Desferal inhibits breast tumor growth and does not interfere with the tumoricidal activity of doxorubicin

Prolactin Drives Iron Release from Macrophages and Uptake in Mammary Cancer Cells through CD44

Iron is an essential element for human health. In humans, dysregulated iron homeostasis can result in a variety of disorders and the development of cancers. Enhanced uptake, redistribution, and retention of iron in cancer cells have been suggested as an "iron addiction" pattern in cancer cells. This increased iron in cancer cells positively correlates with rapid tumor growth and the epithelial-to-mesenchymal transition, which forms the basis for tumor metastasis. However, the source of iron and the mechanisms cancer cells adopt to actively acquire iron is not well understood. In the present study, we report, for the first time, that the peptide hormone, prolactin, exhibits a novel function in regulating iron distribution, on top of its well-known pro-lactating role. When stimulated by prolactin, breast cancer cells increase CD44, a surface receptor mediating the endocytosis of hyaluronate-bound iron, resulting in the accumulation of iron in cancer cells. In contrast, macrophages, when treated by prolactin, express more ferroportin, the only iron exporter in cells, giving rise to net iron output. Interestingly, when co-culturing macrophages with pre-stained labile iron pools and cancer cells without any iron staining, in an iron free condition, we demonstrate direct iron flow from macrophages to cancer cells. As macrophages are one of the major iron-storage cells and it is known that macrophages infiltrate tumors and facilitate their progression, our work therefore presents a novel regulatory role of prolactin to drive iron flow, which provides new information on fine-tuning immune responses in tumor microenvironment and could potentially benefit the development of novel therapeutics.

Transferrin receptor in primary and metastatic breast cancer: Evaluation of expression and experimental modulation to improve molecular targeting

BACKGROUND

Conjugation of transferrin (Tf) to imaging or nanotherapeutic agents is a promising strategy to target breast cancer. Since the efficacy of these biomaterials often depends on the overexpression of the targeted receptor, we set out to survey expression of transferrin receptor (TfR) in primary and metastatic breast cancer samples, including metastases and relapse, and investigate its modulation in experimental models.

METHODS

Gene expression was investigated by datamining in twelve publicly-available datasets. Dedicated Tissue microarrays (TMAs) were generated to evaluate matched primary and bone metastases as well as and pre and post chemotherapy tumors from the same patient. TMA were stained with the FDA-approved MRQ-48 antibody against TfR and graded by staining intensity (H-score). Patient-derived xenografts (PDX) and isogenic metastatic mouse models were used to study in vivo TfR expression and uptake of transferrin.

RESULTS

TFRC gene and protein expression were high in breast cancer of all subtypes and stages, and in 60-85% of bone metastases. TfR was detectable after neoadjuvant chemotherapy, albeit with some variability. Fluorophore-conjugated transferrin iron chelator deferoxamine (DFO) enhanced TfR uptake in human breast cancer cells in vitro and proved transferrin localization at metastatic sites and correlation of tumor burden relative to untreated tumor mice.

CONCLUSIONS

TfR is expressed in breast cancer, primary, metastatic, and after neoadjuvant chemotherapy. Variability in expression of TfR suggests that evaluation of the expression of TfR in individual patients could identify the best candidates for targeting. Further, systemic iron chelation with DFO may upregulate receptor expression and improve uptake of therapeutics or tracers that use transferrin as a homing ligand.

Iron Overload and Breast Cancer: Iron Chelation as a Potential Therapeutic Approach

Breast cancer has historically been one of the leading causes of death for women worldwide. As of 2020, breast cancer was reported to have overtaken lung cancer as the most common type of cancer globally, representing an estimated 11.3% of all cancer diagnoses. A multidisciplinary approach is taken for the diagnosis and treatment of breast cancer that includes conventional and targeted treatments. However, current therapeutic approaches to treating breast cancer have limitations, necessitating the search for new treatment options. Cancer cells require adequate iron for their continuous and rapid proliferation. Excess iron saturates the iron-binding capacity of transferrin, resulting in non-transferrin-bound iron (NTBI) that can catalyze free-radical reactions and may lead to oxidant-mediated breast carcinogenesis. Moreover, excess iron and the disruption of iron metabolism by local estrogen in the breast leads to the generation of reactive oxygen species (ROS). Therefore, iron concentration reduction using an iron chelator can be a novel therapeutic strategy for countering breast cancer development and progression. This review focuses on the use of iron chelators to deplete iron levels in tumor cells, specifically in the breast, thereby preventing the generation of free radicals. The inhibition of DNA synthesis and promotion of cancer cell apoptosis are the targets of breast cancer treatment, which can be achieved by restricting the iron environment in the body. We hypothesize that the usage of iron chelators has the therapeutic potential to control intracellular iron levels and inhibit the breast tumor growth. In clinical settings, iron chelators can be used to reduce cancer cell growth and thus reduce the morbidity and mortality in breast cancer patients.

Understanding the Potential and Risk of Bacterial Siderophores in Cancer

Siderophores are iron chelating molecules produced by nearly all organisms, most notably by bacteria, to efficiently sequester the limited iron that is available in the environment. Siderophores are an essential component of mammalian iron homeostasis and the ongoing interspecies competition for iron. Bacteria produce a broad repertoire of siderophores with a canonical role in iron chelation and the capacity to perform versatile functions such as interacting with other microbes and the host immune system. Siderophores are a vast area of untapped potential in the field of cancer research because cancer cells demand increased iron concentrations to sustain rapid proliferation. Studies investigating siderophores as therapeutics in cancer generally focused on the role of a few siderophores as iron chelators; however, these studies are limited and some show conflicting results. Moreover, siderophores are biologically conserved, structurally diverse molecules that perform additional functions related to iron chelation. Siderophores also have a role in inflammation due to their iron acquisition and chelation properties. These diverse functions may contribute to both risks and benefits as therapeutic agents in cancer. The potential of siderophore-mediated iron and bacterial modulation to be used in the treatment of cancer warrants further investigation. This review discusses the wide range of bacterial siderophore functions and their utilization in cancer treatment to further expand their functional relevance in cancer detection and treatment.

