The evolving use of arsenic in pharmacotherapy of malignant disease

Anticancer Effects of the Trivalent Organoarsenical 2-Amino-4-(dihydroxyarsinoyl) Butanoate

According to the National Cancer Institute, breast cancer is a leading cause of death in women. The lack of progesterone and estrogen receptors in triple-negative breast cancer (TNBC) cells results in a lack of response to hormonal, monoclonal, or tyrosine kinase inhibitor therapies. Despite intensive drug discovery, there is still no approved targeted treatment for TNBC. The metalloid arsenic has been used in herbal medicines, antibiotics, and chemotherapeutic drugs for centuries. This paper demonstrates that a trivalent arsenic-containing, nonproteogenic amino acid, R-AST-OH (2-amino-4-(dihydroxyarsinoyl) butanoate), inhibits kidney-type glutaminase (KGA), the enzyme that controls glutamine metabolism and is correlated with tumor malignancy. Cell-based assays using the TNBC MDA-MB-231 and HCC1569 cell lines showed that R-AST-OH kills TNBC cells and is not cytotoxic to a control cell line. The results of in silico molecular docking predictions indicate that R-AST-OH binds to the glutamine binding site and forms a covalent bond with an active site cysteine residue. We hypothesize that R-AST-OH is a single warhead for KGA that irreversibly binds to KGA through the formation of an As-S bond. We propose that R-AST-OH is a promising lead compound for the design of new drugs for the treatment of TNBC.

Arsinothricin Inhibits Plasmodium falciparum Proliferation in Blood and Blocks Parasite Transmission to Mosquitoes

Malaria, caused by Plasmodium protozoal parasites, remains a leading cause of morbidity and mortality. The Plasmodium parasite has a complex life cycle, with asexual and sexual forms in humans and Anopheles mosquitoes. Most antimalarials target only the symptomatic asexual blood stage. However, to ensure malaria eradication, new drugs with efficacy at multiple stages of the life cycle are necessary. We previously demonstrated that arsinothricin (AST), a newly discovered organoarsenical natural product, is a potent broad-spectrum antibiotic that inhibits the growth of various prokaryotic pathogens. Here, we report that AST is an effective multi-stage antimalarial. AST is a nonproteinogenic amino acid analog of glutamate that inhibits prokaryotic glutamine synthetase (GS). Phylogenetic analysis shows that Plasmodium GS, which is expressed throughout all stages of the parasite life cycle, is more closely related to prokaryotic GS than eukaryotic GS. AST potently inhibits Plasmodium GS, while it is less effective on human GS. Notably, AST effectively inhibits both Plasmodium erythrocytic proliferation and parasite transmission to mosquitoes. In contrast, AST is relatively nontoxic to a number of human cell lines, suggesting that AST is selective against malaria pathogens, with little negative effect on the human host. We propose that AST is a promising lead compound for developing a new class of multi-stage antimalarials.

Arsenic and Diabetes Mellitus: A Putative Role for the Immune System

Diabetes mellitus (DM) is an enormous public health issue worldwide. Recent data suggest that chronic arsenic exposure is linked to the risk of developing type 1 and type 2 DM, albeit the underlying mechanisms are unclear. This review discusses the role of the immune system as a link to possibly explain some of the mechanisms of developing T1DM or T2DM associated with arsenic exposure in humans, animal models, and in vitro studies. The rationale for the hypothesis includes: (1) Arsenic is a well-recognized modulator of the immune system; (2) arsenic exposures are associated with increased risk of DM; and (3) dysregulation of the immune system is one of the hallmarks in the pathogenesis of both T1DM and T2DM. A better understanding of DM in association with immune dysregulation and arsenic exposures may help to understand how environmental exposures modulate the immune system and how these effects may impact the manifestation of disease.

Encouraging Early Outcomes of Treatment With Arsenic Trioxide Combined With Chemotherapy for Alveolar Rhabdomyosarcoma in Children: 4 Case Reports

Background

Alveolar rhabdomyosarcoma (ARMS) is a subtype of rhabdomyosarcoma characterized by its aggressive behavior and poor prognosis, highlighting the need for novel treatment options. Arsenic trioxide (ATO) has been shown to specifically inhibit tumor growth and the metastasis of ARMS in vitro by acting on the hedgehog pathway. Here we report on a pilot clinical study to evaluate the activity of an ATO-combined chemotherapy approach for the treatment of ARMS patients.

