Signal transduction pathways and transcription factors triggered by arsenic trioxide in leukemia cells

Arsenic trioxide and p97 inhibitor synergize against acute myeloid leukemia by targeting nascent polypeptides and activating the ZAKα-JNK pathway

Arsenic trioxide (ATO) has exhibited remarkable efficacy in treating acute promyelocytic leukemia (APL), primarily through promoting the degradation of the PML-RARα fusion protein. However, ATO alone fails to confer any survival benefit to non-APL acute myeloid leukemia (AML) patients and exhibits limited efficacy when used in combination with other agents. Here, we explored the general toxicity mechanisms of ATO in APL and potential drugs that could be combined with ATO to exhibit synergistic lethal effects on other AML. We demonstrated that PML-RARα degradation and ROS upregulation were insufficient to cause APL cell death. Based on the protein synthesis of different AML cells and their sensitivity to ATO, we established a correlation between ATO-induced cell death and protein synthesis. Our findings indicated that ATO induced cell death by damaging nascent polypeptides and causing ribosome stalling, accompanied by the activation of the ZAKα-JNK pathway. Furthermore, ATO-induced stress activated the GCN2-ATF4 pathway, and ribosome-associated quality control cleared damaged proteins with the assistance of p97. Importantly, our data revealed that inhibiting p97 enhanced the effectiveness of ATO in killing AML cells. These explorations paved the way for identifying optimal synthetic lethal drugs to enhance ATO treatment on non-APL AML.

"Double-edged sword" effect of reactive oxygen species (ROS) in tumor development and carcinogenesis

Reactive oxygen species (ROS) are small reactive molecules produced by cellular metabolism and regulate various physiological and pathological functions. Many studies have shown that ROS plays an essential role in the proliferation and inhibition of tumor cells. Different concentrations of ROS can have a "double-edged sword" effect on the occurrence and development of tumors. A certain concentration of ROS can activate growth-promoting signals, enhance the proliferation and invasion of tumor cells, and cause damage to biomacromolecules such as proteins and nucleic acids. However, ROS can enhance the body's antitumor signal at higher levels by initiating oxidative stress-induced apoptosis and autophagy in tumor cells. This review analyzes ROS's unique bidirectional regulation mechanism on tumor cells, focusing on the key signaling pathways and regulatory factors that ROS affect the occurrence and development of tumors and providing ideas for an in-depth understanding of the mechanism of ROS action and its clinical application.

ATO Increases ROS Production and Apoptosis of Cells by Enhancing Calpain-Mediated Degradation of the Cancer Survival Protein TG2

Transglutaminase 2 (TG2) is a critical cancer cell survival factor that activates several signalling pathways to foster drug resistance, cancer stem cell survival, metastasis, inflammation, epithelial-mesenchymal transition, and angiogenesis. All-trans retinoic acid (ATRA) and chemotherapy have been the standard treatments for acute promyelocytic leukaemia (APL), but clinical studies have shown that arsenic trioxide (ATO), alone or in combination with ATRA, can improve outcomes. ATO exerts cytotoxic effects in a variety of ways by inducing oxidative stress, genotoxicity, altered signal transduction, and/or epigenetic modification. In the present study, we showed that ATO increased ROS production and apoptosis ratios in ATRA-differentiated NB4 leukaemia cells, and that these responses were enhanced when TG2 was deleted. The combined ATRA + ATO treatment also increased the amount of nuclear factor erythroid 2-related factor 2 (NRF2) transcription factor, an adaptive regulator of the cellular oxidative stress response, and calpain proteolytic activity, resulting in TG2 degradation and the reduced survival of WT leukaemia cells. We further showed that the induced TG2 protein expression was degraded in the MCF-7 epithelial cell line and primary peripheral blood mononuclear cells upon ATO treatment, thereby sensitising these cell types to apoptotic signals.

ALKBH4 Stabilization Is Required for Arsenic-Induced 6mA DNA Methylation Inhibition, Keratinocyte Malignant Transformation, and Tumorigenicity

Inorganic arsenic is one of the well-known human skin carcinogens. However, the molecular mechanism by which arsenic promotes carcinogenesis remains unclear. Previous studies have established that epigenetic changes, including changes in DNA methylation, are among the critical mechanisms that drive carcinogenesis. N6-methyladenine (6mA) methylation on DNA is a widespread epigenetic modification that was initially found on bacterial and phage DNA. Only recently has 6mA been identified in mammalian genomes. However, the function of 6mA in gene expression and cancer development is not well understood. Here, we show that chronic low doses of arsenic induce malignant transformation and tumorigenesis in keratinocytes and lead to the upregulation of ALKBH4 and downregulation of 6mA on DNA. We found that reduced 6mA levels in response to low levels of arsenic were mediated by the upregulation of the 6mA DNA demethylase ALKBH4. Moreover, we found that arsenic increased ALKBH4 protein levels and that ALKBH4 deletion impaired arsenic-induced tumorigenicity in vitro and in mice. Mechanistically, we found that arsenic promoted ALKBH4 protein stability through reduced autophagy. Together, our findings reveal that the DNA 6mA demethylaseALKBH4 promotes arsenic tumorigenicity and establishes ALKBH4 as a promising target for arsenic-induced tumorigenesis.

Molecular relation between biological stress and carcinogenesis

This paper aims to overview different types of stress, including DNA replication stress, oxidative stress, and psychological stress. Understanding the processes that constitute a cellular response to varied types of stress lets us find differences in how normal cells and cancer cells react to the appearance of a particular kind of stressor. The revealed dissimilarities are the key for targeting new molecules and signaling pathways in anticancer treatment. For this reason, molecular mechanisms that underlay DNA replication stress, oxidative stress, and psychological stress have been studied and briefly presented to indicate biochemical points that make stressors contribute to cancer development. What is more, the viewpoint in which cancer constitutes the outcome and the cause of stress has been taken into consideration. In a described way, this paper draws attention to the problem of cancer-related post-traumatic stress disorder and proposes a novel, multidimensional oncological approach, connecting anticancer treatment with psychiatric support.

