Chromone-deferiprone hybrids as novel MAO-B inhibitors and iron chelators for the treatment of Alzheimer's disease.

A series of chromone-deferiprone hybrids were designed, synthesized, and evaluated as inhibitors of human monoamine oxidase B (hMAO-B) with iron-chelating activity for the treatment of Alzheimer's disease (AD). The majority exhibited moderate inhibitory activity towards hMAO-B and potent iron-chelating properties. Particularly, compound 25c demonstrated remarkable selectivity against hMAO-B with an IC50 value of 1.58 µM and potent iron-chelating ability (pFe3+ = 18.79) comparable to that of deferiprone (pFe3+ = 17.90). Molecular modeling and kinetic studies showed that 25c functions as a non-competitive hMAO-B inhibitor. According to the predicted results, compound 25c can penetrate the blood-brain barrier (BBB). Additionally, it has been proved to display significant antioxidant activity and the ability to inhibit neuronal ferroptosis. More importantly, compound 25c reduced the cognitive impairment induced by scopolamine and showed significant non-toxicity in short-term toxicity assays. In summary, compound 25c was identified as a potential anti-AD agent with hMAO-B inhibitory, iron-chelating and anti-ferroptosis activities.

Rigid Fe(III) Chelate with Phosphonate Pendants: A Stable and Effective Extracellular MRI Contrast Agent.

A novel Fe(III) complex, Fe-tBPCDTA, was synthesized and explored as a potential contrast agent for MRI. Compared to established agents like Fe-EDTA and Fe-tCDTA, Fe-tBPCDTA exhibited moderate relaxivity (r1 = 1.17 s-1·mmol-1) due to its enhanced second-sphere mechanism. It also displayed improved kinetic inertness, lower cytotoxicity, and enhanced redox stability. In vivo studies demonstrated its function as an extracellular fluid agent, providing tumor contrast comparable to that of Gd-DTPA at a higher dosage. Complete renal clearance occurred within 24 h. These findings suggest Fe-tBPCDTA as a promising candidate for further development as a safe and effective extracellular MRI contrast agent.

N-Propargylamine-hydroxypyridinone hybrids as multitarget agents for the treatment of Alzheimer's disease.

AD is a progressive brain disorder. Because of the lack of remarkable single-target drugs against neurodegenerative disorders, the multitarget-directed ligand strategy has received attention as a promising therapeutic approach. Herein, we rationally designed twenty-nine hybrids of N-propargylamine-hydroxypyridinone. The designed hybrids possessed excellent iron-chelating activity (pFe3+ = 17.09-22.02) and potent monoamine oxidase B inhibitory effects. Various biological evaluations of the optimal compound 6b were performed step by step, including inhibition screening of monoamine oxidase (hMAO-B IC50 = 0.083 ± 0.001 µM, hMAO-A IC50 = 6.11 ± 0.08 µM; SI = 73.5), prediction of blood-brain barrier permeability and mouse behavioral research. All of these favorable results proved that the N-propargylamine-hydroxypyridinone scaffold is a promising structure for the discovery of multitargeted ligands for AD therapy.

Design and synthesis of N-hydroxyalkyl substituted deferiprone: a kind of iron chelating agents for Parkinson's disease chelation therapy strategy.

The blood-brain barrier (BBB) permeability of molecules needs to meet stringent requirements of Lipinski's rule, which pose a difficulty for the rational design of efficient chelating agents for Parkinson's disease chelation therapy. Therefore, the iron chelators employed N-aliphatic alcohols modification of deferiprone were reasonably designed in this work. The chelators not only meet Lipinski's rule for BBB permeability, but also ensure the iron affinity. The results of solution thermodynamics demonstrated that the pFe3+ value of N-hydroxyalkyl substituted deferiprone is between 19.20 and 19.36, which is comparable to that of clinical deferiprone. The results of 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays indicated that the N-hydroxyalkyl substituted deferiprone also possesses similar radical scavenging ability in comparison to deferiprone. Meanwhile, the Cell Counting Kit-8 assays of neuron-like rat pheochromocytoma cell-line demonstrated that the N-hydroxyalkyl substituted deferiprone exhibits extremely low cytotoxicity and excellent H2O2-induced oxidative stress protection effect. These results indicated that N-hydroxyalkyl substituted deferiprone has potential application prospects as chelating agents for Parkinson's disease chelation therapy strategy.

