Inhibition of X-ray-induced potentially lethal damage (PLD) repair by cordycepin (3'-deoxyadenosine) and enhancement of its action by 2'-deoxycoformycin in Chinese Hamster hai cells in the stationary phase in Vitro

The effects of growth phase and chemicals on PLD repair were studied in X-irradiated Chinese hamster hai cells. The change in capacity of cells in different growth phases to repair PLD was investigated. Starting from cells in the log phase, the magnitude of PLD repair during 10 hr of postirradiation incubation in Hanks' balanced salt solution increased for 2.5 to 18 as the cultures approached the stationary phase, which occurred on the 7th or 8th day. The effects of chemicals dissolved in Hanks' BSS on PLD repair were studied using 10th- or 12th-day cultures. Among the chemicals tested, caffeine and cordycepin were effective in inhibiting PLD repair. When 2'-deoxycoformycin, an inhibitor of adenosine deaminase, was combined with cordycepin, the effect of cordycepin was enhanced. Due to this prevention of the deamination of cordycepin by 2'-deoxycoformycin, the inhibition of PLD repair was prolonged, indicating a possible clinical application of cordycepin as a radiosensitizer