Phenylboronic Acid-functionalized Intelligent Nano-drug Delivery Systems

To fully exploit the enhanced permeability and retention(EPR)effect of solid tumors,nanomedicines need to achieve long circulation in vivo.Therefore,nanomedicines are commonly modified by polyethylene glycol(PEG)to decrease protein adsorption,reduce the clearance by mononuclear phagocyte system,and prolong drug circulation lifetimes.However,PEGylation also limits the cellular uptake of nanomedicine and therefore effective drug delivery to target cancer cells.To address these issues,phenylboronic acid(PBA)moiety was used as targeting ligand in this thesis,and a series of drug-loaded micelles were prepared and analyzed.In Chapter 1,we made an overview of drug delivery nano-systems,polymeric micelles,PEGylation,PEG dilemma and biological application of PBA.And then we described the research ideas and contents of this thesis.In Chapter 2,we developed a type of camptothecin(CPT)prodrug micelles based on phenylboronate ester-linked diblock copolymer named as PEG-BC-PGlu-ss-CPT,aiming to enhance endocytosis and realize reduction-triggered CPT release.Acidtriggered de-PEGylation with succeeding enhanced cellular uptake was achieved by introducing phenylboronate ester bond.In addition,disulfide bond was adopted to construct prodrug monomer,yielding reduction-triggered CPT release.The prodrug polymer could form spherical micelles in aqueous solution by self-assembly.Meanwhile,compared with HL7702 cells(low expression of sialic acid),prodrug micelles demonstrated enhanced endocytosis against HepG2 cells(high expression of sialic acid).In addition,the degradation of phenylboronate ester was accelerated with the increment of acidity,and therefore the cellular uptake of HepG2 cells was increased,as well as the antiproliferative effect of resultant micelles against HepG2 cells.Although Chapter 2 provides new ideas for overcoming the PEG dilemma and strategies for de-PEGylation,extracellular de-PEGylation is a time-dependent process.Therefore,in Chapter 3,in order to enable the nano-drug delivery system to anchor the tumor cells as soon as possible,we directly used phenylboric acid as the targeting group,and we developed a bioinspired nanoplatform based on PBA-PEG-b-P(Glu-co-GluDA)copolymer.The nanoplatform could realize fast endocytosis,lysosomal pH-triggered drug release,and reduced drug efflux.The synthesized polymer structure was favorable for the encapsulation of doxorubicin(DOX),and the prepared drug-loaded micelles could achieve higher drug loading capacity and efficiency.A core cross-linking strategy based on coordination between dopamine and ferric ion was adopted to stabilize nanoparticles and achieve lysosome pH-controlled drug release.The nanoplatform maintains structural integrity even when dispersed in a good solvent,demonstrating the potential to resist infinite plasma dilution after intravenous injection.In addition,compared with doxorubicin hydrochloride,the nanoplatform also enhanced cellular uptake of DOX,demonstrated significant anti-proliferation effect,and significantly reduced drug efflux.The inhibition rate on tumor growth of the nanoplatform was 70%,demonstrating the multifunctionality of the nanoplatform.In Chapter 4,on the foundation of the polymer structure in Chapter 3,we developed a novel intelligent prodrug delivery nanoplatform with reversible core crosslinking strategy based on prodrug polymer PBA-PEG-P(Glu-co-GlussCPT),aiming to better stabilize nanomicelles and enhance endocytosis.CPT was conjugated to the polymer by disulfide bond to realize drug release triggered by reduction conditions in tumor cells.Besides,disulfide bond was used to form reversible core crosslinking structure,which could respond to the reduction environment in the tumor cells,realizing the decrosslinking of micelles inside the tumor cells.Combing prodrug strategy and crosslinking strategy,the CPT prodrug micelles could withstand infinite dilution,carry more therapeutic molecules to tumor tissues,and minimize premature drug release.Moreover,prodrug micelles exhibited enhanced endocytosis efficiency and significant antiproliferative activity against tumor cells.This prodrug nanoplatform also exhibited significant in vivo antitumor efficacy on both murine hepatoma xenograft and human hepatoma xenograft model,without showing significant systemic toxicity but demonstrating good biocompatibility.Because multidrug resistance and metastasis of tumor cells are the major barriers to chemotherapy,in Chapter 5,we constructed a nanocarrier for encapsulation of DOX by adjusting the CPT ratio based on the synthesis method in chapter 4.The resultant co-delivery micelles could enhance the cellular uptake of multidrug resistant cells by the specific binding of PBA and sialic acid on cell surface,reduce the drug efflux,release the CPT and DOX under microenvironmental stimuli within the tumor cells,achieve synergy antiproliferative effect against multidrug resistant cells,and inhibit the migration and invasion of multidrug resistant cells.In summary,aiming at fully exploiting the EPR effect of solid tumor,improving the targeting efficiency,overcoming the PEG dilemma,enhancing the cellular uptake of tumor cells,realizing the intracellular microenvironment-controlled drug release,reducing the side effects of drugs,and inhibiting the proliferation and metastasis of tumor cells,four types of polymeric micelles based on phenylboronic acid as the important functional groups were constructed as anti-tumor drug delivery systems in this thesis.The study and the evaluation of polymeric micelles were conducted from the polymeric molecular level,micellar level,cellular level,and animal level,respectively.The research results provides new ways of thinking for building multifunctional polymeric micelles as targeting drug delivery systems for anti-tumor drugs.