Disulfiram Facilitates Intracellular Cu Uptake and Induces Apoptosis in Human Melanoma Cells

New uses for old copper-binding drugs: converting the pro-angiogenic copper to a specific cancer cell death inducer

BACKGROUND

The conventional approach toward anticancer drug development is a time-consuming and expensive procedure.

OBJECTIVE/METHODS

One approach to expedite this process and achieve more affordable means is to discover new applications of existing drugs, since their pharmacokinetics and pharmacological profiles are well known.

RESULTS

Our encouraging findings in recent studies reveal anticancer activities of several copper-binding ligands including disulfiram (an antialcoholism drug), clioquinol (used to treat Alzheimer's and Huntington's diseases) and diethyldithiocarbamate (an agent for HIV-1 infection treatment).

CONCLUSION

These in vitro and in vivo studies have demonstrated that these archaic drugs can target and react with tumor cellular copper, forming complexes that act as potent proteasome inhibitors and apoptosis inducers.

Melanosomal damage in normal human melanocytes induced by UVB and metal uptake--a basis for the pro-oxidant state of melanoma

Melanins are ubiquitous catecholic pigments, formed in organelles called melanosomes within melanocytes, the function of which is to protect skin against harmful effects of UV radiation. Melanosomes within melanoma cells are characteristically abnormal, with fragmented melanin and disrupted membranes. We hypothesize that the disruption of melanosomal melanin might be an early event in the etiology and progression of melanoma, leading to increased oxidative stress and mutation. In this report, we examine the effect of a combination of UV treatment and metal ion exposure on melanosomes within melanocytes, as well as their ability to act as pro-oxidants in ex situ experiments, and assay the effects of this treatment on viability and cell cycle progression. UVB exposure causes morphologic changes of the cells and bleaching of melanosomes in normal melanocytes, both significantly enhanced in Cu(II) and Cd(II)-treated cells, as observed by microscopy. The promoted bleaching by Cu(II) is due to its ability to redox cycle under oxidative conditions, generating reactive oxygen species; verified by the observed enhancement of hydroxyl radical generation when isolated melanosomes were treated with both Cu(II) ions and UVB, as assayed by DNA clipping. Single-dose UVB/Cu treatment does not greatly affect cell viability or cell cycle progression in heavily pigmented cells, but did so in an amelanotic early stage melanoma cell line.

Unexpected C-H activation of Ru(II)-dithiomaltol complexes upon oxidation

Thione-substituted derivatives of maltol are of interest in several applications of metal-based drugs. In order to investigate the effect of the oxygenation on such thione chelates, Ru complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol or Htma) and 3-hydroxy-2-methyl-4H-thiopyran-4-thione (dithiomaltol or Httma), [Ru(bpy)2(tma)](+), 1, and [Ru(bpy) 2(ttma)] (+), 2, were synthesized as diamagnetic PF6(-) salts. Peroxidation of 2 unexpectedly generated products of C-H activation at its pendant methyl group; an air-stable aldehyde [Ru(bpy)2(ttma-aldehyde)](+), 4, was the major product. In addition, an intermediate oxidation product [Ru(bpy) 2(ttma-alcohol)](PF6), 3, was characterized. Both 3 and 4 are also formed by reaction of 2 with outersphere oxidants (e.g., Na2IrCl6) and by bulk electrolysis under anaerobic conditions. Similar oxidations of the analogous [Ru(bpy)2(ettma)](+), 2' , complex (3-hydroxy-2-ethyl-4H-thiopyran-4-thione; ethyl dithiomaltol or Hettma) formed the corresponding ketone, [Ru(bpy)2(ettma-ketone)](PF6), 4', by oxidation at the same position adjacent to the conjugated ring. The structures of the aldehyde 4 and starting materials 1 and 2 have been confirmed by X-ray crystallography, and all complexes have been characterized by UV-vis, (1)H NMR, and IR spectroscopies. Initial mechanistic investigations are discussed.

