γ-glutamyl transpeptidase activatable NIR photosensitizer for visualization and selective killing of liver cancer cells

Photodynamic therapy (PDT) is a treatment model that involves using light sources to excite photosensitizers (PSs), generating reactive oxygen species. This method is considered a potential treatment for tumors. However, the non-selective toxicity of traditional PSs to both tumors and normal tissues hinders the advancement of PDT. This lack of selectivity is a major obstacle in the development of effective PDT. The activatable PS can only function in a specific environment, which enhances the selectivity and safety of PDT. In this paper, we focus on GGT (γ-glutamyltranspeptidase) overexpressed in liver cancer as the biological target. We designed and synthesized the activatable PS BrCy-Glu by modifying the substrate of GGT (l-glutamic acid) onto the brominated hemicyanine PS (BrCy-OH). The intramolecular charge transfer (ICT) effect of BrCy-Glu is inhibited, which leads to low fluorescence quantum yield and singlet oxygen yield. However, in the presence of GGT, it can undergo selective hydrolysis and be converted into BrCy-OH through a series of elimination reactions. This process is accompanied by a significant increase in fluorescence quantum yield and singlet oxygen yield. In vitro studies demonstrate that BrCy-Glu is suitable for precise fluorescence identification of liver cancer and selective eradication of cancer cells under light conditions.