Modulation of p53, c-fos, RARE, cyclin A, and cyclin D1 expression in human leukemia (HL-60) cells exposed to arsenic trioxide

Heavy Metal Contamination of Natural Foods Is a Serious Health Issue: A Review

Heavy metals play an important role in the homeostasis of living cells. However, these elements induce several adverse environmental effects and toxicities, and therefore seriously affect living cells and organisms. In recent years, some heavy metal pollutants have been reported to cause harmful effects on crop quality, and thus affect both food security and human health. For example, chromium, cadmium, copper, lead, and mercury were detected in natural foods. Evidence suggests that these elements are environmental contaminants in natural foods. Consequently, this review highlights the risks of heavy metal contamination of the soil and food crops, and their impact on human health. The data were retrieved from different databases such as Science Direct, PubMed, Google scholar, and the Directory of Open Access Journals. Results show that vegetable and fruit crops grown in polluted soil accumulate higher levels of heavy metals than crops grown in unpolluted soil. Moreover, heavy metals in water, air, and soil can reduce the benefits of eating fruits and vegetables. A healthy diet requires a rational consumption of foods. Physical, chemical, and biological processes have been developed to reduce heavy metal concentration and bioavailability to reduce heavy metal aggregation in the ecosystem. However, mechanisms by which these heavy metals exhibit their action on human health are not well elucidated. In addition, the positive and negative effects of heavy metals are not very well established, suggesting the need for further investigation.

Effects of co-administration of arsenic trioxide and Schiff base oxovanadium complex on the induction of apoptosis in acute promyelocytic leukemia cells

Acute promyelocytic leukaemia (APL) is commonly treated with arsenic trioxide (As2O3) that has many side effects. Given the increasing trend of studies on beneficial therapeutic properties of synthetic compounds containing vanadium, the present study sought to use Schiff base oxovanadium complex to reduce the needed concentration of arsenic trioxide. The HL-60 cell line, which is a model of APL, was selected and the effects of arsenic trioxide and Schiff base oxovanadium complex were individually and simultaneously evaluated on the cell viability by the MTT assay. Flow cytometry and Real-time RT-PCR were also performed to investigate the rate of apoptosis and the expression of P53 and P21 genes, respectively. The IC50 of arsenic trioxide and Schiff base oxovanadium complex on Hl-60 cells was 8.37 ± 0.36 µM and 34.12 ± 1.52 µg/ml, respectively. At the simultaneous administration of both compounds, the maximum decrease in the cell viability was seen in co-administration of 40 µg/ml of Schiff base oxovanadium complex and 0.001 µM of arsenic trioxide. Real-time RT-PCR indicated that the co-administration of Schiff base oxovanadium complex 40 µg/ml and arsenic trioxide 0.001 µM could increase the expression of P53 and P21 genes by 3.76 ± 0.19 and 6.57 ± 1.29 fold change, respectively to the control sample. The flow cytometry studies also indicated that this co-administration could induce apoptosis up to 67% ± 0.9% significantly higher than the control sample. The use of Schiff base oxovanadium complex could significantly reduce the required dose of arsenic trioxide to induce apoptosis in HL-60 cells.

UBE2N Regulates Paclitaxel Sensitivity of Ovarian Cancer via Fos/P53 Axis

Background

Chemo-resistance is still considered one of the key factors in the mortality of ovarian cancer. In this work, we found that ubiquitin-conjugating enzyme E2 N (UBE2N) is downregulated in paclitaxel-resistant ovarian cancer cells. It suggests UBE2N to be critical in the regulation of paclitaxel sensitivity in ovarian cancer.

Materials and Methods

Ovarian cancer cells with stably overexpressed UBE2N were injected into nude mice to assess tumor growth and paclitaxel sensitivity in vivo. The MTT assay was applied to observe the effect of UBE2N expression on paclitaxel sensitivity. A real-time PCR array, specific for human cancer drug resistance, was used to examine the potential downstream target genes of UBE2N. The expression of UBE2N and potential downstream target genes was determined by Western blotting. The analysis of Gene Ontology and protein–protein interactions of these differentially expressed genes (DEGs) was performed using online tools. To evaluate the prognostic value of hub genes expression for ovarian cancer patients treated with paclitaxel, we applied the online survival analysis tool.

