Metabolism of arsenic trioxide in acute promyelocytic leukemia cells

Targeting the sulfur-containing amino acid pathway in leukemia

sulfur-containing amino acids have been reported to patriciate in gene regulation, DNA methylation, protein synthesis and other physiological or pathological processes. In recent years, metabolism-related molecules of sulfur-containing amino acids affecting the occurrence, development and treatment of tumors have been implicated in various disorders, especially in leukemia. Here, we summarize current knowledge on the sulfur-containing amino acid metabolism pathway in leukemia and examine ongoing efforts to target this pathway, including treatment strategies targeting (a) sulfur-containing amino acids, (b) metabolites of sulfur-containing amino acids, and (c) enzymes and cofactors related to sulfur-containing amino acid metabolism in leukemia. Future leukemia therapy will likely involve innovative strategies targeting the sulfur-containing amino acid metabolism pathway.

Traditional Chinese medicine for acute myelocytic leukemia therapy: exploiting epigenetic targets

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy with historically high mortality rates. The treatment strategies for AML is still internationally based on anthracyclines and cytarabine, which remained unchanged for decades. With the rapid advance on sequencing technology, molecular targets of leukemogenesis and disease progression related to epigenetics are constantly being discovered, which are important for the prognosis and treatment of AML. Traditional Chinese medicine (TCM) is characterized by novel pharmacological mechanisms, low toxicity and limited side effects. Several biologically active ingredients of TCM are effective against AML. This review focuses on bioactive compounds in TCM targeting epigenetic mechanisms to address the complexities and heterogeneity of AML.

Monomethylarsonous acid binds to Cys-104α and Cys-112β of hemoglobin in acute promyelocytic leukemia patients treated with arsenic trioxide

Arsenic trioxide (As₂O₃) has prominent effect in treating acute promyelocytic leukemia (APL). Identification of arsenic-binding proteins has gained attention for their important biological functions. However, none has been published concerning the binding mechanism of arsenic with hemoglobin (Hb) in APL patients after treatment of As₂O₃. The present study discloses the binding sites of arsenic on Hb in APL patients. Concentrations of inorganic arsenic (iAs), monomethyl arsenic (MMA), and dimethyl arsenic (DMA) in erythrocytes of APL patients were quantified using HPLC-inductively coupled plasma-mass spectroscopy (HPLC-ICP-MS). Hb-bound arsenic was identified by size-exclusion chromatography ICP-MS. The binding sites of arsenic on Hb were determined by mass spectrometry (MS). The concentration trend of arsenic species in erythrocytes of 9 APL patients treated with As₂O₃ was iAs>MMA>DMA, and MMA was the predominant methylated arsenic metabolite. Size-exclusion chromatography separation of free and protein-bound arsenic by simultaneous monitoring of ⁵⁷Fe and ⁷⁵As demonstrated the presence of Hb-bound arsenic. MS information suggested monomethylarsonous (MMA^III) was the dominant arsenic bound to Hb, and further identified that Cys-104α and Cys-112β were two binding sites of MMA^III in Hb. MMA^III binding to Cys-104α and Cys-112β was responsible for arsenic accumulation in erythrocytes of APL patients. This interaction may contribute to understand the therapeutic effect of As₂O₃ as an anticancer drug and its toxicity on APL patients.

Genomic DNA hydroxymethylation reveals potential role in identification of lung injury in coal-burning arsenicosis populations

