| It’s an effective way to develop multifunctional molecular CT imaging contrast agents with high sensitivity and specificity for the purpose of enhancing the early diagnosis accurancy of tumors, which are also the current tendency of nanomedicine and diagnostic imaging. In recent years, as a class of promising CT contrast agents, gold nanoparticles (Au NPs) have received extensive attention due to their unique optical properties, good biocompatibility, higher atomic number and electron density. In this article, the fifth generation amine-terminated poly(amidoamine) dendrimers (G5.NH2) were used as templates to encapsulate or stabilize gold nanoparticles, and then they were surface modified sequentially with iodinated small molecules of diatrizoic acid (DTA), targeting molecules of folic acid (FA) and polyethylene glycol (PEG). In this way, gold (Au) and iodine (I) elements were successfully combined within one nanoparticle system and obtained the targeted dual-element CT contrast agents with long blood circulation time and tissue specificity.First of all, taking G5.NH2as templates and using a novel step-by-step reducing approach, we synthesized the colloidal stable dendrimer-entrapped gold nanoparticles (Au DENPs) with their mean diameter ranging from2-4nm. Afterwards, the prepared Au DENPs with a molar ratio of Au:G5.NH2=120:1were selected to be further multifunctionally modified, during which the iodinated small molecules of DTA, targeting moities of HOOC-PEG-FA which were prepared beforehand, and also methoxypolyethylene glycol of CH3O-PEG-COOH were attached onto the surface of Au DENPs sequentially. And lastly we obtained the multifunctional targeted dual-element CT contrast agents after complete acetylation by acetic anhydride. The prepared Au DENPs and the multifunctional targeted dual-element CT contrast agents were respectively characterized with’H NMR, FTIR, UV-Vis spectrometry, TEM images, ζ-potential measurements and X-ray attenuation measurements. In addition to that, the synthesized multifunctional Au NPs were analysed using MTT assay, inverted microscopy and hemolytic analysis, so as to investigate the cytotoxicity and blood compatibility of the multifunctional Au NPs. Finally, the in vivo/vitro targeting ability and CT imaging properties of the obtained targeted dual-element CT contrast agents were evaluated by KB cells over-expressing FA receptors.It turned out that the acetylated Au DENPs with the mean size of2～4nm prepared via step-by-step reducing approach have excellent stability under different temperature (4～50℃) and pH (5-8) conditions when the Au/dendrimer molar ratio≤150:1. After the series of functionalization, the Au DENPs were transformed into dendrimer-stabilized gold nanoparticles (Au DSNPs) with an average diameter enlarged to5.9nm. The multifunctional Au DSNPs exhibited good biocompatibility, including cell and blood compatibility, even when the concentration reached up to2000nM. The in vivo/vitro targeting and imaging performance displayed that the synthesized multifunctional Au DSNPs showed well targeting effects both for KB cells in vitro and the xenograft KB tumor model in vivo. Besides, the targeted dual element Au DSNPs produced higher X-ray attenuation intensity than the single element CT imaging system containing Au elements only and also stronger attenuation than the non-targeted dual-element system without FA.In summary, our results indicate that the prepared targeted multifunctional dual-element CT contrast agents with excellent stability and biocompatibility have great potential to be applied in the early diagnosis of cancers in future. |
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