Construction And In Vitro Evaluation Of Dendritic Polyurethane Based Antitumor Drug Delivery System

In recent years,malignant tumors are seriously endangering human life and health.The number of new cases and deaths of cancer patients in the world has reached tens of millions of cases every year.Although surgical treatment is still the main method of cancer treatment,it still has some shortcomings,such as indistinguishable tumor boundaries,excessive excision,ineffective treatment for metastases,and so on.With the rapid development of intelligent drug delivery systems（DDSs）,chemotherapy is an important auxiliary method of tumor therapy.The DDSs loaded with anti-tumor small molecule active drugs in physical or chemical forms can effectively improve the water solubility of small molecule drugs,prolong the stability and circulation time of drugs in the body,reduce the toxic and side effects of drugs on the whole body and drug resistance,effectively improve the pharmacokinetics,and better achieve the purpose of tumor therapy.Through the continuous understanding and exploration of tumor tissue,the development of accurately targeted responsive nano-drug delivery system is of great significance for the treatment of tumor.In addition,monomolecular micelles have superior stability compared to self-assembled supramolecular micelles as drug carriers for tumor chemotherapy.The polar structure of dendritic polymers can encapsulate chemotherapy drugs through hydrogen bonding,and the cavity of their hydrophobic core can also encapsulate drugs,which is a promising alternative material.Based on this,this thesis mainly focuses on the design of dendritic single molecule micelles,loads small molecule antitumor drugs in the form of physical or chemical,constructs a responsive nano dendritic monomolecular micelle drug delivery system,and realizes the precise release of active drugs at the target site through external stimulation or internal chemical signal stimulation.This thesis mainly includes the following six parts:1.Dendritic polymers based on polyurethane chemistry can be easily synthesized by constructing isocyanate based dendritic units,and can be used for further modification to impart specific functional properties.Using dipentaerythritol as the core and glycerol and triethanolamine as branched monomers,two kinds of dendritic polyurethanes(Ph-DPU_Gly-PEG and Ph-DPU_TEA-PEG)with the same degree of polyethylene glycol were designed.Then,the effects of molecular structure on the drug loading and controlled release properties of their monomolecular micelles were mainly studied by using phenol as a capping agent.The results showed that the Ph-DPU_TEA-PEG with tertiary amine structure could be protonated in acidic solution,resulting in the swelling of the internal dendritic structure of the molecule,Therefore,it exhibited different particle sizes and drug release in solutions with different acidity,and p H response characteristics.However,the core of dendritic polyurethane prepared using glycerol as a branching unit had strong hydrophobicity,making it difficult to release the drug in solutions with different acidity.Therefore,the difference in molecular structure makes the dendritic polyurethanes exhibit significantly different drug release characteristics.2.Due to the strong interaction between the hydrophobic core of the prepared dendritic polyurethane and the hydrophobic small molecule drugs,the prepared drugs have very low drug leakage in the solution.Therefore,ultrasound triggered drug targeting delivery of pegelated dendritic polyurethane monomolecular micelles was designed.Using glycerol as the branched monomer and dipentaerythritol as the core,pegylated dendritic polyurethane monomolecular micelles with hydrophobic cores is synthesized by a simple one pot method,and the nano monomolecular micelles drug(DOX@Ph-DPU_Gly-PEG)is obtained by physically encapsulating small antitumor drug doxorubicin（DOX）.The results showed that DOX@Ph-DPU_Gly-PEG was difficult to release in different acidity media without ultrasound,but showed good ultrasound-triggered release performance.Under the action of ultrasound in the simulated tumor cell microenvironment,the cumulative drug release could reach 81.6%within 12 hours.In addition,CLSM showed that ultrasound-triggered intracellular drug release enhanced the growth inhibition