Administration of a hypoxic cell sensitizer increases hypoxic fraction of a large tumor

Heterogeneity of large tumor was investigated with respect to radiosensitizing efficiencies of a new hypoxic cell sensitizer KU-2285. The NF-Sa fibrosarcomas transplanted into hind legs of syngeneic C3H mouse served for experiments when the tumors reached 25 mm in diameter. Colony efficiency (C. E.) of the tumor cells collected from the central area was significantly lower than C. E. from the peripheral area (p<0.05). D0 values of the central area and the peripheral area showed no difference between each other. Administration of KU-2285 reduced D0 values to 60% irrespective of the central area and the peripheral area. However, hypoxic fraction (H. F.) in the central area was significantly increased (p<0.01) by administration of KU-2285 whereas H. F. in the peripheral area was not affected by the drug treatment. These results suggested that KU-2285 may have radioprotective effect for the tumor cells in the central area, and that size of radiation dose would be critical for effective use of the drug. (author)