Drug uptake and pharmacological modulation of drug sensitivity in leukemia by AQP9

Data mining of arsenic-based small molecules geometrics present in Cambridge structural database

Arsenic, ubiquitous in various industrial processes and consumer products, presents both essential functions and considerable toxicity risks, driving extensive research into safer applications. Our investigation, drawing from 7182 arsenic-containing molecules in the Cambridge Structural Database (CSD), outlines their diverse bonding patterns. Notably, 51% of these molecules exhibit cyclic connections, while 49% display acyclic ones. Arsenic forms eight distinct bonding types with other elements, with significant interactions observed, particularly with phenyl rings, O3 and F6 moieties. Top interactions involve carbon, nitrogen, oxygen, fluorine, sulfur, and arsenic itself. We meticulously evaluated average bond lengths under three conditions: without an R-factor cut-off, with R-factor ≤0.075, and with R-factor ≤0.05, supporting the credibility of our results. Comparative analysis with existing literature data enriches our understanding of arsenic's bonding behaviour. Our findings illuminate the structural attributes, molecular coordination, geometry, and bond lengths of arsenic with 68 diverse atoms, enriching our comprehension of arsenic chemistry. These revelations not only offer a pathway for crafting innovative and safer arsenic-based compounds but also foster the evolution of arsenic detoxification mechanisms, tackling pivotal health and environmental challenges linked to arsenic exposure across different contexts.

Alteration of Hepatic Cytochrome P450 Expression and Arachidonic Acid Metabolism by Arsenic Trioxide (ATO) in C57BL/6 Mice

The success of arsenic trioxide (ATO) in acute promyelocytic leukemia has driven a plethora studies to investigate its efficacy in other malignancies. However, the inherent toxicity of ATO limits the expansion of its clinical applications. Such toxicity may be linked to ATO-induced metabolic derangements of endogenous substrates. Therefore, the primary objective of this study was to investigate the effect of ATO on the hepatic formation of arachidonic acid (AA) metabolites, hydroxyeicosatetraenoic acids (HETEs), as well as their most notable producing machinery, cytochrome P450 (CYP) enzymes. For this purpose, C57BL/6 mice were intraperitoneally injected with 8 mg/kg ATO for 6 and 24 h. Total RNA was extracted from harvested liver tissues for qPCR analysis of target genes. Hepatic microsomal proteins underwent incubation with AA, followed by identification/quantification of the produced HETEs. ATO downregulated Cyp2e1, while induced Cyp2j9 and most of Cyp4a and Cyp4f, and this has resulted in a significant increase in 17(S)-HETE and 18(R)-HETE, while significantly decreased 18(S)-HETE. Additionally, ATO induced Cyp4a10, Cyp4a14, Cyp4f13, Cyp4f16, and Cyp4f18, resulting in a significant elevation in 20-HETE formation. In conclusion, ATO altered hepatic AA metabolites formation through modulating the underlying network of CYP enzymes. Modifying the homeostatic production of bioactive AA metabolites, such as HETEs, may entail toxic events that can, at least partly, explain ATO-induced hepatotoxicity. Such modification can also compromise the overall body tolerability to ATO treatment in cancer patients.

Microbial biochemical pathways of arsenic biotransformation and their application for bioremediation

Arsenic is a ubiquitous toxic metalloid, the concentration of which is beyond WHO safe drinking water standards in many areas of the world, owing to many natural and anthropogenic activities. Long-term exposure to arsenic proves lethal for plants, humans, animals, and even microbial communities in the environment. Various sustainable strategies have been developed to mitigate the harmful effects of arsenic which include several chemical and physical methods, however, bioremediation has proved to be an eco-friendly and inexpensive technique with promising results. Many microbes and plant species are known for arsenic biotransformation and detoxification. Arsenic bioremediation involves different pathways such as uptake, accumulation, reduction, oxidation, methylation, and demethylation. Each of these pathways has a certain set of genes and proteins to carry out the mechanism of arsenic biotransformation. Based on these mechanisms, various studies have been conducted for arsenic detoxification and removal. Genes specific for these pathways have also been cloned in several microorganisms to enhance arsenic bioremediation. This review discusses different biochemical pathways and the associated genes which play important roles in arsenic redox reactions, resistance, methylation/demethylation, and accumulation. Based on these mechanisms, new methods can be developed for effective arsenic bioremediation.

Clinical value and molecular mechanism of AQGPs in different tumors

Aquaglyceroporins (AQGPs), including AQP3, AQP7, AQP9, and AQP10, are transmembrane channels that allow small solutes across biological membranes, such as water, glycerol, H₂O₂, and so on. Increasing evidence suggests that they play critical roles in cancer. Overexpression or knockdown of AQGPs can promote or inhibit cancer cell proliferation, migration, invasion, apoptosis, epithelial-mesenchymal transition and metastasis, and the expression levels of AQGPs are closely linked to the prognosis of cancer patients. Here, we provide a comprehensive and detailed review to discuss the expression patterns of AQGPs in different cancers as well as the relationship between the expression patterns and prognosis. Then, we elaborate the relevance between AQGPs and malignant behaviors in cancer as well as the latent upstream regulators and downstream targets or signaling pathways of AQGPs. Finally, we summarize the potential clinical value in cancer treatment. This review will provide us with new ideas and thoughts for subsequent cancer therapy specifically targeting AQGPs.

AQP9 (Aquaporin 9) Determines Arsenic Uptake and Tolerance in Human Hepatocellular Carcinoma Cells In Vitro

Arsenic-based therapeutic strategies, even though promising for acute promyelocytic leukemia (APL), are limited by arsenic-related toxic effect and resistance with unknown mechanisms. The purpose of this study is to better understand the different sensitivities of hepatocellular carcinoma cells to arsenic and its mechanism. Arsenic-sensitive liver cancer cell line (HepG2) and arsenic-resistant HepG2 (AsHepG2) cells are employed to study the role of aquaporin 9 (AQP9) in arsenic uptake and tolerance. The half-maximal inhibitory concentration (IC₅₀) value of arsenic in AsHepG2 cells (15.59 ± 1.36 µM) is significantly higher than that in HepG2 cells (7.33 ± 0.93 µM; p= 0.0288). We demonstrated that, with the treatment of sodium arsenite (NaAsO₂), arsenic was accumulated at a significantly lower level in AsHepG2 cells in comparison with HepG2 cells (p= 0.00549). Further, arsenic level in AsHepG2 cells reaches a plateau after six hours of treatment, whereas arsenic continues to increase in HepG2 cells during the entire experimental period. Mechanistic study showed that the expression of AQP9 is decreased in a dose-dependent manner in AsHepG2 cells, but no significant difference in HepG2 cells. Furthermore, NaAsO₂ dramatically increases AQP9 and p38 phosphorylation, which may partially regulate arsenic sensitivity in both cell lines. In conclusion, the expression and phosphorylation of AQP9 regulated by p38 kinase are involved in the arsenic uptake, thus regulating cellular arsenic sensitivity.