Results

Overexpressed UBE2N enhanced the paclitaxel sensitivity of ovarian cancer cells in vitro and in vivo. Thirteen upregulated DEGs and 11 downregulated DEGs were identified when we knockdown UBE2N. Meanwhile, 9 hub genes with a high degree of connectivity were selected. Only Fos proto-oncogene, AP-1 transcription factor subunit (Fos), was overexpressed upon decreasing UBE2N levels, indicating a poor outcome for patients treated with paclitaxel. Moreover, reduced UBE2N could increase Fos expression and reduce P53. Furthermore, reversed regulation of Fos and P53 based on UBE2N reduction could reverse paclitaxel sensitivity, respectively.

Conclusion

Our study suggests that UBE2N could be used as a therapeutic agent for paclitaxel-resistant ovarian cancer through Fos/P53 pathway. Further studies are needed to elucidate the specific mechanism.

Trisenox Disrupts MDM2-DAXX-HAUSP Complex and Induces Apoptosis in a Mouse Model of Acute Leukemia

Trisenox (TX) is successfully used for both de novo and relapsed acute promyelocytic leukemia (APL) treatment. Although TX toxicity to APL cells is mediated by oxidative stress, DNA damage, cell cycle arrest, and apoptosis, its mode of action in the transgenic mice model of APL is poorly understood. We hypothesized that TX regulates cell cycle and apoptosis in APL mice by p53 activation, DNA damage, and reduced expression of MDM2-DAXX-HAUSP complex. To test hypothesis, we treated APL mice with different doses (0, 1.25.2.5.5.0 & 7.5 mg/kg body wt) of TX and collected the liver and bone marrow cells. We applied several techniques to check the expression of PML-RARα, complex molecules, and DNA damage in APL mice bone marrow cells and liver. Our findings indicate that TX reduced the expression of PML-RARα and complex molecules, induced DNA damage and activated p53 leading to cell cycle arrest and apoptosis in APL mice liver. We found that TX promoted more promyelocytes formation with dense granules in bone marrow cells. It also transmitted the DNA damage signal through protein kinase (ATM & ATR) leading to disruption of complex and activation of p53 in APL mice liver. TX induced cell cycle arrest through activation of p53, p21, and reduced expression of cyclin D1 and cyclin dependent kinases (CDK 2, 4 & 6) in mice liver. It also caused apoptosis through upregulation of caspase 3 and Bax expression, and down-regulation of Bcl2 expression. Taken together, these molecular targets provide new insights into TX mode of action in APL mice.

Trisenox disrupts MDM2-DAXX-HAUSP complex and activates p53, cell cycle regulation and apoptosis in acute leukemia cells

Trisenox (TX) has been used in the treatment of both de novo and relapsed acute promyelocytic leukemia (APL) patients. Using in vitro APL cell lines model in this research, we report on a new target of TX action through disruption of MDM2-DAXX-HAUSP complex, degradation of MDM2, and activation of p53 expression. TX–induced stress signal was transmitted by protein kinase (ATM & ATR) and phosphorylation of its downstream targets CHK1, CHK2, ATM, and ATR, respectively at the Ser 345, Thr68, Ser1981 and Ser 428 residues involved in complex disruption and p53 up-regulation. TX-activated p53 led to cell cycle arrest and apoptosis in APL cells. Our results showed that TX inhibited cell proliferation, disrupted complex molecules expression and association in APL cells. Our functional studies indicated that TX-induced down-regulation of complex molecules expression was mostly neutralized in both p53 knockdown NB4 cells and nutilin-3 treated KG1a cells. Hence our findings provide a functional evidence of TX action on cell cycle regulation and apoptosis in APL cells. This novel target of TX activity may be useful for designing new APL drugs.

