Nanomedicine Based on Hydroxyethyl Starch-paclitaxel Prodrug Self-assembly

Author:Li Yi Hui

Supervisor:li zi fu yang xiang liang


Degree Year:2019





Malignant tumor is a critical disease threatening human health.Although tremendous progress has been made in the research of antineoplastic drugs,numerous shortcomings,including poor solubility,short half-life time,significant side effects and no targeting,obstruct the clinical use of antineoplastic drugs.Due to the enhanced permeability and retention effect(EPR)and surface modifiability,nano-drug delivery system plays a vital role in improving drug bioavailability,enhancing tumor targeting and reducing side effects.Paticularly,with the advancement of precision medicine,nano-drug delivery system has emerged as an important tool for the integration of diagnosis and cancer therapy owning to its capacity of loading diverse components.Currently,nano-drug delivery system is generally constructed by using nanoparticles as carriers,in which the therapeutic and diagnostic agents are encapsulated through hydrophobic,electrostatic and van der Waals force interactions.However,nanomedicine that based on non-covalent effect is strongly challenged by its complexed preparation process,inevitable drug leakage during storage and delivery in vivo,and unsatisfying uniformity of co-delivery system.Given these problems,polymer prodrugs,based on amphiphilic covalent-conjugated polymer prodrug with self-assembly ability,provides a novel drug delivering strategy.On the one hand,drugs could be more hydrophilic by polymeric modification,accompanied by extended circulation time.Hence,the therapeutic efficiency is improved and the side effects is reduced.On the other hand,since the drug becomes part of the delivery vectors,the prodrug self-assembly could load other theranostic agents,thus achieve multi-function with a simplified structure.Despite the self-assembled prodrug delivery system have important significance for cancer diagnosis and therapy,there are still some issues to be solved in the development of the polymer prodrug self-assembled system.First,to improve the drug pharmacokinetic and phamadynamic behavior without increasing the metabolic burden in vivo,suitable polymer with great biocompatibility should be carefully selected.Second,to provide multifunctional nano-systems with structure as simple as possible,suitable theranostic agent with flexible performance need be taken into account.Based on the above discussion,here a self-assembled nanoparticle based on hydroxyethyl starch-paclitaxel prodrug(HES-SS-PTX NPs)was fabricated and applied in antitumor therapy against breast cancer.HES has good water solubility,which can effectively solve the problem of insolubility of Taxol,and its good biocompatibility also increases the safety during the treatment.In particular,the biodegradability of HES can reduce the size of the HES-SS-PTX NPs in the process of in vivo circulation,so as to penetrate deep in tumors.Additionally,a disulfide linker was utilized to bridge HES and PTX,thus PTX can release from the nanoparticle in response to high cellular redox level.To further develop the multi-functionality of this prodrug-based system,a multifunctional theranostic smart nanoparticle DiR@HES-SS-PTX(DHP)was fabricated by loading near-infrared cyanine molecule DiR into the hydrophobic core of HES-SS-PTX NPs.The PTX release behavior was monitored by taking advantage of the aggregation-caused quenching(ACQ)effect of DiR.Moreover,since DiR has superior near-infrared absorption and photo-thermal conversion efficiency,the DHP nanoparticle was further utilized for tumor fluorescence imaging,photoacoustic imaging,and chemo-photothermal combination therapy.The main contents and conclusions of this thesis are listed follows:(1)Study on the construction of α-amylase-and redox-responsive nanoparticles based on hydroxyl starch-paclitaxel prodrug and its antitumor effects against breast cancer.First,HES-SS-PTX NPs were prepared by a modified emulsification method combined with high-pressure homogenization(HPH).The water solubility of PTX was significantly improved by HES-SS-PTX NPs,with which a core-shell structure and diameter of 160 nm.The hydrophilic HES shell was degraded by α-amylase,thus the particle size was reduced and the tumor penetration capacity was improved.In addition,the disulfide bonds on the prodrug was cleaved in response to the reducing agent,the PTX was released.Therefore,this HES-SS-PTX NPs could specifically kills tumor cells with high GSH level.The results of pharmacokinetic and biodistribution assays demonstrated that after intravenous administration,the half-life time of HES-SS-PTX NPs was prolonged compared with Taxol,and the nanoparticles could accumulated to tumor by EPR effect.Based on these features,the HES-SS-PTX NPs showed significant higher in vivo antitumor efficiency than Taxol.(2)Study on the fabrication of DiR-loaded HES-SS-PTX NPs(DHP)and its drug release monitoring ability.To further develop the function of the prodrug-based nanomedicine,a multifunctional theranostic system,DHP,was fabricated by using the HES-SS-PTX NPs as a carrier to encapsulate a NIR cyanine molecule DiR.Compared with HES-SS-PTX NPs,the hydrophobic core of DHP was increased by loading DiR,while the diameter of these two nanoparticles were comparable.The fluorescence of the encapsulated DiR was quenched by aggregation-caused quenching(ACQ)effect.In contrast,after incubation with 10 mM GSH,the disulfide bonds was cleaved,followed by disintegration of DHP and release of free DiR.The fluorescence thus turned on,accompanied by release of PTX.The fluorescence variation positively correlated with the cytotoxicity when changing the cellular redox level.Accordingly,DHP could applied as a fluorescent indicator for monitoring cellular drug release and the cytotoxic activity.(3)Study on the in vivo dual-modal imaging capacity and chemo-photothermal therapy effect of DHP.Based on the NIR absorption and photothermal conversion capacity of DiR,the fluorescent imaging and photoacoustic imaging ability of DHP,as well as its chemo-photothermal antitumor effect was investigated.First,DHP under the NIR laser exposure exhibited obviously higher photothermal conversion efficiency than the photosensitizer bear DiR.The tumor temperature of the mice that i.v.injected with DHP increased to 43 °C.When used as imaging contrast agent,DHP had higher sensitivity than bear DiR probe for NIR fluorescent imaging.The in vivo photoacoustic microscopic imaging showed that the photoacoustic signal produced by DHP was uniformly distributed in the tumors,with high resolution and signal-to-noise ratio.The contour of the tumors was clearly observed by photoacoustic signals.As a result,the DHP nanoparticle could be applied in tumoral fluorescence-photoacoustic dual-modal imaging.Finally,the in vivo antitumor study indicated that compared with mono-therapy,the chemo-photothermal combined therapy by DHP significantly inhibited the tumor growth and had enhanced combined antitumor effect.In summary,in the present work,a α-amylase-and redox-responsive nanoparticles based on hydroxyl starch-paclitaxel prodrug was successfully constructed,and this self-assembly was further used for encapsulating a multifunctional theranostic agent DiR.This multifunctional drug delivery system was utilized in tumor diagnosis and therapy,and this self-assmbled prodrug nanoparticle is expected to provide new strategy for drug co-delivery and better integration of tumor diagnosis and therapy.