Curcumin Synergistically Enhances the Cytotoxicity of Arsenic Trioxide in U266 Cells by Increasing Arsenic Uptake

Despite the constant emergence of new methods for the treatment of multiple myeloma (MM), relapse and drug resistance still exist, especially in MM with p53 mutations. Arsenic trioxide (ATO) can be used in MM treatment, but this single drug has poor effectiveness and also side effects. Curcumin is a safe and effective compound that can enhance the anticancer effects of many drugs. Previous studies have suggested that tumor cell sensitivity to ATO is related to the intracellular arsenic content, and aquaporin 9 (AQP9) is the key factor that determines intracellular arsenic content. This study aimed to explore whether curcumin can increase ATO cytotoxicity in MM and whether the mechanism is related to the regulation of intracellular arsenic content. U266 was treated with ATO, curcumin, and their combination, and cell proliferation, apoptosis, and intracellular arsenic content were detected by CCK-8 assay, flow cytometry, and HPLC-ICP-MS, respectively. AQP9 mRNA and protein levels were detected by qPCR and western blotting. The levels of Mcl-1, Bcl-2, Bax, caspase-3, and cleaved caspase-3 protein were detected by western blotting. ATO-induced cytotoxicity to U266 occurred in a time- and dose-dependent manner, but the therapeutic efficacy at low drug concentrations was modest. The arsenic content in U266 was lower than that in NB4, and the arsenic uptake by U266 was concentration-dependent. The expression levels of AQP9 mRNA and AQP9 protein in U266 were lower than those in NB4. Curcumin significantly enhanced the lethality of ATO to U266. The arsenic content in U266 in the combined drug group increased significantly compared with ATO treatment alone. After curcumin treatment, the AQP9 mRNA and AQP9 protein expression levels in U266 also increased. Compared with the control group, the expression of antiapoptotic proteins Mcl-1 and Bcl-2 decreased, the expression of proapoptotic protein Bax increased, the ratio of Bax/Bcl-2 increased, and the expression of caspase-3 decreased and cleaved caspase-3 increased in the combined drug groups. Curcumin can enhance the killing effects of ATO on U266 by increasing the intracellular arsenic content, which may be related to the upregulation of AQP9 expression. The combination of these two drugs is expected to be a potential clinical treatment for MM.

Identification of a prognostic 4-mRNA signature in laryngeal squamous cell carcinoma

Background: Laryngeal squamous cell carcinoma (LSCC) is one of the most common malignancy in the respiratory tract and could reduce the quality of life seriously like dyspnea, dysphonia and dysphagia. Moreover, 5-year survival rate has decreased over the past 40 years. This study was designed to identify mRNAs that related to prognosis in LSCC to enable early detection and outcome improvement.

Methods: Gene expression profiles from Gene Expression Omnibus (GEO) (GSE59102, GSE84957) and The Cancer Genome Atlas (TCGA) were analyzed to identify differentially expressed genes (DEGs) with the help of bioinformatics tools. Functional enrichment analyses including Gene Ontology (GO) and pathway analysis were carried out to investigate the role of those genes and underlying molecular mechanisms in LSCC. Cox's regression analyses (univariate, LASSO and multivariate in order) were utilized to identify DEGs related with patients' overall survival and a 4-mRNA-based prognostic risk score model was established. Univariate and multivariate Cox's regression analyses were then performed on LSCC data (90 patients left) to identify independent predictors of OS, including the signature and clinicopathologic variables. The prognostic value of the gene signature was further validated and the genes were analyzed by GEPIA to get pan-cancer expression profiles.

Results: 444 differentially expressed mRNAs (250 up-regulated, 194 down-regulated) were identified based on the threshold of fold change > 2 and adjusted p value < 0.05. Univariate Cox's regression analysis showed that high risk score (HR: 3.056, 95% confidence interval [CI]: 0.135-0.649, p<0.001) and female (HR: 0.296, 95% CI: 2.020-4.624, p=0.002) were associated with relatively poor prognosis. Further multivariate Cox's regression analysis indicated that risk score and gender were independent prognostic factors (p<0.05). The risk score model could stratify patients into high- and low‑risk groups, which presents significantly differential overall survival (p= 8.252e-04). The AUCs of 1-, 3- and 5-year OS were 0.724, 0.783 and 0.818, respectively.

Conclusions: Our study provides evidence that the four-mRNA signature could serve as a biomarker to predict prognosis in LSCC, especially in long-term.

Human Aquaporins: Functional Diversity and Potential Roles in Infectious and Non-infectious Diseases

Aquaporins (AQPs) are integral membrane proteins and found in all living organisms from bacteria to human. AQPs mainly involved in the transmembrane diffusion of water as well as various small solutes in a bidirectional manner are widely distributed in various human tissues. Human contains 13 AQPs (AQP0-AQP12) which are divided into three sub-classes namely orthodox aquaporin (AQP0, 1, 2, 4, 5, 6, and 8), aquaglyceroporin (AQP3, 7, 9, and 10) and super or unorthodox aquaporin (AQP11 and 12) based on their pore selectivity. Human AQPs are functionally diverse, which are involved in wide variety of non-infectious diseases including cancer, renal dysfunction, neurological disorder, epilepsy, skin disease, metabolic syndrome, and even cardiac diseases. However, the association of AQPs with infectious diseases has not been fully evaluated. Several studies have unveiled that AQPs can be regulated by microbial and parasitic infections that suggest their involvement in microbial pathogenesis, inflammation-associated responses and AQP-mediated cell water homeostasis. This review mainly aims to shed light on the involvement of AQPs in infectious and non-infectious diseases and potential AQPs-target modulators. Furthermore, AQP structures, tissue-specific distributions and their physiological relevance, functional diversity and regulations have been discussed. Altogether, this review would be useful for further investigation of AQPs as a potential therapeutic target for treatment of infectious as well as non-infectious diseases.

