title: Chronic modulation of AMP-Kinase, Akt and mTOR pathways by ionizing radiation in human lung cancer xenografts.
abstract: BACKGROUND
  Earlier, we showed that in cancer cells, AMP-activated kinase (AMPK) participates in a signal transduction pathway involving ATM-AMPK-p53/p21cip1 which is activated by ionizing radiation (IR) to mediate G2-M arrest and enhanced cytotoxicity. We also observed that AMPK modulates ATM expression and activity and the IR response of the Akt-mTOR pathway. Since the ATM, AMPK and Akt pathways are key targets of novel radio-sensitizing therapeutics, we examined the chronic modultion of expression and activity of those pathways by IR alone in xenograft models of lung cancer.
  
  
  METHODS
  Immuno-compromised mice were grafted with human lung A549 and H1299 cells, were treated with a single fraction of 0 or 10 Gy, and left to grow for 8 weeks. Extracted tumors were subjected to lysis and immunoblotting or fixation and immunohistochemical analysis.
  
  
  RESULTS
  IR inhibited significantly xenograft growth and was associated with increased expression of Ataxia Telengiectasia Mutated (ATM) and enhanced phosphorylation of two ATM targets, H2Ax and checkpoint kinase Chk2. Irradiated tumours showed increased total AMPK levels and phosphorylation of AMPK and its substrate Acetyl-CoA Carboxylase (ACC). IR led to enhanced expression and phosphorylation of p53 and cyclin dependent kinase inhibitors p21cip1 and p27kip1. However, irradiated tumours had reduced phosphorylation of Akt, mTOR and it's target translation initiation inhibitor 4EBP1. Irradiated xenografts showed reduced microvessel density, reduced expression of CD31 but increased expression of hypoxia-induced factor 1A (HIF1a) compared to controls.
  
  
  CONCLUSIONS
  IR inhibits epithelial cancer tumour growth and results in sustained expression and activation of ATM-Chk2, and AMPK-p53/p21cip1/p27kip1 but partial inhibition of the Akt-mTOR signaling pathways. Future studies should examine causality between those events and explore whether further modulation of the AMPK and Akt-mTOR pathways by novel therapeutics can sensitize lung tumours to radiation.
authors.affiliation: Translational Radiation Biology Laboratory, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Yaryna
authors.initials: Y
authors.lastname: Storozhuk
authors.forename: Toran
authors.initials: T
authors.lastname: Sanli
authors.forename: Sarah N
authors.initials: SN
authors.lastname: Hopmans
authors.forename: Carrie
authors.initials: C
authors.lastname: Schultz
authors.forename: Tom
authors.initials: T
authors.lastname: Farrell
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Cutz
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Steinberg
authors.forename: James
authors.initials: J
authors.lastname: Wright
authors.forename: Gurmit
authors.initials: G
authors.lastname: Singh
authors.forename: Theodoros
authors.initials: T
authors.lastname: Tsakiridis
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism*; D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D011839:Radiation, Ionizing; D015398:Signal Transduction / Q000528:radiation effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D013997:Time Factors; D023041:Xenograft Model Antitumor Assays
chemical_list: D051058:Oncogene Protein v-akt; D058570:TOR Serine-Threonine Kinases; D000263:Adenylate Kinase