Monoclonal antibody conjugated to gadolinium as a contrast agent for magnetic resonance imaging of human rectal...

Local disease is the most frequent recurrence pattern of rectal carcinoma, and its prognosis is not good. One reason for the poor prognosis is the difficulty of making the diagnosis at an early stage. 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, and stability of Mab A7-EDTA-Gd in human serum. Its in vivo distribution in nude mice with human colorectal carcinoma was also examined.

Mab A7-Gd retained binding activities that were nearly identical to intact Mab A7. Mab A7-Gd was stable in human serum. More radiolabeled 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.

Mab A7 conjugated to gadolinium selectively accumulated in the tumor. Our results suggest that it is potentially suitable as a contrast agent for MR imaging to detect local rectal carcinoma recurrence.