of Hep G2 cells compared with pure DOX.3.In order to achieve accurate targeted drug delivery,a novel monomolecular dendritic polyurethane-based nano prodrug micelle(DOX-DPU_Gly-PEG)was designed and prepared by bonding the anticancer active drug DOX to the terminal group of functionalized dendritic polyurethanes(HBA-DPU_Gly-PEG)in the form of acid sensitive imine bonds.Compared with DOX@Ph-DPU_Gly-PEG monomolecule micelle drug prepared with non-covalent bond loading,only 4%of the drug was lost in the buffer solution with p H 7.4 under ultrasound,while the drug release rates were 88%and 14%in the solution of p H 5.0 with or without ultrasound mediation.It showed excellent p H/ultrasound dual response drug release performance.The ultrasonic responsiveness is attributed to the unique strawberry topology formed by embedding DOX in the surface layer of the hydrophobic core of DPU.Under the condition of ultrasound,the anti-tumor toxicity of DOX-DPU_Gly-PEG monomolecule micelles is similar to that of pure DOX,but there is no obvious cytotoxicity in the absence of ultrasound.4.Based on the rich terminal groups and internal spatial structure of dendritic polyurethane,a functionalized dendritic polyurethane DPU_TEA-PEG with triethanolamine as the branched monomer and aldehyde as the dendritic terminal group was designed.DOX was bonded to the“skin”layer of the dendritic core through acid sensitive imine bonds,and another antitumor active drug,hydroxycamptothecin（CPT）,was physically loaded on the“depth”layer of dendritic core.A“skin-depth”type combined chemotherapy system of dendritic polyurethane monomolecule micelle loaded with two antitumor active drugs was obtained.The“depth”layer of hydrophobic dendritic polyurethane core tightly enclosed CPT molecules,while the hydrophobic DOX bonded to the"skin"layer played a role as a goalkeeper,further preventing the leakage of CPT molecules.The results showed that the prepared“skin-depth”type combined chemotherapy drug CPT@DOX-DPUTEA-PEG has the characteristics of small nano size,narrow particle size distribution,low drug leakage rate,and excellent acid responsive drug release,as well as significant drug synergy and excellent anti-tumor activity.5.Dendritic polymer-based unimolecular micelles have attracted more interests in tumor chemotherapy.However,the drug release behavior was significantly affected by the hydrophilic-hydrophobic property of the dendritic cores.In the present work,carbon quantum dot（CQD）was used as bridge between the dendritic cores and drugs to achieve a better drug release performance.Strawberry-shaped hybrid prodrug unimolecular micelles(DOX-Hy-CQD-DPU_TEA)were successfully designed with DOX content of 16.7%and mean hydrodynamic diameter around 82 nm.A sustained acid-triggered DOX release was obtained with a minimized drug leakage,possessing an enhanced anti-tumor efficacy than free DOX.Furthermore,the hybrid unimolecular micelles could be used for the tumor imaging after drug release therein.It would open new ideas in future tumor theranostics.6.The design of drug carriers containing disulfide bonds can break disulfide bonds due to the reduction of glutathione in the microenvironment of tumor cells,thereby endowing the carrier with reduced responsiveness.In the microenvironment of tumor cells,glutathione can break disulfide bonds,thereby endowing drug carriers containing disulfide bonds with reductive responsiveness.Using cysteamine diisocyanate prepared from cysteamine dihydrochloride as the monomer,dipentaerythritol as the core and glycerol as the branching unit,a reductive responsive pegelated dendritic polyurethane(DPU_Gly-SS-PEG)was constructed.After loading DOX with hydrogen bonds and hydrophobic interactions,dendritic monomolecular micelle drug(DOX@DPU_Gly-SS-PEG)with nano size were obtained（drug loading 33.70%）.The results showed that the dense and hydrophobic dendritic core of the drug system interacted strongly with DOX,resulting in low drug leakage in simulated normal tissue media.The presence of disulfide bonds on its various branches made DDS exhibit excellent reductive responsiveness in simulated tumor cell microenvironment.In addition,its low half lethal dose(IC50=3.81μg m L^-1)and good biocompatibility of the carrier indicate that the DDS is expected to achieve intelligent targeted delivery of antitumor active drugs.