A FAP-α-activatable near-infrared theranostic probe for fluorescence imaging of pancreatic cancer and potent in vitro photodynamic activity.

Fibroblast activation protein-alpha (FAP-α), a highly specific biomarker in the tumor microenvironment of pancreatic cancer, is an exceptional target for precision medicine. However, creating a single molecule that integrates both diagnostic and therapeutic functions remains a significant challenge. Herein, we report a novel FAP-α-responsive near-infrared (NIR) theranostic probe, ZGP-LL-ICy. The probe was rationally designed for tumor imaging and phototherapy by conjugating a FAP-α-cleavable peptide to a NIR fluorophore-photosensitizer hybrid (ICyOH) via a self-immolative linker, which effectively quenches its fluorescence and photosensitizing activity. Upon enzymatic cleavage by FAP-α, the probe releases the active payload ICyOH, causing a 27-fold fluorescence enhancement at 710 nm. The probe exhibits high sensitivity with a limit of detection of 0.015 μg/mL and excellent selectivity for FAP-α. Cell-based assays demonstrated that ZGP-LL-ICy not only successfully visualized endogenous FAP-α in pancreatic cancer cells but also exhibited potent, light-induced cytotoxicity through reactive oxygen species (ROS) generation. Furthermore, in a subcutaneous xenograft mouse model, the probe enabled high-contrast in vivo tumor imaging with a tumor-to-normal tissue signal ratio reaching 5.2. This work validates a pro-theranostic design that enables high-fidelity tumor imaging in vivo and demonstrates potent photodynamic efficacy in vitro. While further in vivo therapeutic evaluation is required, this study offers a promising strategy and a valuable molecular tool for the future development of FAP-α-targeted image-guided cancer therapies.