Sentinel lymph node (SLN) biopsy is a reliable technique for the diagnosis of metastases in breast cancer. However, the tracers used (blue dye and radiocolloid) are not optimal because they can cause allergic reactions and major costs in waste processing. Our strategy was to use near-infrared emitting nanoparticles for the mapping of SLN: indium-based Quantum Dots (QDs) and cyanine 7 embedded in silica nanoparticles (SiNP). We investigated indium-based QDs, which are presumed to be less toxic than their cadmium-based counterparts. Considering that SLN mapping is impaired if lymph nodes are invaded by metastatic cells, we therefore used a murine model of mammary carcinoma with lymphatic metastases. Metastatic cells did not influence the migration of QDs in the SLN since no difference in fluorescence intensity could be observed between healthy and metastatic SLN. The biodistribution study concluded that the major organs of retention were the injection point and lymph nodes whereas liver and spleen accumulated fewer QDs. The cytotoxicity tests demonstrated a weak in vitro toxicity of indium- compared to cadmium-based QDs. SiNP have been already used for tumor imaging but reports on the mapping of SLN with near-infrared emitting SiNP are sparse. The benefits of the encapsulation of the hydrophobic near-infrared emitting fluorophore cyanine 7 included a better retention in the SLN and a reduced in vitro toxicity compared to free fluorophore. The in vivo toxicity in mice was followed during 3 months after injection and did not reveal any signs of general or hepatic toxicity. Both fluorescent nanoparticles are thus well adapted for the mapping of the SLN and could be a favourable substitute to the actually tracers.