Arsenic (As) is a toxic metalloid element that causes lung cancer and multiple non-malignant respiratory diseases. The toxicity of arsenic is mediated in part by epigenetic mechanisms, such as alterations in DNA methylation. While increasing studies have highlighted the potential importance of arsenic exposure to DNA methylation patterns and the subsequent risks for arsenic toxicity, there has been little focus on DNA hydroxymethylation-a negative regulation mechanism of DNA methylation. Therefore, this study aimed to investigate the relationship between genomic DNA methylation/hydroxymethylation and lung injury in arsenicosis populations. First, an increased risk of lung injury and exacerbation of lung function impairment in the arsenicosis population was confirmed. Levels of 5-methylcytosine/deoxycytidine (5 mC/dC), 5-hydroxymethylcytosine/deoxycytidine (5 hmC/dC) and 5 hmC/5 mC in genomic DNA of peripheral blood were decreased in the arsenicosis population compared to in the control. Additionally, multivariate logistic regression models showed an increased risk of chest digital radiography (DR) abnormalities when 5 hmC/dC and 5 hmC/5 mC levels were lower (OR = 3.12 and 3.96, all P < 0.001). For 3 years follow-up, regression analysis showed that a decline in 5 hmC/dC was significantly associated with the decline of lung function parameters [forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) and maximal mid-expiratory flow (MMEF); β = 0.167, 0.122 and 0.073, respectively; all P < 0.05]. Using the receiver operating characteristic (ROC) curve, a combination of 5 hmC/5 dC and 5 hmC/5 mC obtained the highest value for distinguishing lung injury in all subjects (AUC = 0.82, P < 0.01). In contrast, in arsenicosis subjects, 5 hmC/dC was better at distinguishing lung injury (AUC = 0.84, P < 0.01). Together, the results revealed that a decrease in genomic DNA hydroxymethylation markers was associated with lung injury in coal-burning arsenicosis populations. Genomic DNA hydroxymethylation could be a novel biomarker for identifying the risk of lung injury caused by coal-burning arsenicosis.

Pharmacokinetic Characteristics, Tissue Bioaccumulation and Toxicity Profiles of Oral Arsenic Trioxide in Rats: Implications for the Treatment and Risk Assessment of Acute Promyelocytic Leukemia

Oral arsenic trioxide (ATO) has demonstrated a favorable clinical efficiency in the treatment of acute promyelocytic leukemia (APL). However, the pharmacokinetic characteristics, tissue bioaccumulation, and toxicity profiles of arsenic metabolites in vivo following oral administration of ATO have not yet been characterized. The present study uses high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) to assess the pharmacokinetics of arsenic metabolites in rat plasma after oral and intravenous administration of 1 mg kg^-1 ATO. In addition, the bioaccumulation of arsenic metabolites in blood and selected tissues were evaluated after 28 days oral administration of ATO in rats at a dose of 0, 2, 8, and 20 mg kg^-1 d^-1. The HPLC-HG-AFS analysis was complemented by a biochemical, hematological, and histopathological evaluation conducted upon completion of ATO treatment. Pharmacokinetic results showed that arsenite (As^III) reached a maximum plasma concentration rapidly after initial dosing, and the absolute bioavailability of As^III was 81.03%. Toxicological results showed that the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and white blood cells (WBC) in the 20 mg kg^-1 d^-1 ATO group were significantly increased compared to the control group (p < 0.05). The distribution trend of total arsenic in the rat was as follows: whole blood > kidney > liver > heart. Dimethylated arsenic (DMA) was the predominant bioaccumulative metabolite in the whole blood, liver, and heart, while monomethylated arsenic (MMA) was the predominant one in the kidney. Collectively, these results revealed that oral ATO was rapidly absorbed, well-tolerated, and showed organ-specific and dose-specific bioaccumulation of arsenic metabolites. The present study provides preliminary evidence for clinical applications and the long-term safety evaluation of oral ATO in the treatment of APL.

Monomethylated arsenic was the Major methylated arsenic in Red blood cells of acute promyelocytic leukemia patients treated with arsenic trioxide

BACKGROUND

Arsenic trioxide (ATO) has been successfully applied in the treatment of acute promyelocytic leukemia (APL). Arsenic metabolites including inorganic arsenic and methylated arsenic could lead to different toxicity and curative effect. This study aims to establish a method to determine arsenic species in red blood cells (RBCs), clarify the distribution characteristics of arsenic species in RBCs.

METHODS

Steady state blood samples were collected from 97 APL patients. H₂O₂ and HClO₄ were used to release the hemoglobin bounding arsenic and precipitate protein. Arsenite (iAs^III), arsenate (iAs^V), monomethylarsonic acid (MMA^V) and dimethylarsinic acid (DMA^V) in plasma and RBCs were detected by HPLC-HG-AFS. Free and bound arsenic species in RBCs were separated by 30 kDa molecular mass cutoff filters and determined to evaluate hemoglobin binding capacity of different arsenic species.

RESULTS

The method was validated with accuracy ranged from 84.75% to 104.13%. Arsenic species in RBCs followed the trend iAs > MMA > DMA (p < 0.01), while the concentration of DMA was significantly higher than iAs and MMA in plasma (p < 0.01). The correlation between iAs concentration in plasma and corresponding RBCs arsenic level was weak. And the concentrations of DMA and MMA in plasma were moderately positive correlated with those in RBCs. Hemoglobin-binding ratios of iAs, MMA and DMA were all over 70 %.

