Balicatib(AAE-581) is a potent and selective inhibitor of cathepsin K; 10-100 fold more potent in cell-based enzyme occupancy assays than against cathepsin B, L, and S. IC50 value: Target: cathepsin K The cathepsin K inhibitor AAE-581 (balicatib) as the most advanced of them passed Phase II clinical trials in 2005. Eighty adult female Macaca fascicularis underwent bilateral ovariectomies and were dosed twice daily by oral gavage with balicatib at 0, 3, 10, and 50 mg/kg for 18 months (groups O, L, M, H, respectively). Approximately 1 month after treatment initiation, the 50 mg/kg dose was decreased to 30 mg/kg. Twenty animals underwent sham-ovariectomies (group S). Bone mass was measured at 3-6 month intervals. At 18 months, vertebra and femur were collected for histomorphometry.