Sentinel lymph node metastasis imaging by using nanoparticle carriers in an animal study

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We propose a new approach using multimodality imaging to facilitate sentinel node biopsy examinations, in which radioactive and near infrared(NIR) fluorescent nanoparticles can depict deep situated sentinel nodes and fluorescent nodes, as well as simultaneously visualize anatomical configurations in the field of interest. For this reason we have developed polyamidoamine(PAMAM) coated silica nanoparticles loaded with technetium-99m(Tc-99m) and ICG. To test the feasibility and utility of this dual-modality imaging system we conducted animal studies. The mean diameter of PAMAM coated silica nanoparticles was 30-50 nm as evaluated by images of transmission electron microscopy and scanning electron microscopy. The distribution of the particle size was measured by a laser scattering particle size analyzer(SALD-7100, Shimadzu, Japan). The peak of the distribution was 30 nm in ethanol solution. The combined labeling with both Tc-99m and ICG-Sulfo-OSu was verified by thin layer chromatography, … More TLC, before each experiment. 0.1 ml of the nanoparticle solution(7.4 MBq, except for one rat ; with 3.7 MBq, and 1 micro-gramm ICG) was submucosally injected in the tongue of six male Wister rats. Lymphoscintigraphy(sequential static images, every 5 minutes) was performed for 6 rats for one hour immediately after injection. Scintigraphic images showed an increased accumulation of Tc-99m in the neck with a markedly increased uptake at the injection site. Single increased nodal uptake was seen in 4 of 6 rats in the final static images. After completion of lymphoscintigraphy, animals were euthanized. As skin incision was made and 19 lymph nodes were identified in the dissected necks of 6 rats. After lymph node excision, contact-radiography was performed which revealed 3 markedly increased uptake nodes and 3 weak uptake nodes. NIR fluorescence imaging was performed on all dissected necks. The PDE system(Hamamatsu Photonics Co, Japan) provided clear fluorescence images of lymph nodes in the neck with anatomical configurations real time. The intensity of fluorescence was arbitrarily evaluated and 6 lymph nodes were weak to strong, (+)～(+++), and other lymph nodes were evaluated as having no fluorescence. Increased radioactive nodes coincided with fluorescent nodes. Radioactivity of 15 excised lymph nodes in 4 rats was assayed with a gamma-well counter. The radioactivity comparison revealed a large difference between the high fluorescence intensity group(4 lymph nodes, mean%; 0.109±0.067) and thelow or no fluorescence intensity group(8 lymph nodes, mean%; 0.001±0.000), (p<0.05). TEM revealed that small black granules were localized and dispersed within the cytoplasm of macrophages in lymph nodes. The appearance of small sphericalgranules was restricted to macrophages but not other lymphatic cells. Although further studies are needed to determine the appropriate sensitivity and safety of thisdual imaging nanoparticles, the results may promise for a better target nodes detection by the dual modality method in sentinel node biopsy. Less