Pollen-Structured Gold Nanoclusters for X-ray Induced Photodynamic Therapy

Abstract

Photodynamic therapy (PDT) is a cancer treatment that employs the production of cytotoxic reactive oxygen species (ROS), subsequently triggering tumor apoptosis and tumor size reduction. However, this approach suffers from insufficient light penetration depth. In order to mitigate this issue, pollen-structured gold clusters (PSGCs) were designed for mediating X-ray-induced PDT for radiotherapy enhancement. The structure of PSGCs provides a large surface area that is able to generate ROS upon X-ray irradiation. The synthesized PSGCs were exposed to different X-ray doses and the generated ROS was then quantified by dihydroethidium (DHE) assay. Furthermore, at the cellular level, the PDT efficacy of PSGCs was evaluated via immunofluorescence staining with γ-H2AX and comet assay. The results demonstrated that PSGCs possess a significantly high ROS-generating capacity and a remarkable PDT efficacy in the treatment of breast cancer cells, thus showing potential clinical uses in deep-tissue cancer treatment.

Keywords: mesoporous silica; photodynamic therapy; pollen-structured gold clusters; reactive oxygen species.

Figure 1

Schematic illustration of X-ray-induced photodynamic therapy (PDT) with pollen-structured gold clusters (PSGCs).

Figure 2

(a) Schematic illustration the synthetic route of pollen-structured gold clusters (PSGCs). TEM images of (b) mesoporous silica nanoparticle (MSN)-NH₂, (c) seed particles, and (d) PSGCs.

Figure 3

(a) Fluorescence emission spectra of dihydroethidium (DHE) in PSGCs aqueous solution with different irradiation doses. (b) DHE fluorescence intensity enhancement for water, gold nanoparticles (AuNPs), and PSGCs with a variety X-ray irradiation doses. Statistical significance is denoted as follows: * represents a p value ≤ 0.05 and *** represents a p value ≤ 0.001. NS indicates that a value is not statistically significant.

Figure 4

Graphical description of the production of reactive oxygen species (ROS) as a function of surface area and Au diameter, d.

Figure 5

(a) Immunofluorescence staining of γ-H2AX (red) for MD-MBA-231 cells treated with AuNPs and PSGCs after 0, 2, and 5 Gy X-ray irradiation. Scale bar is 15 µm. (b) Quantitative fluorescence intensity ratio of γ-H2AX to nucleus (red/blue, R/B) for MD-MBA-231 cells treated without and treated with AuNPs and PSGCs after irradiation at 0, 2, and 5 Gy. Inset shows the immunoblotting analysis of caspase 3 protein expression for cells treated with PSGCs after 0, 1, 2, and 5 Gy X-ray irradiation. Statistical significance is denoted as follows: *** represents a p value ≤ 0.001. NS indicates that a value is not statistically significant.

Figure 6

(a) Evaluation of effectiveness X-ray-induced PDT via comet assay. Scale bar is 10 µm. (b) The DNA damage was detected by quantifying the mean tail DNA (%) and was plotted against X-ray doses. Statistical significance is denoted as follows: * represents a p value ≤ 0.05 and *** represents a p value ≤ 0.001. NS denotes that a value is not statistically significant.