Combined Systematic Review and Transcriptomic Analyses of Mammalian Aquaporin Classes 1 to 10 as Biomarkers and Prognostic Indicators in Diverse Cancers

Aquaporin (AQP) channels enable regulated transport of water and solutes essential for fluid homeostasis, but they are gaining attention as targets for anticancer therapies. Patterns of AQP expression and survival rates for patients were evaluated by systematic review (PubMed and Embase) and transcriptomic analyses of RNAseq data (Human Protein Atlas database). Meta-analyses confirmed predominantly negative associations between AQP protein and RNA expression levels and patient survival times, most notably for AQP1 in lung, breast and prostate cancers; AQP3 in esophageal, liver and breast cancers; and AQP9 in liver cancer. Patterns of AQP expression were clustered for groups of cancers and associated with risk of death. A quantitative transcriptomic analysis of AQP1-10 in human cancer biopsies similarly showed that increased transcript levels of AQPs 1, 3, 5 and 9 were most frequently associated with poor survival. Unexpectedly, increased AQP7 and AQP8 levels were associated with better survival times in glioma, ovarian and endometrial cancers, and increased AQP11 with better survival in colorectal and breast cancers. Although molecular mechanisms of aquaporins in pathology or protection remain to be fully defined, results here support the hypothesis that overexpression of selected classes of AQPs differentially augments cancer progression. Beyond fluid homeostasis, potential roles for AQPs in cancers (suggested from an expanding appreciation of their functions in normal tissues) include cell motility, membrane process extension, transport of signaling molecules, control of proliferation and apoptosis, increased mechanical compliance, and gas exchange. AQP expression also has been linked to differences in sensitivity to chemotherapy treatments, suggesting possible roles as biomarkers for personalized treatments. Development of AQP pharmacological modulators, administered in cancer-specific combinations, might inspire new interventions for controlling malignant carcinomas.

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.

Pathways of arsenic uptake and efflux

Arsenic is a non-essential, environmentally ubiquitous toxic metalloid. In response to this pervasive environmental challenge, organisms evolved mechanisms to confer resistance to arsenicals. Inorganic pentavalent arsenate is taken into most cells adventitiously by phosphate uptake systems. Similarly, inorganic trivalent arsenite is taken into most cells adventitiously, primarily via aquaglyceroporins or sugar permeases. The most common strategy for tolerance to both inorganic and organic arsenicals is by efflux that extrude them from the cytosol. These efflux transporters span across kingdoms and belong to various families such as aquaglyceroporins, major facilitator superfamily (MFS) transporters, ATP-binding cassette (ABC) transporters and potentially novel, yet to be discovered families. This review will outline the properties and substrates of known arsenic transport systems, the current knowledge gaps in the field, and aims to provide insight into the importance of arsenic transport in the context of the global arsenic biogeocycle and human health.

Mechanisms of Aquaporin-Facilitated Cancer Invasion and Metastasis

Cancer is a leading cause of death worldwide, and its incidence is rising with numbers expected to increase 70% in the next two decades. The fact that current mainline treatments for cancer patients are accompanied by debilitating side effects prompts a growing demand for new therapies that not only inhibit growth and proliferation of cancer cells, but also control invasion and metastasis. One class of targets gaining international attention is the aquaporins, a family of membrane-spanning water channels with diverse physiological functions and extensive tissue-specific distributions in humans. Aquaporins−1,−2,−3,−4,−5,−8, and−9 have been linked to roles in cancer invasion, and metastasis, but their mechanisms of action remain to be fully defined. Aquaporins are implicated in the metastatic cascade in processes of angiogenesis, cellular dissociation, migration, and invasion. Cancer invasion and metastasis are proposed to be potentiated by aquaporins in boosting tumor angiogenesis, enhancing cell volume regulation, regulating cell-cell and cell-matrix adhesions, interacting with actin cytoskeleton, regulating proteases and extracellular-matrix degrading molecules, contributing to the regulation of epithelial-mesenchymal transitions, and interacting with signaling pathways enabling motility and invasion. Pharmacological modulators of aquaporin channels are being identified and tested for therapeutic potential, including compounds derived from loop diuretics, metal-containing organic compounds, plant natural products, and other small molecules. Further studies on aquaporin-dependent functions in cancer metastasis are needed to define the differential contributions of different classes of aquaporin channels to regulation of fluid balance, cell volume, small solute transport, signal transduction, their possible relevance as rate limiting steps, and potential values as therapeutic targets for invasion and metastasis.

Plant and Mammal Aquaporins: Same but Different

Aquaporins (AQPs) constitute an ancient and diverse protein family present in all living organisms, indicating a common ancient ancestor. However, during evolution, these organisms appear and evolve differently, leading to different cell organizations and physiological processes. Amongst the eukaryotes, an important distinction between plants and animals is evident, the most conspicuous difference being that plants are sessile organisms facing ever-changing environmental conditions. In addition, plants are mostly autotrophic, being able to synthesize carbohydrates molecules from the carbon dioxide in the air during the process of photosynthesis, using sunlight as an energy source. It is therefore interesting to analyze how, in these different contexts specific to both kingdoms of life, AQP function and regulation evolved. This review aims at highlighting similarities and differences between plant and mammal AQPs. Emphasis is given to the comparison of isoform numbers, their substrate selectivity, the regulation of the subcellular localization, and the channel activity.

Role of AQP9 in transport of monomethyselenic acid and selenite

AQP9 is an aquaglyceroporin with a very broad substrate spectrum. In addition to its orthodox nutrient substrates, AQP9 also transports multiple neutral and ionic arsenic species including arsenic trioxide, monomethylarsenous acid (MAs^III) and dimethylarsenic acid (DMA^V). Here we discovered a new group of AQP9 substrates which includes two clinical relevant selenium species. We showed that AQP9 efficiently transports monomethylselenic acid (MSeA) with a preference for acidic pH, which has been demonstrated in Xenopus laevis oocyte following the overexpression of human AQP9. Specific inhibitors that dissipate transmembrane proton potential or change the transmembrane pH gradient, such as FCCP, valinomycin and nigericin did not significantly inhibit MSeA uptake, suggesting MSeA transport is not proton coupled. AQP9 was also found to transport ionic selenite and lactate, with much less efficiency compared with MSeA uptake. Selenite and lactate uptake via AQP9 is pH dependent and inhibited by FCCP and nigericin, but not valinomycin. The selenite and lactate uptake via AQP9 can be inhibited by different lactate analogs, indicating that their translocation share similar mechanisms. AQP9 transport of MSeA, selenite and lactate is all inhibited by a previously identified AQP9 inhibitor, phloretin, and the AQP9 substrate arsenite (As^III). These newly identified AQP9 selenium substrates imply that AQP9 play a significant role in MSeA uptake and possibly selenite uptake involved in cancer therapy under specific microenvironments.

