Purpose: Cisplatin nanocapsules, nanoprecipitates of cisplatin encapsulated in phospholipid
bilayers, exhibit increased in vitro toxicity compared with the free drug toward a panel of human
ovarian carcinoma cell lines. To elucidate the mechanism of cell killing by nanocapsules and to
understand the cell line dependence of nanocapsule efficacy, the route of uptake and the intracellular
fate of the nanocapsules were investigated.
Experimental Design: Intracellular platinum accumulation and cisplatin-DNA-adduct formation
were measured in cell lines that differ in sensitivity to cisplatin nanocapsules. Confocal fluorescence
microscopy in combination with down-regulation with small interfering RNAwas used to
map the route of cellular uptake of nanocapsules containing fluorescein-labeled cisplatin.
Results: In sensitive cell lines, cisplatin fromnanocapsules is takenupmuchmore efficiently than
the free compound. In IGROV-1cells, the increased platinum accumulation results in augmented
cisplatin-DNA-adduct formation. Confocal fluorescence microscopy revealed that the uptake of
nanocapsules is energy dependent. Colocalization with markers of early and late endosomes
indicated uptake via endocytosis. Down-regulation of caveolin-1 with small interfering RNA
inhibited the uptake and cytotoxic effect of nanocapsules in IGROV-1cells. Ovarian carcinoma
cells, in which the nanocapsules are less effective than in IGROV-1 cells, do not internalize
the nanocapsules (OVCAR-3) or accumulate them in an endocytic compartment after clathrinmediated
Conclusions: The high cytotoxicity of cisplatin nanocapsules requires caveolin-1-dependent
endocytosis that is followed by release of the drug from a late endosomal/lysosomal compartment
and cisplatin-DNA-adduct formation.The findings may be applied in predicting the efficacy
of nanoparticulate anticancer drug delivery systems in treating different tumor types.