Conjugates of desferrioxamine and aromatic amines improve markers of iron-dependent neurotoxicity.

Alzheimer's Disease (AD) is a complex neurodegenerative disorder associated in some instances with dyshomeostasis of redox-active metal ions, such as copper and iron. In this work, we investigated whether the conjugation of various aromatic amines would improve the pharmacological efficacy of the iron chelator desferrioxamine (DFO). Conjugates of DFO with aniline (DFOANI), benzosulfanylamide (DFOBAN), 2-naphthalenamine (DFONAF) and 6-quinolinamine (DFOQUN) were obtained and their properties examined. DFOQUN had good chelating activity, promoted a significant increase in the inhibition of ß-amyloid peptide aggregation when compared to DFO, and also inhibited acetylcholinesterase (AChE) activity both in vitro and in vivo (Caenorhabditis elegans). These data indicate that the covalent conjugation of a strong iron chelator to an AChE inhibitor offers a powerful approach for the amelioration of iron-induced neurotoxicity symptoms.

Fabrication of deferasirox-decorated aptamer-targeted superparamagnetic iron oxide nanoparticles (SPION) as a therapeutic and magnetic resonance imaging agent in cancer therapy.

In the current study, the synthesis of a theranostic platform composed of superparamagnetic iron oxide nanoparticles (SPION)-deferasirox conjugates targeted with AS1411 DNA aptamer was reported. In this regard, SPION was amine-functionalized by (3-aminopropyl)trimethoxysilane (ATPMS), and then deferasirox was covalently conjugated onto its surface. Finally, to provide guided drug delivery to cancerous tissue, AS1411 aptamer was conjugated to the complex of SPION-deferasirox. The cellular toxicity assay on CHO, C-26 and AGS cell lines verified higher cellular toxicity of targeted complex in comparison with non-targeted one. The evaluation of in vivo tumor growth inhibitory effect in C26 tumor-bearing mice illustrated that the aptamer-targeted complex significantly enhanced the therapeutic outcome in comparison with both non-targeted complex and free drug. The diagnostic capability of the prepared platform was also evaluated implementing C26-tumor-bearing mice. Obtained data confirmed higher tumor accumulation and higher tumor residence time for targeted complex through MRI imaging due to the existence of SPION as a contrast agent in the core of the prepared complex. The prepared multimodal theranostic system provides a safe and effective platform for fighting against cancer.

Design, synthesis and biological evaluation of potential anti-AD hybrids with monoamine oxidase B inhibitory and iron-chelating effects.

A series of active hybrids combining 3-hydroxypyridin-4(1H)-one and coumarin pharmacophores were designed and synthesized as potential agents for the treatment of Alzheimer's disease (AD). All the compounds exhibited excellent iron-chelating activities (pFe3+ = 14.8-19.2) and showed favorable monoamine oxidase B (MAO-B) inhibitory effects compared to the reference drug Pargyline (IC50 = 86.9 nM). Among them, compound 11 g displayed the best MAO-B inhibitory activity with an IC50 value of 99.3 nM. Molecular docking analysis showed that compound 11 g could enter the entrance cavity and substrate cavity of MAO-B. Furthermore, the compound 11 g had an excellent antioxidant effect and was capable of protecting from the amyloid-ß1-42 (Aß1-42) induced PC12 cell damage. In silico tools were applied for predicting the blood-brain barrier (BBB) penetration and compound 11 g was proved to overcome the brain exposure challenge. In the mice behavioral study, compound 11 g significantly ameliorated cognitive impairment induced by Scopolamine. More importantly, compound 11 g displayed favorable pharmacokinetic profiles in a rat model. In summary, compound 11 g, with both anti-MAO-B and iron-chelating ability, was proved to be a promising potential anti-AD agent for further optimization.

Solid-Phase Synthesis and In-Silico Analysis of Iron-Binding Catecholato Chelators.

