Chronic hypoxia and radiosensitivity <i>in vitro</i>.

<p>A431 cells cultured under normoxic and chronic hypoxic condition show decreased sensitivity to irradiation following long-term hypoxia. 24 hour hypoxic incubation (0.5% O₂) prior to 4 Gy irradiation has no effect upon cell survival (A). Chronic (72 hour) hypoxia decreases radiosensitivity at 5 and 10 Gy, but reoxygenation for 6 hours prior to IR restores radiosensitivity (B). Data presented as mean surviving fraction ± SEM. In all cases cells were plated in triplicate at two cell densities.