Enhanced Intracellular Uptake of Indocyanine Green by Polymeric Nanoparticulate Delivery Systems

The objective of this study is to investigate the intracellular uptake of ICG when delivered through polymeric nanoparticles. Nanoparticles entrapping ICG were engineered and characterized. The intracellular Indocyanine Green (ICG) uptake, subcellular localization and effect on cell viability were investigated in two different cell lines (B16-F10 melanoma and C-33A cervix cancer) for ICG-loaded polymeric nanoparticles in comparison to ICG solution. The ICG intracellular uptake in both cell lines was concentration and time dependent, presumably through an active endocytotic transport mechanism, when ICG-loaded nanoparticles were used. The cellular uptake of ICG in B16-F10 and C-33A cells reached up to an intracellular ICG concentration of 54.3 ± 3.1 ng per 2 × 10⁵ cells and 21.9 ± 2.1 ng per 2 × 10⁵ cells in twenty-four hours, when nanoparticles with initial extracellular ICG concentration of 0.022 M were used. Conversely, ICG intracellular uptake in both cell lines was less than a hundredth when ICG solution was used with the same extracellular concentration ranges. Once taken up by the cells, ICG showed a cytoplasmic distribution as revealed by fluorescence microscopy and binding to the cellular proteins and structures. The effect on cell viabilities observed for both ICG-loaded nanoparticles and ICG solution, even at high concentrations, was null. Thus, when delivered through nanoparticles an enhanced intracellular uptake was observed for ICG, which could be a basis for use of ICG-loaded nanoparticles for tumor diagnosis and therapy.