Expression and clinical significance of aquaglyceroporins in human hepatocellular carcinoma

Aquaglyceroporins (AQPs) are a subset of the aquaporin family, and are permeable to water and glycerol. The aim of the present study was to determine the expression and clinical significance of three AQPs, AQP3, 7 and 9 in hepatocellular carcinoma (HCC). Fresh HCC and adjacent non‑tumorous liver tissues were collected from 68 patients diagnosed with HCC. The expression levels of AQP3, 7 and 9 were detected by reverse transcription‑quantitative polymerase chain reaction, western blotting and immunohistochemical analysis. The association between the expression of AQPs and clinicopathological parameters of HCC were investigated. Compared with non‑tumorous liver tissue, HCC tissues exhibited a significant (P<0.05) increase in the expression of AQP3 and a concomitant reduction in the expression levels of AQP7 and AQP9, at both the mRNA and protein levels. Immunohistochemistry revealed that AQP9 was dominantly localized on the plasma membrane of hepatocytes, while AQP3 and AQP7 exhibited a predominantly cytoplasmic and nuclear distribution. High expression of AQP3 was significantly (P<0.05) associated with low expression levels of AQP7 and AQP9. High expression of AQP3 was correlated with tumor grade (P=0.017), tumor stage (P=0.010) and lymphatic metastasis (P=0.031). Low expression of AQP7 was correlated with tumor grade (P=0.043). AQP3 was upregulated, and AQP7 and AQP9 were downregulated in HCC. A high expression of AQP3 and low expression of AQP7 was significantly associated with the aggressive features of HCC.

New mechanisms of bacterial arsenic resistance

Arsenic is the most pervasive environmental substance and is classified by the International Agency for Research on Cancer as a Group 1 human carcinogen. Nearly every organism has resistance pathways for inorganic arsenic, and in bacteria, their genes are found in arsenic resistance (ars) operons. Recently, a parallel pathway for organic arsenicals has been identified. The ars genes responsible for the organoarsenical detoxification includes arsM, which encodes an As(III) S-adenosylmethionine methyltransferase, arsI, which encodes a C–As bond lyase, and arsH, which encodes a methylarsenite oxidase. The identification and properties of arsM, arsI and arsH are described in this review.

Multidrug resistance-associated protein 4 is a determinant of arsenite resistance

Although arsenic trioxide (arsenite, As^III) has shown a remarkable efficacy in the treatment of acute promyelocytic leukemia patients, multidrug resistance is still a major concern for its clinical use. Multidrug resistance-associated protein 4 (MRP4), which belongs to the ATP-binding cassette (ABC) superfamily of transporters, is localized to the basolateral membrane of hepatocytes and the apical membrane of renal proximal tubule cells. Due to its characteristic localization, MRP4 is proposed as a candidate in the elimination of arsenic and may contribute to resistance to As^III. To test this hypothesis, stable HEK293 cells overexpressing MRP4 or MRP2 were used to establish the role of these two transporters in As^III resistance. The IC₅₀ values of As^III in MRP4 cells were approximately 6-fold higher than those in MRP2 cells, supporting an important role for MRP4 in resistance to As^III. The capacity of MRP4 to confer resistance to As^III was further confirmed by a dramatic decrease in the IC₅₀ values with the addition of MK571, an MRP4 inhibitor, and cyclosporine A, a well-known broad-spectrum inhibitor of ABC transporters. Surprisingly, the sensitivity of the MRP2 cells to As^III was similar to that of the parent cells, although insufficient formation of glutathione and/or Se conjugated arsenic compounds in the MRP2 cells might limit transport. Given that MRP4 is a major contributor to arsenic resistance in vitro, further investigation into the correlation between MRP4 expression and treatment outcome of leukemia patients treated with arsenic-based regimens is warranted.

Azacytidine sensitizes acute myeloid leukemia cells to arsenic trioxide by up-regulating the arsenic transporter aquaglyceroporin 9

Background

The therapeutic efficacy of arsenic trioxide (As₂O₃) in acute myeloid leukemia (AML) is modest, which is partly related to its limited intracellular uptake into the leukemic cells. As₂O₃ enters cells via the transmembrane protein aquaglyceroporin 9 (AQP9). Azacytidine, a demethylating agent that is approved for the treatment of AML, has been shown to have synergistic effect with As₂O₃. We tested the hypothesis that azacytidine might up-regulate AQP9 and enhances As₂O₃-mediated cytotoxicity in AML.

Methods

Arsenic-induced cytotoxicity, the expression of AQP9, and the intracellular uptake of As₂O₃ were determined in AML cell lines and primary AML cells with or without azacytidine pre-treatment. The mechanism of AQP9 up-regulation was then investigated by examining the expression of transcription factors for AQP9 gene and the methylation status of their gene promoters.

Results

As₂O₃-induced cytotoxicity in AML cell lines was significantly enhanced after azacytidine pre-treatment as a result of AQP9 up-regulation, leading to increased arsenic uptake and hence intracellular concentration. Blocking AQP9-mediated As₂O₃ uptake with mercury chloride abrogated the sensitization effect of azacytidine. AQP9 promoter does not contain CpG islands. Instead, azacytidine pre-treatment led to increased expression of HNF1A, a transcription activator of AQP9, through demethylation of HNF1A promoter. HNF1 knockdown abrogated azacytidine-induced AQP9 up-regulation and almost completely blocked intracellular As₂O₃ entry, confirming that azacytidine enhanced As₂O₃-mediated cell death via up-regulation of HNF1A and hence increased AQP9 and As₂O₃ intracellular concentration. Azacytidine sensitization to As₂O₃ treatment was re-capitulated also in primary AML samples. Finally, azacytidine did not enhance arsenic toxicity in a liver cell line, where HNF1A was largely unmethylated.

Conclusions

Azacytidine sensitizes AML cells to As₂O₃ treatment, and our results provide proof-of-principle evidence that pharmacological up-regulation of AQP9 potentially expands the therapeutic spectrum of As₂O₃. Further clinical trial should evaluate the efficacy of azacytidine in combination with As₂O₃ in the treatment of AML.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0143-3) contains supplementary material, which is available to authorized users.

