Pediatric brain tumor cancer stem cells: cell cycle dynamics, DNA repair, and etoposide extrusion

Abstract

Reliable model systems are needed to elucidate the role cancer stem cells (CSCs) play in pediatric brain tumor drug resistance. The majority of studies to date have focused on clinically distinct adult tumors and restricted tumor types. Here, the CSC component of 7 newly established primary pediatric cell lines (2 ependymomas, 2 medulloblastomas, 2 gliomas, and a CNS primitive neuroectodermal tumor) was thoroughly characterized. Comparison of DNA copy number with the original corresponding tumor demonstrated that genomic changes present in the original tumor, typical of that particular tumor type, were retained in culture. In each case, the CSC component was approximately 3–4-fold enriched in neurosphere culture compared with monolayer culture, and a higher capacity for multilineage differentiation was observed for neurosphere-derived cells. DNA content profiles of neurosphere-derived cells expressing the CSC marker nestin demonstrated the presence of cells in all phases of the cell cycle, indicating that not all CSCs are quiescent. Furthermore, neurosphere-derived cells demonstrated an increased resistance to etoposide compared with monolayer-derived cells, having lower initial DNA damage, potentially due to a combination of increased drug extrusion by ATP-binding cassette multidrug transporters and enhanced rates of DNA repair. Finally, orthotopic xenograft models reflecting the tumor of origin were established from these cell lines. In summary, these cell lines and the approach taken provide a robust model system that can be used to develop our understanding of the biology of CSCs in pediatric brain tumors and other cancer types and to preclinically test therapeutic agents.

Musashi1 Impacts Radio-Resistance in Glioblastoma by Controlling DNA-Protein Kinase Catalytic Subunit

“…30 Increased DNA repair capacity of cancer stem cells has been associated with resistance to radiotherapy. 31 We suggest in this work that the functional involvement of MSI1 in the efficient repair of double-strand breaks by the NHEJ pathway is a possible mechanism of the observed chemoresistance. NHEJ is the predominant repair pathway in the mammalian system during the G1 and M phases, although it is active throughout the cell cycle.…”

Polo-Like Kinase 1 Inhibition Kills Glioblastoma Multiforme Brain Tumor Cells in Part Through Loss of SOX2 and Delays Tumor Progression in Mice

“…Similar to ''stem cells,'' tumor initiating cells (TICs) exhibit self-renewal and multilineage differentiation capabilities; moreover, TICs form tumors upon serial transplantation in immuno-compromised mice [3][4][5][6]. Brain tumor initiating cells (BTICs) have been found to be resistant to both chemo-and radiation therapies due to elevated expression of drug efflux proteins, enhanced DNA repair activity, and evasion of apoptosis [7][8][9][10][11]. Therefore, BTICs may play a role in tumor relapse.…”

Cancer stem cells: a challenging paradigm for designing targeted drug therapies

“…CSCs have now been reported in most human tumors, including those in breast, brain, colon, ovary, pancreas, and prostate, and melanoma and multiple myeloma [14,[26][27][28][29]. To isolate and identify CSCs from solid and hematological tumors, biomarkers that are specific for normal stem cells of the same organ(s) can be deployed.…”

“…Given their ability to develop new tumors, and evade chemo-and/or radiotherapy, CSCs were implicated in the exacerbation of tumor metastatic potential and subsequent cancer recurrence [13][14][15][16]. CSCs further have the ability to migrate and undergo rapid clonal proliferation [3,5,17,18] and differ from normal cancer cells in the expression of key cancer-specific markers, which are primarily located in hypoxic regions and subject to modulation by niche signal(s) [2,5,6,8,19,20].…”