2-Nitroimidazole-Functionalized Superparamagnetic Iron Oxide Nanoparticles Detect Hypoxic Regions of Glioblastomas on...

The presence of hypoxic regions in tumors is associated with malignancy and is an important target for the high-precision diagnosis and treatment of tumors. Radioresistant hypoxic regions can be precisely identified and treated without the use of high doses of radiation if hypoxic region-specific contrast agents have a therapeutic effect. In this study, we synthesized a therapeutic-diagnostic complex agent (SPION-PG-NI) by combining polyglycerol-functionalized superparamagnetic iron oxide nanoparticles (SPION-PG, core diameter of 8.8 ± 1.9 nm) as an MRI contrast agent and 2-nitroimidazole (NI, a pimonidazole derivative) as a hypoxia-targeted ligand to visually evaluate hypoxic regions using MRI and improve radiotherapy efficacy at those sites. SPION-PG-NI showed a concentration-dependent contrast effect and had significantly higher accumulation in subcutaneous glioblastomas than the control agent, SPION-PG, 24 h after administration. Immunohistological evaluations showed that the SPION-PG-NI-accumulated regions corresponded well to hypoxic regions. SPION-PG-NI showed neither migration into the brain parenchyma nor neurotoxicity. Both SPION-PG and SPION-PG-NI decrease reactive oxygen species (ROS); however, they improve radiotherapy efficacy in hypoxic glioblastoma cells due to cytotoxicity. This effect of SPION-PG-NI was significantly higher than that of SPION-PG (p < 0.01). After 12 Gy irradiation, the mean normalized glioblastoma tumor volume on day 38 in the SPION-PG-NI group (288%) was significantly lower than that in the control group (882%) (p < 0.05). Collectively, these findings suggest the potential of SPION-PG-NI as a useful and safe tumor theranostic nanodevice for hypoxic imaging and improving radiotherapy efficacy.