25 research outputs found

    Synthesis and biological evaluation of metal chelators of the hydroxypyridinone family as potential treatment of Parkinson’s disease and cancer

    Get PDF
    A series of 9 hydroxypyridinones (HOPO) metal-based iron chelators (from which 6 of them are novel) have been prepared, characterised and derivatized in a manner to exploit an active transport mechanism; Large neutral Amino Acid Transporter-1 (LAT-1), which is found to be overexpressed in various types of cancer as well as to be presented in the blood-brain barrier (BBB) (Figure i). Figure (i): Structure of HOPO based compounds synthesised. Novel compounds are in the dotted frames. Additionally, it appears that the involvement of iron into metabolic pathways and/or the formation of low levels of reactive oxygen species (ROS) enhances the survival and proliferation of various types of cancer including malignant melanoma. The anticancer capacity of the series of HOPO based metal chelators, have been evaluated in an in vitro model ii consisting of human (eg. A375, VVM1, HS-294T) and rodent (eg. B16F-10) melanoma cells as well as non-melanoma epidermoid carcinoma (eg. A431) and immortalized, non-malignant keratinocyte (eg. HaCaT) cells. The results of this study demonstrated that a single compound a methylated analogue of L-mimosine, can exert anticancer capacity as at the administered concentration it acts as a pro-oxidant triggering the production of high (toxic) levels of ROS, selectively in melanoma cell lines. The accumulation of ROS, drives the cells to apoptosis via activation of a well characterised downstream cascade that includes that activation of the terminal caspase 3/7 via the action of intrinsic (activation of caspase-9 pathway) and extrinsic (activation of caspase-8 pathway). Additionally, the excessive production of oxidative cellular stress and iron misregulation may be substantially involved in the dopaminergic neuron degeneration seen in the brains of Parkinson's disease (PD) patients. Here we evaluated the effectiveness of the synthesised iron chelators, based on the hydroxypyridinone core with the ability to cross the BBB and penetrate the brain. Immortalised human dopaminergic neuronal precursor cells (LUHMES) were treated with the PD-related toxins 6-hydroxydopamine (6-OHDA), which generates superoxide radicals, 1-methyl-4-phenylpyridinium (MPP+), a mitochondrial complex I inhibitor, and the ferroptosis activator, erastin. Extensive cytotoxicological profiling revealed that three (rac-SK-2, rac-SK-3 and L-SK-4) out of the five tested compounds (rac-SK-1, rac-SK-2, rac-SK-3, L-SK-4 and rac-SK-5) rescue dopaminergic neuronal cells without inducing any toxic effects to cells, revealed through multiple cytotoxicological assays. In order to validate which structural features were essential for the transportation and the action of the compound, a series of control compounds (which they were lacking either the amino acid moiety or the coordination unit) have also been designed and screened against both melanoma cancer as well as PD cell lines. These control compounds of the associated molecules supported the rational design behind them according to which, the HOPO core is essential for the metal binding and the amino acid side vector for the transportation across the biological membranes via LAT-1

    The use of alginates and polyphenols in medicinal iron chelation for the improvement of colonic health

    Get PDF
    Iron is central to the aetiology of gastrointestinal disease. Specifically, the toxic effects of excess, unabsorbed "luminal" iron ingested from the diet has been shown to be important in the development of inflammatory bowel disease and intestinal cancer. A platform for therapeutic intervention is likely to involve chelation of this luminal pool of iron. As such, a range of dietary iron chelators have been tested for their iron binding capacity. Natural biopolymers extracted from seaweed (alginates) and a variety of natural polyphenolic compounds were stratified in terms of their iron binding potential. One alginate, Manucol LD, was unique in its iron binding and demonstrated luminal iron chelation properties. With respect to the polyphenols, only one of the tested compounds (quercetin) displayed iron chelation activity in vitro and was able to suppress cellular concentrations of reactive oxygen species acting as an antioxidant. As such, it has been demonstrated that a unique alginate, Manucol LD, is an excellent candidate for sequestering luminal iron present in the gastrointestinal tract. These results underpin the rationale in utilising these types of natural and safe bio-polymers for the prevention and treatment of gastrointestinal disease

    Integrate approach to the study of chelating agents for the effects of toxic metal ions

