Construction Of Stimuli-Responsive Fluorescent Topological Polymers And Their Applications In Controlled Release Of Anticancer Drugs

Cancer,one of the deadliest diseases in the world,remains the most important health issue.Due to the complexity and diversity of tumor cells,chemotherapy is still the most common method for cancer therapy.However,the drawbacks of chemotherapy,such as the poor water solubility,rapid metabolism,as well as toxicity and side effects on normal tissues,also limit the therapeutic effect.As a result,the drug delivery system(DDS)has been developed.The DDS aims to improve the water solubility,prolong the drug’s circulation time in the body,and increase the concentration of dugs in the tumor sites,thus to reduce the damage to normal tissues and improve the efficacy of tumor treatment.Up to now,the development of traditional DDS has been accompanied by commercial nanomedicines and a large number of pharmaceuticals under clinical evaluation.But there still remains huge room for improvement,such as controlling the DDS for releasing drugs as needed,while remaining stable as it circulates through the body;combining with various diagnostic and therapeutic agents to obtain a multifunctional diagnosis and treatment system.These are the trends in DDS and also show the importance of nanomaterials in the medical field.This dissertation focuses on the fluorescence and imaging properties and drug delivery performances of fluorescent stimuli-responsive linear polymers and hyperbranched polymers.As we know that the microenvironment of tumor tissues is characterized by high glutathione(GSH)concentration and low p H values.According to these characteristics,fluorescent block copolymers with reduction-responsiveness or p H responsiveness were synthesized for cell imaging and anticancer drug carrier research.The hyperbranched polymers possess larger cavities than linear polymers,and thereby,have a potential in higher drug loading capacity.Subsequently,hyperbranched polymers with fluorescence properties were synthesized for drug delivery and anticancer mechanism investigation of the potential anticancer drug,avasimibe(Ava).Finally,due to the drawbacks of single-drug delivery system and combining the different anticancer mechanism of Ava,a fluorescent hyperstar polymer was synthesized to encapsulate doxorubicin(DOX)and Ava for combined therapy.In chapter 2,a novel bifunctional amphiphilic block copolymer containing disulfide bond and fluorescent DTM group was successfully synthesized by the combination of atom transfer radical polymerization(ATRP),ring opening polymerization(ROP)and “click” reaction.The disulfide bond in the backbone afforded the reduction-responsive characteristic and the DTM group in the hydrophobic chain gave the fluorescence characteristic.The amphiphilic block copolymers had obvious self-assembly behavior in aqueous solution and could remain stable under normal physiological conditions.The obtained drug-loaded micelles possessed nanometer size and bright fluorescence,which could realize the function of cell imaging.And in a thiol-rich environment,these drug-loaded micelles could quickly dissociate to release the drug.Compared to free camptothecin(CPT),the drug-loaded micelles showed considerable cytotoxicity on A549 lung cancer cells and could effectively inhibit the proliferation of tumor cells.In chapter 3,amphiphilic block copolymers PEG-b-poly(DPA-co-DTM)and PEG-bpoly(DBA-co-DTM)with p H responsiveness and fluorescence were synthesized.These two block copolymers exhibited relatively stable fluorescence properties in different solvent and excitation-independent fluorescence behaviours.By copolymerizing the responsive segments in the molecule chain,the DOX-loaded micelles could be triggered to disassemble,thus releasing DOX at the corresponding p H values.These block copolymers showed excellent biocompatibilities,and between the two DOX-loaded micelles,DOX-loaded PEG-b-poly(DPAco-DTM)micelles showed better antitumor efficacy than DOX-loaded PEG-b-poly(DBA-coDTM)micelles.In chapter 4,due to the drawbacks of Ava,such as poor water solubility,short half-life,and lack of fluorescence for detection,a fluorescent hyperstar polymer FHSP with a strongly positively charged surface was designed and synthesized.The proposed polymer was composed of a biodegradable hyperbranched polymer in the core and a hydrophilic PDMAEMA chain in the shell with fluorescent DTM group incorporated in.The positively charged surface could improve the Ava loading content by electrostatic interaction,and the fluorescent group could be used to trace the distribution of polymer and Ava in cells.Ava showed high cytotoxicity both for solid tumor He La cells and suspension leukemia K562 cells.The reduction in cell size,nuclear membrane disruption,nuclear lysis,chromatin clumps and condensation,as well as S phase cell cycle arrest were all observed in the Ava and Ava-FHSP treated groups.Mechanism analysis showed that both Ava and Ava-FHSP significantly downregulated the gene and protein expression of ACAT-1 to increase the intracellular free cholesterol amount,which could cause the endoplasmic reticulum(ER)stress and induce the apoptosis of tumor cells.In chapter 5,according to that the combination therapy by using two or more chemotherapeutic agents with different action mechanisms can offer synergistic and/or additive effects on cancer treatment,an amphiphilic hyperstar copolymer with an H40 hyperbranched polyester as the core and PCL-P(DMAEMA-co-DTM)copolymer incorporated with fluorescent DTM group as the arms were designed to encapsulate the model anticancer drugs,DOX and Ava.After the encapsulation,the obtained dual-drug-loaded micelles,DOX/Ava-P,possessed a spherical structure with approximate size of 180 nm.The micelles DOX/Ava-P kept their structure almost stable in PBS with 10% FBS.Among three ratios(DOX:Ava=3:1,1:1,1:3),both 1:1 and 1:3 showed synergistic cytotoxic activity against K562 and He La cells.For apoptosis,all the three ratios had high apoptosis rates,among which the cytotoxic effect of 3:1was slightly higher than that of 1:1 and 1:3,which was almost the same as that of 1:0.In addition,all the drug-loaded micelles in different proportions showed G2/M retardation.In the cell scratch-healing experiment,1:1 showed the most obvious migration inhibition.In summary,the combined drug-loaded system containing DOX and Ava drugs with different anti-cancer mechanisms could adjust the synergistic effect by changing the drug ratios.