Inhibitory effects of iron depletion plus eribulin on the breast cancer microenvironment

Background

Iron is required for the proliferation of cancer cells, and its depletion suppresses tumor growth. Eribulin mesylate (eribulin), a non-taxane microtubule inhibitor, disrupts the tumor microenvironment via vascular remodeling and obstruction of the epithelial-mesenchymal transition (EMT). Herein, we investigated the effects of the iron chelator on tumor-related properties of breast cancer cells and the effects of iron chelator plus eribulin on tumor growth in vivo.

Methods

Two triple-negative breast cancer (TNBC) cell lines, MDA-MB-231 and BT-549, and one hormone-receptor positive breast cancer cell line, MCF-7, were used in our study. Cell proliferation, cell migration, cell cycle position, and gene expression were analyzed via MTT assays, wound-healing assays, flow cytometry, and quantitative real-time-polymerase chain reaction, respectively. For the in vivo experiments, mice with breast cancer xenografts were treated with the inhibitors, alone or together, and tumor volume was determined.

Results

Iron chelator inhibited breast cancer cell proliferation and decreased the proportion of S-phase cells. Conversely, it induced hypoxia, angiogenesis, EMT, and immune checkpoints, as determined by quantifying the expression of marker mRNAs in MDA-MB-231 and MCF-7 cells. Eribulin suppressed the expression of the hypoxia and EMT related marker mRNAs in the presence of iron chelator. Iron chelator plus eribulin inhibited tumor growth in vivo to a greater extent than did either inhibitor alone.

Conclusions

Although iron chelator induces oncogenic events (hypoxia, angiogenesis, EMT, and immune checkpoints), it may be an effective treatment for breast cancer when administered in combination with eribulin.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07673-9.

Iron alters Ca2+ homeostasis in doxorubicin-resistant K562 cells

Iron is an essential trace element especially in cell proliferation, and growth for various cellular events. An increasing amount of research has shown that iron metabolism is altered in tumour cells which usually have rapid growth rates. However, the number of studies on iron metabolism, and calcium regulation are limited in drug-resistant tumour cells. Previously, we have shown that modulation of iron metabolism through iron chelation regulated the intracellular calcium, and increased the doxorubicin sensitivity. In the present study, we investigated the effects of iron on mRNA expression profiles of fifteen key genes (IP3 R1/2/3, RYR1/2, SERCA1/2/3, NCX1/2/3, PMCA1/2/3, and PMCA4) related to calcium homeostasis in the parental cell line K562 and its subclone doxorubicin-resistant K562 cells. According to the ΔΔCt method with a two-fold expression difference (P < .05) as a cut-off level, although iron showed differential effects on most of the genes, IP3 R and PMCA genes were especially determined to have changed significantly. These results show that iron metabolism is an important metabolism due to changes in the expression of genes involved in calcium regulation and is a new perspective to overcome cancer/drug resistance.

DIBI, a novel 3-hydroxypyridin-4-one chelator iron-binding polymer, inhibits breast cancer cell growth and functions as a chemosensitizer by promoting S-phase DNA damage

Breast cancer is a leading cause of cancer-related death in women; however, chemotherapy of breast cancer is often hindered by dose-limiting toxicities, demonstrating the need for less toxic approaches to treatment. Since the rapid growth and metabolism of breast cancer cells results in an increased requirement for iron, withdrawal of bioavailable iron using highly selective iron chelators has been suggested to represent a new approach to breast cancer treatment. Here we show that the recently developed iron-binding polymer DIBI inhibited the growth of five different breast cancer cell lines (SK-BR3, MDA-MB-468, MDA-MB-231, MCF-7, and T47D). In cultures of MDA-MB-468 breast cancer cells, which were most sensitive to DIBI-mediated growth inhibition, iron withdrawal was associated with increased expression of transferrin receptor 1 and ferritin H mRNA but decreased expression of ferroportin mRNA. MDA-MB-468 cells that were exposed to DIBI experienced double-strand DNA breaks during the S phase of the cell cycle. DNA damage was not mediated by reactive oxygen species (ROS) since DIBI-treated MDA-MB-468 cells exhibited a reduction in intracellular ROS. DIBI-treated MDA-MB-468 cells also showed increased sensitivity to growth inhibition by the chemotherapeutic drugs cisplatin, doxorubicin, and 4-hydroperoxy cyclophosphamide (active metabolite of cyclophosphamide). Combination treatment of MDA-MB-468 cells with DIBI and cisplatin caused greater DNA damage than either treatment alone, which was also associated with an increase in apoptotic cell death. Taken together, these findings suggest that DIBI-mediated iron withdrawal may enhance the effect of chemotherapeutic agents used in breast cancer treatment.

Doxorubicin loaded carboxymethyl Assam bora rice starch coated superparamagnetic iron oxide nanoparticles as potential antitumor cargo

In recent years, polysaccharide-decorated superparamagnetic iron oxide nanoparticles (SPIONs) have gained attention in the field of “nanotheranostics” with integrated diagnostic and therapeutic functions. Carboxymethyl Assam bora rice starch-stabilized SPIONs (CM-ABRS SPIONs), synthesized by co-precipitation method, has already shown exciting potential towards magnetic drug targeting potential. After establishing it as a promisable targeting carrier, the present study is focused on the next step i.e. to evaluate its In vitro anti-tumor potential by loading anticancer drug “Doxorubicin hydrochloride (DOX)” onto CM-ABRS SPIONs. DOX-loaded CM-ABRS SPIONs were physico-chemically characterized by DLS, zeta-potential, TEM, FT-IR, XRD, and VSM analysis. Spectroflourimetric analysis confirmed the maximum loading of DOX up to 6% (w/w) onto CM-ABRS SPIONs via electrostatic interactions. Further, molecular level drug performance was investigated by docking study against receptors (HER-2 and Folate receptor-α) over expressed in cancer cells and MTT assay (in MCF-7 and HeLa cell line), which conferred promisable results of DOX-CM-ABRS SPIONs as compared to standard DOX solution.

