Abstract 4276: In-vivo imaging of glioma cancer stem cells
Authors: Vlashi Erina , Evers Patrick , Lee Percy , Selch Michael , DeMarco John , Agazaryan Nzhde , Sayre James W. , Kim Kwanghee , Selch Michael , Frank Pajonk 
Published: February 2011

Abstract
Recent data support that glioblastoma (GB) is organized hierarchically with a small population of cancer stem cells (CSCs), able to repopulate an entire tumor. The cell of origin in GB is currently unknown, but animal data suggest that CSCs derive from the normal SC population and that the normal stem cell niche in the brain may harbor CSCs in patients with GB. Because therapies targeting CSCs directly may potentially improve patient outcome, novel means are needed to track CSCs and their interaction with the tumor microenvironment to develop and test novel therapeutic approaches.
Using limiting dilution assays we studied if glioma CSCs (GCSCs) can be serially transplanted in Rag2−/− γc −/− KO mice. Radiation responses of the population of glioma GCSCs were investigated using FACS. Radiation sensitivity assessed in sphere forming capacity assays. To studying proteasome activity in normal neuronal stem cells a transgenic animal model was generated that reports activities of the proteasome. Finally, the role of the normal tissue SC niche for radiation therapy outcome was investigated in a retrospective analysis of patient data.
GCSCs showed increased tumorigenicity over non-tumorigenic cells in the Rag2−/− γc −/− mouse model supporting a hierarchical CSC model in GB. GCSCs could be serially transplanted over at least 5 generations and reassembled the typical histopathology of GB. When unselected glioma cells were subjected to fractionated irradiation, cells were highly enriched for GSCSs. We did not detect differences in H2AX phosphorylation directly after irradiation, which was consistent with previous studies reporting comparable amounts of initial DNA damage in GCSCs and non-tumorigenic cells. Single cell sphere formation after irradiation indicated a 1.3-fold increase in radioresistance for GCSCs (measured at 10% survival) supporting previously reported increased DNA repair in CSCs. Using sections of brains from transgenic animals, which report lack of proteasome function by accumulation of ZsGreen, we identified a rare cell population in the subventricular zone of the brain that lacks proteasome function, consistent with normal stem cell origin of GCSCs.
Clinically, radiation dose of 43Gy and higher delivered to the periventricular region of the brain of patients with high-grade glioma was correlated with improved progression-free survival and (n=55, 7.2 vs. 15 months, p=0.028, log-rank) and a decreased risk ratio in a Cox proportional Hazard model (p=0.034).
We conclude that lack of proteasome activity is a valuable marker for tracking GCSCs and their treatment responses. Low proteasome activity seems to be shared by malignant and normal stem cells in the brain, supporting the hypothesis that normal tissue stem cells in the brain are the cells of origin in GB. Our clinical data indicate that the normal tissue stem cell niche in the brain may harbor GCSCs and that targeted treatment of this region could improve patient outcome.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4276.