Preparation and radiolabeling of a lyophilized (kit) formulation of DOTA-rituximab with (90)Y and (111)In for domestic radioimmunotherapy and radioscintigraphy of Non-Hodgkin’s Lymphoma

BACKGROUND: On the basis of results of our previous investigations on (90)Y-DTPA-rituximab and in order to fulfil national demands to radioimmunoconjugates for radioscintigraphy and radioimmunotherapy of Non-Hodgkin’s Lymphoma (NHL), preparation and radiolabeling of a lyophilized formulation (kit) of DOTA-rituximab with (111)In and (90)Y was investigated. METHODS: (111)In and (90)Y with high radiochemical and radionuclide purity were prepared by (112)Cd (p,2n)(111)In nuclear reaction and a locally developed (90)Sr/(90)Y generator, respectively. DOTA-rituximab immunoconjugates were prepared by the reaction of solutions of p-SCN-Bz-DOTA and rituximab in carbonate buffer (pH = 9.5) and the number of DOTA per molecule of conjugates were determined by transchelation reaction between DOTA and arsenaso yttrium(III) complex. DOTA-rituximab immunoconjugates were labeled with (111)In and (90)Y and radioimmunoconjugates were checked for radiochemical purity by chromatography methods and for immunoreactivity by cell-binding assay using Raji cell line. The stability of radiolabeled conjugate with the approximate number of 7 DOTA molecules per one rituximab molecule which was prepared in moderate yield and showed moderate immunoreactivity, compared to two other prepared radioimmunoconjugates, was determined at different time intervals and against EDTA and human serum by chromatography methods and reducing SDS-polyacrylamide gel electrophoresis, respectively. The biodistribution of the selected radioimmunoconjugate in rats was determined by measurement of the radioactivity of different organs after sacrificing the animals by ether asphyxiation. RESULTS: The radioimmunoconjugate with approximate DOTA/rituximab molar ratio of 7 showed stability after 24 h at room temperature, after 96 h at 4°C, as the lyophilized formulation after six months storage and against EDTA and human serum. This radioimmunoconjugate had a biodistribution profile similar to that of (90)Y-ibritumomab, which is approved by FDA for radioimmunotherapy of NHL, and showed low brain and lung uptakes and low yttrium deposition into bone. CONCLUSION: Findings of this study suggest that further investigations may result in a lyophilized (kit) formulation of DOTA-rituximab which could be easily radiolabeled with (90)Y and (111)In in order to be used for radioimmunotherapy and radioscintigraphy of B-cell lymphoma in Iran.