The iron chelator deferasirox synergises with chemotherapy to treat triple-negative breast cancers

To ensure their high proliferation rate, tumor cells have an iron metabolic disorder causing them to have increased iron needs, making them more susceptible to iron deprivation. This vulnerability could be a therapeutic target. In breast cancers, the development of new therapeutic approaches is urgently needed for patients with triple-negative tumors, which frequently relapse after chemotherapy and suffer from a lack of targeted therapies. In this study, we demonstrated that deferasirox (DFX) synergises with standard chemotherapeutic agents such as doxorubicin, cisplatin and carboplatin to inhibit cell proliferation and induce apoptosis and autophagy in triple-negative breast cancer (TNBC) cells. Moreover, the combination of DFX with doxorubicin and cyclophosphamide delayed recurrences in breast cancer patient-derived xenografts without increasing the side-effects of chemotherapies alone or altering the global iron storage of mice. Antitumor synergy of DFX and doxorubicin seems to involve downregulation of the phosphoinositide 3-kinase and nuclear factor-κB pathways. Iron deprivation in combination with chemotherapy could thus help to improve the effectiveness of chemotherapy in TNBC patients without increasing toxicity. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Effect of the FE2+ chelation by 2,2'-dipyridyl in the doxorubicin-induced lethality in breast tumor cell lines

Breast cancer cells may exhibit changes in iron homeostasis, which results in increased labile iron pool (LIP) levels. Several studies highlight the crucial role of high LIP levels in the maintenance of tumor cell physiology. Iron chelators have been tested in anticancer therapy in combination with chemotherapeutic agents, to improve drug efficacy. Thus, the aim of this study was to evaluate the effect of 2,2'-dipyridyl (DIP), a Fe²⁺ chelator, in combination with doxorubicin (DOX) in breast tumor cells. The maximum concentration of DIP that did not significantly reduce the viability of MDA-MB-231 cells was 10μM and for MCF-7 cells was 50μM. We observed that MCF-7 had higher LIP levels than MDA-MB-231 cells. DIP alone increased ROS generation in MCF-7 cells, and DIP pretreatment reduced ROS generation induced by DOX treatment. In conclusion, the increase in MCF-7 cell viability induced by DIP pretreatment in DOX-treated cells seems to be related to an increase in the cellular antioxidant capacity and the iron chelator did not improve drug efficacy in the two breast tumor cell lines analyzed.

Granulopoiesis and granules of human neutrophils

Granules are essential for the ability of neutrophils to fulfill their role in innate immunity. Granule membranes contain proteins that react to environmental cues directing neutrophils to sites of infection and initiate generation of bactericidal oxygen species. Granules are densely packed with proteins that contribute to microbial killing when liberated to the phagosome or extracellularly. Granules are, however, highly heterogeneous and are traditionally subdivided into azurophil granules, specific granules, and gelatinase granules in addition to secretory vesicles. This review will address issues pertinent to formation of granules, which is a process intimately connected to maturation of neutrophils from their precursors in the bone marrow. We further discuss possible mechanisms by which decisions are made regarding sorting of proteins to constitutive secretion or storage in granules and how degranulation of granule subsets is regulated.

Tissue-protective activity of selenomethionine and D-panthetine in B16 melanoma-bearing mice under doxorubicin treatment is not connected with their ROS scavenging potential

Aim

To evaluate molecular mechanisms of tissue-protective effects of antioxidants selenomethionine (SeMet) and D-pantethine (D-Pt) applied in combination with doxorubicin (Dx) in B16 melanoma-bearing-mice.

Methods

Impact of the chemotherapy scheme on a survival of tumor-bearing animals, general nephro- and hepatotoxicity, blood cell profile in vivo, and ROS content in B16 melanoma cells in vitro was compared with the action of Dx applied alone. Nephrotoxicity of the drugs was evaluated by measuring creatinine indicator assay, hepatotoxicity was studied by measuring the activity of ALT/AST enzymes, and myelotoxicity was assessed by light microscopic analysis of blood smears. Changes in ROS content in B16 melanoma cells under Dx, SeMet, and D-Pt action in vitro were measured by incubation with fluorescent dyes dihydrodichlorofluoresceindiacetate (DCFDA, H₂O₂-specific) and dihydroethidium (DHE, O₂^--specific), and further analysis at FL1 (DCFDA) or FL2 channels (DHE) of FACScan flow cytometer. The impact of aforementioned compounds on functional status of mitochondria was measured by Rhodamine 123 assay and further analysis at FL1 channel of FACScan flow cytometer.

Results

Selenomethionine (1200 µg/kg) and D-pantethine (500 mg/kg) in combination with Dx (10 mg/kg) significantly reduced tumor-induced neutrophilia, lymphocytopenia, and leukocytosis in comparison to Dx treatment alone. Moreover, SeMet and D-Pt decreased several side effects of Dx, namely an elevated creatinine level in blood and monocytosis, thus normalizing health conditions of B16 melanoma-bearing animals.

Conclusions

Our results showed that antioxidants selenomethionine and D-pantethine possess significant nephroprotective and myeloprotective activity toward Dx action on murine B16 melanoma in vivo, but fail to boost a survival of B16 melanoma-bearing animals. The observed cytoprotective effects of studied antioxidants are not directly connected with their ROS scavenging.

Rapid generation of hydrogen peroxide contributes to the complex cell death induction by the angucycline antibiotic landomycin E

Landomycin E (LE) is an angucycline antibiotic produced by Streptomyces globisporus. Previously, we have shown a broad anticancer activity of LE which is, in contrast to the structurally related and clinically used anthracycline doxorubicin (Dx), only mildly affected by multidrug resistance-mediated drug efflux. In the present study, cellular and molecular mechanisms underlying the anticancer activity of landomycin E towards Jurkat T-cell leukemia cells were dissected focusing on the involvement of radical oxygen species (ROS). LE-induced apoptosis distinctly differed in several aspects from the one induced by Dx. Rapid generation of both extracellular and cell-derived hydrogen peroxide already at one hour drug exposure was observed in case of LE but not found before 24h for Dx. In contrast, Dx but not LE induced production of superoxide radicals. Mitochondrial damage, as revealed by JC-1 staining, was weakly enhanced already at 3h LE treatment and increased significantly with time. Accordingly, activation of the intrinsic apoptosis pathway initiator caspase-9 was not detectable before 12h exposure. In contrast, cleavage of the down-stream caspase substrate PARP-1 was clearly induced already at the three hour time point. Out of all caspases tested, only activation of effector caspase-7 was induced at this early time points paralleling the LE-induced oxidative burst. Accordingly, this massive cleavage of caspase-7 at early time points was inhibitable by the radical scavenger N-acetylcysteine (NAC). Additionally, only simultaneous inhibition of multiple caspases reduced LE-induced apoptosis. Specific scavengers of both H2O2 and OH• effectively decreased LE-induced ROS production, but only partially inhibited LE-induced apoptosis. In contrast, NAC efficiently blocked both parameters. Summarizing, rapid H2O2 generation and a complex caspase activation pattern contribute to the antileukemic effects of LE. As superoxide generation is considered as the main cardiotoxic mechanism of Dx, LE might represent a better tolerable drug candidate for further (pre)clinical development.

