Advanced Resistance Studies Identify Two Discrete Mechanisms in Staphylococcus aureus to Overcome Antibacterial Compounds that Target Biotin Protein Ligase

Fighting Antimicrobial Resistance: Innovative Drugs in Antibacterial Research

In the fight against bacterial infections, particularly those caused by multi-resistant pathogens known as "superbugs", the need for new antibacterials is undoubted in scientific communities and is by now also widely perceived by the general population. However, the antibacterial research landscape has changed considerably over the past years. With few exceptions, the majority of big pharma companies has left the field and thus, the decline in R&D on antibacterials severely impacts the drug pipeline. In recent years, antibacterial research has increasingly relied on smaller companies or academic research institutions, which mostly have only limited financial resources, to carry a drug discovery and development process from the beginning and through to the beginning of clinical phases. This review formulates the requirements for an antibacterial in regard of targeted pathogens, resistance mechanisms and drug discovery. Strategies are shown for the discovery of new antibacterial structures originating from natural sources, by chemical synthesis and more recently from artificial intelligence approaches. This is complemented by principles for the computer-aided design of antibacterials and the refinement of a lead structure. The second part of the article comprises a compilation of antibacterial molecules classified according to bacterial target structures, e.g. cell wall synthesis, protein synthesis, as well as more recently emerging target classes, e.g. fatty acid synthesis, proteases and membrane proteins. Aspects of the origin, the antibacterial spectrum, resistance and the current development status of the presented drug molecules are highlighted.

New Potent Sulfonamide-Based Inhibitors of S. aureus Biotin Protein Ligase

The key regulatory metabolic enzyme, biotin protein ligase (BPL), is an attractive target for the development of novel antibiotics against multi-drug-resistant bacteria, such as Staphylococcus aureus. Here we report the synthesis and assay of a new series of inhibitors (6-9) against S. aureus BPL (SaBPL), where a component sulfonamide linker was used to mimic the acyl-phosphate group of the natural intermediate biotinyl-5'-AMP (1). A pivotal correlation between the acidity of the central NH of the sulfonamide linker of 6-9 and in vitro inhibitory activity against SaBPL was observed. Specifically, sulfonylcarbamate 8, with its highly acidic sulfonyl central NH, as evaluated by 1H NMR spectroscopy, showed exceptional potency (K i = 10.3 ± 3.8 nM). Furthermore, three inhibitors demonstrated minimum inhibitory concentrations of 16-32 μg/mL against clinical methicillin-resistant S. aureus (MRSA) strains.

Layered Black Phosphorus Nanoflakes Reduce Bacterial Burden and Enhance Healing of Murine Infected Wounds

Current treatment modalities of cutaneous wound infections are largely ineffective, attributed to the increasing burden of antimicrobial resistance. S. aureus, a commonly wound‐associated pathogen continues to pose a clinical challenge, suggesting that new alternative therapeutic materials are urgently required to provide optimal treatment. A layered allotrope of phosphorus termed Black Phosphorus nanoflakes (BPNFs) has emerged as a potential alternative antibacterial material. However, wider deployment of this material requires extensive biological validation using the latest pre‐clinical models to understand its role in wound management. Here, the antibacterial potential of BPNFs against wound pathogens demonstrates over 99% killing efficiency at ambient conditions, while remaining non‐toxic to mammalian skin cells. In addition, in vivo validation of BPNFs using a preclinical model of S. aureus acute wound infection demonstrates that daily topical application significantly reduces infection (3‐log reduction) comparable to ciprofloxacin antibiotic control. Furthermore, the application of BPNFs also accelerates wound closure, increases wound re‐epithelization, and reduces tissue inflammation compared to controls, suggesting a potential role in alleviating the current challenges of infected cutaneous wounds. For the first time, this study demonstrates the potential role of BPNFs in ambient light conditions for clearing a clinically relevant wound infection with favorable wound healing properties.

A New 1,2,3-Triazole Scaffold with Improved Potency against Staphylococcus aureus Biotin Protein Ligase

Staphylococcus aureus, a key ESKAPE bacteria, is responsible for most blood-based infections and, as a result, is a major economic healthcare burden requiring urgent attention. Here, we report in silico docking, synthesis, and assay of N1-diphenylmethyl triazole-based analogues (7-13) designed to interact with the entire binding site of S. aureus biotin protein ligase (SaBPL), an enzyme critical for the regulation of gluconeogenesis and fatty acid biosynthesis. The second aryl ring of these compounds enhances both SaBPL potency and whole cell activity against S. aureus relative to previously reported mono-benzyl triazoles. Analogues 12 and 13, with added substituents to better interact with the adenine binding site, are particularly potent, with K_i values of 6.01 ± 1.01 and 8.43 ± 0.73 nM, respectively. These analogues are the most active triazole-based inhibitors reported to date and, importantly, inhibit the growth of a clinical isolate strain of S. aureus ATCC 49775, with minimum inhibitory concentrations of 1 and 8 μg/mL, respectively.

Biochemical characterisation of class III biotin protein ligases from Botrytis cinerea and Zymoseptoria tritici

Biotin protein ligase (BPL) is an essential enzyme in all kingdoms of life, making it a potential target for novel anti-infective agents. Whilst bacteria and archaea have simple BPL structures (class I and II), the homologues from certain eukaryotes such as mammals, insects and yeast (class III) have evolved a more complex structure with a large extension on the N-terminus of the protein in addition to the conserved catalytic domain. The absence of atomic resolution structures of any class III BPL hinders structural and functional analysis of these enzymes. Here, two new class III BPLs from agriculturally important moulds Botrytis cinerea and Zymoseptoria tritici were characterised alongside the homologue from the prototypical yeast Saccharomyces cerevisiae. Circular dichroism and ion mobility-mass spectrometry analysis revealed conservation of the overall tertiary and secondary structures of all three BPLs, corresponding with the high sequence similarity. Subtle structural differences were implied by the different thermal stabilities of the enzymes and their varied Michaelis constants for their interactions with ligands biotin, MgATP, and biotin-accepting substrates from different species. The three BPLs displayed different preferences for fungal versus bacterial protein substrates, providing further evidence that class III BPLs have a 'substrate validation' activity for selecting only appropriate proteins for biotinylation. Selective, potent inhibition of these three BPLs was demonstrated despite sequence and structural homology. This highlights the potential for targeting BPL for novel, selective antifungal therapies against B. cinerea, Z. tritici and other fungal species.