Arsenite sensitizes human melanomas to apoptosis via tumor necrosis factor alpha-mediated pathway

The synergistic inhibitory effect of combining therapies targeting EGFR and mitochondria in sarcomas

Our group previously demonstrated that sarcoma cell lines were insensitive to epidermal growth factor receptor (EGFR) inhibitor gefitinib monotherapy. PENAO, an anti-tumour metabolic compound created in our laboratory, is currently in clinical trials. Considering the positive regulation of tumour energy production by both the EGFR signalling and tumour metabolism pathways, this study aimed to investigate the effect and mechanisms of combination therapy using gefitinib and PENAO in sarcoma cell lines in vitro and in vivo.

PENAO monotherapy reduced proliferation in 12 sarcoma cell lines. Combining gefitinib and PENAO resulted in synergistic inhibition in both a time- and dose-dependent manner in 3 sarcoma cell lines with less prominent monotherapy effects. Combined treatment significantly enhanced cell death and perturbed mitochondrial function. In vivo combination therapy with PENAO and gefitinib was non-toxic to mice and significantly delayed tumour growth and prolonged survival. At 20 days after treatment, tumours from the combination treated mice were significantly smaller than those from untreated and single drug treated mice. The survival curves also showed significant difference across and between groups.

The combination of PENAO and gefitinib in vitro and in vivo, shows promise as a treatment pathway in this poor outcome tumour.

Activation of integrated stress response pathway regulates IL-1β production through posttranscriptional and translational reprogramming in macrophages

Immune cells sense and programme its cellular machinery appropriately to the environmental changes through the activation of cytoprotective adaptive pathway so-called the "integrated stress response (ISR)". However, the mechanisms implicated in ISR-induced protective responses are poorly understood. Here, we show that ISR activation by arsenite (Ar) results in suppression of IL-1β production in macrophages and inhibition of DSS-induced colitis in a murine model through a novel posttranscriptional and translation regulatory (PTR) mechanism. Ar triggers PTR events through eIF2α-phosphorylation, which results in the attenuation of active polysome formation leading to the accumulation of translationally stalled IL-1β mRNAs. Translationally stalled IL-1β mRNAs recruit RNA-binding proteins (TIA-1/TIAR), resulting in the formation of RBP-RNA complexes known as stress granules (SGs). The SGs bound IL-1β mRNAs might undergo degradation through induction of autophagy. Also, we show that Ar posttranslationally impairs processing and secretion of IL-1β by diminishing inflammasome activation. Altogether, this study unveils a novel mechanism of IL-1β regulation and further suggests that pharmacological activation of cytoprotective ISR pathway might provide an effective therapeutic intervention against inflammatory diseases.

Complex role of titanium dioxide nanoparticles in the trophic transfer of arsenic from Nannochloropsis maritima to Artemia salina nauplii

Increasing concern has been focused on the potential risks associated with the trophic transfer to aquatic organisms of ambient contaminants in the presence of titanium dioxide nanoparticles (nano-TiO₂). This study investigated the influence of nano-TiO₂ on the trophic transfer of arsenic (As) from the microalgae Nannochloropsis maritima to the brine shrimp Artemia salina nauplii. We found that nano-TiO₂ could significantly facilitate As sorption on N. maritima within an exposure period of 24 h, and this sorption subsequently led to higher As trophic transfer from the algae to A. salina according to trophic transfer factors (TTF_As+nano-TiO2 > TTF_As). However, after 48 h of depuration, the retention of As in A. salina fed As-nano-TiO₂-contaminated algae was even lower than that in A. salina fed As-contaminated algae at the same exposure concentrations. This result indicates that the increased food chain transfer of As in the presence of nano-TiO₂ can be explained by adsorption of As onto nano-TiO₂ in contaminated food (algae), but the bioavailability of As in A. salina is reduced after the introduction of nanoparticles. Although the stress enzyme activities of superoxide dismutase (SOD) and acetylcholinesterase (AChE) in A. salina at a lower As concentration treatment in the presence of nano-TiO₂ were not significantly changed, they increased with higher exposure concentrations of As with or without nano-TiO₂. Our study highlighted the complex role of nanomaterials in the transfer of ambient contaminants via trophic chains and the potential of nano-TiO₂ to reduce the bioavailability of As via trophic transfer to saltwater zooplankton.

Regulation of viability, differentiation and death of human melanoma cells carrying neural stem cell biomarkers: a possibility for neural trans-differentiation

During embryonic development, melanoblasts, the precursors of melanocytes, emerge from a subpopulation of the neural crest stem cells and migrate to colonize skin. Melanomas arise during melanoblast differentiation into melanocytes and from young proliferating melanocytes through somatic mutagenesis and epigenetic regulations. In the present study, we used several human melanoma cell lines from the sequential phases of melanoma development (radial growth phase, vertical growth phase and metastatic phase) to compare: (i) the frequency and efficiency of the induction of cell death via apoptosis and necroptosis; (ii) the presence of neural and cancer stem cell biomarkers as well as death receptors, DR5 and FAS, in both adherent and spheroid cultures of melanoma cells; (iii) anti-apoptotic effects of the endogenous production of cytokines and (iv) the ability of melanoma cells to perform neural trans-differentiation. We demonstrated that programed necrosis or necroptosis, could be induced in two metastatic melanoma lines, FEMX and OM431, while the mitochondrial pathway of apoptosis was prevalent in a vast majority of melanoma lines. All melanoma lines used in the current study expressed substantial levels of pluripotency markers, SOX2 and NANOG. There was a trend for increasing expression of Nestin, an early neuroprogenitor marker, during melanoma progression. Most of the melanoma lines, including WM35, FEMX and A375, can grow as a spheroid culture in serum-free media with supplements. It was possible to induce neural trans-differentiation of 1205Lu and OM431 melanoma cells in serum-free media supplemented with insulin. This was confirmed by the expression of neuronal markers, doublecortin and β3-Tubulin, by significant growth of neurites and by the negative regulation of this process by a dominant-negative Rac1N17. These results suggest a relative plasticity of differentiated melanoma cells and a possibility for their neural trans-differentiation without the necessity for preliminary dedifferentiation.

2,3,5,6-Tetramethylpyrazine (TMP) down-regulated arsenic-induced heme oxygenase-1 and ARS2 expression by inhibiting Nrf2, NF-κB, AP-1 and MAPK pathways in human proximal tubular cells

Our recent study demonstrated that sodium arsenite at a clinically relevant dose induced nephrotoxicity in human renal proximal tubular epithelial cell line HK-2, which could be inhibited by natural product 2,3,5,6-tetramethylpyrazine (TMP) with antioxidant activity. The present study demonstrated that arsenic exposure resulted in protein and enzymatic induction of heme oxygenase-1 (HO-1) in dose- and time-dependent manners in HK-2 cells. Blocking HO-1 enzymatic activity by zinc protoporphyrin (ZnPP) augmented arsenic-induced apoptosis, ROS production and mitochondrial dysfunction, suggesting a critical role for HO-1 as a renal protectant in this procession. On the other hand, TMP, upstream of HO-1, inhibited arsenic-induced ROS production and ROS-dependent HO-1 expression. TMP also prevented mitochondria dysfunction and suppressed activation of the intrinsic apoptotic pathway in HK-2 cells. Our results revealed that the regulation of arsenic-induced HO-1 expression was performed through multiple ROS-dependent signal pathways and the corresponding transcription factors, including p38 MAPK and JNK (but not ERK), AP-1, Nrf2 and NF-κB. TMP inhibited arsenic-induced activations of JNK, p38 MAPK, ERK, AP-1 and Nrf2 and block HO-1 protein expression. The present study, furthermore, demonstrated arsenic-induced expression of arsenic response protein 2 (ARS2) that was regulated by p38 MAPK, ERK and NF-κB. To our knowledge, this is the first report showing that ARS2 involved in arsenic-induced nephrotoxicity, while TMP pretreatment prevented such an up-regulation of ARS2 in HK-2 cells. Given ARS2 and HO-1 sharing the similar regulation mechanism, we speculated that ARS2 might also mediate cell survival in this procession. In summary, our study highlighted a role of HO-1 in the protection against arsenic-induced cytotoxicity downstream from the primary targets of TMP and further indicated that TMP may be used as a potential therapeutic agent in the treatment of arsenic-induced nephrotoxicity.

