title: Dual tracer evaluation of dynamic changes in intratumoral hypoxic and proliferative states after radiotherapy of human head and neck cancer xenografts using radiolabeled FMISO and FLT.
abstract: BACKGROUND
  Radiotherapy is an important treatment strategy for head and neck cancers. Tumor hypoxia and repopulation adversely affect the radiotherapy outcome. Accordingly, fractionated radiotherapy with dose escalation or altered fractionation schedule is used to prevent hypoxia and repopulation. 18F-fluoromisonidazole (FMISO) and 18F-fluorothymidine (FLT) are noninvasive markers for assessing tumor hypoxia and proliferation, respectively. Thus, we evaluated the dynamic changes in intratumoral hypoxic and proliferative states following radiotherapy using the dual tracers of 18F-FMISO and 3H-FLT, and further verified the results by immunohistochemical staining of pimonidazole (a hypoxia marker) and Ki-67 (a proliferation marker) in human head and neck cancer xenografts (FaDu).
  
  
  METHODS
  FaDu xenografts were established in nude mice and assigned to the non-radiation-treated control and two radiation-treated groups (10- and 20-Gy). Tumor volume was measured daily. Mice were sacrificed 6, 24, and 48 hrs and 7 days after radiotherapy. 18F-FMISO, and 3H-FLT and pimonidazole were injected intravenously 4 and 2 hrs before sacrifice, respectively. Intratumoral 18F-FMISO and 3H-FLT levels were assessed by autoradiography. Pimonidazole and Ki-67 immunohistochemistries were performed.
  
  
  RESULTS
  In radiation-treated mice, tumor growth was significantly suppressed compared with the control group, but the tumor volume in these mice gradually increased with time. Visual inspection showed that intratumoral 18F-FMISO and 3H-FLT distribution patterns were markedly different. Intratumoral 18F-FMISO level did not show significant changes after radiotherapy among the non-radiation-treated control and radiation-treated groups, whereas 3H-FLT level markedly decreased to 59 and 45% of the non-radiation-treated control at 6 hrs (p<0.0001) and then gradually increased with time in the 10- and 20-Gy-radiation-treated groups. The pimonidazole-positive hypoxic areas were visually similar in both the non-radiation-treated control and radiation-treated groups. No significant differences were observed in the percentage of pimonidazole-positive cells and Ki-67 index.
  
  
  CONCLUSIONS
  Intratumoral 18F-FMISO level did not change until 7 days, whereas 3H-FLT level markedly decreased at 6 hrs and then gradually increased with time after a single dose of radiotherapy. The concomitant monitoring of dynamic changes in tumor hypoxia and proliferation may provide important information for a better understanding of tumor biology after radiotherapy and for radiotherapy planning, including dose escalation and altered fractionation schedules.
authors.forename: Chowdhury Nusrat
authors.initials: CN
authors.lastname: Fatema
authors.affiliation: Department of Tracer Kinetics & Bioanalysis, Graduate School of Medicine, Hokkaido University, Kita 15, Nishi 7, Kita-ku, Sapporo 060-8638, Japan. zsi@med.hokudai.ac.jp.
authors.forename: Songji
authors.initials: S
authors.lastname: Zhao
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Wenwen
authors.initials: W
authors.lastname: Yu
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Nishijima
authors.forename: Koichi
authors.initials: K
authors.lastname: Yasuda
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Kitagawa
authors.forename: Nagara
authors.initials: N
authors.lastname: Tamaki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kuge
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D004195:Disease Models, Animal; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000532:radiotherapy; D064593:Heterografts; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D008297:Male; D051379:Mice; D008920:Misonidazole / Q000031:analogs & derivatives* / Q000378:metabolism; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000378:metabolism; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; C031843:fluoromisonidazole; D008920:Misonidazole