Abstract B38: Quiescence as a marker of treatment resistance and malignancy in GBM

Abstract

Abstract Glioblastoma multiforme (GBM) is a World Health Organization grade IV astrocytic tumor, and is the most common primary brain malignancy. GBM is characterized as being highly malignant and rapidly progressive with a high mitotic index, diffuse invasion, microvascular proliferation and pseudopalisading necrosis. Current best treatment for GBM involves maximal safe surgical resection, with radiotherapy (XRT) and temozolomide (TMZ), but even with this regime patients survive for an average of only ~15 months. GBM’s position within the brain and diffuse progression profile prevents a surgical cure, and the cells left behind following surgery contain a quiescent, treatment-resistant subpopulation of cells with a stem-like capacity for self-renewal which survive chemoradiotherapy and cause relapse. These resistant cells have been referred to as cancer stem cells, but while stem cell markers have been useful in enriching stem populations in some cancers, a marker that reliably defines the glioma stem cell has remained elusive. The critical feature that allows these resistant cells to survive treatment is their slow division rate, which helps them to avoid chemoradiotherapy-induced cell death by virtue of their condensed chromatin and reduced requirement for DNA replication. In the present study we use a pulse-chase assay to ubiquitously label glioma cell lines with the fluorescent dye Oregon Green and observe the label dilution as an indicator of cell division. Based on their slower division rates, quiescent cells retain the dye longer than rapidly-dividing cells and are easily identified by fluorescence imaging and FACS analysis. Once such a population is isolated it can then be compared to a rapidly-dividing (Oregon Green-diluting) subpopulation of cells to analyze differences in treatment resistance, migration, invasion, and gene expression between the two populations. It is hoped that by elucidating the molecular mechanisms that drive treatment resistance and migration/invasion we will be able to inform novel GBM treatments that improve patient outcomes. We have shown that quiescent cells are innately resistant to the current gold standard GBM treatments and display more malignant features in vitro than rapidly dividing cells. We have developed a platform for quick, easy, and reliable isolation of this quiescent fraction of cells to facilitate its interrogation. This method has the potential to identify future treatment targets, and could, in principle, be extended to other malignancies. Citation Format: Ryan J. Atkins, Stanley S. Stylli, Rodney B. Luwor, Thomas MB Ware, Andrew H. Kaye, Christopher M. Hovens. Quiescence as a marker of treatment resistance and malignancy in GBM. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B38.