title: Radiosensitization of tumor cells by modulation of ATM kinase.
abstract: OBJECTIVE
  To elucidate the relationship between the radiation-induced activation of ataxia telangiectasia mutated (ATM) kinase, G2 arrest and the caffeine-induced radiosensitization.
  
  
  METHODS
  RKO cells (human colorectal cancer cells) and ATM kinase over-expressing RKO/ATM cells were used. The cellular radiosensitivity was determined with clonogenic survival assay and the cell cycle progression, including G2 arrest, was studied with flow cytometry. The activity of ATM kinase, check point 2 (Chk2) kinase and cycline B1/cell division cycle 2 (Cdc2) kinase was investigated. The radiosensitivity of RKO xenografts grown in nude mice was studied.
  
  
  RESULTS
  RKO/ATM cells were radioresistant as compared with RKO cells. There was a greater increase in ATM kinase activity and G2 arrest in RKO/ATM cells than in RKO cells. Caffeine also sensitized both RKO cells and RKO/ATM cells to radiation. The caffeine treatment suppressed the radiation-induced activation of ATM kinase, suppressed the activation of Chk2 kinase and inhibited the accumulation of cells in G2 phase. The activity of cycline B1/Cdc2 kinase increased earlier but decayed rapidly in the presence of caffeine. Caffeine enhanced radiation-induced growth delay of RKO xenografts.
  
  
  CONCLUSIONS
  Caffeine inhibited the radiation-induced activation of ATM kinase, thereby preventing the accumulation of cells in G2 phase. Consequently, radiosensitivity of cells increased in the presence of caffeine both in vitro and in vivo.
authors.affiliation: Department of Therapeutic Radiology, College of Medicine, University of Ulsan, Seoul, South Korea.
authors.forename: Eun Kyung
authors.initials: EK
authors.lastname: Choi
authors.forename: In Mi
authors.initials: IM
authors.lastname: Ji
authors.forename: So Ryung
authors.initials: SR
authors.lastname: Lee
authors.forename: Yeon Hee
authors.initials: YH
authors.lastname: Kook
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Griffin
authors.forename: Byung Uk
authors.initials: BU
authors.lastname: Lim
authors.forename: Jin-Seok
authors.initials: JS
authors.lastname: Kim
authors.forename: Doo Sung
authors.initials: DS
authors.lastname: Lee
authors.forename: Chang Won
authors.initials: CW
authors.lastname: Song
authors.forename: Heon Joo
authors.initials: HJ
authors.lastname: Park
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000008:administration & dosage; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000473:pathology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D011838:Radiation-Sensitizing Agents; D025521:Tumor Suppressor Proteins; D002110:Caffeine; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases