Development of Neutropenic Murine Models of Iron Overload and Depletion To Study the Efficacy of Siderophore-Antibiotic Conjugates

Tn-seq of the Candida glabrata reference strain CBS138 reveals epigenetic plasticity, structural variation, and intrinsic mechanisms of resistance to micafungin

C. glabrata is an opportunistic pathogen that can resist common antifungals and rapidly acquire multidrug resistance. A large amount of genetic variation exists between isolates, which complicates generalizations. Portable Tn-seq methods can efficiently provide genome-wide information on strain differences and genetic mechanisms. Using the Hermes transposon, the CBS138 reference strain and a commonly studied derivative termed 2001 were subjected to Tn-seq in control conditions and after exposure to varying doses of the clinical antifungal micafungin. The approach revealed large differences between these strains, including a 131 kb tandem duplication and a variety of fitness differences. Additionally, both strains exhibited up to 1000-fold increased transposon accessibility in subtelomeric regions relative to the BG2 strain, indicative of open subtelomeric chromatin in these isolates and large epigenetic variation within the species. Unexpectedly, the Pdr1 transcription factor conferred resistance to micafungin through targets other than CDR1 . Other micafungin resistance pathways were also revealed including mannosyltransferase activity and biosynthesis of the lipid precursor sphingosine, the drugging of which by SDZ 90-215 or myriocin enhanced the potency of micafungin in vitro . These findings provide insights into complexity of the C. glabrata species as well as strategies for improving antifungal efficacy.

Summary

Candida glabrata is an emerging pathogen with large genetic diversity and genome plasticity. The type strain CBS138 and a laboratory derivative were mutagenized with the Hermes transposon and profiled using Tn-seq. Numerous genes that regulate innate and acquired resistance to an important clinical antifungal were uncovered, including a pleiotropic drug resistance gene (PDR1) and a duplication of part of one chromosome. Compounds that target PDR1 and other genes may augment the potency of existing antifungals.

Cefiderocol: Clinical application and emergence of resistance

Antibacterial drug resistance of gram-negative bacteria (GNB) results in high morbidity and mortality of GNB infection, seriously threaten human health globally. Developing new antibiotics has become the critical need for dealing with drug-resistant bacterial infections. Cefiderocol is an iron carrier cephalosporin that achieves drug accumulation through a unique "Trojan horse" strategy into the bacterial periplasm. It shows high antibacterial activity against multidrug-resistant (MDR) Enterobacteriaceae and MDR non-fermentative bacteria. The application of cefiderocol offers new hope for treating clinical drug-resistant bacterial infections. However, limited clinical data and uncertainties about its resistance mechanisms constrain the choice of its therapeutic use. This review aimed to summarize the clinical applications, drug resistance mechanisms, and co-administration of cefiderocol.

Bibliometric Review on New Possibilities of Antimycobacterial Agents: Exploring Siderophore Desferrioxamine's Applications as an Antimicrobial Agent

Mycobacteria cause tuberculosis and other serious diseases. Understanding their mechanisms of resistance to our immune system and exploring novel drugs are critical strategies to combat infections. A bibliometric analysis was performed to identify publication trends and critical research areas in the field of the antimicrobial activity of desferrioxamine. A total of twenty-four publications on the topic, from 2012 to 2023, were retrieved from databases including Web of Science, Scopus, PubMed, and Embase, using specific keywords. The quality of the publications was assessed using impact and productivity metrics, with an average annual publication rate of 2.1 articles. The United States emerged as the most productive country, with medicine (23.4%, 11 publications) and biochemistry, genetics, and molecular biology (21.3%, 10 publications) as the top research fields. The five most cited publications accounted for 672 citations, with a relatively low h-index (11:11). In conclusion, there has been a lack of publications on this topic in the last decade. The United States dominates production and publication in this area, and there appears to be limited exchange of knowledge, ideas, and technology within the field. Therefore, fostering international cooperation through funding is essential to facilitate further research and development of desferrioxamine-related studies.

