The cytotoxic effects of polymer-coated quantum dots and restrictions for live cell applications

Abstract

The interest in the biomedical use of highly fluorescent and photostable nanoparticles such as quantum dots (QDots) is vastly increasing. One major hurdle that impedes QDot use in live cells and animals is their potential toxicity. Here, we employ a recently described multiparametric setup to determine the concentration at which common polymer-coated QDots become non-cytotoxic. We found that toxic effects are strongly related to the intracellular QDot amount that can be controlled by their specific surface coating. Using lysosomal buffer systems and proliferation-restricted cells, intracellular QDots were found to localize in endosomes, where they generate reactive oxygen species, interfere with cell cytoskeleton and leach free Cd 2+ ions due to QDot dissolution, resulting in increased toxicity and impeded QDot fluorescence. Furthermore, we find that asymmetric partitioning of QDots upon recurrent cell division results in the sacrifice of heavily-loaded cells and a rapid loss of particles in live cells, limiting the use of currently available QDots for long-term imaging and defining the non-cytotoxic concentration as 10-fold lower than commonly used concentrations.3

Cytosolic Delivery of Nanolabels Prevents Their Asymmetric Inheritance and Enables Extended Quantitative in Vivo Cell Imaging

“…1a. Cells are first incubated with plasmonic NPs, such as gold NPs (AuNPs), for [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] min. During that time the AuNP can adsorb to the cells and are internalized just below the plasma membrane by endocytic uptake (see TEM images in Figure S1).…”

“…Sequestration in the acidic and degradative endolysosomes results in quenching of the fluorescein label (which is strongly pH dependent) and degradation of the CdSe QD 29 . Instead, when the same labels were delivered into the cytosol by photoporation, the signal decrease over multiple cell generations was only due to dilution in the daughter cells.…”

“…A third disadvantage of endocytic cell labelling is that the vast majority of the contrast agents are trafficked to the endolysosomes where they are exposed to an acidic and overall degrading environment 26,28 . This can lead to degradation of the contrast agent, lowering the signal intensity, as reported for fluorescent labels [28][29][30] as well as MRI contrast agents [31][32][33] . In addition, it has been reported that nanomaterials trapped in endolysosomal vesicles are not distributed equally over daughter cells upon cell division 30,34,35 .…”

“…In addition, it has been reported that nanomaterials trapped in endolysosomal vesicles are not distributed equally over daughter cells upon cell division 30,34,35 . While this process has been proposed to be a protective mechanism where the daughter cell with the highest NP load can be sacrificed in favour of the daughter cell with the lowest NP content 29,36 , recent findings show that asymmetric inheritance of vesicles is an inherent cell-biological phenomenon 37 . For quantitative cell tracking applications asymmetric inheritance of contrast agents over daughter cells is disadvantageous as it hinders accurate quantification of cell numbers over time, apart from the fact that the brightest signals are coming from cells that are suffering from the highest cytotoxicity.…”

Assessing nanoparticle toxicity in cell-based assays: influence of cell culture parameters and optimized models for bridging the in vitro–in vivo gap

“…The effect on cell wellbeing depends on the chemical composition of the NP. For Cd-containing QD, for example, the leaching of highly toxic Cd 2+ -ions is considered to be the main cause of any observed toxicity 63,64 .…”