U937 cell apoptosis induced by arsenite is prevented by low concentrations of mitochondrial ascorbic acid with hardly any effect mediated by the cytosolic fraction of the vitamin

Arsenite directly triggers cytochrome c and Smac/DIABLO release in mitochondria isolated from U937 cells. These effects were not observed in mitochondria pre-exposed for 15 min to 10 µM L-ascorbic acid (AA). In other experiments, intact cells treated for 24-72 h with arsenite were found to die by apoptosis through a mechanism involving mitochondrial permeability transition. Pre-exposure (15 min) to low micromolar concentrations of AA and dehydroascorbic acid (DHA), resulting in identical cytosolic levels of the vitamin, had a diverse impact on cell survival, as cytoprotection was only observed after treatment with AA. Also the mitochondrial accumulation of the vitamin was restricted to AA exposure. An additional indication linking cytoprotection to the mitochondrial fraction of the vitamin was obtained in experiments measuring susceptibility to arsenite in parallel with loss of mitochondrial and cytosolic AA at different times after vitamin exposure. Finally, we took advantage of our recent findings that DHA potently inhibits AA transport to demonstrate that DHA abolishes all the protective effects of AA, under the same conditions in which the mitochondrial accumulation of the vitamin is prevented without affecting the overall cellular accumulation of the vitamin.

Molecular control of arsenite-induced apoptosis in Caenorhabditis elegans: roles of insulin-like growth factor-1 signaling pathway

Apoptosis is one of the main cellular processes in responses to arsenic, the well known environmental carcinogen. By using the nematode Caenorhabditis elegans as an in vivo model, we found that insulin-like growth factor-1 networks and their target protein DAF-16/FOXO, known as key regulators of energy metabolism and growth, played important roles in arsenite-induced apoptosis. Inactivation of DAF-2, AGE-1 and AKT-1 caused worms more susceptible to arsenite-induced apoptosis, which could be attenuated by DAF-16 knockout. Worms with inactivated AKT-2 and SGK-1 or with constitutively activated PDK-1 and AKT-1 showed low levels of apoptosis, which could be elevated by DAF-16 mutation. Our results demonstrated that DAF-2/IGF-1R, AGE-1/PI3K, PDK-1/PDK1 and AKT-1/PKB negatively regulated the arsenite-induced apoptosis, whereas AKT-2 and SGK-1 acted proapoptotically. DAF-16/FOXO antagonized IGF-1 signals in signaling the arsenite-induced apoptosis, and apoptosis promoted by DAF-16 inactivation was attributed to its higher sensitivity to oxidative stress.

Tetramethylpyrazine (TMP) protects against sodium arsenite-induced nephrotoxicity by suppressing ROS production, mitochondrial dysfunction, pro-inflammatory signaling pathways and programed cell death

Although kidney is a target organ of arsenic cytotoxicity, the underlying mechanisms of arsenic-induced nephrotoxicity remain poorly understood. As tetramethylpyrazine (TMP) has recently been found to be a renal protectant in multiple kidney injuries, we hypothesize that TMP could suppress arsenic nephrotoxicity. In this study, human renal proximal tubular epithelial cell line HK-2 was used to elucidate the precise mechanisms of arsenic nephrotoxicity as well as the protective mechanism of TMP in these cells. Sodium arsenite exposure dramatically increased cellular reactive oxygen species (ROS) production, decreased levels of cellular glutathione (GSH), decreased cytochrome c oxidase activity and mitochondrial membrane potential, which indicated mitochondrial dysfunction. On the other hand, sodium arsenite activated pro-inflammatory signals, including β-catenin, nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (MAPK), tumor necrosis factor alpha and cyclooxygenase-2 (COX-2). Small molecule inhibitors of NF-κB and p38 MAPK blocked arsenic-induced COX-2 expression, suggesting arsenic-induced COX-2 up-regulation was NF-κB- and p38 MAPK-dependent. Finally, sodium arsenite induced autophagy in HK-2 cells at early phase (6 h) and the subsequent apoptosis at 24 h. Treatment by TMP or by the antioxidant N-acetylcysteine decreased arsenic-induced ROS production, enhanced GSH levels, prevented mitochondria dysfunction and suppressed the activation of pro-inflammatory signals and the development of autophagy and apoptosis. Our results suggested that TMP may be used as a new potential therapeutic agent to prevent arsenic-induced nephrotoxicity by suppressing these pathological processes.

Impact of long-term exposure to sodium arsenite on cytogenetic radiation damage

The aim of this work was to investigate the impact of long-term exposure to low concentrations of sodium arsenite on the cellular response to ionising radiation. Human lymphoblastoid GM1899a cells were cultured in the presence of sodium arsenite for up to six months. Following chemical exposure, acute challenge doses of X-rays were given and chromosome damage (dicentrics, acentric fragments, translocations, micronuclei) as well as cell growth and changes in cell cycle kinetics were determined. Initial short-term chemical exposures determined 8 ng/ml (60 nM) sodium arsenite as a suitable concentration for chronic exposures, which is below the current World Health Organization limit for arsenic in drinking water. At this concentration, cell growth was slightly, but consistently, slower than in untreated cultures throughout the six-month exposure period. Long-term exposure to the chemical induced no dicentrics and did not significantly alter the yield of dicentrics induced by 1 Gy acute X-irradiation. Similar results were obtained for chromosome translocations. In contrast, exposure to 8 ng/ml sodium arsenite induced significant levels of acentric fragments and micronuclei. Fragment/micronuclei data in combined treatment samples compared with single treatments were consistent with an additive effect of chemical and radiation exposure. As for X-rays, micronuclei induced by sodium arsenite tended to show no centromere in situ hybridisation signal, indicating that they represent structural aberrations rather than mis-segregated chromosomes. Similar results were obtained in human peripheral lymphocytes following short-term exposure to sodium arsenite or X-rays. Overall, an additive effect was observed for all combined exposures. Cellular radiation responses therefore seem to operate without any modulatory effects from chronic low level exposure to sodium arsenite in the systems analysed here.

Melanocytes and keratinocytes have distinct and shared responses to ultraviolet radiation and arsenic

The rise of melanoma incidence in the United States is a growing public health concern. A limited number of epidemiology studies suggest an association between arsenic levels and melanoma risk. Arsenic acts as a co-carcinogen with ultraviolet radiation (UVR) for the development of squamous cell carcinoma and proposed mechanisms include generation of oxidative stress by arsenic and UVR and inhibition of UVR-induced DNA repair by arsenic. In this study, we investigate similarities and differences in response to arsenic and UVR in keratinocytes and melanocytes. Normal melanocytes are markedly more resistant to UVR-induced cytotoxicity than normal keratinocytes, but both cell types are equally sensitive to arsenite. Melanocytes were more resistant to arsenite and UVR stimulation of superoxide production than keratinocytes, but the concentration of arsenite necessary to inhibit the activity of the DNA repair protein poly(ADP-ribose)polymerase and enhance retention of UVR-induced DNA damage was essentially equivalent in both cell types. These findings suggest that although melanocytes are less sensitive than keratinocytes to initial UVR-mediated DNA damage, both of these important target cells in the skin share a mechanism related to arsenic inhibition of DNA repair. These findings suggest that concurrent chronic arsenic exposure could promote retention of unrepaired DNA damage in melanocytes and act as a co-carcinogen in melanoma.

Sodium arsenite exposure inhibits AKT and Stat3 activation, suppresses self-renewal and induces apoptotic death of embryonic stem cells

Sodium arsenite exposure at concentration >5 μM may induce embryotoxic and teratogenic effects in animal models. Long-term health effects of sodium arsenite from contaminated drinking water may result in different forms of cancer and neurological abnormalities. As cancer development processes seem to be originated in stem cells, we have chosen to examine the effects of sodium arsenite on signaling pathways and the corresponding transcription factors that regulate cell viability and self-renewal in mouse embryonic stem cells (ESC) and mouse neural stem/precursor cells. We demonstrated that the crucial signaling pathway, which was substantially suppressed by sodium arsenite exposure (4 μM) in ESC, was the PI3K-AKT pathway linked with numerous downstream targets that control cell survival and apoptosis. Furthermore, the whole core transcription factor circuitry that control self-renewal of mouse ESC (Stat3-P-Tyr705, Oct4, Sox2 and Nanog) was strongly down-regulated by sodium arsenite (4 μM) exposure. This was followed by G2/M arrest and induction of the mitochondrial apoptotic pathway that might be suppressed by caspase-9 and caspase-3 inhibitors. In contrast to mouse ESC with very low endogenous IL6, mouse neural stem/precursor cells (C17.2 clone immortalized by v-myc) with high endogenous production of IL6 exhibited a strong resistance to cytotoxic effects of sodium arsenite that could be decreased by inhibitory anti-IL6 antibody or Stat3 inhibition. In summary, our data demonstrated suppression of self-renewal and induction of apoptosis in mouse ESC by sodium arsenite exposure, which was further accelerated due to simultaneous inhibition of the protective PI3K-AKT and Stat3-dependent pathways.

