Harnessing the toxicity of dysregulated iron uptake for killing Staphylococcus aureus: reality or mirage?

Induction of ferroptosis: A new strategy for the control of bacterial infections

The continued rise of drug-resistant bacterial infections heightens a threat of a pandemic of antimicrobial resistance to the global health. The urgency of infection control against antimicrobial-resistant bacteria is evident. Ferroptosis, a newly defined form of iron-dependent cell death characterized by lipid peroxidation, has garnered substantial interest since this programmed cell death was associated with pathophysiological processes of many diseases. Exploring whether ferroptosis could be utilized in infectious diseases holds significant importance for discovering novel antimicrobial approaches. Recent years have witnessed significant progress with respect to elucidating the mechanisms that govern ferroptosis induction and its roles in bacterial pathogenesis and host-pathogen interactions. In this review, we discuss the mechanisms of targeting ferroptosis and/or iron homeostasis for the control of antimicrobial-resistant bacterial infections. These implications may inform and enable effective therapeutic strategies against pathogen infection and provide novel insights into the potential applications of ferroptosis to address the global bacterial resistance crisis.

Ferroptosis inhibitors: past, present and future

Ferroptosis is a non-apoptotic mode of programmed cell death characterized by iron dependence and lipid peroxidation. Since the ferroptosis was proposed, researchers have revealed the mechanisms of its formation and continue to explore effective inhibitors of ferroptosis in disease. Recent studies have shown a correlation between ferroptosis and the pathological mechanisms of neurodegenerative diseases, as well as diseases involving tissue or organ damage. Acting on ferroptosis-related targets may provide new strategies for the treatment of ferroptosis-mediated diseases. This article specifically describes the metabolic pathways of ferroptosis and summarizes the reported mechanisms of action of natural and synthetic small molecule inhibitors of ferroptosis and their efficacy in disease. The paper also describes ferroptosis treatments such as gene therapy, cell therapy, and nanotechnology, and summarises the challenges encountered in the clinical translation of ferroptosis inhibitors. Finally, the relationship between ferroptosis and other modes of cell death is discussed, hopefully paving the way for future drug design and discovery.

Transferrin-inspired iron delivery across the cell membrane using [(L2Fe)2(μ-O)] (L = chlorquinaldol) to harness anticancer activity of ferroptosis

Although iron is a bio-essential metal, dysregulated iron acquisition and metabolism result in production of reactive oxygen species (ROS) due to the Fenton catalytic reaction, which activates ferroptotic cell death pathways. The lipophilic Fe(III)-chelator chlorquinaldol (L; i.e., 5,7-dichloro-8-hydroxy-2-methylquinoline) strongly favors the formation of a highly stable binuclear Fe(III) complex [(L2Fe)2(μ-O)] (1) that can mimic the function of the Fe(III)-transferrin complex in terms of the strong binding to Fe(III) and facile release of Fe(II) when the metal center is reduced. It should be noted that the cellular uptake of 1 is not transferrin receptor-mediated but enhanced by the high lipophilicity of chlorquinaldol. Once 1 is transported across the cell membrane, Fe(III) can be reduced by ferric reductase or other cellular antioxidants to be released as Fe(II), which triggers the Fenton catalytic reaction, thus harnessing the anticancer activity of iron. As the result, this transferrin-inspired iron-delivery strategy significantly reduces the cytotoxicity of 1 in normal human embryonic kidney cells (HEK 293) and the hemolytic activity of 1 in human red blood cells (hRBCs), giving rise to the unique tumor-specific anticancer activity of this Fe(III) complex.

Lipophilic Fe(III)-Complex with Potent Broad-Spectrum Anticancer Activity and Ability to Overcome Pt Resistance in A2780cis Cancer Cells

Although iron is essential for all forms of life, it is also potentially toxic to cells as the increased and unregulated iron uptake can catalyze the Fenton reaction to produce reactive oxygen species (ROS), leading to lipid peroxidation of membranes, oxidation of proteins, cleavage of DNA and even activation of apoptotic cell death pathways. We demonstrate that Fe(hinok)₃ (hinok = 2-hydroxy-4-isopropyl-2,4,6-cycloheptatrien-1-one), a neutral Fe(III) complex with high lipophilicity is capable of bypassing the regulation of iron trafficking to disrupt cellular iron homeostasis; thus, harnessing remarkable anticancer activity against a panel of five different cell lines, including Pt-sensitive ovarian cancer cells (A2780; IC₅₀ = 2.05 ± 0.90 μM or 1.20 μg/mL), Pt-resistant ovarian cancer cells (A2780cis; IC₅₀ = 0.92 ± 0.73 μM or 0.50 μg/mL), ovarian cancer cells (SKOV-3; IC₅₀ = 1.23 ± 0.01 μM or 0.67 μg/mL), breast cancer cells (MDA-MB-231; IC₅₀ = 3.83 ± 0.12 μM or 2.0 μg/mL) and lung cancer cells (A549; IC₅₀ = 1.50 ± 0.32 μM or 0.82 μg/mL). Of great significance is that Fe(hinok)₃ exhibits unusual selectivity toward the normal HEK293 cells and the ability to overcome the Pt resistance in the Pt-resistant mutant ovarian cancer cells of A2780cis.

