Surface modification of monodisperse magnetite nanoparticles for improved intracellular uptake to breast cancer cells
Introduction
Nanoparticles with functional properties have been extensively used in a wide range of bioapplications [1], [2], [3], [4]: for example, drug and gene delivery, cell and tissue engineering, and medical imaging, for diagnostic and therapeutic purposes. For these applications, there is a growing need for a highly specific, efficient, and rapid internalization of nanoparticles into specific target cells, but this is severely limited by several factors [2], [5]: (a) nanoparticle aggregation (nanoparticles have a large surface area/volume ratio and tend to agglomerate); (b) short blood half-life of the particles in circulation (When nanoparticles agglomerate, or adsorb plasma proteins, they are quickly eliminated from the bloodstream by macrophages of the mononuclear phagocyte system (MPS) before they can reach target cells); (c) low efficiency of intracellular uptake of nanoparticles; and (d) nonspecific targeting. One possible approach to improving the dispersivity and biocompatibility of nanoparticles and their ability to target specific cells is to coat nanoparticles with biocompatible polymers and targeting agents. In our previous study [6], [7], the protein-resistive, nonantigenic, and biocompatible polyethylene glycol (PEG) has been coated on nanoparticle surfaces to disperse the nanoparticles, reduce nonspecific protein adsorption and clearance by macrophages, and render the nanoparticles capable of crossing the cell membrane. To achieve specific cancer cell recognition and increased efficiency of nanoparticle intracellular uptake via receptor-mediated endocytosis, a low-molecular-weight targeting agent such as folic acid (FA) has been coated on nanoparticles because it can couple to the folate receptors overexpressed on cancer cell membranes.
Moreover, there is growing interest in attaching PEG-FA conjugate to the surfaces of nanoparticles through chemical bonding to combine the advantages of PEG and FA. PEG is attached to the nanoparticle surface to prevent the nanoparticles from agglomerations, to make them more biocompatible, and to increase their nonspecific intracellular uptake. FA is grafted onto the distal end of PEG chains to target cancer cells specifically. Because PEG and FA play different roles in intracellular uptake of nanoparticles, it is expected that the uptake efficiency will be further improved after the PEG-FA conjugates are attached to their surfaces.
In this work, PEG, FA, and their conjugate, PEG-FA, were attached to the surfaces of monodisperse magnetite nanoparticles. Magnetite nanoparticles were chosen for this study because they are useful in many bioapplications. The coatings on individual nanoparticles were characterized and intracellular uptake of the nanoparticles into human breast cancer cells, BT-20, was investigated.
Section snippets
Materials
Methoxy-PEG-silane (MW 5000) and amino-PEG-carboxyl (MW 5000) were purchased from Shearwater, Huntsville, AL. (3-Aminopropyl)-trimethoxysilane, FA, and other chemicals were purchased from Sigma–Aldrich, St. Louis, MO. Breast cancer cells (BT-20) and RPMI-1640 medium were purchased from American Type Culture Collection (ATCC, TIB-186, Rockville, MD).
Surface modification of magnetite nanoparticles
The preparation of monodisperse magnetite nanoparticles and attachment of PEG to the nanoparticles were performed following a procedure as reported
Results and discussion
The surface modification of magnetite nanoparticles with PEG, FA, and PEG-FA conjugate was confirmed by FTIR, as shown in Fig. 2. The appearance of COC (stretching, 1104 cm−1; antisymmetric stretching, 1347 cm−1) and CH (out-of-plane bending, 952 cm−1) peaks in the FTIR spectrum of the nanoparticles after PEG modification demonstrated that PEG was chemically bonded to the nanoparticles (Fig. 2A). The FTIR spectrum of the nanoparticles modified with FA in Fig. 2B indicated that the
Summary
In this study, PEG, FA, and their conjugate PEG-FA were attached to magnetite nanoparticles to compare their effects on the improvement of intracellular uptake of the nanoparticles to human breast cancer cells, BT-20. The results indicated that the nanoparticles after surface modification were monodisperse with coatings on individual nanoparticles. In comparison with nanoparticles coated with only PEG or FA, the PEG-FA conjugate coated nanoparticles demonstrated higher efficiency of
Acknowledgment
This work was supported by NUS research grants WBS R-397-000-009-112 and R-398-000-005-112.
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