Novel nitroxoline derivative combating resistant bacterial infections through outer membrane disruption and competitive NDM-1 inhibition

Uncovering nitroxoline activity spectrum, mode of action and resistance across Gram-negative bacteria

Nitroxoline is a bacteriostatic quinoline antibiotic, known to form complexes with metals. Its clinical indications are limited to uncomplicated urinary tract infections, with a susceptibility breakpoint only available for Escherichia coli. Here, we test > 1000 clinical isolates and demonstrate a much broader activity spectrum and species-specific bactericidal activity, including Gram-negative bacteria for which therapeutic options are limited due to multidrug resistance. By combining genetic and proteomic approaches with direct measurement of intracellular metals, we show that nitroxoline acts as a metallophore, inducing copper and zinc intoxication in bacterial cells. The compound displays additional effects on bacterial physiology, including alteration of outer membrane integrity, which underpins nitroxoline's synergies with large-scaffold antibiotics and resensitization of colistin-resistant Enterobacteriaceae in vitro and in vivo. Furthermore, we identify conserved resistance mechanisms across bacterial species, often leading to nitroxoline efflux.

Nitroxoline evidence amoebicidal activity against Acanthamoeba castellanii through DNA damage and the stress response pathways

Acanthamoeba castellanii is a widespread unicellular eukaryote found in diverse environments, including tap water, soil, and swimming pools. It is responsible for severe infections, such as Acanthamoeba keratitis and granulomatous amebic encephalitis, particularly in individuals with immunocompromisation. The ability of protozoans to form dormant and persistent cysts complicates treatment, as current therapies are ineffective against cyst stages and suffer from poor specificity and side effects. Nitroxoline, a quinoline derivative with well-established antibacterial, antifungal, and antiviral properties, is a promising therapeutic candidate. This study aimed to elucidate cellular signalling events that counteract the effects of nitroxoline. In this study, nitroxoline significantly reduced the viability of A. castellanii trophozoites in a dose- and time-dependent manner, inducing morphological changes and apoptosis. Transcriptomic analysis revealed substantial alterations in gene expression, including enrichment of metabolic pathways, DNA damage responses, and iron ion binding. Nitroxoline treatment upregulated genes involved in DNA repair and oxidative stress response while regulating genes in the methionine and cysteine cycles. It also decreased the mitochondrial membrane potential, H₂S production, and total iron amount in A. castellanii. Bioinformatic analyses and molecular docking studies suggest direct interactions between nitroxoline and several A. castellanii proteins. Our research provides a comprehensive molecular map of the response of A. castellanii to nitroxoline, revealing significant changes in gene expression related to the stress response and metabolic pathways. These findings underscore the potential of nitroxoline as a potent anti-Acanthamoeba agent, offering new insights into its mechanism of action and paving the way for effective combinational therapeutic strategies.

Treatment Approaches for Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii has been associated with over three hundred thousand annual deaths globally. It is resistant to most available antibiotics and associated with high morbidity and mortality. No global consensus currently exists for treatment strategies that balance safety and efficacy because of heterogeneity of treatment regimens in current clinical practice and scarcity of large-scale controlled studies arising from difficulties in establishing robust clinical outcomes. This review outlines the epidemiology and resistance mechanisms of carbapenem-resistant A. baumannii, then summarizes available clinical data on each approved agent with activity against this pathogen. Emerging treatment options such as cefiderocol and sulbactam-durlobactam show promise, but their success hinges on comprehensive clinical validation and access in regions most impacted by this pathogen. New therapeutic modalities that are in various stages of clinical development are also discussed.

