Noncovalent Tripeptidyl Benzyl- and Cyclohexyl-Amine Inhibitors of the Cysteine Protease Caspase-1

Interleukin-1β converting enzyme (ICE): A comprehensive review on discovery and development of caspase-1 inhibitors

Caspase-1 is a critical mediator of the inflammatory process by activating various pro-inflammatory cytokines such as pro-IL-1β, IL-18 and IL-33. Uncontrolled activation of caspase-1 leads to various cytokines-mediated diseases. Thus, inhibition of Caspase-1 is considered therapeutically beneficial to halt the progression of such diseases. Currently, rilonacept, canakinumab and anakinra are in use for caspase-1-mediated autoinflammatory diseases. However, the poor pharmacokinetic profile of these peptides limits their use as therapeutic agents. Therefore, several peptidomimetic inhibitors have been developed, but only a few compounds (VX-740, VX-765) have advanced to clinical trials; because of their toxic profile. Several small molecule inhibitors have also been progressing based on the three-dimensional structure of caspase-1. However there is no successful candidate available clinically. In this perspective, we highlight the mechanism of caspase-1 activation, its therapeutic potential as a disease target and potential therapeutic strategies targeting caspase-1 with their limitations.

Tripeptide analogues of MG132 as protease inhibitors

The 26S proteasome and calpain are linked to a number of important human diseases. Here, we report a series of analogues of the prototypical tripeptide aldehyde inhibitor MG132 that show a unique combination of high activity and selectivity for calpains over proteasome. Tripeptide aldehydes (1-3) with an aromatic P3 substituent show enhanced activity and selectivity against ovine calpain 2 relative to chymotrypsin-like activity of proteasome. Docking studies reveal the key contacts between inhibitors and calpain to confirm the importance of the S3 pocket with respect to selectivity between calpains 1 and 2 and the proteasome.

Preferred Hydrogen-Bonding Partners of Cysteine: Implications for Regulating Cys Functions

The hydrogen-bonding interactions of cysteine, which can serve as a hydrogen-bond donor and/or acceptor, play a central role in cysteine's diverse functional roles in proteins. They affect the balance between the neutral thiol (SH) or thiolate (S^-) and the charge distribution in the rate-limiting transition state of a reaction. Despite their importance, no study has determined the preferred hydrogen-bonding partners of cysteine serving as a hydrogen-bond donor or acceptor. By computing the free energy for displacing a peptide backbone hydrogen-bonded to cysteine with amino acid side chains in various protein environments, we have evaluated how the strength of the hydrogen bond to the cysteine thiol/thiolate depends on its hydrogen-bonding partner and its local environment. The predicted hydrogen-bonding partners preferred by cysteine are consistent with the hydrogen-bonding interactions made by cysteines in 9138 nonredundant X-ray structures. Our results suggest a mechanism to regulate the reactivity of cysteines and a strategy to design drugs based on the hydrogen-bonding preference of cysteine.

Small Molecule Active Site Directed Tools for Studying Human Caspases

Caspases are proteases of clan CD and were described for the first time more than two decades ago. They play critical roles in the control of regulated cell death pathways including apoptosis and inflammation. Due to their involvement in the development of various diseases like cancer, neurodegenerative diseases, or autoimmune disorders, caspases have been intensively investigated as potential drug targets, both in academic and industrial laboratories. This review presents a thorough, deep, and systematic assessment of all technologies developed over the years for the investigation of caspase activity and specificity using substrates and inhibitors, as well as activity based probes, which in recent years have attracted considerable interest due to their usefulness in the investigation of biological functions of this family of enzymes.

New β-strand templates constrained by Huisgen cycloaddition

New peptidic templates constrained into a β-strand geometry by linking acetylene and azide containing P(1) and P(3) residues of a tripeptide by Huisgen cycloaddition are presented. The conformations of the macrocycles are defined by NMR studies and those that best define a β-strand are shown to be potent inhibitors of the protease calpain. The β-strand templates presented and defined here are prepared under optimized conditions that should be suitable for targeting a range of proteases and other applications requiring such a geometry.