Oxidative stress in leukemia and antioxidant treatment

Oxidative stress is caused by the imbalance between the generation of free radicals/reactive oxygen species (ROS) and the antioxidant defense systems, which can activate various transcription factors and affect their transcriptional pathways. Oxidative stress plays an important role in the occurrence and development of leukemia and is closely related to the treatment and prognosis of leukemia. The standard chemotherapy strategies for the pre-treatment of leukemia have many drawbacks. Hence, the usage of antioxidants and oxidants in the treatment of leukemia is being explored and has been preliminarily applied. This article reviews the research progress of oxidative stress and leukemia. In addition, the application of antioxidants treatment in leukemia has been summarized.

Silver nanoparticles protect against arsenic induced genotoxicity via attenuating arsenic bioaccumulation and elevating antioxidation in mammalian cells

Arsenic (As) and its compounds have been classified as Group I carcinogenic agents by the International Agency for Research on Cancer (IARC); however, there is few specific and efficient antidotes used for As detoxification. The present study aimed to investigate the protective effects of silver nanoparticles (AgNPs) at non-toxic concentrations on As(Ⅲ) induced genotoxicity and the underlying mechanism. Our data showed that AgNPs pretreatment significantly inhibited the generation of phosphorylated histone H2AX (γ-H2AX, marker of nuclear DNA double strand breaks) and the mutation frequencies induced by As(Ⅲ) exposure. Atomic fluorescence spectrometer (AFS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis revealed that the intracellular accumulation of As(Ⅲ) in human-hamster hybrid A_L cells was declined by AgNPs via suppressing the expression of specific As(Ⅲ)-binding protein (Gal-1). Moreover, the activities of antioxidant enzymes were greatly up-regulated by AgNPs, which eventually inhibited the generation of reactive oxygen species (ROS) induced by As(Ⅲ) and the downstream stress-activated protein kinases/c-Jun amino-terminal kinases (SAPK/JNK) signaling pathway. These results provided clear evidence that AgNPs dramatically suppressed the genotoxic response of As(Ⅲ) in mammalian cells via decreasing As(Ⅲ) bioaccumulation and elevating intracellular antioxidation, which might provide a new clue for AgNPs applications in As(Ⅲ) detoxification.

Control of Oxidative Stress in Cancer Chemoresistance: Spotlight on Nrf2 Role

Chemoresistance represents the main obstacle to cancer treatment with both conventional and targeted therapy. Beyond specific molecular alterations, which can lead to targeted therapy, metabolic remodeling, including the control of redox status, plays an important role in cancer cell survival following therapy. Although cancer cells generally have a high basal reactive oxygen species (ROS) level, which makes them more susceptible than normal cells to a further increase of ROS, chemoresistant cancer cells become highly adapted to intrinsic or drug-induced oxidative stress by upregulating their antioxidant systems. The antioxidant response is principally mediated by the transcription factor Nrf2, which has been considered the master regulator of antioxidant and cytoprotective genes. Nrf2 expression is often increased in several types of chemoresistant cancer cells, and its expression is mediated by diverse mechanisms. In addition to Nrf2, other transcription factors and transcriptional coactivators can participate to maintain the high antioxidant levels in chemo and radio-resistant cancer cells. The control of expression and function of these molecules has been recently deepened to identify which of these could be used as a new therapeutic target in the treatment of tumors resistant to conventional therapy. In this review, we report the more recent advances in the study of Nrf2 regulation in chemoresistant cancers and the role played by other transcription factors and transcriptional coactivators in the control of antioxidant responses in chemoresistant cancer cells.

Peroxiredoxin 3 Has Important Roles on Arsenic Trioxide Induced Apoptosis in Human Acute Promyelocytic Leukemia Cell Line via Hyperoxidation of Mitochondrial Specific Reactive Oxygen Species

NB4 cell, the human acute promyelocytic leukemia (APL) cell line, was treated with various concentrations of arsenic trioxide (ATO) to induce apoptosis, measured by staining with 7-amino-actinomycin D (7-AAD) by flow cytometry. 2', 7'-dichlorodihydro-fluorescein-diacetate (DCF-DA) and MitoSOXTM Red mitochondrial superoxide indicator were used to detect intracellular and mitochondrial reactive oxygen species (ROS). The steady-state level of SO2 (Cysteine sulfinic acid, Cys-SO2H) form for peroxiredoxin 3 (PRX3) was measured by a western blot. To evaluate the effect of sulfiredoxin 1 depletion, NB4 cells were transfected with small interfering RNA and analyzed for their influence on ROS, redox enzymes, and apoptosis. The mitochondrial ROS of NB4 cells significantly increased after ATO treatment. NB4 cell apoptosis after ATO treatment increased in a time-dependent manner. Increased SO2 form and dimeric PRX3 were observed as a hyperoxidation reaction in NB4 cells post-ATO treatment, in concordance with mitochondrial ROS accumulation. Sulfiredoxin 1 expression is downregulated by small interfering RNA transfection, which potentiated mitochondrial ROS generation and cell growth arrest in ATO-treated NB4 cells. Our results indicate that ATO-induced ROS generation in APL cell mitochondria is attributable to PRX3 hyperoxidation as well as dimerized PRX3 accumulation, subsequently triggering apoptosis. The downregulation of sulfiredoxin 1 could amplify apoptosis in ATO-treated APL cells.

