Therapeutic potential of iron chelators in cancer therapy

DFO treatment protects against depression-like behaviors and cognitive impairment in CUMS mice

Depression has several negative effects on emotion as well as learning and memory abilities. Previous studies showed that depression could exacerbate inflammation, which in turn further aggravated depression. Deferoxamine (DFO) is a chelating agent binding iron and aluminium, and is clinically applied to treat acute ion poisoning and hemochromatosis. Researches showed that it could reduce inflammation via increasing the expression of hypoxia-inducible factor-1alpha (HIF-1α). Here, we established a chronic unpredictable mild stress (CUMS) model to investigate whether DFO exerted a neuroprotective function in depression. The results demonstrated that CUMS (4 weeks) effectively induced depression-like behaviors in mice based on sucrose preference test (SPT), forced swim test (FST), tail suspension test (TST), open field test (OFT), and elevated plus-maze test (EPT). It also brought cognitive deficits based on Morris water maze (MWM) test and the impairment of synaptic plasticity based on in vivo electrophysiological recordings. Additionally, CUMS exposure significantly decreased the expression of hippocampal synapse related proteins and the spine density of neurons in the DG region, accompanied by increasing the expression of hippocampal inflammatory cytokines, and promoted the activation of microglia in the hippocampus. The expression of HIF-1α was down-regulated as expected. However, DFO distinctly reversed the CUMS-induced impairments. The mechanism is associated with the DFO inhibition of inflammation by upregulating HIF-1 expression, thereby alleviating a series of pathology changes. Together, these findings suggest that DFO likely plays a protective role in cognitive impairments and synaptic plasticity deficits resulting from depression.

Role of Iron in the Molecular Pathogenesis of Diseases and Therapeutic Opportunities

Iron is an essential mineral that serves as a prosthetic group for a variety of proteins involved in vital cellular processes. The iron economy within humans is highly conserved in that there is no proper iron excretion pathway. Therefore, iron homeostasis is highly evolved to coordinate iron acquisition, storage, transport, and recycling efficiently. A disturbance in this state can result in excess iron burden in which an ensuing iron-mediated generation of reactive oxygen species imparts widespread oxidative damage to proteins, lipids, and DNA. On the contrary, problems in iron deficiency either due to genetic or nutritional causes can lead to a number of iron deficiency disorders. Iron chelation strategies have been in the works since the early 1900s, and they still remain the most viable therapeutic approach to mitigate the toxic side effects of excess iron. Intense investigations on improving the efficacy of chelation strategies while being well tolerated and accepted by patients have been a particular focus for many researchers over the past 30 years. Moreover, recent advances in our understanding on the role of iron in the pathogenesis of different diseases (both in iron overload and iron deficiency conditions) motivate the need to develop new therapeutics. We summarized recent investigations into the role of iron in health and disease conditions, iron chelation, and iron delivery strategies. Information regarding small molecule as well as macromolecular approaches and how they are employed within different disease pathogenesis such as primary and secondary iron overload diseases, cancer, diabetes, neurodegenerative diseases, infections, and in iron deficiency is provided.

Development of Iron Sequester Antioxidant Quercetin@ZnO Nanoparticles with Photoprotective Effects on UVA-Irradiated HaCaT Cells

BACKGROUND

Solar ultraviolet radiation A (UVA, 320-400 nm) is a significant risk factor leading to various human skin conditions such as premature aging or photoaging. This condition is enhanced by UVA-mediated iron release from cellular iron proteins affecting huge populations across the globe.

PURPOSE

Quercetin-loaded zinc oxide nanoparticles (quercetin@ZnO NPs) were prepared to examine its cellular iron sequestration ability to prevent the production of reactive oxygen species (ROS) and inflammatory responses in HaCaT cells.

METHODS

Quercetin@ZnO NPs were synthesized through a homogenous precipitation method, and the functional groups were characterized by Fourier transform infrared (FTIR) spectroscopy, whereas scanning electron microscopy (SEM) described the morphologies of NPs. MTT and qRT-PCR assays were used to examine cell viability and the expression levels of various inflammatory cytokines. The cyclic voltammetry (CV) was employed to evaluate the redox potential of quercetin-Fe³⁺/quercetin-Fe²⁺ complexes.

