Enhanced radioimmunotargeting of 125I-labeled L6-biotin monoclonal antibody (MAb) by combining preload of cold L6 MAb and subsequent immunoadsorption in rats

The present study investigates whether tumor:normal tissue uptake ratios of radiolabeled monoclonal antibodies can be further improved by a combination of extracorporeal immunoadsorption (ECIA) and preload with unlabeled idiotypic monoclonal antibody. Athymic rats, heterotransplanted with human lung carcinoma under the kidney capsule (SR tumor) and i.m. (IM tumor), were divided into four study groups: controls, ECIA, preload, and combined preload+ECIA. The preload+ECIA procedure reduced the whole-body and plasma activity by 48 and 89%, respectively. After such combined procedure, the uptake of 125I-labeled L6-biotin in SR tumors was unchanged, while the uptake in normal tissues was considerably reduced. Tumor (T):bone marrow ratio was then increased by 17.5 times (after ECIA) and by 4.5 times (24 h after ECIA). Similar enhancements were achieved for T:liver and T:kidney ratios. For the IM tumors, the ratios were not as high as for SR tumors. The effects on T:normal ratios of preload+ECIA in combination were synergistic. The combined procedure resulted both in an increased uptake and prolonged persistence of 125I-labeled L6-biotin in the SR tumors and also in a reduction of corresponding uptake values in organs critical for radiation.