Benefits of Combined All-Trans Retinoic Acid and Arsenic Trioxide Treatment of Acute Promyelocytic Leukemia Cells and Further Enhancement by Inhibition of Atypically Expressed Transglutaminase 2

Randomized trials in acute promyelocytic leukemia patients have shown that treatment with a combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) is superior in efficacy to monotherapy, with significantly decreased mortality. So far, there are little data available to explain the success of the ATRA and ATO combination treatment in molecular terms. We showed that ATRA- and ATO-treated cells had the same capacity for superoxide production, which was reduced by two-thirds in the combined treatment. Secreted inflammatory biomarkers (monocyte chemoattractant protein-1 [MCP-1], interleukin-1 beta [IL-1β] and tumor necrosis factor-α [TNF-α]) were significantly decreased and were further reduced in a transglutaminase 2 (TG2) expression-dependent manner. The amount of secreted TNF-α in the supernatant of NB4 TG2 knockout cells was close to 50 times lower than in ATRA-treated differentiated wild-type NB4 cells. The irreversible inhibitor of TG2 NC9 not only decreased reactive oxygen species production 28-fold, but decreased the concentration of MCP-1, IL-1β and TNF-α 8-, 15- and 61-fold, respectively in the combined ATRA + ATO-treated wild-type NB4 cell culture. We propose that atypical expression of TG2 leads to the generation of inflammation, which thereby serves as a potential target for the prevention of differentiation syndrome.

Effect of Occupational Exposure to Radar Radiation on Cancer Risk: A Systematic Review and Meta-Analysis

OBJECTIVE

Microwave radiation is one of the most growing environmental workplace factors that exposes too many workers in the various workplaces. Regard to concerns about cancer incidence in these workers and lack of systematic or meta-analytic studies about this object, so, we conducted a meta-analysis to acquire an understanding of the association between cancer risk and occupational exposure to radar radiation.

METHODS

A systematic search was carried out on case-control, cohort and clinical control trial studies that published in the Cochrane Library, PubMed, ISI Web of Science, Scopus and Google scholar databases that accomplished from March 2017 to March 2018 and updated on 30 September, 2018 in English and Persian articles without time limit in publication date. Keywords were selected based on PICO principle and collected from MeSH database. After removal of duplicated studied, taking into inclusion and exclusion criteria, the process of screening was carried out and data were extracted after preparation of the full text of included articles. Article collection was completed by manually searching for a reference list of eligible studies. For quality assessment of included studies, Newcastle-Ottawa scale was used.

RESULTS

a total of 533 studies was found in the first step of literature search, only 6 were included with 53,008 sample size according to inclusion and exclusion criteria. Estimated pooled random effects size analysis showed no significant increasing effect of occupational exposure to radar radiation on mortality rate (MR=0.81, 95%CI: 0.78, 0.83) and relative risk (RR=0.87, 95%CI: 0.75, 0.99, P <0.0001) of cancer with a significant heterogeneity between the selected studies.

CONCLUSIONS

In conclusion, the results of this meta-analysis study have shown no significant increase in overall mortality ratio and cancer risk ratio from occupational exposure to the radar frequency of workers. But, these results are not conclusive. As regards to some limitation such as fewer numbers of included studies, lack of data about exposure characterizations and demographic characterizations in this meta-analysis, this result is not certain and conclusive. It is recommended to conduct future studies.

Amelioration of arsenic-induced toxic effects in mice by dietary supplementation of Syzygium cumini leaf extract

Arsenic created a serious public health problem in Bangladesh due to its presence in groundwater and dissemination of the toxic effects to millions of people. The scarcity of the treatment options to manage this affected population has made the situation much worse. To find a promising treatment option, this study was undertaken to examine the ameliorating roles of Syzygium cumini leaf extract (SLE) against arsenic-induced toxic effects in mice. Swiss albino mice were divided into four groups where ‘control’ group received pure water + normal feed, ‘arsenic (As)’ group received sodium arsenite (NaAsO₂)-containing water (10 μg/g body weight/day) + normal feed, ‘As+SLE’ group received NaAsO₂-containing water + feed supplemented with SLE (50 µg/g body weight/day) and finally the ‘SLE’ group received pure water + feed supplemented with SLE. A gradual increase in body weight gain was observed in control mice; however, the body weight gain in As-exposed mice was decreased. This decrease in body weight gain was prevented in As+SLE group mice that received SLE supplemented feed. Arsenic showed a secondary effect by causing enlargement of spleen, kidney and liver of ‘As’ group mice and this enlargement of the organs was minimized with SLE supplementation. In addition, SLE abrogated arsenic-mediated elevation of serum alkaline phosphatase (ALP), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), uric acid and glucose. These results, therefore, suggest that SLE might have future therapeutic value for preventing or reducing arsenic-induced toxic effects.

Anti-inflammatory and antitumor action of hydrogen via reactive oxygen species

Hydrogen (H₂) has advantages that lead it to be used as a novel antioxidant in preventive and therapeutic applications. H₂ can permeate into biomembranes, cytosol, mitochondria and nuclei, and can be dissolved in water or saline to produce H₂ water or H₂-rich saline. H₂ selectively reduces oxidants of the detrimental reactive oxygen species (ROS), including hydroxyl radicals (·OH) and peroxynitrite (ONOO^-), which serve a causative role in the promotion of tumor cell proliferation, invasion and metastasis, but do not disturb metabolic oxidation-reduction reactions in cell signaling. Compared with traditional antioxidants, H₂ is a small molecule that can easily dissipate throughout the body and cells; thus, it may be a safe and effective antioxidant for inflammatory diseases and cancer, since ROS usually initiates tumor progression. Treatment with H₂ may involve correction of the oxidative/anti-oxidative imbalance and suppression of inflammatory mediators. Therefore the present review will discuss the anti-inflammatory and anti-tumorigenic action of H₂ via ROS.

Annexin A6 regulates adipocyte lipid storage and adiponectin release

Lipid storage and adipokine secretion are critical features of adipocytes. Annexin A6 (AnxA6) is a lipid-binding protein regulating secretory pathways and its role in adiponectin release was examined. The siRNA-mediated AnxA6 knock-down in 3T3-L1 preadipocytes impaired proliferation, and differentiation of AnxA6-depleted cells to mature adipocytes was associated with higher soluble adiponectin and increased triglyceride storage. The latter was partly attributed to reduced lipolysis. Accordingly, AnxA6 overexpression in 3T3-L1 adipocytes lowered cellular triglycerides and adiponectin secretion. Indeed, serum adiponectin was increased in AnxA6 deficient mice. Expression analysis identified AnxA6 protein to be more abundant in intra-abdominal compared to subcutaneous adipose tissues of mice and men. AnxA6 protein levels increased in white adipose tissues of obese mice and here, levels were highest in subcutaneous fat. AnxA6 protein in adipocytes was upregulated by oxidative stress which might trigger AnxA6 induction in adipose tissues and contribute to impaired fat storage and adiponectin release.

