TP0586532, a Novel Non-Hydroxamate LpxC Inhibitor: Potentiating Effect on In Vitro Activity of Meropenem against Carbapenem-Resistant Enterobacteriaceae

Research progress of LpxC inhibitor on Gram-negative bacteria

UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC) is a metalloprotein that utilizes zinc as a cofactor. LpxC plays a crucial role in catalyzing the synthesis of Lipid A, a major component of the outer membrane lipopolysaccharide in Gram-negative (G-) bacteria, and LpxC shares no common amino acid sequence with various mammalian enzyme proteins. LpxC is essential for the survival of Gram-negative bacteria, making it a promising target for the antibacterial drug development. In recent years, numerous LpxC inhibitors have been reported, which can be broadly categorized into hydroxamic acid and non-hydroxamic acid based on their structural characteristics. Although no LpxC inhibitors are currently available on the market, several candidate small molecules are anticipated to enter clinical trials. The current manuscript offers a comprehensive review of the structures, enzyme catalytic mechanisms, and research progress of novel LpxC inhibitors, with the objective of providing insights and directions for future research in the development of LpxC inhibitors as new antibacterial agents.

Modulating the biosynthesis and TLR4-interaction of lipopolysaccharide as an approach to counter gut dysbiosis and Parkinson's disease: Role of phyto-compounds

The prevalence of the world's second leading neurodegenerative disorder Parkinson's disease (PD) is well known while its pathogenesis is still a topical issue to explore. Clinical and experimental reports suggest the prevalence of disturbed gut microflora in PD subjects, with an abundance of especially Gram-negative bacteria. The endotoxin lipopolysaccharide (LPS) released from the outer cell layer of these bacteria interacts with the toll-like receptor 4 (TLR4) present on the macrophages and it stimulates the downstream inflammatory cascade in both the gut and brain. Recent research also suggests a positive correlation between LPS, alpha-synuclein, and TLR4 levels, which indicates the contribution of a parallel LPS-alpha-synuclein-TLR4 axis in stimulating inflammation and neurodegeneration in the gut and brain, establishing a body-first type of PD. However, owing to the novelty of this paradigm, further investigation is mandatory. Modulating LPS biosynthesis and LPS-TLR4 interaction can ameliorate gut dysbiosis and PD. Several synthetic LpxC (UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase; LPS-synthesizing enzyme) inhibitors and TLR4 antagonists are reported to show beneficial effects including neuroprotection in PD models, however, are not devoid of side effects. Plant-derived compounds have been long documented for their benefits as nutraceuticals and thus to search for effective, safer, and multitarget therapeutics, the present study focused on summarizing the evidence reporting the potential of phyto-compounds as LpxC inhibitors and TLR4 antagonists. Studies demonstrating the dual potential of phyto-compounds as the modulators of LpxC and TLR4 have not yet been reported. Also, very few preliminary studies have reported LpxC inhibition by phyto-compounds. Nevertheless, remarkable neuroprotection along with TLR4 antagonism has been shown by curcumin and juglanin in PD models. The present review thus provides a wide look at the research progressed to date in discovering phyto-compounds that can serve as LpxC inhibitors and TLR4 antagonists. The study further recommends the need for expanding the search for potential candidates that can render dual protection by inhibiting both the biosynthesis and TLR4 interaction of LPS. Such multitarget therapeutic intervention is believed to bring fruitful yields in countering gut dysbiosis, neuroinflammation, and dopaminergic neuron damage in PD patients through a single treatment paradigm.

LpxC inhibition: Potential and opportunities with carbohydrate scaffolds

Uridine diphosphate-3-O-(hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a key enzyme involved in the biosynthesis of lipid A, an essential building block, for the construction and assembly of the outer membrane (OM) of Gram-negative bacteria. The enzyme is highly conserved in almost all Gram-negative bacteria and hence has emerged as a promising target for drug discovery in the fight against multi-drug resistant Gram-negative infections. Since the first nanomolar LpxC inhibitor, L-161,240, an oxazoline-based hydroxamate, the two-decade-long ongoing search has provided valuable information regarding essential features necessary for inhibition. Although the design and structure optimization for arriving at the most efficacious inhibitor of this enzyme has made good use of different heterocyclic moieties, the use of carbohydrate scaffold is scant. This review briefly covers the advancement and progress made in LpxC inhibition. The field awaits the use of potential associated with carbohydrate-based scaffolds for LpxC inhibition and the discovery of anti-bacterial agents against Gram-negative infections.

