| Cancer is one of the major grievous diseases imperiling human health。The genesis of tumorigenesis is a complex process and can be induced by the deregulated cell proliferation and the suppressed apoptosis. Most of chemotherapeutic drugs exerted their cytotoxic effects through inhibiting the growth of cancer cells and inducing the apoptosis. Thus, the approach of inducing apoptosis of cancer cells is one of the major promising treatments for targeting cancers.Arsenic trioxide (As2O3) is an effective clinical remedy applying on acute promyelocytic leukemia (APL). However, its clinical application to non-APL tumors was limited because that only the higher concentrations of As2O3 could display the action of apoptosis. Literatures reported that some antioxidants could promote the apoptosis induced by lower concentrations of As2O3 in vitro.Trolox (6 - hydroxy - 2, 5, 7, 8 - tetramethylchroman-2-carboxylic acid) is a hydrophlic vitamin E analog. It has been widely used in researches because of its outstanding antioxidant capacity in the manners of enhanced cell permeability in recent years. For example, As2O3 combined with Trolox could induce apoptosis, and also could reduce the toxicity of As2O3. As a result, As2O3 can be used extensively in clinical application.The effects of As2O3 alone and As2O3 combined with Trolox on proliferation inhibition, apoptotic effect, DNA damage, cell growth inhibition and ROS content of HL-60 cells were investigated by the methods of MTT assay, typanblue exclusion method, Hoechst 33258 staining, Giemsa staining, single cell gel electrophoresis, flow cytometry analysis and ROS content determination, respectively. Further more, the effects of As2O3 alone and combined with Trolox on DNA damage of human peripheral blood mononuclear cells (PBMCs) were investigated by single cell gel electrophoresis. The results are shown as follows:(1) Lower levels of As2O3(≤4μmol·L-1)alone exhibited inhibitory effect on HL-60 cells, and the inhibitory effect were significantly enhanced in combination with 100μmol·L-1 Trolox; higher concentrations of As2O3(≥8μmol·L-1)combined with Trolox resulted in the death of HL-60 cells. Both the growth inhibitions and lethal effects were in a time- and dose-dependent manner.(2) As2O3 alone exhibited DNA damage effect on HL-60 cells and the damage ratio was in a does-dependent manner. As2O3 combined with 100μmol·L-1 Trolox could induce seriously DNA danmage than As2O3 alone. DNA damage may be one of the major causes resulting in cell growth inhibition and apoptosis by As2O3 alone and combination use.(3) The G2/M phases was significantly arrested by As2O3 combined with 100μmol·L-1 Trolox in HL-60 cells. This arrest can be caused by the activation of DNA damaged cell cycle checkpoint, perhaps also can be caused by interfering the function of cytoskeleton and the formation of mitosis equipment. The latter reason can be supported by the Giemsa staining and fluorescence staining method. The cell cycle arrest was probably the upstream event that inducing HL-60 cells apoptosis by As2O3 combined Trolox .(4) As2O3 alone significantly increased intracellular ROS content of HL-60 cells in a dose-dependent manner, while intracellular ROS content was also significantly higher by the lower concentrations of As2O3 combined with Trolox.(5) The flow cytometry analysis exhibited that the apoptotic ratio was not changed when catalase was added to the combination treatments. The results suggested that the apoptotic effect of As2O3 enhanced by Trolox was independent of the formation of extracellular H2O2 on HL-60 cells.(6) The DNA damage of human peripheral blood mononuclear cells (PBMCs) was significantly decreased after treated with combined Trolox than As2O3 alone. This indicated that the combination with Trolox could reduce the toxicity of As2O3 on normal cells, which is very important in clinical application in the future.
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