Definition

A fluorescently quenched, cysteine cathepsin-cleavable near infrared (NIR) substrate probe containing the dye indocyanine green (ICG), that may be used for cancer imaging purposes using an NIR imaging system. In 6QC-NIR, the cathepsin-activatable fluorescent probe contains the fluorophore, ICG, linked, via a cathepsin protease cleavable peptide, with a core Cbz-Phe-Lys peptide sequence, to a fluorescent quencher, QC-1. Upon administration of 6QC-NIR, the amide bond of the peptide can be cleaved by cathepsin proteases overexpressed by tumor cells and highly abundant in the tumor microenvironment (TME). Upon proteolysis, the quencher is released, the fluorophore becomes activated and accumulates in the lysosome. Upon clinical NIR imaging, using the da Vinci Si surgical system, tumor cells expressing cathepsin family proteases can be detected which allows for visualization of the tumor.