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Gadolinium neutron capture therapy (GdNCT) is considered as a new promising cancer therapeutic technique. Nevertheless, limited GdNCT applications have been reported so far. In this study, surface-modified ultrasmall gadolinium oxide nanoparticles (UGNPs) with cancer-targeting ability (davg = 1.8 nm) were for the first time applied to the in vivo GdNCT of cancer using nude model mice with cancer, primarily because each nanoparticle can deliver hundreds of Gd to the cancer site. For applications, the UGNPs were grafted with polyacrylic acid (PAA) for biocompatibility and colloidal stability, which was then conjugated with cancer-targeting arginylglycylaspartic acid (RGD) (shortly, RGD-PAA-UGNPs). The solution sample was intravenously administered into the tails of nude model mice with cancer. At the time of the maximum accumulation of the RGD-PAA-UGNPs at the cancer site, which was monitored using magnetic resonance imaging, the thermal neutron beam was locally irradiated onto the cancer site and the cancer growth was monitored for 25 days. The cancer growth suppression was observed due to the GdNCT effects of the RGD-PAA-UGNPs, indicating that the surface-modified UGNPs with cancer-targeting ability are potential materials applicable to the in vivo GdNCT of cancer.

We report a convenient approach to prepare ultrasmall Fe3O4 nanoparticles (NPs) functionalized with an arginylglycylaspartic acid (RGD) peptide for in vitro and in vivo magnetic resonance (MR) imaging of gliomas. In our work, stable sodium citrate-stabilized Fe3O4 NPs were prepared by a solvothermal route. Then, the carboxylated Fe3O4 NPs stabilized with sodium citrate were conjugated with polyethylene glycol (PEG)-linked RGD. The formed ultrasmall RGD-functionalized nanoprobe (Fe3O4-PEG-RGD) was fully characterized using different techniques. We show that these Fe3O4-PEG-RGD particles with a size of 2.7 nm are water-dispersible, stable, cytocompatible and hemocompatible in a given concentration range, and display targeting specificity to glioma cells overexpressing αvβ3 integrin in vitro. With the relatively high r1 relaxivity (r1 = 1.4 mM(-1) s(-1)), the Fe3O4-PEG-RGD particles can be used as an efficient nanoprobe for targeted T1-weighted positive MR imaging of glioma cells in vitro and the xenografted tumor model in vivo via an active RGD-mediated targeting pathway. The developed RGD-functionalized Fe3O4 NPs may hold great promise to be used as a nanoprobe for targeted T1-weighted MR imaging of different αvβ3 integrin-overexpressing cancer cells or biological systems.