Biotinylated Monoclonal Antibody Conjugated to Gadolinium as a Contrast Agent for Magnetic Resonance Imaging of Human Rectal Carcinoma

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Local disease is the most frequent recurrence pattern of rectal carcinoma, and its prognosis is not good. To detect local recurrence as early as possible, we produced the monoclonal antibody A7-gadolinium (Mab A7-Gd) conjugate as a contrast agent for magnetic resonance imaging to distinguish between carcinoma and normal tissue.We examined the in vitro immunoreactivity of Mab A7 coupled to Gd by chelate, isothiocyanobenzyl EDTA and its in vivo distribution in nude mice with human colorectal carcinoma.Mab A7-Gd retained binding activities that were nearly identical to intact Mab A7. More radiolabelled Mab A7-Gd accumulated in the tumor than normal mouse IgG-Gd. Both Mab A7-Gd and normal mouse IgG-Gd disappeared from blood linearly over time. Accumulation levels in normal tissues decreased linearly over time but were lower than those in tumors.The accumulation of biotinylated chA7Fab in the blood and the kidneys decreased significantly after the injection of avidin.