In FY '97, LDRR was transferred from the Office of Director, NIH to the Clinical Center. STAR BURST Dendrimers (D), and Ultra Small Iron Oxide Particles (USPIO) were developed for possible cellular tags in molecular imaging. A series of high generation (G) dendrimers (G=5, 7, 9, 10) were conjugated to DOTA and Gadolinium (III) ion was added to the macromolecules. The 1/T1 and 1/T2 NMR Dispursion profiles were measured at 23 degrees C and the 1/T1 ion relaxivity increased from 30 mM-1s-1 for the G=5 to 35 mM-1s-1 for the G=7, with plateau at 36 mM-1s-1 for the G=9 and G=10 D. A similar plateau was observed for 1/T2 with values of 36 mM-1s-1 for G=5, 42 mM-1s-1 for G=7, and 45 mM-1s-1 for the G=9 and G=10 Ds. This OsaturationO of ion relaxivity for high generation dendrimers occurred over the entire frequency range studied. The 1/T1 and 1/T2 relaxivities decreased with temperature and for each generation of D studied, implying that slow water exchange of bound water molecules with the bulk solvent limits the relaxivity. This suggests that there is an increase in the rotational correlation times associated with higher generations of dendrimer and, therefore, these large macromolecules do not show significant increases in the ion relaxivity. The total molecular relaxivities increased from 2880 mM-1s-1 for the G=5 to 66960 mM-1s-1 for the G=10 dendrimer. Studies of the G=7, 9, and 10 GdDOTA dendrimers are planned in the rodent along with magnetic resonance imaging to characterize the biodistribution and blood clearance of these macromolecules.Ultra small iron oxide particles, as specific targeting agents to cerebral endothelial markers for transferring receptor (Tfr), were used to tag the rat oligodendrocyte precursor cell line CG-4 with MION-46L. Using the periodate-oxidation/borohydride-reduction method, mouse anti-rat Tfr monoclonal antibodies (MoAb) OX-26 is covalently linked to the contrast agent MION-46L. The Tfr has been used as a shuttle vector to deliver macromolecules into cells via direct internalization of the Tfr-ligand complex. Incubation of the CG-4 in situ for 48 hours with OX-26-MION46-L in tissue culture medium demonstrated that the CG-4 were packed with magnetic nanoparticles as determined by NMR relaxometry and Prussian Blue staining. CG-4-labeled cells had a viability greater than 95 percent and at 7 days was greater than 80 percent. Further experiments using different amounts of contrast agent and different cellular densities are planned as well as obtaining transmission electron micrographs of the magnetically-labeled CG-4 cells. OX-26-MION-46L preparations will be implanted into a hypomyelinated rat model. Plans are to perform MR imaging following labeled CG-4 implantation and correlate with histopathological staining to determine the degree of cellular migration and remyelination.
Showing the most recent 10 out of 30 publications
