Carbobenzoxy-Capped Phe-Lys(BODIPY TMR-X-Acyloxymethyl Ketone(QSY7)

The document discussed the development and application of near-infrared fluorescent activity-based probes (NIRF-ABPs) for imaging cysteine protease activity, particularly in the context of disease diagnosis and therapeutic testing. These probes, synthesized by Blum et al., were designed to target cysteine cathepsins, which are involved in various physiological processes and diseases. The study highlighted the advantages of quenched ABPs, such as GB117, which become fluorescent upon binding with an enzyme, allowing for earlier imaging of protease activity compared to substrate-based methods. Despite challenges in imaging specific locations due to high cathepsin activity in large organs, these probes were found to be nontoxic, water-soluble, and valuable for preclinical and clinical testing. The synthesis and analysis of quenched GB117 were compared with the nonquenched GB111, marking the first generation of these imaging agents.