Siderophores are iron-complexing compounds synthesized by bacteria and fungi. They are low molecular weight compounds (500-1500 Daltons) possessing high affinity for iron(III). Since 1970 a large number of siderophores have been characterized, the majority using hydroxamate or catecholate as functional groups. The biosynthesis of siderophores is typically regulated by the iron levels of the environment where the organism is located. Because of their exclusive affinity and specificity for iron(III), natural siderophores and their synthetic derivatives have been exploited in the treatment of human iron-overload diseases, as both diagnostic and therapeutic agents. Here, solid-phase approach for the preparation of hexadentate, peptide-based tricatecholato containing peptides is described. The versatility of the synthetic method allows for the design of a common scaffolding structure whereby diverse ligands can be conjugated. With so many possibilities, a computational approach has been developed which will facilitate the identification of those peptides which are capable of providing a high affinity iron(III) binding site. This study reports an integrated computational/synthetic approach towards a rational development of peptide-based siderophores.

High throughput fluorimetric assessment of iron traffic and chelation in iron-overloaded Caenorhabditis elegans.

The nematode Caenorhabditis elegans (C. elegans) is a convenient tool to evaluate iron metabolism as it shares great orthology with human proteins involved in iron transport, in addition to being transparent and readily available. In this work, we describe how wild-type (N2) C. elegans nematodes in the first larval stage can be loaded with acetomethoxycalcein (CAL-AM) and study it as a whole-organism model for both iron speciation and chelator permeability of the labile iron pool (LIP). This model may be relevant for high throughput assessment of molecules intended for chelation therapy of iron overload diseases.

Polyglycerol-Based Macromolecular Iron Chelator Adjuvants for Antibiotics To Treat Drug-Resistant Bacteria.

Iron is an essential micronutrient for life. Its redox activity is a key component in a plethora of vital enzymatic reactions that take place in processes such as drug metabolism, DNA synthesis, steroid synthesis, gene regulation, and cellular respiration (oxygen transport and the electron transport chain). Bacteria are highly dependent on iron for their survival and growth and have specific mechanisms to acquire iron. Limiting the availability of iron to bacteria, thereby preventing their growth, provides new opportunities to treat infection in the era of the persistent rise of antibiotic-resistant bacteria. In this work, we have developed macromolecular iron chelators, conjugates of a high-affinity iron chelator (HBEDS) with polyglycerol, in an attempt to sequester iron uptake by bacteria to limit their growth in order to enhance antibiotic activity. The new macromolecular chelators are successful in slowing the growth of Staphylococcus aureus and worked as an efficient bacteriostatic against S. aureus. Further, these cytocompatible macrochelators acted as effective adjuvants to prevent bacterial growth when used in conjunction with antibiotics. The adjuvant activity of the macrochelators depends on their molecular weight and the chelator density on these molecules. These selective macro iron(III) chelators are highly efficient in growth inhibition and killing of methicillin-resistant S. aureus in conjunction with a low concentration of rifampicin.

Rational design, synthesis and biological evaluation of novel multitargeting anti-AD iron chelators with potent MAO-B inhibitory and antioxidant activity.

A series of (3-hydroxypyridin-4-one)-coumarin hybrids were developed and investigated as potential multitargeting candidates for the treatment of Alzheimer's disease (AD) through the incorporation of iron-chelating and monoamine oxidase B (MAO-B) inhibition. This combination endowed the hybrids with good capacity to inhibit MAO-B as well as excellent iron-chelating effects. The pFe3+ values of the compounds were ranging from 16.91 to 20.16, comparable to more potent than the reference drug deferiprone (DFP). Among them, compound 18d exhibited the most promising activity against MAO-B, with an IC50 value of 87.9 nM. Moreover, compound 18d exerted favorable antioxidant activity, significantly reversed the amyloid-ß1-42 (Aß1-42) induced PC12 cell damage. More importantly, 18d remarkably ameliorated the cognitive dysfunction in a scopolamine-induced mice AD model. In brief, a series of hybrids with potential anti-AD effect were successfully obtained, indicating that the design of iron chelators with MAO-B inhibitory and antioxidant activities is an attractive strategy against AD progression.

New deferiprone derivatives as multi-functional cholinesterase inhibitors: design, synthesis and in vitro evaluation.

