Facile method to radiolabel glycol chitosan nanoparticles with (64)Cu via copper-free click chemistry for MicroPET imaging.

An efficient and straightforward method for radiolabeling nanoparticles is urgently needed to understand the in vivo biodistribution of nanoparticles. Herein, we investigated a facile and highly efficient strategy to prepare radiolabeled glycol chitosan nanoparticles with (64)Cu via a strain-promoted azide-alkyne cycloaddition strategy, which is often referred to as click chemistry. First, the azide (N3) group, which allows for the preparation of radiolabeled nanoparticles by copper-free click chemistry, was incorporated to glycol chitosan nanoparticles (CNPs). Second, the strained cyclooctyne derivative, dibenzyl cyclooctyne (DBCO) conjugated with a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator, was synthesized for preparing the preradiolabeled alkyne complex with (64)Cu radionuclide. Following incubation with the (64)Cu-radiolabeled DBCO complex (DBCO-PEG4-Lys-DOTA-(64)Cu with high specific activity, 18.5 GBq/µmol), the azide-functionalized CNPs were radiolabeled successfully with (64)Cu, with a high radiolabeling efficiency and a high radiolabeling yield (>98%). Importantly, the radiolabeling of CNPs by copper-free click chemistry was accomplished within 30 min, with great efficiency in aqueous conditions. In addition, we found that the (64)Cu-radiolabeled CNPs ((64)Cu-CNPs) did not show any significant effect on the physicochemical properties, such as size, zeta potential, or spherical morphology. After (64)Cu-CNPs were intravenously administered to tumor-bearing mice, the real-time, in vivo biodistribution and tumor-targeting ability of (64)Cu-CNPs were quantitatively evaluated by microPET images of tumor-bearing mice. These results demonstrate the benefit of copper-free click chemistry as a facile, preradiolabeling approach to conveniently radiolabel nanoparticles for evaluating the real-time in vivo biodistribution of nanoparticles.

Tannic acid-functionalized boron nitride nanosheets for theranostics.

Here, we report a tannic acid-Fe3+ coordination complex coating that confers magnetic resonance imaging (MRI) theranostic properties to inert nanomaterials. Boron nitride nanosheets (BNS), which lack magnetic field and light responsiveness, were used as a model nonfunctional nanomaterial. Among various catechol derivatives tested (i.e., dopamine, 3,4-dihydroxyphenylacetic acid, gallic acid, and tannic acid), a coating of tannic acid-Fe3+ coordination complex provided the highest magnetic field relaxivity and near infrared (NIR) laser light responsiveness. An in vitro study showed that KB tumor cells treated with tannic acid-Fe3+ coordination complex adsorbed on BNS (TA-Fe/BNS) exhibited higher T1-weighted magnetic resonance contrast compared with plain BNS, and BNS coated with tannic acid or Fe alone. NIR irradiation at 808 nm caused a significant increase in KB tumor cell death after treatment with TA-Fe/BNS compared with other treatments. In vivo MRI imaging revealed tumor accumulation of intravenously administered TA-Fe/BNS. Guided by MRI information, application of focused laser irradiation onto tumor tissues resulted in complete tumor ablation. These results support the potential of TA-Fe/BNS for MRI theranostics. Moreover, this study suggests the wide applicability of TA-Fe noncovalent coating as biocompatible and facile tool for converting nonfunctional early-generation nanomaterials into functional new nanomaterials, opening new opportunities for their use in translational biomedical applications such as MRI theranostics.

Multi-layer surface modification of pancreatic islets for magnetic resonance imaging using ferumoxytol.

