Design And Synthesis Of Protein-targeted Molecular Photosensitizers And Their Application In Photodynamic Therapy Of Tumor

Cancer has always been one of the most deadly diseases.The World Health Organization predicts that the number of new cancer patients will reach 15 million and continue to rise.Therefore,the control of cancer is the focus of the health strategies of governments around the world,and the cancer treatment has become a main research topic of worldwide concern.Photodynamic therapy(PDT),as a potential cancer treatment strategy for clinical use,has attracted wide attention due to its high safety,good controllability,easy operation,and small side effects.The treatment mechanism of PDT is to use a specific wavelength of light to excite the photosensitizer.The excited photosensitizer transfers energy to the surrounding oxygen and generates a large number of reactive oxygen species(ROS).ROS reacts with the surrounding macromolecules,causing the cell structure to be destroyed,which has the effect of killing tumor cells.The therapeutic effect of PDT is highly dependent on the degree of oxidative damage caused by ROS.However,the killing effect of ROS to cancer cells could be weakened due to the short life span of ROS,the limited diffusion distance of ROS,and rich antioxidant enzymes in cancer cell.Therefore,developing a new strategy to enhance the efficiency of ROS utilization is needed to improve the therapeutic effect of PDT.As an important participant in life activities,protein is one of the most important components of an organism.By analyzing and study protein structure and function,proteins are involved in many important physiological and pathological processes.Proteins have become important molecular targets for new drug designs in cancer detection,imaging,and treatment.In particular,thiol proteins affect the physiological functions of many cells,such as anti-oxidation,regulating cell growth,inhibiting apoptosis,and regulating intracellular transport processes.Thiol groups play an important role in maintaining the redox environment of proteins.Once the protein is damaged,dysfunction in the cell leads to apoptosis.Therefore,shortening the distance between the photosensitizer and the protein causes the ROS produced by PDT to directly act on the protein,which can more efficiently cause protein damage and induce oxidative stress,and enhance the killing effect on cancer cells.Based on this,two protein-targeted organic small molecule photosensitizers are designed and synthesized in this thesis,which greatly enhance the utilization efficiency of ROS for PDT of tumor.This thesis includes the following two aspects:1.A protein-targeted near-infrared small-molecule photosensitizer(PIPS808)was designed to enhance PDT.In view of the abundant thiol groups in proteins,bismaleimide derivatives were chosen as protein-targeted group and were covalently linked to small molecule photosensitizers via amide bonds.In order to prevent small molecule photosensitizers from being rapidly removed during blood circulation and unnecessary reactions with other active substances,a folic acidfunctionalized amphiphilic block polymer F127 was selected to self-assemble with photosensitizers to form nanomicelles.It can actively target cancer cells and then release small molecule photosensitizers after internalization.Under NIR laser irradiation,the produced ROS can directly inactivate the protein,cause oxidative stress in the cell and induce tumor ablation,because the small molecule photosensitizer is covalently bound to the thiol group on the intracellular protein.Compared with non-modified photosensitizers,the therapeutic effect on tumors was greatly improved because the photosensitizer is anchored to the intracellular proteins to avoid molecular efflux.2.A protein-targeted molecular photosensitizer(PS-TPP-PI)was designed and synthesized to induce mitochondrial ROS burst and enhance the efficacy of PDT.One end of the synthesized molecular photosensitizer was modified with triphenylphosphine(TPP)through an amide bond,and the other end was modified with a protein targeting group N-(2-aminoethyl)-2-chloroacetamide(PI).The small molecule photosensitizer can be covalently binded to a thiolcontaining protein in the mitochondria.In order to enhance the biocompatibility,F127 polymer modified with folic acid was selected to encapsulate the photosensitizer,which can bind to the folate receptor overexpressed on the cancer cell membrane and actively target the tumor tissue.The molecular photosensitizers can target mitochondria through triphenylphosphine.At the same time,the photosensitizers will covalently bind to thiol groups of proteins in the mitochondria.The decrease of membrane potential make more photosensitizers accumulate in the mitochondria to prevent molecular photosensitizers efflux.When irradiated with laser light for a short period of time,ROS burst occur in mitochondria,which induced mitochondrial-mediated intrinsic apoptotic pathways,leading to the decrease in membrane potential,release of cytochrome C,and activation of caspase 3/7 to induce apoptosis.The activated caspase can further induce the production of more ROS,cause irreversible cell death.In addition,the produced ROS directly function in thiolcontaining proteins in the mitochondria,causing serious damage to the proteins and mitochondrial dysfunction.This protein-targeting molecular photosensitizer design strategy could enhance the effectiveness of mitochondrial-targeted PDT treatment.