Multifactorial Modes of Action of Arsenic Trioxide in Cancer Cells as Analyzed by Classical and Network Pharmacology

Arsenic trioxide is a traditional remedy in Chinese Medicine since ages. Nowadays, it is clinically used to treat acute promyelocytic leukemia (APL) by targeting PML/RARA. However, the drug's activity is broader and the mechanisms of action in other tumor types remain unclear. In this study, we investigated molecular modes of action by classical and network pharmacological approaches. CEM/ADR5000 resistance leukemic cells were similar sensitive to As2O3 as their wild-type counterpart CCRF-CEM (resistance ratio: 1.88). Drug-resistant U87.MG ΔEGFR glioblastoma cells harboring mutated epidermal growth factor receptor were even more sensitive (collateral sensitive) than wild-type U87.MG cells (resistance ratio: 0.33). HCT-116 colon carcinoma p53-/- knockout cells were 7.16-fold resistant toward As2O3 compared to wild-type cells. Forty genes determining cellular responsiveness to As2O3 were identified by microarray and COMPARE analyses in 58 cell lines of the NCI panel. Hierarchical cluster analysis-based heat mapping revealed significant differences between As2O3 sensitive cell lines and resistant cell lines with p-value: 1.86 × 10-5. The genes were subjected to Galaxy Cistrome gene promoter transcription factor analysis to predict the binding of transcription factors. We have exemplarily chosen NF-kB and AP-1, and indeed As2O3 dose-dependently inhibited the promoter activity of these two transcription factors in reporter cell lines. Furthermore, the genes identified here and those published in the literature were assembled and subjected to Ingenuity Pathway Analysis for comprehensive network pharmacological approaches that included all known factors of resistance of tumor cells to As2O3. In addition to pathways related to the anticancer effects of As2O3, several neurological pathways were identified. As arsenic is well-known to exert neurotoxicity, these pathways might account for neurological side effects. In conclusion, the activity of As2O3 is not restricted to acute promyelocytic leukemia. In addition to PML/RARA, numerous other genes belonging to diverse functional classes may also contribute to its cytotoxicity. Network pharmacology is suited to unravel the multifactorial modes of action of As2O3.

Inhibition of early T cell cytokine production by arsenic trioxide occurs independently of Nrf2

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a stress-activated transcription factor that induces a variety of cytoprotective genes. Nrf2 also mediates immunosuppressive effects in multiple inflammatory models. Upon activation, Nrf2 dissociates from its repressor protein, Keap1, and translocates to the nucleus where it induces Nrf2 target genes. The Nrf2-Keap1 interaction is disrupted by the environmental toxicant and chemotherapeutic agent arsenic trioxide (ATO). The purpose of the present study was to determine the effects of ATO on early events of T cell activation and the role of Nrf2 in those effects. The Nrf2 target genes Hmox-1, Nqo-1, and Gclc were all upregulated by ATO (1–2 μM) in splenocytes derived from wild-type, but not Nrf2-null, mice, suggesting that Nrf2 is activated by ATO in splenocytes. ATO also inhibited IFNγ, IL-2, and GM-CSF mRNA and protein production in wild-type splenocytes activated with the T cell activator, anti-CD3/anti-CD28. However, ATO also decreased production of these cytokines in activated splenocytes from Nrf2-null mice, suggesting the inhibition is independent of Nrf2. Interestingly, ATO inhibited TNFα protein secretion, but not mRNA expression, in activated splenocytes suggesting the inhibition is due to post-transcriptional modification. In addition, c-Fos DNA binding was significantly diminished by ATO in wild-type and Nrf2-null splenocytes activated with anti-CD3/anti-CD28, consistent with the observed inhibition of cytokine production by ATO. Collectively, this study suggests that although ATO activates Nrf2 in splenocytes, inhibition of early T cell cytokine production by ATO occurs independently of Nrf2 and may instead be due to impaired AP-1 DNA binding.

