Lactobionic Acid-modified Low-generation Poly(Amidoamine) Dendrimer-entrapped Gold Nanoparticles: Preparation, Functionalization, And Tumor CT Imaging Applications

Computed tomography (CT) has been identified as one of the most widespreadmolecular imaging technologies. Conventionally used CT contrast agents areiodine-based small molecules (e. g., Omnipaque), which suffer defects and limitations.As the fast developing technology, especially nanotechnology, various nanomaterialshave been developed to be used as CT contrast agents having higher X-ray attenuationproperty, excellent biocompatibility, low cytotoxicity and targeting specificity. One ofthe notable representatives is gold nanoparticles (AuNPs) formed usingpoly(amidoamine) dendrimers (PAMAM) as carriers. In the previous work, we tookadvantage of the large number of functional groups on generation5(G5) dendrimers(G5.NH2) that can be pre-modified with polyethylene glycol (PEG), targetingmolecules, and drugs, and used the G5dendrimers to form dendrimer-entrapped ordendrimer-stabilized AuNPs, followed by the acetylation of the remaining dendrimerterminal amines to neutralize the surface charge of the particles. These newlydeveloped CT contrast agents had proloned circulation time, better X-ray attenuationproperty, and even the ability for theranostics of cancer.Anyway, the high cost of the commercially avabilable G5.NH2dendrimers limitstheir translational medicine applications. Therefore, we have investiagted thedevelopment of AuNPs using G2.NH2as carriers and achieved successful preparationof G2dendrimer-stabilized or G2dendrimer-entrapped Au NPs with good CTimaging contrast enhancement via hydrothermal approach or NaBH4reductionchemistry. The partial PEGylation of dendrimer periphery is able to significantlyimprove the Au loading content within the dendrimer interior, and the conjugation of folic acid (FA) is able to realize the targeting specificity of the particles to FAreceptor-expressing cancer cells.In this thesis, we report the synthesis of dendrimer-entrapped AuNPs (Au DENPs)using G2.NH2pre-modified with fluorescein isothiocyanate via a thiourea linkage andlactobionic acid (LA) via a polyethylene glycol (PEG) spacer as templates. Theformed Au DENPs were characterized via different techniques and were used as ananoprobe for targeted CT imaging of hepatocellular carcinoma (HCC). We show thatthe LA-modified Au DENPs with a mean Au core size of1.8nm are water-dispersible,colloidally stable under different temperature (4-50℃) and pH (5-8) conditions, andcytocompatible in the studied concentration range (up to3000nM). Flow cytometryresults reveal that the LA-Au DENPs are able to specifically target HepG2cells (ahuman HCC cell line) overexpressing asialoglycoprotein receptors via areceptor-mediated targeting pathway. Importantly, the developed LA-Au DENPs areable to be used as a nanoprobe for targeted CT imaging of HepG2cells in vitro andthe xenografted tumor model in vivo. With the demonstrated organ compatibility viahistological studies, the developed LA-Au DENPs using low-generation dendrimersas templates may hold great promise to be used as a highly efficient and cost-effectivenanoprobe for targeted CT imaging of HCC.