Lipocalin-2 and iron trafficking in the tumor microenvironment

Iron is an essential element for virtually all organisms. It facilitates cell proliferation and growth but also contributes to major hallmarks of cancer such as tumor initiation, growth, and metastasis. Often, iron handling of tumor cells is disturbed, with altered iron acquisition, efflux, and storage. Targeting perturbed iron metabolic pathways might open opportunities towards novel approaches in cancer treatment. It is becoming clear that cells of the tumor microenvironment such as macrophages contribute to tumor progression. Since macrophages evolved a multitude of mechanisms to sequester, transport, store, and release iron it can be speculated that tumor cells educate them to supply iron to support tumor growth. Recent evidence supports the existence of transferrin-independent iron transport mechanisms in the tumor microenvironment, which points to local iron transport proteins such as lipocalin-2 and/or low molecular weight iron-trafficking substances such as siderophores. We hypothesize that tumor cells educate immune cells, i.e. macrophages in their neighborhood to make them delivering iron for the benefit of cancer progression. In particular, we pay attention to recent developments, pointing to lipocalin-2 and siderophores as alternative iron transport molecules in the tumor microenvironment.

Effect of microbial siderophores on mammalian non-malignant and malignant cell lines

BACKGROUND

Iron is a vital nutrient for all cells, and malignant cells have a higher requirement for the metal due to their rapid multiplication. Bacterial siderophores can be used to reduce free ferric ion concentration from the cellular environment.

METHODS

In the present study, we have evaluated effect of three siderophores - exochelin-MS, mycobactin S and deferoxamine B on the proliferation of mammalian cell lines using MTT assay.

RESULTS

These siderophores caused a significant decrease in the viability of malignant cells, without significantly affecting non-malignant cells.

CONCLUSIONS

Based on these results, we suggest that iron-chelation therapy could be explored as an adjunctive therapeutic option against cancer along with other therapies.

Deferasirox, a novel oral iron chelator, shows antiproliferative activity against pancreatic cancer in vitro and in vivo

Background

Iron is essential for cell replication, metabolism and growth. Because neoplastic cells have high iron requirements due to their rapid proliferation, iron depletion may be a novel therapeutic strategy for cancer. Deferasirox (DFX), a novel oral iron chelator, has been successful in clinical trials in iron-overload patients and has been expected to become an anticancer agent. However, no studies have investigated the effects of DFX on pancreatic cancer. This study aimed to elucidate the effects of DFX against pancreatic cancer.

Methods

The effects of DFX on cell cycle, proliferation, and apoptosis were examined in three human pancreatic cancer cell lines: BxPC-3, HPAF-II, and Panc 10.05. The effect of orally administered DFX on the growth of BxPC-3 pancreatic cancer xenografts was also examined in nude mice. Additionally, microarray analysis was performed using tumors excised from xenografts.

Results

DFX inhibited pancreatic cancer cell proliferation in a dose-dependent manner. A concentration of 10 μM DFX arrested the cell cycle in S phase, whereas 50 and 100 μM DFX induced apoptosis. In nude mice, orally administered DFX at 160 and 200 mg/kg suppressed xenograft tumor growth with no serious side effects (n = 5; average tumor volumes of 674 mm³ for controls vs. 327 mm³ for 160 mg/kg DFX, p <0.05; average tumor volumes of 674 mm³ for controls vs. 274 mm³ for 200 mg/kg DFX, p <0.05). Importantly, serum biochemistry analysis indicated that serum levels of ferritin were significantly decreased by the oral administration of 160 or 200 mg/kg DFX (n = 5; average serum ferritin of 18 ng/ml for controls vs. 9 ng/ml for 160 mg/kg DFX, p <0.05; average serum ferritin of 18 ng/ml for controls vs. 10 ng/ml for 200 mg/kg DFX, p <0.05). Gene expression analysis revealed that most genes in pancreatic adenocarcinoma signaling, especially transforming growth factor-ß1 (TGF-ß1), were downregulated by DFX.

Conclusions

DFX has potential as a therapeutic agent for pancreatic cancer. Iron depletion was essential for the antiproliferative effect of DFX in a preclinical model, and DFX acted through the suppression of TGF-ß signaling.

In vitro and in vivo chemo-phototherapy of magnetic TiO2 drug delivery system formed by pH-sensitive coordination bond

To achieve tumor-specific delivery of doxorubicin, TiO2@Fe3O4/PEI/delivery of doxorubicin conjugates were designed and synthesized. Fe3O4 could act as magnetically responsive carriers and enhance the visible light photodynamic activities of TiO2. Delivery of doxorubicin was conjugated via coordination bond. The drug release rate at pH 5.2 was much faster than that at pH 7.4, due to pH-sensitive coordination bond. Besides, TiO2@Fe3O4/PEI/delivery of doxorubicin showed high antitumor efficacy combining with phototherapy, good bio-safety, higher cellular uptake with an external magnetic field, and less toxicity in vitro and in vivo. These results suggested that TiO2@Fe3O4/PEI/delivery of doxorubicin may be promising for high tumor treatment efficacy with minimal side effects in future.

Dual preventive benefits of iron elimination by desferal in asbestos-induced mesothelial carcinogenesis

Asbestos‐induced mesothelial carcinogenesis is currently a profound social issue due to its extremely long incubation period and high mortality rate. Therefore, procedures to prevent malignant mesothelioma in people already exposed to asbestos are important. In previous experiments, we established an asbestos‐induced rat peritoneal mesothelioma model, which revealed that local iron overload is a major cause of pathogenesis and that the induced genetic alterations are similar to human counterparts. Furthermore, we showed that oral administration of deferasirox modified the histology from sarcomatoid to the more favorable epithelioid subtype. Here, we used i.p. administration of desferal to evaluate its effects on asbestos‐induced peritoneal inflammation and iron deposition, as well as oxidative stress. Nitrilotriacetate was used to promote an iron‐catalyzed Fenton reaction as a positive control. Desferal significantly decreased peritoneal fibrosis, iron deposition, and nuclear 8‐hydroxy‐2′‐deoxyguanosine levels in mesothelial cells, whereas nitrilotriacetate significantly increased all of them. Desferal was more effective in rat peritoneal mesothelial cells to counteract asbestos‐induced cytotoxicity than in murine macrophages (RAW264.7). Furthermore, rat sarcomatoid mesothelioma cells were more dependent on iron for proliferation than rat peritoneal mesothelial cells. Because inflammogenicity of a fiber is proportionally associated with subsequent mesothelial carcinogenesis, iron elimination from the mesothelial environment can confer dual merits for preventing asbestos‐induced mesothelial carcinogenesis by suppressing inflammation and mesothelial proliferation simultaneously.

