Glutathione depletion increases the cytotoxicity of melphalan to PC-3, an androgen-insensitive prostate cancer cell line

Abstract

Prostate cancer that is androgen-insensitive is unresponsive to a wide spectrum of cytotoxic agents, including all of the alkylating agents. Since a major pathway for the detoxification of the alkylating agents is conjugation with glutathione (GSH), GSH depletion has proved to be effective as a technique to restore melphalan sensitivity in melphalan-resistant cancer cell lines. However, the effect of GSH depletion has not been widely studied in tumor cell lines that have not developed resistance due to previous exposure to alkylating agents. Thus, we decided to investigate GSH depletion as a technique to increase melphalan cytotoxicity to PC-3 cells, an androgen-insensitive prostate cancer line. After 2 and 6 h incubation with 0.25-5 microM melphalan, virtually no effect was observed on either clonogenic lethality or MTT viability until 5 microM exposures. A 24-h incubation of the cells with 100 microM buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, reduced the GSH content by 70%-75%. Following GSH depletion, an increase in clonogenic lethality and a decrease in MTT viability occurred after exposure to concentrations as low as 0.25 microM. The dose modification factor ranged from 2.9 after 2 h incubation to 4.5 at 6 h. These results provide support for additional studies in prostate cancer for further investigation of GSH depletion as a technique to induce sensitivity to alkylating agents in this chemotherapy-resistant tumor.

Changes in endogenous tissue glutathione level in relation to murine ascites tumor growth and the anticancer activity of cisplatin

“…Cisplatin also behaves like an alkylating agent, and therefore a similar modulation mechanism might be involved. Both GSH depletion by BSO and GST inhibition have increased the tumoricidal activity of melphalan, a proteolytic alkylating drug (38), supporting the present view of involvement of cisplatin-mediated decrease of GSH and inhibition of GST in its anticancer activity. This is further strengthened by the results of the experiments involving combined treatment with BSO, a GSH depleting agent, with cisplatin.…”

Thiol-mediated apoptosis in prostate carcinoma cells

“…GSH depletion through buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, has been shown to increase PC-3 prostate carcinoma cell cytotoxicity to melphalan. 39 Depletion of intracellular thiols and shifting the redox potential to a more reduced state has also been demonstrated in vitro, as a means of sensitizing Bcl-2 overexpressing human prostate tumor cell lines to radiation-induced apoptosis. 40 BSO, however, has been shown to be unable to enhance significantly the potentiation of cytotoxicity of melphalan and other chemotherapeutic agents, including menadione and helanlin, in other tumor cell lines.…”

Chemical modulation of chemotherapy resistance in cultured oesophageal carcinoma cells

“…In addition, it has been shown that acquired resistance to cisplatin and alkylating agents is frequently accompanied by an elevation in intracellular GSH content [2+26]. Depletion of intracellular GSH as a strategy to increase the cytotoxic response to various chemotherapeutic agents in a variety of tumour cell lines has been the subject of a number of studies [27]. The majority of these have focused on bifunctional alkylating agents, although this approach has also proved useful in increasing the cytotoxicity of doxorubicin and platinum complexes both in cell culture and in in situ tumours [27].…”

“…Depletion of intracellular GSH as a strategy to increase the cytotoxic response to various chemotherapeutic agents in a variety of tumour cell lines has been the subject of a number of studies [27]. The majority of these have focused on bifunctional alkylating agents, although this approach has also proved useful in increasing the cytotoxicity of doxorubicin and platinum complexes both in cell culture and in in situ tumours [27]. GSTs are a family of multifunctional proteins that act both as enzymes and as binding proteins in various detoxification and excretory pathways.…”