Abstract 3560: 6-diazo-5-oxo-norleucine resistant MYC-driven medulloblastoma tumors are sensitive to inhibition of glutaminase suggesting a possible glutaminase-independent mechanism of resistance
Authors: Hanaford Allison Rose , Poore Bradley , Eberhart Charles G. , Raabe Eric H. 
Published: July 2017

Abstract
Increased MYC levels can alter cellular metabolism, creating a reliance on glutamine. Glutamine PET and MRI spectroscopy demonstrate that aggressive brain malignancies have increased uptake of glutamine and increased glutamate relative to normal brain, suggesting that agents targeting glutamine metabolism may be active in brain tumors. 6-diazo-5-oxo norleucine (DON) is a glutamine analog that was tested extensively in adult and pediatric malignancies but never advanced beyond phase I clinical trials. We hypothesized that DON would be effective against the MYC-driven subgroup of the pediatric brain tumor medulloblastoma. DON treatment increased the median survival of mice bearing D425Med xenografts by 246 percent (26 days for vehicle treated mice compared to 90 days DON treated mice, p=0.0018) and the median survival of mice bearing the MYC-driven patient derived xenograft MED211 by 80 percent (49 days for vehicle treated mice compared to 88 days for DON treated mice, p=0.0017). We also tested DON prodrugs designed for improved oral bioavailability and CNS penetration. Our novel DON prodrugs increased the median survival of mice bearing MYC-driven D425MED orthotopic xenografts by 60 percent (22 days for vehicle treated mice compared to 35 days for prodrug treated mice, p&lt;0.01). In non-human primates, our DON prodrugs exhibited superior 10-fold enhanced CSF/plasma ratio versus regular DON. Though DON treatment causes a dramatic increase in survival, resistance eventually develops. To investigate the mechanism of DON resistance, we tested the effect of other glutamine metabolic inhibitors on multiple cell lines generated from DON-resistant xenografts. DON-resistant xenograft derived cell lines maintained DON resistance in culture, but were sensitive to treatment with the glutaminase inhibitor compound 968 and the glutamine analog Acivicin. Compound 968 treatment decreased growth of DON-resistant cell lines by an average of 79 percent (p&lt;0.0008), and Acivicin treatment decreased growth by an average of 78 percent (p&lt;0.00003). Glutaminase catalyzes the first step in glutamine metabolism–the conversion of glutamine to glutamate. The sensitivity of DON-resistant cells to glutaminase inhibition indicates continued tumor reliance on glutaminase activity. We are continuing to investigate the mechanism DON resistance, with the goal of developing a rational combinatorial therapy to treat resistant tumors. This knowledge could increase the potential utility of DON as a clinical agent.
Citation Format: Allison Rose Hanaford, Bradley Poore, Charles G. Eberhart, Eric H. Raabe. 6-diazo-5-oxo-norleucine resistant MYC-driven medulloblastoma tumors are sensitive to inhibition of glutaminase suggesting a possible glutaminase-independent mechanism of resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3560. doi:10.1158/1538-7445.AM2017-3560