Definition

A cysteine cathepsin-cleavable near infrared (NIR) substrate probe, that may be used for cancer imaging purposes using an NIR imaging system. In 6QC-NIR, the cathepsin-activatable fluorescent probe contains the NIR fluorophore, Dylight 780-B1, 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 cathepsins overexpressed by tumor cells and highly abundant in the tumor microenvironment (TME). Upon cleavage, the quencher is released, the fluorophore becomes activated and accumulates in the lysosome. Upon fluorescence imaging, using the da Vinci Si surgical system, tumor cells expressing cathepsin family proteases can be detected which allows for visualization of the tumor.