Identification of novel molecules supporting the impact of β-lactams against clinically-relevant Gram-negativemultidrug resistant organisms

Antimicrobial resistance spread represents an enormous global health crisis. Particularly worrying are multidrug-resistant Gram-negative (MDR-GN) bacteria, for whom few therapeutic options are available: β-lactams represent frontline antibiotics but resistance towards them is widespread. To limit the impact of this largely unmet medical need, we aim at discovering novel antibiotic adjuvants to be used in combination with β- lactams against MDR-GN bacteria. To achieve this purpose, we first selected five clinically-relevant models of β-lactam resistance in MDR-GN. Then, we proceeded with the high-throughput biological activity-guided screening of a filamentous actinomycetes/fungi-based microbial library (containing 39,000 crude extracts) and of a chemical library (with 9,000 pure compounds) to identify molecules able to restore the activity of β-lactams against the selected resistant isolates. No HITs were identified from the screening of the chemical library, while >200 putative HITs were discovered from the microbial extract library. From them, an activity-guided purification process allowed us to isolate 22 bioactive compounds, which underwent chemical and biological characterization to proceed with dereplication and novelty evaluation. Preliminary data collected attributed the observed bioactivities mostly to metal chelating agents (e.g., gobichelin, 2N-methylcoprogen, coprogen). In the next months, a further characterization of the molecules will be conducted, to better define their mode of action by in vitro and in silico tests, to evaluate their activity on a wider panel of MDR-GN clinicalnisolates, and to assess their cytotoxicity on different eukaryotic cells, ultimately paving the way for their possible preclinical development and future medical use.