Fabrication Of Specifically Responsive Drug Carrier And Nano MR Contrast Agent

In the past twenty years, nanotechnology has made great progress and been applied for many fields, especially for biomedical field. Currently, cancer is still one of the leading causes of death in China. According to official statistics,2.8 millions of people die from cancer every year which has been the most serious health issue in our country. To solve this problem, the researchers have focused on combination of nanotechnology and biomedicine as new breakthrough. This combination could integrate nanomedicine and bioimaging agent into the same delivery system, which helps observe the treatment effect by bioimaging. Therefore, the system could be designated as nano-therapy and diagnostic (nano-therostic), which is promising for curing cancer.In this dissertation, porous materials and functional nanomagnetic materials were chosen as drug carrier because of their high special surface area and porosity. We combined drug carrier and MR contrast agent to a single nanosystem for the dual purpose:targeted drug delivery and in vivo drug monitoring. As we known, the microenviroment of tumor tissue is weak acidity, and possesses high redox potential. Therefore, according to these special microenvironments, smart nanodrug delivery system (such as specifically responsive delivery system) could be designed to improve treatment and bioimaging effect of disease tissue. The specifically responsive delivery system could recognize the change of microenvironment, resulting in drug release from nanocarrier because of physical or chemical reaction. In light of the difference between tumor tissue and normal tissue (such as pH, temperature, redox potential etc.), some specifically responsive nanomedicines could be designed to obtain targeting delivery and controlled-release abilities. Based on the mentioned above, four different types of drug delivery systems that controlled the release of anticancer drugs by pH or enzyme stimuli were developed and verified in vitro or vivo. Additionally, in the seventh chapter, we developed a high performance MR contrast agent to detect boric acid or borate ester by magnetic relaxation time switch. In summary, the results include six chapters as follows:1. Mesoporous silica coated on iron oxide could possess good application prospect as drug delivery system and MR contrast agent. However, during study process it was found that porous silica could significantly decrease MR contrast enhancement of iron oxide core. Therefore, in the second chapter of this dissertation, we fabricated pH-sensitive nest-like HSiO2@Fe3O4 as drug carrier and MR contrast agent. The shell of HSiO2@Fe3O4 could shed under acid condition, which would not cause the detrimental effect for MR enhancement of iron oxide core. Firstly, superparamagnetic Fe3O4 with diameter of 80 nm was fabricated by solvothermal method. Subsequently, the Fe3O4@SiO2 core-shell nanoparticle was synthesized from monodispersed Fe3O4 nanocrystal as a core and tetraethyl orthosilicate (TEOS) as a silica source by the Stober method. Finally, pH-sensitive porous Fe3O4@HSiO2 core-shell nanoparticles were gained through the reduction of Fe3O4@SiO2 core-shell nanoparticles. This nanocomposite could effectively load anticancer drug and control drug release by adjusting pH value. Plus, this nanocomposite shows good MR relaxivity and contrast enhancement in vitro. For this nanosystem, nanoparticle could be guided to specific disease tissue by external magnetic field, obtaining targeting ability. Therefore, nanocomposite could supply the targeted treatment for cancer and meanwhile enhance MR imaging signal, which provides a new method for cancer therapy.2. The aqueous solubility of nanomaterials was considered as a key problem for obstacle nanomedicine in clinical use. Along with development of nanotechnology, some hydrophilic organic substances were used to modify nanomaterials for achieving good solubility, and enhancing their stability of nanomaterials in water, which is benefical to solve these problems. In the third charpter of this dissertation, we introduced a nanoplatform based on mesoporous nanosilica (MNS) as targeted drug carrier and MR contrast agent. Anticancer drug (DOX) was loaded into hydroxylated MNS (HMNS), then the system was coated by branched polyethylenimine (PEI) coupled with Gd-DTPA and folic acid (Gd-FA-Si). Therein, PEI was coated to HMNS through electrostatic attraction and hydrogen bond and acted as a pH-sensitive "gate" to control the release of drugs in HMNS because electrostatic interaction and hydrogen bond between PEI and HMNS could be easily affected by proton. Gd-DTPA and FA were linked to the PEI through the condensation reaction of the amide bond, which could make Gd-FA-Si possess high payload of Gd and good targeting for tumor cell. This Gd-FA-Si nanoplatform exhibited a high relaxivity