Difference in glycerol levels between leukemia and normal bone marrow stem cells

Aquaglyceroporin 9 (AQP9) is considered to be involved in numerous types of carcinogenic processes, particularly in liver carcinoma. AQP9 expression is significantly decreased in the human hepatocellular carcinoma when compared with the non-tumourigenic liver, which leads to increased resistance to apoptosis. In addition, AQP9 is permeable to glycerol and urea. The involvement of AQP9 in leukemia has not been fully delineated. It is proposed that abnormal proliferation of hematopoietic stem cells (HSCs) contributes to leukemia carcinogenesis. Therefore, the present study aimed to investigate the possible roles of AQP9 in HSCs and its effect on the intracellular glycerol content. HSCs and non-HSCs (nHSCs) were isolated via magnetic-activated cell sorting and then subjected to flow cytometry for evaluation of purity. White blood cells (WBCs) were isolated from peripheral blood from healthy volunteers. Furthermore, AQP9 expression was examined at the mRNA and protein levels using western blotting and reverse transcription-polymerase chain reaction (RT-PCR). The glycerol content of HSCs, nHSCs and WBCs was evaluated by ELISA. Finally, in order to observe the morphology of HSCs and nHSCs, a blood smear was conducted and the cells were observed with Wright-Giemsa staining. The results indicated that the glycerol content in the HSCs was markedly greater than that in the nHSCs. AQP9 mRNA and protein expression was not detected in the HSCs and nHSCs, but was identified in the WBCs. Moreover, the HSC morphological characteristics included round or oval cells with round, slightly oval or irregularly shaped nuclei. Additionally, the nuclei occupied almost the entire cell, were located in the middle or were biased toward one side, and were stained light purple or red. Overall, our results indicated that intracellular glycerol is involved in HSC proliferation, despite the fact that glycerol is not mediated by AQP9. Hence, our findings may be useful in further understanding the mechanism of leukemia carcinogenesis, and these data may be valuable in developing future therapeutic strategies.

Triple A therapy: the molecular underpinnings of the unique sensitivity of leukemic promyelocytes to anthracyclines, all-trans-retinoic acid and arsenic trioxide

If looking for a mnemonic to remember the relevant facts about acute promyelocytic leukemia (APL), one just has to remember that APL is a disease of A's. It is acute and it is highly sensitive to treatment with anthracyclines, all-trans-retinoic acid (RA) and arsenic trioxide (ATO). The presence of fusions involving the retinoic acid receptor alpha (RARA) is without question the central player driving APL and dictating the response of this disease to these therapeutic agents. However, beyond this knowledge, the molecular mechanisms that contribute to the complicated pathogenesis and the response to treatment of APL are not completely defined. As more is understood about this hematological malignancy, there are more opportunities to refine and improve treatment based on this knowledge. In this review article, we discuss the response of APL to these "A" therapies.

Aquaglyceroporins: generalized metalloid channels

BACKGROUND

Aquaporins (AQPs), members of a superfamily of transmembrane channel proteins, are ubiquitous in all domains of life. They fall into a number of branches that can be functionally categorized into two major sub-groups: i) orthodox aquaporins, which are water-specific channels, and ii) aquaglyceroporins, which allow the transport of water, non-polar solutes, such as urea or glycerol, the reactive oxygen species hydrogen peroxide, and gases such as ammonia, carbon dioxide and nitric oxide and, as described in this review, metalloids.

SCOPE OF REVIEW

This review summarizes the key findings that AQP channels conduct bidirectional movement of metalloids into and out of cells.

MAJOR CONCLUSIONS

As(OH)3 and Sb(OH)3 behave as inorganic molecular mimics of glycerol, a property that allows their passage through AQP channels. Plant AQPs also allow the passage of boron and silicon as their hydroxyacids, boric acid (B(OH)3) and orthosilicic acid (Si(OH)4), respectively. Genetic analysis suggests that germanic acid (GeO2) is also a substrate. While As(III), Sb(III) and Ge(IV) are toxic metalloids, borate (B(III)) and silicate (Si(IV)) are essential elements in higher plants.

GENERAL SIGNIFICANCE

The uptake of environmental metalloids by aquaporins provides an understanding of (i) how toxic elements such as arsenic enter the food chain; (ii) the delivery of arsenic and antimony containing drugs in the treatment of certain forms of leukemia and chemotherapy of diseases caused by pathogenic protozoa; and (iii) the possibility that food plants such as rice could be made safer by genetically modifying them to exclude arsenic while still accumulating boron and silicon. This article is part of a Special Issue entitled Aquaporins.

Anticancer activity of small-molecule and nanoparticulate arsenic(III) complexes

Starting in ancient China and Greece, arsenic-containing compounds have been used in the treatment of disease for over 3000 years. They were used for a variety of diseases in the 20th century, including parasitic and sexually transmitted illnesses. A resurgence of interest in the therapeutic application of arsenicals has been driven by the discovery that low doses of a 1% aqueous solution of arsenic trioxide (i.e., arsenous acid) lead to complete remission of certain types of leukemia. Since Food and Drug Administration (FDA) approval of arsenic trioxide (As2O3) for treatment of acute promyelocytic leukemia in 2000, it has become a front-line therapy in this indication. There are currently over 100 active clinical trials involving inorganic arsenic or organoarsenic compounds registered with the FDA for the treatment of cancers. New generations of inorganic and organometallic arsenic compounds with enhanced activity or targeted cytotoxicity are being developed to overcome some of the shortcomings of arsenic therapeutics, namely, short plasma half-lives and a narrow therapeutic window.

Leishmania panamensis infection and antimonial drugs modulate expression of macrophage drug transporters and metabolizing enzymes: impact on intracellular parasite survival

OBJECTIVES

Treatment failure is multifactorial. Despite the importance of host cell drug transporters and metabolizing enzymes in the accumulation, distribution and metabolism of drugs targeting intracellular pathogens, their impact on the efficacy of antileishmanials is unknown. We examined the contribution of pharmacologically relevant determinants in human macrophages in the antimony-mediated killing of intracellular Leishmania panamensis and its relationship with the outcome of treatment with meglumine antimoniate.

METHODS

Patients with cutaneous leishmaniasis who failed (n = 8) or responded (n =8) to treatment were recruited. Gene expression profiling of pharmacological determinants in primary macrophages was evaluated by quantitative RT-PCR and correlated to the drug-mediated intracellular parasite killing. Functional validation was conducted through short hairpin RNA gene knockdown.

RESULTS

Survival of L. panamensis after exposure to antimonials was significantly higher in macrophages from patients who failed treatment. Sixteen macrophage drug-response genes were modulated by infection and exposure to meglumine antimoniate. Correlation analyses of gene expression and intracellular parasite survival revealed the involvement of host cell metallothionein-2A and ABCB6 in the survival of Leishmania during exposure to antimonials. ABCB6 was functionally validated as a transporter of antimonial compounds localized in both the cell and phagolysosomal membranes of macrophages, revealing a novel mechanism of host cell-mediated regulation of intracellular drug exposure and parasite survival within phagocytes.

