title: Gold nanoparticles enhance anti-tumor effect of radiotherapy to hypoxic tumor.
abstract: OBJECTIVE
  Hypoxia can impair the therapeutic efficacy of radiotherapy (RT). Therefore, a new strategy is necessary for enhancing the response to RT. In this study, we investigated whether the combination of nanoparticles and RT is effective in eliminating the radioresistance of hypoxic tumors.
  
  
  METHODS
  Gold nanoparticles (GNPs) consisting of a silica core with a gold shell were used. CT26 colon cancer mouse model was developed to study whether the combination of RT and GNPs reduced hypoxia-induced radioresistance. Hypoxia inducible factor-1α (HIF-1α) was used as a hypoxia marker. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were conducted to evaluate cell death.
  
  
  RESULTS
  Hypoxic tumor cells had an impaired response to RT. GNPs combined with RT enhanced anti-tumor effect in hypoxic tumor compared with RT alone. The combination of GNPs and RT decreased tumor cell viability compare to RT alonein vitro. Under hypoxia, tumors treated with GNPs + RT showed a higher response than that shown by tumors treated with RT alone. When a reactive oxygen species (ROS) scavenger was added, the enhanced antitumor effect of GNPs + RT was diminished.
  
  
  CONCLUSIONS
  In the present study, hypoxic tumors treated with GNPs + RT showed favorable responses, which might be attributable to the ROS production induced by GNPs + RT. Taken together, GNPs combined with RT seems to be potential modality for enhancing the response to RT in hypoxic tumors.
authors.affiliation: Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Mi Sun
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Eun-Jung
authors.initials: EJ
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Kim
authors.affiliation: Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, Korea.
authors.forename: Ui Seok
authors.initials: US
authors.lastname: Chung
authors.affiliation: Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, Korea.
authors.forename: Won-Gun
authors.initials: WG
authors.lastname: Koh
authors.affiliation: Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Ki Chang
authors.initials: KC
authors.lastname: Keum
authors.affiliation: Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Woong Sub
authors.initials: WS
authors.lastname: Koom
keywords: Hypoxia; Nanoparticle; Radiotherapy