Radiology, Vol 193, 527-531, Copyright © 1994 by Radiological Society of North America

ARTICLES

Pancreatic receptors: initial feasibility studies with a targeted contrast agent for MR imaging

P Reimer, R Weissleder, T Shen, WT Knoefel and TJ Brady
Department of Radiology, MGH-NMR Center, Massachusetts General Hospital, Boston.

PURPOSE: To evaluate cholecystokinin (CCK) as a target-specific vector for magnetic resonance (MR) receptor imaging of rat pancreas. MATERIALS AND METHODS: Monocrystalline iron oxide (MION) was labeled with CCK by noncovalent attachment. Receptor specificity of the conjugate was determined with competitive binding studies. Pharmacologic determinations were blood half-lives, biodistribution, time responses, dose responses, and limited toxicity. RESULTS: Specific cell binding of MION-20-CCK was saturable and inhibitable by a CCK antagonist. Blood half-life of MION-20-CCK was 20 minutes, which was shorter than that of unlabeled MION. Biodistribution studies showed a statistically significant decrease in relaxation times in pancreatic tissues from 42.7 msec +/- 2.0 to 33.8 msec +/- 1.4 (P < or = .05) but not in tumor after administration of MION-20-CCK. The half-life of MION-20-CCK in the pancreas was 3 weeks; no signs of toxicity were shown at the level tested. CONCLUSION: Target-specific MR imaging of pancreatic receptors is feasible. Additional studies are necessary to perfect binding strategies, optimize preparations, and scale up synthesis for imaging in other species.

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