Automated Preparation of [<sup>68</sup>Ga]Ga-3BP-3940 on a Synthesis Module for PET Imaging of the Tumor Microenvironment

A fast, efficient method has been developed on the GAIA synthesis module for automated gallium-68 radiolabeling of 3BP-3940, a molecular imaging probe targeting the fibroblast activation protein for positron emission tomography imaging of the tumor microenvironment. The reaction conditions involved acetate buffer (final concentration: 0.1 M), methionine as an anti-radiolysis agent (final concentration: 5.4 mg/mL), and 30 µg of 3BP-3940, with heating for 8 min at 98 °C. A final purification step on a C18 cartridge was necessary to obtain a radiolabeled product of high purity. In contrast, the generator-produced 68Ga was used directly without a concentration step on a cation exchange cartridge. The production of three validation batches confirmed the method's reliability, allowing the synthesis of [68Ga]Ga-3BP-3940 in 22.3 ± 0.6 min with high radiochemical purity (RCP), as determined by both radio-HPLC (99.1% ± 0.1%) and radio-TLC (99.2% ± 0.1%). The average radiochemical yield, based on RCP values measured by radio-HPLC, was 74.4% ± 3.3%. The stability of the radiolabeled product was demonstrated for up to 4 h after preparation. This protocol provides a reliable, rapid, and efficient methodology for the preparation of [68Ga]Ga-3BP-3940, which can easily be transposed to a clinical setting.