Unrealized targets in the discovery of antibiotics for Gram-negative bacterial infections

Advances in areas that include genomics, systems biology, protein structure determination and artificial intelligence provide new opportunities for target-based antibacterial drug discovery. The selection of a 'good' new target for direct-acting antibacterial compounds is the first decision, for which multiple criteria must be explored, integrated and re-evaluated as drug discovery programmes progress. Criteria include essentiality of the target for bacterial survival, its conservation across different strains of the same species, bacterial species and growth conditions (which determines the spectrum of activity of a potential antibiotic) and the level of homology with human genes (which influences the potential for selective inhibition). Additionally, a bacterial target should have the potential to bind to drug-like molecules, and its subcellular location will govern the need for inhibitors to penetrate one or two bacterial membranes, which is a key challenge in targeting Gram-negative bacteria. The risk of the emergence of target-based drug resistance for drugs with single targets also requires consideration. This Review describes promising but as-yet-unrealized targets for antibacterial drugs against Gram-negative bacteria and examples of cognate inhibitors, and highlights lessons learned from past drug discovery programmes.

Making a chink in their armor: Current and next-generation antimicrobial strategies against the bacterial cell envelope

Gram-negative bacteria are uniquely equipped to defeat antibiotics. Their outermost layer, the cell envelope, is a natural permeability barrier that contains an array of resistance proteins capable of neutralizing most existing antimicrobials. As a result, its presence creates a major obstacle for the treatment of resistant infections and for the development of new antibiotics. Despite this seemingly impenetrable armor, in-depth understanding of the cell envelope, including structural, functional and systems biology insights, has promoted efforts to target it that can ultimately lead to the generation of new antibacterial therapies. In this article, we broadly overview the biology of the cell envelope and highlight attempts and successes in generating inhibitors that impair its function or biogenesis. We argue that the very structure that has hampered antibiotic discovery for decades has untapped potential for the design of novel next-generation therapeutics against bacterial pathogens.

Bacterial Zinc Metalloenzyme Inhibitors: Recent Advances and Future Perspectives

Human deaths caused by Gram-negative bacteria keep rising due to the multidrug resistance (MDR) phenomenon. Therefore, it is a priority to develop novel antibiotics with different mechanisms of action. Several bacterial zinc metalloenzymes are becoming attractive targets since they do not show any similarities with the human endogenous zinc-metalloproteinases. In the last decades, there has been an increasing interest from both industry and academia in developing new inhibitors against those enzymes involved in lipid A biosynthesis, and bacteria nutrition and sporulation, e.g., UDP-[3-O-(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC), thermolysin (TLN), and pseudolysin (PLN). Nevertheless, targeting these bacterial enzymes is harder than expected and the lack of good clinical candidates suggests that more effort is needed. This review gives an overview of bacterial zinc metalloenzyme inhibitors that have been synthesized so far, highlighting the structural features essential for inhibitory activity and the structure-activity relationships. Our discussion may stimulate and help further studies on bacterial zinc metalloenzyme inhibitors as possible novel antibacterial drugs.

Small molecule LpxC inhibitors against gram-negative bacteria: Advances and future perspectives

Uridine diphosphate-3-O-(hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a metalloenzyme with zinc ions as cofactors and is a key enzyme in the essential structural outer membrane lipid A synthesis commitment step of gram-negative bacteria. As LpxC is extremely homologous among different Gram-negative bacteria, it is conserved in almost all gram-negative bacteria, which makes LpxC a promising target. LpxC inhibitors have been reported extensively in recent years, such as PF-5081090 and CHIR-090 were found to have broad-spectrum antibiotic activity against P. aeruginosa and E. coli. They are mainly classified into hydroxamate inhibitors and non-hydroxamate inhibitors based on their structure, but no LpxC inhibitors have been marketed due to safety and activity issues. This review, therefore, focuses on small molecule inhibitors of LpxC against gram-negative pathogenic bacteria and covers recent advances in LpxC inhibitors, focusing on their structural optimization process, structure-activity relationships, and future directions, with the aim of providing ideas for the development of LpxC inhibitors and clinical research.