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Introduction and Objectives: Arsenic trioxide (As2O3) induces clinical remission in acute promyelocytic leukemic patients and apoptosis in various tumor cells in vitro. To develop As2O3-based combination chemotherapy for renal cell carcinoma (RCC), we investigated the cytotoxic effects of As2O3 in combination with chemotherapeutic agents or L-buthionine sulfoximine (BSO), a glutathione (GSH) synthesis inhibitor. Methods: Cytotoxicity and synergy were assessed by microculture tetrazolium dye assay and isobolographic analysis, respectively. Intracellular reactive oxygen species (ROS), superoxide, and hydrogen peroxide (H2O2) levels were examined by flow cytometry. Intracellular GSH content and GSH-S-transferase (GST) activity were determined by enzymatic assays. Results: Treatment of ACHN cells with therapeutic concentrations of As2O3 in combination with BSO resulted in synergistic cytotoxic effect, although in combination with driamycin, vinblastine, and 5-fluorouracil produced antagonistic effect. Synergy was also obtained in three other RCC cell lines and freshly derived RCC cells from six patients. As2O3 and BSO combination also induced apoptosis, while each agent did not. This combination markedly decreased intracellular GSH content and GST activity, but did not affect ROS, super oxide, or H2O2 levels. However, neither the intracellular GSH nor GST was decreased by As2O3 with adriamycin, vinblastine, or 5-fluorouracil. In contrast to no inhibitory effect being achieved by H2O2 or nitrogen oxide inhibitors, the GSH-increasing agents N-acetylcysteine and lipoic acid significantly inhibited the combined cytotoxicity of As2O3 and BSO. Conclusions: BSO sensitizes RCC cells to As2O3-induced apoptosis through the down-regulation of intracellular GSH redox system, suggesting that the combination therapy of As2O3 and BSO might be effective for RCC.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]