Modulation of iron metabolism by iron chelation regulates intracellular calcium and increases sensitivity to doxorubicin

Increased intracellular iron levels can both promote cell proliferation and death, as such; iron has a "two-sided effect" in the delicate balance of human health. Though the role of iron in the development of cancer remains unclear, investigations of iron chelators as anti-tumor agents have revealed promising results. Here, we investigated the influence of iron and desferrioxamine (DFO), the iron chelating agent on intracellular calcium in a human leukemia cell line, K562. Iron uptake is associated with increased reactive oxygen species (ROS) generation. Therefore, we showed that iron also caused dose-dependent ROS generation in K562 cells. The measurement of intracellular calcium was determined using Furo-2 with a fluorescence spectrophotometer. The iron delivery process to the cytoplasmic iron pool was examined by monitoring the fluorescence of cells loaded with calcein-acetoxymethyl. Our data showed that iron increased intracellular calcium, and this response was 8 times higher when cells were incubated with DFO. K562 cells with DFO caused a 3.5 times increase of intracellular calcium in the presence of doxorubicin (DOX). In conclusion, DFO induces intracellular calcium and increases their sensitivity to DOX, a chemotherapeutic agent.

Inhibitory effect of iron withdrawal by chelation on the growth of human and murine mammary carcinoma and fibrosarcoma cells

Since iron uptake is essential for cell growth, rapidly dividing cancer cells are sensitive to iron depletion. To explore the effect of iron withdrawal on cancer cell growth, mouse and human mammary carcinoma cells (4T1 and MDA-MB-468, respectively) and mouse and human fibrosarcoma cells (L929 and HT1080, respectively) were cultured in the absence or presence of DIBI, a novel iron-chelating polymer containing hydroxypyridinone iron-ligand functionality. Cell growth was measured by a colorimetric assay for cell metabolic activity. DIBI-treated 4T1, MDA-MB-468, L929 and HT1080 cells, as well as their normal counterparts, showed a dose- and time-dependent reduction in growth that was selective for human cancer cells and mouse fibrosarcoma cells. The inhibitory effect of DIBI on fibrosarcoma and mammary carcinoma cell growth was reversed by addition of exogenous iron in the form of iron (III) citrate, confirming the iron selectivity of DIBI and that its inhibitory activity was iron-related. Fibrosarcoma and mammary carcinoma cell growth inhibition by DIBI was associated with S-phase cell cycle arrest and low to moderate levels of cell death by apoptosis. Consistent with apoptosis induction following DIBI-mediated iron withdrawal, fibrosarcoma and mammary carcinoma cells exhibited mitochondrial membrane permeabilization. A comparison of DIBI to other iron chelators showed that DIBI was superior to deferiprone and similar to or better than deferoxamine for inhibition of fibrosarcoma and mammary carcinoma cell growth. These findings suggest that iron withdrawal from the tumor microenvironment with a selective and potent iron chelator such as DIBI may prevent or inhibit tumor progression.

Intracellular reduction/activation of a disulfide switch in thiosemicarbazone iron chelators

Iron scavengers (chelators) offer therapeutic opportunities in anticancer drug design by targeting the increased demand for iron in cancer cells as compared to normal cells. Prochelation approaches are expected to avoid systemic iron depletion as chelators are liberated under specific intracellular conditions. In the strategy described herein, a disulfide linkage is employed as a redox-directed switch within the binding unit of an antiproliferative thiosemicarbazone prochelator, which is activated for iron coordination following reduction to the thiolate chelator. In glutathione redox buffer, this reduction event occurs at physiological concentrations and half-cell potentials. Consistent with concurrent reduction and activation, higher intracellular thiol concentrations increase cell susceptibility to prochelator toxicity in cultured cancer cells. The reduction of the disulfide switch and intracellular iron chelation are confirmed in cell-based assays using calcein as a fluorescent probe for paramagnetic ions. The resulting low-spin Fe(III) complex is identified in intact Jurkat cells by EPR spectroscopy measurements, which also document a decreased concentration of active ribonucleotide reductase following exposure to the prochelator. Cell viability and fluorescence-based assays show that the iron complex presents low cytotoxicity and does not participate in intracellular redox chemistry, indicating that this antiproliferative chelation strategy does not rely on the generation of reactive oxygen species.

Iron homeostasis and anemia markers in early breast cancer

Iron plays a fundamental role in cell life and its concentration in living organisms is precisely regulated. Different molecules for iron storage and transport are used to maintain its intracellular homeostasis which is often altered in cancer cells. Specifically, recent studies have demonstrated that in breast cancer cells, the expression/activity of several iron-related proteins, such as ferritin, hepcidin and ferroportin, is deregulated and that these alterations may have a prognostic impact in patients with breast cancer. Moreover, molecules that regulate iron metabolism could become therapeutic targets. This review focuses on recent findings on iron metabolism particularly in breast cancer and on the development of new biomarkers that may be used in the clinical routine for the diagnosis, prognosis and management of cancer-associated anemia as well as for monitoring personalized treatments.

Iron metabolism disturbances in the MCF-7 human breast cancer cells with acquired resistance to doxorubicin and cisplatin

The development of resistance of cancer cells to therapeutic agents is the major obstacle in the successful treatment of breast cancer and the main cause of breast cancer recurrence. The results of several studies have demonstrated an important role of altered cellular iron metabolism in the progression of breast cancer and suggested that iron metabolism may be involved in the acquisition of a cancer cell drug-resistant phenotype. In the present study, we show that human MCF-7 breast cancer cells with an acquired resistance to the chemotherapeutic drugs doxorubicin (MCF-7/DOX) and cisplatin (MCF-7/CDDP) exhibited substantial alterations in the intracellular iron content and levels of iron-regulatory proteins involved in the cellular uptake, storage and export of iron, especially in profoundly increased levels of ferritin light chain (FTL) protein. The increased levels of FTL in breast cancer indicate that FTL may be used as a diagnostic and prognostic marker for breast cancer. Additionally, we demonstrate that targeted downregulation of FTL protein by the microRNA miR-133a increases sensitivity of MCF-7/DOX and MCF-7/CDDP cells to doxorubicin and cisplatin. These results suggest that correction of iron metabolism abnormalities may substantially improve the efficiency of breast cancer treatment.

