Glutathione depletion, radiosensitization, and misonidazole potentiation in hypoxic Chinese hamster ovary cells by buthionine sulfoximine

Abstract

Buthionine sulfoximine (BSO) inhibits the synthesis of glutathione (GSH), the major nonprotein sulfhydryl (NPSH) present in most mammalian cells. BSO concentrations from 1 μM to 0.1 mM reduced intracellular GSH at different rates, while BSO ≥ 0.1 mM (i.e., 0.1 to 2.0 mM), resulting in inhibitor-enzyme saturation, depleted GSH to ≤10% of control within 10 hr at about equal rates. BSO exposures used in these experiments were not cytotoxic with the one exception that 2.0 mM BSO/24 hr reduced cell viability to ~50%. However, alterations in either the cell doubling time(s) or the cell age density distribution(s) were not observed with the BSO exposures used to determine its radiosensitizing effect. BSO significantly radiosensitized (ER = 1.41 with 0.1 mM BSO/24 hr) hypoxic, but not aerobic, CHO cells when the GSH and NPSH concentrations were reduced to <10 and 20% of control, respectively, and maximum radiosensitivity was even achieved with μM concentrations of BSO (ER = 1.38 with 10 μM BSO/24 hr). Furthermore, BSO exposure (0.1 mM BSO/24 hr) also enhanced the radiosensitizing effect of various concentrations of misonidazole on hypoxic CHO cells.