Optimization of Manual Radiolabeling of [68Ga]Ga-DOTA-FAPI-46 Based on 68Ge/68Ga Generator

Abstract

Cancer diagnosis increasingly requires molecular imaging agents with high tumor specificity and rapid biodistribution. [⁶⁸Ga]Ga-DOTA-FAPI-46 is a promising PET radiopharmaceutical that targets fibroblast activation protein (FAP); however, limited access to automated synthesis modules necessitates the development of reliable manual radiolabeling protocols. This study aimed to determine the optimal pH and temperature conditions for manual [⁶⁸Ga]Ga-DOTA-FAPI-46 radiolabeling using a ⁶⁸Ge/⁶⁸Ga generator and to evaluate its pharmaceutical quality. A 3 × 2 full factorial design was employed, combining three sodium acetate buffer pH levels (3.7, 4.0, and 4.5) with two reaction temperatures (95°C and 105°C), with each condition performed in triplicate. Radiochemical yield and purity were assessed, along with serum-free and human serum stability, sterility, and bacterial endotoxin levels. The optimal condition was pH 4.0 at 105°C for 10 minutes, producing a radiochemical yield of 87.516% ± 0.601%. pH significantly affected radiochemical yield, whereas temperature alone had no significant effect; however, their interaction was significant (F = 17.531; p < 0.001; η² = 0.745). Radiochemical purity exceeded 99% and remained above 95% during three-hour stability testing, while all samples passed sterility and endotoxin tests. These findings support the consistent production and broader accessibility of FAP-targeted oncological PET imaging services. Therefore, the optimized manual protocol provides a feasible and reliable alternative for nuclear medicine facilities without automated synthesis modules.