Fu_2023_Bioorg.Chem_141_106878

Fibroblast activation protein (FAP) is a promising molecular target for imaging in various types of cancers. Several (18)F-labeled FAP inhibitor (FAPI) tracers have been evaluated in clinical study. However, these tracers display high physiological uptake in gallbladder and bile duct system. To overcome the limitation, we herein designed a novel radiotracer named (18)F-FAPTG. (18)F-FAPTG was produced with a non-decay-corrected radiochemical yield of 24.0 +/- 6.0% and 22.0 +/- 7.0% for manual and automatic synthesis, respectively. (18)F-FAPTG exhibited high hydrophilicity and stability in vitro. The studies of cellular uptake, internalization, efflux properties and competitive binding to FAP of (18)F-FAPTG indicated that the tracer showed high specificity, rapid internalization and low cellular efflux in FAP-positive cells. Biodistribution studies and microPET in mice bearing FAP-positive xenografts demonstrated extremely low uptake in the majority of other organs and main excretion of (18)F-FAPTG through the urinary system. Furthermore, compared to (18)F-FAPI-42, (18)F-FAPTG showed significantly lower uptake in gallbladder, higher tumor uptake and longer tumor retention. In the pilot clinical study, (18)F-FAPTG PET/CT demonstrated favorable tumor-to-background ratios in most organs and clearly displayed the malignant lesions. Our findings indicated that (18)F-FAPTG had an advantage over (18)F-FAPI-42 in PET imaging for cancers located in gallbladder the bile duct system. Thus, (18)F-FAPTG could be an alternative to the currently available FAPI tracers.