Emodin Enhances Arsenic Trioxide-Induced Apoptosis via Generation of Reactive Oxygen Species and Inhibition of Survival Signaling

Abstract

Although arsenic trioxide (As 2 O 3 ) induces apoptosis in a relatively wide spectrum of tumors, the sensitivity of different cell types to this treatment varies to a great extent. Because reactive oxygen species (ROS) are critically involved in As 2 O 3 -induced apoptosis, we attempted to explore the possibility that elevating the cellular ROS level might be an approach to facilitate As 2 O 3 -induced apoptosis. Emodin, a natural anthraquinone derivative, was selected because its semiquinone structure is likely to increase the generation of intracellular ROS. Its independent and synergistic effects with As 2 O 3 in cytotoxicity were studied, and the plausible signaling mechanism was investigated in HeLa cells. Cell Proliferation Assay and flow cytometry were used to assess cell viability and apoptosis. Electrophoretic mobility shift assay, luciferase reporter assay, and Western blotting were performed to analyze signaling alteration. The results demonstrated that coadministration of emodin, at low doses of 0.5-10 M, with As 2 O 3 enhanced As 2 O 3 -rendered cytotoxicity on tumor cells, whereas these treatments caused no detectable proproliferative or proapoptotic effects on nontumor cells. ROS generation was increased, and activation of nuclear factor B and activator protein 1 was suppressed by coadministration. All enhancements by emodin could be abolished by the antioxidant N-acetyl-L-cysteine. Therefore, we concluded that emodin sensitized HeLa cells to As 2 O 3 via generation of ROS and ROS-mediated inhibition on two major prosurvival transcription factors, nuclear factor B and activator protein 1. This result allows us to propose a novel strategy in chemotherapy that uses mild ROS generators to facilitate apoptosisinducing drugs whose efficacy depends on ROS.

Gene expression alteration during redox-dependent enhancement of arsenic cytotoxicity by emodin in HeLa cells

“…In our previous studies, we found that exposure of HeLa cells to As 2 O 3 /emodin caused a suppressed expression of NF-κB-driven genes [8], and this suppression might be linked to an attenuated DNA binding capacity of NF-κB (data unpublished). We also demonstrated that NF-κB activation plays an antiapoptotic role under resting state and in response to As 2 O 3 exposure [7]. Taken together, we conclude that emodin exerts an inhibitory effect on anti-apoptotic NF-κB activation at multiple levels.…”

“…In our previous studies the dose of emodin used in combination with As 2 O 3 was 10 µM [7,8]. In order to visualize the gene expression profile clearly in the present study a higher dose was tested.…”

“…Two transcription factors known to be sensitive to cellular redox, nuclear factor κB (NF-κB) and activator protein (AP-1) were inhibited by emodin-elicited ROS elevation, whereas a series of major apoptotic signaling events, i.e. MTP collapse, cytochrome C release and caspases activation were promoted [7,8]. But the precise molecular mechanism through which ROS facilitates As 2 O 3 -induced tumor cell apoptosis has not been elucidated.…”

The biphasic redox sensing of SENP3 accounts for the HIF-1 transcriptional activity shift by oxidative stress

“…After exposed to the various concentration of H 2 O 2 as indicated for 24 h, cell viability was assayed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) (Sigma-Aldrich, St Louis, MO, USA) [32] .…”

Differential effect of ascorbic acid and n‐acetyl‐l‐cysteine on arsenic trioxide‐mediated oxidative stress in human leukemia (HL‐60) Cells

“…Many antioxidants have been reported to enhance or inhibit ATO-mediated apoptosis in tumor cells [3]. Ascorbic acid (AA) is an anti-oxidant and free radical scavenger effective against peroxyl-and hydroxyl-radicals, superoxide, singlet oxygen and peroxynitrite.…”