Ultrastructure of a Carbon Nanotube-based Delivery System for Cancer Therapy

带有药物和导向配体的碳纳米管具有很好的靶向药物传递的潜力。单壁碳纳米管(SWNT)具有非常高的比表面积，可以通过化学附着、吸附或包埋的方式与生物分子衍生化。这种单壁碳纳米管上的生物偶联物具有将生物活性分子穿过细胞膜甚至进入细胞核的能力。我们进行了超微结构实验，以表征纳米生物结合物，并研究功能化碳纳米管在口腔癌细胞治疗药物输送中的应用。抗癌药物顺铂被共价结合到单壁碳纳米管(SWNTs)上，这些单壁碳纳米管又与口腔癌细胞高水平表达的表皮生长因子(EGF)结合。这种纳米生物结合物的表征对于这些功能生物材料的成功开发是非常重要的。我们已经应用原子尺度扫描电子显微镜(STEM)来可视化和定量单个基于铂的药物分子附着在用于靶向药物输送的单壁碳纳米管上。环形暗视野STEM成像使一线抗癌药物顺铂能够在单分子水平上在纳米管上可视化。用能量色散X射线光谱和傅里叶变换红外光谱证实了顺铂在纳米管上的存在。茎断层扫描也被用来提供关于顺铂在纳米管生物结合物上的负载的额外信息。 将功能化纳米颗粒与培养的头颈部鳞状细胞癌(HNSCC)细胞孵育后，用戊二醛和四氧化三铯固定，脱水包埋在EPON中，制备电子显微镜。使用120千伏电子显微镜数字化记录的电子显微镜显示，成束的单壁碳纳米管已经进入细胞。在大多数HNSCC细胞中，SWNT束分布在细胞质中，而一些细胞在细胞核附近显示出较高浓度的纳米管。结果证实了从共聚焦荧光显微镜获得的较低分辨率的数据，但提供了关于进入纳米管后与亚细胞结构相关的更详细的信息。超微结构数据与NIDCR进行的光学测量和细胞存活率分析相关联。我们还使用扫描电子显微镜(STEM)和X射线纳米分析来表征单个纳米管，并确定结合的铂原子的分布。这些纳米颗粒生物偶联物的表征对于这一方法的未来进展是至关重要的。特别是，纳米管的大小和每根纳米管的生物分子数是重要的参数，特别是对于药物输送而言。我们的STEM结果首次显示了单个基于铂的药物分子附着在单壁碳纳米管上的原子尺度可视化和量化。

Carbon nanotubes with attached drugs and directing ligands have excellent potential for targeted drug delivery. Single wall carbon nanotubes (SWNT) with very highly specific surface areas can be derivatized with biomolecules either through chemical attachment, adsorption or encapsulation. Such bioconjugates on SWNTs have the ability to deliver bioactive molecules across cell membranes and even into cell nuclei. We have performed ultrastructural experiments to characterize the nanobioconjugates and to investigate the application of functionalized carbon nanotubes to deliver therapeutic drugs to oral cancer cells. The anti-cancer drug cisplatin was covalently bound to single walled carbon nanotubes (SWNTs) and these were in turn bound to epidermal growth factor (EGF), which is expressed at very high levels by oral cancer cells. Characterization of such SWNT nanobioconjugates is important for the successful development of these functional bionanomaterials. We have applied atomic-scale scanning transmission electron microscopy (STEM) to visualize and quantitate single Pt-based drug molecules attached to single-wall carbon nanotubes designed for targeted drug-delivery. Annular dark-field STEM imaging enabled visualization of the first-line anticancer drug cisplatin on the nanotubes at single molecule levels. The identity and presence of cisplatin on the nanotubes were confirmed using energy-dispersive x-ray spectroscopy and Fourier transform infrared spectroscopy. STEM tomography was also used to provide additional information about the loading of cisplatin on the nanotube bioconjugates. Cultured head and neck squamous cell carcinoma (HNSCC) cells of epithelial origin incubated with the functionalized nanoparticles were prepared for electron microscopy by fixation in glutaraldehyde and osmium tetroxide, followed by dehydration and embedding in epon. Electron micrographs, recorded digitally using a 120 kV TEM, revealed that bundles of SWNTs had entered the cells. In most HNSCC cells the SWNT bundles were distributed throughout the cytoplasm, whereas some cells showed a higher concentration of nanotubes adjacent to the cell nucleus. The results confirmed lower resolution data obtained from confocal fluorescence microscopy but provided more detailed information about the subcellular structures associated with the nanotubes after entry. The ultrastructural data are being correlated with optical measurements and cell viability assays conducted in NIDCR. We have also used scanning transmission electron microscopy (STEM) and x-ray nanoanalysis to characterize individual nanotubes and to determine the distribution of bound platinum atoms. Characterization of these nanoparticle bioconjugates is essential for the future progress of this approach. In particular, nanotube size, and number of biomolecules per nanotube length are important parameters, especially for drug delivery. Our STEM results show for the first time atomic scale visualization and quantification of single Pt-based drug molecules attached to SWNTs.