Nuclear translocation of nuclear factor kappa B is regulated by G protein signaling pathway in arsenite-induced apoptosis in HBE cell line

Arsenite is a certainly apoptosis inducer in various cell types. However, the detailed mechanism underlying how arsenite trigger apoptosis remains elusive. In this study, using human bronchial epithelial cell as a culture system, we demonstrated that arsenite-induced nuclear translocation of nuclear factor kappa B (NF-κB) resulted in the release of cytochrome c, the modulation of Fas and FasL, caspase activation, and ultimately leading to cell apoptosis. Importantly, we showed for the first time that the NF-κB-mediated apoptosis induced by arsenite was regulated by G protein-adenylate cyclase (AC)-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway. Inhibition of this classical G protein signaling pathway by a typical PKA inhibitor, H-89, caused the inactivation of NF-κB, the depletion of caspase-3, 8 and 9 activities, and thus reducing the level of cell apoptosis. Taken together, our results indicate that arsenite is able to trigger cell apoptosis in human bronchial epithelial cells through the nuclear translocation of NF-κB, which can be modulated by G protein signaling pathway. These findings further suggest that inhibition of G protein-mediated pathway by specific inhibitors may be a potential strategy for the prevention of arsenite toxicity. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1819-1833, 2016.

Deficiency of SUMO-specific protease 1 induces arsenic trioxide-mediated apoptosis by regulating XBP1 activity in human acute promyelocytic leukemia

Small ubiquitin-like modifier (SUMO)/sentrin-specific protease 1 (SENP1), a member of the SENP family, is highly expressed in several neoplastic tissues. However, the effect of SENP1 in acute promyelocytic leukemia (APL) has not been elucidated. In the present study, it was observed that SENP1 deficiency had no effect on the spontaneous apoptosis or differentiation of NB4 cells. Arsenic trioxide (As₂O₃) could induce the upregulation of endoplasmic reticulum (ER) stress, resulting in the apoptosis of NB4 cells. Additionally, knockdown of SENP1 significantly increased As₂O₃-induced apoptosis in NB4 cells transfected with small interfering RNA targeting SENP1. SENP1 deficiency also increased the accumulation of SUMOylated X-box binding protein 1 (XBP1), which was accompanied by the downregulation of the messenger RNA expression and transcriptional activity of the XBP1 target genes endoplasmic reticulum-localized DnaJ 4 and Sec61a, which were involved in ER stress and closely linked to the apoptosis of NB4 cells. Taken together, these results revealed that the specific de-SUMOylation activity of SENP1 for XBP1 was involved in the ER stress-mediated apoptosis caused by As₂O₃ treatment in NB4 cells, thus providing insight into potential therapeutic targets for APL treatment via manipulating XBP1 signaling during ER stress by targeting SENP1.

Osteoblasts activate the Nrf2 signalling pathway in response to arsenic trioxide treatment

Arsenic trioxide is used to treat a variety of leukaemia types and causes tumour cell death. However, it is not well known whether arsenic trioxide is toxic to bone osteoblast cells, the precursor cells from which leukaemia cells originate. The aim of this study was to examine the response of osteosarcoma cell line MG63 and primary cultured osteoblasts to arsenic trioxide treatment. After 24h of treatment, arsenic trioxide was more effective at inhibiting cell growth and increasing oxidative stress and DNA damage in MG63 cells than in osteoblasts. In addition, arsenic trioxide arrested cell cycle progression in the G2/M phase, and induced apoptosis in MG63 cells, but not in primary cultured osteoblasts. The results further showed that the expression of transcription factor Nrf2 and its downstream antioxidant effectors, including hemeoxygenase-1, glutathione, and superoxide dismutase, was increased in primary cultured osteoblasts. Additionally, expression of heat shock proteins was also increased. Experiments using inhibitors of antioxidant enzymes in the presence of arsenic trioxide-treated osteoblasts demonstrated that glutathione and superoxide dismutase were responsible for reducing oxidative stress, caspase-3 activity, and apoptosis and that heat shock proteins helped reduce caspase-3 activity. Unexpectedly, there was no apparent effect of the markedly increased hemeoxygenase-1, suggesting that other functions might exist for hemeoxygenase-1. These findings demonstrate that osteosarcoma cells are more sensitive to arsenic trioxide treatment than primary cultured osteoblasts and that primary cultured osteoblasts activate the Nrf2 signalling pathway in response to arsenic trioxide exposure to escape from oxidative damage and apoptosis.

Diabetes as a risk factor to cancer: functional role of fermented papaya preparation as phytonutraceutical adjunct in the treatment of diabetes and cancer

Oncologists and diabetologists quote scientific data from epidemiological and in vitro studies to show that high levels of insulin and glucose, in combination with oxidative stress and chronic inflammation, can heighten the risk of developing cancer amongst patients with diabetes. Although the cancers that have been consistently associated with type 2 diabetes include pancreatic, colorectal, breast and liver cancer, the preponderance of the disease risk factors such as obesity, inflammation, hyperglycemia, hyperinsulinaemia (as a result of insulin resistance and oxidative β-cell damage) and the indirect influence of anti-diabetic medications are increasingly being defined. Fermented papaya preparation (FPP) has defined antioxidant and immune-modulating potentials. The ability of FPP influence signaling cascades associated with cell growth and survival presents a rational for chemopreventive adjunct that can be used in combination with traditional redox based therapies that target oxidative stress in the cancer micro environment. It is further suggested that the demonstrated efficacy FPP to control blood glucose, excessive inflammation and modulate free radical-induced oxidative damage which are triggers of liver, bladder, breast and prostate cancers in type 2 diabetics, may favorably mitigate the side effects of ensuing diabetes and cancer therapy. What remains paramount is early cancer detection and early determination of propensity risks for diabetes. The education of patients, proper dietary management and compliance with therapeutic regime directed at cancer and diabetes encapsulate challenges of global magnitude.

