Ascorbic Acid Potentiation of Arsenic Trioxide Anticancer Activity Against Acute Promyelocytic Leukemia

INTRODUCTION: Acute promyelocytic leukemia (APL) is a malignant disorder of the white blood cells. Arsenic trioxide (As(2)O(3)) has been used as a therapeutic agent to treat APL and other tumors. Studies suggest that ascorbic acid (AA) supplementation may improve the clinical outcome of As(2)O(3) for APL patients. Our aim was to use human leukemia (HL-60) APL-cells as an in vitro test model to evaluate the effect of physiologic doses of AA on As(2)O(3)-induced toxicity and apoptosis of HL-60 cells. METHODS: HL-60 cells were treated either with a pharmacologic dose of As(2)O(3) alone and with several physiologic doses of AA. Cell survival was determined by trypan blue exclusion test. The extent of oxidative cell/tissue damage was determined by measuring lipid hydroperoxide concentration by spectrophotometry. Cell apoptosis was measured by flow cytometry using Annexin-V and propidium iodide (PI) staining. RESULTS: AA treatment potentiates the cytotoxicity of As(2)O(3) in HL-60 cells. Viability decreased from (58 +/- 3)% in cells with As(2)O(3) alone to (47 +/- 2)% in cells treated with 100 microM AA and 6 microg/mL As(2)O(3) with P < 0.05. There was a significant (P < 0.05) increase in lipid hydroperoxide concentrations in HL-60 cells co-treated with AA compared to As(2)O(3) alone. Flow cytometry assessment (Annexin V FITC/PI) suggested that AA co-treatment induces more apoptosis of HL-60 cells than did As(2)O(3) alone, but this was not statistically significant. Taken together, our experiment indicates that As(2)O(3) induced in vitro cell death and apoptosis of HL-60 cells. Administration of physiologic doses of AA enhanced As(2)O(3)-induced cytotoxicity, oxidative cell/tissue damage, and apoptosis of HL-60 cells through externalization of phosphatidylserine. CONCLUSIONS: These suggest that AA may enhance the cytotoxicity of As(2)O(3), suggesting a possible future role of AA/As(2)O(3) combination therapy in patients with APL.