Methods

We designed a therapeutic schedule of an ATO-combined chemotherapy, incorporating comprehensive management according to the Intergroup Rhabdomyosarcoma Study Group protocol. ATO was administered at 0.16 mg/kg per day over 8 h via an IV for 10 days combined with a chemotherapeutic regimen of vincristine, actinomycin, and cyclophosphamide (VAC regimen) on the third day, which was repeated every 21 days. A total of eight cycles of ATO-combined chemotherapy were applied throughout the entire scheme.

Results

A total of three refractory/recurrent and one untreated ARMS patient, three male and one female, with a median age of 5.8 years (range, 5.1 to 12.5 years), were enrolled in the present study. All patients were sensitive to combined chemotherapy with ATO and achieved partial or complete remission during treatment. Except for reversible gastrointestinal reaction and myelosuppression, no other adverse events were observed during the process of treatment.

Conclusions

The combined chemotherapy of ATO and the VAC regimen exhibited beneficial activities against ARMS in pediatrics and was well tolerated, but prospective large-scale clinical trials are warranted to determine the long-term efficacy, optimal courses, and late toxicity in this population.

Chemoembolizing hepatocellular carcinoma with microsphere cored with arsenic trioxide microcrystal

Chemoembolization for hepatocellular carcinoma (HCC) is often suboptimal due to multiple involved signaling and lack of effective drugs. Arsenic trioxide (ATO) is a potent chemotherapeutic agent, which can target multiple signaling and have substantial efficacy on HCC. However, its usage is limited due to systemic toxicity. Using ATO-eluting beads/microspheres for chemoembolization can have locoregional drug delivery and avoid systemic exposure but will require high drug load, which has not been achieved due to low solubility of ATO. Through an innovative approach, we generated the transiently formed ATO microcrystals via micronization and stabilized these microcrystals by solvent exchange. By encapsulating ATO microcrystals, but not individual molecules, with poly(lactide-co-glycolic acid) (PLGA), we developed microspheres cored with extremely high dense ATO. The molar ratio between ATO and PLGA was 157.4:1 and drug load was 40.1%, which is 4–20 fold higher than that of reported ATO nano/microparticles. These microspheres sustainably induced reactive oxygen species, apoptosis, and cytotoxicity on HCC cells and reduced tumor growth by 80% via locoregional delivery. Chemoembolization on mice model showed that ATO-microcrystal loaded microspheres, but not ATO, inhibited HCC growth by 60–75%, which indicates ATO within these microspheres gains the chemoembolizing function via our innovative approach.

Drug-eluting bead trans-arterial chemoembolization combined with microwave ablation therapy vs. microwave ablation alone for early stage hepatocellular carcinoma: a preliminary investigation of clinical value

Purpose

To assess the clinical value of drug-eluting bead trans-arterial chemoembolization (DEB-TACE) combined with microwave ablation (MWA) vs. MWA treatment alone for early stage hepatocellular carcinoma (HCC).

Materials and methods

Consecutive data from 102 HCC patients at early stage who were referred to our hospital from December 2014 to May 2016 were retrospectively collected. Forty-seven patients underwent DEB-TACE combined with MWA treatment, whereas 55 patients underwent MWA alone. After 1 month of treatment, the tumour responses of the patients were assessed using the mRECIST criteria. Treatment-related complications and hepatic function were also analysed for the two groups. In addition, overall survival (OS) and progression-free survival (PFS) were calculated and compared.

Results

Patients in the combined treatment group (DEB-TACE combined with MWA) presented a better objective response rate (ORR) and disease control rate (DCR) compared with those in the monotherapy group (MWA treatment). The median OS and PFS were longer in the combined treatment group compared with the monotherapy group. Multivariate Cox’s regression further illustrated that DEB-TACE + MWA vs. MWA was an independent protective factor for PFS and OS. No serious treatment-related complications were observed in any of the patients.