Synergistic apoptosis of CML cells by buthionine sulfoximine and hydroxychavicol correlates with activation of AIF and GSH-ROS-JNK-ERK-iNOS pathway

Background

Hydroxychavicol (HCH), a constituent of Piper betle leaf has been reported to exert anti-leukemic activity through induction of reactive oxygen species (ROS). The aim of the study is to optimize the oxidative stress –induced chronic myeloid leukemic (CML) cell death by combining glutathione synthesis inhibitor, buthionine sulfoximine (BSO) with HCH and studying the underlying mechanism.

Materials and Methods

Anti-proliferative activity of BSO and HCH alone or in combination against a number of leukemic (K562, KCL22, KU812, U937, Molt4), non-leukemic (A549, MIA-PaCa2, PC-3, HepG2) cancer cell lines and normal cell lines (NIH3T3, Vero) was measured by MTT assay. Apoptotic activity in CML cell line K562 was detected by flow cytometry (FCM) after staining with annexinV-FITC/propidium iodide (PI), detection of reduced mitochondrial membrane potential after staining with JC-1, cleavage of caspase- 3 and poly (ADP)-ribose polymerase proteins by western blot analysis and translocation of apoptosis inducing factor (AIF) by confocal microscopy. Intracellular reduced glutathione (GSH) was measured by colorimetric assay using GSH assay kit. 2′,7′-dichlorodihydrofluorescein diacetate (DCF-DA) and 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) were used as probes to measure intracellular increase in ROS and nitric oxide (NO) levels respectively. Multiple techniques like siRNA transfection and pharmacological inhibition were used to understand the mechanisms of action.

Results

Non-apoptotic concentrations of BSO significantly potentiated HCH-induced apoptosis in K562 cells. BSO potentiated apoptosis-inducing activity of HCH in CML cells by caspase-dependent as well as caspase-independent but apoptosis inducing factor (AIF)-dependent manner. Enhanced depletion of intracellular GSH induced by combined treatment correlated with induction of ROS. Activation of ROS- dependent JNK played a crucial role in ERK1/2 activation which subsequently induced the expression of inducible nitric oxide synthase (iNOS). iNOS- mediated production of NO was identified as an effector molecule causing apoptosis of CML cells.

Conclusion/Significance

BSO synergizes with HCH in inducing apoptosis of CML cells through the GSH-ROS-JNK-ERK-iNOS pathway.

Regulation of apoptosis in human melanoma and neuroblastoma cells by statins, sodium arsenite and TRAIL: a role of combined treatment versus monotherapy

Treatment of melanoma cells by sodium arsenite or statins (simvastatin and lovastatin) dramatically modified activities of the main cell signaling pathways resulting in the induction of heme oxygenase-1 (HO-1) and in a downregulation of cyclooxygenase-2 (COX-2) protein levels. Through heme degradation and the production of carbon monoxide and biliverdin, HO-1 plays a protective role in different scenario of oxidative stress followed by mitochondrial apoptosis. Both sodium arsenite and statins could be efficient inducers of apoptosis in some melanoma cell lines, but often exhibited only modest proapoptotic activity in others, due to numerous protective mechanisms. We demonstrated in the present study that treatment by sodium arsenite or statins with an additional inhibition of HO-1 expression (or activation) caused a substantial upregulation of apoptosis in melanoma cells. Sodium arsenite- or statin-induced apoptosis was independent of BRAF status (wild type versus V600E) in melanoma lines. Monotreatment required high doses of statins (20-40 μM) for effective induction of apoptosis. As an alternative approach, pretreatment of melanoma cells with statin at decreased doses (5-20 μM) dramatically enhanced TRAIL-induced apoptosis, due to suppression of the NF-κB and STAT3-transcriptional targets (including COX-2) and downregulation of cFLIP-L (a caspase-8 inhibitor) protein levels. Furthermore, combined treatment with sodium arsenite and TRAIL or simvastatin and TRAIL efficiently induced apoptotic commitment in human neuroblastoma cells. In summary, our findings on enhancing effects of combined treatment of cancer cells using statin and TRAIL provide the rationale for further preclinical evaluation.

The cystine/cysteine cycle and GSH are independent and crucial antioxidant systems in malignant melanoma cells and represent druggable targets

AIMS

Cancer chemoresistance is often due to upregulation of antioxidant systems. Therapeutic targeting of these systems is however hampered by their redundancy. Here, we have performed a functional dissection of the antioxidant systems in different melanoma cases aimed at the identification of the most effective redox active drug.

RESULTS

We have identified two crucial antioxidant mechanisms: glutathione (GSH), the major intracellular redox buffer, and the cystine/cysteine cycle, which switches the extracellular redox state from an oxidized to a reduced state. The two mechanisms are independent in melanoma cells and may be substitutes for each other, but targeting both of them is lethal. Exposure to the pro-oxidant compound As(2)O(3) induces an antioxidant response. However, while in these cells the intracellular redox balance remains almost unaffected, a reduced environment is generated extracellularly. GSH depletion by buthioninesulfoximine (BSO), or cystine/cysteine cycle inhibition by (S)-4-carboxyphenylglycine (sCPG), enhanced the sensitivity to As(2)O(3). Remarkably, sCPG also prevented the remodeling of the microenvironment redox state.

INNOVATION

We propose that the definition of the prevalent antioxidant system(s) in tumors is crucial for the design of tailored therapies involving redox-directed drugs in association with pro-oxidant drugs.

CONCLUSION

In melanoma cells, BSO is the best enhancer of As(2)O(3) sensitivity. However, since the strong remodeling of the microenvironmental redox state caused by As(2)O(3) may promote tumor progression, the concomitant use of cystine/cysteine cycle blockers is recommended.

Suppression of the proinflammatory response of metastatic melanoma cells increases TRAIL-induced apoptosis

Melanoma is the most lethal form of human skin cancer. However, only limited chemotherapy is currently available for the metastatic stage of the disease. Since chemotherapy, radiation and sodium arsenite treatment operate mainly through induction of the intrinsic mitochondrial pathway, a strongly decreased mitochondrial function in metastatic melanoma cells, could be responsible for low efficacy of the conventional therapy of melanoma. Another feature of metastatic melanoma cells is their proinflammatory phenotype, linked to endogenous expression of the inflammatory cytokines, such as TNFα IL6 and IL8, their receptors, and constitutive NF-κB- and STAT3-dependent gene expression, including cyclooxygenase-2 (PTGS2/COX2). In the present study, we treated melanoma cells with immunological (monoclonal antibody against TNFα or IL6), pharmacological (small molecular inhibitors of IKKβ-NF-κB and JAK2-STAT3) or genetic (specific RNAi for COX-2) agents that suppressed the inflammatory response in combination with induction of apoptosis via TRAIL. As a result of these combined treatments, exogenous TRAIL via interactions with TRAIL-R2/R1 strongly increased levels of apoptosis in resistant melanoma cells. The present study provides new understanding of the regulation of TRAIL-mediated apoptosis in melanoma and will serve as the foundation for the potential development of a novel approach for a therapy of resistant melanomas.

Potential molecular mechanisms for combined toxicity of arsenic and alcohol

Arsenic is a ubiquitous environmental factor that has been identified as a risk factor for a wide range of human diseases. Alcohol is clearly a toxic substance when consumed in excess. Alcohol abuse results in a variety of pathological effects, including damages to liver, heart, and brain, as well as other organs, and is associated with an increased risk of certain types of cancers. In history, arsenic-contaminated beers caused severe diseases. There are populations who are exposed to relatively high levels of arsenic in their drinking water and consume alcohol at the same time. In this focused review, we aim to discuss important molecular mechanisms responsible for arsenic toxicity and potential combined toxic effects of alcohol and arsenic.

