Effect of hypoxia on the cytotoxicity of misonidazole in HELA S3 cells in vitro.

A simple method to establish hypoxic conditions in vitro is described and the cytotoxicity and radiation dose-modifying effect of misonidazole were investigated; using HeLa S3 cells. Under hypoxic conditions, 5-hr exposure to 50mM misonidazole resulted in severe cytotoxicity, though the toxicity at 1mM was low. The survival curves of cells exposed to 5 or 10mM misonidazole showed an initial exponential portion followed by a less steep decline. Under aerobic conditions, exposure to 1mM for 5 days showed no cytotoxicity, while the surviving fraction of cells exposed to 50mM for 10 hr was reduced to 0.3. Acute conversion from hypoxic to aerobic conditions revealed persistence of the cytotoxicity for 2 hr after the conversion. Under hypoxic conditions, a dose-modifying factor of 1.9 was achieved for cells irradiated with gamma rays.