Cefiderocol for the Treatment of Multidrug-Resistant Gram-Negative Bacteria: A Systematic Review of Currently Available Evidence

Cefiderocol is a novel synthetic siderophore-conjugated antibiotic that hijacks the bacterial iron transport systems facilitating drug entry into cells, achieving high periplasmic concentrations. This systematic review analyzed the currently available literature on cefiderocol. It summarized in vitro susceptibility data, in vivo antimicrobial activity, pharmacokinetics/pharmacodynamics (PK/PD), clinical efficacy, safety and resistance mechanisms of cefiderocol. Cefiderocol has potent in vitro and in vivo activity against multidrug-resistant (MDR) Gram-negative bacteria, including carbapenem-resistant isolates. But New Delhi Metallo-β-lactamase (NDM)- positive isolates showed significantly higher MICs than other carbapenemase-producing Enterobacterales, with a susceptible rate of 83.4% for cefiderocol. Cefiderocol is well-tolerated, and the PK/PD target values can be achieved using a standard dose regimen or adjusted doses according to renal function. Clinical trials demonstrated that cefiderocol was non-inferiority to the comparator drugs in treating complicated urinary tract infection and nosocomial pneumonia. Case reports and series showed that cefiderocol was a promising therapeutic agent in carbapenem-resistant infections. However, resistant isolates and reduced susceptibility during treatment to cefiderocol have already been reported. In conclusion, cefiderocol is a promising powerful weapon for treating MDR recalcitrant infections.

Human Serum Proteins and Susceptibility of Acinetobacter baumannii to Cefiderocol: Role of Iron Transport

Cefiderocol, a recently introduced antibiotic, has a chemical structure that includes a cephalosporin that targets cell wall synthesis and a chlorocatechol siderophore moiety that facilitates cell penetration by active iron transporters. Analysis of the effect that human serum, human serum albumin, and human pleural fluid had on growing Acinetobacter baumannii showed that genes related to iron uptake were down-regulated. At the same time, β-lactamase genes were expressed at higher levels. The minimum inhibitory concentrations of this antimicrobial in A. baumannii cells growing in the presence of human serum, human serum albumin, or human pleural fluid were higher than those measured when these fluids were absent from the culture medium. These results correlate with increased expression levels of β-lactamase genes and the down-regulation of iron uptake-related genes in cultures containing human serum, human serum albumin, or human pleural fluid. These modifications in gene expression could explain the less-than-ideal clinical response observed in patients with pulmonary or bloodstream A. baumannii infections. The exposure of the infecting cells to the host’s fluids could cause reduced cefiderocol transport capabilities and increased resistance to β-lactams. The regulation of genes that could impact the A. baumannii susceptibility to cefiderocol, or other antibacterials, is an understudied phenomenon that merits further investigation.

Iron serum levels and iron homeostasis parameters in patients with nosocomial pneumonia treated with cefiderocol: post hoc analysis of the APEKS-NP study

Critically ill patients often present with low serum iron levels or anemia. We evaluated the impact of iron levels and iron homeostasis on the efficacy and safety of cefiderocol, an iron-chelator siderophore cephalosporin, in patients with nosocomial pneumonia in a post hoc analysis of the randomized, double-blind, Phase 3 APEKS-NP study (NCT03032380). Patients with Gram-negative nosocomial pneumonia received cefiderocol 2 g, 3-h infusion, q8h, or high-dose, extended-infusion meropenem 2 g, 3-h infusion, q8h, for 7-14 days. Efficacy and safety parameters, including specific iron homeostasis parameters (i.e., hepcidin, iron, total iron binding capacity, transferrin saturation), were analyzed according to baseline iron levels. In the cefiderocol and meropenem arms, 79.1% (117/148) and 83.3% (125/150) randomized patients, respectively, had low baseline serum iron levels. Rates of 14-day (12.3% [14/114] vs 11.6% [14/121]) and 28-day all-cause mortality (20.5% [23/112] vs 19.0% [23/121]), clinical cure (63.2% [72/114] vs 67.2% [82/122]), and microbiological eradication (43.6% [41/94] vs 48.1% [51/106]) at test of cure were similar in cefiderocol vs meropenem arms, respectively. In the overall safety population, rates of anemia-related adverse events were similar (cefiderocol arm 18.2% [27/148], meropenem arm 18.7% [28/150]). Changes from baseline to test of cure in hepcidin, iron, total iron binding capacity, and transferrin saturation were similar between treatment arms. Cefiderocol treatment did not affect iron homeostasis, and its efficacy and safety were not influenced by baseline serum iron levels. Clinicaltrials.gov registration: NCT03032380. Date of registration: 26 January 2017.

