LONG-CIRCULATING BLOOD-POOL IMAGING AGENTS

Two generally accepted methods are currently in use to ensure to prolong the circulation of imaging agents in an effort to make them suitable for blood pool (vascular) imaging. The first method uses in vivo or ex vivo labeling of blood cells or plasma components with diagnostic labels. The second method employs synthetic (covalently modified) macromolecules, colloids and/or liposomes capable of carrying diagnostic labels. Current blood pool imaging technologies where both methods may be successfully applied include mainly MR, CT and scintigraphy. Medical applications for the use of vascular imaging include cardiovascular disease (stenosis, aneurysm, atherosclerosis, trauma), abnormal capillary permeability (cancer detection, inflammation) and tumor neovascularity (metastatic potential). However, only selected agents are expected to have the potential of being useful for a variety of potential blood pool imaging tasks. We describe here a novel class of grafted macromolecular agents (methoxy poly(ethylene)glycol-succinyl-(N-epsilon-poly(L-lysy l)diethylene) pentaacetamide (MPEG-PL-DTPA)) that fulfills the prerequisites of long blood half-life, exclusive intravascular distribution and low immunogenicity/toxicity. We report physico-chemical and biological properties of these agents as well as their major applications in radiology.