Potential Health Benefits and Metabolomics of Camel Milk by GC-MS and ICP-MS

None of the research reports reveals the metabolomics and elemental studies on camel milk. Recent studies showed that camel milk possesses anticancer and anti-inflammatory activity. Metabolomics and elemental studies were carried out in camel milk which showed us the pathways and composition that are responsible for the key biological role of camel milk. Camel milk was dissolved in methanol and chloroform fraction and then vortexed and centrifuged. Both the fractions were derivatized by N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA) and TMCS after nitrogen purging and analyzed by GC-MS. Camel milk was also analyzed by ICP-MS after microwave digestion. We found that higher alkanes and fatty acids are present in the chloroform fraction and amino acids, sugars and fatty acid derivatives are present in aqueous fractions. All the heavy metals like As, Pb, Cd, Co, Cu, and Ni were in the safe limits in terms of maximum daily intake of these elements. Na, K, Mg, and Ca were also present in the safe limits in terms of maximum daily intake of these elements. These results suggested that the camel milk drinking is safe and there is no health hazard. The present data of GC-MS and ICP-MS correlate the activities related to camel milk.

Therapeutic Potential of Arsenic Trioxide (ATO) in Treatment of Hepatocellular Carcinoma: Role of Oxidative Stress in ATO-Induced Apoptosis

Hepatocellular carcinoma (HCC), the dominant form of primary liver cancer, is the sixth most common cancer in the world with more than 700,000 people diagnosed annually. Arsenic trioxide (ATO) has been shown to be a potent anticancer agent in various carcinomas, proving particularly effective in the clinical treatment of relapsed and refractory acute promyelocytic leukemia. However, its bioactivity and molecular mechanisms against HCC has not been fully studied. Using human HCC (HepG2) cells as a test model, we studied the effects of ATO and examined the role of oxidative stress (OS) and apoptosis in cytotoxicity. OS biomarkers showed a significant increase (p< 0.05) of malondialdehyde concentrations, and a gradual decrease of antioxidant enzymes (GPx & CAT) activities with increasing ATO doses. Flow cytometry data showed a dose dependent increase in annex in V positive cells and caspase 3 activities. These results were confirmed by data of the DNA laddering assay showing a clear evidence of nucleosomal DNA fragmentation, as well as data from Western blotting showing a significant modulation of specific apoptotic related proteins, including the activation of p53 and p21 expression and the down-regulation of Bcl-2 expression in ATO-treated cells. Taken together, our research demonstrates that ATO has a potential therapeutic effect against HCC, and its cytotoxicity may be mediated via oxidative stress and activation of the mitochondrial or intrinsic pathway of apoptosis.

Molecular mechanisms of cisplatin cytotoxicity in acute promyelocytic leukemia cells

Cis-diamminedichloroplatinum (II) (cisplatin) is a widely used anti-tumor drug for the treatment of a broad range of human malignancies with successful therapeutic outcomes for head and neck, ovarian, and testicular cancers. It has been found to inhibit cell cycle progression and to induce oxidative stress and apoptosis in acute promyelocytic leukemia (APL) cells. However, its molecular mechanisms of cytotoxic action are poorly understood. We hypothesized that cisplatin induces cytotoxicity through DNA adduct formation, oxidative stress, transcriptional factors (p53 and AP-1), cell cycle regulation, stress signaling and apoptosis in APL cells. We used the APL cell line as a model, and applied a variety of molecular tools to elucidate the cytotoxic mode of action of cisplatin. We found that cisplatin inhibited cell proliferation by a cytotoxicity, characterized by DNA damage and modulation of oxidative stress. Cisplatin also activated p53 and phosphorylated activator protein (AP-1) component, c-Jun at serine (63, 73) residue simultaneously leading to cell cycle arrest through stimulation of p21 and down regulation of cyclins and cyclin dependent kinases in APL cell lines. It strongly activated the intrinsic pathway of apoptosis through alteration of the mitochondrial membrane potential, release of cytochrome C, and up-regulation of caspase 3 activity. It also down regulated the p38MAPK pathway. Overall, this study highlights the molecular mechanisms that underline cisplatin toxicity to APL cells, and provides insights into selection of novel targets and/or design of therapeutic agents to treat APL.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

The effect of c-Fos demethylation on sodium fluoride-induced apoptosis in L-02 cells