CONCLUSIONS

These results provide insight into host cell mechanisms regulating the intracellular exposure of Leishmania to antimonials and variations among individuals that impact parasite survival. Understanding of host cell determinants of intracellular pharmacokinetics/pharmacodynamics opens new avenues to improved drug efficacy for intracellular pathogens.

Aquaporin 9, a promising predictor for the cytocidal effects of arsenic trioxide in acute promyelocytic leukemia cell lines and primary blasts

A close correlation between the cytocidal effects of arsenic trioxide (ATO) and aquaporin-9 (AQP9) expression levels has been proposed, yet detailed studies are still needed to confirm this association. Thus, in the present study, the correlation between the expression levels of AQP9 and sensitivity to ATO was investigated using two acute promyelocytic leukemia (APL) cell lines, NB4 and HT93A, as well as primary APL cells from newly diagnosed and relapsed APL patients. A substantially higher sensitivity to ATO-mediated induction of apoptosis was observed in the NB4 cells when compared to that in the HT93A cells. In addition, markedly higher expression levels of AQP9, as assessed using flow cytometry, along with more intracellular arsenic accumulation, were observed in the NB4 cells. More importantly, similar to APL cell lines, the trend of expression levels of AQP9 correlated closely with the differential sensitivity to ATO-mediated induction of apoptosis in primary APL cells. In contrast, no correlation was observed between ATO sensitivity associated with AQP9 expression levels and the expression profiles of cell surface markers as well as chromosomal alterations. These results provide direct evidence that the expression levels of AQP9, rather than other biomarkers such as cell surface markers and chromosomal alterations, correlate closely with the sensitivity to ATO in both APL cell lines and primary blasts. These findings suggest that the AQP9 expression status of APL patients is a predictive marker for the successful outcome of ATO treatment, since AQP9 plays a pivotal role in various arsenite-mediated biological effects on normal and cancer cells. Moreover, flow cytometry may be a new convenient and valuable tool for analyzing the AQP9 status of APL patients compared to current methods such as western blotting.

Pathways of arsenic uptake and efflux

Arsenic is the most prevalent environmental toxic substance and ranks first on the U.S. Environmental Protection Agency's Superfund List. Arsenic is a carcinogen and a causative agent of numerous human diseases. Paradoxically arsenic is used as a chemotherapeutic agent for treatment of acute promyelocytic leukemia. Inorganic arsenic has two biological important oxidation states: As(V) (arsenate) and As(III) (arsenite). Arsenic uptake is adventitious because the arsenate and arsenite are chemically similar to required nutrients. Arsenate resembles phosphate and is a competitive inhibitor of many phosphate-utilizing enzymes. Arsenate is taken up by phosphate transport systems. In contrast, at physiological pH, the form of arsenite is As(OH)(3), which resembles organic molecules such as glycerol. Consequently, arsenite is taken into cells by aquaglyceroporin channels. Arsenic efflux systems are found in nearly every organism and evolved to rid cells of this toxic metalloid. These efflux systems include members of the multidrug resistance protein family and the bacterial exchangers Acr3 and ArsB. ArsB can also be a subunit of the ArsAB As(III)-translocating ATPase, an ATP-driven efflux pump. The ArsD metallochaperone binds cytosolic As(III) and transfers it to the ArsA subunit of the efflux pump. Knowledge of the pathways and transporters for arsenic uptake and efflux is essential for understanding its toxicity and carcinogenicity and for rational design of cancer chemotherapeutic drugs.

Reversal effect of arsenic sensitivity in human leukemia cell line K562 and K562/ADM using realgar transforming solution

The success of arsenic trioxide (ATO) in treatment of acute promyelocytic leukemia (APL) attracts a great deal of attention to researchers to explore its activity of anti-leukemia. However, ATO has unavailable effect on chronic myeloid leukemia (CML), especially multidrug resistant (MDR)-CML, unless using high concentration. Realgar (As(4)S(4)) has been employed in Chinese traditional medicine for 1500 years. Research evidences confirmed realgar has similar effect on treating with APL as ATO, but the problem of large dose and long period in the CML/MDR-CML treatment still exist. By using a microbial leaching process with Acidithiobacillus ferrooxidans, we obtained realgar transforming solution (RTS) which showed significantly higher extent in inhibiting CML cell line K562 and MDR-CML cell line K562/ADM, and then trigger apoptosis. Both K562 and K562/ADM showed arsenic-dose-dependent effect on RTS. Interestingly, the overexpression of MDR1 mRNA and P-glucoprotein (P-gp) in K562/ADM cells were down-regulated by RTS, where there are no obvious effects on ATO and realgar and arsenic can be subsequently accumulated in K562/ADM cells efficiently. The intracellular accumulation of arsenic in K562/ADM cells treated with RTS for 4 h was 2-fold and 16-folds higher than those treated with realgar or ATO. Meanwhile, Western blot analysis of AQP9, the main transporter of arsenic, was increased by RTS treatment particularly in K562/ADM. Thus, these results suggested that the effect from a certain arsenical or a variety of arsenicals in RTS might be a promising candidate both for treating CML/MDR-CML alone and as combinations with currently used anti-CML/MDR-CML drug, although arsenical forms in RTS are undefined.

Bismuth protects against arsenite-induced inhibition of proteoglycan synthesis in cultured vascular endothelial cells

Chronic ingestion of arsenic is associated with an increased risk of vascular disease such as atherosclerosis. Previously, we showed that arsenite inhibits the synthesis of general proteoglycans (PGs), which are key molecules in the progression of atherosclerosis, in vascular endothelial cells. In the present study, we investigated the effect of several metals on arsenite-induced inhibitory effect in endothelial cells. The results indicate that, after 24-hr incubation, the inhibition of PG synthesis caused by sodium arsenite was protected by bismuth nitrate but not zinc sulfate, manganese chloride, nickel chloride or cobalt chloride. The accumulation of arsenic in the cell layer was significantly decreased by bismuth after 12-hr incubation and that of bismuth was also decreased by arsenite. It was therefore suggested that the protective effect of bismuth against the inhibitory effect of arsenite on PG synthesis in vascular endothelial cells may be due, at least in part, to the decrease in cellular arsenic accumulation.

