Characterization of titanium dioxide nanoparticles modified with polyacrylic acid and H₂O₂ for use as a novel radiosensitizer

Abstract

An induction of polyacrylic acid-modified titanium dioxide with hydrogen peroxide nanoparticles (PAA-TiO₂/H₂O₂ NPs) to a tumor exerted a therapeutic enhancement of X-ray irradiation in our previous study. To understand the mechanism of the radiosensitizing effect of PAA-TiO₂/H₂O₂ NPs, analytical observations that included DLS, FE-SEM, FT-IR, XAFS, and Raman spectrometry were performed. In addition, highly reactive oxygen species (hROS) which PAA-TiO₂/H₂O₂ NPs produced with X-ray irradiation were quantified by using a chemiluminescence method and a EPR spin-trapping method. We found that PAA-TiO₂/H₂O₂ NPs have almost the same characteristics as PAA-TiO₂. Surprisingly, there were no significant differences in hROS generation. However, the existence of H₂O₂ was confirmed in PAA-TiO₂/H₂O₂ NPs, because spontaneous hROS production was observed w/o X-ray irradiation. In addition, PAA-TiO₂/H₂O₂ NPs had a curious characteristic whereby they absorbed H₂O₂ molecules and released them gradually into a liquid phase. Based on these results, the H₂O₂ was continuously released from PAA-TiO₂/H₂O₂ NPs, and then released H₂O₂ assumed to be functioned indirectly as a radiosensitizing factor.

Keywords:

• Titanium dioxide
• nanoparticles
• hydrogen peroxide
• radiation therapy
• reactive oxygen species
• radiosensitizer

Disclosure statement

We have no conflict of interest in connection with this paper.

Funding

This work was partly supported by a Grant-in-Aid for Scientific Research (C) from the Japan Science and Technology Agency, Japan (25420831 to C.O.), a Grant-in-Aid for Challenging Exploratory Research (25670535 to R.S.), a Grant-in-Aid for Young Scientists (B) (15K21156 to Y.N.), and Special Coordination Funds for Promoting Science and Technology, Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Innovative Bioproduction, Kobe) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This work was also partly supported by the Hosokawa powder technology foundation (to C.O.) and the Suzuken memorial foundation (to C.O.).