Ningning Ma

Shape-Dependent Radiosensitization Effect of Gold Nanostructures in Cancer Radiotherapy: Comparison of Gold Nanoparticles, Nanospikes, and Nanorods

The shape effect of gold (Au) nanomaterials on the efficiency of cancer radiotherapy has not been fully elucidated. To address this issue, Au nanomaterials with different shapes but similar average size (∼50 nm) including spherical gold nanoparticles (GNPs), gold nanospikes (GNSs), and gold nanorods (GNRs) were synthesized and functionalized with poly(ethylene glycol) (PEG) molecules. Although all of these Au nanostructures were coated with the same PEG molecules, their cellular uptake behavior differed significantly. The GNPs showed the highest cellular responses as compared to the GNSs and the GNRs (based on the same gold mass) after incubation with KB cancer cells for 24 h. The cellular uptake in cells increased in the order of GNPs > GNSs > GNRs. Our comparative studies indicated that all of these PEGylated Au nanostructures could induce enhanced cancer cell-killing rates more or less upon X-ray irradiation. The sensitization enhancement ratios (SERs) calculated by a multitarget single-hit model were 1.62, 1.37, and 1.21 corresponding to the treatments of GNPs, GNSs, and GNRs, respectively, demonstrating that the GNPs showed a higher anticancer efficiency than both GNSs and GNRs upon X-ray irradiation. Almost the same values were obtained by dividing the SERs of the three types of Au nanomaterials by their corresponding cellular uptake amounts, indicating that the higher SER of GNPs was due to their much higher cellular uptake efficiency. The above results indicated that the radiation enhancement effects were determined by the amount of the internalized gold atoms. Therefore, to achieve a strong radiosensitization effect in cancer radiotherapy, it is necessary to use Au-based nanomaterials with a high cellular internalization. Further studies on the radiosensitization mechanisms demonstrated that ROS generation and cell cycle redistribution induced by Au nanostructures played essential roles in enhancing radiosensitization. Taken together, our results indicated that the shape of Au-based nanomaterials had a significant influence on cancer radiotherapy. The present work may provide important guidance for the design and use of Au nanostructures in cancer radiotherapy.

Action of Gold Nanospikes-Based Nanoradiosensitizers: Cellular Internalization, Radiotherapy, and Autophagy

A major challenge to achieve effective X-ray radiation therapy is to use a relatively low and safe radiation dose. Various radiosensitizers, which can significantly enhance the radiotherapeutic performance, have been developed. Gold-based nanomaterials, as a new type of nanoparticle-based radiosensitizers, have been extensively used in researches involving cancer radiotherapy. However, the cancer therapeutic effect using the gold nanoparticle-based radiotherapy is usually not significant because of the low cellular uptake efficiency and the autophagy-inducing ability of these gold nanomaterials. Herein, using gold nanospikes (GNSs) as an example, we prepared a series of thiol-poly(ethylene glycol)-modified GNSs terminated with methoxyl (GNSs), amine (NH2-GNSs), folic acid (FA) (FA-GNSs), and the cell-penetrating peptide TAT (TAT-GNSs), and evaluated their effects on X-ray radiotherapy. For the in vitro study, it was found that the ionizing radiation effects of these GNSs were well correlated with their cellular uptake amounts, with the same order of GNSs < NH2-GNSs < FA-GNSs < TAT-GNSs. The sensitization enhancement ratio (SER), which is commonly used to evaluate how effectively radiosensitizers decrease cell proliferation, reaches 2.30 for TAT-GNSs. The extremely high SER value for TAT-GNSs indicates the superior radiosensitization effect of this nanomaterial. The radiation enhancement mechanisms of these GNSs involved the increased reactive oxygen species (ROS), mitochondrial depolarization, and cell cycle redistribution. Western blotting assays confirmed that the surface-modified GNSs could induce the up-regulation of autophagy-related protein (LC3-II) and apoptosis-related protein (active caspase-3) in cancer cells. By monitoring the degradation of the autophagy substrate p62 protein, GNSs caused impairment of autolysosome degradation capacity and autophagosome accumulation. Our data demonstrated that autophagy played a protective role against caner radiotherapy, and the inhibition of protective autophagy with inhibitors would result in the increase of cell apoptosis. Besides the above in vitro experiments, the in vivo tumor growth study also indicated that X-ray + TAT-GNSs treatment had the best tumor growth inhibitory effect, which confirmed the highest radiation sensitizing effect of TAT-GNSs. This work furthered our understanding on the interaction mechanism between gold nanomaterials and cancer cells and should be able to promote the development of nanoradiosensitizers for clinical applications.

Glutathione-Depleting Gold Nanoclusters for Enhanced Cancer Radiotherapy through Synergistic External and Internal Regulations

The therapeutic performance of cancer radiotherapy is often limited by the overexpression of glutathione (GSH) in tumors and low radiation sensitivity of cancerous cells. To address these issues, the facilely prepared histidine-capped gold nanoclusters (Au NCs@His) were adopted as a radiosensitizer with a high sensitization enhancement ratio of ∼1.54. On one hand, Au NCs@His can inherit the local radiation enhancement property of gold-based materials (external regulation); on the other hand, Au NCs@His can decrease the intracellular GSH level, thus preventing the generated reactive oxygen species (ROS) from being consumed by GSH, and arrest the cells at the radiosensitive G2/M phase (internal regulation).