Bilinska_2026_Eur.J.Nucl.Med.Mol.Imaging_53_1887

PURPOSE: This study aims to assess DOTAGA.Glu.(FAPI)(2) and DO3A.Glu.(FAPI)(2), specifically engineered as precursors for the development of theranostic FAPI-targeted radioligands. METHODS: DOTAGA.Glu.(FAPI)(2) and DO3A.Glu.(FAPI)(2) were radiolabeled with gallium-68 and lutetium-177, followed by in vitro (lipophilicity, protein binding, saturation, internalization and externalization) studies on FAP(+) CAFs. In vivo (biodistribution, metabolic stability, blood kinetics, PET/SPECT/CT imaging) and ex vivo, (autoradiography, immunohistochemistry) conducted on PC3-mice. Murine dosimetry data were extrapolated to human estimates. RESULTS: All radioligands achievied>98% radiochemical purity, demonstrating high FAP affinity (K(d):0.7-0.9 nM) and rapid internalization in CAFs, with differences in lipophilicity and serum protein binding. In vivo studies, for [(68)Ga]Ga-DOTAGA.Glu.(FAPI)(2) and [(68)Ga]Ga-DO3A.Glu.(FAPI)(2) showed high and sustained tumor uptake up to 3 h p.i. (18-19%I.A./g). For [(177)Lu]Lu-DOTAGA.Glu.(FAPI)(2) and [(177)Lu]Lu-DO3A.Glu.(FAPI)(2) tumor uptake was 16.2+/-2.5 and 15+/-1.2% IA/g at 4 h p.i., reaching 5.1+/-0.1 and 2.8+/-0.4%IA/g at 48 h, respectively. All radioligands exhibited low blood retention levels. PET/SPECT/CT imaging confirmed high tumor-to-background ratios. Uptake patterns correlate well with autoradiography images of heterogeneous FAP distribution in PC3-mice, while the detection of both murine and human FAP in PC3-tumors was demonstrated through immunohistochemistry. The extrapolated human absorbed dose estimates (Gy/GBq) for [(177)Lu]Lu-DOTAGA.Glu.(FAPI)(2) were generally higher across most organs compared to [(177)Lu]Lu-DO3A.Glu.(FAPI)(2). Human extrapolation of the (161)Tb-labeled radioligands delivered on average~38% higher absorbed doses in tissues as compared to their (177)Lu-labeled counterparts. CONCLUSION: These results support the potential clinical translation of DOTAGA.Glu.(FAPI)(2) and DO3A.Glu.(FAPI)(2), as promising candidates for precise diagnosis and treatment of FAP-expressing malignancies.