Responsive Theranostic Nano-Vectors With AIE Performance And Photo Dynamic Therapy

Because of their irreplaceable advantages in nano medicine,during the last decade,stimuli-responsive polymers and their assemblies arouse wide attention.With the continuous development of theranostic concept,biomedical applications of stimuli-responsive polymers have been further promoted.A combination of imaging modalities and therapeutical agents on a single nano-carrier is of increasing interest.This dissertation focuses on introducing aggregation induced fluorescence(AIE)functional molecules to stimuli-responsive polymer-based nanomedicine systems for cancer diagnosis and treatment.Moreover,we developed a singlet oxygen generating hydrogel based on singlet oxygen generating AIE molecules.Aiming at some problems in photodynamic therapy,we developed novel singlet oxygen delivery system with amphiphilic diblock polymers.Based on the above scientific background,this thesis work is divided into the following four chapetors:1.The mimicking of biological supramolecular interactions and their mutual transitions to fabricate intelligent artificial systems has been of increasing interest. Herein,we report the fabrication of supramolecular micellar nanoparticles consisting of quaternized poly(ethylene oxide)-b-poly(2-dimethylaminoethyl methacrylate)(PEG-b-PQDMA)and tetrakis(4-carboxylmethoxyphenyl)ethene (TPE-4COOH),which was capable of reversible transition between polyion complexes(PIC)and hydrogen bonding complexes(HBC)with tunable aggregation-induced emission(AIE)mediated by solution pH.At pH 8, TPE-4COOH chromophores can be directly dissolved in aqueous milieu without evident fluorescence emission.However,upon mixing with PEG-b-PQDMA, polyion complexes were formed by taking advantage of electrostatic interaction between carboxylate anions and quaternary ammonium cations and the most compact PIC micelles were achieved at the isoelectric point(i.e., [QDMA+]/[COO-]= 1),as confirmed by dynamic light scattering(DLS) measurement.Simultaneously,fluorescence spectroscopy revealed an evident emission turn-on and the maximum fluorescence intensity was observed near the isoelectric point due to the restriction of intramolecular rotation of TPE moieties within the PIC cores.The kinetic study supported a micelle fusion/fission mechanism on the formation of PIC micelles at varying charge ratios,exhibiting a quick time constant(?1)relating to the formation of quasi-equilibrium micelles and a slow time constant(?2)corresponding to the formation of final equilibrium micelles.Upon deceasing the pH of PIC micelles from 8 to 2 at the [QDMA+]/[COO-]molar ratio of 1,TPE-4COOH chromophores became gradually protonated and hydrophobic.The size of micellar nanoparticles underwent a remarkable decrease,whereas the fluorescence intensity exhibited a further increase by approximately 7.35-fold,presumably because of the formation of HBC micelles comprising cationic PQDMA coronas and PEG/TPE-4COOH hydrogen-bonded cores,an inverted micellar structures compared to initial PIC micelles.Moreover,the pH-mediated schizophrenic micellar transition from PIC to HBC with tunable AIE characteristic was reversible.2.The fabrication of novel theranostic nanovectors that combine diagnostic and therapeutic capabilities into one single platform is of particular interest in treating formidable diseases(e.g.,cancers).Herein,we report a new tumor-targetable theranostic agent based on core crosslinked(CCL)micelles,possessing pH low insertion targeting peptide(pHLIP)and T1-tpye magnetic resonance imaging (MRI)contrast agent,DOTA(Gd),in the coronas,and 1,1,2,2-tetrakis[4-(2-mercaptoethoxy)phenyl]ethane(TPE-4SH)crosslinked cores with unique aggregation-induced emission(AIE)feature.Azide-terminated diblock copolymer,N3-POEGMA-b-P(DPA-co-GMA),was synthesized via consecutive atom transfer radical polymerization(ATRP),where OEGMA,DPA,and GMA are oligo(ethylene glycol)methyl ether methacrylate.2-(diisopropylamino)ethyl methacrylate,and glycidyl methacrylate,respectively.The resulting diblock copolymer was further functionalized with DOTA(Gd)or benzaldehyde moieties via copper(I)-catalyzed alkyne-azide cycloaddition(CuAAC)chemistry,resulting in the formation of DOTA(Gd)-POEGMA-b-P(DPA-co-GMA)and benzaldehyde-POEGMA-b-P(DPA-co-GMA)copolymers.The resultant functionalized block copolymers co-assembled into mixed micelles at neutral pH in the presence of TPE-4SH,which underwent spontaneous crosslinking reactions with GMA residues embedded within the micellar cores,simultaneously switching on TPE fluorescence due to the restriction of intramolecular rotation.Moreover,tumor-targeting pHLIP moieties were attached to the coronas through the Schiff base chemistry.Finally,anticancer drug(e.g.,camptothecin,CPT)was also encapsulated into the crosslinked cores at neutral pH,yielding a theranostic nanovector with fluorescence and MR dual imaging modalities and unique tumor-targeting capability.The nanovectors can be efficiently taken up by cancer cells(e.g.,A549 cells),as monitored by TPE fluorescence.After internalization,intracellular acidic pH triggered the release of loaded CPT,killing cancer cells in an on-demand manner.On the other hand,the nanovectors labeled with DOTA(Gd)contrast agents exhibited increased relaxivity(r1 = 16.97 mM-1s-1)compared to alkynyl-DOTA(Gd)small molecule precursor(r1 =3.16 mM-1s-1).Moreover,in vivo MRI measurements revealed CCL micelles with pHLIP peptide exhibiting better tumor accumulation and MR imaging performance than CCL micelles without targeting peptide.3.Biodegradable hydrogel with AIE and singlet oxygen generation capabilities was fabricated for photodynamic therapy.TPECN is a TPE derivative with red emission and singlet oxygen generating ability upon light illumination.We first synthesizd a hydroxyl group-functionalized molecule termed as TPECN-OH,which was further modified with a dipeptide(FF).The as-synthesized TPECN-FF was able to form hydrogel in proper condition,exhibiting intense emissionin the hydrogel state.Interestingly,in the presence of oxygen,the hydrogel can spontaneously generate singlet oxygen upon light irradiation.On the other hand,since the TPECN group could react with thiol groups,the hydrogel was thus thiol-responsive.When treated with GSH,a gel-to-sol transition was observed with drastic fluorescence quenching.Notably,the hydrogel was biocompatible as cell culture medium and no remarkable cell death was discerned without light irradiation,yet upon light irradiation the cells could be killed by singlet oxygen.The generation of singlet oxygen can be facilely regulated by GSH.4.A Singlet oxygen delivery platform was constructed based on pyridone unit-bearing amphiphilic diblock copolymers.Pyridone units can reversibly bind with singlet oxygen and spontaneously release singlet oxygen under certain conditions.We designed novel pyridone-based monomers and synthesized amphiphilic diblock copolymers comprising pyridone moieties via RAFT polymerization.The diblock copolymer can efficiently load singlet oxygen upon irradiation in the presence of photosensitizer(e.g.,methylene blue)and singlet oxygen could be released in dark.Since the release rates were higly dependent on temperature,we further attached the polymers to the surface of gold nanorods via ligand exchange reactions,a photothermal agent.The release of singlet oxygen can thus be mediated by irradiating the hybrid nanorods with a NIR laser as a result of local temperature change.The combination of photothermal and photodynamic therapy modalities augur better tissue penetration and thus better performance in practical applications.