Reoxygenation in the SCCVII tumor after KU-2285 sensitization plus single or fractionated irradiation.
OBJECTIVE
Because reoxygenation of solid tumors after irradiation with a hypoxic cell sensitizer has never previously been investigated, we assessed the reoxygenation in SCCVII tumors after treatment with KU-2285 plus single or fractionated irradiation.


METHODS
KU-2285 (100 mg/kg) was injected intraperitoneally into C3H mice bearing 1-cm SCCVII tumors at 30 min before a single dose of 12 Gy or three fractions of 5 Gy at 12 h intervals. Changes of the hypoxic fraction (HF) were then evaluated by the paired survival curve method.


RESULTS
Since the radiosensitizing effect of KU-2285 was relatively persistent, the HF was only evaluable after 6 h of irradiation. The HF of untreated SCCVII tumors was 9.1%. After treatment with KU-2285 and 12 Gy, the HF was 25% at 6 h, 32% at 12 h, 24% at 24 h, and 7.6% at 72 h. The HF was lower at 6 h than that after radiation alone, but was similar at later periods. After three fractions of 5 Gy with or without KU-2285, the HF was 33% at 6 h in both groups, while it was 12% and 13% at 24 h for tumors pretreated with KU-2285 and those receiving radiation alone, respectively. However, a sensitizing effect of KU-2285 was indicated by the downward shift of the survival curves for tumors irradiated after exposure to this agent.


CONCLUSIONS
Reoxygenation occurred quite efficiently in tumors receiving KU-2285 and 12 Gy. After fractionated irradiation, however, reoxygenation was similar in the KU-2285-pretreatment and irradiation alone groups.
Shibamoto
Y
Y
Department of Radiology, Faculty of Medicine, Kyoto University, Japan.
Kitakabu
Y
Y
Murata
R
R
Oya
N
N
Shibata
T
T
Sasai
K
K
Takahashi
M
M
Abe
M
M
D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D015687:Cell Hypoxia; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008809:Mice, Inbred C3H; D009593:Nitroimidazoles / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D009593:Nitroimidazoles; D011838:Radiation-Sensitizing Agents; C069296:KU 2285; D010100:Oxygen