Arsenic and antimony transporters in eukaryotes

Arsenic and antimony are toxic metalloids, naturally present in the environment and all organisms have developed pathways for their detoxification. The most effective metalloid tolerance systems in eukaryotes include downregulation of metalloid uptake, efflux out of the cell, and complexation with phytochelatin or glutathione followed by sequestration into the vacuole. Understanding of arsenic and antimony transport system is of high importance due to the increasing usage of arsenic-based drugs in the treatment of certain types of cancer and diseases caused by protozoan parasites as well as for the development of bio- and phytoremediation strategies for metalloid polluted areas. However, in contrast to prokaryotes, the knowledge about specific transporters of arsenic and antimony and the mechanisms of metalloid transport in eukaryotes has been very limited for a long time. Here, we review the recent advances in understanding of arsenic and antimony transport pathways in eukaryotes, including a dual role of aquaglyceroporins in uptake and efflux of metalloids, elucidation of arsenic transport mechanism by the yeast Acr3 transporter and its role in arsenic hyperaccumulation in ferns, identification of vacuolar transporters of arsenic-phytochelatin complexes in plants and forms of arsenic substrates recognized by mammalian ABC transporters.

Arsenic and its combinations in cancer therapeutics

Arsenic is a metalloid that is considered to be a paradox in terms of its role both as a carcinogen and as a therapeutic agent. Chronic exposure to arsenic in drinking water has been linked with the development of various pathological conditions including cancer. Nevertheless, the therapeutic potential of arsenic and its derivatives in a variety of diseases have been exploited in the past. However, its role and mechanism of action as a therapeutic agent still remain an active area of research and investigation. Our ongoing work also suggests varied responses in cancer cells exposed to lower versus higher concentrations of arsenic. Furthermore, the arsenic combinations with chemopreventive or anticancer agents have been observed to sensitize the cell for cell-cycle arrest and cell death. Here, we have provided the account of recent updates on the mechanism of action of arsenic and its derivatives that lead to various disorders, and its role as a therapeutic agent both as a single agent as well as in combination chemotherapy.

Arsenic toxicity in mammals and aquatic animals: a comparative biochemical approach

Arsenic (As) is a widespread pollutant in the world and its toxicity is related to its chemical form, with inorganic forms being considered more toxic than the organic form, and huge differences in effects and processes of metabolism. This paper reviews the potential biochemical mechanisms of uptake of arsenic by aquaporins, capacity for metabolism and cellular efflux of As. It is known that As can affect signaling pathways since it can activate proteins such as ERK2, p38 and JNK, as shown in mammals. A comparison between phosphorylation sites of these proteins is presented in order to determine whether the same effect triggered by As in mammals might be observed in aquatic animals. The toxicity resulting from As exposure is considered to be linked to an imbalance between pro-oxidant and antioxidant homeostasis that results in oxidative stress. So, present review analyzes examples of oxidative stress generation by arsenic. Biotransformation of As is a process where firstly the arsenate is converted into arsenite and then transformed into mono-, di-, and trimethylated products. In the methylation process, the role of the omega isoform of glutathione-S-transferase (GST) is discussed. In addition, a phylogenetic tree was constructed for aquaporin proteins of different species, including aquatic animals, taking into account their importance in trivalent arsenic uptake.

Arsenic transport in prokaryotes and eukaryotic microbes

Aquaporins (AQPs) and aquaglyceroporins facilitate transport of a broad spectrum of substrates such as water, glycerol and other small uncharged solutes. More recently, AQPs ave also been shown to facilitate diffusion of metalloids such as arsenic (As) and antimony (Sb). At neutral pH, the trivalent forms of these metalloids are structurally similar to glycerol and hence they can enter cells through AQPs. As- and Sb-containing compounds are toxic to cells, yet both metalloids are used as chemotherapeutic agents for treating acute promyelocytic leukemia and diseases caused by protozoan parasites. In this chapter, we will review the role of AQPs and other proteins in metalloid transport in prokaryotes and eukaryotic microbes.

Arsenite induces aquaglyceroporin 9 expression in murine livers

Mice exposed to sodium arsenite show a dose-related accumulation of inorganic arsenic (iAs) and its methylated metabolites in the liver. While the accumulation of iAs forms increased linearly with dose in liver cells, a different pattern was observed in other tissues such as the brain and lung, as well as in the peripheral nerves of the rat. As such, trivalent iAs enters the cells, using aquaglyceroporin transporters to modulate cell arsenic accumulation and cytotoxicity. We investigated here if the dose-related accumulation of arsenic in the liver was related to the expression of aquaglyceroporin 9 (AQP9) in the same organ. CD1 male mice were treated with different concentrations (0, 2.5, 5 or 10mg/kg/day) of sodium arsenite during 1, 3 or 9 days. A significant dose-related, up-regulation of AQP9 mRNA and protein was observed and which was verified by immunohistochemistry in liver sections using specific antibodies. The increased transcription of AQP9 has been observed in fasting and diabetic rats, suggesting that this channel could play a role in the diabetogenic effect of arsenic.

Aquaglyceroporins are involved in uptake of arsenite into murine gastrointestinal tissues

Aquaglyceroporins (AQGPs) are members of aquaporin (AQP) family and belong to a subgroup of this water channel family; they are transmembrane proteins that transport water as well as glycerol and other solutes of small molecules. Recent studies have also identified that AQGPs are important transporters of trivalent metalloid in some mammalian cells. However, the uptake routes of arsenite in mammals are still less defined. In this study, to understand the routes of arsenite intake in mammals, mice were treated with Hg(II), glycerol, and As(III) and uptake of As(III) into the gastrointestinal tissues was measured. The level of inorganic arsenic (iAs) in gastrointestinal tissues after As(III) stimulation was much higher than Hg(II) +As(III) or glycerol+As(III) group. RT-PCR results showed that AQGPs were extensively expressed in gastrointestinal tissues of mice. We also treated Caco-2 cells with Hg(II) and As(III); the level of iAs in a group treated with Hg(II)+As(III) decreased compared with As(III)-treated group. Our results suggested that AQGPs could be important transporters in arsenite uptake into gastrointestinal tissues of mice, but more data are need to prove if AQGPs is the only pathway involved in As transport in mammals or just one of them.

Pathway-BasedFeature Selection Algorithm for Cancer Microarray Data

Classification of cancers based on gene expressions produces better accuracy when compared to that of the clinical markers. Feature selection improves the accuracy of these classification algorithms by reducing the chance of overfitting that happens due to large number of features. We develop a new feature selection method called Biological Pathway-based Feature Selection (BPFS) for microarray data. Unlike most of the existing methods, our method integrates signaling and gene regulatory pathways with gene expression data to minimize the chance of overfitting of the method and to improve the test accuracy. Thus, BPFS selects a biologically meaningful feature set that is minimally redundant. Our experiments on published breast cancer datasets demonstrate that all of the top 20 genes found by our method are associated with cancer. Furthermore, the classification accuracy of our signature is up to 18% better than that of vant Veers 70 gene signature, and it is up to 8% better accuracy than the best published feature selection method, I-RELIEF.

