Preparation of ^177Lu-Rituximab and Comparison with ^131I-Rituximab Radiolabeled with Chloramine-T Method

Background: The main purpose of radioimmunotherapy is delivered lethal dose to the tumor cells which depends on the immunological and pharmacological of the antibody (Ab) property and the conjugated radionuclide characteristics. Objectives: The aim of this study is preparation of DOTA-Rituximab complex and radiolabeling with Lu-177 and comparison with the results of 131I-Rituximab radiolabed with Chloramine-T method that was obtained before. Methods: The number of chelator molecules (DOTA) attached to the DOTA-Rituximab complex was determined by Arsenazo III reagent. After radiolabeling with Lu -177, the stability in normal saline and the biodistribution in the healthy mice was evaluated. The Immunoreactivity of Ab was checked on Raji cell lines and the results were compared with 131I-Rituximab. Results: Each 300 g of antibody was labeled with 6 mCi Lu-177. After 48 hours, 82% of the radiolabeled antibody was stable and about 18% of the radiotracer was in the blood. The immunoreactivity was calculated 85% 2%. Conclusions: The results showed that radiolabeling with Lu-177 was done with higher yield than iodine-131 and the produced radiopharmacy has more stability and immunoreactivity. The biodistribution results were acceptable in both radiopharmacy.