Conclusion

Combined treatment with DEB-TACE appeared to have advantages in prolonging OS and PFS compared to MWA. Therefore, combined treatment was efficient and should be strongly recommended to early stage HCC patients.

Antimicrobial Activity of Metals and Metalloids

Competition shapes evolution. Toxic metals and metalloids have exerted selective pressure on life since the rise of the first organisms on the Earth, which has led to the evolution and acquisition of resistance mechanisms against them, as well as mechanisms to weaponize them. Microorganisms exploit antimicrobial metals and metalloids to gain competitive advantage over other members of microbial communities. This exerts a strong selective pressure that drives evolution of resistance. This review describes, with a focus on arsenic and copper, how microorganisms exploit metals and metalloids for predation and how metal- and metalloid-dependent predation may have been a driving force for evolution of microbial resistance against metals and metalloids. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Curcumin supplementation shows modulatory influence on functional and morphological features of hippocampus in mice subjected to arsenic trioxide exposure

Since, oxidative stress has been suggested as one of the mechanisms underlying arsenic-induced toxicity, the present study focused on the role of antioxidant (curcumin) supplementation on behavioral, biochemical, and morphological alterations with context to mice hippocampus (CA1) following arsenic trioxide (As₂O₃) administration. Healthy male Swiss albino mice were divided into control and experimental groups. As₂O₃ (2 mg/kg bw) alone or along with curcumin (100 mg/kg bw) was administered to experimental groups by oral route for 45 days whereas the control groups received either no treatment or vehicle for curcumin. Animals were subjected to behavioral study towards the end of the experimental period (day 33-45). On day 46, the brain samples were obtained and subjected either to immersion fixation (for morphometric observations) or used afresh for biochemical test. Behavioral tests (open field, elevated plus maze, and Morris water maze) revealed enhanced anxiety levels and impairment of cognitive functions in As₂O₃ alone treated groups whereas a trend of recovery was evident in mice simultaneously treated with As₂O₃ and curcumin. Morphological observations showed noticeable reduction in stratum pyramidale thickness (CA1), along with decrease in density and size of pyramidal neurons in As₂O₃ alone exposed group as compared to As₂O₃+Cu co-treated group. Hippocampal glutathione levels were found to be downregulated in animals receiving As₂O₃ as against the levels of controls and curcumin supplemented animals, thereby, suggestive of beneficial role of curcumin on As₂O₃ induced adverse effects.

Erythrocyte Membrane-Coated Arsenic Trioxide-Loaded Sodium Alginate Nanoparticles for Tumor Therapy

Arsenic trioxide (ATO) has a significant effect on the treatment of acute promyelocytic leukemia (APL) and advanced primary liver cancer, but it still faces severe side effects. Considering these problems, red blood cell membrane-camouflaged ATO-loaded sodium alginate nanoparticles (RBCM-SA-ATO-NPs, RSANs) were developed to relieve the toxicity of ATO while maintaining its efficacy. ATO-loaded sodium alginate nanoparticles (SA-ATO-NPs, SANs) were prepared by the ion crosslinking method, and then RBCM was extruded onto the surface to obtain RSANs. The average particle size of RSANs was found to be 163.2 nm with a complete shell-core bilayer structure, and the average encapsulation efficiency was 14.31%. Compared with SANs, RAW 264.7 macrophages reduced the phagocytosis of RSANs by 51%, and the in vitro cumulative release rate of RSANs was 95% at 84 h, which revealed a prominent sustained release. Furthermore, it demonstrated that RSANs had lower cytotoxicity as compared to normal 293 cells and exhibited anti-tumor effects on both NB4 cells and 7721 cells. In vivo studies further showed that ATO could cause mild lesions of main organs while RSANs could reduce the toxicity and improve the anti-tumor effects. In brief, the developed RSANs system provides a promising alternative for ATO treatment safely and effectively.

