CNSC-83. A CHARACTERIZATION OF QUIESCENCE AND STEMNESS IN PATIENT-DERIVED GLIOBLASTOMA CELLS

Abstract This project seeks to improve understanding of glioblastoma recurrence and resistance, which has often been linked to a population of cells that are quiescent and have stem-like properties, so that better treatment modalities can be developed for the most aggressive primary CNS cancer. In particular, this paper seeks to quantify stem cells, quiescent cells, and their overlap in normoxia, hypoxia, and under other conditions associated with the tumor microenvironment. We have utilized Fluorescent Ubiquitination-based Cell Cycle Indicator (FUCCI) along with Ki-67 and P27 staining in patient-derived glioblastoma neurospheres to identify a G0 phase along with other key points in the cell cycle, and co-stained with CD133 and CD44 to identify glioblastoma stem cells (GSCs). Using this system, we found that both quiescence and stemness were significantly increased in hypoxia and under co-culture with THP-1 monocytes. There was also a significant increase in the percentage of quiescent cells under hypoxia for the subpopulation of cells that were identified as stem cells. Interestingly, there was a significant decrease in the percentage of quiescent cells from the entire cell population compared to the subpopulation that was identified as stem cells. When various stages of the cell cycle were looked at for stem cell enrichment, there was a significantly higher percentage of stem cells in the G1/S phase as compared to all of the other stages of the cell cycle. Overall, this research shows a shift towards quiescence and stemness individually under both hypoxia and monocyte coculture, but a weak overlap between the two. The distribution of stem cells among the various stages of the cell cycle could also indicate that stemness is increased when glioblastoma cells re-enter the cell cycle, rather than co-existing with quiescence, as is commonly believed. Further work needs to follow these changes with treatment and understand their mechanistic underpinnings.