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

Abstract

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) 2 , 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 [ 68 Ga]Ga-(FAPI-04) 2 and [ 177 Lu]Lu-(FAPI-04) 2 showed a radiochemical purity of >99% and remained stable in vitro. In vivo, micro-PET images of SKOV3, A431, and H1299 xenografts revealed that the tumor uptake of [ 68 Ga]Ga-(FAPI-04) 2 was about twice that of [ 68 Ga]Ga-FAPI-04 and that the accumulation of [ 68 Ga]Ga-(FAPI-04) 2 at the tumor site did not significantly decrease even 3h after injection. The tumor−abdomen ratio of [ 68 Ga]Ga-(FAPI-04) 2 images was significantly higher than that of [ 18 F]F-FDG images. For radionuclide therapy, [ 177 Lu]Lu-(FAPI-04) 2 effectively retarded tumor growth and displayed good tolerance. In conclusion, the DOTA-Suc-Lys-(FAPI-04) 2 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) 2 provides a new approach for applying FAPI derivatives in tumor theranostics.

Design, Synthesis, and Evaluation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein for Brain Imaging

“…Improving the target-to-non target ratio of tumor imaging, reducing the toxic side effects of normal tissues, and increasing the therapeutic efficiency of tumors are important goals for the development of FAP-targeted radiopharmaceuticals. By introducing albumin binder moieties or PEG side chains, ,− increasing the number of target molecules, ,− conjugating with other target molecules, and using peptide structures as alternative target molecules, the short tumor residence time and low target-to-nontarget ratio of [ 68 Ga]­FAPI04 was optimized, which greatly improved the application of FAP-targeted radiopharmaceuticals in tumor diagnosis and treatment. A series of related tumor diagnosis and treatment clinical trials was carried out.…”

Emerging biomedical imaging-based companion diagnostics for precision medicine

“… 41 As shown in Figure 2 I and 48 h after injection, 111 In-labeled actively targeted nanoparticle levels accumulated to around 6% ID/g and stayed rather stable throughout time. 111 In-labeled untargeted nanoparticles, on the other hand, exhibited a greater tumor uptake of 8% ID/g at 48 h post-infection and a more pronounced clearance between 48 and 96 h. There are also strategies to modify the targeting moiety, such as fibroblast activation protein (FAP), 42 somatostatin receptor, 43 and PSMA 44 on the tracers. For example, Zhong and co-workers synthesized [ 68 Ga]Ga-(FAPI-04)2 using fibroblast activation protein inhibitor (FAPI).…”

“…For example, Zhong and co-workers synthesized [ 68 Ga]Ga-(FAPI-04)2 using fibroblast activation protein inhibitor (FAPI). 42 Micro-PET imaging of [ 68 Ga]Ga-(FAPI-04) 2 was done on SKOV3, A431, and H1299 tumor-bearing mice to evaluate tumor imaging and dimer retention time. [ 18 F]F-FDG and [ 68 Ga]Ga-FAPI-04 were used for the control groups.…”