Multidrug Resistance Protein 1 (MRP1/ABCC1)-Mediated Cellular Protection and Transport of Methylated Arsenic Metabolites Differs between Human Cell Lines

The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) protects cells from arsenic (a proven human carcinogen) through the cellular efflux of arsenic triglutathione [As(GS)3] and the diglutathione conjugate of monomethylarsonous acid [MMA(GS)2]. Previously, differences in MRP1 phosphorylation (at Y920/S921) and N-glycosylation (at N19/N23) were associated with marked differences in As(GS)3 transport kinetics between HEK293 and HeLa cell lines. In the current study, cell line differences in MRP1-mediated cellular protection and transport of other arsenic metabolites were explored. MRP1 expressed in HEK293 cells reduced the toxicity of the major urinary arsenic metabolite dimethylarsinic acid (DMAV), and HEK-WT-MRP1-enriched vesicles transported DMAV with high apparent affinity and capacity (Km 0.19 µM, Vmax 342 pmol⋅mg-1protein⋅min-1). This is the first report that MRP1 is capable of exporting DMAV, critical for preventing highly toxic dimethylarsinous acid formation. In contrast, DMAV transport was not detected using HeLa-WT-MRP1 membrane vesicles. MMA(GS)2 transport by HeLa-WT-MRP1 vesicles had a greater than threefold higher Vmax compared with HEK-WT-MRP1 vesicles. Cell line differences in DMAV and MMA(GS)2 transport were not explained by differences in phosphorylation at Y920/S921. DMAV did not inhibit, whereas MMA(GS)2 was an uncompetitive inhibitor of As(GS)3 transport, suggesting that DMAV and MMA(GS)2 have nonidentical binding sites to As(GS)3 on MRP1. Efflux of different arsenic metabolites by MRP1 is likely influenced by multiple factors, including cell and tissue type. This could have implications for the impact of MRP1 on both tissue-specific susceptibility to arsenic-induced disease and tumor sensitivity to arsenic-based therapeutics.

Cellular arsenic transport pathways in mammals

Natural contamination of drinking water with arsenic results in the exposure of millions of people world-wide to unacceptable levels of this metalloid. This is a serious global health problem because arsenic is a Group 1 (proven) human carcinogen and chronic exposure is known to cause skin, lung, and bladder tumors. Furthermore, arsenic exposure can result in a myriad of other adverse health effects including diseases of the cardiovascular, respiratory, neurological, reproductive, and endocrine systems. In addition to chronic environmental exposure to arsenic, arsenic trioxide is approved for the clinical treatment of acute promyelocytic leukemia, and is in clinical trials for other hematological malignancies as well as solid tumors. Considerable inter-individual variability in susceptibility to arsenic-induced disease and toxicity exists, and the reasons for such differences are incompletely understood. Transport pathways that influence the cellular uptake and export of arsenic contribute to regulating its cellular, tissue, and ultimately body levels. In the current review, membrane proteins (including phosphate transporters, aquaglyceroporin channels, solute carrier proteins, and ATP-binding cassette transporters) shown experimentally to contribute to the passage of inorganic, methylated, and/or glutathionylated arsenic species across cellular membranes are discussed. Furthermore, what is known about arsenic transporters in organs involved in absorption, distribution, and metabolism and how transport pathways contribute to arsenic elimination are described.

Global Fitness Profiling Identifies Arsenic and Cadmium Tolerance Mechanisms in Fission Yeast

Heavy metals and metalloids such as cadmium [Cd(II)] and arsenic [As(III)] are widespread environmental toxicants responsible for multiple adverse health effects in humans. However, the molecular mechanisms underlying metal-induced cytotoxicity and carcinogenesis, as well as the detoxification and tolerance pathways, are incompletely understood. Here, we use global fitness profiling by barcode sequencing to quantitatively survey the Schizosaccharomyces pombe haploid deletome for genes that confer tolerance of cadmium or arsenic. We identified 106 genes required for cadmium resistance and 110 genes required for arsenic resistance, with a highly significant overlap of 36 genes. A subset of these 36 genes account for almost all proteins required for incorporating sulfur into the cysteine-rich glutathione and phytochelatin peptides that chelate cadmium and arsenic. A requirement for Mms19 is explained by its role in directing iron–sulfur cluster assembly into sulfite reductase as opposed to promoting DNA repair, as DNA damage response genes were not enriched among those required for cadmium or arsenic tolerance. Ubiquinone, siroheme, and pyridoxal 5′-phosphate biosynthesis were also identified as critical for Cd/As tolerance. Arsenic-specific pathways included prefoldin-mediated assembly of unfolded proteins and protein targeting to the peroxisome, whereas cadmium-specific pathways included plasma membrane and vacuolar transporters, as well as Spt–Ada–Gcn5-acetyltransferase (SAGA) transcriptional coactivator that controls expression of key genes required for cadmium tolerance. Notable differences are apparent with corresponding screens in the budding yeast Saccharomyces cerevisiae, underscoring the utility of analyzing toxic metal defense mechanisms in both organisms.