ALDH1A1 and ALDH3A1 expression in lung cancers: correlation with histologic type and potential precursors

We hypothesize that aldehyde dehydrogenase (ALDH) isozymes may be upregulated in lung tissue as a result of exposure to carcinogenic aldehydes found in cigarette smoke. To investigate this hypothesis, we studied the expression of two ALDH isozymes in lung cancer from patient samples and its relationship to the history of cigarette smoking. Immunohistochemical staining for ALDH1A1 and ALDH3A1 was performed on archival specimens from control patients without lung cancer, and patients with one of the primary lung cancers: squamous cell cancer (SCCA), adenocarcinoma (AdenoCA), and small cell lung cancer (SCLC). An overall score was obtained for each sample based upon multiplying the staining intensity (0-3) and the extensiveness (0-100%). Mean+/-S.E.M. for each experimental group was calculated and compared. Our results indicate a significantly higher level of expression of ALDH1A1 and ALDH3A1 in SCCA (155+/-19 and 162+/-17, respectively) and AdenoCA (116+/-12 and 107+/-10) than SCLC (39+/-11 and 42+/-12) (P<0.01). Atypical pneumocytes demonstrated significantly higher levels of expression of ALDH1A1 and ALDH3A1 than normal pneumocytes (a normal counterpart of AdenoCA), which is suggestive of up regulation during malignant transformation to AdenoCA. A subset analysis of all samples studied revealed increased expression of ALDH1A1 (P=0.055) and ALDH3A1 (P=0.0093) in normal pneumocytes of smokers (n=32) in comparison to those of non-smokers (n=17). Non-small cell lung cancer (NSCLC) express very high levels of ALDH1A1 and ALDH3A1 in comparison with SCLC, elevated expression of both enzymes may be associated with malignant transformation to AdenoCA, and cigarette smoking seems to result in increased expression of these enzymes in normal pneumocytes.

Complex, unusual conformational changes in kidney betaine aldehyde dehydrogenase suggested by chemical modification with disulfiram

The NAD+-dependent animal betaine aldehyde dehydrogenases participate in the biosynthesis of glycine betaine and carnitine, as well as in polyamines catabolism. We studied the kinetics of inactivation of the porcine kidney enzyme (pkBADH) by the drug disulfiram, a thiol-reagent, with the double aim of exploring the enzyme dynamics and investigating whether it could be an in vivo target of disulfiram. Both inactivation by disulfiram and reactivation by reductants were biphasic processes with equal limiting amplitudes. Under certain conditions half of the enzyme activity became resistant to disulfiram inactivation. NAD+ protected almost 100% at 10 microM but only 50% at 5mM, and vice versa if the enzyme was pre-incubated with NAD+ before the chemical modification. NADH, betaine aldehyde, and glycine betaine also afforded greater protection after pre-incubation with the enzyme than without pre-incubation. Together, these findings suggest two kinds of active sites in this seemingly homotetrameric enzyme, and complex, unusual ligand-induced conformational changes. In addition, they indicate that, in vivo, pkBADH is most likely protected against disulfiram inactivation.

Role of peroxidases, thiols and Bak/Bax in tumor cell susceptibility to Cu[DEDTC]2

Copper and two molecules of diethyl dithiocarbamate [DEDTC] form the Cu[DEDTC](2) complex, which shows cytotoxicity against melanoma and carcinoma cells, making it a potentially useful anti-cancer agent. The differential response to Cu[DEDTC](2) in susceptible human SKBR3 carcinoma and C8161 melanoma cell variants of moderate and high resistance to this organometallic complex was evaluated in this study. Both cell lines underwent apoptosis-associated PARP cleavage, changes in expression of nuclear NFkB p65, p21WAF1 and cyclin A, with loss of clonogenicity in response to this agent. However, a threefold greater concentration [IC(50) 0.6 microM DEDTC: 0.3 microM Cu] was required to kill moderately resistant C8161 melanoma compared to highly susceptible SKBR3 cells. Decreased susceptibility to Cu[DEDTC](2) in C8161 melanoma correlated with greater levels of glutathione peroxidase and catalase, and a fourfold lower requirement for N-acetyl cysteine (1mM) to overcome toxicity. Whereas melanoma cells selected for resistance to [0.8 microM DEDTC: 0.4 microM Cu] showed persistent catalase and GPx activity, melanoma cells with moderate susceptibility showed decreased catalase and Gpx when responding to treatment. Cytotoxic response in moderately susceptible C8161 melanoma cells involved an early accumulation of pro-apoptotic Bax in the G2 cell cycle phase, followed by an increased ratio of pro-apoptotic Bak to anti-apoptotic Mcl-1 in mitochondria. Our data suggests that Cu[DEDTC](2) toxicity is mediated through an increase in pro-apoptotic Bak/Bax via disruption of the peroxide and thiol metabolism.