In order to obtain multi-functional molecules for Alzheimer's disease, a series of deferiprone derivatives has been synthesized and evaluated in vitro with the hypothesis that they can restore the cholinergic tone and attenuate the dyshomeostasis of the metals mainly involved in the pathology. These compounds were designed as dual binding site AChE inhibitors: they possess an arylalkylamine moiety connected via an alkyl chain to a 3-hydroxy-4-pyridone fragment, to allow the simultaneous interaction with catalytic active site (CAS) and peripheral anionic site (PAS) of the enzyme. Deferiprone moiety and 2-aminopyridine, 2-aminopyrimidine or 2,4-diaminopyrimidine groups have been incorporated into these compounds, in order to obtain molecules potentially able to chelate bio-metals colocalized in Aß plaques and involved in the generation of radical species. Synthesized compounds were tested by enzymatic inhibition studies towards EeAChE and eqBChE using Ellman's method. The most potent EeAChE inhibitor is compound 5a, with a Ki of 788 ± 51 nM, while the most potent eqBChE inhibitors are compounds 12 and 19, with Ki values of 182 ± 18 nM and 258 ± 25 nM respectively. Selected compounds, among the most potent cholinesterases inhibitors, were able to form complex with iron and in some cases with copper and zinc. Moreover, these compounds were characterized by low toxicity on U-87 MG Cell Line from human brain (glioblastoma astrocytoma).

The influence of linkages between 1-hydroxy-2(1H)-pyridinone coordinating groups and a tris(2-aminoethyl)amine core in a novel series of synthetic hexadentate iron(III) chelators on antimicrobial activity.

Resistance of pathogens to antimicrobials is a major current healthcare concern. In a series of linked studies, we have investigated synthetic iron chelators based on hydroxy-pyridinone ligands as novel bacteriostatic agents. Herein we describe our synthesis of several useful building blocks based on the 1-hydroxy-2(1H)-pyridinone moiety, including a novel formyl derivative, which were combined with a tris(2-aminoethyl)amine core to obtain a series of new high-affinity hexadentate Fe(III) chelators. The design principle examined by this series is the size and flexibility of the linker between the core and the metal ligands. Measurement of the pKa and stability constants (Fe3+ and Cu2+) of representative coordinating groups was performed to help rationalise the biological activity of the chelators. The novel chelators were tested on a panel of representative microorganisms with some effectively inhibiting microbial growth. We demonstrate that the nature and position of the linker between the hydroxypyridinone and the tris(2-aminoethyl)amine core has considerable impact upon microbial growth inhibition and that both amide or amine linkages can give efficacious chelators.

Dual-target anti-Alzheimer's disease agents with both iron ion chelating and monoamine oxidase-B inhibitory activity.

MAO-B leads to an increase in the levels of hydrogen peroxide and oxidative free radicals, which contribute to the aetiology of the AD. Thus, both iron ion chelators and MAO-B inhibitors can be used to treat AD. Taking the coumarin derivatives and hydroxypyridinones as the lead compounds, a series of dual-target hybrids were designed and synthesised by Click Chemistry. The compounds were biologically evaluated for their iron ion chelating and MAO-B inhibitory activity. Most of the compounds displayed excellent iron ion chelating activity and moderate to good anti-MAO-B activity. Compounds 27b and 27j exhibited the most potent MAO-B inhibitory activity, with IC50 values of 0.68 and 0.86 µM, respectively. In summary, these dual-target compounds have the potential anti-AD activity.

Design, synthesis and biological evaluation of hydroxypyridinone-coumarin hybrids as multimodal monoamine oxidase B inhibitors and iron chelates against Alzheimer's disease.

A series of hybrids of hydroxypyridinone and coumarin were rationally designed, synthesized and biologically evaluated for their iron ion chelating and MAO-B inhibitory activities. Most of the compounds displayed excellent iron ion chelating effects and moderate to good anti-MAO-B activities. Compound 27a exhibited the most potent activity against MAO-B, with an IC50 value of 14.7 nM. Importantly, 27a showed good U251 cell protective effect and significantly ameliorated the cognitive dysfunction of scopolamine-induced AD mice. Moreover, molecular docking was performed to elucidate the probable ligand-receptor interaction, and the structure-activity relationships were also summarized.

Synthesis and Study of Multifunctional Cyclodextrin-Deferasirox Hybrids.