Polymorphic variants of MRP4/ABCC4 differentially modulate the transport of methylated arsenic metabolites and physiological organic anions

Broad inter-individual variation exists in susceptibility to arsenic-induced tumours, likely involving differences in the ability of individuals to eliminate this metalloid. We recently identified human multidrug resistance protein 4 (MRP4/ABCC4) as a novel pathway for the cellular export of dimethylarsinic acid (DMA^V), the major urinary arsenic metabolite in humans, and the diglutathione conjugate of the highly toxic monomethylarsonous acid [MMA(GS)₂]. These findings, together with the basolateral and apical membrane localization of MRP4 in hepatocytes and renal proximal tubule cells, respectively, suggest a role for MRP4 in the urinary elimination of hepatic arsenic metabolites. Accordingly, we have now investigated the influence of non-synonymous single nucleotide polymorphisms (SNPs) on MRP4 levels, cellular localization, and arsenical transport. Of eight MRP4 variants (C171G-, G187W-, K304N-, G487E-, Y556C-, E757K-, V776I- and C956S-MRP4) characterized, two (V776I- and C956S-MRP4) did not localize appropriately to the plasma membrane of HEK293T and LLC-PK1 cells. Characterization of the six correctly localized mutants revealed that MMA(GS)₂ transport by C171G-, G187W-, and K304N-MRP4 was 180%, 73%, and 30% of WT-MRP4 activity, respectively, whereas DMA^V transport by K304N- and Y556C-MRP4 was 30% and 184% of WT-MRP4, respectively. Transport of the prototypical physiological MRP4 substrates prostaglandin E₂ and 17β-estradiol 17-(β-d-glucuronide) by the six variants was also differentially affected. Thus, MRP4 variants have differing abilities to transport arsenic and endogenous metabolites through both altered function and membrane localization. Further investigation is warranted to determine if genetic variations in ABCC4 contribute to inter-individual differences in susceptibility to arsenic-induced (and potentially other) diseases.

Arsenic Triglutathione [As(GS)3] Transport by Multidrug Resistance Protein 1 (MRP1/ABCC1) Is Selectively Modified by Phosphorylation of Tyr920/Ser921 and Glycosylation of Asn19/Asn23

The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) is responsible for the cellular export of a chemically diverse array of xenobiotics and endogenous compounds. Arsenic, a human carcinogen, is a high-affinity MRP1 substrate as arsenic triglutathione [As(GS)3]. In this study, marked differences in As(GS)3 transport kinetics were observed between MRP1-enriched membrane vesicles prepared from human embryonic kidney 293 (HEK) (Km 3.8 µM and Vmax 307 pmol/mg per minute) and HeLa (Km 0.32 µM and Vmax 42 pmol/mg per minute) cells. Mutant MRP1 lacking N-linked glycosylation [Asn19/23/1006Gln; sugar-free (SF)-MRP1] expressed in either HEK293 or HeLa cells had low Km and Vmax values for As(GS)3, similar to HeLa wild-type (WT) MRP1. When prepared in the presence of phosphatase inhibitors, both WT- and SF-MRP1-enriched membrane vesicles had a high Km value for As(GS)3 (3-6 µM), regardless of the cell line. Kinetic parameters of As(GS)3 for HEK-Asn19/23Gln-MRP1 were similar to those of HeLa/HEK-SF-MRP1 and HeLa-WT-MRP1, whereas those of single glycosylation mutants were like those of HEK-WT-MRP1. Mutation of 19 potential MRP1 phosphorylation sites revealed that HEK-Tyr920Phe/Ser921Ala-MRP1 transported As(GS)3 like HeLa-WT-MRP1, whereas individual HEK-Tyr920Phe- and -Ser921Ala-MRP1 mutants were similar to HEK-WT-MRP1. Together, these results suggest that Asn19/Asn23 glycosylation and Tyr920/Ser921 phosphorylation are responsible for altering the kinetics of MRP1-mediated As(GS)3 transport. The kinetics of As(GS)3 transport by HEK-Asn19/23Gln/Tyr920Glu/Ser921Glu were similar to HEK-WT-MRP1, indicating that the phosphorylation-mimicking substitutions abrogated the influence of Asn19/23Gln glycosylation. Overall, these data suggest that cross-talk between MRP1 glycosylation and phosphorylation occurs and that phosphorylation of Tyr920 and Ser921 can switch MRP1 to a lower-affinity, higher-capacity As(GS)3 transporter, allowing arsenic detoxification over a broad concentration range.