Radiation-induced bystander signaling pathways in human fibroblasts: a role for interleukin-33 in the signal transmission

The main goal of this study is to elucidate the mechanisms of the signal transmission for radiation-induced bystander response. The NF-kappaB-dependent gene expression of IL8, IL6, PTGS2/COX2, TNF and IL33 in directly irradiated human skin fibroblasts produced the cytokines and prostaglandin E2 (PGE2) with autocrine/paracrine functions, which further activated signaling pathways and induced NF-kappaB-dependent gene expression in bystander cells. As a result, bystander cells also started expression and production of interleukin-8, interleukin-6, COX-2-generated PGE2 and interleukin-33 (IL-33) followed by autocrine/paracrine stimulation of the NF-kappaB and MAPK pathways. A blockage of IL-33 transmitting functions with anti-IL-33 monoclonal antibody added into the culture media decreased NF-kappaB activation in directly irradiated and bystander cells. On the other hand, the IGF-1-Receptor kinase regulated the PI3K-AKT pathway in both directly irradiated and bystander fibroblasts. A pronounced and prolonged increase in AKT activity after irradiation was a characteristic feature of bystander cells. AKT positively regulated IL-33 protein expression levels. Suppression of the IGF-R1-AKT-IL-33 pathway substantially increased radiation-induced or TRAIL-induced apoptosis in fibroblasts. Taken together, our results demonstrated the early activation of NF-kappaB-dependent gene expression first in directly irradiated and then bystander fibroblasts, the further modulation of critical proteins, including IL-33, by AKT in bystander cells and late drastic changes in cell survival and in enhanced sensitivity to TRAIL-induced apoptosis after suppression of the IGF-1R-AKT-IL-33 signaling cascade in both directly irradiated and bystander cells.

GADD45alpha mediates arsenite-induced cell apoptotic effect in human hepatoma cells via JNKs/AP-1-dependent pathway

Arsenite (As(III)), an effective chemotherapeutic agent for the acute promyelocytic leukemia (APL) and multiple myeloma (MM), might be also a promise for the therapy of other cancers, including the solid tumors. However, the molecular bases of arsenite-induced cytotoxicity in the tumor cells have not been fully defined. In this study, we have disclosed that arsenite effectively induces the apoptotic response in the HepG2 human hepatoma cells by triggering GADD45alpha induction and the subsequent activation of JNKs/AP-1 cell death pathway. However, signaling events relating to GADD45alpha/JNKs/AP-1 pathway activation have not been observed in HL7702 human diploid hepatic cells under the same arsenite exposure condition. Our results thus have illustrated the selective pro-apoptotic role of arsenite in the hepatoma cells by activating GADD45alpha-dependent cell death pathway whereas with little effect on the normal hepatic cells. The approaches to up-regulate GADD45alpha levels might be helpful in improving the chemotherapeutic action of arsenite on certain solid tumors including hepatoma.

Disruption of IGF-1R signaling increases TRAIL-induced apoptosis: a new potential therapy for the treatment of melanoma

Resistance of cancer cells to apoptosis is dependent on a balance of multiple genetic and epigenetic mechanisms, which up-regulate efficacy of the surviving growth factor-receptor signaling pathways and suppress death-receptor signaling pathways. The Insulin-like Growth Factor-1 Receptor (IGF-1R) signaling pathway is highly active in metastatic melanoma cells by mediating downstream activation of PI3K-AKT and MAPK pathways and controlling general cell survival and proliferation. In the present study, we used human melanoma lines with established genotypes that represented different phases of cancer development: radial-growth-phase WM35, vertical-growth-phase WM793, metastatic LU1205 and WM9 [1]. All these lines have normal NRAS. WM35, WM793, LU1205 and WM9 cells have mutated BRAF (V600E). WM35 and WM9 cells express normal PTEN, while in WM793 cells PTEN expression is down-regulated; finally, in LU1205 cells PTEN is inactivated by mutation. Cyclolignan picropodophyllin (PPP), a specific inhibitor of IGF-1R kinase activity, strongly down-regulated the basal levels of AKT activity in WM9 and in WM793 cells, modestly does so in LU1205, but has no effect on AKT activity in the early stage WM35 cells that are deficient in IGF-1R. In addition, PPP partially down-regulated the basal levels of active ERK1/2 in all lines used, highlighting the role of an alternative, non-BRAF pathway in MAPK activation. The final result of PPP treatment was an induction of apoptosis in WM793, WM9 and LU1205 melanoma cells. On the other hand, dose-dependent inhibition of IGF-1R kinase activity by PPP at a relatively narrow dose range (near 500 nM) has different effects on melanoma cells versus normal cells, inducing apoptosis in cancer cells and G2/M arrest of fibroblasts. To further enhance the pro-apoptotic effects of PPP on melanoma cells, we used a combined treatment of TNF-Related Apoptosis-Inducing Ligand (TRAIL) and PPP. This combination substantially increased death by apoptosis for WM793 and WM9 cells, but did so only modestly for LU1205 cells with very high basal activity of AKT. The ultimate goal of this direction of research is the discovery of a new treatment method for highly resistant human metastatic melanomas. Our findings provide the rationale for further preclinical evaluation of this novel treatment.

Arsenic trioxide and ascorbic acid demonstrate promising activity against primary human CLL cells in vitro

The compromised antioxidant defense system in chronic lymphocytic leukemia (CLL) suggested a potential use for reactive oxygen species (ROS) generating arsenic trioxide (ATO) and ascorbic acid. While both ATO and ascorbic acid mediate cytotoxicity in CLL B cells as single agents, the efficacy of ATO is enhanced by ascorbic acid. This effect is dependent on increased ROS accumulation, as pretreatment of B-CLL cells with a glutathione reducing buthionine sulfoximine or catalase inhibiting aminotriazole, enhanced ATO/ascorbic acid-mediated cytotoxicity. Pretreatment with reducing agents such as catalase, or thiol antioxidant, N-acetyl cysteine or GSH also abrogated ATO/ascorbic acid-mediated cytotoxicity. Furthermore, Hu1D10-mediated cell death was enhanced with ATO and ascorbic acid, thus justifying potential combination of ATO/arsenic trioxide therapy with antibodies such as Hu1D10 that also cause accumulation of ROS.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration-related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 microM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10-100 microM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor-derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor-derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl-2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose-response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA.

The PTEN-AKT3 signaling cascade as a therapeutic target in melanoma

Melanocytes undergo extensive genetic changes during transformation into aggressive melanomas. These changes deregulate genes whose aberrant activity promotes the development of this disease. The phosphoinositide-3-kinase (PI3K) and mitogen-activated protein (MAP) kinase pathways are two key signaling cascades that have been found to play prominent roles in melanoma development. These pathways relay extra-cellular signals via an ordered series of consecutive phosphorylation events from cell surface throughout the cytoplasm and nucleus regulating diverse cellular processes including proliferation, survival, invasion and angiogenesis. It is generally accepted that therapeutic agents would need to target these two pathways to be an effective therapy for the long-term treatment of advanced-stage melanoma patients. This review provides an overview of the PI3 kinase pathway focusing specifically on two members of the pathway, called PTEN and Akt3, which play important roles in melanoma development. Mechanisms leading to deregulation of these two proteins and therapeutic implications of targeting this signaling cascade to treat melanoma are detailed in this review.

Biological responses to arsenic compounds

Arsenic is a metalloid that generates various biological effects on cells and tissues. Depending on the specific tissue exposed and the time and degree of exposure, diverse responses can be observed. In humans, prolonged and/or high dose exposure to arsenic can have a variety of outcomes, including the development of malignancies, severe gastrointestinal toxicities, diabetes, cardiac arrhythmias, and death. On the other hand, one arsenic derivative, arsenic trioxide (As(2)O(3)), has important antitumor properties. This agent is a potent inducer of antileukemic responses, and it is now approved by the Food and Drug Administration for the treatment of acute promyelocytic leukemia in humans. The promise and therapeutic potential of arsenic and its various derivatives have been exploited for hundreds of years. Remarkably, research focused on the potential use of arsenic compounds in the treatment of human diseases remains highly promising, and it is an area of active investigation. An emerging approach of interest and therapeutic potential involves efforts to target and block cellular pathways activated in a negative feedback manner during treatment of cells with As(2)O(3). Such an approach may ultimately provide the means to selectively enhance the suppressive effects of this agent on malignant cells and render normally resistant tumors sensitive to its antineoplastic properties.