CONCLUSIONS

In this study, we provided a reliable method to determine arsenic species in RBCs of APL patients treated with ATO by HPLC-HG-AFS. It was confirmed that the concentration of DMA is the highest in plasma, while MMA is the most predominant methylated arsenic in RBCs. High affinity of MMA with human Hb was responsible for the accumulation of arsenic in RBCs of APL patients.

Induction of Cell Cycle Arrest in MKN45 Cells after Schiff Base Oxovanadium Complex Treatment Using Changes in Gene Expression of CdC25 and P53

Compounds containing heavy metals such as vanadium, nickel, and cobalt may be useful for the treatment of various diseases. Multiple studies have been carried out on the anticancer effects of vanadium-contained compounds on different cell types. This study aimed to evaluate the role of schiff base oxovanadium complex ([N,N'-bis(3-methoxy-salicylidene)-1,2-phenylenediamine]Vanadium(IV) Oxide Complex) on cell cycle arrest and different cell cycle phases in MKN45 cell of gastric cancer. Schiff base oxovanadium complex was used to assessthe amount of cytotoxicity via cell viability test. PI color and flow cytometry technique were applied to evaluate the effects of vanadium synthetic compounds on cell cycle phases; subsequently, we analyzed the change rates of gene expression in P53, GADD45, and CDC25 genes, which are involved in cell division phases. The findings indicated that the vital activities of time-dependent and concentration-dependent MKN45 cells with schiff base oxovanadium complex were significantly reduced; therefore, this complex is able to inhibit the migration of cancer cells and metastatic activities in a time-dependent mode. Cell cycle arrest was obtained after 48 h of treatment in phase G2/M at 1 microgram/milliliter (μg/ml) concentration. This is probably attributed to the increased gene expression of P53 and GADD45 genes and reduced gene expression of CDC25 gene. Compounds containing such heavy metals as vanadium decrease the growth, proliferation, and migration of MKN45 cells. They arrest cell cycle in phase G2/M via changing the controllers of cell division phases activated due to DNA damage.

Arsenic induced epigenetic changes and relevance to treatment of acute promyelocytic leukemia and beyond

Epigenetic alterations regulate gene expression without changes in the DNA sequence. It is well-demonstrated that aberrant epigenetic changes contribute to the leukemogenesis of acute promyelocytic leukemia (APL). Arsenic trioxide (ATO) is one of the most common drugs used in the frontline treatment of APL that act through targeting and destabilizing the PML/RARα oncofusion protein. ATO together with all-trans retinoic acid (ATRA) lead to durable remission of more than 90% non-high-risk APL patients, turning APL treatment into a paradigm of oncoprotein targeted cure. Although relapse and drug resistance in APL are yet to be resolved in the clinic, epigenetic machineries might hold the key to address this issue. Further, ATO also showed promising anticancer activities against a variety of malignancies, but its application is particularly restricted due to limited understanding of the mechanism. Thus, a thorough understanding of epigenetic mechanism behind anti-leukemic effects of ATO would benefit the development of ATO-based anticancer strategy. Role of ATRA on APL associated epigenetic alterations has been extensively studied and reviewed. Recently, accumulating evidence suggest that ATO also induces some epigenetic changes that might favor APL eradication. In this article, we comprehensively discuss arsenic induced epigenetic changes and its relevance in APL treatment and beyond, so as to provide novel insights into overcoming arsenic resistance in APL and promote application of this drug to other malignancies.

Biotransformation of arsenic trioxide by AS3MT favors eradication of acute promyelocytic leukemia: revealing the hidden facts

Arsenic trioxide (ATO) is one of the most effective drugs for treatment of acute promyelocytic leukemia (APL). It could specifically target the PML/RARα fusion oncoprotein stability and induces APL cell differentiation as well as apoptosis. Although many studies have been conducted to document the anticancer effects and mechanism of ATO, there is little information about the association between biotransformation of ATO to active arsenic metabolites and APL therapy. Generally, ATO can be rapidly converted into trivalent methylated metabolites by arsenic (+3 oxidation state) methyltransferase (AS3MT) mostly in liver and redistributed to bloodstream of APL patients who receiving ATO treatment, thereby leading to a balance between cytotoxicity and differentiation, which is proposed to be the key event in successful treatment of APL. In this review, we comprehensively discussed possible roles of AS3MT and methylated arsenic metabolites in APL therapy, so as to reveal the association between individual differences of AS3MT expression and activity with the therapeutic efficacy of ATO in APL patients.

