Iclaprim, a dihydrofolate reductase inhibitor antibiotic in Phase III of clinical development: a review of its pharmacology, microbiology and clinical efficacy and safety

Navigating Antibacterial Frontiers: A Panoramic Exploration of Antibacterial Landscapes, Resistance Mechanisms, and Emerging Therapeutic Strategies

The development of effective antibacterial solutions has become paramount in maintaining global health in this era of increasing bacterial threats and rampant antibiotic resistance. Traditional antibiotics have played a significant role in combating bacterial infections throughout history. However, the emergence of novel resistant strains necessitates constant innovation in antibacterial research. We have analyzed the data on antibacterials from the CAS Content Collection, the largest human-curated collection of published scientific knowledge, which has proven valuable for quantitative analysis of global scientific knowledge. Our analysis focuses on mining the CAS Content Collection data for recent publications (since 2012). This article aims to explore the intricate landscape of antibacterial research while reviewing the advancement from traditional antibiotics to novel and emerging antibacterial strategies. By delving into the resistance mechanisms, this paper highlights the need to find alternate strategies to address the growing concern.

Emerging treatment options for skin and soft tissue infections tailoring drug selection to individual patients

PURPOSE OF REVIEW

To provide a brief overview of drugs in Phase II and III of development for the treatment of acute bacterial skin and skin structure infections (ABSSSI), offering insights into potential customized treatment options.

RECENT FINDINGS

Several drugs are currently in advanced stages of evaluation for the treatment of ABSSSI, and numerous molecules are entering in the early development phases. Notably, many of these drugs exhibit unique mechanisms of action and interesting antimicrobial spectrum.

SUMMARY

Tailoring antibiotic therapy based on patient characteristics, likely pathogens, type, site and severity of ABSSSI is crucial. Given the inherent limitations of available treatments, the development of novel agents is a pivotal avenue. Such advancements hold promise for enhancing treatment efficacy and simplifying drug selection for ABSSSI in everyday clinical practice.

Design, Synthesis, and Biological Evaluation of 5-(5-Iodo-2-isopropyl-4-methoxyphenoxy)pyrimidine-2,4-diamine (AF-353) Derivatives as Novel DHFR Inhibitors against Staphylococcus aureus

The high lethality of Staphylococcus aureus infections and the emergence of antibiotic resistance make the development of new antibiotics urgent. Our previous work identified a hit compound h1 (AF-353) as a novel Mycobacterium tuberculosis (Mtb) dihydrofolate reductase (DHFR) inhibitor. Herein, we analyzed the antimicrobial profile of h1 and performed a comprehensive structure-activity relationship (SAR) assay based on h1. The representative compound j9 exhibited potent antibacterial activity against S. aureus without cross-resistance to other antimicrobial classes. Multiple genetic and biochemical approaches showed that j9 directly binds to SaDHFR, resulting in strong inhibition of its enzymatic activity (IC50 = 0.97 nM). Additionally, j9 had an acceptable in vivo safety profile and oral bioavailability (F = 40.7%) and also showed favorable efficacy in a mouse model of methicillin-resistant S. aureus (MRSA) skin infection. Collectively, these findings identified j9 as a novel SaDHFR inhibitor with the potential to combat drug-resistant S. aureus infections.

Pharmacological validation of dihydrofolate reductase as a drug target in Mycobacterium abscessus

The Mycobacterium abscessus drug development pipeline is poorly populated, with particularly few validated target-lead couples to initiate de novo drug discovery. Trimethoprim, an inhibitor of dihydrofolate reductase (DHFR) used for the treatment of a range of bacterial infections, is not active against M. abscessus. Thus, evidence that M. abscessus DHFR is vulnerable to pharmacological intervention with a small molecule inhibitor is lacking. Here, we show that the pyrrolo-quinazoline PQD-1, previously identified as a DHFR inhibitor active against Mycobacterium tuberculosis, exerts whole cell activity against M. abscessus. Enzyme inhibition studies showed that PQD-1, in contrast to trimethoprim, is a potent inhibitor of M. abscessus DHFR and over-expression of DHFR causes resistance to PQD-1, providing biochemical and genetic evidence that DHFR is a vulnerable target and mediates PQD-1's growth inhibitory activity in M. abscessus. As observed in M. tuberculosis, PQD-1 resistant mutations mapped to the folate pathway enzyme thymidylate synthase (TYMS) ThyA. Like trimethoprim in other bacteria, PQD-1 synergizes with the dihydropteroate synthase (DHPS) inhibitor sulfamethoxazole (SMX), offering an opportunity to exploit the successful dual inhibition of the folate pathway and develop similarly potent combinations against M. abscessus. PQD-1 is active against subspecies of M. abscessus and a panel of clinical isolates, providing epidemiological validation of the target-lead couple. Leveraging a series of PQD-1 analogs, we have demonstrated a dynamic structure-activity relationship (SAR). Collectively, the results identify M. abscessus DHFR as an attractive target and PQD-1 as a chemical starting point for the discovery of novel drugs and drug combinations that target the folate pathway in M. abscessus.

Efficacy and Safety of Iclaprim for the Treatment of Skin Structures and Soft Tissue Infections: A Methodological Framework

Background: Skin and soft tissue infections (SSTIs) are among the most common infections worldwide. They manifest in a variety of forms, such as erysipelas, cellulitis, and necrotizing fasciitis. Antibiotics are the significant method for clinical treatment of SSTIs. This study reported a methodology framework to determine the efficacy and safety of iclaprim in treatment of SSTIs.

