Category: Assay Development and Screening
The aim of this project is the identification and optimization of new small molecules drugs against Hemolysin-α (HIa), a pore-forming toxin and the most prominent virulence factor of Staphylococcus aureus (S. aureus), causing tissue damage and inactivation of immune cells particularly in lung infections. HIa inhibition follows the “pathoblocker concept” by ameliorating/blocking severe pathophysiological HIa effects of a S. aureus infection while not killing the pathogen.
A strategy towards hit identification, validation and lead nomination was developed and implemented. A High Throughput Screen (Fluo4-based Ca2+ influx assay in human U937 leukocyte cell line; 182,122 compounds) was established and performed, followed by hit confirmation and validation studies in secondary assays (hemolysis of rabbit erythrocytes, LDH based cytotoxicity on human airway epithelial cell line A549, Ca2+ influx and cytotoxicity in human primary NK cells). After chemical filtering and clustering 91 primary hits were confirmed with a cellular IC50 value below 10 µM. Five validated hit classes were selected as starting point for generation of initial structure-activity relationship (SAR) and assessment of early ADME characteristics. Based on these results two hit classes were selected for further hit to lead optimization.
In both classes a set of compounds with cellular anti HIa activities below 100 nM has been generated. These were profiled in vitro regarding physicochemical and pharmacological properties. For these hit series the cellular primary and secondary assay results correlated well.
Optimized hits were selected based on the favourable in vitro profile to be tested in vivo in pharmacokinetic/tolerability studies in mice. The compounds were well tolerated thus confirming the in vitro cytotoxicity data.
This promising new approach could open the route to a new and alternative treatment option to combat S. aureus infections in combination with standard antibiotics. This could complement and/or improve currently available strategies and overcome their limitations.
Carsten Degenhart– Scientist, Lead Discovery Center GmbH, Dortmund, Nordrhein-Westfalen, Germany