Controlled Inhibition of Apoptosis by Photoactivatable Caspase Inhibitors.

Caspases control regulated cell death (apoptosis), a process that is crucial in the development of multicellular organisms as well as in various diseases. In order to spatiotemporally study apoptosis, we here develop photoactivatable caspase inhibitors. These are based on cysteine-reactive acyloxymethyl ketone electrophiles connected to a peptide targeting caspases. Importantly, the aspartate crucial for recognition by caspases is caged with a photoprotecting group. Ester photocages were found to be labile, and it was critical to have a nitroindoline cage, which forms a stable amide bond with the aspartate side chain. The nitroindoline-protected inhibitors lead to an efficient turn-on of inhibitory activity after irradiation with light. They are applicable in live cells, where they prevent anti-FAS-induced apoptosis only upon irradiation. Overall, these reagents will allow a better understanding of the spatial and temporal dimensions of apoptosis in complex, dynamic systems.