Functionalized antibacterial peptide with DNA cleavage activity for enhanced bacterial disinfection

Antibiotics are commonly used to treat bacterial infections, but the misuse and abuse of antibiotics have given rise to a severe problem of the drug resistance of bacteria. Solving this problem has been a vitally important task in the modern medical arena. Antibacterial peptide (AMPs) has become a promising candidate drug to replace antibiotics because of their broad-spectrum antibacterial activity and their difficulty in making bacteria resistant. However, its wider clinical application is limited by the shortcomings of high cytotoxicity and low antibacterial efficiency. In this paper, we constructed an antibacterial peptide (Cu-GGH-KKLRKIAFK, abbreviated as Cu-GGH-AMP) with a DNA cleavage function. The peptide has two functional regions, the C-terminal antibacterial peptide PaDBS1R6F10 (KKLRLKIAFK) and the N-terminal Cu-GGH complex. PaDBS1R6F10 is a unique antibacterial peptide, which shows lower tendency to produce bacterial resistance than traditional antibiotics. Cu-GGG complexes are formed by chelating Cu with the classical amino terminal Cu (II)- and Ni (II) -Binding (ATCUN) motif GGH. In the presence of ascorbic acid, Cu-GGH can efficiently catalyze the oxidative cleavage of bacterial DNA, thus playing a synergistic antibacterial role with antibacterial peptides. The in vitro and in vivo experiments demonstrated this functionalized antibacterial peptide possesses excellent antibacterial and anti-skin infection capability, as well as the activity of promoting wound healing.

Hinokitiol-iron complex is a ferroptosis inducer to inhibit triple-negative breast tumor growth

BACKGROUND

Ferroptosis is a unique cell death, dependent on iron and phospholipid peroxidation, involved in massive processes of physiopathology. Tremendous attention has been caught in oncology, particularly for those therapy-resistant cancers in the mesenchymal state prone to metastasis due to their exquisite vulnerability to ferroptosis. Therefore, a therapeutical ferroptosis inducer is now underway to be exploited.

RESULTS

A natural compound, hinokitiol (hino), has been considered to be an iron chelator. We have a novel finding that hino complexed with iron to form Fe(hino)3 can function as a ferroptosis inducer in vitro. The efficiency, compared with the same concentration of iron, increases nearly 1000 folds. Other iron chelators, ferroptosis inhibitors, or antioxidants can inhibit Fe(hino)3-induced ferroptosis. The complex Fe(hino)3 efficacy is further confirmed in orthotopic triple-negative breast cancer (TNBC) tumor models that Fe(hino)3 significantly boosted lipid peroxidation to induce ferroptosis and significantly reduced the sizes of TNBC cell-derived tumors. The drug's safety was also evaluated, and no detrimental side effects were found with the tested dosage.

CONCLUSIONS

When entering cells, the chelated iron by hinokitiol as a complex Fe(hino)3 is proposed to be redox-active to vigorously promote the production of free radicals via the Fenton reaction. Thus, Fe(hino)3 is a ferroptosis inducer and, therapeutically, exhibits anti-TNBC activity.

Harnessing the Dual Antimicrobial Mechanism of Action with Fe(8-Hydroxyquinoline)3 to Develop a Topical Ointment for Mupirocin-Resistant MRSA Infections