Arsenic trioxide inhibits DNA methyltransferase and restores TMS1 gene expression in K562 cells

BACKGROUND

Gene silencing associated with aberrant methylation of promoter region CpG islands is an acquired epigenetic alteration that serves as an alternative to genetic defects in the inactivation of tumor suppressor genes in human cancers. The demethylating, dose-dependent effect of arsenic trioxide (As2O3) on several tumor-related genes has already been postulated. However, whether such a demethylating effect also applies to the TMS1 gene in chronic myeloid leukemia cell line K562 cells has not been studied so far. The aim of the present study was to detect the methylation status of the TMS1 gene in K562 cells and the demethylation effect of As2O3 on TMS1 as well as TMS1 apoptosis-associated protein Bcl-2/Bax and DNA methyltransferase (DNMT) expression.

METHODS

TMS1 mRNA expression in K562 cells and normal bone marrow was determined by reverse transcription (RT) polymerase chain reaction (PCR), and the DNA methylation status of the TMS1 promoter in K562 cells treated with different concentrations of As2O3 for 48 h was determined by methylation-specific PCR. RT-PCR and Western blot were used to detect TMS1 and DNMT expression. We also assessed TMS1-associated apoptosis protein Bcl-2/Bax expression by Western blot and apoptosis rates by flow cytometry using annexin V/propidium iodide double staining.

RESULTS

In K562 cells, TMS1 was completely methylated and both TMS1 mRNA and protein showed a low expression, but 2 μmol/l As2O3 could significantly restore the expression of the TMS1 gene both at mRNA and protein level (p < 0.01) by fully reversing DNA methylation. As2O3 decreased mRNA and protein expression of DNMT1 (p < 0.05) in a dose-dependent manner. Flow cytometry showed that in the experimental group (2 μmol/l As2O3), cell apoptosis was significantly increased compared with the control group (no As2O3; p < 0.05). In the experimental group, Western blot showed that the expression of the anti-apoptotic protein Bcl-2 was significantly decreased; however, the proapoptotic protein Bax was markedly increased and the Bcl-2/Bax ratio was markedly reduced (p < 0.01).

CONCLUSIONS

As2O3 could restore the expression of TMS1 by inhibiting DNMT to reverse the hypermethylation and induced apoptosis of K562 cells by downregulation of Bcl-2/Bax expression.

As2O3 synergistically reactivate latent HIV-1 by induction of NF-κB

None of the current agents can safely and effectively eliminate latent HIV-1 reservoirs, meaning that there is a major barrier to the final cure of AIDS. Arsenic trioxide (As2O3), a drug used to treat acute promyelocytic leukemia (APL), was reported to affect the transcription factors and pathways involved in modulating HIV-1 expression. However, little is known about the effect and molecular basis of As2O3 in inducing HIV-1 expression in latently infected cells. Using the Jurkat T cell model of HIV-1 latency, we found that As2O3 activated latent HIV-1 replication with a similar potency to valproic acid (VPA) and did so in a dose- and time-dependent manner. We also found that As2O3 synergistically reactivated latent HIV-1 transcription with prostratin, tumor necrosis factor alpha (TNF-α) or VPA. Moreover, we provide evidence indicating that As2O3-induced HIV-1 activation involves the nuclear factor kappa B (NF-κB) signaling pathway. In conclusion, we have found that As2O3 can synergistically reactivate latent HIV-1 with other activators, which may provide a new tool to unravel the mechanisms of virus latency and reactivation.

Inorganic arsenic exposure induces E2F-dependent G0/G1 arrest via an increase in retinoblastoma family protein p130 in B-cell lymphoma A20 cells

Inorganic arsenic exerts toxic effect on multiple systems including the immune system. We previously showed in a study on mouse thymocytes and B-cell lymphoma A20 cells that arsenite induces cell cycle arrest at G0/G1 by suppressing expression of E2F-target genes. In this study, we furthermore investigated the involvement of retinoblastoma (RB) family proteins in E2F-dependent cell cycle arrest by arsenite. Arsenite exposure of A20 cells was showed to increase the protein level of p130, a RB family member, without changing the mRNA level. Suppression of arsenite-induced p130 by siRNA reduced the G0/G1 phase, indicating that p130 accumulation is responsible for arsenite-induced G0/G1 arrest. The accumulated p130 was shown to increase the p130 complex with E2F4, a transcription-suppressing E2F. Comparison by Western blotting of arsenite-induced p130 and p130 accumulated by a proteasome inhibitor suggested that arsenite-induced p130 is hypophosphorylated and hypoubiquitinated and refractory to proteasome-dependent degradation. We also showed that arsenite increases mRNA and protein of p16(INK4a), an inhibitor of CDK4/6 that phosphorylates p130. Down-regulation of arsenite-induced p16(INK4a) by siRNA suppressed the p130 accumulation. We propose a novel mechanism in which arsenite inhibits phosphorylation/ubiquitin-dependent proteasome degradation of p130 by inducing p16(INK4a) and the accumulated p130 causes cell cycle arrest with E2F4.

Sodium arsenite induced reactive oxygen species generation, nuclear factor (erythroid-2 related) factor 2 activation, heme oxygenase-1 expression, and glutathione elevation in Chang human hepatocytes

Liver is one of the major target organs of arsenic toxicity and carcinogenesis. Nuclear factor (erythroid-2 related) factor 2 (Nrf2) is a redox-sensitive transcription factor, regulating critically cellular defense responses against the toxic metallic arsenic in many cell types and tissues. This study was conducted to evaluate the hepato-cellular Nrf2 and Nrf2-regulated antioxidant reactions of sodium arsenite exposure in Chang human hepatocytes. Nrf2 and heme oxygenase-1 (HO-1) protein levels were detected by Western blot, and Nrf2-regulated HO-1 mRNA expressions were determined using semiquantitative RT-PCR by 0∼50 μmol/L of sodium arsenite exposure for 2, 6, 12, and 24 h. We also observed the changes of intracellular reactive oxygen species (ROS) and total cellular glutathione (GSH) by flow cytometry and spectrophotometry, respectively. Our results showed that intracellular ROS were both dose- and time-dependent induced by inorganic arsenic; Cellular Nrf2 protein levels increased rapidly after 2 h of exposure, elevated significantly at 6 h, and reached the maximum at 12 h. The endogenous Nrf2-regulated downstream HO-1 mRNA and protein were also induced dramatically and lasted for as long as 24 h. In addition, intracellular GSH levels elevated in consistent with Nrf2 activation. Our findings here suggest that inorganic arsenic alters cellular redox balance in hepatocytes to trigger Nrf2-regulated antioxidant responses promptly, which may represent an adaptive cell defense mechanism against inorganic arsenic induced liver injuries and hepatoxicity.

