Cathepsin

Cathepsin inhibitors act on lysosomal proteases, mainly the papain-like cysteine cathepsins B, C, K, L and S. Cysteine cathepsins degrade proteins in the endolysosomal system and, after secretion, also remodel the extracellular matrix. In 1996 loss of cathepsin K was shown to cause pycnodysostosis, a lysosomal disease with dense, brittle bones. Cathepsin K is the main collagen-degrading protease of osteoclasts, which makes it a target in bone resorption studies. Odanacatib and balicatib inhibit cathepsin K, petesicatib targets cathepsin S, and CA-074 is selective for cathepsin B. CA-074 methyl ester is a membrane-permeable form for work in intact cells. Gly-Phe-beta-naphthylamide, a cathepsin C substrate, is used to rupture lysosomes in live cells.