Corrigendum to "Immunotoxicity and biodistribution analysis of arsenic trioxide in C57B1/6 mice following a 2-week inhalation exposure": [Toxicol. Appl. Pharmacol. 241 (2009) 253-259]

An extracellular pH-driven targeted multifunctional manganese arsenite delivery system for tumor imaging and therapy

Expanding the use of arsenic trioxide (ATO, As2O3) in cancer chemotherapy has received extensive attention in recent years owing to its remarkable efficacy in treating acute promyelocytic leukemia (APL). To date, the use of ATO for clinical treatment of solid tumors is still limited by its poor biocompatibility and severe toxic side effects. To address these limitations, here we developed a pH-low insertion peptide (pHLIP) modified ATO-based multifunctional drug-delivery system (DDS), which is termed MnAs@SiO2-pHLIP. With the coating of pHLIP, MnAs@SiO2-pHLIP could efficiently target the acidic tumor microenvironment, resulting in high intracellular accumulation of the DDS. As a "smart" nanoparticle (NP) platform, the DDS could controllably discharge the loaded ATO in response to acidic environments, which promotes the apoptosis of cancer cells. The features of controlled release capacity and the outstanding targeting ability contribute to better anticancer efficacy and less toxicity towards normal tissues compared with free ATO. It is worth noting that the acidic tumor microenvironment would also trigger the release of manganese ions (Mn2+) that brighten the T1 signal, which is exploited for real-time monitoring via contrast-enhanced magnetic resonance imaging (MRI). These multifunctional features, as demonstrated by both in vitro and in vivo experiments, could potentially expand the use of ATO to the treatment of solid tumors. We believe that MnAs@SiO2-pHLIP could serve as an auspicious agent for cancer theranostics and find tremendous applications in cancer management.

Sestrins as a Therapeutic Bridge between ROS and Autophagy in Cancer

The regulation of Reactive Oxygen Species (ROS) levels and the contribution therein from networks regulating cell metabolism, such as autophagy and the mTOR-dependent nutrient-sensing pathway, constitute major targets for selective therapeutic intervention against several types of tumors, due to their extensive rewiring in cancer cells as compared to healthy cells. Here, we discuss the sestrin family of proteins—homeostatic transducers of oxidative stress, and drivers of antioxidant and metabolic adaptation—as emerging targets for pharmacological intervention. These adaptive regulators lie at the intersection of those two priority nodes of interest in antitumor intervention—ROS control and the regulation of cell metabolism and autophagy—therefore, they hold the potential not only for the development of completely novel compounds, but also for leveraging on synergistic strategies with current options for tumor therapy and classification/stadiation to achieve personalized medicine.

Effect of As2O3 on colorectal CSCs stained with ALDH1 in primary cell culture in vitro

Colorectal carcinoma (CRC) is one of the most common types of malignant tumor in humans, and its morbidity is on the increase in economically transitioning countries. Due to its high toxicity, the use of the Chinese Traditional Medicine arsenic (As₂O₃) is limited. However, certain studies have reported that As₂O₃ induces differentiation of tumor cells, promotes tumor cell apoptosis and inhibits tumor cell proliferation, although the number of studies on the effects of As₂O₃ on cancer stem cells (CSCs) of CRC is limited. In order to research the effects of different concentrations of As₂O₃ on CRC cells and colorectal CSCs in vitro, aldehyde dehydrogenase 1 (ALDH1) was sued to stain the cytoplasm of colorectal CSCs and DAPI was used to stain the nuclei of all tumor cells. Through observing the effect of different concentrations of As₂O₃ on CRC cells and colorectal CSCs, it was demonstrated that a sufficient concentration of As₂O₃ clearly inhibited the conversion from colorectal CSCs to CRC cells and increased the density of CSCs.

