Abstract 3484: In vivo metabolomics reveals a potentially potent combination therapy for MYC-driven medulloblastoma

Abstract The MYC oncogene is associated with aggressive forms of the pediatric brain tumor medulloblastoma. MYC promotes oncogenesis in part by altering cellular glucose and glutamine metabolism. We hypothesized that MYC-driven medulloblastoma would be sensitive to the glutamine metabolic inhibitor 6-diazo-5-oxo-l-norleucine (DON). In MYC-driven medulloblastoma cell lines, 10uM DON treatment increases apoptosis by up to 280% (p<0.04) as compared to vehicle control. In human neural stem cells transformed with MYC, but not in untransformed cells, DON treatment caused up to a 127% increase in apoptosis compared to vehicle (p<0.001). Once-weekly DON therapy increased median survival by up to 246% (p<0.004) in three different MYC-driven medulloblastoma orthotopic xenograft models. To elucidate the mechanism of DON, we performed stable isotope resolved metabolomics (SIRM) on two MYC-driven medulloblastoma tumor models. SIRM revealed that tumors from DON treated animals had decreased production of asparagine (p<0.016). Production of aspartate was not decreased (p>0.4), suggesting that DON was inhibiting asparaginase synthetase, the enzyme that transfers the ammonia group from glutamine to aspartate to generate asparagine. We hypothesized that DON efficacy could be enhanced by asparaginase (ASNase), an enzyme that breaks down asparagine into aspartate and ammonia. ASNase is a commonly used therapy in pediatric patients with leukemia and lymphoma. In MYC-driven medulloblastoma cell lines, treatment with low-dose DON or ASNase as single agents did not significantly increase apoptosis by cleaved caspase-3 immunofluoresence or cleaved-PARP western blot. The combination of low-dose DON and ASNase increased apoptosis by up to 577% (p<0.0001). Similarly, in human neural stem cells transformed with MYC, the combination of low-dose DON and ASNase increased apoptosis by up to 523% (p<0.0001). We hypothesized that depletion of asparagine from both intracellular and extracellular pools would induce the uncharged tRNA/endoplasmic reticulum stress response. Western blotting revealed that the combination of DON and ASNase increased expression of the transcription factor ATF4 and the pro-apoptotic protein CHOP, which are critical components of the uncharged tRNA response. ATF4 is a known regulator of endoplasmic reticulum stress induced apoptosis through transcription of pro-apoptotic proteins. These data suggest that DON and ASNase could be a powerful therapeutic combination for treating MYC-driven medulloblastoma and possibly other MYC-driven malignancies. Citation Format: Allison R. Hanaford, Brad Poore, Jesse Alt, Barbara Slusher, Charles G. Eberhart, Eric H. Raabe. In vivo metabolomics reveals a potentially potent combination therapy for MYC-driven medulloblastoma [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 3484.