Cathepsin Inhibitor 1 (CTS-IN-1) is a novel and potent inhibitor of Cathepsin (L, L2, S, K, B) with the potential to be used in the treatment of osteoarthritis. It inhibits Cathepsin (L, L2, S, K, B) with pIC50 values of 7.9, 6.7, 6.0, 5.5 and 5.2, respectively. Osteoarthritis is currently recognized as a chronic degenerative disease, which is caused by the loss of articular cartilage and damage to underlying bone, resulting in joint instability and pain. The lysosomal cysteine protease2 Cathepsin L (CatL) is found to be a potential target for intervention in treatment of osteoarthritis. After secreted into the extracellular matrix, CatL can degrade proteoglycans such as aggrecan4 and type II collagen, which are the major components of articular cartilage.