Enhanced antitumor activity of combined megestrol acetate and arsenic trioxide treatment in liver cancer cells

Liver cancer is an aggressive malignancy with a very high fatality rate. Although megestrol acetate (MA) and arsenic trioxide (ATO) have shown an antitumor effect in liver cancer cells, the therapeutic benefits of MA or ATO alone in patients with liver cancer were limited. The aim of the present study was to elucidate whether the co-treatment of MA/ATO could enhance antitumor efficacy in liver cancer cell lines (Hep G2 and BEL 7402) and explore the underlying anti-cancer mechanisms. The cell viability, apoptotic response and expression levels of associated proteins were detected by Cell Counting Kit-8 assay, flow cytometry and western blotting, respectively. An xenograft model in nude mice bearing a Hep G2 tumor was used to estimate tumor growth in vivo. Co-treatment with MA/ATO markedly improved the inhibition of cell viability, enhanced apoptosis, and increased the phosphorylation of p38, c-Jun N-terminal kinase 1/2 and extracellular signal-regulated kinase 1/2 on liver cancer cell lines. Furthermore, the tumor growth in the murine Hep G2 cancer xenograft model was significantly inhibited by combined treatment with MA/ATO. The results indicated that MA/ATO combined treatment enhanced antitumor efficacy and possessed potential application for treating liver cancer.

Distinct toxicological characteristics and mechanisms of Hg2+ and MeHg in Tetrahymena under low concentration exposure

Inorganic divalent mercury complexes (Hg²⁺) and monomethylmercury complexes (MeHg) are the main mercury species in aquatic systems and their toxicity to aquatic organisms is of great concern. Tetrahymena is a type of unicellular eukaryotic protozoa located at the bottom of food chain that plays a fundamental role in the biomagnification of mercury. In this work, the dynamic accumulation properties, toxicological characteristics and mechanisms of Hg²⁺ and MeHg in five Tetrahymena species were evaluated in detail. The results showed that both Hg²⁺ and MeHg were ingested and exhibited inhibitory effects on the proliferation or survival of Tetrahymena species. However, the ingestion rate of MeHg was significantly higher than that of Hg²⁺. The mechanisms responsible for the toxicity of MeHg and Hg²⁺ were different, although both chemicals altered mitochondrial membrane potential (MMP). MeHg disrupted the integrity of membranes while Hg²⁺ had detrimental effects on Tetrahymena as a result of the increased generation of reactive oxygen species (ROS). In addition, the five Tetrahymena species showed different capacities in accumulating Hg²⁺ and MeHg, with T. corlissi exhibiting the highest accumulations. The study also found significant growth-promoting effect on T. corlissi under low concentration exposure (0.003 and 0.01μg Hg/mL (15 and 50nM)), suggesting different effect and mechanism that should be more closely examined when assessing the bioaccumulation and toxicity of mercury in aquatic ecosystems.

Effects of arsenic trioxide on the expression of ezrin in hepatocellular carcinoma

The aim of the study was to investigate the effects of arsenic trioxide (As2O3) treatment on the expression of ezrin and serum alpha-fetoprotein (AFP) levels in hepatocellular carcinoma (HCC).A total of 24 patients (20 males and 4 females) with resectable HCC were treated with venous injection of As2O3 for 14 days (10 mg/d) before surgery. The ezrin expression and serum AFP levels were assessed before and after treatment, respectively.The serum AFP levels were 325.5 ng/L before treatment and 278.6 ng/L after treatment, with statistical significant difference (Z = -2.360, P < .05). The expression of ezrin was negative, weak positive, and strong positive in 11, 7, and 6 cases, respectively, before As2O3 treatment, and 17, 5, 2 cases respectively after the treatment. The difference between the 2 groups was statistically significant (χ = 5.619, P < .05). Also, the results showed that there was a significant correlation between the high serum AFP level (AFP ≥ 500 ng/L) and high expression of ezrin (χ = 8.080, P < .05).As2O3 treatment can significantly downregulate the expression of ezrin in HCC.

Targeting hepatocellular carcinoma with piperine by radical-mediated mitochondrial pathway of apoptosis: An in vitro and in vivo study

Redox mediated cancer therapeutics are of immense interest in the recent decade due to their anticancer activity. Piperine is the principal alkaloid of black and long pepper. Although its anticancer activity has been reported in number of cancers , the precise molecular mechanism of action remains to be unravelled. Hence, in this study, for the first time, we delineated the mechanistic insight into the effect of piperine against hepatocellular carcinoma (HCC).MTT analysis determined the dose and time dependent cytotoxicity of piperine against Hep G2 cells. Further molecular studies evidenced the prooxidant property of piperine by inducing H₂O₂ driven mitochondria-mediated apoptosis in Hep G2 cells by inhibiting the peroxide detoxifying enzyme Catalase. Molecular docking and western blotting analysis uncovered the piperine mediated receptor tyrosine kinase inhibition and mitigation of HCC progression. In addition, histological investigations of piperine - treated, DEN-induced HCC rats showed significant prognosis with apoptotic cell death. Whereas,co-treatment of an antioxidant EUK-134 significantly abrogated its chemotherapeutic activity substantiating its radical-mediated anticancer property. Altogether, this study shows that the piperine may be a promising prooxidant drug for the amelioration of hepatocellular carcinoma.

