PT - JOURNAL ARTICLE AU - Eun Jung Kim AU - Byoung Soo Kim AU - Tae Hyun Choi TI - Enhanced stability of radioiodinated anti-epidermal growth factor receptor antibody using novel bifunctional iodination linker for radioimmunotherapy DP - 2016 May 01 TA - Journal of Nuclear Medicine PG - 1454--1454 VI - 57 IP - supplement 2 4099 - http://jnm.snmjournals.org/content/57/supplement_2/1454.short 4100 - http://jnm.snmjournals.org/content/57/supplement_2/1454.full SO - J Nucl Med2016 May 01; 57 AB - 1454Objectives Radioimmunotherapy (RIT) uses an antibody labeled with a radionuclide to deliver cytotoxic radiation to a target tumor cells. Radioiodine is most commonly employed to prepare radiolabeled proteins (antibodies, peptides) for in vitro and in vivo applications. A major shortcoming of radioiodinated proteins prepared by direct labeling methods is their deiodination in vivo. For the preparation of more stable radioiodinated antibodies, we developed a new linker, (N-(4-isothiocyanatobenzyl)-2-(3-(tributyl stannyl) phenyl) acetamide (IBPA). This study evaluated the stability of IBPA in vitro and in vivo as a linker for the stable radioiodinated internalizing antibody, cetuximab.Methods Directly labeled cetuximab ([125I]-cetuximab) was prepared by the chloramine T method. To prepare indirectly labeled cetuximab using IBPA ([125I]-IBPA-cetuximab), IBPA was radioiodinated using chloramine-T to give N-(4-isothiocyanatobenzyl)-2-(3-[125I]phenyl)acetamide ([125I]-IBPA). [125I]-IBPA was then conjugated to cetuximab. In vitro stability was performed in serum and liver microsome. In vivo studies were performed at 48 h after i.v. injection of [125I]-cetuximab or [125I]-IBPA-cetuximab in nude mice and nude mice bearing LS174T tumor xenografts. Blood samples for pharmacokinetics were collected at 2, 4, 8, 24, 48, 72, 168, 336, and 504 h after i.v. injection of [125I]-cetuximab or [125I]-IBPA-cetuximab in nude mice and nude mice bearing LS174T tumor xenografts.Results In vitro studies, [125I]-IBPA-cetuximab was very stable in human serum, mouse serum, human liver microsome and mouse liver microsome. The percentages of [125I]-cetuximab and [125I]-IBPA-cetuximab remaining at 0, 0.5, 1, 2, 4, and 8 h after incubation in mouse serum exceeded 94%. The percentages of [125I]-cetuximab and [125I]-IBPA-cetuximab remaining at 0, 0.5, 1, 2, 4, and 8 h after incubation in human serum exceeded 91%. The percentages of [125I]-cetuximab and [125I]-IBPA-cetuximab remaining at 5, 10, and 30 min after incubation in mouse and human liver microsomes exceeded 96%. In vivo studies, radioactivity uptake in thyroid glands was obviously decreased by injection of [125I]-IBPA-Cetuximab instead of [125I]-Cetuximab. The thyroidal uptake value (%ID) after injection of [125I]-IBPA-cetuximab (0.09 ± 0.05) was approximately 8-fold lower than that after injection of [125I]-cetuximab (0.69 ± 0.36) with a statistically significant difference (P < 0.005). The tumor uptake value (%ID/g) after injection of [125I]-IBPA-cetuximab (12.42 ± 1.63) was approximately 2-fold higher than that after injection of [125I]-cetuximab (7.10 ± 1.54) (P < 0.0005). In pharmacokinetics, the half-life of [125I]-cetuximab and [125I]-IBPA-cetuximab were 91.0 ± 8.0 and 73.8 ± 4.8 h, respectively. The half-life of [125I]-IBPA-cetuximab in plasma was shorter than that of [125I]-cetuximab in nude mice bearing subcutaneous LS174T tumor xenografts (P < 0.005) in contrast to the normal nude mice.Conclusions [125I]-IBPA-cetuximab is stable and resistant to deiodination in vitro and in vivo. IBPA is a promising bi-functional linker for radioiodination of internalizing monoclonal antibodies for in vivo applications including radioimmunotherapy.