Expression of AFP and STAT3 is involved in arsenic trioxide-induced apoptosis and inhibition of proliferation in AFP-producing gastric cancer cells

Alpha-fetoprotein (AFP)-producing gastric cancer (AFPGC), represented by the production of AFP, has a more aggressive behavior than common gastric cancer. The underlying mechanisms are not well understood. Arsenic trioxide (As₂O₃) is used clinically to treat acute promyelocytic leukemia(APL) and has activity in vitro against several solid tumor cell lines, with induction of apoptosis and inhibition of proliferation the prime effects. Signal transducer and activator of transcription 3 (STAT3) has an important role in tumorigenesis of various primary cancers and cancer cell by upregulating cell-survival and downregulating tumor suppressor proteins. Here, we found decreased expression of AFP and STAT3 after induction of apoptosis by As₂O₃ in the AFPGC FU97 cells. Also, the level of the STAT3 target oncogene Bcl-2 was decreased with As₂O₃, and that of the tumor suppressor Bax was increased. Furthermore, STAT3 expression and depth of invasion and lymph node metastasis were associated. Survival of patients with gastric cancer was lower with AFP and STAT3 double overexpression than with overexpression of either alone. Downregulation of AFP and STAT3 expression plays an important role in As₂O₃-induced apoptosis of AFPGC cells, which suggests a new mechanism of As₂O₃-induced cell apoptosis. As₂O₃ may be a possible agent for AFPGC treatment.

The critical role of redox homeostasis in shikonin-induced HL-60 cell differentiation via unique modulation of the Nrf2/ARE pathway

Among various cancer cell lines, the leukemia cell line HL-60 was most sensitive to Shikonin, with evidence showing both the prooxidative activities and proapoptotic effects of micromolar concentrations of Shikonin. However, the mechanism involved in the cytotoxicity of Shikonin in the submicromolar range has not been fully characterized. Using biochemical and free radical biological experiments in vitro, we identified the prodifferentiated profiles of Shikonin and evaluated the redox homeostasis during HL-60 differentiation. The data showed a strong dose-response relationship between Shikonin exposure and the characteristics of HL-60 differentiation in terms of morphology changes, nitroblue tetrazolium (NBT) reductive activity, and the expression level of surface antigens CD11b/CD14. During drug exposure, intercellular redox homeostasis changes towards oxidation are necessary to support Shikonin-induced differentiation, which was proven by additional enzymatic and non-enzymatic redox modulators. A statistically significant and dose-dependent increase (P < 0.05) was recorded with regard to the unique expression levels of the Nrf2/ARE downstream target genes in HL-60 cells undergoing late differentiation, which were restored with further antioxidants employed with the Shikonin treatment. Our research demonstrated that Shikonin is a differentiation-inducing agent, and its mechanisms involve the Nrf2/ARE pathway to modulate the intercellular redox homeostasis, thus facilitating differentiation.

Differential effects of arsenic trioxide on chemosensitization in human hepatic tumor and stellate cell lines

BACKGROUND

Crosstalk between malignant hepatocytes and the surrounding peritumoral stroma is a key modulator of hepatocarcinogenesis and therapeutic resistance. To examine the chemotherapy resistance of these two cellular compartments in vitro, we evaluated a well-established hepatic tumor cell line, HepG2, and an adult hepatic stellate cell line, LX2. The aim was to compare the chemosensitization potential of arsenic trioxide (ATO) in combination with sorafenib or fluorouracil (5-FU), in both hepatic tumor cells and stromal cells.

METHODS

Cytotoxicity of ATO, 5-FU, and sorafenib, alone and in combination against HepG2 cells and LX2 cells was measured by an automated high throughput cell-based proliferation assay. Changes in survival and apoptotic signaling pathways were analyzed by flow cytometry and western blot. Gene expression of the 5-FU metabolic enzyme, thymidylate synthase, was analyzed by real time PCR.

RESULTS

Both HepG2 and LX2 cell lines were susceptible to single agent sorafenib and ATO at 24 hr (ATO IC(50): 5.3 μM in LX2; 32.7 μM in HepG2; Sorafenib IC(50): 11.8 μM in LX2; 9.9 μM in HepG2). In contrast, 5-FU cytotoxicity required higher concentrations and prolonged (48-72 hr) drug exposure. Concurrent ATO and 5-FU treatment of HepG2 cells was synergistic, leading to increased cytotoxicity due in part to modulation of thymidylate synthase levels by ATO. Concurrent ATO and sorafenib treatment showed a trend towards increased HepG2 cytotoxicity, possibly due to a significant decrease in MAPK activation in comparison to treatment with ATO alone.

CONCLUSIONS

ATO differentially sensitizes hepatic tumor cells and adult hepatic stellate cells to 5-FU and sorafenib. Given the importance of both of these cell types in hepatocarcinogenesis, these data have implications for the rational development of anti-cancer therapy combinations for the treatment of hepatocellular carcinoma (HCC).

