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Extended depletion of glutathione to approximately equal to 5% of control in the murine mammary carcinoma cell line 66 was achieved with a concentration of 0.05 mM buthionine sulfoximine. At 24 hours, there was no evidence for cellular toxicity from the BSO treatment per se; however, by 48 hours, there was inhibition of protein and DNA synthesis and cell growth and cell kinetic data was suggestive of both a G1 and a G2 block. Glutathione depletion to this extent (i.e., 0.13 mM vs. 2.24 mM in control) did not modify the aerobic radiation response for cells in the physiological states of proliferation, quiescence, or stimulated quiescent cells. This degree of cellular toxicity may well be cell-type dependent, but the results do suggest that caution is in order if one should attempt long-term GSH depletion in vivo.

Our data show that A549 cells are increasingly radiosensitive with prolonged exposure to L-BSO. The resulting glutathione and protein thiol depleted cells show both loss of shoulder and slope modification. Furthermore, there is an increase in single strand DNA breaks and irrepairable cross-linking. The aerobic radiation damage in the thiol depleted state appears to be different from that obtained with hypoxic cells. Any postulated role for GSH in reducing or preventing peroxidative radiation damage must also include protection against single strand DNA breaks as well as involvement in repairing DNA-protein cross-links. The latter effect may be related to decreased protein thiol content as reflected in a decreased enzyme capacity to repair DNA damage.