SWNTs Used to Translocate RNA Polymer
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RESEARCH/RESEARCHERS
SWNTs Used to Translocate RNA Polymer A critical component in the development of gene therapy involves transfection—the uptake of foreign DNA into cells. However, the physicochemical properties of DNA are themselves impediments to the transfer of DNA across cell membranes (translocation). Viral transfection vectors are currently most effective because viruses have a natural ability to introduce genetic material into cells. However, the immune responses to viruses frequently prevent successful gene delivery. Nonviral transfection vectors avoid this difficulty but suffer from low efficiency rates for nuclear membrane penetration and gene expression. Those few nonviral transfection vectors that have achieved high efficiency also exhibit cytotoxicity. Recently, P.C. Ke and colleagues from Clemson University have considered as transfection vectors single-walled carbon nanotubes (SWNTs) because of their large surface area, stability, flexibility, and biocompatibility. As reported in the December 8, 2004, issue of Nano Letters (p. 2473; DOI: 10.1021/nl048326j), the researchers demonstrated the delivery of RNA polymer poly(rU) into breast cancer cells using SWNTs as transporters. The researchers synthesized SWNT bundles using the arcdeposition method. The prevalent SWNT diameter was about 1.4 nm. SWNT–RNA poly(rU) hybrids were formed through nonspecific binding, which allows the hybrid to dissociate into its two components upon delivery. The researchers fluorescently labeled SWNT-poly(rU) hybrids with propidium iodide (PI) and then incubated the hybrids with MCF7 breast cancer cells (cell membranes are known to be impermeable to PI). The researchers used as controls PI and PI-labeled poly(rU). For imaging, the researchers used confocal fluorescence microscopy because it allows for axial discrimination of the labeled SWNT-poly(rU) hybrids on cell membranes, within cytoplasm or within the nucleus. The research team also employed radioisotopic labeling, cell enumeration, and a standard metabolic activity assay (MTS) to quantitatively evaluate direct cellular uptake and SWNT cytotoxicity. The researchers found the labeled SWNT-poly(rU) hybrids across the cellular and nuclear membranes of the MCF7 cells, while the controls were excluded. Furthermore, the research team showed, by means of cell growth and MTS assays, that SWNTs have no cytotoxicity for concentrations of up to 1 mg/mL. Ke and co-workers said that their studies show the potential of 4
SWNTs as transporters for gene delivery. They believe that SWNTs and biomedicine can be more fully integrated once the mechanisms of SWNT translocation are deciphered and gene transfection assays with SWNT transporters are performed. STEVEN TROHALAKI
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