Inhibition of ataxia telangiectasia mutated kinase activity enhances TRAIL-mediated apoptosis in human melanoma cells

The aim of the present study was to elucidate the effects of ataxia telangiectasia mutated (ATM) kinase on the regulation of the extrinsic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2/DR5-mediated death pathway in human melanoma cells. We revealed that total ATM protein levels were high in some human melanoma lines compared with normal cells. The basal levels of active form ATM phospho-Ser(1981) were also detectable in many melanoma lines and could be further up-regulated by gamma-irradiation. Pretreatment of several melanoma lines just before gamma-irradiation with the inhibitor of ATM kinase KU-55933 suppressed p53 and nuclear factor-kappaB (NF-kappaB) activation but notably increased radiation-induced DR5 surface expression, down-regulated cFLIP (caspase-8 inhibitor) levels, and substantially enhanced exogenous TRAIL-induced apoptosis. Furthermore, gamma-irradiation in the presence of KU-55933 rendered TRAIL-resistant HHMSX melanoma cells susceptible to TRAIL-mediated apoptosis. In addition, suppression of ATM expression by the specific short hairpin RNA also resulted in down-regulation of cFLIP levels, up-regulation of surface DR5 expression, and TRAIL-mediated apoptosis in melanoma cells. Besides p53 and NF-kappaB, crucial regulators of DR5 expression, transcription factor STAT3 is known to negatively regulate DR5 expression. Suppression of Ser(727) and Tyr(705) phosphorylation of STAT3 by KU-55933 reduced STAT3 transacting activity accompanied by elevation in DR5 expression. Dominant-negative STAT3beta also efficiently up-regulated the DR5 surface expression and down-regulated cFLIP levels in melanoma cells in culture and in vivo. Taken together, our data show the existence of an ATM-dependent STAT3-mediated antiapoptotic pathway, which on suppression sensitizes human melanoma cells to TRAIL-mediated apoptosis.

The tumor suppressor function of mitochondria: translation into the clinics

Recently, the inevitable metabolic reprogramming experienced by cancer cells as a result of the onset of cellular proliferation has been added to the list of hallmarks of the cancer cell phenotype. Proliferation is bound to the synchronous fluctuation of cycles of an increased glycolysis concurrent with a restrained oxidative phosphorylation. Mitochondria are key players in the metabolic cycling experienced during proliferation because of their essential roles in the transduction of biological energy and in defining the life-death fate of the cell. These two activities are molecularly and functionally integrated and are both targets of commonly altered cancer genes. Moreover, energetic metabolism of the cancer cell also affords a target to develop new therapies because the activity of mitochondria has an unquestionable tumor suppressor function. In this review, we summarize most of these findings paying special attention to the opportunity that translation of energetic metabolism into the clinics could afford for the management of cancer patients. More specifically, we emphasize the role that mitochondrial beta-F1-ATPase has as a marker for the prognosis of different cancer patients as well as in predicting the tumor response to therapy.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

Radiosensitization of melanoma cells through combined inhibition of protein regulators of cell survival

The incidence of melanoma continues to dramatically increase in most Western countries with predominantly Caucasian populations. However, only limited therapies for the metastatic stage of the disease are currently available. The main purpose of this study is to determine approaches that can substantially increase radiosensitivity of melanoma cells. The PI3K-AKT, NF-kappaB and COX-2 pathways, which are involved in the radioprotective response, are highly active in melanoma cells. Pharmacological suppression of COX-2 and PI3K-AKT, or RNAi-mediated knockdown of COX-2, substantially increased levels of G2/M arrest of the cell cycle and decreased clonogenic survival of gamma-irradiated melanomas, predominantly via a necrotic mechanism. On the other hand, resveratrol, a polyphenolic phytoalexin, selectively targets numerous cell signaling pathways, decreasing clonogenic survival primarily via an apoptotic mechanism. In melanoma cells, resveratrol inhibits STAT3 and NF-kappaB-dependent transcription, culminating in suppression of cFLIP and Bcl-xL expression, while activating the MAPK- and the ATM-Chk2-p53 pathways. Resveratrol also upregulates TRAIL promoter activity and induces TRAIL surface expression in some melanoma cell lines, resulting in a rapid development of apoptosis. Sequential treatment of melanoma cells, first with gamma-irradiation to upregulate TRAIL-R surface expression, and then with resveratrol to suppress antiapoptotic proteins cFLIP and Bcl-xL and induce TRAIL surface expression, had dramatic effects on upregulation of apoptosis in some melanoma lines, including SW1 and WM35. However, for melanoma lines exhibiting suppressed translocation of TRAIL to the cell surface, a necrotic mechanism of cell death was primarily involved in radiation response. Hence, surface expression of TRAIL induced by resveratrol appears to be a decisive event, one which determines an apoptotic versus a necrotic response of melanoma cells to sequential treatment.

Sensitivity to sodium arsenite in human melanoma cells depends upon susceptibility to arsenite-induced mitotic arrest

Arsenic induces clinical remission in patients with acute promyelocytic leukemia and has potential for treatment of other cancers. The current study examines factors influencing sensitivity to arsenic using human malignant melanoma cell lines. A375 and SK-Mel-2 cells were sensitive to clinically achievable concentrations of arsenite, whereas SK-Mel-3 and SK-Mel-28 cells required supratherapeutic levels for toxicity. Inhibition of glutathione synthesis, glutathione S-transferase (GST) activity, and multidrug resistance protein (MRP) transporter function attenuated arsenite resistance, consistent with studies suggesting that arsenite is extruded from the cell as a glutathione conjugate by MRP-1. However, MRP-1 was not overexpressed in resistant lines and GST-pi was only slightly elevated. ICP-MS analysis indicated that arsenite-resistant SK-Mel-28 cells did not accumulate less arsenic than arsenite-sensitive A375 cells, suggesting that resistance was not attributable to reduced arsenic accumulation but rather to intrinsic properties of resistant cell lines. The mode of arsenite-induced cell death was apoptosis. Arsenite-induced apoptosis is associated with cell cycle alterations. Cell cycle analysis revealed arsenite-sensitive cells arrested in mitosis whereas arsenite-resistant cells did not, suggesting that induction of mitotic arrest occurs at lower intracellular arsenic concentrations. Higher intracellular arsenic levels induced cell cycle arrest in the S-phase and G(2)-phase in SK-Mel-3 and SK-Mel-28 cells, respectively. The lack of arsenite-induced mitotic arrest in resistant cell lines was associated with a weakened spindle checkpoint resulting from reduced expression of spindle checkpoint protein BUBR1. These data suggest that arsenite has potential for treatment of solid tumors but a functional spindle checkpoint is a prerequisite for a positive response to its clinical application.

Resveratrol sensitizes melanomas to TRAIL through modulation of antiapoptotic gene expression

Although many human melanomas express the death receptors TRAIL-R2/DR5 or TRAIL-R1/DR4 on cell surface, they often exhibit resistance to exogenous TRAIL. One of the main contributors to TRAIL-resistance of melanoma cells is upregulation of transcription factors STAT3 and NF-kappaB that control the expression of antiapoptotic genes, including cFLIP and Bcl-xL. On the other hand, the JNK-cJun pathway is involved in the negative regulation of cFLIP (a caspase-8 inhibitor) expression. Our observations indicated that resveratrol, a polyphenolic phytoalexin, decreased STAT3 and NF-kappaB activation, while activating JNK-cJun that finally suppressed expression of cFLIP and Bcl-xL proteins and increased sensitivity to exogenous TRAIL in DR5-positive melanomas. Interestingly, resveratrol did not increase surface expression of DR5 in human melanomas, while gamma-irradiation or sodium arsenite treatment substantially upregulated DR5 expression. Hence, an initial increase in DR5 surface expression (either by gamma-irradiation or arsenite), and subsequent downregulation of antiapoptotic cFLIP and Bcl-xL (by resveratrol), appear to constitute an efficient approach to reactivate apoptotic death pathways in TRAIL-resistant human melanomas. In spite of partial suppression of mitochondrial function and the mitochondrial death pathway, melanoma cells still retain the potential to undergo the DR5-mediated, caspase-8-dependent death pathway that could be accelerated by either an increase in DR5 surface expression or suppression of cFLIP. Taken together, these results suggest that resveratrol, in combination with TRAIL, may have a significant efficacy in the treatment of human melanomas.

