Application Of Low Molecular Weight PEI Nanogel Loaded With Ultra-small Fe₃O₄ Nanoparticles In Tumor MR Imaging And Gene Therapy

The growth and metastasis of tumor is the root cause of the high mortality rate for cancer patients.Thus,radically curing the spread of cancer remains a major challenge in the current biomedical field.Real-time monitoring of the development in cancer progress while inhibiting its growth and metastasis is a new strategy for the treatment of malignant tumors.Previous studies have found that ultra-small Fe₃O₄Nanoparticles（NPs）with a size of less than 5 nm is an excellent T₁ MR contrast agent as well as a good biocompatibility materials.Transforming growth factor-β1（TGF-β1）effectively promotes the growth and metastasis in tumor cells.Therefore,inhibiting the expression of TGF-β1,such as silencing it by siRNA gene therapy,can effectively inhibit the growth and metastasis of cancer.The key technology to realize MR imaging diagnosis and gene therapy at the same time is to develop suitable and efficient delivery MR contrast agents and siRNA carriers.Previous research have found that crosslinking polyethyleneimine（PEI）enable to form nanogels（NGs）.The construction of low-toxicity and low-molecular-weight PEI NGs vectors can not only improve their gene loading capacity,but also can simultaneously load other therapeutic agents in their periphery or internal three-dimensional network structure to implement therapeutic integration.Therefore,this paper will use low molecular weight PEI as the main material of the nanogel,polyethylene glycol acrylic acid（PEG-DA）as the cross-linking agent,at the same time add the pre-prepared ultra-small Fe₃O₄ NPs,and synthesize the PEI nanogels（Fe₃O₄/PEI-PEG NGs）with ultra-small Fe₃O₄ NPs by the reverse microemulsion method,and then loaded with TGF-β1 siRNA gene drugs by electrostatic adsorption for MR imaging diagnosis and gene therapy in tumor-bearing mice.In the second chapter,this work first synthesized an ultra-small Fe₃O₄ NPs with a size of 2.2 nm.Then,the Fe₃O₄/PEI-PEG composite nanogel was synthesized by the inverse microemulsion method,and then TGF-β1 siRNA was adsorbed onto the material（TGF-β1 NGs）.The material performance characterization results prove that the functional nanosphere material has uniform size distribution,good colloidal stability and biocompatibility,high T₁ relaxation rate,good gene loading capacity and excellent gene transfection ability.In Chapter 3,we evaluated the in vitro therapeutic effects of the materials,and the results showed that TGF-β1 NGs successfully silenced the expression of TGF-β1,while inhibiting the growth and metastasis of S180 sarcoma cells.In Chapter 4,we evaluated the MR imaging and gene therapy effect of Fe₃O₄/PEI-PEG composite nanogel on mouse sarcoma（S180）tumor model.The results of in vivo experiments prove that the Fe₃O₄/PEI-PEG composite nanogel has good biological safety and can be successfully applied to MR imaging and gene therapy of the S180tumor model.The experimental results of this paper provide new ideas for the development of new nanocarrier systems loaded with siRNA for imaging diagnosis and treatment.