Research On The Synthesis And Properties Of Poly(Ethylene Glycol)-Poly(Amino Acid) Block Copolymer

Tumor is a common disease of great threat to the health of human, which hasbeen considered as "the top killer" to humanity. Chemical drug therapy and genetherapy are two important methods that have been applied in tumor therapia. However,unfortunately, toxic side effect of drugs used in chemotherapy and extremevulnerability of gene to nuclease degradation in vivo are obstacles that result incurrent poor efficiency. Thus, low-toxic but efficient carriers of chemotherapeuticagents or therapeutic genes for targeted treatment have attracted an increasing numberof attention. Amphiphilic block copolymer micelle is the most frequently used andstudied nanocarrier material, due to its stable structure, suitable size of tens ofnanometer, and lower critical micelle concentration （CMC）. They can be transportedto tumor cells by passive targeting or active targeting mode, the former of which isendowed with evasion of the reticuloendothelial systems （RES） absorption andenhancement of permeability and retention effect （EPR effect）, and consequentaccumulation in tumor cells, while in the latter one, receptor mediated specificbinding between tumor cells and micelles modified with targeting ligands, biologicalmarker and so on acts as the main driving force. In this thesis, we designed andsynthesized a series of micelle carriers from amphiphilic block polymer based onpoly（amino acid）（PAA）, which have good bioactivity, biocompatibility and biodegra-dability when used as carriers of drug, gene or their co-delivery. Herein, the researchreported in this thesis is expected to contribute to the solvement of problems involvedin anticancer drugs, such as high cytotoxicity, poor solubility, poor targeting to thetumor site, poor biocompatibility and so on. The research provides the basis to thedevelopment of high efficiency and low toxicity of antineoplastic drug, which isgiving a relevant technical support to develop individualized treatment.This thesis is composed of four aspects as follows:The first part is a breif introduction of biodegradable polymer materials, inwhich, firstly, characteristics and synthetic methods of PAA and poly（ethylene glyco-l）-b-poly（amino acid）（PEG-b-PAA） are introduced respectively. Then characteristicsof amphiphilic block copolymer micelles as well as application based on them fordrug delivery, gene transfer and their co-delivery are introduced.The second part: Through MPEG-NH₂triggered ring opening polymerization ofN^ε-carbobenzoxy L-lysine N-carboxyanhydrides （Lys（Z）-NCA）, methoxy poly（ethyle- neglycol）-b-poly（N^ε-carbobenzoxy-L-lysine）（MPEG-b-PZLL-NH₂） is synthesized,then MPEG-b-poly（N^ε-carbobenzoxy-L-lysine）-b-poly（L-leucine）（MPEG-b-PZLL-b-PLLeu） is prepared by polymerization of appropriate L-leucine N-carboxyanhydrides（Leu-NCA） from a terminal amine group on MPEG-b-PZLL, followed by deprotecti-on of amines group in acid to acquire a new type of triblock copolymers of MPEG-b-poly（L-lysine）-b-poly（L-leucine）（MPEG-b-PLL-b-PLLeu）. FT-IR,¹H NMR and GPCresults demonstrate the successful synthesis of the triblock copolymer.Part Three: Stability, particle size and electrokinetic potential for the MPEG-b-P-LL-b-PLLeu triblock copolymer micelles are investigated by DLS, TEM and Zetapotential. From the results, it is found that the polymeric micelles are sub-100nm indiameter, positively charged （around50mv） and possess good stability. After loadedwith doxorubicin （DOX）, the micelles show a well controlled release behavior andexhibit apparent environmental pH response in vitro drug controlled release behaviorresearch. Moreover, it is found that the copolymers can condense plasmid DNA（pDNA）, and importantly, the resulted polymer/DNA complexes show excellenttransfection efficiency in HEK293T cells at certain N/P ratios. Thus, as preparedblock copolymer micelle is worth further study and may have potential applications inboth drug and gene delivery systems.Part Four: Triblock copolymer HOOC-PEG-b-PZLL-b-PLLeu is synthesized by asimilar method to that in the second part, then fluorescent pyrenebutyric acid （PBA） isconnected to the end of PLLeu, while1-adamantanamine （AD） which can interactwith cyclodextrin （CD） via the specific “host-guest” recognition is combined to thePEG terminal. followed by deprotection of the PZLL side chain’s carbobenzoxy groupin acid using33%HBr/AcOH to get AD-PEG-b-PLL-b-PLLeu-PBA. Characterizationby FT-IR,¹H NMR and DLS reveals that we successfully synthesize the designedpolymer which has a small micelle size.