title: Dual mTORC1/2 blockade inhibits glioblastoma brain tumor initiating cells in vitro and in vivo and synergizes with temozolomide to increase orthotopic xenograft survival.
abstract: OBJECTIVE
  The EGFR and PI3K/mTORC1/2 pathways are frequently altered in glioblastoma (GBM), but pharmacologic targeting of EGFR and PI3K signaling has failed to demonstrate efficacy in clinical trials. Lack of relevant models has rendered it difficult to assess whether targeting these pathways might be effective in molecularly defined subgroups of GBMs. Here, human brain tumor-initiating cell (BTIC) lines with different combinations of endogenous EGFR wild-type, EGFRvIII, and PTEN mutations were used to investigate response to the EGFR inhibitor gefitinib, mTORC1 inhibitor rapamycin, and dual mTORC1/2 inhibitor AZD8055 alone and in combination with temozolomide (TMZ) EXPERIMENTAL DESIGN: In vitro growth inhibition and cell death induced by gefitinib, rapamycin, AZD8055, and TMZ or combinations in human BTICs were assessed by alamarBlue, neurosphere, and Western blotting assays. The in vivo efficacy of AZD8055 was assessed in subcutaneous and intracranial BTIC xenografts. Kaplan-Meier survival studies were performed with AZD8055 and in combination with TMZ.
  
  
  RESULTS
  We confirm that gefitinib and rapamycin have modest effects in most BTIC lines, but AZD8055 was highly effective at inhibiting Akt/mTORC2 activity and dramatically reduced the viability of BTICs regardless of their EGFR and PTEN mutational status. Systemic administration of AZD8055 effectively inhibited tumor growth in subcutaneous BTIC xenografts and mTORC1/2 signaling in orthotopic BTIC xenografts. AZD8055 was synergistic with the alkylating agent TMZ and significantly prolonged animal survival.
  
  
  CONCLUSIONS
  These data suggest that dual inhibition of mTORC1/2 may be of benefit in GBM, including the subset of TMZ-resistant GBMs.
authors.affiliation: 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.forename: H Artee
authors.initials: HA
authors.lastname: Luchman
authors.affiliation: 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.forename: Owen D M
authors.initials: OD
authors.lastname: Stechishin
authors.affiliation: 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.forename: Stephanie A
authors.initials: SA
authors.lastname: Nguyen
authors.affiliation: Clark Smith Brain Tumour 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.forename: Xueqing Q
authors.initials: XQ
authors.lastname: Lun
authors.affiliation: Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Clark Smith Brain Tumour 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.forename: J Gregory
authors.initials: JG
authors.lastname: Cairncross
authors.affiliation: 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 Tumour Research Centre, Southern Alberta Cancer Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. weiss@ucalgary.ca.
authors.forename: Samuel
authors.initials: S
authors.lastname: Weiss
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D003606:Dacarbazine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004195:Disease Models, Animal; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors*; D009154:Mutation; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D000077204:Temozolomide; D047368:Tumor Burden / Q000187:drug effects / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D046912:Multiprotein Complexes; D047428:Protein Kinase Inhibitors; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D066246:ErbB Receptors; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases; D051059:PTEN Phosphohydrolase; D045643:DNA Repair Enzymes; D000077204:Temozolomide