Rational Design and Pharmacomodulation of ¹⁸F-Labeled Biotin/FAPI-Conjugated Heterodimers

Due to the complex heterogeneity in different cancer types, the heterodimeric strategy has been intensively practiced to improve the effectiveness of tumor diagnostics. In this study, we developed a series of novel ¹⁸F-labeled biotin/FAPI-conjugated heterobivalent radioligands ([¹⁸F]AlF-NSFB, [¹⁸F]AlF-NSFBP₂, and [¹⁸F]AlF-NSFBP₄), synergistically targeting both fibroblast activation protein (FAP) and biotin receptor (BR), to enhance specific tumor uptake and retention. The in vitro and in vivo biological properties of these dual-targeting tracers were evaluated, with a particular focus on positron emission tomography imaging in A549 and HT1080-FAP tumor-bearing mice. Notably, in comparison to the corresponding FAP-targeted monomer [¹⁸F]AlF-NSF, biotin/FAPI-conjugated heterodimers exhibited a high uptake in tumor and prolong retention. In conclusion, as a proof-of-concept study, the findings validated the superiority of biotin/FAPI-conjugated heterodimers and the positive influence of biotin and linker on pharmacokinetics of radioligands. Within them, the bispecific [¹⁸F]AlF-NSFBP₄ holds significant promise as a candidate for further clinical translational studies.