Low dose of arsenic trioxide inhibits multidrug resistant-related P-glycoprotein expression in human neuroblastoma cell line

This study investigated arsenic trioxide (As2O3), cisplatin (DDP) and etoposide (Vp16) on the anticancer effects and P-glycoprotein (P-gp) expression in neuroblastoma (NB) SK-N-SH cells. The potential influence of As2O3, DDP and Vp16 currently included in NB routine treatment protocols on cytotoxicity in SK-N-SH cells was measured by flow cytometry and drug half-maximal inhibitory concentration (IC50) was established. Moreover, chemotherapeutic agent-mediated changes of cellular expression levels of resistant-related P-gp, was monitored using western blotting. The data showed that As2O3, DDP and Vp16 significantly inhibited the growth and survival of the SK-N-SH cells at different concentration. Notably, the levels of apoptosis were upregulated in SK-N-SH cells with an acceleration of the exposure time and the concentration of As2O3, DDP and Vp16. As2O3, DDP and Vp16 were observed with their IC50 values on SK-N-SH cells being 3 µM, 8 and 100 µg/ml, respectively. Flow cytometry analysis showed that As2O3 at low concentrations in SK-N-SH cells led to enhanced accumulation of cell populations in G2/M phase with increasing the exposure time, and increased levels of apoptosis. In contrast, we observed that SK-N-SH cell populations arrested in S phase by DDP and Vp16. In vitro examination revealed that following pretreatment of SK-N-SH cells with As2O3, the expression of P-gp was not increased. The expression of P-gp downregulation were noted following the group treated by As2O3 at 2 and 3 µM. Exposed to As2O3 at 3 µM for 72 h, SK-N-SH cells exhibited lower expression of P-gp than 2 µM As2O3 for 72 h. In contrast, the expression of P-gp was upregulated by DDP and VP16. In summary, SK-N-SH cells were responsive to chemotherapeutic agent-induced apoptosis in a dose-dependent and time-dependent manner. In particular, ours findings showed that low dose of As2O3 markedly reduced the P-gp expression and increased apoptotic cell death in human NB cell line.

Protective effect of anthocyanidins against sodium dithionite-induced hypoxia injury in C6 glial cells

The present study investigated the neuroprotective effect of anthocyanidins, including cyanidin, delphinidin, malvidin, pelargonidin, and peonidin, against hypoxia in C6 glial cells. The cells were first incubated with a medium containing anthocynidin in normoxia condition and then with a medium containing sodium dithionite (Na2S2O4) in an anaerobic incubator for the hypoxia treatment. Methylthiazole tetrazolium test and evaluation of antioxidant enzyme activities and glutathione concentration were performed on the treated cells. At least 74% of the C6 cells preincubated with 25 mg/L of any of the five anthocyanidins in serum-free Dulbecco's modified Eagle's medium at 37 °C for 24 h survived the hypoxia treatment as compared with a survival rate between 47 and 59% for the control that was preincubated without an anthocyanidin. The cells preincubated with any of the five anthocyanidins showed higher catalase activity and glutathione concentration after the hypoxia treatment as compared with the corresponding samples without the preincubation with anthocyanidin. The cells preincubated with malvidin, pelargonidin, or peonidin also showed higher superoxide dismutase activities. The results of this study justify further research for the development of anthocyanidins into neuroprotective food ingredients against hypoxia injury.

The inhibition of constitutive androstane receptor-mediated pathway enhances the effects of anticancer agents in ovarian cancer cells

BACKGROUND

Ovarian cancer is commonly treated with anticancer agents; however, many tumors become resistant. Resistance is regulated, in part, by P-glycoprotein, which is encoded by the gene multiple drug resistance 1 (MDR1) and functions as a transmembrane efflux pump for the elimination of anticancer agents. Constitutive androstane receptor (CAR) is a nuclear receptor that regulates drug metabolism through control of MDR1 and other genes.