Lymphokine-activated killer T-cell-originated protein kinase phosphorylation of histone H2AX prevents arsenite-induced apoptosis in RPMI7951 melanoma cells

PURPOSE

Arsenic is a valuable therapeutic tool in cancer treatment. Lymphokine-activated killer T-cell-originated protein kinase (TOPK) is highly expressed in cancer cells, but its specific function is still unknown. We investigated the role of TOPK in arsenic-induced apoptosis in RPMI7951 human melanoma cells.

EXPERIMENTAL DESIGN

Expression of TOPK was evaluated in different melanoma cell lines, and liquid chromatography-tandem mass spectrometry analysis was used to identify proteins binding with TOPK. Immunofluorescence, Western blot, and flow cytometry were used to assess the effect of arsenic on TOPK, histone H2AX, and apoptosis in RPMI7951 cells.

RESULTS

Melanoma cell lines expressing high levels of TOPK were more resistant to arsenite (As(3+))-induced apoptosis. As(3+) treatment induced phosphorylation of TOPK and histone H2AX in RPMI7951 human melanoma cells. Liquid chromatography-tandem mass spectrometry results indicated that TOPK could bind with histone H2AX, and in vitro and in vivo assays confirmed that TOPK binds with and phosphorylates histone H2AX. As(3+) treatment caused phosphorylation of TOPK, which colocalized with phosphorylated histone H2AX in the nucleus. TOPK small interfering RNA cells exhibited a decreased phosphorylation of histone H2AX with As(3+) treatment. As(3+)-induced apoptosis was decreased in H2AX(-/-) cells but increased in TOPK small interfering RNA cells.

CONCLUSIONS

TOPK binds with histone H2AX and inhibits As(3+)-induced apoptosis through phosphorylation of histone H2AX. Melanoma cell lines with high levels of TOPK are more resistant to As(3+)-induced apoptosis. Therefore, inhibition of TOPK activity combined with As(3+) treatment may be helpful in the treatment of melanomas.

Sequential treatment by ionizing radiation and sodium arsenite dramatically accelerates TRAIL-mediated apoptosis of human melanoma cells

Melanoma is the most lethal form of skin cancer. There is a lack of effective treatments for individuals with advanced disease. Many melanomas exhibit high levels of radioresistance. The direct consequence of gamma-irradiation for most melanoma cells is growth arrest at the G2-M phase of cell cycle. However, radiation-induced signaling pathways may affect numerous additional targets in cancer cells. We show in the present study that gamma-irradiation, as well as alpha-particle exposure, dramatically increases the susceptibility of melanoma cells to recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis via up-regulation of surface TRAIL-receptor 1/receptor 2 (DR4/DR5) levels and to Fas ligand-mediated apoptosis via up-regulation of surface Fas levels. Additionally, increased dynamin-2 expression after irradiation is critically important in the translocation of death receptor to the cell surface. Moreover, sodium arsenite treatment may up-regulate expression of endogenous TRAIL and induces its translocation to cell surface and further down-regulates cFLIP levels in melanoma cells. We have evaluated the effects of sequential gamma-irradiation and arsenite treatment of melanoma cells for the induction of death signaling. Such treatment results in an efficient TRAIL-mediated apoptosis via a paracrine mechanism. These data highlight the efficacy of combined modality treatment involving radiation and arsenite in clinical management of this often fatal form of skin cancer.

Pharmacologic inhibitors of extracellular signal-regulated kinase (ERKs) and c-Jun NH(2)-terminal kinase (JNK) decrease glutathione content and sensitize human promonocytic leukemia cells to arsenic trioxide-induced apoptosis

Treatment with 1-4 microM As(2)O(3) slightly induced apoptosis in U-937 human promonocitic leukemia cells. This effect was potentiated by co-treatment with MEK/ERK (PD98059, U0126) and JNK (SP600125, AS601245) inhibitors, but not with p38 (SB203580, SB220025) inhibitors. However, no potentiation was obtained using lonidamine, doxorubicin, or cisplatin instead of As(2)O(3). Apoptosis potentiation by mitogen-activated protein kinase (MAPK) inhibitors involved both the intrinsic and extrinsic executionary pathways, as demonstrated by Bax activation and cytochrome c release from mitochondria, and by caspase-8 activation and Bid cleavage, respectively; and the activation of both pathways was prevented by Bcl-2 over-expression. Treatment with MEK/ERK and JNK inhibitors, but not with p38 inhibitors, caused intracellular glutathione (GSH) depletion, which was differentially regulated. Thus, while it was prevented by N-acetyl-L-cysteine (NAC) in the case of U0126, it behaved as a NAC-insensitive process, regulated at the level of DL-buthionine-(S,R)-sulfoximine (BSO)-sensitive enzyme activity, in the case of SP600125. The MEK/ERK inhibitor also potentiated apoptosis and decreased GSH content in As(2)O(3)-treated NB4 human acute promyelocytic leukemia (APL) cells, but none of these effects were produced by the JNK inhibitor. MEK/ERK and JNK inhibitors did not apparently affect As(2)O(3) transport activity, as measured by intracellular arsenic accumulation. SP600126 greatly induced reactive oxygen species (ROS) accumulation, while BSO and U0126 had little or null effects. These results, which indicate that glutathione is a target of MAP kinases in myeloid leukemia cells, might be exploited to improve the antitumor properties of As(2)O(3), and provide a rationale for the use of kinase inhibitors as therapeutic agents.

Sodium arsenite accelerates TRAIL-mediated apoptosis in melanoma cells through upregulation of TRAIL-R1/R2 surface levels and downregulation of cFLIP expression

AP-1/cJun, NF-kappaB and STAT3 transcription factors control expression of numerous genes, which regulate critical cell functions including proliferation, survival and apoptosis. Sodium arsenite is known to suppress both the IKK-NF-kappaB and JAK2-STAT3 signaling pathways and to activate the MAPK/JNK-cJun pathways, thereby committing some cancers to undergo apoptosis. Indeed, sodium arsenite is an effective drug for the treatment of acute promyelocytic leukemia with little nonspecific toxicity. Malignant melanoma is highly refractory to conventional radio- and chemotherapy. In the present study, we observed strong effects of sodium arsenite treatment on upregulation of TRAIL-mediated apoptosis in human and mouse melanomas. Arsenite treatment upregulated surface levels of death receptors, TRAIL-R1 and TRAIL-R2, through increased translocation of these proteins from cytoplasm to the cell surface. Furthermore, activation of cJun and suppression of NF-kappaB by sodium arsenite resulted in upregulation of the endogenous TRAIL and downregulation of the cFLIP gene expression (which encodes one of the main anti-apoptotic proteins in melanomas) followed by cFLIP protein degradation and, finally, by acceleration of TRAIL-induced apoptosis. Direct suppression of cFLIP expression by cFLIP RNAi also accelerated TRAIL-induced apoptosis in these melanomas, while COX-2 suppression substantially increased levels of both TRAIL-induced and arsenite-induced apoptosis. In contrast, overexpression of permanently active AKTmyr inhibited TRAIL-mediated apoptosis via downregulation of TRAIL-R1 levels. Finally, AKT overactivation increased melanoma survival in cell culture and dramatically accelerated growth of melanoma transplant in vivo, highlighting a role of AKT suppression for effective anticancer treatment.

Coordination of JNK1 and JNK2 is critical for GADD45alpha induction and its mediated cell apoptosis in arsenite responses

Arsenite is a well documented environmental pathogen, whereas it has also been applied as medication to treat various neoplasmas. The pathogenic and therapeutic effects of arsenite are associated with cellular apoptotic responses. However, the molecular mechanisms of arsenite-induced apoptosis are not very well understood. Our previous study has shown that arsenite exposure is able to activate JNKs, which subsequently mediate the apoptotic outcome. The present study further revealed that the coordination of JNK1 and JNK2 was critical for the arsenite-induced expression of GADD45alpha (growth arrest and DNA damage 45alpha), which in turn mediated the cellular apoptosis. The arsenite-induced apoptosis and GADD45alpha expression were significantly impaired in mouse embryonic fibroblasts deficient in either jnk1 (JNK1-/-) or jnk2 (JNK2-/-). Knockdown of GADD45alpha by its specific small interfering RNA also dramatically reduced the apoptotic responses, and overexpression of GADD45alpha in either JNK1-/- or JNK2-/- mouse embryonic fibroblasts partially resensitized the cell death. Furthermore, it was found that the regulation of GADD45alpha by JNK1 and JNK2 was achieved through mediating the activation of c-Jun, since in the JNK1-/- and JNK2-/- cells the c-Jun activation was impaired, and overexpression of the dominant negative mutant of c-Jun (TAM67) in wild type cells could also block GADD45alpha induction as well as cellular apoptosis. Our results demonstrate that the coordination of JNK1 and JNK2 is critical for c-Jun/GADD45alpha-mediated cellular apoptosis induced by arsenite.

