Synthesis Of PH-Responsive Polymer-Drug Conjugate Based On Polysaccharides For Malignant Chemotherapy

With obvious increase in incidence and mortality,malignancy has become a major threat to human health and life.Nowadays,chemotherapy,especially small molecule antitumor drugs,is still the main treatment for cancer in clinical practice.However,small molecule antitumor drugs exhibt poor water solubility,short circulating time in vivo,and prompt metabolism.Moreover,frequently developed multi-drug resistance and lack of targeting to cancer cells also largely limit their application.To overcome the shortness,much attention has been focused on polymer nanomedicine,which combines the antitumor drugs with polymer via physical encapsulation or chemical conjugation.In this thesis,we engineered a series of polymer-conjugated drugs,in which the biocompatible polysaccharide was adopted as the backbone and conjugated with small molecule antitumor drugs.The influence of drug bonding rate on delivery efficacy was researched.We further investigated the antitumor effect of passive targeting polymer-conjugated drug,active targeting polymer conjugated drug,as well as active targeting polymer combined with dual drugs.The main content of our research is as follows:(1)pH-sensitive hydroxyethyl starch-doxorubicin conjugate(HES=DOX)HES was selected as backbone of the nanocarrier.Three kinds of pH-sensitive HES=DOX conjugate were facilely fabricated through an efficient Shiff base reaction between the aldehyde group(-CHO)in oxidized HES and amino group(-NH2)of DOX.The natural polysaccharide-drug conjugates self-assembled into micelles in aqueous medium and their morphologies and sizes were observed by transmission electron microscopy(TEM)and dynamic light scattering(DLS).Then the in vitro release,cytotoxicity,endocytosis,and tumor inhibition in vivo of the three conjugated drugs were also determined.The HES=DOX reached tumor tissue via the enhanced permeability and retention(EPR)effect.As internalized into the tumor cells,oxime bond of the polymer drug conjugate was rapidly cleaved in low pH,and DOX was immediately released to kill tumor cells.All the three conjugates significantly inhibited the tumor growth,which not only prolonged the circulating time but also effectively reduced the toxicity of small molecule drugs towards normal tissues.Besides,it was exhibited that the antitumor effect was enhanced as the increase of drug bonding rates.(2)cRGD targeted HES-DOX conjugate(HES=DOX/cRGD)for active targeting deliveryBased on the previous research,cRGD,which specifically combines with the ?v?3 integrin expressed on tumor cells,was introduced into the natural polysaccharides-drug conjugate.cRGD and DOX were connected to the aldehyde group of HES via Shiff base bond,respectively.The natural polysaccharides-drug conjugate was accumulated at the tumor sites via active targeting of cRGD and subsequently the release of DOX was triggered in acid environment.Endocytosis and intracellular release were observed for a period of 2 h,suggesting that A375 cells that overexpressed ?v?3 integrin showed higher intake of HES=DOX/cRGD.The active targeting HES=DOX/cRGD exhibited favorable therapeutic capability for its effective suppression of tumor growth in vivo accompanied with reduced damage to normal organs.(3)Self-targeted pH-sensitive dextran-graft-DOX conjugate(Dex-g-DOX)To solve the drug burst release and improve the water-soluble of natural polysaccharides-drug conjugate,Dex,a natural polysaccharide was employed as basic backbone.Dextran showes excellent dissolubility and easier modification,making it a suitable candidate for pH-sensitive polymer conjugated drug.Dex-g-DOX was formed by condensation reaction between Dex and cis-aconitic anhydride-modified DOX(CAD).The two moieties were connected via acid-cleavable amide bond.Dex-g-DOX can be highly accumulated in the liver,so Dex-g-DOX can treat hepatocellular carcinoma by active targeting.Afterwards,DOX was released from the micelle within acidic endosomes or lysosomes following endocytosis because of the cleavage of amide linker,and the antitumor effect was evidently improved.(4)cRGD-targeted pH-sensitive dextran-DOX/BTZ conjugate(dextran-g-DOX/BTZ/cRGD)synergistic therapyTo reduce or eliminate the drug resistance caused by single-drug therapy,and further inhibit the tumor growth,we combined DOX,inhibiting the synthesis of nucleic acid,and BTZ,impeding the activation of NF-?B,with dextran aldehyde by Schiff base or boron ester bond,respectively.cRGD was also connected to Dex via pH-sensitive Shiff base for targeting?v?3 integrin on tumor cells.It was determined that the Dex-g-DOX/BTZ/cRGD micelle effectively entered tumor cells via receptor-mediated pathway and released antitumor drugs in low pH environment,achieving the combination therapy of DOX and BTZ.We expect the simply-designed and remarkably effective DOX conjugated drug system investigated in the thesis would provide experimental basis for clinical researches of polymer conjugates,and offer new thought for development of advanced nanomedicine.