CONTROLLED DELIVERY OF GD-CONTAINING LIPOSOMES TO LYMPH-NODES - SURFACE MODIFICATION MAY ENHANCE MRI CONTRAST PROPERTIES

Surface modification of liposomes containing hylenetriaminepentaacetyl -phosphatidylethanolamine (Gd-DTPA-PE) as an amphiphilic paramagnetic label influences their contrast properties as MRI agents. Liposomes wi th the mean diameter ca. 220 nm and 10% mol content of Gd-DTPA-PE were modified with dextran (molecular weight 6 kDa) or polyethyleneglycol (PEG, molecular weight 5 kDa). The preparations obtained were used for MR visualization of axillary and subscapular lymph nodes after SC inj ection into rabbit's paw. Dextran-modified liposomes were found to hav e limited or no effect on lymph node/muscle MR signal intensity ratio during the first 2 h after the administration when compared to nonmodi fied plain liposomes, whereas the liposomes modified with PEG demonstr ated a 3-3.5-fold enhancement of lymph node signal. However, the parti al biodistribution studies with the In-111-labeled liposomes revealed that PEG-modified vesicles accumulated in the axillary lymph node at h alf the amount comparing with nonmodified and dextran-modified liposom es. The phenomenon found might be explained by noticeably increased re laxivity of PEG-modified Gd-liposomes.