Study On Transferrin Receptor-Targeted Polymersomes As Drug Carriers

Active targeted nanocarriers based on ligand-receptor specific binding patterns have great potential in drug delivery systems.They can transport and accumulate drugs to targeted cells in order to decrease the toxicity of medicines to normal tissues,control drug release rate and improve its bioavailability,and also inhibit the multidrug resistance in tumor cells.Transferrin（Tf）is a kind of widely studied ligand,which has the characteristics of biodegradability,nontoxicity and non-immunogenicity.Several targeted nano-drug carriers based on transferrin-transferrin receptor have been entered clinical trials.In this thesis,a transferrin-targeted nano-sized polymersomes,transferrin-Biotin/Avidin/Biotin-F127-PLA polymersomes（Tf-F127-PLA）was successfully prepared by a biotin-avidin bridging technique.Hydrophilic anticancer drug doxorubicin（DOX）was successfully embedded into Tf-F127-PLA polymersomes.The in vitro targeting properties of Tf-F127-PLA/DOX polymersomes and its ability to inhibit multidrug resistance in cancer cells were studied.Two kinds of block copolymers were synthesized by using the ring-opening polymerization,namely transferrin-targeted precursor Biotin-F127-PLA and non-targeted PLA-F127-PLA.Biotin-F127-PLA polymersomes were prepared firstly by using the nano-precipitation method,and then Tf-F127-PLA polymersomes with targeting transferrin ligand were obtained by Biotin-Avidin bridging technology.The data of the particle size analyzer showed that the size of the DOX-loaded polymersomes（75-95 nm）was larger than that of the blank polymersomes（30-70 nm）and all polymersomes had good dispersion and negative charges.The transmission electron microscope pictures showed that DOX-loaded polymersomes were bi-layer spherical vesicles.In vitro release experiments showed that the DOX-loaded polymersomes were released fast initially followed by a slow release.The cumulative release rates of DOX-loaded polymersomes at p H 5.0 were about 20%higher than those at p H 7.4.At the same time,the cumulative release rate of Biotin-F127-PLA/DOX polymersomes was about 10%higher than those of PLA-F127-PLA/DOX polymersomes.Human non-small cell lung cancer A549 cells with high expression of transferrin receptor were selected as cell models.The cytotoxicity and quantitative cell assay were used to explore in vitro targeting of Tf-F127-PLA/DOX polymersomes and the effect of transferrin ligand density on the targeting property of Tf-F127-PLA/DOX polymersomes.The results showed that the cytotoxicity and cellar uptake amount of targeted drug-loaded polymersomes were better than those of non-targeted drug-loaded polymersomes.The targeting ability of 2%Tf-F127-PLA/DOX polymersomes was higher than that of 4%Tf-F127-PLA/DOX polymersomes and 5%Tf-F127-PLA/DOX polymersomes in turn.In addition,PLA-F127-PLA/DOX polymersomes showed better cytotoxicity and cellar uptake amount than PLA-PEO-PLA/DOX polymersomes did,which proved that the delivery ability of Pluronic block as the hydrophilic layer of drug-loaded polymersomes was better than that of frequently-used PEO block.Doxorubicin-resistant A549/ADR cells of human non-small cell lung cancer were selected as cell models to further explore the effect of transferrin-targeted polymersomes on the inhibition of multidrug resistance in cancer cells.The results of MTT and quantitative cell assay showed that the capacity of transferrin targeted drug-loaded polymersomes to inhibit multidrug resistance in cancer cells was significantly stronger than that of non-targeted drug-loaded polymersomes,and the IC₅₀ value of Tf-F127-PLA/DOX polymersomes at 72h was 1.57 times lower than that of PLA-F127-PLA/DOX polymersomes.In addition,the results also showed that the ROS level in multidrug resistance cells treated with targeted drug-loaded polymersomes was higher than that of non-targeted drug-loaded polymersomes,indicating that transferrin-targeted drug-loaded polymersomes had better potential to promote cell death.Finally,the uptake mechanism of Tf-F127-PLA/DOX polymersomes by A549/ADR cells was further explored.The results showed that the uptake of drug-loaded polymersomes by A549/ADR cells was an energy dependent endocytosis process,which was related to the macrocytosis,clathrin,and caveolin.Furthermore,it was proved that the cellar uptake of Tf-F127-PLA/DOX polymersomes was also connected with the endocytosis mediated by transferrin receptor.To sum up,transferrin-targeted polymersomes have potential application value and good development prospects in drug delivery systems,especially as hydrophilic drug carriers.