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Preparation and biological evaluation of 177Lu-labeled rituximab for B-lymphoma treatmentKeywords: 177Lu Rituximab , Radioimmunotherapy , Biodistribution Abstract: Introduction: 177Lu is a beta emitter with suitable decay mode [T1/2=6.7 d, Eβmax=497 keV, EΥ=112keV (6.4%) & 208 keV (11%)] for using in radio therapy. Various radiolabeled monoclonal antibodies have been developed in treatment. Rituximab is a chimeric mouse-human monoclonal antibody. Rituximab binds with human B-lymphocate-restricted differentiation antigen: CD20. Rituxsimab was used successfully as an anti-CD20 radiolabeled antibody before. Methods: 177Lu was produced by thermal neutron irradiation of 1 mg of natural Lu2O3 with 4*10^13 n cm-2 s-1 neutron flux at Tehran Research Reactor. The irradiation target was dissolved in 200 μL of 1.0 M HCl, to prepare 177LuCl3. The radionuclide purity of product was measured by using ITLC and gamma spectroscopy by HPGe detector. The macrocyclic bifunctional chelating agent, N-succinimidyl-1,4,7, 10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-NHS) was prepared at 25 C using DOTA, N-hydroxy succinimide (NHS) in CH2Cl2. DOTA-Rituximab was obtained by the adding 0.5 mL of a rituximab pharmaceutical solution (10 mg/mL, in phosphate buffer, pH 7.8) to a glass tube pre-coated with DOTA-NHS (0.01-0.1 mg) at 25C with continuous mild stirring for 15 h. The stability of radiolabeled was studied in human serum. The biodistributions of 177Lu-DOTA-Rituximab and 177LuCl3 were determined for normal rats. The tissue uptakes of each injection were measured. Results: Radiolabeling was performed at 37C in 24 h. Radio-thin layer chromatography showed an overall radiochemical purity of >98% at optimized conditions. The percents of Injected Dose per gram of tissue were compared in different selected times (2-168 h). The peak of uptakes for 177LuCl3 was observed in bone, liver and kidney. High uptakes of 177Lu-DOTA-Rituximab were in spleen, liver and lungs. Conclusion: The radiolabeled complex was stable in human serum at 37C for 24 h. The biodistribution of the radiolabeled antibody is in agreement with other radiolabeled antiCD20 species already reported. 177Lu-DOTA-Rituximab is potential radioimmunotherapeutic agent for B-lymphoma treatment.
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