Ferumoxytol is the only clinically available ultrasmall superparamagnetic iron oxide. However, the labeling efficacy of islet magnetic resonance imaging (MRI) using ferumoxytol is not suitable for use in clinical pancreatic islet transplantation (PIT). We evaluated the feasibility of pancreatic islet MRI using ferumoxytol through multi-layer surface modification. A four-layer nanoshield with poly (ethylene) glycol (PEG, 2 layers), ferumoxytol, and heparin was formed on the pancreatic islets. We compared pancreatic islet function, viability, and labeling efficacy of control, ferumoxytol alone-labeled, heparin-PEGylated, and ferumoxytol-heparin-PEGylated islets. With optimization of the ferumoxytol concentration during the ferumoxytol-heparin-PEGylation process, the labeling contrast in ex vivo MRI of ferumoxytol-heparin-PEGylated pancreatic islets was stronger than that of pancreatic islets labeled with ferumoxytol alone, without decreasing ex vivo islet viability or function. In a syngeneic mouse renal subcapsular PIT model, heparin-PEGylation and ferumoxytol-heparin-PEGylation delayed the revascularization of pancreatic islet grafts but did not impair glucose tolerance or revascularization of pancreatic islet grafts four weeks post-transplantation. Pancreatic islet visibility after labeling was also confirmed in a syngeneic mouse intraportal PIT model and in preliminary analysis of a non-human primate intraportal PIT model. In conclusion, multi-layer islet surface modification is a promising option for pancreatic islet MRI in intraportal PIT.

Cerebral glucose metabolism changes in rat brain upon forepaw electrical stimulation at different frequencies.

PET imaging techniques and statistical parametric mapping analysis have been developed to identify neuronal functional activation from brain imaging. The purpose of this study was to examine the efficacy of the glucose metabolism in rat brain during forepaw electrical stimulation with different frequencies (3, 10, or 20 Hz) compared with a nonstimulated group (control). Fluorine-18 fluorodeoxyglucose was injected after confirmation of the range of normal physiology. For quantitative analysis, we used cerebral metabolism rate of glucose consumption (CMRglc) responses in the primary somatosensory cortex (S1FL) and motor cortex (M1). On comparing CMRglc responses in the contralateral S1FL and M1 with those of the ipsilateral areas in intragroup analysis, a significant increase (P<0.05) was observed in two electrical stimulation groups (10 and 20 Hz) but not at the 3 Hz level. In intergroup analysis, the CMRglc responses in the contralateral region of interest were compared with those of the control group to validate which electrical frequency conditions were appropriate to induce neuronal functional activation. Among the stimulation groups, significant increases in CMRglc response were only observed at 10 Hz (P<0.05). Therefore, 10 Hz is the most suitable frequency to confirm changes in CMRglc in the S1FL and M1 of the rat brain, and also fluorine-18 fluorodeoxyglucose PET could be useful to investigate recovery and plasticity in neurological diseases associated with primary sensory-motor cortex function.

The use of pH-sensitive positively charged polymeric micelles for protein delivery.

In this investigation, a nano-sized protein-encapsulated polymeric micelle was prepared by self-assembling human serum albumin (HSA) as a model protein and degradable block copolymer methoxy poly(ethylene glycol)-poly(ß-amino ester) (PEG-PAE) with piperidine and imidazole rings. From the zeta potential measurement, the protein-encapsulated polymeric micelle showed a pH-tuning charge conversion from neutral to positive when pH decreases from 7.8 to 6.2. It was envisioned that the pH-tunable positively charged polymeric micelle could enhance the protein delivery efficiency and, simultaneously, target to the pH-stimuli tissue, such as cancerous tissue or ischemia. The pH-dependent particle size and scattering intensity were also measured and showed 50-70 nm particle size. Consequently, the circular dichroism (CD) spectroscopy confirmed that the secondary structure of albumin was unaffected during the pH changing process. The in vitro cytotoxicity for the polymeric micelle was evaluated on MDA-MB-435 cell lines and no obvious toxicity could be observed when the polymer concentration was below 200 µg/mL. To assess the ability of this pH-tunable positively charged polymeric micelle as a vehicle for protein delivery to in vivo acidic tissues, we utilized a disease rat model of cerebral ischemia that produced an acidic tissue due to its pathologic condition. The rat was intravenously injected with the Cy5.5-labled albumin-encapsulated polymeric micelle. We found a gradual increase in fluorescence signals of the brain ischemic area, indicating that the pH-tuning positively charged protein-encapsulated polymeric micelle could be effective for targeting the acidic environment and diagnostic imaging.