DESIGN OF POTENT AND SELECTIVE HUMAN CATHEPSIN-K INHIBITORS THAT SPANTHE ACTIVE-SITE

Potent and selective active-site-spanning inhibitors have been designe d for cathepsin K, a cysteine protease unique to osteoclasts. They act by mechanisms that involve tight binding intermediates, potentially o n a hydrolytic pathway. X-ray crystallographic, MS, NMR spectroscopic, and kinetic studies of the mechanisms of inhibition indicate that dif ferent intermediates or transition states are being represented that a re dependent on the conditions of measurement and the specific groups flanking the carbonyl in the inhibitor. The species observed crystallo graphically are most consistent with tetrahedral intermediates that ma y be close approximations of those that occur during substrate hydroly sis. Initial kinetic studies suggest the possibility of irreversible a nd reversible active-site modification. Representative inhibitors have demonstrated antiresorptive activity both in vitro and in vivo and th erefore are promising leads for therapeutic agents for the treatment o f osteoporosis. Expansion of these inhibitor concepts can be envisione d for the many other cysteine proteases implicated for therapeutic int ervention.