Novel methyldithiocarbazate derivatives as NDM-1 inhibitors to combat multidrug-resistant bacterial infection with β-lactams

Given the ever-evolving landscape of antimicrobial resistance, the emergence of New Delhi metallo-β-lactamase-1 (NDM-1) has introduced a formidable challenge to global public health. In previous research, we identified the Compound Zndm19 as an NDM-1 inhibitor and reported Zndm19 derivatives, which exhibited moderate antibacterial activity when combined with meropenem (MEM). This moderate activity may have been due to the inability of Zndm19 to efficiently penetrate the bacterial outer membrane or its susceptibility to hydrolysis, which prevented it from exerting strong enzyme inhibition in synergy with bacterial cells. In this study, we aimed to overcome these limitations by employing a scaffold hopping strategy, abandoning the original core structure. We designed and synthesized 21 compounds and discovered that Compound A8 could effectively restore the antibacterial activity of MEM against NDM-1-positive Escherichia coli (E. coli). Compound A8 restored the ability of MEM to penetrate the cell wall of gram-negative bacteria, leading to oxidative stress-induced disarray within bacterial cells. This disruption ultimately led to the impairment of bacterial cell membrane integrity and permeability, consequently amplifying the synergistic antimicrobial efficacy of the combined treatment. Furthermore, compared with Zndm19, Compound A8 demonstrated broader therapeutic applications in the Galleria mellonella infection model and the murine peritonitis infection model. Molecular docking, site-directed mutagenesis, and fluorescence quenching assays confirmed that Compound A8 could directly interact with NDM-1, thereby further inhibiting its hydrolytic activity. These findings elucidate the antimicrobial mechanism of novel methyl dithiocarbamate derivatives and provide new insights for the development of new NDM-1 inhibitors.

Combination of aloe emodin, emodin, and rhein from Aloe with EDTA sensitizes the resistant Acinetobacter baumannii to polymyxins

Background

The continuous emergence and spread of polymyxin-resistant Acinetobacter baumannii pose a significant global health challenge, necessitating the development of novel therapeutic strategies. Aloe, with its long-standing history of medicinal use, has recently been the subject of substantial research for its efficacy against pathogenic infections.

Methods

This study investigates the potential application of anthraquinone components in aloe against polymyxin-resistant A. baumannii by liquid chromatography-mass spectrometry, in vitro activity assessment, and construction of animal infection models.

Results

The findings demonstrate that aloe emodin, emodin, rhein, and their mixtures in equal mass ratios (EAR) exhibit strain-specific antibacterial activities against polymyxin-resistant A. baumannii. Co-administration of EAR with EDTA synergistically and universally enhanced the antibacterial activity and bactericidal efficacy of polymyxins against polymyxin-resistant A. baumannii, while also reducing the frequency of polymyxin-resistant mutations in polymyxinssensitive A. baumannii. Following toxicity assessment on human hepatic and renal cell lines, the combination therapy was applied to skin wounds in mice infected with polymyxin-resistant A. baumannii. Compared to monotherapy, the combination therapy significantly accelerated wound healing and reduced bacterial burden.

Conclusions

The combination of EAR and EDTA with polymyxins offers a novel therapeutic approach for managing skin infections caused by polymyxinresistant A. baumannii.

Antibacterial agents active against Gram Negative Bacilli in phase I, II, or III clinical trials

INTRODUCTION

Antimicrobial resistance is a major threat to modern healthcare, and it is often regarded that the antibiotic pipeline is 'dry.'

AREAS COVERED

Antimicrobial agents active against Gram negative bacilli in Phase I, II, or III clinical trials were reviewed.

EXPERT OPINION

Nearly 50 antimicrobial agents (28 small molecules and 21 non-traditional antimicrobial agents) active against Gram-negative bacilli are currently in clinical trials. These have the potential to provide substantial improvements to the antimicrobial armamentarium, although it is known that 'leakage' from the pipeline occurs due to findings of toxicity during clinical trials. Significantly, a lack of funding for large phase III clinical trials is likely to prevent trials occurring for the indications most relevant to loss of life attributed to antimicrobial resistance such as ventilator-associated pneumonia. Non-traditional antimicrobial agents face issues in clinical development such as a lack of readily available and reliable susceptibility tests, and the potential need for superiority trials rather than non-inferiority trials. Most importantly, concrete plans must be made during clinical development for access of new antimicrobial agents to areas of the world where resistance to Gram negative bacilli is most frequent.