Disulfide/thiol switches in thiosemicarbazone ligands for redox-directed iron chelation

A disulfide bond is incorporated in the scaffold of thiosemicarbazone iron chelators as a reduction/activation switch. Following reduction, thiol-containing ligands stabilize iron ions in their trivalent oxidation state. The antiproliferative activity of the new chelating systems is assessed in human cancer cell lines and in normal tissue.

Modulation of intracellular iron metabolism by iron chelation affects chromatin remodeling proteins and corresponding epigenetic modifications in breast cancer cells and increases their sensitivity to chemotherapeutic agents

Iron plays a vital role in the normal functioning of cells via the regulation of essential cellular metabolic reactions, including several DNA and histone-modifying proteins. The metabolic status of iron and the regulation of epigenetic mechanisms are well-balanced and tightly controlled in normal cells; however, in cancer cells these processes are profoundly disturbed. Cancer-related abnormalities in iron metabolism have been corrected through the use of iron-chelating agents, which cause an inhibition of DNA synthesis, G₁-S phase arrest, an inhibition of epithelial-to-mesenchymal transition, and the activation of apoptosis. In the present study, we show that, in addition to these well-studied molecular mechanisms, the treatment of wild-type TP53 MCF-7 and mutant TP53 MDA-MB-231 human breast cancer cells with desferrioxamine (DFO), a model iron chelator, causes significant epigenetic alterations at the global and gene-specific levels. Specifically, DFO treatment decreased the protein levels of the histone H3 lysine 9 demethylase, Jumonji domain-containing protein 2A (JMJD2A), in the MCF-7 and MDA-MB-231 cells and down-regulated the levels of the histone H3 lysine 4 demethylase, lysine-specific demethylase 1 (LSD1), in the MDA-MB-231 cells. These changes were accompanied by alterations in corresponding metabolically sensitive histone marks. Additionally, we demonstrate that DFO treatment activates apoptotic programs in MCF-7 and MDA-MB-231 cancer cells and enhances their sensitivity to the chemotherapeutic agents, doxorubicin and cisplatin; however, the mechanisms underlying this activation differ. The induction of apoptosis in wild-type TP53 MCF-7 cells was p53-dependent, triggered mainly by the down-regulation of the JMJD2A histone demethylase, while in mutant TP53 MDA-MB-231 cells, the activation of the p53-independent apoptotic program was driven predominantly by the epigenetic up-regulation of p21.

Iron chelators with topoisomerase-inhibitory activity and their anticancer applications

SIGNIFICANCE

Iron and topoisomerases are abundant and essential cellular components. Iron is required for several key processes such as DNA synthesis, mitochondrial electron transport, synthesis of heme, and as a co-factor for many redox enzymes. Topoisomerases serve as critical enzymes that resolve topological problems during DNA synthesis, transcription, and repair. Neoplastic cells have higher uptake and utilization of iron, as well as elevated levels of topoisomerase family members. Separately, the chelation of iron and the cytotoxic inhibition of topoisomerase have yielded potent anticancer agents.

RECENT ADVANCES

The chemotherapeutic drugs doxorubicin and dexrazoxane both chelate iron and target topoisomerase 2 alpha (top2α). Newer chelators such as di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone and thiosemicarbazone -24 have recently been identified as top2α inhibitors. The growing list of agents that appear to chelate iron and inhibit topoisomerases prompts the question of whether and how these two distinct mechanisms might interplay for a cytotoxic chemotherapeutic outcome.

CRITICAL ISSUES

While iron chelation and topoisomerase inhibition each represent mechanistically advantageous anticancer therapeutic strategies, dual targeting agents present an attractive multi-modal opportunity for enhanced anticancer tumor killing and overcoming drug resistance. The commonalities and caveats of dual inhibition are presented in this review.

FUTURE DIRECTIONS

Gaps in knowledge, relevant biomarkers, and strategies for future in vivo studies with dual inhibitors are discussed.

Oh the irony: Iron as a cancer cause or cure?

Iron-oxide nanoparticles facilitate cancer diagnosis through enhanced contrast, selectively enhance tumor cell death with magnetic hyperthermia, and improve drug delivery with magnetic drug targeting. One application that remains largely unexplored is using the iron-oxide nanoparticles themselves to selectively inhibit tumor growth. In this leading opinion paper, we propose that high doses of iron-oxide nanoparticles can be used as a treatment for cancer by generating an oxidative assault against cancer. This proposal may be met with resistance considering the controversy surrounding iron in the field of cancer. Iron generates reactive oxygen species through the Fenton reaction, which may both cause - or cure cancer. Additionally, high demand for iron by cancer cells leads to contradictory therapeutic approaches: iron deprivation or overdose are both potential cancer therapies.

Synthetic and natural iron chelators: therapeutic potential and clinical use

Iron-chelation therapy has its origins in the treatment of iron-overload syndromes. For many years, the standard for this purpose has been deferoxamine. Recently, considerable progress has been made in identifying synthetic chelators with improved pharmacologic properties relative to deferoxamine. Most notable are deferasirox (Exjade(®)) and deferiprone (Ferriprox(®)), which are now available clinically. In addition to treatment of iron overload, there is an emerging role for iron chelators in the treatment of diseases characterized by oxidative stress, including cardiovascular disease, atherosclerosis, neurodegenerative diseases and cancer. While iron is not regarded as the underlying cause of these diseases, it does play an important role in disease progression, either through promotion of cellular growth and proliferation or through participation in redox reactions that catalyze the formation of reactive oxygen species and increase oxidative stress. Thus, iron chelators may be of therapeutic benefit in many of these conditions. Phytochemicals, many of which bind iron, may also owe some of their beneficial properties to iron chelation. This review will focus on the advances in iron-chelation therapy for the treatment of iron-overload disease and cancer, as well as neurodegenerative and chronic inflammatory diseases. Established and novel iron chelators will be discussed, as well as the emerging role of dietary plant polyphenols that effectively modulate iron biochemistry.

