title: Increased sensitivity to ionizing radiation by targeting the homologous recombination pathway in glioma initiating cells.
abstract: Glioblastoma is deemed the most malignant form of brain tumour, particularly due to its resistance to conventional treatments. A small surviving group of aberrant stem cells termed glioma initiation cells (GICs) that escape surgical debulking are suggested to be the cause of this resistance. Relatively quiescent in nature, GICs are capable of driving tumour recurrence and undergo lineage differentiation. Most importantly, these GICs are resistant to radiotherapy, suggesting that radioresistance contribute to their survival. In a previous study, we demonstrated that GICs had a restricted double strand break (DSB) repair pathway involving predominantly homologous recombination (HR) associated with a lack of functional G1/S checkpoint arrest. This unusual behaviour led to less efficient non-homologous end joining (NHEJ) repair and overall slower DNA DSB repair kinetics. To determine whether specific targeting of the HR pathway with small molecule inhibitors could increase GIC radiosensitivity, we used the Ataxia-telangiectasia mutated inhibitor (ATMi) to ablate HR and the DNA-dependent protein kinase inhibitor (DNA-PKi) to inhibit NHEJ. Pre-treatment with ATMi prior to ionizing radiation (IR) exposure prevented HR-mediated DNA DSB repair as measured by Rad51 foci accumulation. Increased cell death in vitro and improved in vivo animal survival could be observed with combined ATMi and IR treatment. Conversely, DNA-PKi treatment had minimal impact on GICs ability to resolve DNA DSB after IR with only partial reduction in cell survival, confirming the major role of HR. These results provide a mechanistic insight into the predominant form of DNA DSB repair in GICs, which when targeted may be a potential translational approach to increase patient survival.
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia; The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital Campus, Herston, Queensland 4029, Australia.
authors.forename: Yi Chieh
authors.initials: YC
authors.lastname: Lim
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia; The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital Campus, Herston, Queensland 4029, Australia.
authors.forename: Tara L
authors.initials: TL
authors.lastname: Roberts
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Day
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Brett W
authors.initials: BW
authors.lastname: Stringer
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Sergei
authors.initials: S
authors.lastname: Kozlov
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Shazrul
authors.initials: S
authors.lastname: Fazry
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Zara C
authors.initials: ZC
authors.lastname: Bruce
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Kathleen S
authors.initials: KS
authors.lastname: Ensbey
authors.affiliation: BrizBrain and Spine, The Wesley Hospital, Evan Thomson Building, Level 10, Auchenflower, Queensland 4066, Australia.
authors.forename: David G
authors.initials: DG
authors.lastname: Walker
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Boyd
authors.affiliation: QIMR Berghofer Medical Research Institute, 300 Herston Road, Herston, Queensland 4029, Australia; The University of Queensland Centre for Clinical Research, Royal Brisbane and Women's Hospital Campus, Herston, Queensland 4029, Australia. Electronic address: martin.lavin@qimrberghofer.edu.au.
authors.forename: Martin F
authors.initials: MF
authors.lastname: Lavin
mesh_terms: D002453:Cell Cycle / Q000235:genetics / Q000528:radiation effects; D002470:Cell Survival / Q000235:genetics / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics / Q000528:radiation effects; D005910:Glioma / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008938:Mitosis / Q000235:genetics / Q000528:radiation effects; D009364:Neoplasm Recurrence, Local / Q000235:genetics; D011839:Radiation, Ionizing; D011995:Recombination, Genetic / Q000235:genetics* / Q000528:radiation effects
keywords: ATM inhibitor; DNA damage; DNA double strand break repair; Glioma initiating cell; Homologous recombination; Neural progenitor cell