Arsenic compounds: revived ancient remedies in the fight against human malignancies

Arsenic, the 20th most abundant element in the earth crust, is one of the oldest drugs in the world. It was used in the 18th century in treating hematopoietic malignancies, discarded in 1950s in favor of chemotherapeutic agents (busulphan and others), and was revived in the 1970s due to its dramatic efficacy on acute promyelocytic leukemia (APL) driven by the t(15;17) translocation-generated PML-RARα fusion. Arsenic represents the most potent single agent for APL, and achieves a five-year overall survival of 90% in APL patients when combined with all-trans retinoic acid (ATRA) and chemotherapy (daunorubicin and cytarabine), turning this disease from highly fatal to highly curable. Arsenic triggers sumoylation/ubiquitination and proteasomal degradation of PML-RARα via directly binding to the C3HC4 zinc finger motif in the RBCC domain of the PML moiety and induction of its homodimerization/multimerization and interaction with the SUMO E2 conjugase Ubc9. Because of its multiplicity of targets and complex mechanisms of action, arsenic is widely tested in combination with other agents in a variety of malignancies. Other arsenic containing recipes including oral formulations and organic arsenicals are being developed and tested, and progress in these areas will definitely expand the use of arsenicals in other malignant diseases.

Synergism between arsenite and proteasome inhibitor MG132 over cell death in myeloid leukaemic cells U937 and the induction of low levels of intracellular superoxide anion

Increased oxygen species production has often been cited as a mechanism determining synergism on cell death and growth inhibition effects of arsenic-combined drugs. However the net effect of drug combination may not be easily anticipated solely from available knowledge of drug-induced death mechanisms. We evaluated the combined effect of sodium arsenite with the proteasome inhibitor MG132, and the anti-leukaemic agent CAPE, on growth-inhibition and cell death effect in acute myeloid leukaemic cells U937 and Burkitt's lymphoma-derived Raji cells, by the Chou-Talalay method. In addition we explored the association of cytotoxic effect of drugs with changes in intracellular superoxide anion (O₂⁻) levels. Our results showed that combined arsenite+MG132 produced low levels of O₂⁻ at 6h and 24h after exposure and were synergic on cell death induction in U937 cells over the whole dose range, although the combination was antagonistic on growth inhibition effect. Exposure to a constant non-cytotoxic dose of 80μM hydrogen peroxide together with arsenite+MG132 changed synergism on cell death to antagonism at all effect levels while increasing O₂⁻ levels. Arsenite+hydrogen peroxide also resulted in antagonism with increased O₂⁻ levels in U937 cells. In Raji cells, arsenite+MG132 also produced low levels of O₂⁻ at 6h and 24h but resulted in antagonism on cell death and growth inhibition. By contrast, the combination arsenite+CAPE showed high levels of O₂⁻ production at 6h and 24 h post exposure but resulted in antagonism over cell death and growth inhibition effects in U937 and Raji cells. We conclude that synergism between arsenite and MG132 in U937 cells is negatively associated to O₂⁻ levels at early time points after exposure.

Redox control of the survival of healthy and diseased cells

Abstract Cellular redox homeostasis is the first line of defense against diverse stimuli and is crucial for various biological processes. Reactive oxygen species (ROS), byproducts of numerous cellular events, may serve in turn as signaling molecules to regulate cellular processes such as proliferation, differentiation, and apoptosis. However, when overproduced ROS fail to be scavenged by the antioxidant system, they may damage cellular components, giving rise to senescent, degenerative, or fatal lesions in cells. Accordingly, this review not only covers general mechanisms of ROS production under different conditions, but also focuses on various types of ROS-involved diseases, including atherosclerosis, ischemia/reperfusion injury, diabetes mellitus, neurodegenerative diseases, and cancer. In addition, potentially therapeutic agents and approaches are reviewed in a relatively comprehensive manner. However, due to the complexity of ROS and their cellular impacts, we believe that the goal to design more effective approaches or agents may require a better understanding of mechanisms of ROS production, particularly their multifaceted impacts in disease at biochemical, molecular, genetic, and epigenetic levels. Thus, it requires additional tools of omics in systems biology to achieve such a goal. Antioxid. Redox Signal. 15, 2867-2908.

HIV-1 replication in monocyte-derived dendritic cells is stimulated by melarsoprol, one of the main drugs against human African trypanosomiasis

Human African trypanosomiasis (HAT) is a disease caused by the protozoan parasite Trypanosoma brucei, the causative agent of sleeping sickness that is still endemic in well defined regions of sub-Saharan Africa. Co-infections with this human pathogen and human immunodeficiency virus (HIV) are not uncommon, but their potential interaction has been little studied. The organo-arsenical drug melarsoprol has been widely used for the treatment of late stage trypanosomiasis since the early 1950s and is still widely used despite very serious adverse effects. Because arsenic trioxide, another trivalent arsenical structurally related to melarsoprol, has been shown to markedly increase HIV replication in dendritic cells (DCs), we tested the effect of melarsoprol on virus replication in various primary human immune cell types, including DCs. We show here that this medicinal drug stimulates the replication of several strains of HIV-1, specifically in monocyte-derived DCs, and also renders such cells susceptible to HIV-2 infection. The drug acts mainly through an increase in the efficacy of the reverse transcription process, and this effect is mediated, at least partly, by an inhibition of expression of the cellular restriction factor APOBEC3G. These observations raise concerns about the harmful effect that melarsoprol might exert on the natural history of HIV in co-infected patients and on virus transmission.