RESULTS

The material characterization results supported the loading of quercetin molecules on ZnO NPs. The CV and redox potential assays gave Fe-binding capability of quercetin at 0.15 mM and 0.3 mM of Fe(NO₃)₃. Cytotoxicity assays using quercetin@ZnO NPs with human HaCaT cells showed no cytotoxic effects and help regain cell viability loss following UVA (150 kJ/m²).

CONCLUSION

Quercetin@ZnO NPs showed that efficient quercetin release action is UV-controlled, and the released quercetin molecules have excellent antioxidant, anti-inflammatory, and iron sequestration potential. Quercetin@ZnO NPs have superior biocompatibility to provide UVA protection and medication at once for antiphotoaging therapeutics.

Deferoxamine: An Angiogenic and Antioxidant Molecule for Tissue Regeneration

Deferoxamine (DFO) has been in use for half a century as a Food and Drug Administration-approved iron chelator, but recent studies indicate a variety of properties that could expand this drug's application into the fields of tissue and regenerative engineering. DFO has been implicated as an angiogenic agent in studies on ischemia, wound healing, and bone regeneration because of its ability to upregulate hypoxia-inducible factor-1 alpha (HIF-1α) and other key downstream angiogenic factors. DFO has also demonstrated antioxidant capabilities unrelated to its iron-chelating properties, making it a potential modulator of the oxidative stress involved in the inflammation response. Together, these properties make DFO a potential bioactive molecule to promote wound healing and enhance tissue integration of biomaterials in vivo. Impact Statement Deferoxamine (DFO) is approved by the Food and Drug Administration as an iron chelator and is been used to treat iron overload. Recent studies indicate that DFO may have important applications in the growing field of tissue regeneration because of its unique properties of downregulating inflammation while promoting vascularization, thereby enhancing wound healing in vivo.

MRI reporter gene MagA suppresses transferrin receptor and maps Fe2+ dependent lung cancer

As a magnetic resonance imaging (MRI) reporter gene, MagA has become a powerful tool to monitor dynamic gene expression and allowed concomitant high resolution anatomical and functional imaging of subcellular genetic information. Here we establish a stably expressed MagA method for lung cancer MRI. The results show that MagA can not only enhance both in vitro and in vivo MRI contrast by specifically alternating the transverse relaxation rate of water, but also inhibit the malignant growth of lung tumor. In addition, MagA can regulate magnetic nanoparticle production in grafted tissues and also suppress transferrin receptor expression by acting as an iron transporter, and meanwhile can permit iron biomineralization in the presence of mammalian iron homeostasis. This work provides experimental evidence for the safe preclinical applications of MagA as both a potential inhibitor and an MRI-based tracing tool for iron ion-dependent lung cancer.

3-Chloro-N'-(2-hydroxybenzylidene) benzohydrazide: An LSD1-Selective Inhibitor and Iron-Chelating Agent for Anticancer Therapy

Despite the discovery and development of novel therapies, cancer is still a leading cause of death worldwide. In order to grow, tumor cells require large quantities of nutrients involved in metabolic processes, and an increase in iron levels is known to contribute to cancer proliferation. Iron plays an important role in the active site of a number of proteins involved in energy metabolism, DNA synthesis and repair, such as ribonucleotide reductase, which induce G0/S phase arrest and exert a marked antineoplastic effect, particularly in leukemia and neuroblastoma. Iron-depletion strategies using iron chelators have been shown to result in cell cycle arrest and apoptosis. Deferoxamine (DFO) was the first FDA-approved drug for the treatment of iron overload pathologies, and has also been recognized as having anticancer properties. The high cost, low permeability and short plasma half-life of DFO led to the development of other iron-chelating drugs. Pyridoxal isonicotinoyl hydrazone (PIH) and its analogs chelate cellular iron by tridentate binding, and inhibit DNA synthesis more robustly than DFO, demonstrating an effective antiproliferative activity. Here, we investigated the biological effects of a PIH derivative, 3-chloro-N′-(2-hydroxybenzylidene)benzohydrazide (CHBH), known to be a lysine-specific histone demethylase 1A inhibitor. We showed that CHBH is able to induce cell proliferation arrest in several human cancer cell lines, including lung, colon, pancreas and breast cancer, at micromolar levels. Our findings indicate that CHBH exerts a dual anticancer action by strongly impairing iron metabolism and modulating chromatin structure and function.

