Replication stress drives constitutive activation of the DNA damage response and radioresistance in glioblastoma stem-like cells

Ross D Carruthers, Shafiq U Ahmed, Shaliny Ramachandran, Karen Strathdee, Kathreena M Kurian, Ann Hedley, Natividad Gomez-Roman, Gabriela Kalna, Matthew P Neilson, Lesley Gilmour, Katrina H Stevenson, Ester M Hammond, Anthony J Chalmers

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Glioblastoma (GBM) is a lethal primary brain tumor characterized by treatment resistance and inevitable tumor recurrence, both of which are driven by a subpopulation of GBM cancer stem-like cells (GSC) with tumorigenic and self-renewal properties. Despite having broad implications for understanding GSC phenotype, the determinants of upregulated DNA damage response (DDR) and subsequent radiation resistance in GSC are unknown and represent a significant barrier to developing effective GBM treatments. In this study, we show that constitutive DDR activation and radiation resistance are driven by high levels of DNA replication stress (RS). CD133+ GSC exhibited reduced DNA replication velocity and a higher frequency of stalled replication forks than CD133- non-GSC in vitro; immunofluorescence studies confirmed these observations in a panel of orthotopic xenografts and human GBM specimens. Exposure of non-GSC to low-level exogenous RS generated radiation resistance in vitro, confirming RS as a novel determinant of radiation resistance in tumor cells. GSC exhibited DNA double strand breaks (DSB) which co-localized with 'replication factories' and RNA: DNA hybrids. GSC also demonstrated increased expression of long neural genes (>1Mbp) containing common fragile sites, supporting the hypothesis that replication/transcription collisions are the likely cause of RS in GSC. Targeting RS by combined inhibition of ATR and PARP (CAiPi) provided GSC-specific cytotoxicity and complete abrogation of GSC radiation resistance in vitro. These data identify RS as a cancer stem cell-specific target with significant clinical potential.

Original languageEnglish
JournalCancer Research
Early online date5 Jul 2018
DOIs
Publication statusE-pub ahead of print - 5 Jul 2018

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