Scientists Find New Chemical Leads That Disarm a Deadly Hospital Superbug

Pseudomonas aeruginosa has long been one of the most feared residents of hospital wards, a Gram-negative bacterium that thrives in clinical settings and ranks high on the World Health Organization’s 2024 Bacterial Priority Pathogen List as a high-burden resistant pathogen. Its talent for rapidly evolving resistance to nearly every antibiotic thrown at it has left clinicians with dwindling options, particularly for immunocompromised patients. Now, a team of researchers in India has taken aim not at the bacterium’s survival, but at its ability to cause disease, identifying two promising small-molecule candidates that could open a new front in the war against multidrug-resistant infections.

The study, published in Discover Chemistry, focused on an enzyme called phospholipase A1, or PlaF, a membrane-bound virulence factor first characterized in P. aeruginosa by Bleffert and colleagues in 2022. PlaF sits embedded in the cytoplasmic membrane, where it remodels glycerophospholipids through the so-called Lands cycle, generating medium-chain fatty acids that alter the biophysical properties of the bacterial membrane and regulate signaling cascades. This remodeling allows the pathogen to adapt to nutrient limitation, stress, and host-mediated attacks, and it coordinates iron acquisition through the pyoverdine pathway, a key element of virulence. Crucially, infection models have shown that bacteria lacking PlaF display dramatically reduced virulence without any change in growth kinetics, meaning the enzyme acts as a regulator of pathogenesis rather than a survival determinant.

That distinction matters enormously for drug design. Traditional antibiotics exert strong selective pressure by killing bacteria or halting their growth, which inevitably breeds resistance. Anti-virulence strategies, by contrast, aim to disarm the pathogen while leaving it metabolically viable, theoretically reducing the evolutionary incentive to develop resistance. PlaF also offers a structural advantage for selective targeting: although it shares the classical alpha/beta-hydrolase fold and the conserved Ser-His-Asp catalytic triad with human ABHD6, showing 27 percent sequence identity and 49 percent similarity, its membrane-associated substrate-access tunnels and a unique dimerization-dependent regulatory mechanism diverge substantially from the human enzyme. Recent work confirming that repurposed human phospholipase inhibitors such as GW4869 can sensitize P. aeruginosa to imipenem in a PlaF-dependent manner validated the enzyme as druggable, but those existing inhibitors are bulky, lipophilic molecules designed for mammalian systems, not optimized for bacterial membrane penetration or tunnel-specific engagement.

To fill that gap, the researchers assembled a library of 114 small molecules spanning seven chemical classes, drawn from their previous work on anticancer and anti-tuberculosis compounds, on the rationale that serine hydrolase inhibitors often exhibit cross-domain activity. The collection included thiophene-2-carboxamides, methyl 4-(4-amidoaryl)-3-methoxythiophene-2-carboxylates, urea and thiourea bearing thiophene derivatives, pyrimidine-5-carboxamides, triazinyl carboxamides, thienopyrimidine ureas, and pyrrolopyridine carboxamides. Using the crystal structure of PlaF available in the Protein Data Bank under the identifier 6I8W, the team deployed the Schrodinger Suite to prepare ligands with the OPLS4 force field, generate ionization states and tautomers with Epik, and filter candidates through Lipinski’s rule of five using the QikProp module. One hundred seven compounds survived drug-likeness screening and advanced to molecular docking.

The docking campaign used Glide’s extra precision protocol, ranking compounds by binding affinity and prioritizing those with scores of −6.0 kcal/mol or better. Subsequent MM/GBSA free energy calculations, which combine molecular mechanics energies with solvation models, flagged compounds with binding free energies of −50 kcal/mol or lower. Standouts emerged across the series: compound F11 from the thienopyrimidine class achieved an MM/GBSA score of −56.72 kcal/mol, while D17 from the pyrimidine carboxamides posted the highest binding free energy of the entire screen at −67.22 kcal/mol, attributed to robust halogen bonding. Structural interaction fingerprint analysis then converted residue-level contacts into comparable binary codes, revealing a consistent pharmacophoric pattern across high performers: roughly seven to ten hydrophobic contacts, three to four aromatic stacking interactions with residues such as PHE174 and TYR236, and limited but strategic hydrogen bonding with ARG233 or LEU232. Notably, compounds with excessive polar substitution or bulky aromatic expansion increased total contact counts without improving predicted stability, indicating that geometric complementarity within the narrow substrate-access tunnel matters more than interaction density.

