Abstract 3337: Titanium peroxide nanoparticles enhance antitumor efficacy through reactive oxygen species in pancreatic cancer radiation therapy
Authors: Nakayama Masao , Sasaki Ryohei , Mukohara Toru , Ogino Chiaki , Morita Kenta , Umetsu Mitsuo , Ohara Satoshi , Sato Kazuyoshi , Numako Chiya , Takami Seiichi , Kondo Akihiko 
Published: August 2015

Purpose: Pancreatic cancer is a highly lethal disease and notoriously resistant to many types of cytotoxic chemotherapy and radiotherapy. A novel strategy should be explored for these radioresistant tumors. We originally synthesized a titanium peroxide nanoparticle (TiOxNP) which had a distinct ability to produce reactive oxygen species (ROS) upon X-ray irradiation (IR). Here, the characterization and efficacy of TiOxNP as radiosensitizer for pancreatic cancer therapy were investigated.

Methods: TiOxNPs were synthesized from anatase titanium oxide nanoparticles (TiO2NPs) by H2O2 processing and coated by polyacrylic acid. The ability of TiOxNPs to enhance ROS generation upon X-ray irradiation (IR) was tested by using 3′-(p-Aminophenyl) fluorescein and several antioxidants. A xenograft mouse model using the human pancreatic cancer cell line MIAPaCa-2 was used to evaluate the cytotoxic effects of a combination of TiOxNPs and IR in vivo. MIAPaCa-2 cells were injected subcutaneously into the hind legs of immunodeficient BALB/c mice. Seven days after injection, the tumor was treated with a TiOxNP suspension injected directly into the tumor and application of 5 Gy of IR. Tumor size and health of the mice were monitored for 43 days after the treatment. Induction of apoptosis was evaluated by immunohistochemistry using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining. We also characterized TiOxNPs by ESR and XAFS analyses.

Results: ROS generation was enhanced dramatically by TiOxNPs in a concentration- and radiation dose- dependent manner compared to enhancement by TiO2NPs. At the highest concentration of TiOxNPs, ROS generation upon an irradiation dose of 30 Gy was enhanced by a factor of more than 10. Also, ROS generated by TiOxNPs upon IR were scavenged by vitamin C or glutathione. Growth inhibition of the tumor in the group receiving both TiOxNP and IR was significantly greater than single treatment subgroups (P &lt; 0.05). The number of apoptotic cells was also significantly higher in the combination group (P &lt; 0.05). Histologically, large pools of TiOxNPs around tumor cells and small amounts inside the tumor cells were observed. No mice died within a 43-day observation period or showed any apparent body weight loss. In the ESR spectra, some signals were observed for TiOxNPs. The spectral shapes of Ti K-edge X-ray absorption near edge structure, spectra were the same among the mineral anatase, TiO2NPs and TiOxNPs.

Conclusions: TiOxNPs induced remarkable ROS production upon IR. They were safe and effective in a xenograft mouse model using engrafted human pancreatic cancer cells. Further studies would be necessary to elucidate a mechanism of radical generation and long-term toxicity, however our study shows that TiOxNPs are promising radiosensitizers for application in pancreatic cancer therapy.

Citation Format: Masao Nakayama, Ryohei Sasaki, Toru Mukohara, Chiaki Ogino, Kenta Morita, Mitsuo Umetsu, Satoshi Ohara, Kazuyoshi Sato, Chiya Numako, Seiichi Takami, Akihiko Kondo. Titanium peroxide nanoparticles enhance antitumor efficacy through reactive oxygen species in pancreatic cancer radiation therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3337. doi:10.1158/1538-7445.AM2015-3337