Revolutionizing Solid Tumor Surgery with Fibroblast Activation Protein (FAP)-Targeted Imaging Probes for a Fluorescence-Guided Surgery of Pancreatic Cancer

The development of fluorescent probes that target the tumor stroma to help surgeons detect and remove malignant lesions using near-infrared fluorescence (NIRF)-guided surgery is advancing rapidly. Such advancements show promise for a range of malignancies, expanding the eligibility of patients for surgical intervention and offering improved surgical outcomes. Fibroblast activation protein (FAP), expressed by cancer-associated fibroblasts (CAFs), is highly upregulated within the tumor stroma of nearly all solid tumors. It is a promising tumor target for NIRF-guided surgery, especially in solid tumors with dense tumor stroma, such as pancreatic cancer. In this study, we aimed to develop FAP-targeting fluorescent probes with enhanced pharmacokinetics for the NIRF-guided surgery of pancreatic cancer. Three novel FAP-targeted probes (eFAPs) based on a (4-quinolinoyl)-glycyl-2-cyanopyrrolidine (QCP) structure equipped with the NIRF dye IRDye800CW were designed and synthesized. All of the probes displayed excellent inhibition potency and selectivity to FAP. The probes consistently exhibited strong inhibition and specific uptake in FAP-expressing U87 glioblastoma cells. In in vivo optical imaging studies, eFAP-24 showed a tumor-to-background ratio (TBR) of 3.1 ± 0.6 at 24 h postinjection, enabling the clear delineation of tumors using the clinical Quest Spectrum NIRF imaging system. A strong fluorescence signal in the tumor and a negligible uptake in nontarget tissues were confirmed by biodistribution analyses. The successful development and validation of FAP-targeting fluorescent probes, especially eFAP-24, offers promising prospects for enhancing the visualization of FAP-rich stromal compartments improving surgical outcomes through NIRF-guided surgery, particularly in solid tumors with dense stroma such as pancreatic cancer.