LAUSR

Background: Metal nanoparticles have been proposed as potential radiosensitizers. Among those, titanium nanoparticles are attractive candidates for application as radiosensitizers. We have newly established and evaluated titanium peroxide nanoparticles (TiOxNPs). The TiOxNPs are generated from titanium dioxide nanoparticles (TiO2NPs), manufactured via direct reaction of TiO2NPs with hydrogen peroxide. Distinguished characteristics of the TiOxNPs are continuous generation of reactive oxygen species (ROS) by X-ray irradiation. Bio-availabilities and safety was previously reported (Nanoparticles, 2020; 10(6): 1125). Materials and Methods: Characteristics of TiOxNPs were determined following experiments. Dynamic light scattering analysis was used to measure the diameter and Z-potential of the NPs. Transmission electron microscope (TEM) observation revealed the detailed topology of the NPs. X-ray irradiation was performed using the X-ray generator at a voltage of 150 kV and a current of 5 mA with a 1-mm thick aluminum filter in vitro and in vivo. Reactive oxygen species (ROS) generation was evaluated using human pancreatic cancer cells, named MIAPaCa-2. The cells were stained with 50 μM carboxy-20,70-dichlorofluorescein (C-H2DCF) incubated for 45 min, and then stained with Hoechst for nuclear staining. The degree of fluorescence of C-H2DCF was detected using the fluorescence microscope. To evaluate cytotoxic effects of TiOxNPs, a colony-formation assay was performed. For xenograft experiments, the MIAPaCa-2 cells (2 x 106 cells) were injected subcutaneously into the hind legs of the BALB/cAJcl nude mice. Once the tumor volume reached 100-200 mm3, mice were randomly assigned into six groups: the control group, TiOxNPs alone, 5 Gy alone, and TiOxNPs combined with 5 Gy. Tumor size, body weight, and health condition of all mice were followed every two to three days for 55 days post-treatment. Results: Primary particles smaller than 10 nm gathered and formed secondary particles that were approximately 50 nm in diameter, and their Z-potential was -30 mV. TEM observation revealed the detailed topology of the NPs. The TiOxNPs enhanced H2O2 production more than 7-folds compared to X-ray irradiation alone in MIA PaCa-2 cells. In xenografts, combination effects of the TiOxNPs and X-ray irradiation were significantly greater than X-ray irradiation (5 Gy) alone. Conclusions: The TiOxNPs revealed to be powerful radiosensitizers in pancreatic cancer model. Clinical tests are warranted to clarify the application of TiOxNPs in the nearest future. Citation Format: Ryohei Sasaki, Hiroaki Akasaka, Masao Nakayama, Yoshiko Fujita, Hikaru Kubota, Kenta Morita, Mennaallah Hassan, Mohammed Salah, Yuya Nishimura, Naritoshi Mukumoto, Takeaki Ishihara, Daisuke Miyawaki, Chiaki Ogino. A novel radiosensitizer of titanium peroxide nanoparticles (TiOxNPs) through continuous ROS generation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2837.