Cathepsin S inhibitors: 2004-2010.

INTRODUCTION: Cathepsin S, a lysosomal cysteine protease, plays an important role in antigen presentation. Its inhibition is expected to result in immunosuppression, making this enzyme an attractive target to potentially treat autoimmune and inflammatory diseases. AREAS COVERED: The focus of this review is on patent literature regarding small molecule inhibitors of cathepsin S published from 2004 to April 2010. Different structure classes based on binding strategies (covalent vs non-covalent) are surveyed and listed according to warhead type and research organization. EXPERT OPINION: Although > 40 patent applications have appeared between 2004 and 2010, the decrease in applications focusing on cathepsin S over the past 2 - 3 years may reflect a renewed interest in other cathepsins, especially cathepsin K, for which a small molecule inhibitor is currently in Phase III clinical trials.