Anion exchanger 2 mediates the action of arsenic trioxide

Anion exchanger 2 (AE2) mediates the exchange of C1-/HCO3- across the plasma membrane and plays a role in the regulation of intracellular pH. The present study showed that AE2 protein expression was upregulated immediately after exposure to either low (0.5 micromol/l) or high (1 and 2 micromol/l) concentrations of arsenic trioxide. This suggests that arsenic trioxide may act via regulation of intracellular pH. Changing the culture pH in NB4 cells modulated the degradation of promyelocytic leukaemia-retinoic acid receptor-alpha (PML-RARalpha), PML and RARalpha, which supported this hypothesis. DIDS (4,4'-diisothiocyanodihydrostilbene-2,2'-disulphonic acid) inhibited AE2 function, preventing the arsenic trioxide-induced degradation of RARalpha and low concentration showed synergistic effects on the expression of CD11c, which is related with cell differentiation. In addition, DIDS rescued the cells from 1 micromol/l arsenic trioxide-induced apoptosis. In conclusion, AE2 mediated the action of arsenic trioxide via regulation of intracellular pH and a novel pathway for the mechanism of action of arsenic trioxide is reported.

Distinct gene expression profiles in immortalized human urothelial cells exposed to inorganic arsenite and its methylated trivalent metabolites

Inorganic arsenic is an environmental carcinogen. The generation of toxic trivalent methylated metabolites complicates the study of arsenic-mediated carcinogenesis. This study systematically evaluated the effect of chronic treatment with sodium arsenite (iAs(III)), monomethylarsonous acid (MMA(III)), and dimethylarsinous acid (DMA(III)) on immortalized human uroepithelial cells (SV-HUC-1 cells) using cDNA microarray. After exposure for 25 passages to iAs(III) (0.5 microM), MMA(III) (0.05, 0.1, or 0.2 microM), or DMA(III) (0.2 or 0.5 microM), significant compound-specific morphologic changes were observed. A set of 114 genes (5.7% of the examined genes) was differentially expressed in one or more sets of arsenical-treated cells compared with untreated controls. Expression analysis showed that exposure of cells to DMA(III) resulted in a gene profile different from that in cells exposed to iAs(III) or MMA(III), and that the iAs(III)-induced gene profile was closest to that in the tumorigenic HUC-1-derived 3-methylcholanthrene-induced tumorigenic cell line MC-SV-HUC T2, which was derived from SV-HUC-1 cells by methylcholanthrene treatment. Of the genes affected by all three arsenicals, only one, that coding for interleukin-1 receptor, type II, showed enhanced expression, a finding confirmed by the reduced increase in NF-kappaB (nuclear factor kappa B) activity seen in response to interleukin-1beta in iAs(III)-exposed cells. The expression of 11 genes was suppressed by all three arsenicals. 5-Aza-deoxycytidine partially restored the transcription of several suppressed genes, showing that epigenetic DNA methylation was probably involved in arsenical-induced gene repression. Our data demonstrate that chronic exposure to iAs(III), MMA(III), or DMA(III) has different epigenetic effects on urothelial cells and represses NF-kappaB activity.

Dual treatment with COX-2 inhibitor and sodium arsenite leads to induction of surface Fas Ligand expression and Fas-Ligand-mediated apoptosis in human melanoma cells

Most human melanomas express Fas receptor on the cell surface, and treatment with exogenous Fas Ligand (FasL) efficiently induces apoptosis of these cells. In contrast, endogenous surface expression of FasL is suppressed in Fas-positive melanomas. We report here the use of a combination of sodium arsenite, an inhibitor of NF-kappaB activation, and NS398, a cyclooxygenase-2 (COX-2) inhibitor, for restoration of the surface FasL expression. We observed a large increase of Fas-mediated apoptosis in Fas-positive melanomas. This was due to induction of FasL surface expression and increased susceptibility to Fas death signaling after arsenite and NS398 treatment. Furthermore, silencing COX-2 expression by specific RNAi also effectively increased surface FasL expression following arsenite treatment. Upregulation of the surface FasL levels was based on an increase in the efficiency of translocation to the cell surface and stabilization of FasL protein on the cell surface, rather than on acceleration of the FasL gene transcription. Data obtained demonstrate that the combination of arsenite with inhibitors of COX-2 may affect the target cancer cells via induction of FasL-mediated death signaling.

A phase II trial of arsenic trioxide in patients with metastatic melanoma

BACKGROUND

Arsenic trioxide induces growth inhibition and apoptosis in human melanoma cell lines. Therefore, a Phase II trial was conducted to evaluate the efficacy and toxicity of single-agent arsenic trioxide in patients with Stage IV melanoma.

METHODS

Twenty patients, 10 with metastatic melanoma of cutaneous origin and 10 with metastatic melanoma of choroidal origin, received arsenic trioxide 0.25 mg/kg/day for 5 days, followed by a maintenance dose of 0.35 mg/kg/day twice a week. All patients with melanoma of cutaneous origin and four patients with melanoma of choroidal origin had received prior therapy.

RESULTS

Single-agent arsenic trioxide did not induce clinical response in this patient population. Eight patients (five with melanoma of cutaneous origin, and three with melanoma of choroidal origin) had disease stabilization for at least six weeks. The median overall survival duration for patients with melanoma of cutaneous origin was 7.9 months, and that of patients with melanoma of choroidal origin has not been reached at a median follow-up duration of 11.8 months. Grade 3 toxicity included neutropenia, fatigue, abdominal pain, and arthralgia. Grade 4 toxicity did not occur.

CONCLUSIONS

Single-agent arsenic trioxide was generally well tolerated; however, no tumor regression was observed in this patient population. Future clinical trials should evaluate arsenic trioxide in combination with other anticancer drugs that may improve its clinical activity in melanoma.

Depletion of Securin Increases Arsenite-Induced Chromosome Instability and Apoptosis via a p53-Independent Pathway

Arsenic is a pathologic factor of cardiovascular diseases and cancers; nevertheless, it also acts as an anticancer agent effective on acute promyelocytic leukemia and multiple myeloma. Securin, a proposed proto-oncogene, regulates cell proliferation and tumorigenesis. However, roles of securin on the arsenic-induced cell cycle arrest and apoptosis remain unknown. In this study, the effects of sodium arsenite on the expression of securin in two tissue types of cell lines, the vascular endothelial and colorectal epithelial cells, were investigated. Arsenite (8-16 microM, 24 h) increased the cytotoxicity, apoptosis, and growth inhibition in both endothelial and epithelial cells. The levels of phospho-CDC2 (threonine-161), CDC2, and cyclin B1 proteins were decreased, and the G2/M fractions were increased by arsenite. Concomitantly, arsenite markedly diminished the securin protein expression and induced the abnormal sister chromatid separation. The depletion of securin proteins increased the induction of mitotic arrest, aberrant chromosome segregation, and apoptosis after arsenite treatment. p53, a tumor suppressor protein, balances the cell survival and apoptosis. Arsenite raised the levels of phospho-p53 (serine-15) and p53 (DO-1) proteins in both the securin-wild-type and -null cells. The p53-functional cells were more susceptible than the p53-mutational cells to arsenite on the cytotoxicity and apoptosis. Besides, arsenite decreased the levels of securin proteins to a similar degree in both the p53-functional and -mutational cells. Together, it is the first time to demonstrate that the inhibition of securin expression induced by arsenite increases the chromosomal instability and apoptosis via a p53-independent pathway.

