A Near-Infrared Off-On Fluorescent Probe for Sensitive and Specific Imaging of Fibroblast Activation Protein-α Activity in Pancreatic Cancer.

Fibroblast activation protein-α (FAP-α) is a crucial biomarker for pancreatic cancer, yet developing activatable near-infrared (NIR) fluorescent probes for its real-time imaging faces challenges in achieving high signal-to-background ratios and specificity. Here, we present ZGP-D, a novel FAP-α-activated NIR probe designed to overcome these limitations. ZGP-D integrates a DDAO fluorophore with a FAP-α-specific Cbz-Gly-Pro peptide, creating an efficient intramolecular charge transfer (ICT) quenching mechanism that ensures a minimal background signal. Upon specific enzymatic cleavage by FAP-α, the probe exhibits a robust > 40-fold fluorescence turn-on at 657 nm, demonstrating exceptional sensitivity with a detection limit of 0.024 μg/mL and superior selectivity over various biological interferents. ZGP-D successfully visualized endogenous FAP-α in living cells, clearly distinguishing high-expression pancreatic cancer cells (BXPC-3) from low-expression cells. Furthermore, in a BXPC-3 xenograft mouse model, local administration of ZGP-D enabled high-contrast tumor imaging, achieving a tumor-to-normal tissue signal ratio of 4.2. This work establishes ZGP-D as a highly sensitive and specific molecular tool for monitoring FAP-α activity, highlighting its significant potential for advancing cancer diagnostics and fluorescence-guided surgery.