DDDR-05. Non-enhancing regions of Glioblastoma Harbor Quiescent Stem Like Cells that Contribute to Chemotherapy Resistance

Abstract BACKGROUND Glioblastoma exhibits regional heterogeneity, with distinct cellular phenotypes and molecular features between contrast-enhancing (CE) solid tumor regions and non-enhancing (NE) infiltrative regions. Understanding functional repercussions of this heterogeneity is important. METHODS Image guided biopsies of CE and NE regions of newly diagnosed IDH wild-type glioblastoma were obtained. Tissues were analyzed using single cell sequencing to identify glioma stem cell populations using gene set enrichment analysis and established gene signatures. Cells were treated with temozolomide (TMZ, 1000 μM), paclitaxel (PTX, 50 μM), topotecan (TPT, 50 μM), vincristine (VCR, 50 μM), and doxorubicin (DOX, 20 μM) for 48 hours. Cell viability was measured using a luminescence-based assay to assess regional differences in chemotherapeutic response. RESULTS Matched samples from 5 patients were sequenced and identified NE regions as harboring elevated levels of glioma stem-like cells using multiple established signatures. Multiple cell markers including several HOX genes, PROM1, F3, ID4, PAUPAR were significantly upregulated in NE tumor cells (FC ≥ 4.0; FDR < 0.05). Samples from NE regions grew slower (p<0.001) than CE regions at the 1-week mark, but were able to recapitulate confluent tumor in cortical organoid and xenograft models by 4 weeks. In matched samples from 3 patients, there was significantly reduced chemotherapeutic efficacy in NE regions (CE viability vs NE viability, p = 0.17) in the various chemotherapeutic agents tested. CONCLUSION NE infiltrating regions of glioblastoma maintain high proportions of cells that have characteristics of glioma stem cells transcriptionally. These regions have slow initial growth in in vitro and in vivo models, but are able to recapitulate solid tumor properties. Likely related to this quiescent property, NE regions are more resistant to chemotherapeutic agents.