Screening for caspase-3 inhibitors: a new class of potent small-molecule inhibitors of caspase-3.

From the authors' 650,000 compound collection, they have selected approximately 15,000 potential small-molecule protease inhibitors, which were subjected to high-throughput screening against caspase-3. The screening yielded a series of hits that belong to 11 different scaffolds. Based on the structure of one of the hits, a new class of the small-molecule inhibitors with a double electrophilic warhead, 8-sulfonyl-pyrrolo[3,4-c]quinoline-1,3-diones (SPQ), was synthesized and tested in follow-up mechanistic and anti-apoptosis assays. Mechanistic analysis of a representative compound of this class, CD-001-0011, showed that the compound exhibited a high potency (IC (50)=130 nM), was reversible though noncompetitive, and had a broad selectivity profile to other caspases belonging to groups I to III. The compound was effective in preventing staurosporine induced apoptosis in a few cell lines and retinoic acid-induced apoptosis in zebrafish.