To investigate the effects of sodium fluoride (NaF) on apoptosis, c-Fos mRNA and protein expression levels, and methylation status as well as Dnmt1, Dnmt3a, and Dnmt3b mRNA expression levels in human embryo hepatocyte (L-02) which were exposed to different concentrations of NaF (0, 20, 40, and 80 mg/l) for 24 h in vitro. Results showed that the percentage of apoptosis and c-Fos mRNA and protein expression levels in 40 and 80 mg/l NaF-treated groups were higher than those in the control group (P<0.05). Further, Dnmt1 mRNA expression level was significantly decreased in the 80 mg/l NaF-treated groups compared to the control group (P<0.05); Dnmt3a and Dnmt3b mRNA expression levels were significantly decreased in 40 and 80 mg/l NaF-treated groups compared to the control group (P<0.05). c-Fos methylation levels, according to the bisulfite sequencing results, were decreased in 20, 40, and 80 mg/l NaF-treated groups against the control group. These results suggest that NaF could induce apoptosis and upregulate mRNA and protein expression level of c-Fos as well as decrease mRNA expression levels of Dnmt1, Dnmt3a, and Dnmt3b in L-02 cells. The decrease in c-Fos methylation levels might be involved in the early phase of apoptosis induced by NaF in L-02 cells.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

The cyclins: a family of widely expressed tumor antigens?

Continuous cell division is a hallmark of cancer and cell-cycle regulators therefore represent relevant target molecules for tumor therapy. Among these targets the cyclins are of particular interest as they are overexpressed in various tumor entities with little expression in normal tissue. Here we review evidence that these molecules are recognized by the immune system, summarize why cyclins A, B and D in particular appear to be interesting targets for active and passive immunotherapy, and discuss whether the entire family could be an interesting novel class of tumor antigens for cancer treatment and prevention.

Arsenic trioxide and radiation enhance apoptotic effects in HL-60 cells through increased ROS generation and regulation of JNK and p38 MAPK signaling pathways

The induction of apoptotic cell death is a significant mechanism of tumor cells under the influence of radio-/chemotherapy, and resistance to these treatments has been linked to some cancer cell lines with a low propensity for apoptosis. The present study aimed to investigate the enhanced effects and mechanisms in apoptosis and the cycle distribution of HL-60 cells, a human leukemia cell line lacking a functional p53 protein, after combination treatment with arsenic trioxide (ATO) and irradiation (IR). Our results indicated that combined treatment led to increased cytotoxicity and apoptotic cell death in HL-60 cells, which was correlated with the activation of cdc-2 and increased expression of cyclin B, the induction of intracellular reactive oxygen species (ROS) generation, the loss of mitochondria membrane potential, and the activation of caspase-3. The combined treatment of HL-60 cells pre-treated with Z-VAD or NAC resulted in a significant reduction in apoptotic cells. In addition, activation of JNK and p38 MAPK may be involved in combined treatment-mediated apoptosis. The data suggest that a combination of IR and ATO could be a potential therapeutic strategy against p53-deficient leukemia cells.

Retinoic acid induces HL-60 cell differentiation via the upregulation of miR-663

BACKGROUND

Differentiation of the acute myeloid leukemia (AML) cell line HL-60 can be induced by all trans-retinoic acid (ATRA); however, the mechanism regulating this process has not been fully characterized.

METHODS

Using bioinformatics and in vitro experiments, we identified the microRNA gene expression profile of HL-60 cells during ATRA induced granulocytic differentiation.

RESULTS

Six microRNAs were upregulated by ATRA treatment, miR-663, miR-494, miR-145, miR-22, miR-363* and miR-223; and three microRNAs were downregulated, miR-10a, miR-181 and miR-612. Additionally, miR-663 expression was regulated by ATRA. We used a lentivirus (LV) backbone incorporating the spleen focus forming virus (SFFV-F) promoter to drive miR-663 expression, as the CMV (Cytomegalovirus) promoter is ineffective in some lymphocyte cells. Transfection of LV-miR-663 induced significant HL-60 cell differentiation in vitro.

CONCLUSIONS

Our results show miR-663 may play an important role in ATRA induced HL-60 cell differentiation. Lentivirus delivery of miR-663 could potentially be used directly as an anticancer treatment in hematological malignancies.

