Liposomes encapuslating positron emitters are applicable for diagnostic imaging and are useful to investigate the real-time liposomal trafficking in vivo. Long-circulating
liposomes encapsulaing [2-(18)F]-
2-fluoro-2-deoxyglucose were administrated to
tumor-bearing mice, and a PET scan was performed. Small-sized long-circulating
liposomes (100 nm) tended to accumulate in
tumor tissues of
tumor-bearing mice as compared with conventional
liposomes. Then the size effect on trafficking of long-circulating
liposomes was investigated. Large-sized
liposomes (>300 nm) accumulated in liver and spleen in a time dependent manner. On the contrary, small-sized ones (<200 nm) were transiently accumulated in the liver right after injection, but the accumulation decreased time dependently, suggesting that, although the majority of small long-circulating
liposomes remain in bloodstream, some extravasate once into interstitial spaces in liver which re-enter into bloodstream again. Next the trafficking of so-called long-circulating
liposomes, i.e.,
liposomes modified with
ganglioside GM1, palmityl
glucuronide (
PGlcUA), and
polyethylene glycol (PEG), in
tumor-bearing mice was examined. The accumulation of all three kinds of long-circulating
liposomes in liver decreased time-dependently, and
PGlcUA-
liposomes could avoid liver-trapping the most efficiently.
Tumor accumulation of
liposomes was obvious for
PGlcUA-
liposomes and PEG-
liposomes from immediately after injection, but not for GM1-liposomes. Finally, the trafficking of differently charged
liposomes was investigated in normal mice. The accumulation of positively charged
liposomes containing 1,2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl
bromide was different from that of neutral and negatively charged DCP-
liposomes. The agglutinability of and
serum protein ginding to positively charged
liposomes were marked, suggesting that these factors affect the high accumulation of
DMRIE-
liposomes in liver. Non-invasive PET analysis of liposomal trafficking is beneficial for obtaining information about liposomal
drug delivery, and long-circulating
liposomes might be useful for diagnostic
tumor imaging by PET.