    Get PDF
    Metals are an integral part of many structural and functional components in the body, and the interest on their role in physiological processes, environment and medicine is increasing. Many metal complex are used as metal drugs such as cis-platin for cancer treatment, paramagnetic metal complex as contrast agents for magnetic resonance imaging (MRI); many metal are toxic and metal toxicity may occur due to essential metal overload or exposure to heavy metals from various sources interfering with functions of various organ systems like the central nervous system (CNS), the haematopoietic system, liver, kidneys, etc. New therapeutic strategies, such as chelation therapy, have been developed based on restoring the normal healthy physiology of the body either by direct administration of essential metals, or by chelating out excess or toxic metals, or using them as carriers for targeted drug delivery, or for tagging biomolecules for diagnostics. Thermodynamic studies in the characterization of ligands of biomedical interest are crucial in the design of a new drugs. This thesis is focused on the studies of new molecules that have long been recognized as privileged chelating structures for the design of metal chelating drugs, especially towards hard metal ions, in view of their involvement in metal overload disorders. The approach has been multi-variated, from the chemistry to the biochemistry and biology, which has been possible due to the time spent in others research groups and to the other ones that used to collaborate with us. Because of my stay (research master thesis) in organic chemistry group at Instituto Superior Tecnico of Lisbon guided by Prof. M. Amelia Santos, three hydroxypyridinones ligands have been synthetized, whose biodistribution studies performed at Centro de Ciencias e Tecnologias Nucleares (C2TN) of Lisbon as well. In the Research Group of Chemistry and Stereochemistry of Peptides and Protein headed by Prof. Zbigniew Szewczuk at the University of Wroclaw new strategies of synthesis have been developed involving mimosine peptides derivatives. As opposite to hydroxypyridinones, whose solution equilibria studies have been possible, peptides have been mainly characterized by DFT and biological ones in collaboration with the University of San Sebastian and Cagliari. In the end, three months of my last year of PhD have been spent in the Medicinal Inorganic Chemistry group at the University of British Columbia (Vancouver) under supervision of Prof. Chris Orvig working on solution studies of radiometal complexes of bisphosphonate-picolinic acid derivatives. It needs to be tightened up with regard to PhD that it has industrial characterization under that a collaboration with industry is scheduled. At Innovative Materials I could learn about biology field and how to work with cells, particularly our idea was to test hydroxypyrones ligands on proliferation and differentiation of stamina cells. The study is still uncompleted and results about are not shown in the following chapters This thesis is divided in three chapters: • Chapter 1 – An overview of chelation It describes general aspects of chelation therapy, the rule of metal ions in human body and in human diseases. • Chapter 2 – Ligands It describes structural and chemical properties of a families of ligands studied and shows NTA(PrHP)3, KC18, KC21, SC and six mimosine-peptides derivatives under focus of this thesis. • Chapter 3 – Experimental methods It describes experimental procedures and techniques applied for thesis’s studies

    Design, synthesis and characterization of new iron and aluminium chelating agents

    Get PDF
    Chelation therapy is widely used for metal-unbalance related diseases, namely those due to disorders on metal metabolism, such as beta-thalassemia, hemochromatosis (Fe), and neurodegenerative diseases (Cu, Fe, Zn and Al). The study of metal chelators for clinical applications, either as chelating therapeutics able to target specific metal ions in the body, or as metal-carriers for therapeutic or imaging purposes, is a topical research area which faces up to urgent medical problems. Metal-chelating drugs are used in many ways for the prevention, diagnosis and treatment of cancer, since cancer cells, like normal cells, require essential metal ions such as iron, copper and zinc for growth and proliferation. Chelators can target the metabolic pathways of cancer cells through the control of proteins involved in the regulation of these metals and also of other molecules involved in cell cycle control, angiogenesis and metastatic suppression. The thermodynamic aspects regarding the complexation of metal ions of medical interest are of primary importance for a correct understanding of the role of metals in human diseases in order to rationalize the design of new molecules for diagnostic and therapeutic purposes. A typical case is the treatment of metal overload diseases where the highest thermodynamic stability and largest selectivity of the complexes are crucial factors in the ligand design. This thesis is focused on the development and study of new compounds which, as a result of their strong interaction with specific metal ions, can be potentially used as pharmaceutical drugs for diagnosis or therapy. The work was performed with a multidisciplinary approach regarding mostly chemistry, but including also biochemistry and biology. The work presented in this thesis is devoted to reach the following aims: Design and synthesis of new multivalent ligands in order to enhance the efficiency and selectivity of both metal-interaction and biomolecular recognition of available ligands (or metal complexes), as well as the targeting for drug delivery; Assessment of the most important physical and chemical properties of metal related compounds, namely metal-chelating efficacy and selectivity (thermodynamic and kinetic) with respect to other biometals or biological molecules, mostly in solution but also in silico; Bioevoluation, in vitro and in vivo, for the most promising compounds. This thesis is divided in two chapters. Chapter I is dedicated to a description of Chelation Therapy for treating metal intoxication in humans. The importance of chelating agents in neurodegenerative diseases like Alzheimer disease, is introduced. The main aspects of Fe, Al, and Cu metabolism in humans are presented. The papers I, II, III and IV relative to this chapter has been appended. Chapter II describes the synthesis of the new studied ligands, and the experimental methods and techniques that were used for the investigation of the ligands and of their complexes with a number of metal ions. Important features of the used techniques are briefly described including basic principles, advantages and limitations. The papers V, VI, and VII explain in detail the developed work. The main conclusions of this work are: A new family of hydroxypyrone ligands (L4, L5, L6, L7, L8, and L9) has been synthesized and fully characterized. These ligands are easy and cheap to produce; Complex formation equilibria showed good efficiency and selectivity for iron and aluminium. With Fe3+ various protonated 2:3 Fe:L species have been detected (with exception for L7). Experimental data give evidence of a strong chelating ability for L8 and, in order of decreasing ability, for ligands L5 > L4 > L9 = L6 > L7. Al3+ also forms 2:3 Al:L complexes with the ligands L4, L5, L6, and L9. The ligand with a shorter linker, L8, forms the most stable complexes of stoichiometry 2:2 (Al:L). Also Al3+ forms with L8 the strongest complexes, and in order of decreasing stabilities with the ligands L6 > L5 > L4 > L9 > L7. Studies in mice confirmed the high in vivo metal scavenging ability of the tetradentate ligands (L4, L5, L6, L8, and L9) in comparison with the corresponding bidentate (L7). The excellent chelating properties recommend further toxicological and pharmacological research on these new promising ligands

