Quorum Sensing Inhibitors as Pathoblockers for Pseudomonas aeruginosa Infections: A New Concept in Anti-Infective Drug Discovery

Synthetic approach to 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides based on common β-keto amide precursors

β-Keto amides were used as convenient precursors to both 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides. The utility of this approach is demonstrated with the synthesis of fourteen novel and four known quinolone derivatives, including natural products of microbial origin such as HHQ and its C5-congener. Two compounds with high activity against S. aureus have been identified among the newly obtained quinolones, with MICs ≤ 3.12 and ≤ 6.25 µg/mL, respectively.

Identification of anti-pathogenic activity among in silico predicted small-molecule inhibitors of Pseudomonas aeruginosa LasR or nitric oxide reductase (NOR)

Introduction

Antibiotic-resistant Pseudomonas aeruginosa strains cause considerable morbidity and mortality globally. Identification of novel targets in this notorious pathogen is urgently warranted to facilitate discovery of new anti-pathogenic agents against it. This study attempted to identify small-molecule inhibitors of two important proteins LasR and nitric oxide reductase (NOR) in P. aeruginosa. 'Las' system can be said to be the 'master' regulator of quorum sensing in P. aeruginosa, whose receptor protein is LasR. Similarly, NOR is crucial to detoxification of reactive nitrogen species.

Methods

In silico identification of potential LasR or NOR inhibitors was attempted through a virtual screening platform AtomNet® to obtain a final subset of <100 top scoring compounds. These compounds were evaluated for their in vivo anti-pathogenic activity by challenging the model host Caenorhabditis elegans with P. aeruginosa in the presence or absence of test compounds. Survival of the worm population in 24-well assay plates was monitored over a period of 5 days microscopically.

Results

Of the 96 predicted LasR inhibitors, 11 exhibited anti-Pseudomonas activity (23%-96% inhibition of bacterial virulence as per third-day end-point) at 25-50 µg/mL. Of the 85 predicted NOR inhibitors, 8 exhibited anti-Pseudomonas activity (40%-85% inhibition of bacterial virulence as per second-day end-point) at 25-50 µg/mL.

Conclusion

Further investigation on molecular mode of action of compounds found active in this study is warranted. Virtual screening can be said to be a useful tool in narrowing down the list of compounds requiring actual wet-lab screening, saving considerable time and efforts for drug discovery.

Rational Drug Design for Pseudomonas aeruginosa PqsA Enzyme: An in silico Guided Study to Block Biofilm Formation

Pseudomonas aeruginosa is an opportunistic gram-negative bacterium implicated in acute and chronic nosocomial infections and a leading cause of patient mortality. Such infections occur owing to biofilm formation that confers multidrug resistance and enhanced pathogenesis to the bacterium. In this study, we used a rational drug design strategy to inhibit the quorum signaling system of P. aeruginosa by designing potent inhibitory lead molecules against anthranilate-CoA ligase enzyme encoded by the pqsA gene. This enzyme produces autoinducers for cell-to-cell communication, which result in biofilm formation, and thus plays a pivotal role in the virulence of P. aeruginosa. A library of potential drug molecules was prepared by performing ligand-based screening using an available set of enzyme inhibitors. Subsequently, structure-based virtual screening was performed to identify compounds showing the best binding conformation with the target enzyme and forming a stable complex. The two hit compounds interact with the binding site of the enzyme through multiple short-range hydrophilic and hydrophobic interactions. Molecular dynamic simulation and MM-PBSA/GBSA results to calculate the affinity and stability of the hit compounds with the PqsA enzyme further confirmed their strong interactions. The hit compounds might be useful in tackling the resistant phenotypes of this pathogen.

Anti-infective efficacy of Psidium guajava L. leaves against certain pathogenic bacteria

Water extracts of Psidium guajava leaves prepared by three different extraction methods were compared with respect to their anti-infective activity against Pseudomonas aeruginosa and Staphylococcus aureus in the nematode host Caenorhabditis elegans. The water extract prepared by Microwave Assisted Extraction method was found to have better anti-infective activity, and its activity was further compared with hydroalcoholic extract prepared using the same extraction method against five different pathogenic bacteria. Both these extracts could attenuate virulence of P. aeruginosa, S. aureus, Serratia marcescens, and Chromobacterium violaceum, towards C. elegans. Anti-infective efficacy of P. guajava leaf extract seems partly to stem from its quorum-modulatory property, as it could modulate production of quorum sensing-regulated pigments in all the susceptible bacteria.

Anti-infective efficacy of Psidium guajava L. leaves against certain pathogenic bacteria

Water extracts of Psidium guajava leaves prepared by three different extraction methods were compared with respect to their anti-infective activity against Pseudomonas aeruginosa and Staphylococcus aureus in the nematode host Caenorhabditis elegans. The water extract prepared by Microwave Assisted Extraction method was found to have better anti-infective activity, and its activity was further compared with hydroalcoholic extract prepared using the same extraction method against five different pathogenic bacteria. Both these extracts could attenuate virulence of P. aeruginosa, S. aureus, Serratia marcescens, and Chromobacterium violaceum, towards C. elegans. Anti-infective efficacy of P. guajava leaf extract seems partly to stem from its quorum-modulatory property, as it could modulate production of quorum sensing-regulated pigments in all the susceptible bacteria.

Pseudomonas aeruginosa Quorum Sensing Systems as Drug Discovery Targets: Current Position and Future Perspectives

Antimicrobial resistance (AMR) is a serious threat to public health globally, manifested by the frequent emergence of multidrug resistant pathogens that render current chemotherapy inadequate. Health organizations worldwide have recognized the severity of this crisis and implemented action plans to contain its adverse consequences and prolong the utility of conventional antibiotics. Hence, there is a pressing need for new classes of antibacterial agents with novel modes of action. Quorum sensing (QS), a communication system employed by bacterial populations to coordinate virulence gene expression, is a potential target that has been intensively investigated over the past decade. This Perspective will focus on recent advances in targeting the three main quorum sensing systems ( las, rhl, and pqs) of a major opportunistic human pathogen, Pseudomonas aeruginosa, and will specifically evaluate the medicinal chemistry strategies devised to develop QS inhibitors from a drug discovery perspective.