Functional Profiling Identifies Determinants of Arsenic Trioxide Cellular Toxicity

Arsenic exposure is a worldwide health concern associated with an increased risk of skin, lung, and bladder cancer but arsenic trioxide (AsIII) is also an effective chemotherapeutic agent. The current use of AsIII in chemotherapy is limited to acute promyelocytic leukemia (APL). However, AsIII was suggested as a potential therapy for other cancer types including chronic myeloid leukemia (CML), especially when combined with other drugs. Here, we carried out a genome-wide CRISPR-based approach to identify modulators of AsIII toxicity in K562, a human CML cell line. We found that disruption of KEAP1, the inhibitory partner of the key antioxidant transcription factor Nrf2, or TXNDC17, a thioredoxin-like protein, markedly increased AsIII tolerance. Loss of the water channel AQP3, the zinc transporter ZNT1 and its regulator MTF1 also enhanced tolerance to AsIII whereas loss of the multidrug resistance protein ABCC1 increased sensitivity to AsIII. Remarkably, disruption of any of multiple genes, EEFSEC, SECISBP2, SEPHS2, SEPSECS, and PSTK, encoding proteins involved in selenocysteine metabolism increased resistance to AsIII. Our data suggest a model in which an intracellular interaction between selenium and AsIII may impact intracellular AsIII levels and toxicity. Together this work revealed a suite of cellular components/processes which modulate the toxicity of AsIII in CML cells. Targeting such processes simultaneously with AsIII treatment could potentiate AsIII in CML therapy.

Methyltransferase DNMT3B in leukemia

DNA methyltransferases (DNMTs) are highly conserved DNA-modifying enzymes that play important roles in epigenetic regulation and they are involved in cell proliferation, differentiation, and apoptosis. In mammalian cells, three active DNMTs have been identified: DNMT1 acts as a maintenance methyltransferase to replicate preexisting methylation patterns, whereas DNMT3A and DNMT3B primarily act as de novo methyltransferases that are responsible for establishing DNA methylation patterns by adding a methyl group to cytosine bases. The expression of DNMT3B is widespread in a variety of hematological cells and it is altered in each type of leukemia, which is associated with its pathogenesis, progression, treatment, and prognosis. Here, we review current information on DNMT3B in leukemia, including its expression, single-nucleotide polymorphisms, mutations, regulation, function, and clinical value for anti-leukemic therapy and prognosis.

The suppressive effect of arsenic trioxide on TET2-FOXP3-Lyn-Akt axis-modulated MCL1 expression induces apoptosis in human leukemia cells

Arsenic trioxide (ATO) has been reported to inhibit the activity of Ten-eleven translocation methylcytosine dioxygenase (TET). TET modulates FOXP3 expression, while dysregulation of FOXP3 expression promotes the malignant progression of leukemia cells. We examined the role of TET-FOXP3 axis in the cytotoxic effects of ATO on the human acute myeloid leukemia cell line, U937. ATO-induced apoptosis in U937 cells was characterized by activation of caspase-3/-9, mitochondrial depolarization, and MCL1 downregulation. In addition, ATO-treated U937 cells showed ROS-mediated inhibition of TET2 transcription, leading to downregulation of FOXP3 expression and in turn, suppression of FOXP3-mediated activation of Lyn and Akt. Overexpression of FOXP3 or Lyn minimized the suppressive effect of ATO on Akt activation and MCL1 expression. Promoter luciferase activity and chromatin immunoprecipitation assays revealed the crucial role of Akt-mediated CREB phosphorylation in MCL1 transcription. Further, ATO-induced Akt inactivation promoted GSK3β-mediated degradation of MCL1. Transfection of constitutively active Akt expression abrogated ATO-induced MCL1 downregulation. MCL1 overexpression lessened the ATO-induced depolarization of mitochondrial membrane and increased the viability of ATO-treated cells. Thus, our data suggest that ATO induces mitochondria-mediated apoptosis in U937 cells through its suppressive effect on TET2-FOXP3-Lyn-Akt axis-modulated MCL1 transcription and protein stabilization. Our findings also indicate that the same pathway underlies ATO-induced death in human leukemia HL-60 cells.

