Selective modulation of glutathione levels in human normal versus tumor cells and subsequent differential response to chemotherapy drugs.

Cellular glutathione (GSH) levels were found to be 7-fold higher in a human lung adenocarcinoma cell line (A549) than in a normal human lung fibroblast line (CCL-210). Differential modulation of cellular GSH was explored in these cell lines by (a) stimulation of GSH synthesis by oxothiazolidine-4-carboxylate (OTZ) and (b) inhibition of GSH synthesis by buthionine sulfoximine (BSO). In the tumor cell line, OTZ treatment had no effect; however, GSH levels of 140-170% of control were achieved in the normal fibroblast line. With BSO, the normal cell line was depleted of GSH at a faster relative rate than with the tumor line. Within 7 h, 5% GSH remained in the CCL-210 line while approximately 40% GSH remained in the A549 line. Survival response of normal versus tumor cell lines to selected chemotherapy drugs was compared following modulation of GSH levels. OTZ pretreatment of the A549 line provided no protection to a 1-h exposure to melphalan, cisplatin, or bleomycin; however, OTZ pretreatment of CCL-210 elevated GSH and provided protection to melphalan, cisplatin, and bleomycin (protection ratios at 5% survival of 1.2, 1.4, and 1.4, respectively). Neocarzinostatin toxicity in the normal CCL-210 line pretreated with BSO was greatly reduced (protection ratio at 50% survival = 5.0). The same BSO treatment to A549 cells (40% GSH remaining) yielded a similar survival curve to control cells. These studies demonstrate that selective differential chemotherapy responses of normal versus tumor cells is possible by manipulating the GSH synthetic cycle. Should basic phenotypic differences with regard to reductive capacity exist in vivo, such manipulation in GSH levels might yield a therapeutic gain for carefully selected chemotherapy drugs.