Some examples of anomalous radiosensitizing behaviour of electron-affinic compounds in vitro.

Studies using V79 379A cells on about 50 nitroaromatic and nitroheterocyclic radisosensitizers have confirmed the relationship between sensitizing efficiency and electron affinity. Almost all the compounds studied behaved similarly by sensitizing hypoxic cells to X-irradiation in a dose-modifying manner whilst having no sensitizing effect on oxygenated cells. However, a small number of the radiosensitizers studied exhibited additional or atypical properties. A 4-nitroimidazole ring substituted with chlorine sensitized hypoxic cells much more efficiently than predicted from its redox potential. A 2-nitroimidazole substituted with a carboxylic acid side chain showed a low but constant level of sensitization over 5 decades of concentration. A 5-nitrofuran, in addition to sensitizing hypoxic cells by dose modification, sensitized oxygenated cells by a reduction in extrapolation number.