The utility of iron chelators in the management of inflammatory disorders

Since iron can contribute to detrimental radical generating processes through the Fenton and Haber-Weiss reactions, it seems to be a reasonable approach to modulate iron-related pathways in inflammation. In the human organism a counterregulatory reduction in iron availability is observed during inflammatory diseases. Under pathological conditions with reduced or increased baseline iron levels different consequences regarding protection or susceptibility to inflammation have to be considered. Given the role of iron in development of inflammatory diseases, pharmaceutical agents targeting this pathway promise to improve the clinical outcome. The objective of this review is to highlight the mechanisms of iron regulation and iron chelation, and to demonstrate the potential impact of this strategy in the management of several acute and chronic inflammatory diseases, including cancer.

Underscoring the influence of inorganic chemistry on nuclear imaging with radiometals

Over the past several decades, radionuclides have matured from largely esoteric and experimental technologies to indispensible components of medical diagnostics. Driving this transition, in part, have been mutually necessary advances in biomedical engineering, nuclear medicine, and cancer biology. Somewhat unsung has been the seminal role of inorganic chemistry in fostering the development of new radiotracers. In this regard, the purpose of this Forum Article is to more visibly highlight the significant contributions of inorganic chemistry to nuclear imaging by detailing the development of five metal-based imaging agents: (64)Cu-ATSM, (68)Ga-DOTATOC, (89)Zr-transferrin, (99m)Tc-sestamibi, and (99m)Tc-colloids. In a concluding section, several unmet needs both in and out of the laboratory will be discussed to stimulate conversation between inorganic chemists and the imaging community.

Generation of erythroid cells from fibroblasts and cancer cells in vitro and in vivo

Bone marrow is generally considered the main source of erythroid cells. Here we report that a single hypoxia-mimic chemical, CoCl2, can increase the size of fibroblasts and cancer cells and lead to formation of polyploidy giant cells (PGCs) or polyploidy giant cancer cells (PGCCs), activation of stem cell marker expression, increased growth of normal and cancer spheroid, and lead to differentiation of the fibroblasts and epithelial cells toward erythroid lineage expressing hemoglobins both in vitro and in vivo. Immunohistochemical examination demonstrated that these cells are predominantly made of embryonic hemoglobins, with various levels of fetal and adult hemoglobins. Ectopic expression of c-Myc induced the generation of nucleated erythoid cells expressing variable levels of embryonic and fetal hemoglobins. Generation of these erythroid cells can be also observed via histological examination of other cancer cell lines and human tumor samples. These data suggest that normal and solid cancer cells can directly generate erythroid cells to obtain oxygen in response to hypoxia and may explain the ineffectiveness of conventional anti-angiogenic therapies for cancer, which are directed at endothelium-dependent vessels, and offer new targets for intervention.

Annotating MYC status with 89Zr-transferrin imaging

A non-invasive technology that quantitatively measures the activity of oncogenic signaling pathways could broadly impact cancer diagnosis and treatment using targeted therapies. Here we describe the development of ⁸⁹Zr-desferrioxamine transferrin (⁸⁹Zr-Tf), a novel positron emission tomography (PET) radiotracer that binds the transferrin receptor 1 (TFRC, CD71) with high avidity. ⁸⁹Zr-Tf produces high contrast PET images that quantitatively reflect treatment-induced changes in MYC-regulated TFRC expression in a MYC oncogene-driven prostate cancer xenograft model. Moreover, ⁸⁹Zr-Tf imaging can detect the in situ development of prostate cancer in a transgenic MYC prostate cancer model, as well as prostatic intraepithelial neoplasia (PIN) prior to histological or anatomic evidence of invasive cancer. These preclinical data establish ⁸⁹Zr-Tf as a sensitive tool for non-invasive measurement of oncogene-driven TFRC expression in prostate, and potentially other cancers, with prospective near-term clinical application.

