Production and evaluation of [67Ga]-DTPA-Rituximab

Background: in order to obtain an anti-cd20 conjugate to be used in future therapeutic studies with therapeutic radioisotopes, 67ga-labeled antibody was prepared as a model of metal chelated immunoconjugate for preliminary dosimetric and biodistribution studies. materials and methods: rituximab was labeled with [67ga]-gallium chloride after residulation with freshly prepared cyclic dtpadianhydride. 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 dtpadianhydride (0.01 mg) at 25|o|c with continuous mild stirring for 30 min. the final isotonic 67ga-dtparituximab complex was checked by gel electrophoresis for radiolysis/chemolysis control. radio-tlc was performed to ensure the formation of only one species. preliminary in vivo studies in normal rat model were performed to determine the biodistribution of the radioimmunoconjugate up to 6 hours. results: radio-thin layer chromatography showed an overall radiochemical purity of 96-99% at optimized conditions (specific activity =300-500 mbq/mg, labeling efficiency 77%). gel electrophoresis showed no protein cleavage after radiolabeling. conclusion: preliminary in vivo studies in normal rat model showed [67ga]-dtpa-rituximab is a good probe for bio-dosimetry of therapeutic rituximab conjugates.