NQO1-activated phenothiazinium redox cyclers for the targeted bioreductive induction of cancer cell apoptosis

Altered redox signaling and regulation in cancer cells represent a chemical vulnerability that can be targeted by selective chemotherapeutic intervention. Here, we demonstrate that 3,7-diaminophenothiazinium-based redox cyclers (PRC) induce selective cancer cell apoptosis by NAD(P)H:quinone oxidoreductase (NQO1)-dependent bioreductive generation of cellular oxidative stress. Using PRC lead compounds including toluidine blue against human metastatic G361 melanoma cells, apoptosis occurred with phosphatidylserine externalization, loss of mitochondrial transmembrane potential, cytochrome c release, caspase-3 activation, and massive ROS production. Consistent with reductive activation and subsequent redox cycling as the mechanism of PRC cytotoxicity, coincubation with catalase achieved cell protection, whereas reductive antioxidants enhanced PRC cytotoxicity. Unexpectedly, human A375 melanoma cells were resistant to PRC-induced apoptosis, and PRC-sensitive G361 cells were protected by preincubation with the NQO1 inhibitor dicoumarol. Indeed, NQO1 specific enzymatic activity was 9-fold higher in G361 than in A375 cells. The critical role of NQO1 in PRC bioactivation and cytotoxicity was confirmed, when NQO1-transfected breast cancer cells (MCF7-DT15) stably overexpressing active NQO1 displayed strongly enhanced PRC sensitivity as compared to vector control-transfected cells with baseline NQO1 activity. Based on the known overexpression of NQO1 in various tumors these findings suggest the feasibility of developing PRC lead compounds into tumor-selective bioreductive chemotherapeutics.

Reactive Oxygen Species: A Breath of Life or Death?: Fig. 1

New insights into cancer cell-specific biological pathways are urgently needed to promote development of rationally targeted therapeutics. Reactive oxygen species (ROS) and their role in cancer cell response to growth factor signaling and hypoxia are emerging as verdant areas of exploration on the road to discovering cancer's Achilles heel. One of the distinguishing and near-universal hallmarks of cancer growth is hypoxia. Unregulated cellular proliferation leads to formation of cellular masses that extend beyond the resting vasculature, resulting in oxygen and nutrient deprivation. The resulting hypoxia triggers a number of critical adaptations that enable cancer cell survival, including apoptosis suppression, altered glucose metabolism, and an angiogenic phenotype. Ironically, recent investigations suggest that oxygen depletion stimulates mitochondria to elaborate increased ROS, with subsequent activation of signaling pathways, such as hypoxia inducible factor 1alpha, that promote cancer cell survival and tumor growth. Because mitochondria are key organelles involved in chemotherapy-induced apoptosis induction, the relationship between mitochondria, ROS signaling, and activation of survival pathways under hypoxic conditions has been the subject of increased study. Insights into mechanisms involved in ROS signaling may offer novel avenues to facilitate discovery of cancer-specific therapies. Preclinical and clinical evaluation of agents that modify ROS signaling in cancer offers a novel avenue for intervention. This review will cover recent work in ROS-mediated signaling in cancer cells and its potential as a target for developmental therapeutics.

