Development of an Assay to Identify Novel Inhibitors of Neutrophil Extracellular Trap Formation (NETosis)

NETosis is a specialized mechanism of cell death, achieved through the formation of neutrophil extracellular traps (NETs). NETs are lattices of extracellular fibers formed from released nuclear chromatin and cellular granular peptides, which can immobilize and destroy invading micro-organisms. However, aberrant formation or accumulation of NETs causes inappropriate activation of the host immune response and can contribute to the pathogenesis of several diseases, including diabetes, rheumatoid arthritis, and COVID-19. 

The development of inhibitors that directly target NETs (e.g. DNase 1) or inhibit upstream activation and signaling events provide an attractive therapeutic approach to alleviate immune-inflammatory disorders. Ongoing commercial activity in this field includes the Phase 1 trial of a first-in-class anti-histone therapeutic CIT-013 (Citryll), and Brensocatib (Insmed Inc.), a DDP-1 inhibitor, undergoing Phase 3 trials for non-cystic fibrosis bronchiectasis.  

A high-throughput compound screening platform was developed at Sygnature to quantify NETosis and differentiate NET formation from other cell death pathways such as apoptosis or necrosis. This was achieved using human primary neutrophils sourced from the in-house blood donor panel, in conjunction with IncuCyte® ZOOM live cell imaging and ImageXpress confocal microscopy platforms. Multiplex cell imaging assays were established to analyze the nuclear and plasma membrane morphology combined with fluorescent tagging of nuclear and extracellular DNA fibers. This approach enabled the quantitative detection of NET formation and the determination of literature inhibitor activity, giving scope for new targeted drug discovery programs. Furthermore, neutrophil reactive oxygen species (ROS) production, an important mediator in the NETosis pathway, was detected using a cytochrome C reduction assay, and inhibited by the MAPK-p38 inhibitor SB203580. To enable higher throughput screening, the NETosis assay was successfully transferred to a differentiated HL-60 human leukocyte cell line, enabling more efficient screening to help identify novel NETosis inhibitors.