Biodistribution and imaging studies of technetium-99m-labeled liposomes in rats with focal infection

We have recently developed a procedure to label liposomes containing reduced glutathione (GSH) with ^99mTc using the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO). In the present study, we evaluated the use of ^99mTc-liposomes to detect focal infection sites in rats. Rats were infected in the thigh by intramuscular injection with Staphylococcus aureus followed 24 hr later by an intravenous injection of ^99mTc- liposomes, ⁶⁷Ga-citrate, or ^99mTc-human serum albumin (HSA). The animals were imaged under a gamma camera and subsequently killed at 4, 24 or 48 hr for tissue biodistribution studies. In contrast to infected rats receiving ⁶⁷Ga-citrate or ^99mTc-HSA, abscesses were prominently localized within 2 hr in rats after ^99mTc-liposome injection, and continued to increase in activity up to 24 hr. Abscess-to-muscle ratios calculated from 24-hr biodistribution data obtained from tissue sampling were 35.3 ± 7.6 for ^99mTc-liposomes, 4.1 ± 0.7 for ⁶⁷Ga-citrate and 8.0 ± 1.0 for ^99mTc-HSA. These studies show the potential of using ^99mTc-liposomes to localize infection.