Image-Based Screening for the Identification of Novel Proteasome Inhibitors

The proteasome is a new, interesting target in cancer drug therapy, and the proteasome inhibitor bortezomib has shown an effect in myeloma patients. It is of interest to efficiently discover and evaluate new proteasome inhibitors. The authors describe the development of an image-based screening assay for the identification of compounds with proteasome-inhibiting activity. The stably transfected human embryo kidney cell line HEK 293 ZsGreen Proteasome Sensor Cell Line expressing the ZsProSensor-1 fusion protein was used for screening and evaluation of proteasome inhibitors. Inhibition of the proteasome leads to accumulation of the green fluorescent protein ZsGreen, which is measured in the ArrayScan® High Content Screening system, in which cell morphology is studied simultaneously. When screening the LOPAC1280 substance library, several compounds with effect on the proteasome were found; among the hits were disulfiram and ammonium pyrrolidinedithiocarbamate (PDTC). Cytotoxic analysis of disulfiram and PDTC showed that the compounds induced cytotoxicity in the myeloma cell line RPMI 8226. The average Z' value for the assay was 0.66. The results indicate that the assay rapidly identifies new proteasome-inhibiting substances, and it will be further used as a tool for image-based screening of other chemically diverse compound libraries.

New perspectives on melanoma pathogenesis and chemoprevention

Epidemiologic studies implicate ultraviolet radiation (sunlight) as an etiologic agent for the pathogenesis of melanoma. However, the experimental evidence is less convincing. We present information from recent experimental findings that elevation of reactive oxygen species follows from melanin serving as a redox generator, and that this may play an important role in the etiology and pathogenesis of cutaneous melanoma. These observations offer a new paradigm for the development of preventive (and therapeutic) approaches to this disease.

Pharmacological profiling of disulfiram using human tumor cell lines and human tumor cells from patients

The thiocarbamate drug disulfiram has been used for decades in the treatment of alcohol abuse. Disulfiram induces apoptosis in a number of tumor cell lines and was recently by us proposed to act as a 26S proteasome inhibitor. In this work we characterized disulfiram in vitro with regard to tumor-type specificity, possible mechanisms of action and drug resistance and cell death in human tumor cell lines and in 78 samples of tumor cells from patients using the fluorometric microculture cytotoxicity assay and the automated fluorescence-imaging microscope ArrayScan((R)). Disulfiram induced cytotoxicity in a biphasic pattern in both cell lines and patient tumor cells. Disulfiram induced apoptosis as measured by cell membrane permeability, nuclear fragmentation/condensation and caspase-3/7 activation using high content screening assays. For many of the cell lines tested disulfiram was active in sub-micromolar concentrations. When comparing the logIC(50) patterns with other cytotoxic agents, disulfiram showed low correlation (R<0.5) with all drugs except lactacystin (R=0.69), a known proteasome inhibitor, indicating that the two substances may share mechanistic pathways. Disulfiram was more active in hematological than in solid tumor samples, but substantial activity was observed in carcinomas of the ovary and the breast and in non-small cell lung cancer. Disulfiram also displayed higher cytotoxic effect in cells from chronic lymphocytic leukemia than in normal lymphocytes (p<0.05), which may indicate some tumor selectivity. These results together with large clinical experience and relatively mild side effects encourage clinical studies of disulfiram as an anti-cancer agent.

Disulfiram, a Clinically Used Anti-Alcoholism Drug and Copper-Binding Agent, Induces Apoptotic Cell Death in Breast Cancer Cultures and Xenografts via Inhibition of the Proteasome Activity

Disulfiram (DSF), a member of the dithiocarbamate family capable of binding copper and an inhibitor of aldehyde dehydrogenase, is currently being used clinically for the treatment of alcoholism. Recent studies have suggested that DSF may have antitumor and chemosensitizing activities, although the detailed molecular mechanisms remain unclear. Copper has been shown to be essential for tumor angiogenesis processes. Consistently, high serum and tissue levels of copper have been found in many types of human cancers, including breast, prostate, and brain, supporting the idea that copper could be used as a potential tumor-specific target. Here we report that the DSF-copper complex potently inhibits the proteasomal activity in cultured breast cancer MDA-MB-231 and MCF10DCIS.com cells, but not normal, immortalized MCF-10A cells, before induction of apoptotic cancer cell death. Furthermore, MDA-MB-231 cells that contain copper at concentrations similar to those found in patients, when treated with just DSF, undergo proteasome inhibition and apoptosis. In addition, when administered to mice bearing MDA-MB-231 tumor xenografts, DSF significantly inhibited the tumor growth (by 74%), associated with in vivo proteasome inhibition (as measured by decreased levels of tumor tissue proteasome activity and accumulation of ubiquitinated proteins and natural proteasome substrates p27 and Bax) and apoptosis induction (as shown by caspase activation and apoptotic nuclei formation). Our study shows that inhibition of the proteasomal activity can be achieved by targeting tumor cellular copper with the nontoxic compound DSF, resulting in selective apoptosis induction within tumor cells.