Grape seed and skin extract protects against arsenic trioxide induced oxidative stress in rat heart

Arsenic is a metalloid found in water, soil, and air from natural and anthropogenic sources, and is commonly found in inorganic as well as organic forms. The clinical use of arsenic trioxide (As2O3) in the treatment of acute promyelocytic leukemia (APL) is limited by its cardiotoxic side effects. Grape seed and skin extract (GSSE) is a polyphenolic mixture with antioxidant properties. This study aimed to evaluate the protective effect of GSSE on arsenic-induced cardiac oxidative stress and injury. Animals exposed to 2.5 mg/kg As2O3 for 21 days exhibited a relevant increase in heart lipoperoxidation, protein carbonylation, and inflammation, as well as a drop in the activity of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx). In addition, As2O3 disturbed heart lipidemia and lipase activity, transition metals distribution and the associated enzymes, intracellular mediators such as calcium and the associated calpain activity, as well as myocardial architecture. Treatment with 4 g/kg GSSE protected against most of the deleterious effects provoked by As2O3. Our data suggest that GSSE has the potential to protect against As2O3-induced cardiotoxicity.

Perturbation of cellular oxidative state induced by dichloroacetate and arsenic trioxide for treatment of acute myeloid leukemia

The incidence of acute myeloid leukemia (AML) is rising and the outcome of current therapy, which has not changed significantly in the last 40 years, is suboptimal. Cellular oxidative state is a credible target to selectively eradicate AML cells, because it is a fundamental property of each cell that is sufficiently different between leukemic and normal cells, yet its aberrancy shared among different AML cells. To this end, we tested whether a short-time treatment of AML cells, including cells with FLT3-ITD mutation, with sub-lethal dose of dichloroacetate (DCA) (priming) followed by pharmacologic dose of arsenic trioxide (ATO) in presence of low-dose DCA could produce insurmountable level of oxidative damage that kill AML cells. Using cellular cytotoxicity, apoptotic and metabolic assays with both established AML cell lines and primary AML cells, we found that priming with DCA significantly potentiated the cytotoxicity of ATO in AML cells in a synergistic manner. The combination decreased the mitochondrial membrane potential as well as expression of Mcl-1 and GPx in primary AML cells more than either drug alone. One patient with AML whose disease was refractory to several lines of prior treatments was treated with this combination, and tolerated it well. These data suggest that targeting cellular redox balance in leukemia may provide a therapeutic option for AML patients with relapsed/refractory disease.

The clinical activity of arsenic trioxide, ascorbic acid, ifosfamide and prednisone combination therapy in patients with relapsed and refractory multiple myeloma