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.

Design of clinically useful macromolecular iron chelators

OBJECTIVES

In recent years, macromolecular iron chelators have received increasing attention as human therapeutic agents. The objectives of this article are: one, to discuss the factors which should be considered when designing iron binding macromolecules as human therapeutic agents, and two, to report recent achievements in the design and synthesis of appropriate macromolecular chelators that have resulted in the production of a number of agents with therapeutic potential.

KEY FINDINGS

Macromolecular drugs exhibit unique pharmaceutical properties that are fundamentally different from their traditional small-molecule counterparts. By virtue of their high-molecular-weight characteristics, many are confined to extracellular compartments, for instance, the serum and the gastrointestinal tract. In addition, they have potential for topical administration. Consequently, these macromolecular drugs are free from many of the toxic effects that are associated with their low-molecular-weight analogues.

SUMMARY

The design and synthesis of macromolecular iron chelators provides a novel aspect to chelation therapy. 3-Hydroxypyridin-4-one hexadentate-based macromolecular chelators have considerable potential for the development of new treatments for iron overload and for topical treatment of infection.

Lysosomes in iron metabolism, ageing and apoptosis

The lysosomal compartment is essential for a variety of cellular functions, including the normal turnover of most long-lived proteins and all organelles. The compartment consists of numerous acidic vesicles (pH approximately 4 to 5) that constantly fuse and divide. It receives a large number of hydrolases ( approximately 50) from the trans-Golgi network, and substrates from both the cells' outside (heterophagy) and inside (autophagy). Many macromolecules contain iron that gives rise to an iron-rich environment in lysosomes that recently have degraded such macromolecules. Iron-rich lysosomes are sensitive to oxidative stress, while 'resting' lysosomes, which have not recently participated in autophagic events, are not. The magnitude of oxidative stress determines the degree of lysosomal destabilization and, consequently, whether arrested growth, reparative autophagy, apoptosis, or necrosis will follow. Heterophagy is the first step in the process by which immunocompetent cells modify antigens and produce antibodies, while exocytosis of lysosomal enzymes may promote tumor invasion, angiogenesis, and metastasis. Apart from being an essential turnover process, autophagy is also a mechanism by which cells will be able to sustain temporary starvation and rid themselves of intracellular organisms that have invaded, although some pathogens have evolved mechanisms to prevent their destruction. Mutated lysosomal enzymes are the underlying cause of a number of lysosomal storage diseases involving the accumulation of materials that would be the substrate for the corresponding hydrolases, were they not defective. The normal, low-level diffusion of hydrogen peroxide into iron-rich lysosomes causes the slow formation of lipofuscin in long-lived postmitotic cells, where it occupies a substantial part of the lysosomal compartment at the end of the life span. This seems to result in the diversion of newly produced lysosomal enzymes away from autophagosomes, leading to the accumulation of malfunctioning mitochondria and proteins with consequent cellular dysfunction. If autophagy were a perfect turnover process, postmitotic ageing and several age-related neurodegenerative diseases would, perhaps, not take place.

Lysosomes and oxidative stress in aging and apoptosis

The lysosomal compartment consists of numerous acidic vesicles (pH approximately 4-5) that constantly fuse and divide. It receives a large number of hydrolases from the trans-Golgi network, while their substrates arrive from both the cell's outside (heterophagy) and inside (autophagy). Many macromolecules under degradation inside lysosomes contain iron that, when released in labile form, makes lysosomes sensitive to oxidative stress. The magnitude of generated lysosomal destabilization determines if reparative autophagy, apoptosis, or necrosis will follow. Apart from being an essential turnover process, autophagy is also a mechanism for cells to repair inflicted damage, and to survive temporary starvation. The inevitable diffusion of hydrogen peroxide into iron-rich lysosomes causes the slow oxidative formation of lipofuscin in long-lived postmitotic cells, where it finally occupies a substantial part of the volume of the lysosomal compartment. This seems to result in a misdirection of lysosomal enzymes away from autophagosomes, resulting in depressed autophagy and the accumulation of malfunctioning mitochondria and proteins with consequent cellular dysfunction. This scenario might put aging into the category of autophagy disorders.

