Abstract
The present investigation was undertaken with the hope for elucidating the effect of a radiosensitizer on mouse L cells in culture following X-irradiation. Under the aerobic condition, a survival curve of irradiated cells showed a shoulder region with the extrapolation number of 6.4 and mean lethal dose (D0 value) of 126 rad. On the other hand, under the extremely hypoxic condition prepared with nitrogen gas using a stainless steel apparatus, a survival curve was found to show no shoulder region, having extrapolation number of 1.1 and D0 value of 629 rad. Thus, the oxygen enhancement ratio (o. e. r.) was calculated as a factor 5. An electron affinic radiosensitizer, Ro-07-0582 revealed a pronounced sensitizing effect under the extremely hypoxic condition by an enhancement ratio 3.9 at a concentration of 10 mM. The sensitizer reduced D0 value with increasing concentration of the drug. The evidence obtained suggests that Ro-07-0582 acts as oxygen-mimic, although the drug shows no radiosensitizing effect at low concentration and low irradiation doses.