This study aimed to investigate the activity of arsenic trioxide (As2O3) combined with ascorbic acid, ifosfamide, and prednisone chemotherapy in patients with repeatedly relapsed and refractory multiple myeloma (MM). Here, we retrospectively analyzed medical data of 30 MM patients showing progressive disease after receiving at least two previous lines of treatment including an immunomodulatory agent (thalidomide or lenalidomide) and a proteasome inhibitor. There were 19 men and eleven women, aged 54-73 (median 65) years, in this study. The distribution of different isotypes included immunoglobulin G(IgG) (12 patients), IgA (six patients), IgD (three), and light chain (nine patients). All the patients were Durie-Salmon stage III and had relapsed at least three times; the median cycles of prior therapies was 15 (range 10-18). The patients were treated with As2O3, ascorbic acid, and CP (ifosfamide 1 g on day 1, day 3, day 5, and day 7; prednisone 30 mg taken orally for 2 weeks). As2O3 was administered as an intravenous infusion at a dose of 10 mg/d and ascorbic acid at a dose of 2 g/d for 14 days of each 4-week cycle. The results showed that after 2 cycles of therapy, there were five patients that attained partial response, 15 had minimal response, five had no change, and five had progressive disease. The overall response rate was 66.7% (20/30 cases), 50% (10/20 cases), and 40% (2/5 cases), respectively, after 2, 4, and 6 cycles of the therapy. But there were no patients that attained complete remission. The median time of overall survival and progression-free survival were 48 (29-120) and 6 (2-8) months, respectively. The most common treatment-related adverse events included neutropenia, fatigue, anemia, thrombocytopenia, and infection that could be tolerated. The results showed that As2O3 combined with ascorbic acid, ifosfamide, and prednisone chemotherapy may be a choice treatment for repeatedly relapsed and refractory MM patients.

Apoptotic efficacy of etomoxir in human acute myeloid leukemia cells. Cooperation with arsenic trioxide and glycolytic inhibitors, and regulation by oxidative stress and protein kinase activities

Fatty acid synthesis and oxidation are frequently exacerbated in leukemia cells, and may therefore represent a target for therapeutic intervention. In this work we analyzed the apoptotic and chemo-sensitizing action of the fatty acid oxidation inhibitor etomoxir in human acute myeloid leukemia cells. Etomoxir caused negligible lethality at concentrations up to 100 µM, but efficaciously cooperated to cause apoptosis with the anti-leukemic agent arsenic trioxide (ATO, Trisenox), and with lower efficacy with other anti-tumour drugs (etoposide, cisplatin), in HL60 cells. Etomoxir-ATO cooperation was also observed in NB4 human acute promyelocytic cells, but not in normal (non-tumour) mitogen-stimulated human peripheral blood lymphocytes. Biochemical determinations in HL60 cells indicated that etomoxir (25–200 µM) dose-dependently inhibited mitochondrial respiration while slightly stimulating glycolysis, and only caused marginal alterations in total ATP content and adenine nucleotide pool distribution. In addition, etomoxir caused oxidative stress (increase in intracellular reactive oxygen species accumulation, decrease in reduced glutathione content), as well as pro-apoptotic LKB-1/AMPK pathway activation, all of which may in part explain the chemo-sensitizing capacity of the drug. Etomoxir also cooperated with glycolytic inhibitors (2-deoxy-D-glucose, lonidamine) to induce apoptosis in HL60 cells, but not in NB4 cells. The combined etomoxir plus 2-deoxy-D-glucose treatment did not increase oxidative stress, caused moderate decrease in net ATP content, increased the AMP/ATP ratio with concomitant drop in energy charge, and caused defensive Akt and ERK kinase activation. Apoptosis generation by etomoxir plus 2-deoxy-D-glucose was further increased by co-incubation with ATO, which is apparently explained by the capacity of ATO to attenuate Akt and ERK activation. In summary, co-treatment with etomoxir may represent an interesting strategy to increase the apoptotic efficacy of ATO and (with some limitations) 2-deoxy-D-glucose which, although clinically important anti-tumour agents, exhibit low efficacy in monotherapy.

Arsenate stimulates glutathione export from viable cultured rat cerebellar granule neurons

Arsenate is an environmental pollutant which contaminates the drinking water of millions of people worldwide. Numerous in vitro studies have investigated the toxicity of arsenate for a large number of different cell types. However, despite the known neurotoxic potential of arsenicals, little is known so far about the consequences of an exposure of neurons to arsenate. To investigate acute effects of arsenate on the viability and the glutathione (GSH) metabolism of neurons, we have exposed primary rat cerebellar granule neuron cultures to arsenate. Incubation of neurons for up to 6 h with arsenate in concentrations of up to 10 mM did not acutely compromise the cell viability, although the cells accumulated substantial amounts of arsenate. However, exposure to arsenate caused a time- and concentration-dependent increase in the export of GSH from viable neurons with significant effects observed for arsenate in concentrations above 0.3 mM. The arsenate-induced stimulation of GSH export was abolished upon removal of arsenate and completely prevented by MK571, an inhibitor of the multidrug resistance protein 1. These results demonstrate that arsenate is not acutely toxic to neurons but can affect the neuronal GSH metabolism by stimulating GSH export.