    Siderophore-Dependent Transport Paradigms for Iron Across the Bacterial Cell Envelope in the Human Pathogen Staphylococcus aureus

    Get PDF
    This work is focused on iron trafficking through ABC transporters in Staphylococcus aureus and combatting the growing antimicrobial resistance crisis by exploiting virulence factors as therapeutic targets. Specifically, the goal was to understand the role of a siderophore-binding lipoprotein FhuD2 in S. aureus iron trafficking. While S. aureus endogenously produces three metallophores for metal sequestration from the host, FhuD2 is thought to scavenge metals from hydroxamate-based xenosiderophores encountered in the host environment. FhuD2 is a critical virulence factor and vaccine candidate (Novartis) for MRSA. Since xenosiderophore scavenging systems are often dispensable, it was hypothesized that FhuD2 must be playing another role to enhance pathogen virulence. Through careful investigations using a fluorescent siderophore probe, this work has revealed a new role for FhuD2 in the S. aureus iron trafficking pathway. FhuD2 does tightly bind hydroxamate xenosiderophores, but it does not immediately use the siderophore as a transport substrate. Instead, the siderophore serves as a cofactor for a newly proposed enzymatic function of FhuD2 in iron trafficking from human holo-transferrin. Using a “turn-off” fluorescent siderophore probe it was shown that the FhuD2 apo-siderophore complex is capable of catalyzing iron extraction from transferrin. The interaction of FhuD2 with transferrin better explains its role as a virulence factor and establishes a new paradigm for iron trafficking in bacteria with broad relevance. This same phenomenon was confirmed another human pathogen, Bacillus subtilis. Structure-activity relationship analysis of siderophores governing cell entry revealed a charge-based preference for whole cell uptake in S. aureus

    Siderophore-Dependent Transport Paradigms for Iron Across the Bacterial Cell Envelope in the Human Pathogen Staphylococcus aureus

    Get PDF
    This work is focused on iron trafficking through ABC transporters in Staphylococcus aureus and combatting the growing antimicrobial resistance crisis by exploiting virulence factors as therapeutic targets. Specifically, the goal was to understand the role of a siderophore-binding lipoprotein FhuD2 in S. aureus iron trafficking. While S. aureus endogenously produces three metallophores for metal sequestration from the host, FhuD2 is thought to scavenge metals from hydroxamate-based xenosiderophores encountered in the host environment. FhuD2 is a critical virulence factor and vaccine candidate (Novartis) for MRSA. Since xenosiderophore scavenging systems are often dispensable, it was hypothesized that FhuD2 must be playing another role to enhance pathogen virulence. Through careful investigations using a fluorescent siderophore probe, this work has revealed a new role for FhuD2 in the S. aureus iron trafficking pathway. FhuD2 does tightly bind hydroxamate xenosiderophores, but it does not immediately use the siderophore as a transport substrate. Instead, the siderophore serves as a cofactor for a newly proposed enzymatic function of FhuD2 in iron trafficking from human holo-transferrin. Using a “turn-off” fluorescent siderophore probe it was shown that the FhuD2 apo-siderophore complex is capable of catalyzing iron extraction from transferrin. The interaction of FhuD2 with transferrin better explains its role as a virulence factor and establishes a new paradigm for iron trafficking in bacteria with broad relevance. This same phenomenon was confirmed another human pathogen, Bacillus subtilis. Structure-activity relationship analysis of siderophores governing cell entry revealed a charge-based preference for whole cell uptake in S. aureus

    Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases

    Get PDF
    The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular "reactive oxygen species" (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation. We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation). The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible. This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference

    Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson’s, Huntington’s, Alzheimer’s, prions, bactericides, chemical toxicology and others as examples

    Get PDF
    Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions
    corecore