MYC over-expression can lead to increased glutamine metabolism and glutamine addiction in other cancer types, we hypothesized that MYC-driven MB would exhibit increased glutamine metabolism and be sensitive to inhibitors of glutamine metabolism. In MB cell lines, MYC expression positively correlates with increased expression of enzymes involved in glutamine metabolism as measured by western blot. To investigate the hypothesis that inhibition of glutamine metabolism would preferentially target MYC driven MB, we tested the effects of two glutamine analogs—acivicin and 6-diazo-5-L-norleucine (DON)—that inhibit glutaminolytic enzymes. Acivicin and DON significantly decreased the growth of the high-MYC MB cell lines D425 and D283 as measured by MTS assay (D425 p<0.05 vehicle vs acivicin, D283 p<0.05 vehicle vs 50uM acivicin; D425 p<0.05 vehicle vs DON, D283 p<0.05 vehicle vs DON). Treatment with acivicin and DON also decreased proliferation as measured by BrdU incorporation. Apoptosis increased upon treatment with acivicin and DON treatment as determined by cleaved caspase 3 immunofluorescence positivity and an increased percentage of cells in the sub2N population as measured by flow cytometry. In neurosphere models of MYC and non-MYC driven MB, MYC-expressing cells showed a significant decrease in proliferation after acivicin treatment as measured by BrdU incorporation (p<0.005), while the proliferation of MYC-negative cells was unaffected. MB neurosphere models expressing MYC also showed an increase in apoptosis as measured by cleaved caspase 3 immunofluorescence positivity (p<0.003) and an increased percentage of cells in the sub2N population. Fewer mice receiving acivicin treatment following D425 xenograft developed flank tumors than untreated mice (40% treated mice vs 100% untreated mice). Treated mice also had smaller tumors than untreated mice (80.9mm3 in treated mice vs 273.8mm3 in untreated mice). Knocking down the expression of the glutaminolytic enzyme glutaminase using a short hairpin resulted in a significant decrease in growth in D425 (p<0.05 scramble control vs GLS hairpin) and D283 (p<0.05 scramble control vs GLS hairpins). Our laboratory is currently conducting in vivo orthotopic xenograft experiments using a MB cell line where GLS expression has been knocked-down using a short hairpin, and we predict that GLS knock-down will prolong survival. Taken together, our data suggest that glutamine metabolism may be a therapeutic target in MYC-driven MB and that glutamine analogs may be useful therapeutic agents. Citation Format: Allison Rose Hanaford, Charles G. Eberhart, Eric H. Raabe. Targeting glutamine metabolism as a therapeutic strategy in MYC-driven medulloblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3090. doi:10.1158/1538-7445.AM2014-3090