Desferrioxamine-caffeine (DFCAF) as a cell permeant moderator of the oxidative stress caused by iron overload

New C8-substituted caffeine derivatives as promising antioxidants and cytoprotective agents in human erythrocytes

New structurally diverse groups of C8-substituted caffeine derivatives were synthesized and evaluated for their chemical and biological properties. Mass spectrometry, FT-IR, and NMR characterizations of these derivatives were performed. The cytotoxic activity of the derivatives was estimated in vitro using human red blood cells (RBC) and in silico pharmacokinetic studies. The antioxidant capacity of the compounds was analyzed using a ferrous ion chelating activity assay. The ability of the derivatives to protect RBC from oxidative damage, including the oxidation of hemoglobin to methemoglobin, was assessed using a water-soluble 2,2'-azobis(2-methyl-propionamidine) dihydrochloride (AAPH) as a standard inducer of peroxyl radicals. The level of intracellular oxidative stress was assessed using the fluorescent redox probe 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA). The results indicate that all derivatives are biocompatible compounds with significant antioxidant and cytoprotective potential dependent on their chemical structure. In order to explain the antioxidant and cytoprotective activity of the derivatives, a mechanism of hydrogen atom transfer (HAT), radical adduct formation (RAF), or single electron transfer (SET), as well as the specific interactions of the derivatives with the lipid bilayer of RBC membrane, have been proposed. The results show that selected modifications of the caffeine molecule enhance its antioxidant properties, which expands our knowledge of the structure-activity relationship of caffeine-based cytoprotective compounds.

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 β-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.

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.

Chromium removal from aqueous solutions using new silica gel conjugates of desferrioxamine or diethylenetriaminepentaacetic acid

Desferrioxamine (DFO) and diethylenetriaminepentaacetic acid (DTPA) conjugated with silica gel (IDFOSG and IDTPASG, respectively) were evaluated as adsorbents for chromium in aqueous solutions. Different parameters affecting adsorption such as pH, sorbent dosage, contact time, sample volume and potential of interfering ions have been optimized. The optimum pH for chromium binding was 4 for 100 mg of adsorbents at 5 min of table shaking with 5 mL sample volume of chromium solutions. Langmuir adsorption model described the removal of chromium ions. The adsorption capacity for chromium was 90% for IDFOSG and 83% for IDTPASG in single solutions, and at least 75% in multielemental solutions. Considering the removal efficacy, regeneration and stability, DFO-grafted silica gel was generally superior to its DTPA counterpart and may be applied to the removal of traces of chromium species from natural waters.

Desferrioxamine-caffeine shows improved efficacy in chelating iron and depleting cancer stem cells

Iron chelation has already been proposed to be a feasible strategy for cancer therapeutics in that reinforced iron demand is demonstrated in cancer cells, and quite a few iron chelators have been developed for this purpose. Desferrioxamine (DFO), an iron chelator approved by the U.S. Food and Drug Administration (FDA), has been extensively examined to remove extra iron. However, DFO has been found to harbor limited efficacies in combating cancer cells due to poor cellular permeability. In the current study, we synthesized the DFO derivative, named as desferrioxamine-caffeine dimer (DFCAF) by linking DFO to caffeine with high purity and excellent stability. Our data showed that DFCAF displayed greater cellular permeability to chelate intracellular iron in 4T1 breast cancer cells than DFO, posing more inhibition on cell growth and cellular motility/invasion. Importantly, DFCAF was uncovered to remarkably deplete cancer stem cells (CSCs), as characterized by the remarkable decrease of the CD44^+/high/CD24^-/low and ALDH^+/high subpopulation. In parallel, DFCAF was also found to greatly reverse epithelial-mesenchymal transition (EMT), suggesting the potential application to restrain tumor progression and metastasis. Collectively, these data unveiled the improved efficacy to target cancer cells and to deplete CSCs, thus opening a new path for better cancer therapeutics through iron chelation.

Cell Permeable Imidazole-Desferrioxamine Conjugates: Synthesis and In Vitro Evaluation

Desferrioxamine (DFO), a clinically approved iron chelator used for iron overload, is unable to chelate labile plasma iron (LPI) because of its limited cell permeability. Herein, alkyl chain modified imidazolium cations with varied hydrophobicities have been conjugated with DFO. The iron binding abilities and the antioxidant properties of the conjugates were found to be similar to DFO. The degree of cellular internalization was much higher in the octyl-imidazolium-DFO conjugate (IV) compared with DFO, and IV was able to chelate LPI in vitro. This opens up a new avenue in using N-alkyl imidazolium salts as a delivery vector for hydrophilic cell-impermeable drugs.

Analogues of desferrioxamine B (DFOB) with new properties and new functions generated using precursor-directed biosynthesis

Desferrioxamine B (DFOB) is a siderophore native to Streptomyces pilosus biosynthesised by the DesABCD enzyme cluster as a high affinity Fe(III) chelator. Although DFOB has a long clinical history for the treatment of chronic iron overload, limitations encourage the development of new analogues. This review describes a recent body of work that has used precursor-directed biosynthesis (PDB) to access new DFOB analogues. PDB exploits the native biosynthetic machinery of a producing organism in culture medium augmented with non-native substrates that compete against native substrates during metabolite assembly. The method allows access to analogues of natural products using benign methods, compared to multistep organic synthesis. The disadvantages of PDB are the production of metabolites in low yield and the need to purify complex mixtures. Streptomyces pilosus medium was supplemented with different types of non-native diamine substrates to compete against native 1,5-diaminopentane to generate DFOB analogues containing alkene bonds, fluorine atoms, ether or thioether functional groups, or a disulfide bond. All analogues retained function as Fe(III) chelators and have properties that could broaden the utility of DFOB. These PDB studies have also added knowledge to the understanding of DFOB biosynthesis.

