Multifunctional Nanoparticles for Cancer Imaging and Therapy

Abstract

Advances in nanotechnology have offered new possibilities in cancer detection andtreatment. Through the use of multifunctional nanoparticles, researchers aim to address current limitations of cancer therapy by expediting the detection of the disease and improving the therapeutic efficacy of drugs while confining their effect in the intended tumor sites. Iron oxide nanoparticles present an attractive platform for such avenues in enhancing clinical outcome as they are not only biocompatible and biodegradable, but also provide contrast for magnetic resonance imaging, a method that can be used to visualize the distribution of the therapeutics. Furthermore, the surface of iron oxide nanoparticles can be readily coated with biocompatible polymers that can provide stability as well as chemical conjugation sites for surface modification. In addition to iron oxide, nanoscale allotropes of carbon have gathered great interest recently for their solubility as well as photoluminescent properties for fluorescence imaging. This dissertation presents the design, synthesis, and application of multifunctional iron oxide and carbon nanoparticles in combating a particularly aggressive form of brain tumor, glioma. Delivery of short interfering RNA (siRNA) that can silence gene expression in a highly specific manner is a potent and highly effective approach to combat glioma. Compared to drugs, siRNA-based therapeutic agents have significantly higher specificity to targets and lower toxicity towards healthy tissue, and thus only a very small amount of siRNAs are needed to reach the site of action to be efficacious. However, effective delivery of therapeutic siRNAs has been hindered by their susceptibility to enzymatic degradation and clearance of naked siRNA by the body’s clearance system, as well as limited cellular uptake of siRNAs due to their negative charge. Nanoparticle (NP) systems can facilitate siRNA delivery by providing stability in biological media. Lipid-based NPs suffer from poor long-term stability, while polymeric NP designs could introduce toxicity. Furthermore, without a method to release the siRNA after endocytosis of the NP, the efficacy of siRNA-mediated gene silencing is diminished. We designed an iron oxide nanoparticle conjugated with functional peptides for improved cancer cell targeting and endosomal escape for delivering siRNAs. The nanoparticle displayed excellent stability and biocompatibility as evaluated by hydrodynamic size measurement over time due to the presence of a chitosan-PEG copolymer. The efficiency of gene silencing was evaluated by transfection of anti RFP siRNA in glioma cells. Conjugation of glioma-targeting peptide chlorotoxin on the nanoparticle improved the cellular uptake of the siRNA, and polyarginine peptide on the nanoparticle enhanced the endosomal escape of the siRNA into the cytosol. The efficiency of gene silencing was found to be greatly enhanced with the addition of the both peptide on the nanoparticle. It was also found that the nanoparticle displayed excellent stability and the siRNA were able to silence the drug resistance gene, which led to greater sensitivity of glioma cells to treatment with a chemotherapeutic agent. Organic dyes commonly used for fluorescence staining and imaging often suffer from poor solubility, as well as toxicity. Most nanomaterials used for fluorescence imaging are made from heavy metals or semiconductors, whose long-term toxicity in the biological system is a major concern. To address these limitations in fluorescence imaging, a facile microwave-assisted synthesis method was developed to create a carbon dot-iron oxide nanoparticle as a fluorescence probe. Using microwave irradiation for uniform heating in the reaction vessel, the nanoparticle was synthesized rapidly, and without the need for toxic chemicals. The nanoparticle exhibited excellent solubility and stability, as shown by time-based hydrodynamic size measurements. In addition, the nanoparticle also exhibited excellent photostability. The nanoparticle displayed negligible cytotoxicity in vitro, making it a safe fluorescent probe for cellular imaging. In glioma cells, a dose-dependent fluorescence signal was observed, which allowed quantitative fluorescence imaging. Finally, the hybrid nanoparticle was also able to deliver chemotherapeutic drugs to induce apoptosis of glioma cells.