Targeting the Pseudomonas aeruginosa quorum sensing system to inhibit virulence factors and eradicate biofilm formation using AHL-analogue phytochemicals

Targeting quorum sensing in Pseudomonas aeruginosa with high-affinity inhibitors: A high-throughput screening and in-silico analysis

Pseudomonas aeruginosa is a major pathogen in clinical settings, notorious for its intrinsic resistance to multiple antibiotics and ability to form biofilms, therefore, complicating treatment. This study reporting the results of a high-throughput screen of an antibacterial library targeting LasR, a key QS regulator in P. aeruginosa MB638, isolated from an infected surgical implant. The species identity was confirmed as P. aeruginosa via 16S rDNA analysis (accession number MT643188). The strain demonstrated strong biofilm formation and multidrug resistance, along with significant production of the quorum sensing signalling molecule N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL). We screened a ∼1400-compound library and identified inhibitors compounds that surpass the binding affinity of LasR's native ligand. The ADMET analysis revealed that among these, compounds Inh-1, Inh-2 and Inh-3 demonstrated favourable absorption, permeability and broader bioactivity profiles. Inh-1 exhibited a suitable profile, being non-toxic, non-hepatotoxic, and non-mutagenic, with low carcinogenic and immunotoxin potential. Molecular docking studies using GLIDE identified key binding interactions and residues within the LasR ligand-binding domain (LBD), with Inh-1, Inh-2 and Inh-3 showing the highest binding affinities and favourable docking scores of -14.587, -13.645 and -12.967, respectively. Structural Interaction Molecular dynamics simulation at 100 ns showed Inh-1 maintained stable hydrophobic and hydrophilic contacts within the active site. RMSD analysis confirmed the stability of the Inh-1 complex, while RMSF indicated conformational adaptability. Inh-1 stands out as promising lead for LasR inhibition, warranting further experimental study. These inhibitors hold promise for disrupting quorum sensing in P. aeruginosa and may serve as potential therapeutic agent against resistant infections.

Discovery of quorum sensing inhibitors against Pseudomonas aeruginosa from Aspergillus sp. NB12

Twelve secondary metabolites, including two undescribed steroids, aspesterols A (1) and B (2) and three new triterpenoids, aspertrinoids A-C (5-7), were isolated from the endophytic fungus Aspergillus sp. NB12 obtained from Hypericum patulum. Structurally, aspertrinoids A-C (5-7) were 30-norlanostane triterpenoids with a C9 side-chain moiety and a hemiacetal moiety formed between C-3 and C-19. Their structures were determined through NMR, HRESIMS, X-ray diffraction analyses, and ECD calculations. The activity screening suggested that aspesterols A (1) and B (2) act as quorum sensing inhibitors against Pseudomonas aeruginosa and they not only reduce the mutation frequency of carbapenem-resistant P. aeruginosa but also avoid the development of bacterial drug resistance. It is worth noting that 1 and 2 demonstrated synergy with imipenem at a concentration of 12.5 μM (24 h). Thus, compounds 1 and 2 are potential compounds for dealing with carbapenem-resistant Pseudomonas aeruginosa.

A Systematic Hierarchical Virtual Screening Model for RhlR Inhibitors Based on PCA, Pharmacophore, Docking, and Molecular Dynamics

RhlR plays a key role in the quorum sensing of Pseudomonas aeruginosa. The current structure-activity relationship (SAR) studies of RhlR inhibitors mainly focus on elucidating the functional groups. Based on a systematic review of previous research on RhlR inhibitors, this study aims to establish a systematic, hierarchical screening model for RhlR inhibitors. We initially established a database and utilized principal component analysis (PCA) to categorize the inhibitors into two classes. Based on the training set, pharmacophore models were established to elucidate the structural characteristics of ligands. Subsequently, molecular docking, molecular dynamics simulations, and the calculation of binding free energy and strain energy were performed to validate the crucial interactions between ligands and receptors. Then, the screening criteria for RhlR inhibitors were established hierarchically based on ligand structure characteristics, ligand-receptor interaction, and receptor affinity. Test sets were finally employed to validate the hierarchical virtual screening model by comparing it with the current SAR studies of RhlR inhibitors. The hierarchical screening model was confirmed to possess higher accuracy and a true positive rate, which holds promise for subsequent screening and the discovery of active RhlR inhibitors.

Biofilm formation: mechanistic insights and therapeutic targets

Biofilms are complex multicellular communities formed by bacteria, and their extracellular polymeric substances are observed as surface-attached or non-surface-attached aggregates. Many types of bacterial species found in living hosts or environments can form biofilms. These include pathogenic bacteria such as Pseudomonas, which can act as persistent infectious hosts and are responsible for a wide range of chronic diseases as well as the emergence of antibiotic resistance, thereby making them difficult to eliminate. Pseudomonas aeruginosa has emerged as a model organism for studying biofilm formation. In addition, other Pseudomonas utilize biofilm formation in plant colonization and environmental persistence. Biofilms are effective in aiding bacterial colonization, enhancing bacterial resistance to antimicrobial substances and host immune responses, and facilitating cell‒cell signalling exchanges between community bacteria. The lack of antibiotics targeting biofilms in the drug discovery process indicates the need to design new biofilm inhibitors as antimicrobial drugs using various strategies and targeting different stages of biofilm formation. Growing strategies that have been developed to combat biofilm formation include targeting bacterial enzymes, as well as those involved in the quorum sensing and adhesion pathways. In this review, with Pseudomonas as the primary subject of study, we review and discuss the mechanisms of bacterial biofilm formation and current therapeutic approaches, emphasizing the clinical issues associated with biofilm infections and focusing on current and emerging antibiotic biofilm strategies.