Preparation and comparative evaluation of 99mTc-labeled 2-iminothiolane modified antibodies and CITC-DTPA immunoconjugates of anti-EGF-receptor antibodies

Abstract

The use of antibodies as targeting agents for the delivery of radioisotopes to tumors is a promising concept that has received widespread attention since the advent of monoclonal antibody (mAb) technology. The following studies are described in this article: the 99mTc-randiolabeling of 2-iminothiolane (2-IT) modified antibodies and 6-p-isothiocyanatobenzyl- diethylene-triamine penta-acetic acid (CITC-DTPA) immunoconjugates of anti-EGF-receptor antibodies murine ior egf/r3 and humanized h-R3; the analytical methods for quality control of the radiopharmaceutical such as instant thin layer chromatography-silica gel (ITLC-SG); the biological assessment of the radiolabeled molecule using flow cytometry analysis; in vitro stability studies with cysteine and DTPA challenge and the biodistribution studies in 4NMRI xenografted nude mice with U-87 human glioblastoma multiforme and MDA-MB-468 breast cancer cell lines. Labeling efficency of (96.48 +/- 0.70%) (98.42 +/- 0.38%), (94.8 +/- 1.25%) and (96.41 +/- 0.89%) was achieved for 99mTC-2-IT ior efg/r3, 99mTc-CITC-DTPA- ior egf/r3, 99mTc-CITC-DTPA- h-R3 and 99mTc-DIACIM h-R3, respectively. Radiocolloids were less than 2.0% in all cases. The biological activity measured by flow cytometry analysis using the MDA-MB-468 breast cancer cell line showed an immunoreactivity fraction greater than 85% in all concentrations of each immunoconjugate. Challenge studies demonstrated no evidence of transcomplexation of 99mTc to 1.0 mM DTPA for 2-IT modified antibody ior egf/r3 and CITC-DTPA immunoconjugates and only 8.7%, 4.9% and 5.0% of the 99mTc-radiolabeled was transcomplexed to 1.0 mM cysteine after 1 h incubation at 37 degrees C for 2-IT modified antibody ior egf/r3, CITC-DTPA ior egf/r3 and CITC-DTPA h-R3, respectively. Biodistribution studies with 2-IT modified antibodies and CITC-DTPA immunoconjugates indicated high tumor uptake in both cell lines with both immunoconjugates and no accumulation of the radiolabeled antibodies in normal organs.