Toxicity of depleted uranium complexes is independent of p53 activity

The p53 tumor suppressor protein is one of the key checkpoints in cellular response to a variety of stress mechanisms, including exposure to various toxic metal complexes. Previous studies have demonstrated that arsenic and chromium complexes are able to activate p53, but there is a dearth of data investigating whether uranium complexes exhibit similar effects. The use of depleted uranium (DU) has increased in recent years, raising concern about DU's potential carcinogenic effects. Previous studies have shown that uranyl acetate and uranyl nitrate are capable of inducing DNA strand breaks and potentially of inducing oxidative stress through free radical generation, two potential mechanisms for activation of p53. Based on these studies, we hypothesized that either uranyl acetate or uranyl nitrate could act as an activator of p53. We tested this hypothesis using a combination of cytotoxicity assays, p53 activity assays, western blotting and flow cytometry. All of our results demonstrate that there is not a p53-mediated response to either uranyl acetate or uranyl nitrate, demonstrating that any cellular response to uranium exposure likely occurs in a p53-independent fashion under the conditions studied.

Basic mechanisms of arsenic trioxide (ATO)-induced apoptosis in human leukemia (HL-60) cells

Background

Acute promyelocytic leukemia (APL) is a blood cancer that affects people of all ages and strikes about 1,500 patients in the United States each year. The standard treatment of APL has been based on the combined administration of all-trans retinoic acid and chemotherapy including anthracyclins and cytarabine. However, 10-20% of patients relapse, with their disease becoming resistant to conventional treatment. Recently the Food and Drug Administration has approved the use of arsenic trioxide (ATO) or Trisenox for the treatment of APL, based on clinical studies showing a complete remission, especially in relapsed patients. In a recently published study we demonstrated that ATO pharmacology as an anti-cancer drug is associated with its cytotoxic and genotoxic effects in human leukemia cells.

Methods

In the present study, we further investigated the apoptotic mechanisms of ATO toxicity using the HL-60 cell line as a test model. Apoptosis was measured by flow cytometry analysis of phosphatidylserine externalization (Annexin V assay) and caspase 3 activity, and by DNA laddering assay.

Results

Flow cytometry data showed a strong dose-response relationship between ATO exposure and Annexin-V positive HL-60 cells. Similarly, a statistically significant and dose-dependent increase (p <0.05) was recorded with regard to caspase 3 activity in HL60 cells undergoing late apoptosis. These results were confirmed by data of DNA laddering assay showing a clear evidence of nucleosomal DNA fragmentation in ATO-treated cells.

Conclusion

Taken together, our research demonstrated that ATO represents an apoptosis-inducing agent and its apoptotic mechanisms involve phosphatidylserine externalization, caspase 3 activation and nucleosomal DNA fragmentation.

Arsenite causes down-regulation of Akt and c-Fos, cell cycle dysfunction and apoptosis in glutathione-deficient cells

Arsenic is a well-known environmental toxicant but the mechanism by which it causes cytotoxicity is poorly understood. Arsenite induces apoptosis in glutathione (GSH)-deficient GCS-2 cells by causing cell cycle dysfunction and down-regulating critical signaling pathways. This study was designed to examine the effect of arsenite on redox-sensitive phosphatidylinositol 3-kinase (PI3K)/Akt, a signaling pathway involved in cell survival and growth, and transcription factor, activating protein-1 (AP-1). Arsenite significantly diminished Akt and c-Fos levels and caused accelerated degradation of these proteins by ubiquitnation. Arsenite also induced cell cycle arrest and apoptosis. The cell cycle arrest involved the down-regulation of cyclin A2, cyclin D1, cyclin E, cyclin dependent kinases (CDK) 2, CDK4, and CDK6. Apoptosis involved down-regulation of anti-apoptotic proteins Bcl-2, Bcl-xL, survivin, and inhibitor of apoptosis protein (IAP) and up-regulation of pro-apoptotic protein Bax. Taken together, our results suggest that a possible mechanism of arsenite-induced toxicity under low/no GSH conditions, is to negatively regulate GCS-2 cell proliferation by attenuating Akt and AP-1 by ubiquitination and causing cell cycle dysfunction and apoptosis.

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.