title: Usefulness of combined treatment with continuous administration of tirapazamine and mild temperature hyperthermia in γ-ray irradiation in terms of local tumour response and lung metastatic potential.
abstract: OBJECTIVE
  To evaluate the usefulness of combined treatment with continuous administration of a hypoxic cytotoxin, tirapazamine (TPZ), and mild temperature hyperthermia (MTH) in γ-ray irradiation in terms of local tumour response and lung metastatic potential, referring to the response of intratumour quiescent (Q) cells.
  
  
  METHODS
  B16-BL6 melanoma tumour-bearing C57BL/6 mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells. The tumour-bearing mice then received γ-ray irradiation after a single intraperitoneal injection or 24 h continuous subcutaneous infusion of TPZ, either with or without MTH. Immediately after the irradiation, cells from some tumours were isolated and incubated with a cytokinesis blocker. The responses of the Q and total (= P + Q) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU. In other tumour-bearing mice, 17 days after irradiation, macroscopic lung metastases were enumerated.
  
  
  RESULTS
  Continuous administration elevated the sensitivity of both the total and Q cells, especially the total cells. MTH raised the sensitivity of Q cells more remarkably in both single and continuous administrations, probably because of more exposure to TPZ in intermediately hypoxic areas derived mainly from chronic hypoxia through MTH. With or without irradiation, TPZ, especially administered continuously and combined with MTH, decreased the number of lung metastases.
  
  
  CONCLUSIONS
  The combination of continuous long-term administration of TPZ and MTH in γ-ray irradiation was thought to be promising because of its potential to enhance local tumour response and repress lung metastatic potential.
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan. smasuna@rri.kyoto-u.ac.jp
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Masunaga
authors.forename: Yong
authors.initials: Y
authors.lastname: Liu
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Sakurai
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Minoru
authors.initials: M
authors.lastname: Suzuki
authors.forename: Natsuko
authors.initials: N
authors.lastname: Kondo
authors.forename: Akira
authors.initials: A
authors.lastname: Maruhashi
authors.forename: Koji
authors.initials: K
authors.lastname: Ono
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D003131:Combined Modality Therapy; D005260:Female; D005720:Gamma Rays; D006979:Hyperthermia, Induced; D008175:Lung Neoplasms / Q000556:secondary; D008546:Melanoma, Experimental / Q000473:pathology / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D009362:Neoplasm Metastasis; D000077704:Tirapazamine; D014227:Triazines / Q000008:administration & dosage*; D047368:Tumor Burden / Q000187:drug effects / Q000528:radiation effects
chemical_list: D000970:Antineoplastic Agents; D014227:Triazines; D000077704:Tirapazamine