Sensitization of ultraviolet radiation damage in bacteria and mammalian cells.

Bacteria (Serratia marcescens) and mammalian cell (Chinese hamster V79-379A) were irradiated in monolayers with ultraviolet light at 254 nm or 365 nm in the presence or absence of radiosensitizing drugs. At 254 nm, killing is very efficient (D37 approximately 1 J m-2 exposure, or approximately 6 x 10(4) photons absorbed by DNA per bacterium), and sensitizers have no effect. At 365 nm, cells are not killed in buffer, but are inactivated in the presence of nifurpipone or misonidazole. Lethal exposures (approximately 5 x 10(3) J m-2 at 10micrometer misonidazole) correspond to about 10 (7) photons absorbed by sensitizer molecules per bacterium. Toxicity of stabel photoproducts of the drugs is not involved, nor is oxygen required. Hence the transient species formed by photo-excitation of radiosensitizer molecules are capable of killing cells in the absence of other types of radiation damage.