Abstract
Glioblastoma (GBM) is uniformly fatal with a median survival of just over 1 year. Cranial radiation therapy (RT) alone or with Temozolomide is standard of care. Despite improved survival, the tumor inevitably recurs often more aggressively. The cause for such increased aggressiveness after RT is unclear. Our group previously established the transcriptional signature of radiated brain microglia, wherein 95% of the differentially upregulated genes pertained to inflammation, extracellular matrix (ECM), and mitochondria. Moreover, radiation has been shown to alter structure and maturation of ECM proteins. We hypothesized that changes in the radiated brain microenvironment may account for the observed aggressiveness of the recurrent tumor phenotype. To address this, nude mice were cranially radiated with 0, 10 or 20Gy radiation (N=10, mice per group). After 24hrs, mice underwent intracranial implantation of GBM cells from established xenograft, and tumor growth was monitored until moribund (~52 days) using MRI. At 1 month, microdialysis was performed on the contralateral hemisphere on at least 3 mice from each group, and perfusates were analyzed via unsupervised metabolomic profiling using liquid chromatography-mass spectrometry (LC-MS). After multivariate analysis, 100 metabolites were found to be differentially expressed between groups. Principle component analysis effectively separated groups 0Gy and 10Gy from 20Gy radiation. Among metabolites identified to be significantly upregulated after radiation (q ≤ 0.001), Allantoin, Creatinine and Glyceraldehyde, have been documented as intermediates of inflammatory pathways or neurodegeneration. Additionally, histologic evaluation of the brain sections revealed significant increase in overall tumor burden upon 20Gy radiation (p=0.03), %positive HE stained tumor area as 15% and 27% for 0Gy (N=9) and 20Gy (N=8), respectively; higher infiltrative behavior was confirmed by h-Lamin A+C, IF. These data suggest that changes in the extracellular milieu after RT may facilitate aggressive tumor recurrence. Harnessing metabolomic insights may reveal opportunities to attenuate the RT-associated aggressiveness of recurrent GBM.