Characterisation of biotinylated liposomes for in vivo targeting applications

Liposomes containing monosialoganglioside (G M1) or polyethylene glycol (PEG) lipid derivatives have prolonged circulation in the blood. This favours liposome extravasation to tumour sites. In this report it is shown that inclusion of G M1, PEG 550-DPPE or PEG 2000-DPFE in liposomes containing biotin-DPPE significantly diminished the ability of vesicles to bind to streptavidin in vitro. Steric inhibition due to the bulky head group of these lipids was least for biotin-DPPE liposomes containing G M1. Biodistribution studies in C26 tumour-bearing mice showed that G M1-liposomes containing small amounts of biotin-DPPE have long circulation life-times in the blood. Using fluorescent microscopic techniques, liposomes containing both G M1 and biotin-DPPE were detected within extra-vascular spaces in tumours. In addition it was shown that biotin-DPPE in G M1-liposomes bound streptavidin in situ. These results suggest that G M1-liposomes containing biotin-DPPE have potential use as diagnostic or therapeutic reagents in pre-targeting applications dependent on the high-affinity interaction of biotin with streptavidin.