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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.

Exosomes are a subgroup of extracellular vesicles that are released by all types of cells, including tumor cells, and mediate intercellular communication via the transport of various intracellular components, including microRNAs, messenger RNAs, and proteins. Radiation produces reactive oxygen species and induces DNA double-strand break in cancer cells and normal cells. Cancer cells have severe damage and die by irradiation, but normal cells can keep proliferation with their high DNA repair ability. Irradiated cells generate communication signals and cause biological changes in neighboring or distant non-irradiated cells. This review outlines the role of exosomes in radiation therapy. In the tumor microenvironment, exosomes are considered to regulate cell survival, migration, and resistance to therapy by interacting with vascular endothelial cells and various types of immune cells. Nowadays, radiation therapy is typically combined with immunotherapy. Regulation of the activity of exosomes may overcome the problem of resistance to immunotherapy. Furthermore, exosomes can attenuate resistance to chemotherapy by transporting certain types of microRNA. The current evidence suggests that exosomes may be useful in the diagnosis and treatment of cancer in the future.

The development of potentially safe radiosensitizing agents is essential to enhance the treatment outcomes of radioresistant cancers. The titanium peroxide nanoparticle (TiOxNP) was originally produced using the titanium dioxide nanoparticle, and it showed excellent reactive oxygen species (ROS) generation in response to ionizing radiation. Surface coating the TiOxNPs with polyacrylic acid (PAA) showed low toxicity to the living body and excellent radiosensitizing effect on cancer cells. Herein, we evaluated the mechanism of radiosensitization by PAA-TiOxNPs in comparison with gold nanoparticles (AuNPs) which represent high-atomic-number nanoparticles that show a radiosensitizing effect through the emission of secondary electrons. The anticancer effects of both nanoparticles were compared by induction of apoptosis, colony-forming assay, and the inhibition of tumor growth. PAA-TiOxNPs showed a significantly more radiosensitizing effect than that of AuNPs. A comparison of the types and amounts of ROS generated showed that hydrogen peroxide generation by PAA-TiOxNPs was the major factor that contributed to the nanoparticle radiosensitization. Importantly, PAA-TiOxNPs were generally nontoxic to healthy mice and caused no histological abnormalities in the liver, kidney, lung, and heart tissues.

Purpose/Objectives: The mechanism of intercellular communication after radiation exposure in cancer cells remains fully undetermined. Exosomes are lipid bilayer-constituted, membrane-enclosed small vesicles that are recognized as mediators transporting a variety of intracellular components including miRNA. Here we identified the novel role of exosomes released from irradiated cells to neighboring cancer cells. Materials/Methods: Human pancreatic cancer cell line MIAPaCa-2 was used in this study. Purified exosome product (PEP) was obtained from cultured media by ultra-centrifugation. PEP was morphologically confirmed by transmission electron microscopy (TEM), and analyzed by NanoSight. Exosome-specific surface markers CD9 and CD63 were evaluated by western blotting. Endocytosis of irradiated exosomes was confirmed by fluorescent microscopy by using the PKH26 dye. Cell survival after irradiation was evaluated by a colony-forming assay. Intracellular reactive oxygen species (ROS) levels were determined using the oxidation-sensitive fluorescent probe dye C-H 2 DCF, and DNA damage was evaluated by detecting phosphorylated histone 2AX (γ-H2AX) foci by immunocytochemistry. MiRNAs were isolated from the exosomes after 5 Gy or 8 Gy of irradiation and comprehensive miRNA expression analysis was performed by miRNA microarray analyses. Expressions of Cu/Zn superoxide dismutase enzyme (SOD1) or Mn superoxide dismutase enzyme (SOD2), catalase, and glutathione peroxidase were studied to determine whether the exosomes received by the neighboring cells may have influence to them and lead to production of ROS or not. Results: Exosome characteristics were confirmed by multiple methods. The uptake of irradiated exosomes was significantly higher than that of nonirradiated exosomes. Notably, nonirradiated neighboring cells with irradiated exosomes induced higher intracellular levels of ROS, and a higher frequency of DNA damage. These neighboring cells also showed greater sensitivity to radiation. Seven upregulated and 5 downregulated miRNAs were identified that correlated with the miRNA microarray analyses results obtained after 5 Gy and 8 Gy radiation. Among them, miR-6823-5p was identified as a possible candidate for SOD1 inhibition, leading to intracellular ROS production and DNA damage. Conclusions : This is the first study to determine that irradiated exosomes can enhance the radiation effect via ROS production in cancer cells. This novel finding may lead to the understanding of the bystander effect of neighboring cancer cells.

The precise mechanism of intercellular communication between cancer cells following radiation exposure is unclear. Exosomes are membrane‑enclosed small vesicles comprising lipid bilayers and are mediators of intercellular communication that transport a variety of intracellular components, including microRNAs (miRNAs or miRs). The present study aimed to identify novel roles of exosomes released from irradiated cells to neighboring cancer cells. In order to confirm the presence of exosomes in the human pancreatic cancer cell line MIAPaCa‑2, ultracentrifugation was performed followed by transmission electron microscopy and nanoparticle tracking analysis (NanoSight) using the exosome‑specific surface markers CD9 and CD63. Subsequent endocytosis of exosomes was confirmed by fluorescent microscopy. Cell survival following irradiation and the addition of exosomes was evaluated by colony forming assay. Expression levels of miRNAs in exosomes were then quantified by microarray analysis, while protein expression levels of Cu/Zn‑ and Mn‑superoxide dismutase (SOD1 and 2, respectively) enzymes in MIAPaCa‑2 cells were evaluated by western blotting. Results showed that the uptake of irradiated exosomes was significantly higher than that of non‑irradiated exosomes. Notably, irradiated exosomes induced higher intracellular levels of reactive oxygen species (ROS) and a higher frequency of DNA damage in MIAPaCa‑2 cells, as determined by fluorescent microscopy and immunocytochemistry, respectively. Moreover, six up‑ and five downregulated miRNAs were identified in 5 and 8 Gy‑irradiated cells using miRNA microarray analyses. Further analysis using miRNA mimics and reverse transcription‑quantitative PCR identified miR‑6823‑5p as a potential candidate to inhibit SOD1, leading to increased intracellular ROS levels and DNA damage. To the best of our knowledge, the present study is the first to demonstrate that irradiated exosomes enhance the radiation effect via increasing intracellular ROS levels in cancer cells. This contributes to improved understanding of the bystander effect of neighboring cancer cells.