PURPOSE

We examined whether the inhibition of CAR-mediated pathway could influence the cytotoxicity of three anticancer drugs, cisplatin, paclitaxel, and arsenic trioxide, in ovarian cancer cells.

RESULTS

We observed that the cell proliferation of several ovarian cell lines expressing CAR significantly increased when CITCO was combined with anticancer agents compared with any anticancer agent alone. The up-regulation of MDR1 and UGT1A1 by anticancer agents was further enhanced in the presence of CITCO. We confirmed that combining CITCO with anticancer agents induced significantly lower levels of apoptosis than those achieved with any single anticancer drug. CAR down-regulation by RNA interference caused a significant increase in cell growth inhibition and enhancement of apoptosis in the presence of anticancer agents. Combination of CITCO with any anticancer agents significantly enhanced CAR-mediated transcription compared with any anticancer agents alone and CAR down-regulation completely inhibited the transcription in the presence of CITCO and/or anticancer agents.

CONCLUSION

Inhibition of CAR pathway could be a novel therapeutic approach for the augmentation of sensitivity to anticancer agents, or to overcome resistance, in the treatment of ovarian cancer.

Role of arsenic trioxide in the treatment of malignant tumors of the digestive system

Arsenic trioxide (As₂O₃), also named arsenic, is a main ingredient of numerous traditional Chinese herbal recipes and has a long history of clinical application. It has positive anticancer effects and is effective in treating acute promyelocytic leukemia without toxic and side effects. As₂O₃ can induce apoptosis of cancer cells. In recent years, it has been found that As₂O₃ has an apoptosis-promoting effect on tumor cells in many human solid tumors, including liver cancer. Many in vitro and in vivo studies using digestive tract tumor cell lines or animal model have found that As₂O₃ can induce apoptosis and inhibit growth of digestive tract cancer cells. Therefore, As₂O₃ may have an important role in the prevention of malignant tumors of the digestive system. In this article, we discuss the possible cellular and molecular mechanisms by which As₂O₃ induces apoptosis of digestive tract cancer cells.

Factors determining sensitivity and resistance of tumor cells to arsenic trioxide

Previously, arsenic trioxide showed impressive regression rates of acute promyelocytic leukemia. Here, we investigated molecular determinants of sensitivity and resistance of cell lines of different tumor types towards arsenic trioxide. Arsenic trioxide was the most cytotoxic compound among 8 arsenicals investigated in the NCI cell line panel. We correlated transcriptome-wide microarray-based mRNA expression to the IC(50) values for arsenic trioxide by bioinformatic approaches (COMPARE and hierarchical cluster analyses, Ingenuity signaling pathway analysis). Among the identified pathways were signaling routes for p53, integrin-linked kinase, and actin cytoskeleton. Genes from these pathways significantly predicted cellular response to arsenic trioxide. Then, we analyzed whether classical drug resistance factors may also play a role for arsenic trioxide. Cell lines transfected with cDNAs for catalase, thioredoxin, or the anti-apoptotic bcl-2 gene were more resistant to arsenic trioxide than mock vector transfected cells. Multidrug-resistant cells overexpressing the MDR1, MRP1 or BCRP genes were not cross-resistant to arsenic trioxide. Our approach revealed that response of tumor cells towards arsenic trioxide is multi-factorial.

Darinaparsin is a multivalent chemotherapeutic which induces incomplete stress response with disruption of microtubules and Shh signaling

Chemotherapeutics and other pharmaceuticals are common sources of cellular stress. Darinaparsin (ZIO-101) is a novel organic arsenical under evaluation as a cancer chemotherapeutic, but the drug's precise mechanism of action is unclear. Stress granule formation is an important cellular stress response, but the mechanisms of formation, maintenance, and dispersal of RNA-containing granules are not fully understood. During stress, small, diffuse granules initially form throughout the cytoplasm. These granules then coalesce near the nucleus into larger granules that disperse once the cellular stress is removed. Complete stress granule formation is dependent upon microtubules. Human cervical cancer (HeLa) cells, pre-treated with nocodazole for microtubule depolymerization, formed only small, diffuse stress granules upon sodium arsenite treatment. Darinaparsin, as a single agent, also induced the formation of small, diffuse stress granules, an effect similar to that of the combination of nocodazole with sodium arsenite. Darinaparsin inhibited the polymerization of microtubules both in vivo and in vitro. Interestingly, upon removal of darinaparsin, the small, diffuse stress granules completed formation with coalescence in the perinuclear region prior to disassembly. These results indicate that RNA stress granules must complete formation prior to disassembly, and completion of stress granule formation is dependent upon microtubules. Finally, treatment of cells with darinaparsin led to a reduction in Sonic hedgehog (Shh) stimulated activation of Gli1 and a loss of primary cilia. Therefore, darinaparsin represents a unique multivalent chemotherapeutic acting on stress induction, microtubule polymerization, and Shh signaling.