Lysyl oxidase is essential for hypoxia-induced metastasis

Metastasis is a multistep process responsible for most cancer deaths, and it can be influenced by both the immediate microenvironment (cell-cell or cell-matrix interactions) and the extended tumour microenvironment (for example vascularization). Hypoxia (low oxygen) is clinically associated with metastasis and poor patient outcome, although the underlying processes remain unclear. Microarray studies have shown the expression of lysyl oxidase (LOX) to be elevated in hypoxic human tumour cells. Paradoxically, LOX expression is associated with both tumour suppression and tumour progression, and its role in tumorigenesis seems dependent on cellular location, cell type and transformation status. Here we show that LOX expression is regulated by hypoxia-inducible factor (HIF) and is associated with hypoxia in human breast and head and neck tumours. Patients with high LOX-expressing tumours have poor distant metastasis-free and overall survivals. Inhibition of LOX eliminates metastasis in mice with orthotopically grown breast cancer tumours. Mechanistically, secreted LOX is responsible for the invasive properties of hypoxic human cancer cells through focal adhesion kinase activity and cell to matrix adhesion. Furthermore, LOX may be required to create a niche permissive for metastatic growth. Our findings indicate that LOX is essential for hypoxia-induced metastasis and is a good therapeutic target for preventing and treating metastases.

Suppression of survival in human SKBR3 breast carcinoma in response to metal–chelator complexes is preferential for copper–dithiocarbamate

Since diethyl dithiocarbamate (DEDTC) forms complexes with either zinc or copper, and 8-hydroxyquinoline (8-OHQ) also complexes with copper, we now compared the cytotoxic activity of Cu[DEDTC]2, Zn[DEDTC]2 and Cu[8-OHQ]2. This report shows that at nanomolar levels, only copper-[DEDTC]2, suppresses proliferation and clonogenicity of SKBR3 human breast carcinoma, concurrently with induction of apoptosis-associated PARP fragmentation. Susceptibility to these agents was paralleled by reactive oxygen generation (ROS) and greater expression of anti-oxidant enzymes like MnSOD and catalase, with no comparable effect on Cu/Zn superoxide dismutase. The lethal effects of Cu[DEDTC]2 manifested when adding the two separate aqueous components or the preformed synthetic complexes in DMSO, was prevented by N-acetyl cysteine or glutathione, with no comparable protection afforded by non-thiol anti-oxidants like mannitol or DMSO. Exogenously added catalase also protected cells from Cu[DEDTC]2, suggesting that this complex may kill after the levels of superoxide anion [O2*-] dismutated by MnSOD increase hydrogen peroxide-related stress. Cu[DEDTC]2 also induced p21WAF1, a cdk inhibitor usually not inducible in mutant p53 tumors like SKBR3 carcinoma, correlating with dephosphorylation of the Sp1 transcription factor. Concentrations of Cu[DEDTC]2 cytotoxic for SKBR3 carcinoma did not induce comparable damage versus normal diploid human WI-38 fibroblasts. In contrast to the cytotoxic effect of nM levels of Cu[DEDTC]2 against SKBRR3 cells, no response was seen in the same cells exposed to 20 microM cis-platin. Since neither DEDTC bound to zinc, nor copper bound to 8-OHQ showed comparable cytotoxicity, our results suggest that the greater activity of copper-DEDTC reflects a specific structure-activity relationship for the active complex. Since Cu[DEDTC]2 shows more effectiveness than other metal-chelator complexes, it may be worth further investigation as an alternative to cancer therapies.

