title: Demonstration of Tightly Radiation-Controlled Molecular Switch Based on CArG Repeats by In Vivo Molecular Imaging.
abstract: OBJECTIVE
  Promoters developed for radiogene therapy always show non-negligible transcriptional activities, even when cells are not irradiated. This study developed a tightly radiation-controlled molecular switch based on radiation responsive element (CArG) repeats for in vivo molecular imaging using the Cre/loxP system.
  
  
  METHODS
  Different numbers of CArG repeats were cloned as a basal promoter directly, and its pre- and postirradiation transcriptional activities were analyzed by luciferase assay. Nine CArG repeats (E9) were chosen for use as a radiation-controlled molecular switch for the Cre/loxP system, and the feasibility of the switch in vitro and in vivo was demonstrated by luciferase assay and bioluminescence imaging, respectively.
  
  
  RESULTS
  The E9 promoter, which exhibits extremely low transcriptional activity, showed a 1.8-fold enhancement after irradiation with a clinical dose of 2 Gy. Both in vitro and in vivo results indicated that E9 is relatively inert but sufficient to trigger the Cre/loxP system. The luciferase activity of stable H1299/pSTOP-FLuc cells transfected with pE9-NLSCre and exposed to 2-Gy radiation can reach 44 % of that of the same cells transfected with pCMV-NLSCre and not subjected to irradiation. By contrast, no appreciable difference was observed in reporter gene expression in both H1299/pSTOPFluc cells and tumors transfected with pE4Pcmv-NLSCre before and after irradiation, because the strong basal transcriptional activity of the CMV promoter, which acts as a copartner of E4, masked the response of E4 to radiation.
  
  
  CONCLUSIONS
  Our results provide detailed insight into CArG elements as a radiation-controlled molecular switch that can facilitate the development of radiogene therapy.
authors.affiliation: Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Ya-Ju
authors.initials: YJ
authors.lastname: Hsieh
authors.affiliation: Molecular and Genetic Imaging Core/Taiwan Mouse Clinic, National Comprehensive Mouse Phenotyping and Drug Testing Center, Taipei, Taiwan.|Biomedical Imaging Research Center, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Luen
authors.initials: L
authors.lastname: Hwu
authors.affiliation: Biomedical Imaging Research Center, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Chien-Chih
authors.initials: CC
authors.lastname: Ke
authors.affiliation: Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Ai-Lin
authors.initials: AL
authors.lastname: Huang
authors.affiliation: Biomedical Imaging Research Center, National Yang-Ming University, Taipei, Taiwan.|Hwa Hsia University of Technology, Taipei, Taiwan.
authors.forename: Fu-Du
authors.initials: FD
authors.lastname: Chen
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Shyh-Jong
authors.initials: SJ
authors.lastname: Wu
authors.affiliation: Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Sharon Chia-Ju
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Faculty of Chinese Medicine, Macau University of Science and Technology, Macau, China.
authors.forename: Yong-Hua
authors.initials: YH
authors.lastname: Zhao
authors.affiliation: Molecular and Genetic Imaging Core/Taiwan Mouse Clinic, National Comprehensive Mouse Phenotyping and Drug Testing Center, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|Biomedical Imaging Research Center, National Yang-Ming University, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|Institute of Clinical Medicine, National Yang-Ming University, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|Biophotonic and Molecular Imaging Research Center, National Yang-Ming University, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|National PET/Cyclotron Center and Department of Nuclear Medicine, Taipei Veterans General Hospital, Taipei, Taiwan. rsliu@vghtpe.gov.tw.|Division of Nuclear Medicine, National Yang-Ming University Medical School, 155, Sec. 2, Linong Street, Taipei, 11221, Taiwan. rsliu@vghtpe.gov.tw.
authors.forename: Ren-Shyan
authors.initials: RS
authors.lastname: Liu
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D019426:Integrases / Q000235:genetics; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D057054:Molecular Imaging; D010957:Plasmids; D011401:Promoter Regions, Genetic / Q000528:radiation effects*; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic
chemical_list: C045073:Cre recombinase; D019426:Integrases
keywords: Cre/loxp system; Micropositron emission tomography; Molecular switch; Radiation-responsive elements