In Vitro Antimicrobial Activity of the Siderophore Cephalosporin Cefiderocol against Acinetobacter baumannii Strains Recovered from Clinical Samples

BACKGROUND

Cefiderocol is a siderophore cephalosporin that exhibits antimicrobial activity against most multi-drug resistant Gram-negative bacteria, including Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia.

METHODS

A total of 20 multidrug-resistant A. baumannii strains were isolated from 2020 to 2021, molecularly characterized and tested to assess the in vitro antibacterial activity of cefiderocol. Thirteen strains were carbapenem-hydrolysing oxacillinase OXA-23-like producers, while seven were non-OXA-23-like producers. Minimum inhibitory concentrations (MICs) were determined by broth microdilution, considered as the gold standard method. Disk diffusion test was also carried out using iron-depleted CAMHB plates for cefiderocol.

RESULTS

Cefiderocol MICs ranged from 0.5 to 1 mg/L for OXA-23-like non-producing A. baumannii strains and from 0.25 to >32 mg/L for OXA-23-like producers, using the broth microdilution method. Cefiderocol MIC₉₀ was 8 mg/L. Diameter of inhibition zone of cefiderocol ranged from 18 to 25 mm for OXA-23-like non-producers and from 15 to 36 mm for OXA-23-like producers, using the diffusion disk method. A large variability and a low reproducibility were observed during the determination of diameter inhibition zone. Molecular characterization showed that all isolates presented the ISAba1 genetic element upstream the blaOXA-51. Among OXA-23-like non-producers, four were blaOXA-58 positive and two were negative for all the resistance determinants analyzed.

CONCLUSIONS

Cefiderocol showed in vitro antimicrobial activity against both carbapenem-susceptible and non-susceptible A. baumannii strains, although some OXA-23-like producers were resistant. Further clinical studies are needed to consolidate the role of cefiderocol as an antibiotic against MDR A. baumannii.

Pharmacological and clinical profile of cefiderocol, a siderophore cephalosporin against gram-negative pathogens

Introduction: Increasing resistance of gram-negative bacteria poses a serious threat to global health. Thus, efficacious and safe antibiotics against resistant pathogens are urgently needed. Cefiderocol, a siderophore cephalosporin, addresses this unmet need.Areas covered: For this article, we screened all preclinical and clinical studies on cefiderocol published by January 2021 on PubMed. Also, regulatory documents, recent conference contributions, and selected data of antibiotic competitors are reviewed. We provide a comprehensive overview of the mode of action, in vitro and in vivo activity, pharmacokinetics/pharmacodynamics, and human pharmacokinetics. Last, we discuss the efficacy and safety data from the pivotal trials.Expert opinion: Cefiderocol was in vitro potent against virtually all gram-negative pathogens and resistance was rare. The target site pharmacokinetics (i.e. urinary and lung penetration) have been well described in humans and important PK/PD targets were reached. In the clinical trials, cefiderocol was non-inferior to carbapenems in the treatment of complicated urinary tract infections and nosocomial pneumonia. Against carbapenem-resistant gram-negative pathogens, cefiderocol was similar to the best available therapy, which was mainly based on the backbone agent colistin. Overall, a substantial body of evidence supports the clinical use of cefiderocol in patients with gram-negative infections and limited treatment options.

Evaluating Cefiderocol in the Treatment of Multidrug-Resistant Gram-Negative Bacilli: A Review of the Emerging Data

Infections due to multidrug-resistant Gram-negative bacteria (MDR-GNB), especially when carbapenem resistant, have been very difficult to manage in the last fifteen years, owing to the paucity of dependable therapeutic options. Cefiderocol is a siderophore cephalosporin recently approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) that may have the potential to fill some of the remaining gaps in the treatment of MDR-GNB infections. Among others, cefiderocol demonstrated in vitro activity against carbapenem-resistant Acinetobacter baumannii and metallo-β-lactamases producers. Clinical data from both registrative studies and post-marketing experiences are essential to confirm whether these promises from in vitro studies could readily translate into clinical practice, as well as to delineate the precise place in therapy for cefiderocol for the treatment of MDR-GNB in the near future. Because of its unique potential, it is essential to provide both randomized controlled trials (RCT) and real-life data to improve the ability of clinicians to exploit its benefit in both empirical and targeted treatment of MDR-GNB infections. In this narrative review, we discuss the emerging data from pivotal RCT and initial real-life experiences on the use of cefiderocol for the treatment of MDR-GNB infections.

