Single-nucleus analysis characterizes non-enhancing region of recurrent high-grade glioma

BackgroundNon-enhancing (NE) infiltrating tumor cells beyond the contrast-enhancing (CE) bulk of tumor are potential propagators of recurrence after gross total resection of high-grade glioma. MethodsWe leveraged single-nucleus RNA-sequencing on 15 specimens from 5 high grade gliomas to compare prospectively identified biopsy specimens acquired from CE and NE regions. Additionally, 24 CE and 22 NE biopsies had immunohistochemical staining for Ki67 to identify proliferative cell burden. ResultsTumor cells in NE regions are enriched in neural progenitor cell-like cellular states, while CE regions are enriched for mesenchymal-like states. These NE glioma cells have similar proportions of proliferative and putative glioma stem cells relative to CE regions, without significant differences in % Ki67 staining. Tumor cells in NE regions exhibit upregulation of genes previously associated with lower grade gliomas. Cell-, gene-, and pathway-level analyses of the tumor microenvironment in the NE region reveal relative downregulation of tumor-mediated neovascularization and presence of cell-mediated immune response, but increased glioma-to-non-pathological cellular interactions. ConclusionsThis comprehensive analysis illustrates differing tumor and non-tumor landscapes of CE and NE regions in high-grade gliomas, highlighting the NE region as an area harboring likely initiators of recurrence in a pro-tumor microenvironment and identifying possible targets for future design of NE-specific adjuvant therapy. Key PointsSignificant proliferating tumor burden exist in non-enhancing regions of glioma; non-enhancing regions have unique tumor and non-tumor expression properties Importance of StudyStandard of care treatment for glioblastoma relies on visualization of tumor via contrast-enhanced magnetic resonance imaging. However, non-enhancing regions harbor tumor cells that should be targets for adjuvant therapy given these regions are not resected in surgery. To begin addressing these infiltrating non-enhancing tumor cells, we thoroughly characterize the tumor and non-tumor microenvironment of non-enhancing regions in high grade gliomas. Understanding the total tumor burden, proliferating tumor ratio, and presence of putative glioma stem cells may help design adjuvant therapies for these unique population of tumor cells. Understanding the non-tumor immune and vascular microenvironment may help target these areas in regards to drug delivery and immunotherapy. Overall, in a disease marked by significant intratumoral heterogeneity, we focus identifying therapeutic strategies for areas not addressed at surgery.