The team then moved from computation to the bench, testing all 107 drug-like compounds against P. aeruginosa strain ATCC 27853 using a micro broth dilution assay with resazurin dye as a viability indicator, with ciprofloxacin as a positive control at a measured MIC of 0.25 micrograms per milliliter. Several compounds showed measurable activity, with minimum inhibitory concentrations of 100 to 200 micrograms per milliliter: B4 and B5 from the methoxythiophene series, C2 from the urea-thiourea thiophenes, D6 and D7 from the pyrimidine carboxamides, E6 and E8 from the triazines, F4 from the thienopyrimidines, and G2, G3, G11, and G16 from the pyrrolopyridines. While these MIC values are far weaker than conventional antibiotics, the researchers emphasize that PlaF inhibition is an anti-virulence strategy, so modest growth inhibition is expected and does not negate mechanistic relevance.

To probe how ligands would fare against a shifting target, the investigators engineered point mutations that replaced residues lining the T2 substrate-access tunnel—Asp74, Arg217, Ala218, Ala221, and Asn225—with bulky tryptophan, physically constricting the passage. Docking against these mutants confirmed the T2 tunnel as the principal route for ligand binding and revealed that some mutations actually enhanced affinity for certain scaffolds. Compounds D6 and E6 achieved improved docking scores of −10.55 and −9.38 kcal/mol against the TRP74 and TRP217 variants, while others, such as G16 against the TRP218 mutant, suffered sharp losses in binding, likely from steric clashes. The mutational blueprint suggests that halogenated, aromatic, and amide-bearing scaffolds capable of diverse non-covalent interactions are best positioned to remain effective even if the tunnel architecture shifts.

Molecular dynamics simulations provided the final filter. Each of fourteen protein-ligand complexes, embedded in a POPC lipid bilayer with explicit water and physiological salt, was simulated for 100 nanoseconds under semi-isotropic pressure coupling appropriate for membrane proteins. Six compounds—A3, B4, C2, D6, E6, and F4—maintained backbone RMSD values between 1.5 and 2.8 angstroms, preserved tunnel architecture, and showed restricted ligand mobility throughout the trajectory, outperforming even ciprofloxacin, which drifted beyond 4.5 angstroms in later simulation stages. Radius of gyration, solvent-accessible surface area, molecular surface area, and polar surface area analyses all confirmed that these six ligands kept the tunnel compact and the catalytic electrostatic environment stable, both in the wild-type enzyme and in the more permissive Ala218Trp and Ala221Trp mutant backgrounds.

Toxicity predictions from the ProTox 3.0 server, which applies machine-learning models across 61 toxicity endpoints, narrowed the field further. Compounds A3, D6, E6, and F4 fell into toxicity class 4, with predicted oral LD50 values between 1000 and 1502 milligrams per kilogram and flagged respiratory, immunotoxic, and neurotoxic endpoints. Compounds B4, a methyl 3-methoxythiophene derivative bearing a fluorinated benzamido group, and C2, a thioureido-substituted compound, landed in the more favorable class 5, with predicted LD50 values of 4000 and 4500 milligrams per kilogram respectively, though mild hepatotoxicity risk means neither can be considered non-toxic pending experimental validation. The authors are careful to note that computational binding stability does not guarantee whole-cell target engagement, and that efflux pumps may limit intracellular concentrations. Future work, they argue, should include biochemical PlaF inhibition assays, lipidomic confirmation that glycerophospholipid remodeling is disrupted, complementation studies with the delta-plaF mutant to verify target engagement, and in vivo infection models. If those steps succeed, B4 and C2 could seed a genuinely novel class of anti-virulence agents—one that fights the superbug by stripping away its weapons rather than threatening its life, and in doing so may sidestep the resistance cycle that has defeated so many antibiotics before.

Subject of Research: Structure-based discovery of inhibitors targeting the phospholipase A1 virulence factor of Pseudomonas aeruginosa

Article Title: Structure-based discovery of phospholipase A1 (PlaF) inhibitors in Pseudomonas aeruginosa using integrated in silico and experimental approaches

Article References: Vemula, D., Gulipalli, K. C., Bodige, S., Seelam, N., & Bhandari, V. (2026). Structure-based discovery of phospholipase A1 (PlaF) inhibitors in Pseudomonas aeruginosa using integrated in silico and experimental approaches. Discover Chemistry, 3(1), Article 457. https://doi.org/10.1007/s44371-026-00802-6

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00802-6

Keywords: Pseudomonas aeruginosa, phospholipase A1, PlaF, anti-virulence, antimicrobial resistance, molecular docking, molecular dynamics, virtual screening, drug discovery, MM/GBSA, virulence factor, computer-aided drug design