Oncogenomic disruptions in arsenic-induced carcinogenesis

Chronic exposure to arsenic affects more than 200 million people worldwide, and has been associated with many adverse health effects, including cancer in several organs. There is accumulating evidence that arsenic biotransformation, a step in the elimination of arsenic from the human body, can induce changes at a genetic and epigenetic level, leading to carcinogenesis. At the genetic level, arsenic interferes with key cellular processes such as DNA damage-repair and chromosomal structure, leading to genomic instability. At the epigenetic level, arsenic places a high demand on the cellular methyl pool, leading to global hypomethylation and hypermethylation of specific gene promoters. These arsenic-associated DNA alterations result in the deregulation of both oncogenic and tumour-suppressive genes. Furthermore, recent reports have implicated aberrant expression of non-coding RNAs and the consequential disruption of signaling pathways in the context of arsenic-induced carcinogenesis. This article provides an overview of the oncogenomic anomalies associated with arsenic exposure and conveys the importance of non-coding RNAs in the arsenic-induced carcinogenic process.

Arsenic trioxide exposure accelerates colon preneoplasic aberrant crypt foci induction regionally through mitochondrial dysfunction

Arsenic poisoning is a worldwide problem. Thus, we studied the effects of arsenic trioxide (ATO) administration on a 1,2-dimethylhydrazine (DMH)-induced preneoplasic colon carcinogenesis model. Mice were separated into four study groups; the control group received only vehicles. The ATO group received daily a 2.5 mg kg^-1 dose for 4 weeks. The DMH group received DMH (20 mg kg^-1) twice in two weeks. The third group (D-ATO) had the same as the DMH group with ATO administration starting at week 10. At the end of 14 weeks, colons from sacrificed mice were taken, segmented into distal and proximal and subjected to aberrant crypt foci (ACF), aberrant crypt (AC) counting, alcian blue, H&E and Hoechst histological study and lastly oxidative stress marker analysis as well as mitochondrial swelling assessment. Data showed a significant increase in ACF and AC after DMH treatment, which was further increased after ATO addition. A perturbed histological structure was observed and loss of mucin producing cells in the colon tissue was observed. An important impact on the distal colon compared to the proximal one was noticed. The oxidative stress balance showed a similar pattern with an increase in MPO, NO/l-ornithine balance and MDA, while a decrease was observed in the antioxidant enzymes (CAT, SOD and GSH). In all parameters analyzed, the distal colons showed higher values than proximal. Furthermore, histological cell death analysis in combination with mitochondrial permeability pore opening suggested ATO contribution in the pathological effect. Our study has shown that ATO administration accelerated colon cancer development suggesting the heaviness of such treatments and the need to explore combinations and cycle type formulas.

The antitumor effects of arsenic trioxide in mantle cell lymphoma via targeting Wnt/β‑catenin pathway and DNA methyltransferase-1

Mantle cell lymphoma (MCL) is an aggressive non‑Hodgkin lymphoma (NHL) with poor prognosis. The rapid progression and frequently relapse make it urgent to identify therapeutic agents with potent antitumor effect. Increasing evidence indicated that dysregulation of Wnt/β‑catenin pathway and abnormal methylation appeared to promote tumorigenesis. Arsenic trioxide (As2O3, ATO) has been reported effective in many hematologic malignancies in recent studies, however, the mechanism and effects of ATO in MCL still need further research. In this study, ATO was shown to promote apoptosis and to inhibit cell viability in MCL cell lines, whereas, the expression of DNA methyltransferase-1 (DNMT-1), β‑catenin and the downstream molecules of Wnt/β‑catenin pathway such as c‑myc, cyclin D1 and MMP7 were all decreased in a dose-dependent manner with ATO. ATO also attenuated upregulation of β‑catenin after LiCl stimulation and provided synergistic effect with 5-azacytidine (5-azaC) on the DNMT-1 inhibition. The results indicated that ATO may suppress MCL by targeting Wnt/β‑catenin pathway and DNMT-1. These findings may guide drug usage of ATO in clinical therapy for MCL.