8-Hydroxyquinoline (8-hq) exhibits potent antimicrobial activity against Staphylococcus aureus (SA) bacteria with MIC = 16.0-32.0 µM owing to its ability to chelate metal ions such as Mn²⁺, Zn^2+, and Cu²⁺ to disrupt metal homeostasis in bacterial cells. We demonstrate that Fe(8-hq)₃, the 1:3 complex formed between Fe(III) and 8-hq, can readily transport Fe(III) across the bacterial cell membrane and deliver iron into the bacterial cell, thus, harnessing a dual antimicrobial mechanism of action that combines the bactericidal activity of iron with the metal chelating effect of 8-hq to kill bacteria. As a result, the antimicrobial potency of Fe(8-hq)₃ is significantly enhanced in comparison with 8-hq. Resistance development by SA toward Fe(8-hq)₃ is considerably delayed as compared with ciprofloxacin and 8-hq. Fe(8-hq)₃ can also overcome the 8-hq and mupirocin resistance developed in the SA mutant and MRSA mutant bacteria, respectively. Fe(8-hq)₃ can stimulate M1-like macrophage polarization of RAW 264.7 cells to kill the SA internalized in such macrophages. Fe(8-hq)₃ exhibits a synergistic effect with both ciprofloxacin and imipenem, showing potential for combination therapies with topical and systemic antibiotics for more serious MRSA infections. The in vivo antimicrobial efficacy of a 2% Fe(8-hq)₃ topical ointment is confirmed by the use of a murine model with skin wound infection by bioluminescent SA with a reduction of the bacterial burden by 99 ± 0.5%, indicating that this non-antibiotic iron complex has therapeutic potential for skin and soft tissue infections (SSTIs).

Broad-Spectrum Antimicrobial Activity of Ultrafine (BiO)2CO3 NPs Functionalized with PVP That Can Overcome the Resistance to Ciprofloxacin, AgNPs and Meropenem in Pseudomonas aeruginosa

Although it has no known biochemical role in living organisms, bismuth has been used to treat syphilis, diarrhea, gastritis and colitis for almost a century due to its nontoxic nature to mammalian cells. When prepared via a top-down sonication route from a bulk sample, bismuth subcarbonate (BiO)₂CO₃ nanoparticles (NPs) with an average size of 5.35 ± 0.82 nm exhibit broad-spectrum potent antibacterial activity against both the gram-positive and gram-negative bacteria including methicillin-susceptible Staphylococcus aureus (DSSA), methicillin-resistant Staphylococcus aureus (MRSA), drug-susceptible Pseudomonas aeruginosa (DSPA) and multidrug-resistant Pseudomonas aeruginosa (DRPA). Specifically, the minimum inhibitory concentrations (MICs) are 2.0 µg/mL against DSSA and MRSA and 0.75 µg/mL against DSPA and DRPA. In sharp contrast to ciprofloxacin, AgNPs and meropenem, (BiO)₂CO₃ NPs show no sign of developing Bi-resistant phenotypes after 30 consecutive passages. On the other hand, such NPs can readily overcome the resistance to ciprofloxacin, AgNPs and meropenem in DSPA. Finally, the combination of (BiO)₂CO₃ NPs and meropenem shows a synergistic effect with the fractional inhibitory concentration (FIC) index of 0.45.

Bi2O3 nanoparticles exhibit potent broad-spectrum antimicrobial activity and the ability to overcome Ag-, ciprofloxacin- and meropenem-resistance in P. aeruginosa: the next silver bullet of metal antimicrobials?

Antimicrobial resistance is a persistent threat to global public health. In order to combat the spread of pathogenic bacteria, numerous antimicrobial materials have been incorporated into wound dressings and medical devices such as implants and catheters. The most frequently utilized of these materials are Ag-salts and Ag-nanoparticles (AgNPs) due to their low minimum inhibitory concentrations (MICs) against common Gram-negative pathogenic bacteria such as P. aeruginosa. However, such Ag-based materials are limited to treating Gram-negative bacteria and prone to generating Ag-resistant phenotypes after only 7 consecutive exposures to these materials at a sub-inhibitory concentration. Here, we demonstrate α-Bi2O3 NPs as potential replacements for such materials, i.e., α-Bi2O3 NPs that exhibit potent broad-spectrum antibacterial activity (MIC = 0.75 μg mL-1 against P. aeruginosa; MIC = 2.5 μg mL-1 against S. aureus). Furthermore, these NPs are effective against Ag-resistant and carbapenem-resistant bacteria (MICs = 1.0 μg mL-1 and 1.25 μg mL-1, respectively) and also show a synergistic effect with meropenem (mero) in P. aeruginosa bacteria, allowing for the use of meropenem with smaller therapeutic doses (fractional inhibitory concentration = 0.45). Finally, unlike other materials that have been explored as effective antimicrobials, α-Bi2O3 NPs do not contribute to the development of Bi-resistant phenotypes after 30 passages of consecutive exposure to a sub-lethal dose of such NPs. Our results demonstrate that Bi-based materials represent a critical tool against multidrug resistant bacteria and require greater attention within the community. We anticipate this study to inspire broader investigation into the use of other metal oxides as antimicrobial materials, particularly those that limit the development of resistant phenotypes.