title: Novel MSH6 mutations in treatment-naïve glioblastoma and anaplastic oligodendroglioma contribute to temozolomide resistance independently of MGMT promoter methylation.
abstract: OBJECTIVE
  The current standard of care for glioblastoma (GBM) involves a combination of surgery, radiotherapy, and temozolomide chemotherapy, but this regimen fails to achieve long-term tumor control. Resistance to temozolomide is largely mediated by expression of the DNA repair enzyme MGMT; however, emerging evidence suggests that inactivation of MSH6 and other mismatch repair proteins plays an important role in temozolomide resistance. Here, we investigate endogenous MSH6 mutations in GBM, anaplastic oligodendroglial tumor tissue, and corresponding brain tumor-initiating cell lines (BTIC).
  
  
  METHODS
  MSH6 sequence and MGMT promoter methylation were determined in human tumor samples and BTICs. Sensitivity to temozolomide was evaluated in vitro using BTICs in the absence and presence of O(6)-benzylguanine to deplete MGMT. The influence of MGMT and MSH6 status on in vivo sensitivity to temozolomide was evaluated using intracranial BTIC xenografts.
  
  
  RESULTS
  We identified 11 previously unreported mutations in MSH6 in nine different glioma samples and six paired BTIC lines from adult patients. In addition, MSH6 mutations were documented in three oligodendrogliomas and two treatment-naïve gliomas, both previously unreported findings. These mutations were found to influence the sensitivity of BTICs to temozolomide both in vitro and in vivo, independent of MGMT promoter methylation status.
  
  
  CONCLUSIONS
  These data demonstrate that endogenous MSH6 mutations may be present before alkylator therapy and occur in at least two histologic subtypes of adult glial neoplasms, with this report serving as the first to note these mutations in oligodendroglioma. These findings broaden our understanding of the clinical response to temozolomide in gliomas.
authors: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: Stephanie A
authors: SA
authors: Nguyen
authors: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: Owen D M
authors: OD
authors: Stechishin
authors: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: H Artee
authors: HA
authors: Luchman
authors: Clark Smith Brain Tumor Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: Xueqing Q
authors: XQ
authors: Lun
authors: Clark Smith Brain Tumor Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: Donna L
authors: DL
authors: Senger
authors: Clark Smith Brain Tumor Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: Stephen M
authors: SM
authors: Robbins
authors: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Clark Smith Brain Tumor Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Clinical Neurosciences, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors: J Gregory
authors: JG
authors: Cairncross
authors: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Clark Smith Brain Tumor Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. weiss@ucalgary.ca.
authors: Samuel
authors: S
authors: Weiss
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics; D015254:DNA Modification Methylases / Q000235:genetics; D045643:DNA Repair Enzymes / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D005838:Genotype; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009154:Mutation; D009837:Oligodendroglioma / Q000188:drug therapy / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics; D023041:Xenograft Model Antitumor Assays; D055815:Young Adult
chemical_list: D018906:Antineoplastic Agents, Alkylating; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide