Poly(?-glutamic Acid)-stabilized Iron Oxide Nanoparticles: Synthesis, Functionalization And Biomedical Applications

Magnetic resonance?MR? imaging has been widely applied in clinical diagnosis due to its high spatial resolution and tomographic capabilities. For improved MR imaging applications, contrast agents have been usually required. Superparamagnetic iron oxide?Fe₃O₄? nanoparticles?NPs? have been employed as T2-weighted MR contrast agents due to their capacity to shorten the T2 relaxation time of water protons. In general, the developed Fe₃O₄ NPs should have excellent colloidal stability, biocompatibility, and the ability to escape the nonspecific uptake by reticuloendothelial system?RES?. An effective approach to meet the above requirements is to modify the surface of the Fe₃O₄ NPs with hydrophilic polymers. However, most of the employed approaches are quite time-consuming or involve in multiple-step processes, and some of the approaches even require high temperature or high pressure conditions. Development of new polymer-coated Fe₃O₄ NPs with a simple one-step method for MR imaging applications still remains a great challenge.Poly??-glutamic acid??PGA? is a biodegradable and biocompatible polymer with good water-retention ability due to the presence of a large number of carboxyl groups on its side chain. PGA have been widely applied in different biomedical fields. Nevertheless, there have been no studies concerning the use of PGA as a stabilizing agent to form Fe₃O₄ NPs for biomedical applications.In chapter 2, we developed a facile one-step method to produce PGA-stabilized Fe₃O₄ NPs for MR imaging of tumors. In the presence of PGA, mild reduction of Fe?III? salt using Na2SO3 as a reducing agent resulted in the formation of PGA-stabilized Fe₃O₄ NPs?Fe₃O₄-PGA NPs?. The formed Fe₃O₄-PGA NPs were well characterized v ia different methods. The size and morphology of the Fe₃O₄-PGA NPs were characterized by TEM. the formed Fe₃O₄-PGA NPs display a spherical or semi-spherical shape with quite a uniform size distribution. The mean particle size was estimated to be 5.3 ± 2.6 nm. The coating of PGA onto the Fe₃O₄ NP surfaces rendered the particles with a negative surface potential?-38.6 m V?, which makes them quite colloidally stable. The r2 relaxivity of the Fe₃O₄-PGA NPs was estimated to be 333.7 mM-1s-1, which was much higher than that of other Fe₃O₄ NPs reported in the literature. The in vitro hemocompatibility, cytocompatibility, and macrophage cellular uptake of the particles were then thoroughly investigated. Our results suggest that the Fe₃O₄-PGA NPs can be used as a contrast agent for MR imaging of tumors thanks to the passive EPR effect.In chapter 3, we have synthesized targeting ligand-modif ied Fe₃O₄-PGA NPs to achieve the effect of targeted MR imaging of cancer cells. Clearly, the formed Fe₃O₄-PGA NPs were synthesized via a mild reduction method. Folic acid?FA? and fluorescein isothiocyanate?FI? were connected on generation 2?G2? poly?amidoamine? dendrimers to form G2.NH2-FA-FI dendrimers. Then the formed of Fe₃O₄-PGA NPs were conjugated with the G2.NH2-FA-FI dendrimers, followed by acetylation of the remaining dendrimer amines for targeted MR imaging of cancer cells. The properties of the Fe₃O₄-PGA-G2-FA-FI NPs including the zeta potential and r2 relaxivity were characterized by different techniques. The results show that G2 dendrimers have been conjugated to Fe₃O₄-PGA NPs. The r2 relaxivity of the Fe₃O₄-PGA NPs was estimated to be 332.5 mM-1s-1. The cytocompatibility of the Fe₃O₄-PGA-G2-FA-FI NPs was next assessed by MTT cell viability assay and observation of the morphology. The targeting specificity of the FA-targeted Fe₃O₄ NPs was evaluated by flow cytometry. The results demonstrated the targeting ability of the Fe₃O₄-PGA-G2-FA-FI NPs.In summary, we developed a convenient method to form the Fe₃O₄-PGA NPs for MR imaging. Then Fe₃O₄-PGA NPs can be conjugated with G2 dendrimers to achieve the targeting specificity to FA receptor-expressing He La cells. These developed NPs has promising potential to be used as a contrast agent for MR imaging applications.