Cytotoxic properties of a 4-nitroimidazole (NSC 38087): a radiosensitizer of hypoxic cells in vitro.

5-Phenoxysulphonyl-1-methyl-4-nitroimidazole (NSC 38087) can act as a sensitizer of hypoxic mammalian cells to radiation in vitro. The degree of sensitization achieved is greater than would be predicted from the drug's electron affinity. Cytotoxicity studies have shown that 5 microM NSC 38087 can reduce the surviving fraction of log-phase V79 cells in air at 37 degrees C to 10(-2) after 2 h exposure. This toxicity is considerably increased by small rises in temperature. In contrast to other nitro-heterocyclic radiosensitizers, NSC 38087 and related 5-substituted 4-nitroimidazoles show greater toxicity towards aerobic than to hypoxic cells. Log-phase cells show the highest sensitivity to the toxic action of NSC 38087, with plateau-phase cells, cells with a history of chronic hypoxia, and thermotolerant cells showing greater resistance. These toxicity data are compared to those for the 2-nitroimidazole hypoxic-cell sensitizer misonidazole.