The iron chelator Dp44mT inhibits the proliferation of cancer cells but fails to protect from doxorubicin-induced cardiotoxicity in spontaneously hypertensive rats

PURPOSE

The iron chelator Dp44mT is a potent topoisomerase IIα inhibitor with novel anticancer activity. Doxorubicin (Dox), the current front-line therapy for breast cancer, induces a dose-limiting cardiotoxicity, in part through an iron-mediated pathway. We tested the hypothesis that Dp44mT can improve clinical outcomes of treatment with Dox by alleviating cardiotoxicity.

METHODS

The general cardiac and renal toxicities induced by Dox were investigated in the presence and absence of Dp44mT. The iron chelating cardioprotectant Dexrazoxane (Drz), which is approved for this indication, was used as a positive control. In vitro studies were carried out with H9c2 rat cardiomyocytes and in vivo studies were performed using spontaneously hypertensive rats.

RESULTS

Testing of the GI(50) profile of Dp44mT in the NCI-60 panel confirmed activity against breast cancer cells. An acute, toxic dose of Dox caused the predicted cellular and cardiac toxicities, such as cell death and DNA damage in vitro and elevated cardiac troponin T levels, tissue damage, and apoptosis in vivo. Dp44mT alone caused insignificant changes in hematological and biochemical indices in rats, indicating that Dp44mT is not significantly cardiotoxic as a single agent. In contrast to Drz, Dp44mT failed to mitigate Dox-induced cardiotoxicity in vivo.

CONCLUSIONS

We conclude that although Dp44mT is a potent iron chelator, it is unlikely to be an appropriate cardioprotectant against Dox-induced toxicity. However, it should continue to be evaluated as a potential anticancer agent as it has a novel mechanism for inhibiting the growth of a broad range of malignant cell types while exhibiting very low intrinsic toxicity to healthy tissues.

The antioxidant transcription factor Nrf2 negatively regulates autophagy and growth arrest induced by the anticancer redox agent mitoquinone

Mitoquinone (MitoQ) is a synthetically modified, redox-active ubiquinone compound that accumulates predominantly in mitochondria. We found that MitoQ is 30-fold more cytotoxic to breast cancer cells than to healthy mammary cells. MitoQ treatment led to irreversible inhibition of clonogenic growth of breast cancer cells through a combination of autophagy and apoptotic cell death mechanisms. Relatively limited cytotoxicity was seen with the parent ubiquinone coenzyme Q(10.) Inhibition of cancer cell growth by MitoQ was associated with G(1)/S cell cycle arrest and phosphorylation of the checkpoint kinases Chk1 and Chk2. The possible role of oxidative stress in MitoQ activity was investigated by measuring the products of hydroethidine oxidation. Increases in ethidium and dihydroethidium levels, markers of one-electron oxidation of hydroethidine, were observed at cytotoxic concentrations of MitoQ. Keap1, an oxidative stress sensor protein that regulates the antioxidant transcription factor Nrf2, underwent oxidation, degradation, and dissociation from Nrf2 in MitoQ-treated cells. Nrf2 protein levels, nuclear localization, and transcriptional activity also increased following MitoQ treatment. Knockdown of Nrf2 caused a 2-fold increase in autophagy and an increase in G(1) cell cycle arrest in response to MitoQ but had no apparent effect on apoptosis. The Nrf2-regulated enzyme NQO1 is partly responsible for controlling the level of autophagy. Keap1 and Nrf2 act as redox sensors for oxidative perturbations that lead to autophagy. MitoQ and similar compounds should be further evaluated for novel anticancer activity.

Lipophilic aroylhydrazone chelator HNTMB and its multiple effects on ovarian cancer cells

BACKGROUND

Metal chelators have gained much attention as potential anti-cancer agents. However, the effects of chelators are often linked solely to their capacity to bind iron while the potential complexation of other trace metals has not been fully investigated. In present study, we evaluated the effects of various lipophilic aroylhydrazone chelators (AHC), including novel compound HNTMB, on various ovarian cancer cell lines (SKOV-3, OVCAR-3, NUTU-19).

METHODS

Cell viability was analyzed via MTS cytotoxicity assays and NCI60 cancer cell growth screens. Apoptotic events were monitored via Western Blot analysis, fluorescence microscopy and TUNEL assay. FACS analysis was carried out to study Cell Cycle regulation and detection of intracellular Reactive Oxygen Species (ROS) RESULTS: HNTMB displayed high cytotoxicity (IC50 200-400 nM) compared to previously developed AHC (oVtBBH, HNtBBH, StBBH/206, HNTh2H/315, HNI/311; IC50 0.8-6 microM) or cancer drug Deferoxamine, a hexadentate iron-chelator (IC50 12-25 microM). In a NCI60 cancer cell line screen HNTMB exhibited growth inhibitory effects with remarkable differences in specificity depending on the cell line studied (GI50 10 nM-2.4 microM). In SKOV-3 ovarian cancer cells HNTMB treatment led to chromatin fragmentation and activation of the extrinsic and intrinsic pathways of apoptosis with specific down-regulation of Bcl-2. HNTMB caused delayed cell cycle progression of SKOV-3 through G2/M phase arrest. HNTMB can chelate iron and copper of different oxidation states. Complexation with copper lead to high cytotoxicity via generation of reactive oxygen species (ROS) while treatment with iron complexes of the drug caused neither cytotoxicity nor increased ROS levels.

CONCLUSIONS

The present report suggests that both, non-complexed HNTMB as a chelator of intracellular trace-metals as well as a cytotoxic HNTMB/copper complex may be developed as potential therapeutic drugs in the treatment of ovarian and other solid tumors.