Methods: We will search the PubMed, EMbase, CNKI, WanFang Data, VIP, and ClinicalTrials.gov from their inception to June 2022 for randomized controlled trials and cohort studies on iclaprim with SSTIs. Two authors will independently screen the eligible studies, assess the quality of the included papers, and extract the required information. Randomized controlled trials will be assessed using the Cochrane risk-of-bias tool. The Newcastle–Ottawa Scale will be used to evaluate observational studies. The quality of the evidence will be evaluated using the Grading of Recommendations Assessment Development and Evaluation system. RevMan 5.3 will be used for the data synthesis and quantitative analysis.

Results and Discussions: This study will provide the clinicians with more high-quality evidence to choose iclaprim for patients with SSTIs.

Ethics and Dissemination: This systematic review and meta-analysis will be based on published data, so ethical approval is not necessary. The results of this meta-analysis will be published in a peer-reviewed journal.

Antivitamins: A Silver Lining in the Era of Antimicrobial Resistance

Antivitamins are compounds that negate the biological effects of vitamins. They have been successfully exploited for the development of various classes of drugs. In the early 19th century, the antifolate prontosil was developed for the treatment of puerperal fever. Since then, numerous other antifolates have been used to treat a wide range of infections. Antifolates, such as methotrexate, are potent anticancer agents and antivitamin K, such as warfarin, are used as anticoagulants. Despite several years of research, most antivitamin-based drugs are limited to vitamin K and B9, and the development of antagonists for other vitamins is still in the nascent stage. In the era of antimicrobial resistance, antivitamins can be considered as a promising alternative to develop newer antimicrobials and are worth exploring further. This review discusses key antivitamins at different stages of development which have potential utility as antibiotic drug candidates. The summary of studies of antivitamins in clinical development is also narrated.

New Antibiotics for Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) represent one of the most common hospital-acquired infections, carrying a significant morbidity and risk of mortality. Increasing antibiotic resistance among the common bacterial pathogens associated with HAP and VAP, especially Enterobacterales and nonfermenting gram-negative bacteria, has made the choice of empiric treatment of these infections increasingly challenging. Moreover, failure of initial empiric therapy to cover the causative agents associated with HAP and VAP has been associated with worse clinical outcomes. This review provides an overview of antibiotics newly approved or in development for the treatment of HAP and VAP. The approved antibiotics include ceftobiprole, ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, and cefiderocol. Their major advantages include their high activity against multidrug-resistant gram-negative pathogens.

Iclaprim reduces the incidence and severity of Staphylococcus aureus-induced septic arthritis in a murine model

Staphylococcus aureus is the most common non-gonococcal aetiology of septic arthritis. The efficacy of iclaprim against S. aureus LS-1, a clinical strain identified from a patient with septic arthritis, was studied in MF1 mice to evaluate the activity of iclaprim, which is in clinical development, in preventing joint infections. Iclaprim (2.5–80 mg kg⁻¹) administered as a single dose via the tail vein reduced the incidence of S. aureus septic arthritis and mortality in an experimental murine model of septic arthritis.

Inhibitor design to target a unique feature in the folate pocket of Staphylococcus aureus dihydrofolate reductase

Staphylococcus aureus (Sa) is a serious concern due to increasing resistance to antibiotics. The bacterial dihydrofolate reductase enzyme is effectively inhibited by trimethoprim, a compound with antibacterial activity. Previously, we reported a trimethoprim derivative containing an acryloyl linker and a dihydophthalazine moiety demonstrating increased potency against S. aureus. We have expanded this series and assessed in vitro enzyme inhibition (K_i) and whole cell growth inhibition properties (MIC). Modifications were focused at a chiral carbon within the phthalazine heterocycle, as well as simultaneous modification at positions on the dihydrophthalazine. MIC values increased from 0.0626-0.5 μg/mL into the 0.5-1 μg/mL range when the edge positions were modified with either methyl or methoxy groups. Changes at the chiral carbon affected K_i measurements but with little impact on MIC values. Our structural data revealed accommodation of predominantly the S-enantiomer of the inhibitors within the folate-binding pocket. Longer modifications at the chiral carbon, such as p-methylbenzyl, protrude from the pocket into solvent and result in poorer K_i values, as do modifications with greater torsional freedom, such as 1-ethylpropyl. The most efficacious K_i was 0.7 ± 0.3 nM, obtained with a cyclopropyl derivative containing dimethoxy modifications at the dihydrophthalazine edge. The co-crystal structure revealed an alternative placement of the phthalazine moiety into a shallow surface at the edge of the site that can accommodate either enantiomer of the inhibitor. The current design, therefore, highlights how to engineer specific placement of the inhibitor within this alternative pocket, which in turn maximizes the enzyme inhibitory properties of racemic mixtures.

Folic Acid Antagonists: Antimicrobial and Immunomodulating Mechanisms and Applications

: Bacterial, protozoan and other microbial infections share an accelerated metabolic rate. In order to ensure a proper functioning of cell replication and proteins and nucleic acids synthesis processes, folate metabolism rate is also increased in these cases. For this reason, folic acid antagonists have been used since their discovery to treat different kinds of microbial infections, taking advantage of this metabolic difference when compared with human cells. However, resistances to these compounds have emerged since then and only combined therapies are currently used in clinic. In addition, some of these compounds have been found to have an immunomodulatory behavior that allows clinicians using them as anti-inflammatory or immunosuppressive drugs. Therefore, the aim of this review is to provide an updated state-of-the-art on the use of antifolates as antibacterial and immunomodulating agents in the clinical setting, as well as to present their action mechanisms and currently investigated biomedical applications.