Preparation and biodistribution of [67Ga]-DTPA-rituximab in normal rats

Rituximab was successively labeled with ⁶⁷Ga]-gallium chloride after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a rituximab pharmaceutical solution (5 mg/ml, in phosphate buffer, pH 8) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 °C with continuous mild stirring for 30 minutes. Radio thin-layer chromatography showed an overall radiochemical purity of 96–99% at optimized conditions (specific activity = 300–500 MBq/mg, labeling efficiency 77%). The final isotonic ⁶⁷Ga-DTPA-rituximab complex was checked by gel electrophoresis for radiolysis control. Radio-TLC was performed to ensure the formation of only one species, followed by filtration through a 0.22 μm filter. Preliminary in vivo studies in normal rat model was performed to determine the biodistribution of the radioimmunoconjugate up to 6 hours.