Repair and re oxygenation following irradiation of an in vitro tumor model

Durand, R. E.; Sutherland, R. M.

Chinese hamster V79 lung cells which were grown and irradiated as multicell spheroids exhibited time dependent fluctuations in sensitivity to further irradiation. These variations in radiosensitivity could be attributed to repair of sublethal radiation damage and irradiation induced reoxygenation. The relative influence of each process depended on the magnitude of the initial radiation exposure and the time between fractions. Repair of sublethal radiation damage was predominant after small radiation doses. Despite repair and cellular repopulation between successive exposures, therapy-like regimens produced complete reoxygenation after several days. Single radiation exposures large enough to kill all oxygenated cells resulted in an immediate, but transient sensitization of the surviving hypoxic cells, presumably resulting from a transient, irradiation induced inhibition of the respiration of the aerobic cells of the spheroid. In the in vitro tumor system, postirradiation reoxygenation can be achieved by inhibition of cellular respiration and/or cell killing.