Autophagy, ageing and apoptosis: the role of oxidative stress and lysosomal iron

As an outcome of normal autophagic degradation of ferruginous materials, such as ferritin and mitochondrial metalloproteins, the lysosomal compartment is rich in labile iron and, therefore, sensitive to the mild oxidative stress that cells naturally experience because of their constant production of hydrogen peroxide. Diffusion of hydrogen peroxide into the lysosomes results in Fenton-type reactions with the formation of hydroxyl radicals and ensuing peroxidation of lysosomal contents with formation of lipofuscin that amasses in long-lived postmitotic cells. Lipofuscin is a non-degradable polymeric substance that forms at a rate that is inversely related to the average lifespan across species and is built up of aldehyde-linked protein residues. The normal accumulation of lipofuscin in lysosomes seems to reduce autophagic capacity of senescent postmitotic cells--probably because lipofuscin-loaded lysosomes continue to receive newly formed lysosomal enzymes, which results in lack of such enzymes for autophagy. The result is an insufficient and declining rate of autophagic turnover of worn-out and damaged cellular components that consequently accumulate in a way that upsets normal metabolism. In the event of a more substantial oxidative stress, enhanced formation of hydroxyl radicals within lysosomes jeopardizes the membrane stability of particularly iron-rich lysosomes, specifically of autophagolysosomes that have recently participated in the degradation of iron-rich materials. For some time, the rupture of a limited number of lysosomes has been recognized as an early upstream event in many cases of apoptosis, particularly oxidative stress-induced apoptosis, while necrosis results from a major lysosomal break. Consequently, the regulation of the lysosomal content of redox-active iron seems to be essential for the survival of cells both in the short- and the long-term.

Lysosomal labilization

The lysosomal compartment is the place for cellular degradation of endocytosed and autophagocytosed material and a center for normal turnover of organelles as well as most long-lived proteins. Lysosomes were long considered stable structures that broke and released their many hydrolytic enzymes only following necrotic cell death. It is now realized that lysosomes instead are quite vulnerable, although in a heterogeneous way. Their exposure to a number of events, such as oxidative stress, lysosomotropic detergents and aldhydes, as well as overexpression of the p53 protein, causes time-and-dose-dependent lysosomal rupture that is followed by apoptosis or necrosis. Partial lysosomal rupture has often been found to be an early upstream event in apoptosis, while necrosis results from fulminant lysosomal rupture. Consequently, factors influencing the stability of lysosomes, for instance their content of labile and redox-active iron, seem to be essential for the survival of cells.

Novel trihydroxamate-containing peptides: design, synthesis, and metal coordination

