Study On Mri Contrast Agent With Tumor Targeting Effect

Cancer is still one of the difficulties that can’t be overcome in the medical field.It has a great impact on people’s life and health.If cancer can be detected and treated early,the possibility of cure can be greatly improved.As a diagnostic tool for human diseases,magnetic resonance imaging（MRI）can realize early detection,diagnosis,image-guided treatment and post-treatment monitoring and evaluation.Contrast agent（CA）is an auxiliary of MRI,which can enhance the development intensity of the lesion site and improve the imaging quality.The contrast agents currently used in clinic not only have low imaging quality,short development time,and no specificity in body distribution,but also the use of high doses of gadolinium-based contrast agents may lead to nephrotoxicity.Contrast agents with less toxic and Side effects and targeted effects are very necessary.The content and results of this research are as follows:（1）Conjugate folic acid（FA）,which has a targeting effect on tumor cells,with chitosan（CS）to prepare a folic acid-chitosan complex,using infrared spectroscopy（FT-IR）and hydrogen nuclear magnetic resonance spectroscopy（~1H-NMR）were characterized.The reaction conditions of folic acid-conjugated chitosan were optimized by orthogonal experiments.The experimental results showed that the feeding ratio of folic acid and chitosan was 30:1（n/n）,the reaction time was 24 h,and the reaction temperature was 30℃,which were the optimal reaction conditions,and the binding rate of the product was 32.9%.（2）The small molecule gadolinium-based contrast agent（DTPA-Gd）was linked to chitosan,and the yield was used as the evaluation index,and the reaction conditions were determined by different feeding ratios.The product gadolinium chitosan macromolecular contrast agent（CS-DTPA-Gd）were characterized by FT-IR as well as~1H-NMR.The content of Gd³⁺in CS-DTPA-Gd was determined by inductively coupled plasma optical emission spectrometer（ICP-AES）,and the binding rate of CS to DTPA was calculated.The experimental results show that when the feeding ratio of amino group and DTPA in chitosan is 10:3（n/n）,the binding rate is the highest,reaching 57.9%.（3）Gadolinium-loaded chitosan nanoparticles（CS-DTPA-Gd NPs）and gadolinium-loaded chitosan nanoparticles（FA-CS/CS-DTPA-Gd NPs）with folate receptor targeting were prepared.The average particle size of CS-DTPA-Gd NPs was100.00±2.27 nm by dynamic laser scattering（DLS）and transmission electron microscopy（TEM）.The average particle size of FA-CS/CS-DTPA-Gd NPs is120.37±1.29 nm.The shape of FA-CS/CS-DTPA-Gd NPs is spherical and evenly dispersed.The concentration of gadolinium ion in CS-DTPA-Gd NPs was 178.23 mg/L,and that in FA-CS/CS-DTPA-Gd NPs was 102.93 mg/L.（4）The in vitro magnetic properties of CS-DTPA-Gd,CS-DTPA-Gd NPs and FA-CS/CS-DTPA-Gd NPs were evaluated,and the developing signals generated by the samples were observed using 0.35 T MRI.The results showed that the relaxation rates of DTPA-Gd and CS-DTPA-Gd were 2.97 m M^-1·s^-1,7.95 m M^-1·s^-1 and 7.78 m M^-1·s^-1,respectively.The relaxation rate of FA-CS/CS-DTPA-Gd NPs is 7.51 m M^-1·s^-1.（5）The cytotoxicity and targeting of FA-CS/CS-DTPA-Gd NPs were evaluated.Cervical cancer cells（He La cells）with overexpression of folate receptor on cell surface and human lung adenocarcinoma cells（A549 cells）without expression of folate receptor on cell surface were selected as the test cells.MTT was used to determine the toxicity of DTPA-Gd,CS-DTPA-Gd,CS-DTPA-Gd NPs and FA-CS/CS-DTPA-Gd NPs to the two types of cells with different gadolinium-ion concentrations,and to investigate the targeting ability of FA-CS/CS-DTPA-Gd NPs to cancer cells.Fluorescence microscopy and fluorescence spectrophotometer were used to observe and quantitatively analyze the cell uptake of fluorescein.The results showed that the cell survival rate was above 75%.DTPA-Gd,CS-DTPA-Gd,CS-DTPA-Gd NPs,FA-CS/CS-DTPA-Gd NPs had no toxicity to He La cells and A549 cells.FA-CS/CS-DTPA-Gd NPs showed targeting selectivity to He La cells,but not to A549 cells.The fluorescence intensity was measured by fluorescence spectrophotometer,which further proved the active targeting of FA-CS/CS-DTPA-Gd NPs to He La cells.