TMIC-54. Identifying and exploiting molecular abnormalities of glioma vasculature

Abstract The aberrant properties of brain tumor vasculature are increasingly recognized as barriers to efficient delivery and distribution of bloodborne therapies. These aberrant properties emerge from molecular abnormalities that can be identified through comparisons with normal human brain vasculature. However, vascular cells are difficult to isolate and capture, which leads to under-representation in single-cell datasets and challenges identifying reproducible molecular differences among patient populations. To address these challenges, we have developed a computational strategy to isolate transcriptional profiles of vascular cells through integrative gene coexpression analysis of bulk transcriptomes. We have applied this strategy to ~100 gene expression datasets representing >12K normal adult human brain and adult malignant glioma samples and identified robust markers of glioma vasculature that are not observed in normal adult human brain vasculature. These markers include ENPEP (aminopeptidase A), which encodes a cell-surface protein that is implicated in blood pressure regulation and angiogenesis. We confirmed histologically that ENPEP is profoundly upregulated in hyperplastic blood vessels of glioblastomas (GBMs) and to a lesser extent IDH-mut gliomas but is not detectable in vascular cells of non-neoplastic adult human brain. Furthermore, over 6503 normal adult human brain samples profiled with diverse technology platforms, we found that ENPEP is expressed in the 8th percentile genome-wide. To characterize the functional significance of ENPEP in GBM, we acquired firibastat, an oral prodrug that crosses the blood-brain barrier and selectively inhibits ENPEP. We used the GBM14 FL intracerebral tumor xenograft model to investigate the anti-tumor efficacy of firibastat in vivo. Log-rank survival analysis revealed that firibastat delivered daily by oral gavage (500mg/kg) significantly extended survival (P = 0.04 vs. vehicle). These results support further study of ENPEP and other novel glioma vascular markers for potential applications as biomarkers and therapeutics.