Disulfiram irreversibly aggregates betaine aldehyde dehydrogenase--a potential target for antimicrobial agents against Pseudomonas aeruginosa

In the human pathogen Pseudomonas aeruginosa, betaine aldehyde dehydrogenase (PaBADH) may play the dual role of assimilating carbon and nitrogen from choline or choline precursors--abundant at infection sites--and producing glycine betaine, which protects the bacterium against the high-osmolality stress prevalent in the infected tissues. This tetrameric enzyme contains four cysteine residues per subunit and is a potential drug target. In our search for specific inhibitors, we mutated the catalytic Cys286 to alanine and chemically modified the recombinant wild-type and the four Cys-->Ala single mutants with thiol reagents. The small methyl-methanethiosulfonate inactivated the enzymes without affecting their stability while the bulkier dithionitrobenzoic acid (DTNB) and bis[diethylthiocarbamyl] disulfide (disulfiram) induced enzyme dissociation--at 23 degrees C--and irreversible aggregation--at 37 degrees C. Of the four Cys-->Ala mutants only C286A retained its tetrameric structure after DTNB or disulfiram treatments, suggesting that steric constraints arising upon the covalent attachment of a bulky group to C286 resulted in distortion of the backbone configuration in the active site region followed by a severe decrease in enzyme stability. Since neither NAD(P)H nor betaine aldehyde prevented disulfiram-induced PaBADH inactivation or aggregation, and reduced glutathione was unable to restore the activity of the modified enzyme, we propose that disulfiram could be a useful drug to combat infection by P. aeruginosa.

Clioquinol and pyrrolidine dithiocarbamate complex with copper to form proteasome inhibitors and apoptosis inducers in human breast cancer cells

INTRODUCTION

A physiological feature of many tumor tissues and cells is the tendency to accumulate high concentrations of copper. While the precise role of copper in tumors is cryptic, copper, but not other trace metals, is required for angiogenesis. We have recently reported that organic copper-containing compounds, including 8-hydroxyquinoline-copper(II) and 5,7-dichloro-8-hydroxyquinoline-copper(II), comprise a novel class of proteasome inhibitors and tumor cell apoptosis inducers. In the current study, we investigate whether clioquinol (CQ), an analog of 8-hydroxyquinoline and an Alzheimer's disease drug, and pyrrolidine dithiocarbamate (PDTC), a known copper-binding compound and antioxidant, can interact with copper to form cancer-specific proteasome inhibitors and apoptosis inducers in human breast cancer cells. Tetrathiomolybdate (TM), a strong copper chelator currently being tested in clinical trials, is used as a comparison.

METHODS

Breast cell lines, normal, immortalized MCF-10A, premalignant MCF10AT1K.cl2, and malignant MCF10DCIS.com and MDA-MB-231, were treated with CQ or PDTC with or without prior interaction with copper, followed by measurement of proteasome inhibition and cell death. Inhibition of the proteasome was determined by levels of the proteasomal chymotrypsin-like activity and ubiquitinated proteins in protein extracts of the treated cells. Apoptotic cell death was measured by morphological changes, Hoechst staining, and poly(ADP-ribose) polymerase cleavage.

RESULTS

When in complex with copper, both CQ and PDTC, but not TM, can inhibit the proteasome chymotrypsin-like activity, block proliferation, and induce apoptotic cell death preferentially in breast cancer cells, less in premalignant breast cells, but are non-toxic to normal/non-transformed breast cells at the concentrations tested. In contrast, CQ, PDTC, TM or copper alone had no effects on any of the cells. Breast premalignant or cancer cells that contain copper at concentrations similar to those found in patients, when treated with just CQ or PDTC alone, but not TM, undergo proteasome inhibition and apoptosis.

CONCLUSION

The feature of breast cancer cells and tissues to accumulate copper can be used as a targeting method for anticancer therapy through treatment with novel compounds such as CQ and PDTC that become active proteasome inhibitors and breast cancer cell killers in the presence of copper.

Disulfiram, an old drug with new potential therapeutic uses for human cancers and fungal infections

Disulfiram, a drug used to treat alcoholism, has recently been indicated to play a primary as well as an adjuvant role in the treatment of many cancers and in the reversal of fungal drug-resistance. This review discusses the molecular mechanism of action of disulfiram and its potential use in the treatment of human cancers and fungal infections.