Demethylation and alterations in the expression level of the cell cycle-related genes as possible mechanisms in arsenic trioxide-induced cell cycle arrest in human breast cancer cells

Arsenic trioxide (As₂O₃) has been used clinically as an anti-tumor agent. Its mechanisms are mostly considered to be the induction of apoptosis and cell cycle arrest. However, the detailed molecular mechanisms of its anti-cancer action through cell cycle arrest are poorly known. Furthermore, As₂O₃ has been shown to be a potential DNA methylation inhibitor, inducing DNA hypomethylation. We hypothesize that As₂O₃ may affect the expression of cell cycle regulatory genes by interfering with DNA methylation patterns. To explore this, we examined promoter methylation status of 24 cell cycle genes in breast cancer cell lines and in a normal breast tissue sample by methylation-specific polymerase chain reaction and/or restriction enzyme-based methods. Gene expression level and cell cycle distribution were quantified by real-time polymerase chain reaction and flow cytometric analyses, respectively. Our methylation analysis indicates that only promoters of RBL1 (p107), RASSF1A, and cyclin D2 were aberrantly methylated in studied breast cancer cell lines. As₂O₃ induced CpG island demethylation in promoter regions of these genes and restores their expression correlated with DNA methyltransferase inhibition. As₂O₃ also induced alterations in messenger RNA expression of several cell cycle-related genes independent of demethylation. Flow cytometric analysis revealed that the cell cycle arrest induced by As₂O₃ varied depending on cell lines, MCF-7 at G1 phase and both MDA-MB-231 and MDA-MB-468 cells at G2/M phase. These changes at transcriptional level of the cell cycle genes by the molecular mechanisms dependent and independent of demethylation are likely to represent the mechanisms of cell cycle redistribution in breast cancer cells, in response to As₂O₃ treatment.

Hypomethylation of inflammatory genes (COX2, EGR1, and SOCS3) and increased urinary 8-nitroguanine in arsenic-exposed newborns and children

Early-life exposure to arsenic increases risk of developing a variety of non-malignant and malignant diseases. Arsenic-induced carcinogenesis may be mediated through epigenetic mechanisms and pathways leading to inflammation. Our previous study reported that prenatal arsenic exposure leads to increased mRNA expression of several genes related to inflammation, including COX2, EGR1, and SOCS3. This study aimed to investigate the effects of arsenic exposure on promoter DNA methylation and mRNA expression of these inflammatory genes (COX2, EGR1, and SOCS3), as well as the generation of 8-nitroguanine, which is a mutagenic DNA lesion involved in inflammation-related carcinogenesis. Prenatally arsenic-exposed newborns had promoter hypomethylation of COX2, EGR1, and SOCS3 in cord blood lymphocytes (p<0.01). A follow-up study in these prenatally arsenic-exposed children showed a significant hypomethylation of these genes in salivary DNA (p<0.01). In vitro experiments confirmed that arsenite treatment at short-term high doses (10-100μM) and long-term low doses (0.5-1μM) in human lymphoblasts (RPMI 1788) caused promoter hypomethylation of these genes, which was in concordance with an increase in their mRNA expression. Additionally, the level of urinary 8-nitroguanine was significantly higher (p<0.01) in exposed newborns and children, by 1.4- and 1.8-fold, respectively. Arsenic accumulation in toenails was negatively correlated with hypomethylation of these genes and positively correlated with levels of 8-nitroguanine. These results indicated that early-life exposure to arsenic causes hypomethylation of COX2, EGR1, and SOCS3, increases mRNA expression of these genes, and increases 8-nitroguanine formation. These effects may be linked to mechanisms of arsenic-induced inflammation and cancer development later in life.

Arsenic trioxide induces cell cycle arrest and alters DNA methylation patterns of cell cycle regulatory genes in colorectal cancer cells

AIMS

Cell cycle dysregulation is important in tumorigenesis. Transcriptional silencing of cell cycle regulatory genes, due to DNA methylation, is a common epigenetic event in malignancies. As₂O₃ has been shown to induce cell cycle arrest and also to be a potential hypomethylating agent. Our study aimed to investigate DNA methylation patterns of cell cycle regulatory genes promoters, the effects of Arsenic trioxide (As₂O₃) on the methylated genes and cell cycle distribution in colorectal cancer (CRC) cell lines.

MAIN METHODS

The methylation-specific PCR (MSP) and/or restriction enzyme-based methods were used to study the promoter methylation patterns of 24 cell cycle regulatory genes in CRC cell lines. Gene expression level and cell cycle distribution were determined by Real-time PCR and flow cytometric analyses, respectively.