Metalloid transport by aquaglyceroporins: consequences in the treatment of human diseases

Metalloids can severely harm human physiology in a toxicological sense if taken up from the environment in acute high doses or chronically. However, arsenic or antimony containing drugs are still being used as treatment and are often the sole regime for certain forms of cancer, mainly types of leukemia and diseases caused by parasites, such as sleeping sickness or leishmaniasis. In this chapter, we give an outline of the positive effects of arsenicals and antimonials against such diseases, we summarize data on uptake pathways through human and parasite aquaglyceroporins and we discuss the progress and options in the development of therapeutic aquaporin and aquaglyceroporin inhibitor compounds.

Reduced arsenic clearance and increased toxicity in aquaglyceroporin-9-null mice

Expressed in liver, aquaglyceroporin-9 (AQP9) is permeated by glycerol, arsenite, and other small, neutral solutes. To evaluate a possible protective role, AQP9-null mice were evaluated for in vivo arsenic toxicity. After injection with NaAsO(2), AQP9-null mice suffer reduced survival rates (LD(50), 12 mg/kg) compared with WT mice (LD(50), 15 mg/kg). The highest tissue level of arsenic is in heart, with AQP9-null mice accumulating 10-20 times more arsenic than WT mice. Within hours after NaAsO(2) injection, AQP9-null mice sustain profound bradycardia, despite normal serum electrolytes. Increased arsenic levels are also present in liver, lung, spleen, and testis of AQP9-null mice. Arsenic levels in the feces and urine of AQP9-null mice are only approximately 10% of the WT levels, and reduced clearance of multiple arsenic species by the AQP9-null mice suggests that AQP9 is involved in the export of multiple forms of arsenic. Immunohistochemical staining of liver sections revealed that AQP9 is most abundant in basolateral membrane of hepatocytes adjacent to the sinusoids. AQP9 is not detected in heart or kidney by PCR or immunohistochemistry. We propose that AQP9 provides a route for excretion of arsenic by the liver, thereby providing partial protection of the whole animal from arsenic toxicity.

Amphotericin B up-regulates angiogenic genes in hepatocellular carcinoma cell lines

BACKGROUND

Amphotericin B (AmB) has a discordant influence on epirubicin (4'-epidoxorubicin) cytotoxicity in hepatocellular carcinoma (HCC). This indicates that the cellular function of HCC may be significantly influenced by AmB. Whether the influence of AmB on HCC has any possibility to influence cancer growth has not been studied. This study was to try and clarify this issue.

MATERIALS AND METHODS

Two HCC cell lines including one without augmentation of the epirubicin cytotoxicity by AmB (cell line A; HCC24/KMUH) and one with this effect (cell line B; HCC38/KMUH) were studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and whole human genome microarray (experimental group: 2.5 microg mL(-1) AmB).

RESULTS

Differential expressions of genes induced by AmB in two cell lines had no influence on cell proliferation as determined by MTT assay. Only cell line B showed up-regulation of genes related to oxidative stress, acute phase reaction, cytokine-cytokine receptor interaction and complement and coagulation cascades. Among the chemokine genes up-regulated by AmB, five genes (CCL2, CXCL1, CXCL5, CXCL6, IL8) were angiogenic. Cell line B also showed up-regulation of one angiogenic C10orf10 gene and down-regulation of one angiostatic chemokine gene (CXCL10). Up- or down-regulation of other genes in cell line A and B did not show any evidence to promote angiogenesis.

CONCLUSION

AmB has the capacity to concomitantly up-regulate angiogenic genes in HCC cells susceptible to AmB-induced oxidative stress.

Discovery of the aquaporins and development of the field

The study of water transport began long before the molecular identification of water channels with studies of water-permeable tissues. The discovery of the first aquaporin, AQP1, occurred during experiments focused on the identity of the Rh blood group antigens. Since then the field has expanded dramatically to study aquaporins in all types of organisms. In mammals, some of the aquaporins transport only water. However, there are some family members that collectively transport a diverse set of solutes. The aquaporins can be regulated by factors that affect channel permeability or subcellular localization. An extensive set of studies examines the physiological role of many of the mammalian aquaporins. However, much is still to be discovered about the physiological role of this membrane protein family.

Aquaglyceroporins and metalloid transport: implications in human diseases

Aquaglyceroporin (AQP) channels facilitate the diffusion of a wide range of neutral solutes, including water, glycerol, and other small uncharged solutes. More recently, AQPs have been shown to allow the passage of trivalent arsenic and antimony compounds. Arsenic and antimony are metalloid elements. At physiological pH, the trivalent metalloids behave as molecular mimics of glycerol, and are conducted through AQP channels. Arsenicals and antimonials are extremely toxic to cells. Despite their toxicity, both metalloids are used as chemotherapeutic agents for the treatment of cancer and protozoan parasitic diseases. The metalloid homeostasis property of AQPs can be a mixed blessing. In some cases, AQPs form part of the detoxification pathway, and extrude metalloids from cells. In other instances, AQPs allow the transport of metalloids into cells, thereby conferring sensitivity. Understanding the factors that modulate AQP expression will aid in a better understanding of metalloid toxicity and also provide newer approaches to metalloid based chemotherapy.

Increased aquaglyceroporin 9 expression disrupts arsenic resistance in human lung cancer cells

Resistance to chemotherapy is one of the major problems in treatment responses of lung cancer. This study explored the mechanism underlying the arsenic resistance of lung cancer. Four lung cancer cells with different proliferation activity were characterized for cytotoxicity, arsenic influx/efflux, and arsenic effects on intracellular glutathione and 8-hydroxy-2'-deoxyguanosine (8-OHdG) production. Our data revealed that relative proliferation potency of these cells was H1299>A549>CL3>H1355. Moreover, A549, H1299, and H1355 were markedly resistant to As(2)O(3) with IC50 approximately 100 microM, whereas CL3 was sensitive to As(2)O(3) with IC50 approximately 11.8 microM. After treatment with the respective As(2)O(3) at IC50, arsenic influx/efflux activity in CL3 was comparable to those in the other three arsenic-resistant cells. However, differences in glutathione levels and 8-OHdG production were also detected either before or after arsenic treatment, indicating that a certain degree of variation in anti-oxidative systems and/or 8-OHdG repair activity existed in these cell lines. By transfection of an aquaglyceroporin 9 (AQP9) gene, we showed that increased AQP9 expression significantly enhanced arsenic uptake and disrupted arsenic resistance of A549. The present study strongly suggests that membrane transporters responsible for arsenic uptake, such as AQP9, may play a critical role in development of arsenic resistance in human lung cancer cells.