Nanostructural Modulation And Functionalization Of Responsive Polymeric Assemblies

Stimuli-responsive polymers are capable of exhibiting reversible or irreversible changes in physical properties and/or chemical structures to small changes in external environment,leading to complicated behaviors of their corresponding assemblies,including swelling or collapse,dissociation or aggregation,crosslinking or decrosslinking,shape transformation,and so forth.Moreover,variations in physiological parameters are important hallmarkers for diseased organs,tissues,and cells when compared to their normal counterparts,redering them attractive targets for developing novel responsive polymeric assembies to achieve selective delivery of therapeutic and diagnostic agents.In this thesis,tumor and inflammation microenvironment-sensitive polymeric assemblies,which are redox-responsive polymersomes and micelles,were studied,with emphasis on their fabrication,nanostructural modulation,and integration of multifuntionalities.The dissertation includes the following three parts:1.Reactive oxygen species(ROS)and oxidative stress are implicated in various physiological and pathological processes and this feature provides a vital biochemical basis for designing novel therapeutic and diagnostic nanomedicines. Among them,oxidation-responsive micelles and vesicles(polymersomes)of amphiphilic block copolymers have been extensively explored;however,in previous works,oxidation by ROS including H2O2 exclusively leads to microstructural destruction of polymeric assemblies.For oxidation-responsive polymersomes,fast release of encapsulated hydrophilic drugs and bioactive macromolecules will occur upon microstructural disintegration.Under certain application circumstances,this does not meet design requirements for sustained- release drug nanocarriers and long-acting in vivo nanoreactors.Furthermore, conventional polymersomes possess thick hydrophobic bilayers and compromised membrane permeability,rendering them as ineffective nanocarriers and nanoreactors.We herein report the fabrication of oxidation-responsive multifunctional polymersomes exhibiting intracellular milieu-triggered vesicle bilayer crosslinking,permeability switching,and enhanced imaging/drug release features.Mitochondria-targeted H2O2 reactive polymersomes were obtained through the self-assembly of amphiphilic block copolymers containing arylboronate ester-capped self-immolative side linkages in the hydrophobic block,followed by surface functionalization with targeting peptides.Upon cellular uptake,intracellular H2O2 triggers cascade decaging reactions and generates primary amine moieties;prominent amidation reaction then occurs within hydrophobic bilayer membranes,resulting in concurrent crosslinking and hydrophobic-to-hydrophilic transition of polymersome bilayers inside live cells.This process was further utilized to achieve integrated functions such as sustained drug release,(combination)chemotherapy monitored by fluorescence and magnetic resonance(MR)imaging turn-on,and to construct intracellular fluorogenic nanoreactors for cytosolic thiol-containing bioactive molecules.2.Therapeutic and diagnostic nanomedicines,which exploit differential biochemical signals to achieve selective and spatiotemporal delivery of drugs,peptides,proteins,and imaging agents,have been extensively explored over past decades.Among them,redox-responsive polymeric micellar nanoparticles of amphiphilic block copolymers by taking advantage of the redox potential gradient between oxidizing extracellular milieu and reducing intracellular space,are currently of considerable interest for biological applications.Moreover,a variety of approaches,such as chemical crosslinking with reversible linkers(e.g.,disulfide or ketal linkage),have been widely adopted to further strengthen micellar stability to prevent undesirable disintegration and premature drug release.Note that in all these cases,cleavage of reversible linkage exclusively leads to de-crosslinking and destabilization of micellar nanoparticles,resulting in rapid clearance,and low accumulation and retention at targeted sites.Thus,the development of novel strategies that enable selective targeting to tumor and intracellular microenvironment,and more importantly,can further trigger the localization and retention of theranostic polymeric micelles in vivo remains a critical challenge.Specifically,for most reversible disulfide-crosslinked(DCL)polymeric micellar nanoparticles,cleavage of disulfide linker merely results in de-crosslinking without prominent hydrophobic-to-hydrophilic transition,hindering the complete and efficient payload release.Considering the above challenges,we herein describe the fabrication of redox-responsive self-core-crosslinked micellar nanoparticles exhibiting extended blood circulation half-life and intracellular reductive milieu-triggered transformation of crosslinking module,hydrophobic-to-hydrophilic transition of micellar cores,and enhanced diagnostic imaging/drug release features.Tumor cell- targeted reductive milieu-responsive DCL micelles were obtained through the self-assembly of amphiphilic block copolymers containing disulfide-based self-immolative carbamate side linkages in the hydrophobic block,followed by surface functionalization with targeting peptides and UV-induced reagent-free crosslinking via disulfide reshuffling.Upon integrin-mediated endocytosis,cytoplasmic reductive milieu triggers cascade decaging reactions and generates primary amine moieties;prominent amidation reaction then occurs within hydrophobic micellar cores,resulting in contemporaneous crosslinking module transforming and hydrophobic-to-hydrophilic switching within micellar cores in living cells.This process was further utilized to achieve integrated functions such as chemotherapy guided by fluorescence and magnetic resonance(MR)imaging turn-on.3.Immune cells primarily serve to protect against opportunistic infections,but when they become activated inappropriately,they can participate in the development of inflammatory diseases,such as rheumatoid arthritis,ulcerative colitis, atherosclerosis,and diabetes complications.During progression of these diseases, immune cells such as macrophages may release cytokines(interleukin-1(IL-1), interleukin-6(IL-6),tumor necrosis factor-alpha(TNF-a)),digestive enzymes(e.g., collagenases),prostaglandins,and reactive oxygen species(ROS),which can aggravate or accelerate damage to the normal tissues.Nonsteroidal anti- inflammatory drugs(NSAIDs)are widely used to treat acute pain,fever,and inflammation.Side effects associated with long-term use of NSAIDs such as gastrointestinal damage and elevated risk of stroke,however,can limit their use and exploration in new indications.Herein,we present inflamed site-related oxidative and reductive milieu-responsive anti-inflammatory polymersomes self-assembled from polyprodrug amphiphiles with indomethacin(IMC)prodrugs in hydrophobic block.Furthermore,the controlled release profiles of IMC triggered by redox milieu were evaluated and in vitro anti-inflammatory action of redox-responsive polymersomes was assessed.