Novel trihydroxamate-containing peptides were designed to mimic desferrioxamine (Desferal(R), DFO, a naturally occurring siderophore) but possess distinct conformational restrictions and varied lipophilicity to probe structure vs. metal coordination. The synthesis was performed via fragment condensation of hydroxamate-containing oligopeptides such as Fmoc-Leu- Psi[CON(OBz)]-Phe-Ala-Pro-OH and H-Leu-Psi[CON(OBz)]-Phe-Ala-Pro-OBu(t) (Fmoc: 9-fluor enylmethoxycarbonyl; OBz: benzyl; OBu(t): tert-butyl) either in solution or on a solid support. The metal-binding properties were studied by electrospray ionization-mass spectroscopy (ESI-MS), ultraviolet (UV)-visible spectroscopy, and (1)H nuclear magnetic resonance (NMR). Similar to the dihydroxamate analogs previously explored [Biopolymers (Peptide Science), 2003, Vol. 71, pp. 489-515], the compounds with three hydroxamates arrayed at 10-atom intervals, i.e., H-[Leu-Psi[CON(OH)]-Phe-Ala-Pro](3)-OH (P1), cyclo[Leu-Psi[CON(OH)]-Phe-Ala-Pro](3) (P2), and H-[Leu-Psi(CONOH)-Phe-Ala-Pro](2)-Leu-NHOH (P7), exhibited high affinities for intramolecular coordination with Fe(III) and Ga(III). As expected, both P1 and P2 showed higher relative Fe(III)-binding affinities than the corresponding dihydroxamate-containing peptide analogs (P11 and P12). Even though both P1 and P2 did not compete with DFO in the relative metal-binding affinity in both solution and gas phases, P1, P2, and DFO exhibited similar relative binding selectivities to 11 different metal ions including Fe(III), Fe(II), Al(III), Ga(III), In(III), Zn(II), Cu(II), Co(II), Ni(II), Gd(III), and Mn(II). Compared to the other metal ions, they had higher relative binding affinities with Fe(III), Fe(II), Al(III), Ga(III), and In(III). The decreased metal-binding affinities of P1 and P2 in comparison with DFO suggested the conformational restrictions of their backbones perturb their three hydroxamate groups from optimal hexadentate orientations for metal coordination. As detected by ESI-MS, P2 was distinguished from both P1 and DFO by solvation of its Ga(III) and Fe(III) complexes (such as acetonitrile or water), thereby stabilizing the resulting complexes in the gas phase. Noteworthy, P2 led to 69% death rate in Hela cells at a concentration of 50 microM, exhibiting higher cytotoxicity than DFO in vitro despite its much lower affinity for iron. This enhanced toxicity may simply reflect the increased lipophilicity of the cyclic trihydroxamate (P2) together with the improvements in its cell penetration, and/or subsequent intracellular molecular recognition of both side chains and hydroxamate groups. The cytotoxicity was significantly suppressed by precoordination with Ga(III) or Fe(III), suggesting a mechanism of toxicity via sequestration of essential metal ions as well as the importance of curbing the metal coordination before targeting. The potential of such siderophore-mimicking peptides in oncology needs further exploration.

Activation of transferrin receptor 1 by c-Myc enhances cellular proliferation and tumorigenesis

Overexpression of transferrin receptor 1 (TFRC1), a major mediator of iron uptake in mammalian cells, is a common feature of human malignancies. Therapeutic strategies designed to interfere with tumor iron metabolism have targeted TFRC1. The c-Myc oncogenic transcription factor stimulates proliferation and growth by activating thousands of target genes. Here we demonstrate that TFRC1 is a critical downstream target of c-Myc. Using in vitro and in vivo models of B-cell lymphoma, we show that TFRC1 expression is activated by c-Myc. Chromatin immunoprecipitation experiments reveal that c-Myc directly binds a conserved region of TFRC1. In light of these findings, we sought to determine whether TFRC1 is required for c-Myc-mediated cellular proliferation and cell size control. TFRC1 inhibition decreases cellular proliferation and results in G1 arrest without affecting cell size. Consistent with these findings, expression profiling reveals that TFRC1 depletion alters expression of genes that regulate the cell cycle. Furthermore, enforced TFRC1 expression confers a growth advantage to cells and significantly enhances the rate of c-Myc-mediated tumor formation in vivo. These findings provide a molecular basis for increased TFRC1 expression in human tumors, illuminate the role of TFRC1 in the c-Myc target gene network, and support strategies that target TFRC1 for cancer therapy.

