title: Dependency of the effect of a vascular disrupting agent on sensitivity to tirapazamine and gamma-ray irradiation upon the timing of its administration and tumor size, with reference to the effect on intratumor quiescent cells.
abstract: OBJECTIVE
  The effect of vascular disrupting agent ZD6126 with time on the sensitivity to the hypoxic cytotoxin tirapazamine (TPZ) and gamma-rays was examined in large and small solid tumors.
  
  
  METHODS
  Mice bearing SCC VII tumors 1 or 1.5 cm in diameter received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells, followed by injection with or without ZD6126. In the absence of ZD6126, or 1 or 24 h following ZD6126 injection, the response to TPZ or gamma-ray irradiation in quiescent (Q) cells was assessed in terms of induced micronucleus (MN) frequency using immunofluorescence staining for BrdU. The MN frequency in the total cell population was determined from the tumors not pretreated with BrdU. Another group of tumor-bearing mice received a series of test doses of gamma-rays while alive or after tumor clamping to obtain hypoxic fractions (HFs) in the tumors.
  
  
  RESULTS
  One hour after ZD6126 injection, both small and large tumors showed lower and higher sensitivity, and 24 h after, higher and lower sensitivity, to gamma-rays and TPZ, respectively, than the tumors not treated with ZD6126. Further, they showed larger and smaller HFs 1 and 24 h after ZD6126 injection, respectively. Without ZD6126 and 1 h after injection, small tumors were more sensitive to gamma-rays and less sensitive to TPZ than large tumors, probably due to the smaller HFs than large tumors. In contrast, 24 h after the injection, these differences in sensitivity and the HF between small and large tumors were reversed. The changes in sensitivity and the size of the HF were more marked in the total cell population than in Q cells.
  
  
  CONCLUSIONS
  Following ZD6126 treatment, in terms of tumor control, especially large tumors and total tumor cell population, administering TPZ 1 h later and gamma-ray irradiation 24 h later were effective. Intratumor physiologic factors such as the size of the HF, depending on the time after ZD6126 injection, have to be taken into account when combining another treatment with ZD6126.
authors.affiliation: Radiation Oncology Research Laboratory, 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: Hideko
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Kenji
authors.initials: K
authors.lastname: Nagata
authors.forename: Minoru
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Uto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hori
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kinashi
authors.forename: Koji
authors.initials: K
authors.lastname: Ono
mesh_terms: D020533:Angiogenesis Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000532:radiotherapy / Q000628:therapy*; D045744:Cell Line, Tumor; D005720:Gamma Rays / Q000627:therapeutic use*; D051379:Mice; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000737:chemistry / Q000494:pharmacology*; D011879:Radiotherapy Dosage; D013997:Time Factors; D000077704:Tirapazamine; D014227:Triazines / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D020533:Angiogenesis Inhibitors; D000970:Antineoplastic Agents; C455219:N-acetylcochinol-O-phosphate; D009943:Organophosphorus Compounds; D011838:Radiation-Sensitizing Agents; D014227:Triazines; D000077704:Tirapazamine