Lung tumors in mice induced by "whole-life" inorganic arsenic exposure at human-relevant doses

In mice, inorganic arsenic in the drinking water in the parts per million range via the dam during in utero life or with whole-life exposure is a multi-site carcinogen in the offspring. However, human arsenic exposure is typically in the parts per billion (ppb) range. Thus, we studied "whole-life" inorganic arsenic carcinogenesis in mice at levels more relevant to humans. Breeder male and female CD1 mice were exposed to 0, 50, 500 or 5,000 ppb arsenic (as sodium arsenite) in the drinking water for 3 weeks prior to breeding, during pregnancy and lactation, and after weaning (at week 3) groups of male and female offspring (initial n = 40) were exposed for up to 2 years. Tumors were assessed in these offspring. Arsenic exposure had no effect on pregnant dam weights or water consumption, litter size, offspring birthweight or weight at weaning compared to control. In male offspring mice, arsenic exposure increased (p < 0.05) bronchiolo-alveolar tumor (adenoma or carcinoma) incidence at 50-ppb group (51 %) and 500-ppb group (54 %), but not at 5,000-ppb group (28 %) compared to control (22 %). These arsenic-induced bronchiolo-alveolar tumors included increased (p < 0.05) carcinoma at 50-ppb group (27 %) compared to controls (8 %). An increase (p < 0.05) in lung adenoma (25 %) in the 50-ppb group compared to control (11 %) occurred in female offspring. Thus, in CD1 mice whole-life arsenic exposure induced lung tumors at human-relevant doses (i.e., 50 and 500 ppb).

A novel pathway for arsenic elimination: human multidrug resistance protein 4 (MRP4/ABCC4) mediates cellular export of dimethylarsinic acid (DMAV) and the diglutathione conjugate of monomethylarsonous acid (MMAIII)

Hundreds of millions of people worldwide are exposed to unacceptable levels of arsenic in drinking water. This is a public health crisis because arsenic is a Group I (proven) human carcinogen. Human cells methylate arsenic to monomethylarsonous acid (MMA(III)), monomethylarsonic acid (MMA(V)), dimethylarsinous acid (DMA(III)), and dimethylarsinic acid (DMA(V)). Although the liver is the predominant site for arsenic methylation, elimination occurs mostly in urine. The protein(s) responsible for transport of arsenic from the liver (into blood), ultimately for urinary elimination, are unknown. Human multidrug resistance protein 1 (MRP1/ABCC1) and MRP2 (ABCC2) are established arsenic efflux pumps, but unlike the related MRP4 (ABCC4) are not present at the basolateral membrane of hepatocytes. MRP4 is also found at the apical membrane of renal proximal tubule cells, making it an ideal candidate for urinary arsenic elimination. In the current study, human MRP4 expressed in HEK293 cells reduced the cytotoxicity and cellular accumulation of arsenate, MMA(III), MMA(V), DMA(III), and DMA(V) while two other hepatic basolateral MRPs (MRP3 and MRP5) did not. Transport studies with MRP4-enriched membrane vesicles revealed that the diglutathione conjugate of MMA(III), monomethylarsenic diglutathione [MMA(GS)(2)], and DMA(V) were the transported species. MMA(GS)(2) and DMA(V) transport was osmotically sensitive, allosteric (Hill coefficients of 1.4 ± 0.2 and 2.9 ± 1.2, respectively), and high affinity (K0.5 of 0.70 ± 0.16 and 0.22 ± 0.15 μM, respectively). DMA(V) transport was pH-dependent, with highest affinity and capacity at pH 5.5. These results suggest that human MRP4 could be a major player in the elimination of arsenic.