INFLUENCE OF INTRACELLULAR THIOL AND POLYAMINE LEVELS ON RADIOPROTECTION BY AMINOTHIOLS

We examined the effect of manipulating the levels of two endogenous ra dioprotectors, glutathione (GSH) and polyamines, on the ability of exo genous aminothiols to protect Chinese hamster ovary cells from the let hal effects of gamma-radiation. Treatment with 0.5 mmol dm-3 buthionin e sulfoximine (BSO) for 24 h depleted GSH levels to < 1% of control an d significantly sensitized the cells to irradiation in air. Undepleted control cells were protected by WR-1065 (4 mmol dm-3; 30-min preirrad iation treatment at 37-degrees-C) by 2.09-fold (range 1.98-2.21) at th e 10% survival level, whereas BSO-treated cells were protected by a fa ctor of 1.98 (range 1.95-2.14) at this survival level. Thus, GSH deple tion had no significant effect on the radioprotective capacity of WR-1 065. Treating cells with 1 mmol dm-3 alpha-difluoromethyl ornithine (D FMO) for 48h depleted the polyamines putrescine and spermidine to very low levels, while spermine was not significantly depleted. DFMO also sensitized cells to aerobic irradiation. WR-1065 protected DFMO-treate d cells by 2.29-fold (range 2.08-2.53), whereas undepleted control cel ls were protected by 2.09-fold (range 1.98-2.21) at the 10% survival l evel. Thus, WR-1065 appeared to offset the radiosensitizing effect of the DFMO treatment. Cysteamine, on the other hand, protected control a nd DFMO-treated cells to the same extent. We also examined the effect of combinations of exogenous thiols on radiosensitivity. Cells were tr eated with WR-1065 (4 mmol dm-3) for 30 min and then with increasing c oncentrations of dithiothreitol for 5 min prior to irradiation. The pr otective effects of these two thiols were simply additive.