Dynamics and mechanisms of quantum dot nanoparticle cellular uptake

Yan Xiao,William G Telford,Alessandro Tona,R David Holbrook,Samuel P Forry,Xiugong Gao

doi:10.1186/1477-3155-8-13

Abstract

BackgroundThe rapid growth of the nanotechnology industry and the wide application of various nanomaterials have raised concerns over their impact on the environment and human health. Yet little is known about the mechanism of cellular uptake and cytotoxicity of nanoparticles. An array of nanomaterials has recently been introduced into cancer research promising for remarkable improvements in diagnosis and treatment of the disease. Among them, quantum dots (QDs) distinguish themselves in offering many intrinsic photophysical properties that are desirable for targeted imaging and drug delivery.ResultsWe explored the kinetics and mechanism of cellular uptake of QDs with different surface coatings in two human mammary cells. Using fluorescence microscopy and laser scanning cytometry (LSC), we found that both MCF-7 and MCF-10A cells internalized large amount of QD655-COOH, but the percentage of endocytosing cells is slightly higher in MCF-7 cell line than in MCF-10A cell line. Live cell fluorescent imaging showed that QD cellular uptake increases with time over 40 h of incubation. Staining cells with dyes specific to various intracellular organelles indicated that QDs were localized in lysosomes. Transmission electron microscopy (TEM) images suggested a potential pathway for QD cellular uptake mechanism involving three major stages: endocytosis, sequestration in early endosomes, and translocation to later endosomes or lysosomes. No cytotoxicity was observed in cells incubated with 0.8 nM of QDs for a period of 72 h.ConclusionsThe findings presented here provide information on the mechanism of QD endocytosis that could be exploited to reduce non-specific targeting, thereby improving specific targeting of QDs in cancer diagnosis and treatment applications. These findings are also important in understanding the cytotoxicity of nanomaterials and in emphasizing the importance of strict environmental control of nanoparticles.

Highlights

The rapid growth of the nanotechnology industry and the wide application of various nanomaterials have raised concerns over their impact on the environment and human health
In summary, the results presented here suggest a potential pathway for quantum dots (QDs) cellular uptake mechanism, as illustrated in Figure 6, which comprises of three major stages: (1) endocytosis; (2) sequestering in early endosomes; (3) translocation to later endosomes or lysosomes (Figure 6)
Based on the size of the QDs with emission maxima at 655 nm (QD655)-COOH used in this study, it is very likely that QD endocytosis by breast epithelial cells is mediated through micropinocytosis rather than macropinocytosis

Summary

Introduction

The rapid growth of the nanotechnology industry and the wide application of various nanomaterials have raised concerns over their impact on the environment and human health. QDs are nanometersized fluorescent semiconductor crystals with unique photochemical and photophysical properties Their much greater brightness, rock-solid photostability and unique capabilities for multiplexing, combined with their intrinsic symmetric and narrow emission bands, have made them far better substitutes for organic dyes in existing diagnostic assays [3]. These properties, combined with the development of ways to solubilize QDs in solution and to conjugate them with biological molecules, have led to an explosive growth in their biomedical applications [4]. Following the two seminal papers published on Science in 1998 demonstrating the feasibility of using QDs in biological environments [5,6], many new techniques have been developed during the last decade, utilizing the unique photophysical properties of QDs, for in vitro biomolecular profiling of cancer biomarkers, in vivo tumor imaging, and dual-functionality tumor-targeted imaging and drug delivery [7]

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