Article

Quantitative Imaging of Lymphatic Function with Liposomal Indocyanine Green

Institute of Pharmaceutical Sciences, Swiss Federal Institute of Technology, ETH Zurich, Zurich, Switzerland.
Cancer Research (Impact Factor: 9.28). 09/2010; 70(18):7053-62. DOI: 10.1158/0008-5472.CAN-10-0271
Source: PubMed

ABSTRACT Lymphatic vessels play a major role in cancer progression and in postsurgical lymphedema, and several new therapeutic approaches targeting lymphatics are currently being developed. Thus, there is a critical need for quantitative imaging methods to measure lymphatic flow. Indocyanine green (ICG) has been used for optical imaging of the lymphatic system, but it is unstable in solution and may rapidly enter venous capillaries after local injection. We developed a novel liposomal formulation of ICG (LP-ICG), resulting in vastly improved stability in solution and an increased fluorescence signal with a shift toward longer wavelength absorption and emission. When injected intradermally to mice, LP-ICG was specifically taken up by lymphatic vessels and allowed improved visualization of deep lymph nodes. In a genetic mouse model of lymphatic dysfunction, injection of LP-ICG showed no enhancement of draining lymph nodes and slower clearance from the injection site. In mice bearing B16 luciferase-expressing melanomas expressing vascular endothelial growth factor-C (VEGF-C), sequential near-IR imaging of intradermally injected LP-ICG enabled quantification of lymphatic flow. Increased flow through draining lymph nodes was observed in mice bearing VEGF-C-expressing tumors without metastases, whereas a decreased flow pattern was seen in mice with a higher lymph node tumor burden. This new method will likely facilitate quantitative studies of lymphatic function in preclinical investigations and may also have potential for imaging of lymphedema or improved sentinel lymph detection in cancer.

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Available from: Paola Luciani, May 07, 2015
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    • "Liposomes were prepared by a film hydration/extrusion method [25]. In brief, egg PC and cholesterol were dissolved (60/40% molar ratio, total lipid concentration = 2.5 mM) with por (1.5 mg/mL final concentration) in chloroform and dried overnight. "
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    • "ICG is quickly eliminated by the liver and bile duct after injection into body, but is unstable, self-quenched in solution, and has a low quantum yield (Sevick-Muraca et al., 1997). ICG can be used as an optical agent by binding it to other materials such as human serum albumin (HSA), micelles and liposomes (Kirchherr et al., 2009; Proulx et al., 2010; Sandanaraj et al., 2010). There is a demand for optical agents with a good safety profile to minimize potential toxicity and prevent or diminish side effects. "
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    ABSTRACT: Abstract 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.
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    • "Additionally, there have been concerns of inhibition of lymphatic contractions due to the presence of ICG [25]. The limitations of existing tracers have led us to develop a research program to identify new macromolecular contrast agents for lymphatic imaging [10]. "
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