PAC-1 and isatin derivatives are weak matrix metalloproteinase inhibitors

Dysregulation of apoptotic cell death is observed in a large number of pathological conditions. As caspases are central enzymes in the regulation of apoptosis, a large number of procaspase-activating compounds (PAC-1 derivatives) and inhibitors (isatin derivatives) have been developed. Matrix metalloproteinases (MMPs) have been shown to have a dual role in apoptosis. Hence compounds that either activate or inhibit caspases should ideally not affect MMPs. As many PAC-1 derivatives contain a zinc chelating ortho-hydroxy N-acyl hydrazone moiety and isatin derivatives has two carbonyl groups on the indole core, it was of interest to determine to which extent these compounds can inhibit MMPs.

Eight PAC-1 and five isatin derivatives were docked into MMP-9 and MMP-14. The same compounds were synthesized, characterized, purified and tested as inhibitors of MMP-9 and MMP-14, using fluorescence quenched peptide and biological substrates. Some of the compounds were also tested for fluorescence quenching.

Molecular docking suggested that the different compounds can bind to the MMP active sites. However, kinetic studies showed that neither of these compounds was a strong MMP inhibitor. IC50 values over 100μM were obtained after the enzyme activities were corrected for quenching. These IC50 values are far above the concentrations needed to activate or inhibit the caspases.

The use of PAC-1 and isatin derivatives against caspases should have little or no effect on the activity of MMPs.

Activators and inhibitors of caspases are important potential therapeutic agents for several diseases such as cancer, diabetes and neurodegenerative disorders.