STERICALLY STABILIZED LIPOSOMES LABELED WITH IN-111 TO IMAGE FOCAL INFECTION

To determine the potential of sterically stabilized liposomes to image infectious and inflammatory foci, the in vivo behavior of In-111-labe led PEGylated (coated with polyethylene glycol) liposomes was studied in a rat model. Methods: Indium-111-PEGylated lipsomes were administer ed intravenously to rats infected with S. aureus in the left calf musc le. The distribution of the radiolabel was studied by gamma counting o f dissected tissues and gamma camera imaging for 48 hr. As a reference agent, the preparation of In-111-IgG was included in these studies. R esults: Clearance of the PEGylated liposomes from the blood compartmen t was similar to the clearance of In-111-IgG in this model (t(1/2) app roximate to 20 hr). Uptake of the radiolabel in the abscess with the 1 11In-liposomes was twice as high as the uptake following injection of In-111-IgG (2.7 %ID/g versus 1.1 %ID/g at 48 hr postinjection). Tissue counting revealed that abscess-to-muscle ratios reached values up to 20 and 34 (24 and 48 p.i., respectively). As early as 1 hr postinjecti on, the abscess could be visualized scintigraphically. Conclusion: The in vivo characteristics of this liposomal formulation in this rat mod el indicate that sterically stabilized liposomes labeled with gamma em itters might be a valuable addition to the arsenal of radiopharmaceuti cals currently used for infection imaging.