Structural Optimization of Fibroblast Activation Protein Inhibitors Through Zwitterionic and PEG Modification Strategy: Impact on Pharmacokinetics and Tumor Imaging
Hongmei Yuan, Haiyang Li, Tongtong Wu, Sufan Tang, Yinwen Wang, Zhicong Yang, Yang Liu, Wenlu Zheng, Nan Liu, Yue Chen, Zhijun Zhou
Abstract
Fibroblast activation protein (FAP), highly overexpressed in cancer-associated fibroblasts (CAFs), is crucial in tumor pathogenesis and progression, making it an important target for diagnosis and therapy. This study presents the design of a series of FAP inhibitors (FAPIs) derived from UAMC-1110 derivative, modified with zwitterions and polyethylene glycol (PEG). The novel 68 Ga-labeled tracers show improved pharmacokinetics compared to 68 Ga-FAPI-04. Small animal positron emission tomography/computed tomography (micro-PET/CT) on U87MG tumor-bearing nude mice revealed that 68 Ga-FAPI-BN-1, incorporating boron trifluoride zwitterion, and 68 Ga-FAPI-P8PN, with phosphate zwitterion and PEG8 modifications, demonstrated high tumor uptake and minimal normal tissue uptake. Biodistribution studies confirmed their excellent tumor accumulation and tumor-to-normal tissue ratios (T/NT). Specifically, 68 Ga-FAPI-BN-1 exhibited a tumor uptake of 49.31 ± 2.76%ID/g at 1 h, with a tumor/muscle ratio of 24, while 68 Ga-FAPI-P8PN showed a tumor uptake of 42.19 ± 3.21% ID/g at 0.5 h, with a tumor/muscle ratio of 23. These results indicate that these tracers hold promise as effective molecular imaging agents targeting FAP.