Conference overview: Molecular mechanisms of metal toxicity and carcinogenesis

Chronic exposure to many heavy metals and metal-derivatives is associated with an increased risk of cancer, although the mechanisms of tumorigenesis are largely unknown. Approximately 125 scientists attended the 3rd Conference on Molecular Mechanisms of Metal Toxicity and Carcinogenesis and presented the latest research concerning these mechanisms. Major areas of focus included exposure assessment and biomarker identification, roles of ROS and antioxidants in carcinogenesis, mechanisms of metal-induced DNA damage, metal signalling, and the development of animal models for use in metal toxicology studies. Here we highlight some of the research presented, and summarize the conference proceedings.

Functional and therapeutic significance of Akt deregulation in malignant melanoma

Identification of specific genes or signaling pathways involved in development of melanoma could lead to new therapies that target and correct these defects. Recent studies have revealed deregulation of the Akt signaling pathway occurring in 43-67% of melanomas. Akt kinase family members, Akt1/PKBalpha, Akt2/PKBbeta and Akt3/PKBgamma, share extensive structural similarity and perform common as well as unique functions within cells. The Akt signaling cascade initiates at the cell surface when growth factors or other extracellular stimuli activate phosphoinositide 3-kinase (PI3K). Activated PI3K generates a lipid second messenger, phosphatidylinositol-3,4,5-trisphosphate (PIP3), causing translocation of Akt to the plasma membrane where it becomes phosphorylated and activated. The balance of cellular PIP3 is regulated primarily by a phosphatase called PTEN that reduces PIP3 levels thereby lowering Akt activity. In melanomas, decreased PTEN activity elevates PIP3 levels resulting in Akt activation. Active Akt then phosphorylates downstream cellular proteins that promote melanoma cell proliferation and survival. Recently, Akt3 was discovered to be the predominant isoform activated in sporadic melanomas. Levels of activity increased during melanoma progression with metastatic melanomas having the highest activity. Although mechanisms of Akt3 activation remain to be fully characterized, overexpression of Akt3 and decreased PTEN activity play important roles in this process. Targeted reduction of Akt3 activity decreased survival of melanoma tumor cells leading to inhibition of tumor development, which may be therapeutically effective for shrinking tumors in melanoma patients. This review surveys recent developments in Akt deregulation in melanoma and its potential as a selective therapeutic target in patients in the advanced stages of this disease.

Distinct IκB kinase regulation in adult T cell leukemia and HTLV-I-transformed cells

We have recently shown constitutive IkappaB kinase (IKK) activation and aberrant p52 expression in adult T cell leukemia (ATL) cells that do not express human T cell leukemia virus type I (HTLV-I) Tax, but the mechanism of IKK activation in these cells has remained unknown. Here, we demonstrate distinct regulation of IKK activity in ATL and HTLV-I-transformed T cells in response to protein synthesis inhibition or arsenite treatment. Protein synthesis inhibition for 4 h by cycloheximide (CHX) barely affects IKK activity in Tax-positive HTLV-I-transformed cells, while it diminishes IKK activity in Tax-negative ATL cells. Treatment of ATL cells with a proteasome inhibitor MG132 prior to protein synthesis inhibition reverses the inhibitory effect of CHX, and MG132 alone greatly enhances IKK activity. In addition, treatment of HTLV-I-transformed cells with arsenite for 1 h results in down-regulation of IKK activity without affecting Tax expression, while 8 h of arsenite treatment does not impair IKK activity in ATL cells. These results indicate that a labile protein sensitive to proteasome-dependent degradation governs IKK activation in ATL cells, and suggest a molecular mechanism of IKK activation in ATL cells distinct from that in HTLV-I-transformed T cells.

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Mitochondrial Damage Mediates Genotoxicity of Arsenic in Mammalian Cells

Arsenic is an important environmental carcinogen that affects millions of people worldwide through contaminated water supplies. For decades, arsenic was considered a nongenotoxic carcinogen. Using the highly sensitive A(L) mutation assay, we previously showed that arsenic is, indeed, a potent gene and chromosomal mutagen and that its effects are mediated through the induction of reactive oxygen species. However, the origin of these radicals and the pathways involved are not known. Here we show that mitochondrial damage plays a crucial role in arsenic mutagenicity. Treatment of enucleated cells with arsenic followed by rescue fusion with karyoplasts from controls resulted in significant mutant induction. In contrast, treatment of mitochondrial DNA-depleted (rho(0)) cells produced few or no mutations. Mitochondrial damage can lead to the release of superoxide anions, which then react with nitric oxide to produce the highly reactive peroxynitrites. The mutagenic damage was dampened by the nitric oxide synthase inhibitor, N(G)-methyl-L-arginine. These data illustrate that mitochondria are a primary target in arsenic-induced genotoxic response and that a better understanding of the mutagenic/carcinogenic mechanism of arsenic should provide a basis for better interventional approach in both treatment and prevention of arsenic-induced cancer.

Preferential action of arsenic trioxide in solid-tumor microenvironment enhances radiation therapy

PURPOSE

To investigate the effect of arsenic trioxide, Trisenox (TNX), on primary cultures of endothelial cells and tumor tissue under varying pH and pO(2) environments and the effects of combined TNX and radiation therapy on experimental tumors.

METHODS AND MATERIALS

Human dermal microvascular endothelial cells were cultured in vitro and exposed to TNX under various combinations of aerobic, hypoxic, neutral, or acidic conditions, and levels of activated JNK MAP kinase were assessed by Western blotting. FSaII fibrosarcoma cells grown in the hind limb of female C3H mice were used to study the effect of TNX on tumor blood perfusion and oxygenation. The tumor-growth delay after a single or fractionated irradiation with or without TNX treatment was assessed.

RESULTS

A single intraperitoneal injection of 8 mg/kg TNX reduced the blood perfusion in FSaII tumors by 53% at 2 hours after injection. To increase the oxygenation of the tumor vasculature during TNX treatment, some animals were allowed to breathe carbogen (95% O(2)/5% CO(2)). Carbogen breathing alone for 2 hours reduced tumor perfusion by 33%. When carbogen breathing was begun immediately after TNX injection, no further reduction occurred in tumor blood perfusion at 2 hours after injection. In vitro, TNX exposure increased activity JNK MAP kinase preferentially in endothelial cells cultured in an acidic or hypoxic environment. In vivo, the median oxygenation in FSaII tumors measured at 3 or 5 days after TNX injection was found to be significantly elevated compared with control tumors. Subsequently, radiation-induced tumor-growth delay was synergistically increased when radiation and TNX injection were fractionated at 3-day or 5-day intervals.

CONCLUSIONS

Trisenox has novel vascular-damaging properties, preferentially against endothelium in regions of low pH or pO(2), which leads to tumor cell death and enhancement of the response of tumors to radiotherapy.

Combined treatment with EGFR inhibitors and arsenite upregulated apoptosis in human EGFR-positive melanomas: a role of suppression of the PI3K-AKT pathway

Epidermal growth factor receptor (EGFR) is expressed, albeit at low or intermediate levels, in human melanomas at the different stages of tumor progression. Coexpression of EGFR with its ligand TGFalpha indicates their role in paracrine and autocrine growth regulation of melanomas. As it was previously observed for several types of cancer, specific inhibitors of EGFR-mediated signaling may reduce antiapoptotic properties of cancer cells and sensitize them to cytotoxic drugs. We recently reported that arsenite, particularly in combination with inhibitors of the PI3K-AKT and mitogen-activated protein kinase (MAPK) kinase (MEK)-extracellular signal-regulated kinase (ERK) pathways, induces high levels of apoptosis in different melanomas. Since EGFR signaling operates via activation of the PI3K-AKT and MEK-ERK pathways, we suggested that the combination of arsenite and EGFR inhibitors might also effectively induce apoptosis in melanoma. Here, we demonstrate that a moderate concentration of arsenite (5-10 muM) indeed upregulates apoptosis induced by EGFR inhibitors in EGFR-positive melanomas. In contrast, induction of apoptosis in melanomas with negligible surface expression of EGFR or with defective EGFR signaling requires direct suppression of the PI3K-AKT and MAPK pathways by specific pharmacological inhibitors in the presence of arsenite. Under these conditions, metastatic melanoma cell lines undergo TNF-related apoptosis-inducing ligand (TRAIL)- and tumor necrosis factor alpha (TNFalpha)-mediated apoptosis. Taken together, these data provide additional approaches in sensitizing melanomas to the cytotoxic effects of specific inhibitors of survival pathways.