Arsenic trioxide-induced apoptosis in TM4 Sertoli cells: the potential involvement of p21 expression and p53 phosphorylation

Arsenic is a toxic metalloid that exists ubiquitously in the environment, and exhibits carcinogenicity. Conversely, arsenic trioxide (AsTO) has successfully been employed in the treatment of acute promyelocytic leukemia (APL). It has been shown that AsTO efficiently induces apoptosis in the malignant cells of APL in vitro. Although the mechanisms underlying AsTO-induced apoptosis in certain types of cancer cells, such as APL cells, have been delineated, the mechanism underlying AsTO-induced cell death in non-cancer cells remains unknown. In the present study, we examined AsTO-provoked cytotoxicity and cell death mechanism(s) in TM4 Sertoli cells. Exposure of these cells to AsTO generates reactive oxygen species and alters mitochondrial apoptosis, inducing cell death via both caspase-dependent and caspase-independent pathways. AsTO-induced apoptosis was concomitant with the downregulation of p53, phosphorylation of p53 at serine residues, and G2/M cell cycle arrest. Particularly, the interaction of p21 with caspase-3 proteins during AsTO treatment suggested an antiapoptotic role of p21 against genotoxic stresses in TM4 Sertoli cells. However, clinically relevant concentrations of AsTO failed to induce cell death in TM4 Sertoli cells, indicating that these cells could be resistant to cancer treatment. The results presented herein may not represent the actual effect of AsTO on Sertoli cells in vivo. Thus, further studies on the exposure effects of AsTO on the morphology and function of Sertoli cells in animal experiments will provide a more precise knowledge of AsTO cytotoxicity on male reproduction.

Rat H9c2 cardiac myocytes are sensitive to arsenite due to a modest activation of transcription factor Nrf2

The mechanism underlying the hepatotoxicity induced by arsenic exposure is well investigated. However, little is known about the detailed mechanisms of arsenic-induced cardiotoxicity or cardiac factors involved in high sensitivity to arsenicals in spite of the fact that arsenic trioxide, which is used to treat acute promyelocytic leukemia, causes cardiotoxicity. Here, we show that rat H9c2(2-1) cardiac myocytes exhibit high sensitivity to inorganic arsenite (As(III)) as compared with rat-derived four cell lines (liver epithelial TRL1215 cells, kidney epithelial NRK-52E cells, PC12 phechromocytoma cells and C6 glioma cells). Furthermore, we found a lower steady-state level of glutathione and glutamyl-cysteine ligase (GCL) in H9c2(2-1) cells compared with TRL1215 cells, resulting in an increase in arsenic accumulation. In addition, we detected that the up-regulation of GCL and multi-drug resistance-associated protein (MRP) caused by As(III) was extremely low in H9c2(2-1) cells compared with TRL1215 cells. It is known that Nrf2, which regulates GCL and MRP expression, plays an important role in the protection of cells from arsenicals. We investigated the participation of Nrf2 in the difference of sensitivity to arsenicals between H9c2(2-1) and TRL1215 cells and found that Nrf2 was clearly activated by As(III) exposure in TRL1215 cells but only poorly activated in H9c2(2-1) cells. Considering these results together, we propose that modest activation of Nrf2 during exposure to As(III) in H9c2(2-1) cardiac myocytes leads to reduced ability to metabolize and excrete arsenic.

Arsenic trioxide induces apoptosis of p53 null osteosarcoma MG63 cells through the inhibition of catalase

This study is aimed at investigating the effect of arsenic trioxide (ATO) on p53 null human osteosarcoma MG63 cells and the mechanisms underlying the effect. Apoptotic cells were detected by flow cytometry with Annexin-V-FITC/PI dual staining. Intracellular ROS was measured by flow cytometry using a cell-based ROS assay kit. Catalase activity and mRNAs were analyzed by ELISA and real-time qRT-PCR, respectively. Apoptosis and intracellular ROS of MG63 cells increased in a dose-dependent manner following arsenic treatments. Both were prevented by the presence of the anti-oxidative reagent N-acetyl-L: -cysteine (NAC) or catalase (CAT). Furthermore, the activity and mRNA of catalase were decreased strikingly following arsenic exposure. The present study indicates that p53 null osteosarcoma MG63 cells are susceptible to the ATO; the inhibition of catalase and the resulted intracellular ROS accumulation are an important molecular mechanism under which ATO induces apoptosis of p53-deficient osteosarcoma cells.

Oxidative stress, inflammation, and cancer: how are they linked?

Extensive research during the past 2 decades has revealed the mechanism by which continued oxidative stress can lead to chronic inflammation, which in turn could mediate most chronic diseases including cancer, diabetes, and cardiovascular, neurological, and pulmonary diseases. Oxidative stress can activate a variety of transcription factors including NF-κB, AP-1, p53, HIF-1α, PPAR-γ, β-catenin/Wnt, and Nrf2. Activation of these transcription factors can lead to the expression of over 500 different genes, including those for growth factors, inflammatory cytokines, chemokines, cell cycle regulatory molecules, and anti-inflammatory molecules. How oxidative stress activates inflammatory pathways leading to transformation of a normal cell to tumor cell, tumor cell survival, proliferation, chemoresistance, radioresistance, invasion, angiogenesis, and stem cell survival is the focus of this review. Overall, observations to date suggest that oxidative stress, chronic inflammation, and cancer are closely linked.

Arsenic in cancer treatment: challenges for application of realgar nanoparticles (a minireview)

While intensive efforts have been made for the treatment of cancer, this disease is still the second leading cause of death in many countries. Metastatic breast cancer, late-stage colon cancer, malignant melanoma, multiple myeloma, and other forms of cancer are still essentially incurable in most cases. Recent advances in genomic technologies have permitted the simultaneous evaluation of DNA sequence-based alterations together with copy number gains and losses. The requirement for a multi-targeting approach is the common theme that emerges from these studies. Therefore, the combination of new targeted biological and cytotoxic agents is currently under investigation in multimodal treatment regimens. Similarly, a combinational principle is applied in traditional Chinese medicine, as formulas consist of several types of medicinal herbs or minerals, in which one represents the principal component, and the others serve as adjuvant ones that assist the effects, or facilitate the delivery, of the principal component. In Western medicine, approximately 60 different arsenic preparations have been developed and used in pharmacological history. In traditional Chinese medicines, different forms of mineral arsenicals (orpiment—As₂S₃, realgar—As₄S₄, and arsenolite—arsenic trioxide, As₂O₃) are used, and realgar alone is included in 22 oral remedies that are recognized by the Chinese Pharmacopeia Committee (2005). It is known that a significant portion of some forms of mineral arsenicals is poorly absorbed into the body, and would be unavailable to cause systemic damage. This review primary focuses on the application of arsenic sulfide (realgar) for treatment of various forms of cancer in vitro and in vivo.