Muco-obstructive lung diseases feature extensive
bronchiectasis due to the uncontrolled release of
neutrophil serine proteases into the airways. To assess if
cathepsin G (CG) is a novel key player in chronic lung
inflammation, we developed membrane-bound (mSAM) and
soluble (sSAM) FRET reporters. The probes quantitatively
revealed elevated CG activity in samples from 46 patients. For
future basic science and personalized clinical applications, we
developed a rapid, highly informative, and easily translatable
small-molecule FRET flow cytometry assay for monitoring
protease activity including cathepsin G. We demonstrated that
mSAM distinguished healthy from patient cells by FRET-based
flow cytometry with excellent correlation to confocal microscopy data.