Redox-directed cancer therapeutics: molecular mechanisms and opportunities

Redox dysregulation originating from metabolic alterations and dependence on mitogenic and survival signaling through reactive oxygen species represents a specific vulnerability of malignant cells that can be selectively targeted by redox chemotherapeutics. This review will present an update on drug discovery, target identification, and mechanisms of action of experimental redox chemotherapeutics with a focus on pro- and antioxidant redox modulators now in advanced phases of preclinal and clinical development. Recent research indicates that numerous oncogenes and tumor suppressor genes exert their functions in part through redox mechanisms amenable to pharmacological intervention by redox chemotherapeutics. The pleiotropic action of many redox chemotherapeutics that involves simultaneous modulation of multiple redox sensitive targets can overcome cancer cell drug resistance originating from redundancy of oncogenic signaling and rapid mutation.Moreover, some redox chemotherapeutics may function according to the concept of synthetic lethality (i.e., drug cytotoxicity is confined to cancer cells that display loss of function mutations in tumor suppressor genes or upregulation of oncogene expression). The impressive number of ongoing clinical trials that examine therapeutic performance of novel redox drugs in cancer patients demonstrates that redox chemotherapy has made the crucial transition from bench to bedside.

The iron chelator Dp44mT causes DNA damage and selective inhibition of topoisomerase IIalpha in breast cancer cells

Di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone (Dp44mT) is being developed as an iron chelator with selective anticancer activity. We investigated the mechanism whereby Dp44mT kills breast cancer cells, both as a single agent and in combination with doxorubicin. Dp44mT alone induced selective cell killing in the breast cancer cell line MDA-MB-231 when compared with healthy mammary epithelial cells (MCF-12A). It induces G(1) cell cycle arrest and reduces cancer cell clonogenic growth at nanomolar concentrations. Dp44mT, but not the iron chelator desferal, induces DNA double-strand breaks quantified as S139 phosphorylated histone foci (gamma-H2AX) and Comet tails induced in MDA-MB-231 cells. Doxorubicin-induced cytotoxicity and DNA damage were both enhanced significantly in the presence of low concentrations of Dp44mT. The chelator caused selective poisoning of DNA topoisomerase IIalpha (top2alpha) as measured by an in vitro DNA cleavage assay and cellular topoisomerase-DNA complex formation. Heterozygous Nalm-6 top2alpha knockout cells (top2alpha(+/-)) were partially resistant to Dp44mT-induced cytotoxicity compared with isogenic top2alpha(+/+) or top2beta(-/-) cells. Specificity for top2alpha was confirmed using top2alpha and top2beta small interfering RNA knockdown in HeLa cells. The results show that Dp44mT is cytotoxic to breast cancer cells, at least in part, due to selective inhibition of top2alpha. Thus, Dp44mT may serve as a mechanistically unique treatment for cancer due to its dual ability to chelate iron and inhibit top2alpha activity.

Tripeptide tyroserleutide plus doxorubicin: therapeutic synergy and side effect attenuation

Background

Tripeptide tyroserleutide (YSL) is a novel small molecule anti-tumor polypeptide that has been shown to inhibit the growth of human liver cancer cells. In this study, we investigated the effects of YSL plus doxorubicin on the growth of human hepatocellular carcinoma BEL-7402 cells that had been transplanted into nude mice.

Methods

Nude mice bearing human hepatocellular carcinoma BEL-7402 tumors were treated with successive intraperitoneal injections of saline; low-, mid-, or high-dose doxorubicin; or low-, mid-, or high-dose doxorubicin plus YSL. Effects on the weight and volume of the tumors were evaluated.

Results

Co-administration of YSL and high-dose doxorubicin (6 mg/kg every other day) prolonged the survival time of tumor-bearing mice as compared to high-dose doxorubicin alone. As well, the anti-tumor effects of mid- and low-dose doxorubicin (2 and 0.7 mg/kg every other day, respectively) were enhanced when supplemented with YSL; the tumor growth inhibition rates for YSL plus doxorubicin were greater than the inhibition rates for the same dosages of doxorubicin alone. The combination of YSL and doxorubicin decreased chemotherapy-associated weight loss, leukocyte depression, and heart, liver, and kidney damage as compared to doxorubicin alone.

Conclusion

The combination of YSL plus doxorubicin enhances the anti-tumor effect and reduces the side effects associated with doxorubicin chemotherapy.

Novel method of doxorubicin-SPION reversible association for magnetic drug targeting

A new method of reversible association of doxorubicin (DOX) to superparamagnetic iron oxide nanoparticles (SPION) is developed for magnetically targeted chemotherapy. The efficacy of this approach is evaluated in terms of drug loading, delivery kinetics and cytotoxicity in vitro. Aqueous suspensions of SPION (ferrofluids) were prepared by coprecipitation of ferric and ferrous chlorides in alkaline medium followed by surface oxidation by ferric nitrate and surface treatment with citrate ions. The ferrofluids were loaded with DOX using a pre-formed DOX-Fe(2+) complex. The resulting drug loading was as high as 14% (w/w). This value exceeds the maximal loading known from literature up today. The release of DOX from the nanoparticles is strongly pH-dependent: at pH 7.4 the amount of drug released attains a plateau of approximately 85% after 1h, whereas at pH 4.0 the release is almost immediate. At both pH, the released drug is iron-free. The in vitro cytotoxicity of the DOX-loaded SPION on the MCF-7 breast cancer cell line is similar to that of DOX in solution or even higher, at low-drug concentrations. The present study demonstrates the potential of the novel method of pH-sensitive DOX-SPION association to design novel magnetic nanovectors for chemotherapy.

On the interaction of doxorubicin with oleate ions: fluorescence spectroscopy and liquid-liquid extraction study

Increase of lipophilicity of cationic doxorubicin (DOX) by its association with a fatty acid ion is of interest for pharmaceutical formulations and could have an impact on the drug delivery into cancer cells. On the basis of spectroscopic analysis of intrinsic DOX fluorescence, this study provides an experimental evidence of DOX-oleate interactions as function of ion/drug molar ratio (R) and pH. An electrostatic attraction to oleates is dominant for the cationic form of DOX (pH 6.5) and a hydrophobic interaction is characteristic of the molecular form of DOX (pH 8.6). A high content of sodium oleate vesicles ([oleate]>/=0.2 mM, R>/=20) limits the electrostatic and hydrophobic interactions at pH 6.5 while favoring the hydrophobic interactions at pH 8.6. The influence of these interactions on the lipophilicity of the cationic form of DOX is analyzed by measuring the apparent partition coefficient (aqueous buffer pH 6.5/methylene chloride). The results show a lipophilicity gain for the cationic form of DOX in presence of 10 : 1 ion/drug molar ratio, while no lipophilicity increase is observed at 50 : 1 molar ratio.