Date of Award
Doctor of Philosophy (PhD)
In response to oxidative injury murine tumors depend upon the GSH oxidation-reduction cycle. The susceptibility of tumor cells to lysis by a flux of H2O2, such as generated by granulocytes or activated macrophages, or by the enzyme glucose oxidase, was augmented by interference with the GSH redox cycle. Depletion of tumor cell GSH was by 2 methods: incubation of cells with buthionine sulfoximine (BSO), a nontoxic inhibitor of GSH synthesis, or with l-chloro-2,4-dinitrobenzene_ a substrate for GSH S-transferase. Sensitization to oxidative cytolysis correlated with GSH depletion by either method by the critera of both dose-response and the time course of onset and recovery. A third approach involved inhibition of glutathione reductase (GR) with l,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Here too, interference in tumor cell GSH metabolism enhanced cytolysis by a flux of H2O2• In contrast, inhibition of catalase with aminotriazole had little effect. This theme was extended into another arena of GSH metabolism, the detoxification of reactive electrophiles by the formation of thioether conjugates with GSH. The interaction of tumor cell GSH with four sesquiterpene lactones (SLs), a class of sulfhydryl-reactive antineoplastic agents, was evaluated. SLs are potent depletors of cellular GSH. Prompt resynthesis of GSH is a critical component of tumor cell recovery following exposure to SLs. Cytolysis by SLs was augmented by inhibition of GSH synthesis with BSO. Potent synergy between BSO and the SL vernolepin was evident even if BSO was not present during but added just after exposure to vernolepin. For six additional, unrelated antineoplastics, sulfhydryl reactivity, in terms of their ability to deplete GSH, correlated with synergistic lysis in the presence of BSO. Lysis by BCNU, however, was not enhanced by BSO, in spite of GSH depletion. Vernolepin-mediated cytolysis of P815 cells was dependent upon exogenous cystine, as was GSH synthesis. This dependence upon cystine for cytolysis was not due to a requirement for protein synthesis or GSH synthesis. The formation of H2O2 as a result of cysteine autoxidation may contribute to the toxicity of vernolepin. In accord with this hypothesis, inhibition of GR by BCNU significantly enhanced the toxicity of vernolepin. Inhibition of catalase by aminotriazole resulted in less dramatic augmentation of vernolepin-mediated lysis.
Arrick, Bradley Alan, "Tumor Cell Glutathione Metabolism Therapeutic Implications" (1983). Student Theses and Dissertations. 439.