Radiolabeling of Bi-DOTAGA-cKNGRE with 213Bi

For radiolabelling, ²¹³Bi]BiI₄⁻/BiI₅²⁻ ion was eluted from ²²⁵Ac/²¹³Bi generator (180 MBq, Institute for Transuranium Elements (ITU)) using 0.6 mL of a mixture of 0.1 M HCl and 0.1 M NaI (1:1). Then the [²¹³Bi]BiI₄⁻/BiI₅²⁻ eluate was added to a vial containing 135 μL 2 M TRIS buffer, 50 μL 20% ascorbic acid and 30 μL of 6 mM DOTAGA-cKNGRE solution. The reaction mixture was incubated at 95 °C for 15 min. The ²¹³Bi-labelled complex was purified with SPE using Oasis HLB 1 cc cartridge pre-conditioned with 5 mL EtOH and 10 mL water. After loading the reaction mixture, the cartridge was rinsed with water (1 mL). The ²¹³Bi-labelled complex was eluted with a mixture of water and ethanol (1:1, 250 µL) and diluted with physiological saline (Salsol, TEVA, Debrecen, Hungary). For quality control, the RCP of the purified radiotracer was determined by applying instant thin-layer chromatography (iTLC) by measuring the activity of the 440 keV gamma emission of ²¹³Bi using miniGITA TLC scanner. For radio-iTLC, glass microfiber chromatography paper impregnated with a silica gel (iTLC-SG paper) as a stationary phase and 0.5 M citric acid (pH 5.5) as an eluent were used. Free ²¹³Bi moves with the solvent front, while [²¹³Bi]Bi-DOTAGA-cKNGRE remains at the bottom of the iTLC paper. RCP of the [²¹³Bi]Bi-DOTAGA-cKNGRE was found to be above 99% and the molar activity was 0.5 MBq/nmol.