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.
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.).