Preparation And Functionalization Of Polyethyleneimine–modified Iron Oxide Nanoplatform For Theranostic Of Cancer Applications

With the development of synthetic technology and nanomedicine, iron oxide（Fe₃O₄） nanoparticles（NPs）, as an excellent negative contrast agent, have already been extensively utilized for magnetic resonance（MR） imaging application. To enhance the sensitivity of disease diagnosis, various multifunctional Fe₃O₄ NPs have been successively developed to target the nidus effectively, resulting in a good MR imaging effect. In addition, nanocomposite constructed by introducing gold（Au） NPs into Fe₃O₄-based NPs can be used for multi-mode MR/computed tomography（CT）/photoacustic（PA） imaging and photothermal therapy（PTT）.In our previous work, by using polyethyleneimine（PEI） with large amount of surface amines as stabilizer and further functional modification via PEI amine-mediated conjugation chemistry, multifunctional Fe₃O₄ nanoplatforms（such as, PEI-coated Fe₃O₄ NPs and Fe₃O₄/Au composite nanoparticles（CNPs）） were fabricated for dual- or multi-mode molecular imaging. In this thesis we aimed to enhance the sensitivity of disease diagnosis by synthesizing Fe₃O₄ NPs with higher r2 relaxivity or Fe₃O₄/Au CNPs with targeting ligands, and regulate the morphology and size of Fe₃O₄/Au CNPs for theranostic of tumors.In chapter 2, PEI-coated Fe₃O₄ NPs were first synthesized via mild reduction route, and then modified with tracer fluorescein isothiocyanate（FI） and targeting ligand PEGylated RGD polypeptide, followed by acetylation of remained surface amines. At last, The formed multifunctional RGD targeted Fe₃O₄ NPs were used as contrast agent for T2-weighted MR imaging of cancer cells in vitro and a xenografted tumor in vivo. The experimental results demonstrate that RGD targeted Fe₃O₄ NPs with a mean diameter of 9 nm possess excellent colloidal stability, good biocompatibility and an ultrahigh r2 relaxivity of more than 500 mM-1s-1, as well as excellent targeting specificity to αvβ3 integrin-overexpressing U87 MG cancer cells. MR imaging of both cancer cells in vitro and xenografted tumor model in vivo illustrates that RGD targeted Fe₃O₄ NPs can be used as an efficient constrant agent for targeted MR imaging of cancer cells over expresssing αvβ3 integrin. The data of biodistribution demonstrate that RGD targeted Fe₃O₄ NPs can be excreted from the living body and have negligiblely negative effect after administration, thereby can be safely used for MR imaging in vivo.In chapter 3, PEI was employed as stabilizer to form Au NPs and the Fe₃O₄/Au CNPs was then synthesized by coprecipitation technique with the presence of the formed PEI-stabilized Au NPs. Through PEI chemistry, the products Fe₃O₄/Au CNPs were modified with hyaluronic acid（HA） for in vivo targeted MR/CT imaging of tumor over-expressing CD44. The experimental results show that HA-modified Fe₃O₄/Au CNPs possess good colloidal stability, a high r2 relaxivity up to 264.16 mM-1s-1, good X-ray attenuation property and biocompatibility, as well as a high uptake by cancer cells over-expressing CD44. Dual-mode MR/CT imaging of cancer cells in vitro and xenografted He La tumor model in vivo indicates that HA-modified Fe₃O₄/Au CNPs can be used as an efficient constrant agent for targeted dual-mode MR/CT imaging of tumor over-expressing CD44. The data of biodistribution demonstrate that HA-modified Fe₃O₄/Au CNPs can be excreted from the living body, having negligibly negative effect, and can be potentially used for dual-mode MR/CT imaging of tumors.In chapter 4, we synthesized NIR-absorbed Fe₃O₄@Au core/shell nanostars（NSs） through regulating the shape of Au shell. The NSs with unique morphology hold a great promise for theranostic of cancer. The Fe₃O₄/Ag CNPs, as seeds to form NSs, were first synthesized via a mild reduction route. Fe₃O₄@Au NSs were then produced based on seeds in the Au growing solution containing HAuCl4, CTAB, ascorbic acid and AgNO3. The thus-formed NSs were successively modified with sulfhydrylated PEI（PEI-SH） and PEGylated folic acid（FA）, followed by acetylation of remained surface amines to obtain FA-modified Fe₃O₄@Au NSs for multi-mode MR/CT/PA/thermal imaging and PTT of cancer cells overexpressing FA receptor. The experimental results show that FA-modified Fe₃O₄@Au NSs with a mean diameter of 149.6 nm have a high r2 relaxivity（549.07 mM-1s-1）, good X-ray attenuation property, high performance of PA imaging, high photothermal conversion efficiency and good biocompatibility, as well as high affinity to FA receptor overexpressing cancer cells. MR imaging of the HeLa cells in vitro and a xenografted tumor model in vivo illustrates that FA-modified Fe₃O₄@Au NSs can be used as an efficient constrant agent for targeted multi-mode MR/CT imaging of tumors. Likewise, the strong NIR absorption feature of the prepared NSs enables their uses for PA imaging of a xenografted tumor in vivo and PTT of cancer cells and tumors with high efficiency.In summary, we extensively explored the synthesis and further functionalization of a multifunctional PEI-modified Fe₃O₄ nanoplatform to enhance the diagnostic accuracy and realize theranostic of cancers. The findings from this thesis provided new thoughts to develope novel and accurate contrast agents and establish a new platform for theranostic of cancers.