International Journal of Nanomedicine (Apr 2019)
Highly sensitive electron paramagnetic resonance nanoradicals for quantitative intracellular tumor oxymetric images
Abstract
Nai-Tzu Chen,1 Eugene D Barth,2,3 Tsung-Hsi Lee,4 Chin-Tu Chen,5 Boris Epel,2,3 Howard J Halpern,2,3 Leu-Wei Lo5,61Institute of New Drug Development, China Medical University, Taichung 40402, Taiwan; 2Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA; 3Center for EPR Imaging In Vivo Physiology, University of Chicago, Chicago, IL 60637, USA; 4Department of Biological Science and Technology, China Medical University, Taichung 40402, Taiwan; 5Department of Radiology, University of Chicago, Chicago, IL 60637 USA; 6Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Zhunan 35053, TaiwanPurpose: Tumor oxygenation is a critical parameter influencing the efficacy of cancer therapy. Low levels of oxygen in solid tumor have been recognized as an indicator of malignant progression and metastasis, as well as poor response to chemo- and radiation therapy. Being able to measure oxygenation for an individual’s tumor would provide doctors with a valuable way of identifying optimal treatments for patients.Methods: Electron paramagnetic resonance imaging (EPRI) in combination with an oxygen-measuring paramagnetic probe was performed to measure tumor oxygenation in vivo. Triarylmethyl (trityl) radical exhibits high specificity, sensitivity, and resolution for quantitative measurement of O2 concentration. However, its in vivo applications in previous studies have been limited by the required high dosage, its short half-life, and poor intracellular permeability. To address these limitations, we developed high-capacity nanoformulated radicals that employed fluorescein isothiocyanate-labeled mesoporous silica nanoparticles (FMSNs) as trityl radical carriers. The high surface area nanostructure and easy surface modification of physiochemical properties of FMSNs enable efficient targeted delivery of highly concentrated, nonself-quenched trityl radicals, protected from environmental degradation and dilution.Results: We successfully designed and synthesized a tumor-targeted nanoplatform as a carrier for trityl. In addition, the nanoformulated trityl does not affect oxygen-sensing capacity by a self-relaxation or broadening effect. The FMSN-trityl exhibited high sensitivity/response to oxygen in the partial oxygen pressure range from 0 to 155 mmHg. Furthermore, MSN-trityl displayed outstanding intracellular oxygen mapping in both in vitro and in vivo animal studies.Conclusion: The highly sensitive nanoformulated trityl spin probe can profile intracellular oxygen distributions of tumor in a real-time and quantitative manner using in vivo EPRI.Keywords: tumor oxygenation, electron paramagnetic resonance imaging (EPRI), mesoporous silica nanoparticles (MSNs), triarylmethyl (trityl) spin probe