Metal dyshomeostasis is central to a number of disorders that result from, inter alia, oxidative stress, protein misfolding, and cholesterol dyshomeostasis. In this respect, metal deficiencies are usually readily corrected by treatment with supplements, whereas metal overload can be overcome by the use of metal-selective chelation therapy. Deferasirox, 4-[(3Z,5E)-3,5-bis(6-oxo-1-cyclohexa-2,4-dienylidene)-1,2,4-triazolidin-1-yl]benzoic acid, Exjade, or ICL670, is used clinically to treat hemosiderosis (iron overload), which often results from multiple blood transfusions. Cyclodextrins are cyclic glucose units that are extensively used in the pharmaceutical industry as formulating agents as well as for encapsulating hydrophobic molecules such as in the treatment of Niemann-Pick type C or for hypervitaminosis. We conjugated deferasirox, via an amide coupling reaction, to both 6A -amino-6A -deoxy-ß-cyclodextrin and 3A -amino-3A -deoxy-2A (S),3A (S)-ß-cyclodextrin, at the upper and lower rim, respectively, creating hybrid molecules with dual properties, capable of both metal chelation and cholesterol encapsulation. Our findings emphasize the importance of the conjugation of ß-cyclodextrin with deferasirox to significantly improve the biological properties and to decrease the cytotoxicity of this drug.

Total Synthesis of Hinduchelins A-D, Stereochemical Revision of Hinduchelin A, and Biological Evaluation of Natural and Unnatural Analogues.

Here, we report the first total synthesis of hinduchelins A-D, a family of nontoxic catechol derivatives from Streptoalloteichus hindustanus, possessing a druglike chemotype and modest iron-chelating ability. A concise synthesis was developed employing methyl 5-methyloxazole-4-carboxylate as a single starting material to provide hinduchelins A-D (and unnatural analogues) in only four steps and 5-15% overall yields; moreover, the stereochemistry of hinduchelin A was reassigned from ( S) to ( R). Biological evaluation confirmed that natural and unnatural hinduchelins are weak iron chelators (siderophores).

Hydrazones as novel epigenetic modulators: Correlation between TET 1 protein inhibition activity and their iron(II) binding ability.

Ten-eleven translocation protein (TET) 1 plays a key role in control of DNA demethylation and thereby of gene expression. Dysregulation of these processes leads to serious pathological states such as oncological and neurodegenerative ones and thus TET 1 targeting is highly requested. Therefore, in this work, we examined the ability of hydrazones (acyl-, aroyl- and heterocyclic hydrazones) to inhibit the TET 1 protein and its mechanism of action. Inhibitory activity of hydrazones 1-7 towards TET 1 was measured. The results showed a high affinity of the tested chelators for iron(II). The study clearly showed a significant correlation between the chelator's affinity for iron(II) ions (represented by the binding constant) and TET 1 protein inhibitory activity (represented by IC50 values).

A new tripodal kojic acid derivative for iron sequestration: Synthesis, protonation, complex formation studies with Fe3+, Al3+, Cu2+ and Zn2+, and in vivo bioassays.

This work presents the simple and low cost synthesis of a new tripodal ligand, in which three units of kojic acid are coupled to a tris(2-aminoethyl)amine (tren) backbone molecule. The protonation equilibria, together with the complex formation equilibria of this ligand with Fe3+, Al3+, Cu2+ and Zn2+ ions were studied. The complementary use of potentiometric, spectrophotometric and NMR techniques, and of Density Functional Theory (DFT) calculations, has allowed a thorough characterization of the different species involved in equilibrium. The stability of the formed complexes with Fe3+ and Al3+ are high enough to consider the new ligand for further studies for its clinical applications as a chelating agent. Biodistribution studies were carried out to assess the capacity the ligand for mobilization of gallium in 67Ga-citrate injected mice. These studies demonstrated that this ligand efficiently chelates the radiometal in our animal model, which suggests that it can be a promising candidate as sequestering agent of iron and other hard trivalent metal ions. Furthermore, the good zinc complexation capacity appears as a stimulating result taking into a potential use of this new ligand in analytical chemistry as well as in agricultural and environmental applications.

Synthesis, anticancer activity and mechanism of iron chelator derived from 2,6-diacetylpyridine bis(acylhydrazones).

We synthesized five iron chelator derived from 2,6-diacetylpyridine bis(acylhydrazones) and proved their iron complexes structure by X-ray single crystal diffraction. These ligands have a significant anticancer proliferative activity and low cytotoxicity against normal cells. The Fe(III) complexes show reduced cytotoxic activity compared to the metal-free ligands. Anticancer mechanism studies indicate that ligands with a potential anticancer proliferation activity by inhibiting the activity of ribonucleotide reductase. Ligand rather than iron complexes regulate the expression of cell cycle associated proteins and inhibit cell cycle arrest in S phase. Apoptosis mechanism results showed that both ligand and iron complexes did not significantly promote apoptosis.