The influence of cellular glutathione content on cell survival following photodynamic treatment in vitro.

The influence of cellular glutathione (GSH) levels on the response to photodynamic treatment (PDT) in vitro was determined in cells which either were depleted of GSH by buthionine sulfoximine (BSO) or were genetically GSH deficient. The effects of GSH depletion on cellular radiosensitivity were studied in parallel for the purpose of comparison. BSO treatments which reduced GSH levels in four cell lines (CHO, V79, EMT6, RIF) to approximately 80% of controls, 30% of controls, or undetectable levels uniformly decreased cell survival. This decrease was directly related to GSH depletion levels and was expressed mainly in a reduction of the width of the survival curve shoulder (Dq). GSH level-dependent aerobic radiosensitization following BSO treatment was likewise found in all four cell lines. In contrast to PDT, however, cell survival changes were expressed in the dose slopes (Do's) of the survival curves. Cell survival of GSH-deficient human fibroblasts (GM 3877) was decreased following PDT and gamma irradiation when compared to their normal counterparts (GM 5659). In both modalities the difference was mainly due to a reduction in the Dq's, while the Do's were only slightly affected. The augmented response to PDT was not caused by interference by BSO or GSH with either cellular porphyrin uptake or singlet oxygen production during the photodynamic process. Possible mechanisms of GSH effects on PDT were discussed.