KEY FINDINGS

Our methylation analysis indicated that only promoters of RBL1 (p107), CHFR and p16 genes were aberrantly methylated in three cell lines. As₂O₃ significantly decreased DNA methylation in promoter regions of these genes and restored their expression. We found that As₂O₃ significantly reduced the expression of DNA methyltransferase 1 (DNMT1) and increased arsenic methyltransferase (AS3MT). Furthermore, As₂O₃ altered transcriptional activity of several unmethylated cell cycle regulatory genes including cyclin B1, E1, D1, GADD45A and p21. Cell cycle flow cytometry analysis showed As₂O₃ induced G2/M arrest in all three cell lines.

SIGNIFICANCE

These data suggest that demethylation and alteration in the expression level of the cell cycle-related genes may be possible mechanisms in As₂O₃-induced cell cycle arrest in colorectal cancer cells.

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

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

Methylated arsenic metabolites bind to PML protein but do not induce cellular differentiation and PML-RARα protein degradation

Arsenic trioxide (As₂O₃) is one of the most effective therapeutic agents used for patients with acute promyelocytic leukemia (APL). The probable explanation for As₂O₃-induced cell differentiation is the direct targeting of PML-RARα oncoprotein by As₂O₃, which results in initiation of PML-RARa degradation. However, after injection, As₂O₃ is rapidly methylated in body to different intermediate metabolites such as trivalent monomethylarsonous acid (MMA^III) and dimethylarsinous acid (DMA^III), therefore, it remains unknown that which arsenic specie is actually responsible for the therapeutic effects against APL. Here we have shown the role of As₂O₃ (as iAs^III) and its intermediate metabolites (i.e., MMA^III/DMA^III) in NB4 cells. Inorganic iAs^III predominantly showed induction of cell differentiation, while MMA^III and DMA^III specifically showed to induce mitochondria and endoplasmic reticulum-mediated apoptosis, respectively. On the other hand, in contrast to iAs^III, MMA^III showed stronger binding affinity for ring domain of PML recombinant protein, however, could not induce PML protein SUMOylation and ubiquitin/proteasome degradation. In summary, our results suggest that the binding of arsenicals to the ring domain of PML proteins is not associated with the degradation of PML-RARa fusion protein. Moreover, methylated arsenicals can efficiently lead to cellular apoptosis, however, they are incapable of inducing NB4 cell differentiation.

Comparison of accumulation of four metalloids in Allium sativum

In this study, we evaluated the accumulation and metabolism of four metalloids: arsenic (As), selenium (Se), antimony (Sb), and tellurium (Te) in garlic to determine whether garlic can be used for the phytoremediation of those metalloids. Garlic was able to efficiently accumulate As and Se, the two-fourth-period metalloids. However, it was not able to accumulate Sb and Te, the two-fifth-period metalloids, because their bioaccumulation factors were below one. Speciation analyses revealed that four metalloids could be metabolized in garlic, although their metabolites could not be identified yet. Results also suggested that garlic was able to distinguish the metalloids in groups 15 and 16 and the fourth and fifth periods, i.e., As, Se, Sb, and Te. Therefore, garlic is one of the potential plants for the phytoremediation of the fourth-period metalloids.

Arsenic (+3 oxidation state) methyltransferase is a specific but replaceable factor against arsenic toxicity

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AS3MT catalyzed the methylation of arsenic.

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Selenium and tellurium were not methylated in the presence of AS3MT.

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AS3MT knockdown had no effect on the cytotoxicity of arsenic.

Inorganic metalloids, such as arsenic (As), antimony (Sb), selenium (Se), and tellurium (Te), are methylated in biota. In particular, As, Se, and Te are methylated and excreted in urine. The biomethylation is thought to be a means to detoxify the metalloids. The methylation of As is catalyzed by arsenic (+3 oxidation state) methyltransferase (AS3MT). However, it is still unclear whether AS3MT catalyzes the methylation of the other metalloids. It is also unclear whether other factors catalyze the As methylation instead of AS3MT. Recombinant human AS3MT (rhAS3MT) was prepared and used in the in vitro methylation of As, Se, and Te. As, but not Se and Te, was specifically methylated in the presence of rhAS3MT. Then, siRNA targeting AS3MT was introduced into human hepatocarcinoma (HepG2) cells. Although AS3MT protein expression was completely silenced by the gene knockdown, no increase in As toxicity was found in the HepG2 cells transfected with AS3MT-targeting siRNA. We conclude that AS3MT catalyzes the methylation of As and not other biomethylatable metalloids, such as Se and Te. We speculate that other methylation enzyme(s) also catalyze the methylation of As in HepG2 cells.