per nanoparticle and facilitated cellular internalization. In vitro, cell viability assay showed that IC50 of nanoplatform (3.125 μg/mL) was lower than free DOX (12.5 μg/mL), indicating that targeting nanomedicine significantly enhance drug efficacy for cancer treatment. Plus, in the MR experiment, this nanoplatform significantly enhanced T1 cell MR signals and showed a good MR contrast enhancement. Therefore, this nanoplatform loaded with drugs could maintain a sufficient drug concentration at the disease sites and meanwhile be monitored under MR imaging, which will improve the therapeutic efficacy on patient.3. The combination of dual mode bioimaging agent and nanocarrier could obtain a better drug treatment and timely assess therapeutic effect by MR imaging, enhancing treatment efficiency of tumor. In the fourth chapter, we firstly developed a gadolinium doped iron oxide nanoparticle (GION) by solvothermal decompose reaction. GION showed good tranverse and longitudinal relaxivities, which would be used as T1-T2 dual mode MR contrast agent. Subsequently, folic acid and DOX were conjugated to GION by chemical grafting. For in vitro experiment, under neutral condition, the release amount of DOX molecules from nanoplatform was negligible. However, DOX molecules were released efficiently from nanoplatform under the weakly acidic conditions. In addition, the release rate of DOX was getting faster with decreasing pH value, displaying a typical pH-dependent release behavior. Cell viability assay also demonstrated this nanoplatform could effectively kill cancer cells. For in vivo experiment, nanoplatform showed a significant inhibitory effect in tumor size and enhanced MRI signal intensity of tumor tissue, resulting in high treatment efficacy. Therefore, this nanoplatform is a promising drug delivery system for the targeted and image-guided therapy of cancer.4. Recently, internal specifically responsive drug delivery system has attracted wide attention. In the fifth charpter of the dissertation, we described an enzyme-responsive drug controlled release system using (3-aminopropyl)triethoxysilane (APTES) modified mesoporous silica nanoparticles (AMSNs) encapsulated with the DNA from natural edible plants as the carrier. In the work, DNA of edible plants especially has excellent bioactivity, and its hydrolysate cannot cause damage to normal cells. Thus, the biocompatibility of nanomedicine can be improved. Once mesopores in AMSNs were loaded with drugs, the curly DNA molecules on the surface of nanoparticles could encapsulate the nanoparticles, acting as gates of the mesopores to keep the drugs enclosed. When DNase I enzyme was added into SBF, the DNA was hydrolyzed to plenty of tiny fragments, and obviously, the gates started to open and drugs could be released from the mesopores.5. The development of high quality MR contrast agent is helpful to detect early various diseases, which cause more and more attention. In the sixth part of the dissertation, we demonstrated that Gd-labeled dendrimer can be further functionalized with folic acid (targeting ligand) (DNS), and then this nanoparticle could be loaded into GO nanosheet (GO/DNS) via amide bond and be used for in vivo molecular imaging. Compared to magnevist (Gd-DTPA), the Ti relaxivity of GO/DNS nanosheet was greatly enhanced because GO with large surface area could possess high Gd payload and extend the exchange time between water and Gd chelates. Therefore, this nanoplatform displayed a highly efficient Ti contrast agent for tumor and liver imaging, and high-resolution MR angiography in vivo. Moreover, GO significantly improved the retention time of nano contrast agent in vivo. Systemic delivery of GO/DNS significantly enhanced Ti-weighted contrast ability for accurate imaging of liver and detection of liver lesions, In the process of angiography, clear vascular nets could be observed by injecting GO/DNS nanosheets, indicating that GO/DNS have a great potential application for the diagnosis of cardiovascular diseases.6. Recently, food security has obtained widely attention because of illegal behavior of adding chemical reagent into food products. Therefore, it would be desirable to develop a new assay that is more efficient and reliable for detecting illegal additive. In the seventh charpter of the dissertation, we developed a high performance T2 MR contrast agent as magnetic relaxation time switch (MRS) for detection of boric acid or borate ester. For MRS, monodispersed nanoparticles possess high T2 relaxation time, however the aggregation of the particles show low T2 relaxation time. Therefore, the change of relaxation time could be used to detect chemical compounds. In this work, the addition of BA/BE induced the aggregation of PVA@NMIO particles and reduced the T2 relaxation time of the water. This MRS system showed a good sensitivity and selectivity for the high-throughput detection of BA/BE.