Superparamagnetic Iron Oxide Particles as Marker Substances for Searching Tumor Specific Liposomes with Magnetic Resonance Imaging

Abstract

Superparamagnetic iron oxide particles (SPIOs) encapsulated with oleic acid were incorporated within the lipid phase of different types of liposomes and served as markers in a search for tumor specific drug-carriers by noninvasive Magnetic Resonance Tomography (MRT). The experiments were performed on the model CC531 adenocarcinoma within the liver of WAG/RIJ rats. The reduction of the relative signal intensity (SI) in the tumor in T’2-weighted MR images was assumed as a measure of the liposome enrichment in the tumor or adjacent tissue. The liposome-encapsulated SPIOs were investigated and compared to AMI-227, dextran-coated SPIOs in two different doses, at isomolar doses regarding their iron content and at isodoses concerning their MR relaxivity R2. Reverse phase evaporation vesicles and small unilamellar vesicles showed a remarkably different behavior depending on the applied dose. A steadily strong SI-reduction, starting immediately after injection and extending up to 48 hours was observed for small unilamellar vesicles sterically stabilized with polyethylene glycol.