EFFECT OF 4-HYDROPEROXYIFOSFAMIDE ON THE CELLULAR GLUTATHIONE PATHWAY

Background: The glutathione (GSH) pathway has been implicated in cellu lar resistance to cytotoxic agents. There is strong evidence that oxaz aphosphorine analogues may alter cellular GSH concentrations. Therefor e, we analyzed the effects of the prodrugs 4-hydroperoxy-ifosfamide [4 -OOH-IF] and -cyclophosphamide [4-00H-Cy] on the cellular GSH pathway and the antitumor efficacy of cisplatin in human cancer cells using is obologram analysis. Methods: Cytotoxicities to COOH-IF and 4-OOH-Cy in human ovarian A2780 and cisplatin-resistant A2780CP2 cells, breast ca ncer cell lines MCF-7 and MB231 were determined using the sulphorhodam ine B (SRB) assay. Determinations of cellular GSH concentrations and G SH-peroxidase activities were performed 2 h and 24 h after drug exposu re to either 4-OOH-IF or 4-OOH-Cy. Drug interactions of cisplatin eith er with 4-OOH-IF or 4-OOH-Cy were assessed using standard isobologram methodology (50% isodose), and were classified as synergistic, additiv e or antagonistic. Results: While A2780CP2 cells were 5.4-fold resista nt to cisplatin, only 2.5-fold and 3.9-fold cross-resistance to 4-OOH- Cy and 4-OOH-IF was observed, respectively. Maximum depletion of cellu lar GSH was achieved in breast cancer cell lines and peaked two hours after administration of 4-OOH-IF However, complete restoration of GSH contents were observed 24 h after drug exposure and no significant alt erations of GPx activities were found. Using isobologram analysis conc urrent 2-hour exposure to 4-OOH-IF and cisplatin led to additive drug interactions. Using the same conditions, exposure to 4-OOH-Cy and cisp latin resulted in additive to antagonistic interactions. Conclusions: Exposure to 4-hydroperoxyifosfamide leads to significant depletion of cellular GSH concentrations and may, therefore, schedule dependently p otentiate the antitumor efficacy of other anticancer agents (e. g., ci splatin, anthracyclines).