Human-Simulated Antimicrobial Regimens in Animal Models: Transparency and Validation Are Imperative

Animal infection models are invaluable in optimizing antimicrobial dosage in humans. Utilization of human-simulated regimens (HSRs) in animal models helps to evaluate antimicrobial efficacy at clinically achievable drug concentrations. To that end, pharmacokinetic studies in infected animals and confirmation of the HSR pharmacokinetic profile are essential in evaluating observed versus expected drug concentrations. We present and compare two murine meropenem-vaborbactam HSR profiles, their potential impact on bacterial killing, and clinical translatability.

Cefiderocol for treatment of an empyema due to extensively drug-resistant Pseudomonas aeruginosa: Clinical observations and susceptibility testing considerations

Cefiderocol is a novel siderophore cephalosporin antibacterial with activity against carbapenem-resistant Gram-negative bacteria including Pseudomonas aeruginosa. We report a medically complex patient treated with compassionate use cefiderocol for an empyema caused by extensively drug-resistant P. aeruginosa as well as clinical considerations for cefiderocol use based on our findings. We observed a potential discordance in cefiderocol susceptibility testing results depending if disk diffusion or iron-depleted cation-adjusted Mueller Hinton Broth dilution is used. Furthermore, interpretative criteria differ between the Clinical Laboratory Standards Institute and United States Food and Drug Administration for P. aeruginosa, which makes cefiderocol interpretation potentially challenging for clinicians. We may have also observed selective pressure from prior cefiderocol exposure given the respective increases and decreases in MIC values and zone diameters for P. aeruginosa isolates following cefiderocol treatment. Additional data are needed to further describe cefiderocol use, susceptibility testing, and resistance development as real-world clinical use expands.

Efficacy of Humanized Cefiderocol Exposure Is Unaltered by Host Iron Overload in the Thigh Infection Model

Cefiderocol is a siderophore-cephalosporin conjugate with greater in vitro potency under iron-depleted conditions. During infection, iron is scarce in host tissue; however, it is not known whether iron overload in the host, such as in cases of hereditary hemochromatosis, alters the efficacy of cefiderocol. We compared cefiderocol efficacy between iron-overloaded and standard murine thigh infection models. Female CD-1 mice rendered neutropenic received 2 weeks of iron dextran at 100 mg/kg of body weight/day intraperitoneally (iron-overloaded model) or no injections (standard model). Mice were inoculated (107 CFU/ml) with Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa with previously determined cefiderocol MICs from 0.25 to 64 mg/liter. Human-simulated regimens of cefiderocol or meropenem (2 g every 8 h [q8h], 3-h infusion) were administered for 24 h (31 strains) or 72 h (15 strains; cefiderocol only). Procedures were simultaneously performed in standard and iron-overloaded models. Mean bacterial burdens (log10 CFU/thigh) at baseline were 5.75 ± 0.47 versus 5.81 ± 0.51 in standard versus iron-overloaded models, respectively. At 24 h, mean burdens in standard versus iron-overloaded models decreased by -0.8 ± 1.9 versus -1.2 ± 2.0 (P = 0.25) in meropenem-treated mice and by -1.5 ± 1.4 versus -1.6 ± 1.5 (P = 0.54) in cefiderocol-treated mice. At 72 h, mean burdens in cefiderocol-treated mice decreased by -2.5 ± 1.5 versus -2.5 ± 1.4. No overall differences in efficacy between the models were observed for meropenem or cefiderocol. Human-simulated exposure of cefiderocol is equally efficacious in iron-overloaded and normal hosts. The potential clinical use of cefiderocol to treat Gram-negative infections in patients with iron overload is supported.