Celulas Vs Nanoparticulas

LETTERS
PUBLISHED ONLINE: 6 NOVEMBER 2011 | DOI: 10.1038/NNANO.2011.191

Role of cell cycle on the cellular uptake and dilution of nanoparticles in a cell population
Jong Ah Kim, Christoffer Åberg, Anna Salvati* and Kenneth A. Dawson*
Nanoparticles are considered a primary vehicle for targeted therapies because they can pass biological barriers and enter and distribute within cells byenergy-dependent pathways1–3. So far, most studies have shown that nanoparticle properties, such as size4–6 and surface7,8, can influence how cells internalize nanoparticles. Here, we show that uptake of nanoparticles by cells is also influenced by their cell cycle phase. Although cells in different phases of the cell cycle were found to internalize nanoparticles at similar rates, after 24 h theconcentration of nanoparticles in the cells could be ranked according to the different phases: G2/M > S > G0/G1. Nanoparticles that are internalized by cells are not exported from cells but are split between daughter cells when the parent cell divides. Our results suggest that future studies on nanoparticle uptake should consider the cell cycle, because, in a cell population, the dose of internalizednanoparticles in each cell varies as the cell advances through the cell cycle. Several studies have shown that the cellular uptake of nanoparticles can depend on many factors, including the size4–6,9,10 and/or shape4,11,12 of the nanoparticle, sedimentation effects of large and dense particles13, and the composition of the protein corona on the nanoparticle14–16. Some reports show saturation of theintracellular nanoparticle concentration within hours4,17, others after several days18–20, and the impact of nanoparticles on cellular functions has been studied1,2,21–23. It has also been shown that cell division can dilute the concentration of nanoparticles in the cell24,25 and this has implications for uptake studies3. So far, most studies have identified specific aspects of the nanoparticles thataffect cellular uptake. Here, we show that the state of the cell is equally important when considering how nanoparticles enter cells. The cell cycle is a series of events that lead to cell division and replication. It consists of four phases: G1, S, G2 and M (Fig. 1a). The activation of each phase depends on the proper completion of the previous one26,27. The cell cycle commences with the G1 phase,during which the cell increases its size. During the S phase the cell synthesizes DNA, and in the G2 phase it synthesizes proteins to prepare for cell division. Finally, during the M phase, the cell divides and the two daughter cells enter the G1 phase. Cells that have temporarily stopped dividing can enter a resting phase called G0. During each phase, cellular processes can vary greatly, meaningthat the rate at which a cell takes up foreign material may depend on which phase it is in28–30. The interaction of protein corona–nanoparticle complexes with cells7,8,21 could also depend on the cell cycle, because the expression of membrane proteins can vary during the cell cycle29. Other differences in uptake can arise from how close the cells are to one another31 and how old they are. Thecell cultures commonly used in laboratory studies comprise a mixture of cells in different phases of the cell cycle, simultaneously undergoing progression and cell division (Fig. 1b). When nanoparticle internalization is studied by adding nanoparticles to such cultures, it is therefore important to resolve how the state of the different cells affects the uptake. To study accumulation duringcontinuous nanoparticle uptake, A549 cells (human lung carcinoma) were incubated for up to 72 h with carboxylated polystyrene nanoparticles (PS-COOH) with diameters of 40 nm, fluorescently labelled with a yellow-green dye similar to fluorescein isothiocyanate (see Table 1 for nanoparticle characterization). Nanoparticles were found to enter the cells, and the overlap between the red fluorescence from...