Iodinated Copper-Cysteamine Nanoparticles as Radiosensitizers for Tumor Radiotherapy

Abstract

Background/Objectives: Radiotherapy is a widely applied first-line clinical treatment modality of cancer. Copper-cysteamine (Cu-Cy) nanoparticles represent a new type of photosensitizer that demonstrates significant anti-tumor potential by X-ray-induced photodynamic therapy. Iodide is a high-Z element with superior X-ray absorption ability and has the β-decay radiotherapeutic nuclide, ¹³¹I, which emits Cherenkov light. In this study we aimed to investigate the X-ray-induced photodynamic therapy potential of iodinated Cu-Cy (Cu-Cy-I) nanoparticles and also explore the local treatment efficacy of ¹³¹I-labeled Cu-Cy-I ([¹³¹I]Cu-Cy-I) nanoparticles. Methods: The synthesis of [¹³¹I]Cu-Cy-I nanoparticles was performed with [¹³¹I]I^- anions. The in vitro radiobiological effects on tumor cells incubated with Cu-Cy-I nanoparticles by X-ray irradiation were investigated. The in vivo tumor growth-inhibitory effects of the combination of Cu-Cy-I nanoparticles with X-ray radiotherapy and [¹³¹I]Cu-Cy-I nanoparticles were evaluated with 4T1 tumor-xenografted mice. Results: The in vitro experiment results indicated that the X-ray irradiation with the presence of Cu-Cy-I nanoparticles produced a higher intracellular reactive oxygen species (ROS) level and more DNA damage of 4T1 cells and showed a stronger tumor cell killing ability compared to X-ray irradiation alone. The in vivo experimental results with 4T1 breast carcinoma-bearing mice showed that the combination of an intratumoral injection of Cu-Cy-I nanoparticles and X-ray radiotherapy enhanced the tumor growth-inhibitory effect and prolonged the mice's lives. Conclusions: Cu-Cy-I nanoparticles have good potential as new radiosensitizers to enhance the efficacy of external X-ray radiotherapy. However, the efficacy of local treatment with [¹³¹I]Cu-Cy-I nanoparticles at a low ¹³¹I dose was not verified. The effective synthesis of smaller sizes of nanoparticles is necessary for further investigation of the radiotherapy potential of [¹³¹I]Cu-Cy-I nanoparticles.

Keywords: 131I; X-ray-induced photodynamic therapy; copper–cysteamine nanoparticles; radiosensitization; radiotherapy.

Figure 1

Characterization and optical properties of Cu-Cy-I nanoparticles. (A) XRD spectra of Cu-Cy-I. (B) Particle size and PDI measured by DLS. (C) Photographs of Cu-Cy-I under white light and 365 nm UV light. (D) UV–visible absorption spectrum. (E) Fluorescence excitation spectrum by emission light of 600 nm wavelength (red line) and emission spectrum by excitation at 365 nm UV light (blue line).

Figure 2

(A) Radio-TLC results of the radiolabeling mixture, purified [¹³¹I]Cu-Cy-I nanoparticles and free [¹³¹I]I⁻. (B) Radiolabeling stability of [¹³¹I]Cu-Cy-I in PBS and 10% FBS.

Figure 3

The production of ROS in 4T1 cells after different treatments detected with DCFH-DA probe by (A) confocal fluorescence microscope. (B) Flow cytometer. (C) Fluorescence quantification data of DCF intensity by flow cytometer (MFI, mean fluorescence intensity). **** p < 0.0001.

Figure 4

Cu-Cy-I nanoparticles enhanced radiation-induced DNA damage in 4T1 cells receiving Cu-Cy-I and IR (2Gy). (A) Representative immunofluorescence images of γH₂AX foci. (B) Quantification data of γH₂AX foci. ** p < 0.01.

Figure 5

The cytotoxicity of Cu-Cy-I nanoparticles and X-ray irradiation to tumor cells in vitro as measured by CCK-8 assay. * p < 0.05, ** p < 0.01.

Figure 6

In vivo antitumor effect on the orthotopic 4T1 breast cancer cell-xenografted mice. (A) Tumor sizes, (B) survival curve, (C) body weight, and (D) distribution of Cu-Cy-I nanoparticles within the tumor (black arrow).