Design Of Functional Zwitterion-modified Dendrimer Nanoplatform For Imaging Diagnosis Of Tumors

With rapid development of nanotechnology,varieties of nano-contrast agents have been developed for tumor diagnosis,especially,use of nano-carriers to construct functional multi-mode nanoprobes?one nano-platform integrating multiple contrast agents?enables accurate diagnosis of tumors.Both CT and MR imaging are the most widely used single-mode imaging techniques for clinical diagnosis.Combination of these two techniques to execute dual-mode CT/MR imaging can successfully overcome drawbacks of single imaging and enhance the accuracy and reliability of diagnostic information.Imaging quality depends on whether the nanomaterial-based contrast agent can reach and gather to the tumor site by overcoming non-specific protein adsorption and escaping phagocytosis of macrophages during blood circulation.Recent literatures show that modification of polyethylene glycol?PEG?or zwitterion on nanoparticles?NPs?can improve anti-protein adsorption of NPs,resulting in escaping the phagocytosis of the reticuloendothelial system and extending blood circulation time in vivo.Furthermore,modification of targeting agent endows NPs with tumor cell-specific targeting capability.PEG is not stable in temperature sensitivity while zwitterions with more stable temperature sensitivity than PEG present better protein antifouling capability.In order to simultaneously integrate two contrast agents in one platform and further endow contrast agents functionalities?such as antifouling and targeting capability,etc.?,a carrier is usually required.Among many carriers,due to a great number of functional groups for surface modification and large hydrophobic cavities inside,dendrimers are widely used as carriers to load contrast or therapeutic agents for diagnosis and treatment of tumors.In this study,poly?amidoamine?dendrimer?PAMAM?modified with zwitterion and targeting agent was used as a platform to encapsulate gold NPs in cavity and chaleted with Gd ions peripherally to construct a nano-platform for CT/MR dual mode imaging diagnosis of tumor xenografted models.The nano-platform will be optimized by modifying different zwitterions.The contents are as follows:?1?Generation 5 PAMAM dendrimers?G5?modified with 3 zwitterions?CBAA,MPC,1,3-PS?containing different anions and cations were use as templates to entrap the gold NPs,followed by acetylating the remaining amino groups,to form zwitterion-modified dendrimer entrapped Au NPs.Nuclear magnetic resonance spectroscopy,UV-Vis absorption spectroscopy and transmission electron microscopy were used to characterize the gold nanoparticles.The results showed that zwitterion-modified G5 entrapped gold nanoparticles have been successfully synthesized.Subsequently,anti-protein adsorption and cellular uptake?by macrophage RAW264.7?test and in vivo pharmacokinetic analysis were applied and screen out the best anti-fouling agent1,3-PS.The cytotoxicity test result showed that modification of antifouling agent greatly improved the biocompatibility of the nanomaterial.?2?Modified with optimized anti-fouling agent 1,3-PS and target agent RGD peptide,a dendrimer-based imaging contrast agent with Au NPs encapsulated in cavity and Gd ions chaleted peripherally were synthesized for CT/MR dual mode imaging.Different techniques were used characterize the formed contrast agent.The results showed the multifunctional Au NPs have a uniform size of 2.7-2.8 nm,a better CT imaging effect and higher X-ray attenuation intensity than the clinical contrast agent Omnipaque,as well as improved r₁ relaxation rate after 1,3-PS modification which is higher than that of clinical Magnevist.The CT and MR imaging of tumors in mice's lung indicated that RGD-targeted Au NPs have a better imaging quality and higher imaging signal than non-targeting materials at the same concentration.The in vivo biodistribution result demonstrated that thethe multifunctional Au NPs were able to gradually metabolized and cleared from body by liver and spleen.Therefore,the synthesized dendrimer CT/MR contrast agent with anti-fouling and targeted dual performance is expected to apply in the field of biomedical imaging.