Suppression of low-density lipoprotein oxidation, vascular smooth muscle cell proliferation and migration by a herbal extract of Radix Astragali, Radix Codonopsis and Cortex Lycii

Background

Atherosclerosis is a major cause of death in developed world. Atherosclerosis is characterized by low-density lipoprotein deposition in the arterial wall which ultimately begets the formation of lesions. Rupture of lesions finally leads to clinical events such as heart attack and stroke. Atherosclerosis is a complication associated with diabetes. In patients with diabetes, the risk of atherosclerosis is three to five folds greater than in non-diabetics. Our previous study showed that a herbal extract of Radix Astragali, Radix Codonopsis and Cortex Lycii, namely SR10, could improve glucose homeostasis both in vitro and in vivo. In this study, we want to further investigate the efficacy of SR10 in treating atherosclerosis.

Method

The inhibitory effect of SR10 on low-density lipoprotein oxidation was investigated using free radical-induced erythrocyte hemolysis model and copper ion-induced low-density lipoprotein oxidation model. Since vascular smooth muscle cell proliferation and migration are important processes in atherogenesis, we also examined the effect of SR10 in inhibiting these events.

Results

Our results showed that SR10 inhibited erythrocyte hemolysis with IC₅₀ value at 0.25 mg/ml and significantly prolonged low-density lipoprotein oxidation in vitro. SR10 attenuated platelet derived growth factor-BB-induced vascular smooth muscle cell proliferation by promoting cell cycle arrest at G₀/G₁ phase as well as inhibiting vascular smooth muscle cell migration.

Conclusion

The potential application of SR10 in treating atherosclerosis has been implied in this study. Animal model will be needed to further verify the efficacy of SR10 in future.

Alpha-lipoic acid regulates heme oxygenase gene expression and nuclear Nrf2 activation as a mechanism of protection against arsenic exposure in HepG2 cells

Oxidative stress is a known mechanism induced, among other things, by arsenic toxicity. As a response, the cell triggers the synthesis of antioxidant and stress response elements like glutathione and heme oxygenase. Alpha-lipoic acid (ALA) is a well-known antioxidant that confers protection to oxidative stress conditions. We analyzed the effect of ALA pretreatment on Nrf2-responsive gene expression of HepG2 cells exposed to As(3+). Cells were treated with 5mM ALA and 8h later exposed to 50μM As(3+) for 24h, analyzing MTT-activity, glutathione content, Nrf2 induction and antioxidant gene expression. As(3+) increased glutathione (154%), heme oxygenase, glutamate cystein ligase, modifier subunit and metallothionein (35-fold, 10-fold and 9-fold, respectively). ALA prevented the strong expression of heme oxygenase by As(3+) exposure (from 35- to 5-times of control cells), which correlated with the reduction of Nrf2 observed in As(3+) group. ALA pretreatment can down-modulate the response mediated by Nrf2 and provide protection to As(3+) exposed HepG2 cells.

Photodynamic therapy inhibits P-glycoprotein mediated multidrug resistance via JNK activation in human hepatocellular carcinoma using the photosensitizer pheophorbide a

Background

Multidrug resistance (MDR) is frequently observed after prolonged treatment in human hepatoma with conventional anti-tumor drugs, and photodynamic therapy (PDT) is a recently suggested alternative to overcome MDR. The therapeutic potential of PDT was evaluated in a multidrug resistance (MDR) human hepatoma cell line R-HepG2 with photosensitizer pheophorbide a (Pa).

