| Summary: | 博士 === 國立臺灣大學 === 醫學工程學研究所 === 99 === Non-viral gene carriers composed of biodegradable polymers or lipids have been considered as a safer alternative for gene carriers over viral vectors. Among some of the cationic polymers, polyethyleneimine (PEI) possess high pH-buffering capacity that can provide protection to nucleotides from acidic degradation, and promotes endosomal and lysosomal release. However, it has been reported that cytotoxicity of PEI depends on the molecular weight of the polymer such that high molecular weight (>25kDa) of PEI can elevate the transfection efficiency. Hence modifications of PEI structure for clinical application have been developed in order to reduce the cytotoxicity, and improve the insufficient transfection efficiency of lower molecular weight PEI.
Cationic amphiphilic copolymer consisted of stearyl side chains on polyethyleneimine (PEI) main chain (PEI-SA) was developed previously and demonstrated with the concept of co-delivering siRNA and anti-tumor drug doxorubicin. However, the drug release profile was limited and remained to be an issue to be overcome. In the present study, hybrid PEI in different weight ratios of 10k: 1.8k was proposed to alter this structural formulation by incorporating with low molecular weight PEI. The design was able to maintain the functionalities as gene and drug carrier with efficient binding capability, enhanced drug release rate, also optimized between cellular uptake and low cellular cytotoxicity. Other functionality was also attempted to integrate into the PEI-SA nanoparticles by encapsulation with the SPIOs to formulate as contrast agents for in vivo imaging application. BALB/c mice was injected with PEG conjugated PEI-SA/SPIO nanoparticles to demonstrate the extended half-life in blood plasma, and effective contrast agents comparable to the commercial available contrast agents Resovist.
A new type of polymeric polysaccharide nanoparticles was also proposed and developed. Tremella polysaccharides have been commonly used as herbal medicine, vaccine adjuvant, or orally fed for anti-tumor or anti inflammatory studies. To date, none of them has been formulated as nanoparticles and applied for biological studies. The fruit body of Tremella fuciformis was extracted and cationic modified, followed by oil-in-water solvent evaporation method to formulate into nanoparticles. The physical characteristics of these nanoparticles were then confirmed by dynamic light scattering, AFM, TEM and FTIR with size of 107.1±2.5 nm and zeta potential of 70.6±3.3mV. The tremella nanoparticles were found with enhanced cellular uptake and relatively low cytotoxicity. Gene binding capacity was also investigated to ensure the functionality as potential gene carriers. The anti-inflammatory capability was demonstrated by measuring the nitric oxide produced from LPS-activated macrophages. The use of nano-sized tremella polysaccharide nanoparticles can posses opportunities as delivery carriers for gene and contrast agent by incorporating hydrophobic SPIO to target macrophage-rich tissue at chronic inflammation site.
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