Image contrast assessment of metal-based nanoparticles as applications for image-guided radiation therapy

Metal-based nanoparticles (NPs) have been extensively studied for dose enhancement applications in radiation therapy. This study investigated the utility of such NPs for image-guided radiation therapy (IGRT). Phantom images of gold NPs (AuNPs) and titanium peroxide NPs (TiOxNPs) with different concentrations were acquired using IGRT modalities, including cone-beam computed tomography (CBCT). AuNPs induced strong contrast enhancement in kV energy CBCT images, whereas TiOxNPs at high concentrations showed weak but detectable changes. The results indicated that these NPs can be used to enhance IGRT images as well as dose enhancement for treatment purposes.

In vivo tissue distribution and safety of polyacrylic acid-modified titanium peroxide nanoparticles as novel radiosensitizers

Polyacrylic acid (PAA)-modified titanium peroxide nanoparticles (PAA-TiO_x NPs) are promising radiosensitizers. PAA-TiO_x NPs were synthesized from commercial TiO₂ nanoparticles that were modified with PAA and functionalized by H₂O₂ treatment. To realize practical clinical uses for PAA-TiO_x NPs, their tissue distribution and acute toxicity were evaluated using healthy mice and mice bearing tumors derived from xenografted MIAPaCa-2 human pancreatic cancer cells. Healthy mice were injected with PAA-TiO_x NPs at 25 mg/kg body weight via the tail vein, and tumor-bearing mice were injected either into the tumor locally or via the tail vein. The concentration of PAA-TiO_x NPs in major organs was determined over time using inductively coupled-plasma atomic emission spectrometry. After 1 h, 12% of the PAA-TiO_x NP dose had accumulated in the tumor, and 2.8% of the dose remained after 1 week. Such high accumulation could be associated with enhanced permeability and retention effects of the tumor, as PAA-TiO_x NPs are composed of inorganic particles and polymers, without tumor-targeting molecules. The liver accumulated the largest proportion of the injected nanoparticles, up to 42% in tumor-bearing mice. Blood biochemical parameters were also investigated after intravenous injection of PAA-TiO_x NPs in healthy mice. PAA-TiO_x NPs invoked a slight change in various liver-related biochemical parameters, but no liver injury was observed over the practical dose range. In the future, PAA-TiO_x NPs should be modified to prevent accumulation in the liver and minimize risk to patients.

Titanium peroxide nanoparticles enhanced cytotoxic effects of X-ray irradiation against pancreatic cancer model through reactive oxygen species generation in vitro and in vivo

Background

Biological applications of nanoparticles are rapidly increasing, which introduces new possibilities to improve the efficacy of radiotherapy. Here, we synthesized titanium peroxide nanoparticles (TiOxNPs) and investigated their efficacy as novel agents that can potently enhance the effects of radiation in the treatment of pancreatic cancer.

Methods

TiOxNPs and polyacrylic acid-modified TiOxNPs (PAA-TiOxNPs) were synthesized from anatase-type titanium dioxide nanoparticles (TiO₂NPs). The size and morphology of the PAA-TiOxNPs was evaluated using transmission electron microscopy and dynamic light scattering. The crystalline structures of the TiO₂NPs and PAA-TiOxNPs with and without X-ray irradiation were analyzed using X-ray absorption. The ability of TiOxNPs and PAA-TiOxNPs to produce reactive oxygen species in response to X-ray irradiation was evaluated in a cell-free system and confirmed by flow cytometric analysis in vitro. DNA damage after X-ray exposure with or without PAA-TiOxNPs was assessed by immunohistochemical analysis of γ-H2AX foci formation in vitro and in vivo. Cytotoxicity was evaluated by a colony forming assay in vitro. Xenografts were prepared using human pancreatic cancer MIAPaCa-2 cells and used to evaluate the inhibition of tumor growth caused by X-ray exposure, PAA-TiOxNPs, and the combination of the two.

Results

The core structures of the PAA-TiOxNPs were found to be of the anatase type. The TiOxNPs and PAA-TiOxNPs showed a distinct ability to produce hydroxyl radicals in response to X-ray irradiation in a dose- and concentration-dependent manner, whereas the TiO₂NPs did not. At the highest concentration of TiOxNPs, the amount of hydroxyl radicals increased by >8.5-fold following treatment with 30 Gy of radiation. The absorption of PAA-TiOxNPs enhanced DNA damage and resulted in higher cytotoxicity in response to X-ray irradiation in vitro. The combination of the PAA-TiOxNPs and X-ray irradiation induced significantly stronger tumor growth inhibition compared to treatment with either PAA-TiOxNPs or X-ray alone (p < 0.05). No apparent toxicity or weight loss was observed for 43 days after irradiation.

Conclusions

TiOxNPs are potential agents for enhancing the effects of radiation on pancreatic cancer and act via hydroxyl radical production; owing to this ability, they can be used for pancreatic cancer therapy in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-016-0666-y) contains supplementary material, which is available to authorized users.