Synthesis and Preclinical Evaluation of a Novel FAPI-04 Dimer for Cancer Theranostics.

Overexpression of fibroblast activation protein (FAP) in cancer-associated fibroblasts in a wide variety of tumors enables a highly selective targeting strategy using FAP inhibitors (FAPIs). Quinoline-based FAPIs labeled with radionuclides have been widely developed for tumor-targeted nuclear medicine imaging. However, the short retention time of FAPIs at the tumor site limits their application in radionuclide therapy. In this study, a novel FAPI-04 dimer was synthesized and labeled with radionuclides to prolong the retention time in tumors for imaging and therapy. To prepare the FAPI-04 dimer complex, DOTA-Suc-Lys-(FAPI-04), we used Fmoc-Lys(Boc)-OH as the linker to conjugate two FAPI-04 structures by an amide reaction. The resulting product was further modified by DOTA groups to allow for conjugation with radioactive metals. Both [Ga]Ga-(FAPI-04) and [Lu]Lu-(FAPI-04) showed a radiochemical purity of >99% and remained stable . , micro-PET images of SKOV3, A431, and H1299 xenografts revealed that the tumor uptake of [Ga]Ga-(FAPI-04) was about twice that of [Ga]Ga-FAPI-04 and that the accumulation of [Ga]Ga-(FAPI-04) at the tumor site did not significantly decrease even 3h after injection. The tumor-abdomen ratio of [Ga]Ga-(FAPI-04) images was significantly higher than that of [F]F-FDG images. For radionuclide therapy, [Lu]Lu-(FAPI-04) effectively retarded tumor growth and displayed good tolerance. In conclusion, the DOTA-Suc-Lys-(FAPI-04) design enhanced its uptake in FAP-expressing tumors, improved its retention time at the tumor site, and produced high-contrast imaging in xenografts after radionuclide labeling. Furthermore, it showed a noticeable antitumor effect. DOTA-Suc-Lys-(FAPI-04) provides a new approach for applying FAPI derivatives in tumor theranostics.