Nanosystems Based On Tumor Acidic Microenvironment And Bioorthogonal Reactions For Tumor Imaging And Therapy

Cancer is a leading cause of death worldwide.Accurate diagnosing and treating of cancer remain a research priority.In recent years,researchers have developed a variety of sensitive tumor imaging and detection tools,as well as effective tumor treatment systems by utilizing the excellent physical and chemical properties of nanoparticles and the selectivity and high efficiency of bioorthogonal reactions.However,how to control the bioorthogonal reaction react at the lesion site is difficult,which requires the reactive groups to be inactive or low reactive before reaching the lesion site,while being highly reactive at the lesion site.This study utilized the acidic tumor microenvironment to develop nanosystems based on bioorthogonal reactions to facilitate tumor imaging and therapy.The bioorthogonal reactive groups of the nano-systems were protected to mask their reactivity and were re-exposed upon stimuled by the acidic microenvironment of the tumor,which in turn triggered the bioorthogonal reaction,thereby enabling tumor site-selective imaging and therapy.The research content of this dissertation includes the following three parts:1.We designed a prodrug activation strategy based on tumor acidic microenvironment and bioorthogonal chemistry.Tetrazine（Tz）and vinyl ether（VE）are a pair of bioorthogonal reactive groups,and Tz could convert VE into a hydroxyl group.A Tz-modified polymer PEG-b-P（AEMA-r-Tz）was designed and synthesized,which self-assembled to form micellar ASTNs,thereby masking the reactivity of Tz.The hydroxyl group of the near-infrared hemicyanine dye（Cy OH）was modified with a VE group,and then the modified molecule was coupled with polyethylene glycol（PEG）to obtain the macromolecular prodrug Cy PVE.The modification of VE masked the near-infrared fluorescence（NIRF）and photodynamic therapy（PDT）capabilities of Cy OH.Under the stimulation of the tumor acidic microenvironment,ASTNs dissociated due to protonation,re-exposed Tz and restored its reactivity,which then activated the NIRF and PDT abilities of Cy PVE via bioorthogonal reaction.Compared to free Cy PVE,Cy PVE incubated with ASTNs at p H 6.5 exhibited a 15.2-fold increase in fluorescence intensity and achieved 91.1%tumor cell cytotoxicity after laser irradiation.This strategy could achieve highly selective imaging of mouse 4T1 breast tumor model,and the fluorescence intensity of tumor tissue was 25 times higher than that of normal tissue after administration 2hours.The tumor inhibition rate was 91.5%on the 12th day after photodynamic therapy.2.We designed a dual-modality probe that can selectively aggregate on tumor sites to simultaneously enhance magnetic resonance and near-infrared fluorescence imaging.First,we modified dibenzocyclooctyne（DBCO）on the surface of magnetic iron oxide nanoparticles（IOs）,and subsequently modified polyethylene glycol（PEG）with a tumor acidity-sensitive linker on the surface of IOs to mask DBCO.We then synthesized azide-modified near infrared fluorescent probe,named AATs,which could couple with DBCO through bioorthogonal reaction.Upon tumor-acidity stimulation,the PEG was detached and the DBCO was re-exposed,thereby induced aggregation of IOs and AATs,and enhanced magnetic resonance and near-infrared fluorescence imaging.The aggregation of c DIOs and AATs leaded to a simultaneous enhancement in NIRF intensity（～15.5-fold）and r₂ relaxivity（～2.8-fold）.We observed 19.4-fold fluorescence enhancement in tumor tissue 2 h after dosing on the 4T1 tumor model.And the aggregation of c DIOs and AATs was able to increase the relaxation rate change（ΔR）by 9.6-fold compared with c DIOs alone.Furthermore,the imaging signals at tumor tissue could be retained to 12 h due to the enhanced retention of the probe by aggregation.3.We designed a nanosystem that can rapidly aggregate around tumor blood vessels under the stimulation of tumor acidity.These rapidly formed aggregates can serve as in situ drug delivery platformsfor efficient drug delivery.First,we constructed azide-modified nanoparticles APM-NP and DBCO-modified nanoparticles DC-NP,respectively.APM-NP could rapidly protonate and expose azide groups under tumor acidity,and subsequently react with DBCO on the surface of DC-NPs,inducing aggregation of both particles.We loaded the vascular disrupting agent CA4 into APM-NP and the hypoxia-activated prodrug PR-104A into DC-NP,respectively,to obtain APM-NP^CA4 and DC-NP^PR-104A.After the two particles form aggregates in tumor,APM-NP^CA4 were enriched around blood vessels and released CA4 to destroy tumor blood vessels,while DC-NP^PR-104A released small-sized particles loaded with PR-104A to penetrate deep into tumor.The destruction of blood vessels could cut off the oxygen source of the tumor and increase the tumor hypoxia level,thereby activating the cytotoxicity of PR-104A.In mouse 4T1 breast tumor model,our strategy achieved an 91.1%tumor inhibition rate at day 16 post-dose compared to the untreated group.In addition,in the well-perfused mouse B16-F10 melanoma model and vascular-deficient human SK-OV3 ovarian cancer xenograft model,this strategy achieved tumor inhibition rates of 69.9%and 59.7%on days 14and 18 post-dose,respectively,indicating effective adaptive therapy of tumors with different hypoxia levels.