title: Significance of manipulating intratumor hypoxia in the effect on lung metastases in radiotherapy, with reference to its effect on the sensitivity of intratumor quiescent cells.
abstract: OBJECTIVE
  To evaluate the effect of manipulating intratumor hypoxia during radiotherapy on lung metastasis, referring to its effect on the sensitivity of quiescent tumor cells.
  
  
  METHODS
  B16-BL6 melanoma tumor-bearing C57BL/6 mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells. They received gamma-ray irradiation following loading with the acute hypoxia-releasing agent nicotinamide or local hyperthermia at mild temperatures (MTH). Immediately after the irradiation, cells from some tumors were isolated and incubated with a cytokinesis blocker. The sensitivity of quiescent (Q) cells was assessed in terms of the micronucleus frequency using immunofluorescence staining for BrdU. That of the total (=P + Q) tumor cell population was determined from BrdU non-treated tumors. In other tumor-bearing mice, 17 days after irradiation, macroscopic lung metastases were enumerated.
  
  
  RESULTS
  In the total cells, a more marked enhancement in sensitivity was observed with nicotinamide than MTH. In Q cells, MTH combination induced a more marked enhancement than nicotinamide. Both nicotinamide and MTH reduced the size of the hypoxic fraction in the two cell populations, especially nicotinamide in the total cells and MTH in Q cells. Without gamma-ray irradiation, nicotinamide loading tended to decrease the number of lung metastases. With gamma-ray irradiation, nicotinamide loading and MTH, especially the former, reduced the number of metastases more than gamma-ray irradiation only.
  
  
  CONCLUSIONS
  Hypoxia manipulation in solid tumors has the potential to influence lung metastases. Notably, acute hypoxia-releasing nicotinamide may be promising for reducing the number of lung metastases.
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, 2-1010, Asashiro-nishi, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan. smasuna@rri.kyoto-u.ac.jp
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Masunaga
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.forename: Genro
authors.initials: G
authors.lastname: Kashino
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Minoru
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kinashi
authors.forename: Yong
authors.initials: Y
authors.lastname: Liu
authors.forename: Koichi
authors.initials: K
authors.lastname: Ando
authors.forename: Koji
authors.initials: K
authors.lastname: Ono
mesh_terms: D000818:Animals; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D005455:Fluorescent Antibody Technique; D008175:Lung Neoplasms / Q000378:metabolism / Q000532:radiotherapy / Q000556:secondary*; D008546:Melanoma, Experimental / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL