The tumor microenvironment (TME) surrounding tumor cells is a complex and highly dynamic system that promotes tumorigenesis. Cancer-associated fibroblasts (CAFs) are key elements in TME playing a pivotal role in cancer cells’ proliferation and metastatic spreading. Considering the high expression of the fibroblast activation protein (FAP) on cell membrane, CAFs emerged as appealing TME targets, namely for molecular imaging, leading to a pan-tumoral approach. Therefore, FAP inhibitors (FAPis) have been recently developed for PET imaging and radioligand therapy, exploring the clinical application in different tumor sub-types. The present review aimed to describe recent developments on radiolabeled FAP inhibitors and evaluate the possible translation of this pan-tumoral approach in clinical practice. At present, the application of FAPi-PET has been explored mainly in single-center studies, generally performed in small and heterogeneous cohorts of oncological patients. However, preliminary results were promising, in particular in low FDG-avid tumors such as primary liver and gastro-entero-pancreatic cancer, or in regions with unfavorable tumor-to-background ratio at FDG-PET/CT (i.e. brain), as well as in radiotherapy planning of head and neck tumors. Further promising results have been obtained in the detection of peritoneal carcinomatosis, especially in ovarian and gastric cancer. Data regarding the theranostics approach are still limited at presents, and definitive conclusion about its efficacy cannot be drawn at present. Nevertheless, the use of FAPi-based radio-ligand to treat the TME has been evaluated in first-in-human studies and appears feasible. Although the pan-tumoral approach in molecular imaging showed promising results, its real impact in day-to-day clinical practice has yet to be confirmed, and multi-center, prospective studies powered for efficacy are needed.

68Ga-based radiopharmaceuticals are routinely used for PET imaging of multiple types of tumors tumours. Gallium-68 is commonly obtained from 68Ge/68Ga generators, which are limited in the quantity of activity produced. Alternatively, gallium-68 can easily be produced on a cyclotron using liquid targets. In this study we optimized the GMP production of [68Ga]GaFAPI-46 using gallium-68 produced from a standard medical cyclotron using liquid targets. Starting from the published synthesis and quality control procedures described for other 68Ga-based radiopharmaceuticals, we have validated the synthesis process and the analytical methods to test the quality parameters of the final product to be used for routine clinical studies. [68Ga]GaFAPI-46 was successfully produced with high radiochemical purity and yield using an IBA Synthera® Extension module. Gallium chloride was cyclotron produced on a medical cyclotron using a liquid target with an activity of 4.31 ± 0.36 GBq at the end-of-purification (EOP). Analytical methods were established and validated meeting Ph. Eur. standards. Fully GMP production was also validated in three consecutive batches, producing 2.50 ± 0.46 GBq of [68Ga]Ga-FAPI-46 at the end-of-synthesis (EOS), with 98.94 ± 0.72% radiochemical purity by radio-HPLC. Quality was maintained for up to 3 h after the EOS. Production of [68Ga]GaFAPI-46 was performed and validated using a standard medical cyclotron with liquid targets. Quality control parameters (e.g. sterility, purity, and residual solvents) conform to Eur. Phar. and shelf life of 3 h was established. Activity of [68Ga]GaFAPI-46 produced is substantially higher than the one obtained with generators enabling a better response to the clinical need for this radiopharmaceutical.