Research progress of radioprobes targeting fibroblast activating protein

Fibroblast activating protein (FAP) is an important biomarker of cancer associated fibroblasts and activated fibroblasts, which is highly expressed in activated fibroblasts of many tumor and fibrotic tissues, but not in normal tissues and non malignant lesions. Therefore, FAP has become an excellent target for diagnosis and treatment of tumors and other diseases. PET imaging and internal radiotherapy based on FAP inhibitor (FAPI) have been used in the diagnosis and treatment of many diseases, such as cancer and fibrosis. We first introduce the mechanism of disease occurrence and progression mediated by FAP and its clinical significance as a therapeutic target.Then,we systematically summarize the FAP probes labeled with ¹²⁵I, ⁶⁸Ga, ⁶⁴Cu and other radionuclides, including their structural evolution, imaging, biodistribution and pharmacokinetic properties.After that, the reported strategies to improve the pharmacokinetic properties and target affinity of probes are summarized, including the use of squaramide linkers,modification with albumin binding agent,the development of dual-targeting probes.Finally, some suggestions for the future development of novel radioactive probes targeting FAP and the clinical application of classical probes are proposed.