In vivo tumor growth is inhibited by cytosolic iron deprivation caused by the expression of mitochondrial ferritin

Mitochondrial ferritin (MtFt) is a mitochondrial iron-storage protein whose function and regulation is largely unknown. Our previous results have shown that MtFt overexpression markedly affects intracellular iron homeostasis in mammalian cells. Using tumor xenografts, we examined the effects of MtFt overexpression on tumor iron metabolism and growth. The expression of MtFt dramatically reduced implanted tumor growth in nude mice. Mitochondrial iron deposition in MtFt-expressing tumors was directly observed by transmission electron microscopy. A cytosolic iron starvation phenotype in MtFt-expressing tumors was revealed by increased RNA-binding activity of iron regulatory proteins, and concomitantly both an increase in transferrin receptor levels and a decrease in cytosolic ferritin. MtFt overexpression also led to decreases in total cellular heme content and heme oxygenase-1 levels. In addition, elevated MtFt in tumors was also associated with a decrease in total aconitase activity and lower frataxin protein level. In conclusion, our study shows that high MtFt levels can significantly affect tumor iron homeostasis by shunting iron into mitochondria; iron scarcity resulted in partially deficient heme and iron-sulfur cluster synthesis. It is likely that deprivation of iron in the cytosol is the cause for the significant inhibition of xenograft tumor growth.

On the Role of Iron and one of its Chelating Agents in the Production of Protoporphyrin IX Generated by 5-Aminolevulinic Acid and its Hexyl Ester Derivative Tested on an Epidermal Equivalent of Human Skin

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) or its derivatives as precursors of protoporphyrin IX (PPIX) is routinely used in dermatology for the treatment of various pathologies. However, this methodology suffers to some extent from a limited efficacy. Therefore, the main goal of this study was to investigate the modulation and pharmacokinetics of PPIX buildup after a 5 h incubation with ALA (1.5 mM) and one of its derivatives, the hexyl ester of ALA (h-ALA) (1.5 mM), on the human epidermal equivalent Epidex. PPIX production was modulated with (L+) ascorbic acid iron (II) salt (LAI) or the iron (II)-specific chelating agent deferoxamine (DFO). PPIX fluorescence from the Epidex layers was measured up to 150 h after the precursor administration using a microspectrofluorometer (lambda(ex): 400 +/- 20 nm; lambda(det): 635 nm). The maximum PPIX fluorescence intensity induced by h-ALA was about 1.7 x larger than that induced by ALA. The addition of DFO resulted in a more than 50% increase in PPIX fluorescence for both precursors. The decay half life measured for PPIX fluorescence is 30 and 42.5 h, respectively, for ALA and h-ALA. These half lives are doubled when the samples contain DFO. In the samples with the highest fluorescence intensity, a modified fluorescence spectrum was observed after 10 h, with the emergence of a peak at 590 nm, which is attributed to zinc protoporphyrin IX (Zn PPIX).

Iron chelators deferoxamine and diethylenetriamine pentaacetic acid induce apoptosis in ovarian carcinoma

OBJECTIVES

Ovarian cancer remains a leading cause of death in women and development of new therapies is essential. Deprivation of iron (Fe), an essential micro-nutrient, by chelation is known to inhibit proliferation of several human cancers but its potential in ovarian cancer treatment remains unknown. We have evaluated the anti-proliferative activities of iron chelators, deferoxamine (DFO), and diethylenetriamine pentaacetic acid (DTPA), in human and rat ovarian cancer cells.

METHODS

The effect of DFO and DTPA on CaOV-3 (human) and NUTU-19 (rat) ovarian cancer cells was determined by cell proliferation and apoptosis assays (Hoechst staining, DNA fragmentation, and caspase activation), cell cycle analysis, and Fe supplementation studies.

RESULTS

DFO and DTPA were cytotoxic to ovarian cancer cells in a dose- and time-dependent manner. DFO inhibited proliferation of NUTU-19 and CaOV-3 cells (IC(50) at 45 and 280 microM, respectively), while DTPA inhibited proliferation of only NUTU-19 cells (IC(50) at 50 microM), at 48 h. DNA synthesis was inhibited in CaOV-3 cells by DFO (>90% at 200 microM) and in NUTU-19 by both DFO and DTPA (>90% at 50 microM). Fe supplementation effectively reversed the cytotoxic effects of DFO and DTPA. Cell cycle analysis showed a G0/G1- and S-phase block with increased apoptosis. DNA fragmentation analysis confirmed apoptosis. Increase in caspase-3, -8, and -9 activities ( approximately 2.4-fold) was associated with apoptosis.

