The Loading Of Short Nucleic Acids Within The Mesoporous Structure Of Silica Nanoparticles And The Relative Application Study

Up to date, mesoporous silica materials, of which the synthesis,characterization and applications have been extensively studied. Among thenumerous explored application areas, a drug delivery system based on themesoporous structure is an emerging area under development recently. Such newapplication is triggered by the synthesis and functionalization of the mesoporoussilica nanoparticles (MSNs). Since the great success of being utilized as drugcarriers, MSNs have also been proposed to be the vectors to load and deliverynucleic acids (DNA&siRNA) for gene therapy. Consequently, in this work, westudied the interaction mechanism of short nucleic acids with MSNs in aqueoussolution and thus achieved the loading of salmon DNA and siRNA within themesoporous structure of MSNs. Subsequently, we constructed and utilizedMSNs-based siRNA delivery vehicles to mediate the gene silencing process in averity of tumor cells.In Chapter2, we synthesized a type of magnetic mesoporous silicananoparticles (M-MSNs) with a magnetic core and mesoporous silica shell. Thestudy on the DNA adsorption and desorption behaviors of such nanoparticlesclearly demonstrated that DNA has been captured into the mesopores ofM-MSNs. We also investigated the DNA loading capacities of M-MSNs with changing the solution conditions including the pH values, the salt concentrationsand the types of salts. The results suggested that the driving force for DNAadsorption into M-MSNs could be categorized into three parts: the shieldedelectrostatic repulsion, the dehydration effect and the generation ofintermolecular hydrogen bonds. Thereafter, we investigated the status of DNAexisting within the mesopores and analyzed the types of hydrogen bondsbetween DNA and the wall of mesopores.In Chapter3, siRNA was encapsulated within the mesoporous structure ofM-MSNs under strongly dehydrated solution condition. Through investigatingthe siRNA loading capacity of M-MSNs under various solution conditions, weconfirmed that both the dehydration effect and the shielded electrostatic forcewere propitious to the loading of siRNA within M-MSNs, but the hydrogenbonds had negligible effect on such process. Through coating polyethylenimine(PEI) on the external surface of siRNA-loaded M-MSNs, we obtained a type ofsiRNA delivery vehicles (M-MSN_siRNA@PEI) with excellent siRNAprotective capability and negligible cytotoxicity. Such M-MSN_siRNA@PEIdelivery vehicles could induce RNAi for both exogenous and endogenous genesin cells. Nevertheless, it was found that the RNAi efficiency mediated byM-MSN_siRNA@PEI was lower than that induced by commercial transfectionreagent. This should be attributed to the limited endosome escape capability ofsuch delivery vehicles, which resulted in the entrapment of siRNA within theendolysosomes and thus reduced the amount of siRNA to initiate RNAi. In Chapter4, the surface of M-MSN_siRNA@PEI was functionalizedthrough conjugating KALA peptides or processing PEGylation. The conjugationof KALA peptide facilitated the endosome escape and thus resulted in anenhanced gene silencing effect in cells. For the PEGylation process, the degreeof PEGylation was determined by the amount of PEI surrounding onM-MSN@PEI surface or the dose of PEG reagents applied in the synthesizingprocess. For M-MSN@PEI-PEG, when the degree of PEGylation was highenough, such vectors would stably exist in physiological saline and could hardlyinteract with proteins or cells in aqueous solution.In Chapter5, DNA-silica hybrid materials were synthesized in aqueoussolution through utilizing DNA as the template, APTES as the co-structuredirecting agent and TEOS as the silica source, respectively. Increasing the doseof APTES or TEOS facilitated the synthesis of DNA-silica hybrid materials. Themorphology of such materials was determined by the chain length of the DNAtemplate. Especially, for the DNA template with very short chain length, thefinal products were nanoclusters (not monodispersed nanoparticles). TheDNA-silica hybrid materials would degrade in aqueous solution and release outthe encapsulated DNA molecules. This process could be influenced by threefactors, including the catalysis capability of the amino groups in DNA-silicahybrids, the incubation temperature of the solution condition and theconcentration of DNA-silica hybrid materials in solution. In the cellularexperiments, it was found that the DNA-silica hybrid materials could be internalized into tumor cells efficiently. However, abundant materials would beentrapped within the endolysosomes.