New Non-Saccharide Heparin Mimetics as Inhibitors of Cathepsin G

Cathepsin G (CatG), a neutrophil serine protease, plays several roles in host defense, inflammation, and vascular pathology. Selective inhibition of CatG is therefore a compelling therapeutic strategy, yet existing inhibitors such as sulfated saccharides are limited by structural heterogeneity, instability, and bleeding risk. In this study, sulfonated non-saccharide heparin mimetics were explored as a new class of CatG inhibitors with improved stability and drug-like properties. A focused library of derivatives was screened, and several candidates demonstrated potent inhibition, with the most active compound (inhibitor 7) achieving complete CatG inhibition at nanomolar concentrations (IC₅₀ = 86 nM). Inhibitor 7 exhibited remarkable selectivity over clotting factors, digestive enzymes, and related proteases, effectively protected extracellular matrix proteins from CatG-mediated degradation, and neither prolonged plasma clotting times nor induced cytotoxicity at tested levels. Mechanistic studies revealed an allosteric mode of action, whereby inhibitor 7 bound to a distinct anion-binding site on CatG, inducing local conformational changes that disrupted catalysis without affecting substrate recognition. Structural advantages of sulfonated scaffolds, including chemical stability, resistance to enzymatic cleavage, and synthetic accessibility, make them better than sulfated mimetics for long-term development. These findings identify sulfonated heparin mimetics, particularly inhibitor 7, as promising allosteric inhibitors of CatG with potential for safe and selective therapeutic application in vascular and inflammatory disorders.