Design,Synthesis And In Vitro Anti-cancer Properties Of Cyclic Graft Block Copolymer Prodrug

The controlled synthesis and properties of polymers with advanced topological structures,such as star-like,branched,brush-like and cyclic polymers,have always been research focuses in polymer science.Among these structures,cyclic polymers show distinctive physical and chemical properties from traditionally linear analogues due to the absence of polymer chain ends,such as smaller hydrodynamic volume and higher glass-transition temperature.Moreover,its unique topological structure gives the cyclic polymer as nanocarriers better performance for biomedicine,including higher stability,extended circulation time and greater cellular uptake.Therefore,the studies of cyclic polymer and its derivatives have attracted great attention from researchers.Due to their branched polymer structure and the simultaneous functionalities of cyclic core and radiating grafts,cyclic graft（cg）polymers as nanocarriers have attracted great research interests.Fabrication of cg polymer-based polymeric prodrugs by conjugation of drug molecules to the cg polymers via a dynamic covalent bond capable of responding to the tumor microenvironment integrates simultaneously the merits of cg polymers and polymeric prodrugs for enhanced stability of nanocarriers and precise modulation of drug release kinetics.However,the steric hindrance effect of hydrophilic grafts leads to the compromised drug conjugation efficiency in the traditional cg polymeric prodrug.In order to increase the drug conjugation efficiency of cg polymers,we reported in this thesis the design and synthesis of cg block copolymer prodrug with heterogeneous grafts of hydrophilic oligo（ethylene glycol）（OEG）and reducibly conjugated camptothecin（CPT）.In order to evaluate the properties of this novel polymeric prodrug,we also prepared a linear graft（lg）block copolymer prodrug analogue.The drug conjugation efficiency,self-assembly behavior and in vitro anti-cancer properties of the two polymeric prodrugs with different topologies were systematically compared and studied.The detailed contents and the results of this thesis are summarized as follows,1.In the second chapter,the diblock copolymer,l-P（OEGMA）-b-P（HEMA）-Br,was prepared by successive ATRPs of oligo（ethylene glycol）monomethyl ether methacrylate and 2-hydroxyethyl methacrylate,and the kinetics of the two polymerization steps were studied by SEC-MALLS and ¹H NMR analyses.The results showed that both polymerization processes are well-controlled,and the functional diblock copolymers have a narrow molecular weight distribution and a high terminal bromine retention rate,which ensure the subsequent high-purity preparation of the corresponding cyclic polymers.Then,a diblock copolymer with the greatest hydrophilic weight fraction,i.e.,l-P（OEGMA）₃₈-b-P（HEMA）₉-Br was chosen as a template for further reactions.After conversion of the pendant hydroxyl groups of HEMA units to highly reactive azide functions,the lg block copolymer prodrug（lg-prodrug）was obtained via the CuAAC click reaction between alkynyl-functionalized and disulfide-modified drug derivative alkynyl-SS-CPT and azide side groups.The structure and composition of the polymeric prodrug were characterized by ¹H NMR and SEC-MALLS analyses,and the drug conjugation efficiency was determined by ultraviolet-visible spectrophotometer（UV-vis）.2.After azidation of the bromine terminus,a functional diblock copolymer-based cyclic core template,c-P（OEGMA）₃₈-b-P（HEMA）₉,was obtained by intrachain click cyclization.Then the cg block copolymer prodrug（cg-prodrug）was synthesized based on the functional cyclic diblock copolymer using the same method and reaction conditions as in the preparation of lg-prodrug.UV-vis measurement showed that the drug conjugation efficiency of cg-prodrug is slightly lower than that of lg analogue.The comparative study of self-assembly behavior revealed that the dimension of both self-assemblies formed by the cg and lg-prodrugs depends substantially on the molecular size of cg and lg polymers.The size of micelles based on cg-prodrug is significantly smaller than that of the linear analogue micelles.The study of anti-cancer properties showed that cg-prodrug-based micelles exhibit greater in vitro cytotoxicity against cancer cells despite of the lower drug loading content than the lg-based analogue,which results primarily from the greater cellular uptake efficiency and the faster drug release of the former micelle prodrugs.