Tuning the Anti(myco)bacterial Activity of 3-Hydroxy-4-pyridinone Chelators through Fluorophores

Targeting Metalloenzymes: The "Achilles' Heel" of Viruses and Parasites

Metalloenzymes are central to the regulation of a wide range of essential viral and parasitic functions, including protein degradation, nucleic acid modification, and many others. Given the impact of infectious diseases on human health, inhibiting metalloenzymes offers an attractive approach to disease therapy. Metal-chelating agents have been expansively studied as antivirals and antiparasitics, resulting in important classes of metal-dependent enzyme inhibitors. This review provides the recent advances in targeting the metalloenzymes of viruses and parasites that impose a significant burden on global public health, including influenza A and B, hepatitis B and C, and human immunodeficiency viruses as well as Trypanosoma brucei and Trypanosoma cruzi.

Experimental Methods for Evaluating the Bacterial Uptake of Trojan Horse Antibacterials

The field of antibacterial siderophore conjugates, referred to as Trojan Horse antibacterials, has received increasing attention in recent years, driven by the rise of antimicrobial resistance. Trojan Horse antibacterials offer an opportunity to exploit the specific pathways present in bacteria for active iron uptake, potentially allowing the drugs to bypass membrane-associated resistance mechanisms. Hence, the Trojan Horse approach might enable the redesigning of old antibiotics and the development of antibacterials that target specific pathogens. Critical parts of evaluating such Trojan Horse antibacterials and improving their design are the quantification of their bacterial uptake and the identification of the pathways by which this occurs. In this minireview, we highlight a selection of the biological and chemical methods used to study the uptake of Trojan Horse antibacterials, exemplified with case studies, some of which have led to drug candidates in clinical development or approved antibiotics.

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.

A combined physiological and biophysical approach to understand the ligand-dependent efficiency of 3-hydroxy-4-pyridinone Fe-chelates

Ligands of the 3-hydroxy-4-pyridinone (3,4-HPO) class were considered eligible to formulate new Fe fertilizers for Iron Deficiency Chlorosis (IDC). Soybean (Glycine max L.) plants grown in hydroponic conditions and supplemented with Fe-chelate [Fe(mpp)3] were significantly greener, had increased biomass, and were able to translocate more iron from the roots to the shoots than those supplemented with an equal amount of the commercially available chelate [FeEDDHA]. To understand the influence of the structure of 3,4-HPO ligand on the role of the Fe-chelate to improve Fe-uptake, we investigated and report here the effect of Fe-chelates ([Fe(mpp)3], [Fe(dmpp)3], and [Fe(etpp)3]) in addressing IDC. Chlorosis development was assessed by measurement of morphological parameters, quantification of chlorophyll and Fe, and other micronutrient contents, as well as measurement of enzymatic activity (FCR) and gene expression (FRO2, IRT1, and Ferritin). All [Fe(3,4-HPO)3] chelates were able to provide Fe to plants and prevent IDC but with a different efficiency depending on the ligand. We hypothesize that this may be related with the distinct physicochemical characteristics of ligands and complexes, namely, the diverse hydrophilic-lipophilic balance of the three chelates. To test the hypothesis, we performed an EPR biophysical study using liposomes prepared from a soybean (Glycine3 max L.) lipid extract and spin probes. The results showed that the most effective chelate [Fe(mpp)3] shows a preferential location close to the surface while the others prefer the hydrophobic region inside the bilayer.

SIGNIFICANCE STATEMENT

The 3-hydroxy-4-pyridinone Fe-chelates, [Fe(mpp)3], [Fe(dmpp)3], and [Fe(etpp)3], were all able to provide Fe to plants and prevent IDC. Efficacy is dependent on the structure of the ligand. From an EPR biophysical study using spin probes and liposomes, prepared from a soybean lipid extract, we hypothesize that this may be related with the distinct preferential location close to the surface or on the hydrophobic region of the lipid bilayer. [Fe(mpp)3] provide higher amounts of Fe in the leaves.

Iron as Therapeutic Target in Human Diseases

Iron is essential for almost all organisms, being involved in oxygen transport, DNA synthesis, and respiration; however, it is also potentially toxic via the formation of free radicals [...].

New strong extrafunctionalizable tris(3,4-HP) and bis(3,4-HP) metal sequestering agents: synthesis, solution and in vivo metal chelation

Finding new multifunctional metal binders to be potentially used in diagnosis or therapy has been a subject of major challenge. Hydroxypyridinones have long been recognized as privileged chelating structures for the design of metal chelating drugs, especially towards hard metal ions, in view of their decorporation in metal overload disorders. Thus, pursuing our strategy of engineering new polydentate 3-hydroxy-4-pyridinones (3,4-HP) with extrafunctionalization capacity for sensing or targeting purposes, we report herein the synthesis and full characterization of a hexadentate (tris-3,4-HP) and a tetradentate (bis-3,4-HP) ligand, possessing three and two 3,4-HP arms N-attached to an aminomethanetrispropionic acid backbone, respectively. Thus, as compared with previously reported analogues, each ligand possesses an extra free amino group ready for further functionalization. Their chelating capacity towards Fe and Al was evaluated in aqueous solution, by potentiometric and spectroscopic techniques, and they proved to be strong sequestering agents for these metal ions without depletion of Zn, an essential biometal. Their excellent in vivo metal-decorporation capacity was also evidenced in mice injected with a radiotracer (⁶⁷Ga) as an animal model of metal overload pathological situations. These findings provide encouragement for further ongoing extrafunctionalizations in view of several potential biomedical applications.

A computational study on the redox properties and binding affinities of iron complexes of hydroxypyridinones

The potential of hydroxypyridinones for in vivo iron sequestration, in both biological and medical contexts, has been extensively discussed in the literature. Different chelators can be designed, with distinct lipophilicities that should alter their cell permeability, distribution, and rates of metabolism. However, for effective iron scavenging in biological systems, the redox potential and binding affinity of iron must fall within a proper range. Our objective was to assess the impact of different hydroxypyridinone chelators in 3:1 iron(III) complexes through comparison of these thermodynamic properties. For that purpose, we employed a cluster-continuum approach using density functional theory, on a dataset of 25 iron complexes. Whenever possible, our results were compared with experimental stability constants (log β) and with electrode potentials. We observed a good qualitative agreement between computed free energies of binding and log β values. In addition, we described which substitutions to the 3-hydroxypyridin-4-one ring should not markedly affect the redox properties and metal ion affinity considering iron. Graphical abstract Iron complexes of hydroxypyridinones.