The effect of mannosylation of liposome-encapsulated indocyanine green on imaging of sentinel lymph node

The imaging of sentinel lymph nodes (SLN) has been researched for its role in assessing cancer progression and postsurgical lymphedema. Indocyanine green (ICG) is a near-infrared (NIR) optical dye that has been approved by the Food and Drug Administration. It is known that liposome-encapsulated ICG (LP-ICG) has improved stability and fluorescence signal compared with ICG. We designed mannosylated liposome-encapsulated ICG (M-LP-ICG) as an optical contrast agent for SLN. M-LP-ICG has a higher UV absorbance spectrum and fluorescence intensity than LP-ICG. The stability of M-LP-ICG measured in 50° fetal bovine serum solution by a dialysis method was better than that of LP-ICG. M-LP-ICG demonstrated a high uptake in RAW 264.7 macrophage cell because the density of mannose is high. There were differences between M-LP-ICG and glucosylated liposome-encapsulated ICG (G-LP-ICG), which are geometrical isomers. The result of an inhibition study of M-LP-ICG showed a statistically significant decrease in uptake in RAW 264.7 cells after either co-treatment or pre-treatment with d-(+)-mannose as an inhibitor. Results from an in vitro experiment demonstrated that M-LP-ICG was specifically taken up by macrophage cells through the mannose receptor on its surface. The time-series images acquired from a normal mouse model after subcutaneous injection showed that the signal from M-LP-ICG in SLN and other organs appeared early and disappeared quickly in comparison with signals from LP-ICG. Not only the sentinel but also the draining lymph nodes were observed partly in M-LP-ICG. M-LP-ICG appears to increase the specificity of uptake and retention in macrophages, making it a good candidate contrast agent for an optic imaging system for SLN and the lymphatic system.