Synthesis, structure and spectroscopy of new thiopyrone and hydroxypyridinethione transition-metal complexes

The coordination chemistry of several O,S mixed donor ligands, namely thiopyrone and hydroxypyridinethione chelators, with a variety of middle and late first-row transition-metal ions is described. Complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol) with cobalt(II), copper(II) and zinc(II); 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II); and 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. The structures, absorbance spectroscopy, cyclic voltammetry and superconducting quantum interferometer device (SQUID) measurements of selected metal complexes, as well as ligand protonation constants, are reported. Most of the metal complexes show coordination geometries indicative of a strong trans influence by the O,S chelators. The data presented herein provide the most detailed study of the transition-metal coordination chemistry of both thiopyrone and hydroxypyridinethione O,S donor ligands to date, and provide the basis for the investigation of these ligands in realm of biological inorganic chemistry.

Fatal CNS trichinosis

Background

The current successful clinical use of agents promoting robust anti-tumor immunity in cancer patients warrants noting that radiation therapy (RT) induces immunogenic cell death (ICD) of tumor cells, which can generate anti-tumor immune responses. However, breast cancer stem cells (BCSCs) are resistant to RT and RT alone usually failed to mount an anti-tumor immune response.

Methods

High aldehyde dehydrogenase activity (ALDH)bright and CD44+/CD24−/ESA+ cancer cells, previously shown to have BCSC properties, were isolated from human MDA-MB-231 and UACC-812 breast cancer cell lines by flow cytometer. Flow sorted BCSCs and non-BCSCs were further tested for their characteristic of stemness by mammosphere formation assay. Induction of ICD in BCSCs vs. non-BCSCs in response to different in vitro treatments was determined by assessing cell apoptosis and a panel of damage-associated molecular pattern molecules (DAMPs) by flow and enzyme-linked immunosorbent assay (ELISA).

Results

We found that ionizing radiation (IR) triggered a lower level of ICD in BCSCs than non-BCSCs. We then investigated the ability of disulfiram/cooper (DSF/Cu) which is known to preferentially induce cancer stem cells (CSCs) apoptosis to enhance IR-induced ICD of BCSCs. The results indicate that DSF/Cu induced a similar extent of IDC in both BCSCs and non-BCSCs and rendered IR-resistant BCSCs as sensitive as non-BCSCs to IR-induced ICD. IR and DSF/Cu induced ICD of BCSCs could be partly reversed by pre-treatment of BCSCs with a reactive oxygen species (ROS) scavenger and XBP1s inhibitors.

Conclusion

DSF/Cu rendered IR-resistant BCSCs as sensitive as non-BCSCs to IR-induced ICD. Our data demonstrate the potential of IR and DSF/Cu to induce ICD in BCSCs and non-BCSCs leading to robust immune responses against not only differentiated/differentiating breast cancer cells but also BCSCs, the root cause of cancer formation, progression and metastasis.

Graphical abstract

[Staining of polysaccharides with sudan black B after esterification]

The goal of adjuvant (post-surgery) radiation therapy (RT) for breast cancer (BC) is to eliminate residual cancer cells, leading to better local tumor control and thus improving patient survival. However, radioresistance increases the risk of tumor recurrence and negatively affects survival. Recent evidence shows that breast cancer stem cells (BCSCs) are radiation-resistant and that relatively differentiated BC cells can be reprogrammed into induced BCSCs (iBCSCs) via radiation-induced re-expression of the stemness genes. Here we show that in irradiation (IR)-treated mice bearing syngeneic mammary tumors, IR-induced stemness correlated with increased spontaneous lung metastasis (51.7%). However, IR-induced stemness was blocked by targeting the NF-κB- stemness gene pathway with disulfiram (DSF)and Copper (Cu²⁺). DSF is an inhibitor of aldehyde dehydrogenase (ALDH) and an FDA-approved drug for treating alcoholism. DSF binds to Cu²⁺ to form DSF-Cu complexes (DSF/Cu), which act as a potent apoptosis inducer and an effective proteasome inhibitor, which, in turn, inhibits NF-κB activation. Treatment of mice with RT and DSF significantly inhibited mammary primary tumor growth (79.4%) and spontaneous lung metastasis (89.6%) compared to vehicle treated mice. This anti-tumor efficacy was associated with decreased stem cell properties (or stemness) in tumors. We expect that these results will spark clinical investigation of RT and DSF as a novel combinatorial treatment for breast cancer.