CONCLUSIONS

Our studies show that Fe chelators suppress ovarian cancer growth by inhibiting proliferation and inducing apoptosis. Therefore, Fe chelators can be potentially developed as novel therapeutic agents to treat ovarian cancer.

Induction of tumor arrest and differentiation with prolonged survival by intermittent hypoxia in a mouse model of acute myeloid leukemia

We showed previously that mild real hypoxia and hypoxia-mimetic agents induced in vitro cell differentiation of acute myeloid leukemia (AML). We here investigate the in vivo effects of intermittent hypoxia on syngenic grafts of leukemic blasts in a PML-RARalpha transgenic mouse model of AML. For intermittent hypoxia, leukemic mice were housed in a hypoxia chamber equivalent to an altitude of 6000 m for 18 hours every consecutive day. The results show that intermittent hypoxia significantly prolongs the survival of the leukemic mice that received transplants, although it fails to cure the disease. By histologic and cytologic analyses, intermittent hypoxia is shown to inhibit the infiltration of leukemic blasts in peripheral blood, bone marrow, spleen, and liver without apoptosis induction. More intriguingly, intermittent hypoxia also induces leukemic cells to undergo differentiation with progressive increase of hypoxia-inducible factor-1alpha protein, as evidenced by morphologic criteria of maturating myeloid cells and increased expression of mouse myeloid cell differentiation-related antigens Gr-1 and Mac-1. Taken together, this study represents the first attempt to characterize the in vivo effects of hypoxia on an AML mouse model. Additional investigations may uncover ways to mimic the differentiative effects of hypoxia in a manner that will benefit human patients with AML.

Anticancer metal compounds in NCI's tumor-screening database: putative mode of action

Clustering analysis of tumor cell cytotoxicity profiles for the National Cancer Institute (NCI)'s open compound repository has been used to catalog over 1100 metal or metalloid containing compounds with potential anticancer activity. The molecular features and corresponding reactivity of these compounds have been analyzed in terms of properties of their metals, their associated organic components (ligands) and their capacity to inhibit tumor cell growth. Cytotoxic responses are influenced by both the identity of the metal and the properties of its coordination ligand, with clear associations between structural similarities and cytotoxicity. Assignments of mechanisms of action (MOAs) for these compounds could be segregated into four broad response classes according to preference for binding to biological sulfhydryl groups, chelation, generation of reactive oxygen species (ROS), and production of lipophilic ions. Correlations between specific cytotoxic responses and differential gene expression profiles within the NCI's tumor cell panel serve as a validation for candidate biological targets and putative MOA classes. In addition, specific sensitivity toward subsets of metal containing agents has been found for certain tumor cell panels. Taken together, our results expand the knowledge base available for evaluating, designing and developing new metal-based anticancer drugs that may provide the basis for target-specific therapeutics.

Pharmacological activity of DTPA linked to protein-based drug carrier systems

The chelating agent diethylenetriaminepentaacetic acid (DTPA) inhibits human cytomegalovirus replication. Since chelating agents are known to exhibit anti-cancer effects, DTPA-induced cytotoxicity was evaluated in breast cancer cells (MCF-7) and neuroblastoma cells (UKF-NB-3). DTPA inhibited cancer cell growth in threefold lower concentrations compared to human foreskin fibroblasts (HFF). Antiviral and anti-cancer activity of chelating agents is caused by intracellular complexation of metal ions. DTPA, an extracellular chelator, was covalently coupled to human serum albumin (HSA) molecules, HSA nanoparticles (HSA-NP), gelatin type B (GelB) molecules, and GelB nanoparticles (GelB-NP) to increase cellular uptake. Coupling of DTPA to drug carrier systems increased its cytotoxic and antiviral activity by 5- to 8-fold. Confocal laser scanning microscope examination revealed uptake of DTPA-HSA-NP in UKF-NB-3 cells and HFF. Therefore, coupling of DTPA to protein-based drug carrier systems increases its antiviral and anti-cancer activity probably by mediating cellular uptake.