@article {Brouwers327, author = {Adrienne H. Brouwers and Julli{\"e}tte E.M. van Eerd and Cathelijne Frielink and Egbert Oosterwijk and Wim J.G. Oyen and Frans H.M. Corstens and Otto C. Boerman}, title = {Optimization of Radioimmunotherapy of Renal Cell Carcinoma: Labeling of Monoclonal Antibody cG250 with 131I, 90Y, 177Lu, or 186Re }, volume = {45}, number = {2}, pages = {327--337}, year = {2004}, publisher = {Society of Nuclear Medicine}, abstract = {Radioimmunotherapy (RIT) can be performed with various radionuclides. We tested the stability, biodistribution, and therapeutic efficacy of various radioimmunoconjugates (131I, 88/90Y, 177Lu, and 186Re) of chimeric antirenal cell cancer monoclonal antibody G250 (mAb cG250) in nude mice with subcutaneous renal cell cancer (RCC) tumors. Methods: The 88/90Y and 177Lu labeling procedures of cG250 conjugated with cyclic diethylenetriaminepentaacetic acid anhydride (cDTPA), isothiocyanatobenzyl-DTPA (SCN-Bz-DTPA), or 1,4,7,10-tetraazacyclododecanetetraacetic acid (DOTA) were characterized. Stability of the labeled conjugates in plasma at 37{\textdegree}C was assessed. Biodistribution and therapeutic efficacy of labeled cG250 were compared in nude mice with SK-RC-52 human RCC xenografts. Results: Both SCN-Bz-DTPA and DOTA were stable in vitro (\<5\% release of the radiolabel during 14 and 21 d of incubation) and in vivo (uptake in bone <= 1.5 percentage injected dose per gram [\%ID/g] at 7 d after injection) when used to label 88Y or 177Lu to cG250. The DOTA conjugate was slightly but significantly more stable than SCN-Bz-DTPA at 7 d after injection. In vivo, these cG250 preparations showed high tumor uptake (70 {\textpm} 15 \%ID/g {\textpm} SD at 7 d after injection). Maximum tumor uptake for 125I-cG250 and 186Re-mercaptoacetyltriglycine-(MAG3)-cG250 (\<20 {\textpm} 3 \%ID/g {\textpm} SD) was reached at 3 d after injection and was much lower in comparison with cG250 labeled with the residualizing radionuclides. Because the highest specific activities could be prepared using SCN-Bz-DTPA, and relatively low protein doses of cG250 could be administered without saturating the tumor, cG250-SCN-Bz-DTPA conjugates were used in RIT studies. In RIT experiments at maximum tolerated dose, tumor growth was delayed most effectively by cG250 labeled with 177Lu, next most effectively by 90Y and 186Re (which were approximately equal), and least by 131I (delayed by approximately 185, 125, 90, and 25 d, respectively). The best median survival (300 d) was observed for 177Lu-SCN-Bz-DTPA-cG250. Median survival for control groups was \<150 d. Conclusion: DOTA-conjugated radiolabeled antibodies were the most stable radioimmunoconjugates in vitro and in vivo as manifested by the lowest bone uptake. However, specific activity was higher for SCN-Bz-DTPA. The RIT studies clearly showed that the therapeutic efficacy of mAb cG250 labeled with 177Lu, 90Y, or 186Re was superior to that of 131I-cG250. The residualizing radionuclides 177Lu and 90Y led to higher radiation doses to the tumor and most likely are better candidates than conventionally radiolabeled 131I for RIT with cG250 in patients with RCC.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/45/2/327}, eprint = {https://jnm.snmjournals.org/content/45/2/327.full.pdf}, journal = {Journal of Nuclear Medicine} }