Advances in the Chemical Biology of Desferrioxamine B

Desferrioxamine B (DFOB) was discovered in the late 1950s as a hydroxamic acid metabolite of the soil bacterium Streptomyces pilosus. The exquisite affinity of DFOB for Fe(III) identified its potential for removing excess iron from patients with transfusion-dependent hemoglobin disorders. Many studies have used semisynthetic chemistry to produce DFOB adducts with new properties and broad-ranging functions. More recent approaches in chemical biology have revealed some nuances of DFOB biosynthesis and discovered new DFOB-derived drugs and radiometal imaging agents. The current and potential applications of DFOB continue to inspire a rich body of chemical biology research focused on this bacterial metabolite.

Triphenylphosphonium-desferrioxamine as a candidate mitochondrial iron chelator

Cell-impermeant iron chelator desferrioxamine (DFO) can have access to organelles if appended to suitable vectors. Mitochondria are important targets for the treatment of iron overload-related neurodegenerative diseases. Triphenylphosphonium (TPP) is a delocalized lipophilic cation used to ferry molecules to mitochondria. Here we report the synthesis and characterization of the conjugate TPP-DFO as a mitochondrial iron chelator. TPP-DFO maintained both a high affinity for iron and the antioxidant activity when compared to parent DFO. TPP-DFO was less toxic than TPP alone to A2780 cells (IC₅₀ = 135.60 ± 1.08 and 4.34 ± 1.06 μmol L^-1, respectively) and its native fluorescence was used to assess its mitochondrial localization (Rr = +0.56). These results suggest that TPP-DFO could be an interesting alternative for the treatment of mitochondrial iron overload e.g. in Friedreich's ataxia.

Sulfated dehydropolymer of caffeic acid: In vitro anti-lung cell death activity and in vivo intervention in emphysema induced by VEGF receptor blockade

Induced lung cell death and impaired hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) signaling are proposed as a pathobiologic mechanism for alveolar structural destruction and loss in emphysema. We hypothesized that our sulfated dehydropolymer of caffeic acid, CDSO3, exerts anti-cell death activities and therapeutic interventions in emphysema by virtue of Fe²⁺ chelation-based HIF-1α/VEGF stabilization and elevation. The Fe²⁺ chelating activity was determined in the chromogenic ferrozine-Fe²⁺ chelation inhibitory assay. The in vitro anti-cell death activities and their Fe²⁺ and HIF-1α dependence were assessed against a range of emphysematous insults in the lung endothelial (HMVEC-L) and epithelial (A549) cells. CDSO3 was spray-dosed to the lung for three weeks (day 1-21) in an in vivo rat model of apoptotic emphysema induced with a VEGF receptor antagonist SU5416. Post-treatment treadmill exercise endurance, airspace enlargement, and several lung biomarkers/proteins were measured. CDSO3 was a potent Fe²⁺ chelating molecule. At 10 μM, CDSO3 inhibited HMVEC-L and A549 cell death induced by histone deacetylase inhibition with trichostatin A, VEGF receptor blockade with SU5416, and cigarette smoke extract by 65-99%, which were all significantly opposed by addition of excess Fe²⁺ or HIF-1α inhibitors. As a potent elastase inhibitor and antioxidant, CDSO3 also inhibited elastase- and H₂O₂-induced cell death by 92 and 95%, respectively. In the rat model of SU5416-induced apoptotic emphysema, CDSO3 treatment at 60 μg/kg 1) produced 61-77% interventions against exercise endurance impairment, airspace enlargement [mean linear intercept] and oxidative lung damage [malondialdehyde activity]; 2) normalized the apoptotic marker [cleaved caspase-3]; 3) stimulated the VEGF signaling [VEGF receptor 2 phosphorylation] by 1.4-fold; and 4) elevated the HIF-1α and VEGF expression by 1.8- and 1.5-fold, respectively. All of these were consistent with CDSO3's Fe²⁺ chelation-based HIF-1α/VEGF stabilization and elevation against their pathobiologic deficiency, inhibiting lung cell death and development of apoptotic emphysema.

Desferrioxamine and desferrioxamine-caffeine as carriers of aluminum and gallium to microbes via the Trojan Horse Effect

Iron acquisition by bacteria and fungi involves in several cases the promiscuous usage of siderophores. Thus, antibiotic resistance from these microorganisms can be circumvented through a strategy of loading toxic metals into siderophores (Trojan Horse Effect). Desferrioxamine (dfo) and its cell-permeant derivative desferrioxamine-caffeine (dfcaf) were complexed with aluminum or gallium for this purpose. The complexes Me(dfo) and Me(dfcaf) (Me=Al³⁺ and Ga³⁺) were synthesized and characterized by mass spectroscopy and cyclic voltammetry. Their relative stabilities were studied through competitive equilibria with fluorescent probes calcein, fluorescein-desferrioxamine and 8-hydroxyquinoline. Me(dfo) and Me(dfcaf) were consistently more toxic than free Me³⁺ against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans, demonstrating the Trojan Horse Effect. Wide spectrum antimicrobial action can be obtained by loading non-essential or toxic metal ions to microbes via a convenient siderophore carrier.

Analogues of desferrioxamine B designed to attenuate iron-mediated neurodegeneration: synthesis, characterisation and activity in the MPTP-mouse model of Parkinson's disease

One dual-function (2) and one first-generation (9) conjugate of the Fe(iii) chelator desferrioxamine B (DFOB,1) showed significant rescue of neurons in the MPTP mouse model of Parkinson's disease.

Melanin nanoparticles as an endogenous agent for efficient iron overload therapy

Melanin was an efficient endogenous agent for iron-overload therapy in living mice due to its native biocompatibility, biodegradability and high iron-capturing volume.