Results

Our results demonstrated that intracellular accumulation of Pa was not reduced by the overexpression of P-glycoprotein. Pa-based PDT (Pa-PDT) significantly inhibited the growth of R-HepG2 cells with an IC50 value of 0.6 μM. Mechanistic study demonstrated that genomic DNA fragmentation and phosphatidylserine externalization occurred where increase of intracellular singlet oxygen level triggers the phosphorylation of c-Jun N-terminal Kinase (JNK) and leads to activation of intrinsic apoptotic caspases cascade during the Pa-PDT treatment. The cytotoxicity of Pa-PDT, accumulation of sub-G1 population, and depolarization of mitochondrial membrane could be inhibited by JNK inhibitor in the Pa-PDT treated cells. Interestingly, the Pa-PDT induced JNK activation showed inhibitory effect on MDR by the down-regulation of P-glycoprotein in R-HepG2 cells in a dose-dependent manner. In addition, significant reduction of tumor size was obtained in Pa-PDT treated R-HepG2-bearing nude mice with no significant damages in liver and heart.

Conclusion

In summary, our findings provided the first evidence that PDT could inhibit the MDR activity by down-regulating the expression of P-glycoprotein via JNK activation using pheophorbide a as the photosensitizer, and our work proved that Pa-PDT inhibited the growth of MDR hepatoma cells by mitochondrial-mediated apoptosis induction.

Haem-regulated eIF2alpha kinase is necessary for adaptive gene expression in erythroid precursors under the stress of iron deficiency

Haem-regulated eIF2alpha kinase (HRI) is essential for the regulation of globin gene translation and the survival of erythroid precursors in iron/haem deficiency. This study found that that in iron deficiency, fetal definitive erythropoiesis is inhibited at the basophilic erythroblast stage with increased proliferation and elevated apoptosis. This hallmark of ineffective erythropoiesis is more severe in HRI deficiency. Microarray gene profiling analysis showed that HRI was required for adaptive gene expression in erythroid precursors during chronic iron deficiency. The number of genes with expression affected more than twofold increased, from 213 in iron deficiency and 73 in HRI deficiency, to 3135 in combined iron and HRI deficiencies. Many of these genes are regulated by Gata1 and Fog1. We demonstrate for the first time that Gata1 expression in developing erythroid precursors is decreased in iron deficiency, and is decreased further in combined iron and HRI deficiencies. Additionally, Fog1 expression is decreased in combined deficiencies, but not in iron or HRI deficiency alone. Our results indicate that HRI confers adaptive gene expression in developing erythroblasts during iron deficiency through maintaining Gata1/Fog1 expression.

Dithiothreitol abrogates the effect of arsenic trioxide on normal rat liver mitochondria and human hepatocellular carcinoma cells

Arsenic trioxide (ATO) is a known environmental toxicant and a potent chemotherapeutic agent. Significant correlation has been reported between consumption of arsenic-contaminated water and occurrence of liver cancer; moreover, ATO-treated leukemia patients also suffers from liver toxicity. Hence, modulation of ATO action may help to prevent populations suffering from arsenic toxicity as well as help reduce the drug-related side effects. Dithiothreitol (DTT) is a well-known dithiol agent reported to modulate the action of ATO. Controversial reports exist regarding the effect of DTT on ATO-induced apoptosis in leukemia cells. To the best of our knowledge, no report illustrates the modulatory effect of DTT on ATO-induced liver toxicity, the prime target for arsenic. Mitochondria serve as the doorway to apoptosis and have been implicated in ATO-induced cell death. Hence, we attempted to study the modulatory effect of DTT on ATO-induced dysfunction of mammalian liver mitochondria and human hepatocellular carcinoma cell line (Hep3B). We, for the first time, report that ATO produces complex I-mediated electron transfer inhibition, reactive oxygen species (ROS) generation, respiration inhibition, and ATO-induced ROS-mediated mitochondrial permeability transition (MPT) opening. DTT at low concentration (100 muM and less) prevents the effect of ATO-induced complex I-malfunctions. DTT protects mitochondria from ATO-mediated opening of MPT and membrane potential depolarization. DTT also prevented ATO-induced Hep3B cell death. Thus, at low concentrations DTT abrogates the effect of ATO on rat liver mitochondria and Hep3B cell line. Therefore, the present result suggests, that use of low concentration of dithiols as food supplement may prevent arsenic toxicity in affected population.