Identification and Evaluation of Small Molecule Pan-Caspase Inhibitors in Huntington's Disease Models

Abstract

SUMMARY Huntington’s Disease (HD) is characterized by a mutation in the huntingtin gene encoding an expansion of glutamine repeats on the N-terminus of the huntingtin (Htt) protein. Numerous studies have identified Htt proteolysis as a critical pathological event in post mortem human tissue and mouse HD models, and proteases known as caspases have emerged as attractive HD targets. We report the use of the substrate activity screening method against caspases-3 and -6 to identify three novel, pan-caspase inhibitors that block proteolysis of Htt at caspase-3 and -6 cleavage sites. In HD models, these irreversible inhibitors suppressed Hdh111Q/111Q-mediated toxicity and rescued rat striatal and cortical neurons from cell death. In this study the identified nonpeptidic caspase inhibitors were used to confirm the role of caspase-mediated Htt proteolysis in HD. These results further implicate caspases as promising targets for HD therapeutic development.

Inhibition of Lipid Signaling Enzyme Diacylglycerol Kinase ϵ Attenuates Mutant Huntingtin Toxicity

“…1). As reported previously, serum withdrawal results in a dramatic increase in caspase activity in Hdh 111Q/111Q when compared with Hdh 7Q/7Q cells (13,17). We found several inhibitors that reduce caspase-3/7 activity when Hdh 111Q/111Q cells undergo serum withdrawal.…”

Mechanistic and Structural Understanding of Uncompetitive Inhibitors of Caspase-6

“…To address these challenges, a number of alternative chemical approaches have been used. Leyva, et al, recently disclosed the design of novel, nonpeptidic inhibitors identified through “substrate assisted screening”; while potent, these compounds are non-selective and still contain an irreversible covalent warhead [16]. There has also been significant interest in developing noncompetitive or allosteric inhibitors, with the idea that non-active site binding could achieve greater selectivity and improved physicochemical properties over competitive inhibitors [17], [18].…”

A Multipronged Approach for Compiling a Global Map of Allosteric Regulation in the Apoptotic Caspases

“…This suggests that different substrates interact uniquely with caspase-6. Two active-site tetra-fluorophenoxymethyl inhibitors with extremely similar biochemical inhibition of caspase-3 and caspase-6 also show very different inhibition of cleavage of mutant huntingtin protein intracellularly (Leyva, et al, 2010), further underscoring this idea. Together these observations and data that will be described below suggest that inhibitors that function at different caspase allosteric sites should yield different cellular outcomes, which should prove to be therapeutically useful.…”