Relacatib (SB-462795) is a novel, potent, and orally active inhibitor of human cathepsins K, L, and V. It exhibits high affinity for these enzymes, with Ki values of 41 pM, 68 pM, and 53 pM, respectively. Moreover, Relacatib effectively inhibits endogenous cathepsin K in situ in human osteoclasts, as well as human osteoclast-mediated bone resorption, with IC 50 values of 45 nM and 70 nM, respectively. Additionally, in vitro studies demonstrate Relacatib's inhibitory effect on bone resorption in human tissue, while in vivo studies on cynomolgus monkeys further validate its efficacy in reducing bone resorption.