Functionalized Nanoparticles For Improving Tumor Photodynamic Therapy And Photothermal Therapy

Malignant tumor,also known as cancer,was developed by abnormal cells induced from normal cells under endogenous or exogenous carcinogen.As a threatening and deadly disease,cancer has become a major killer for human life and health due to the rapid proliferation and differentiation,metastasis and invasion of cancer cells.How to cure cancer is still a great challenge in the field of medicine.Besides traditional therapeutic methods,e.g.surgery,radiotherapy and chemotherapy,some new methods have emerged for cancer therapy,e.g.photodynamic therapy?PDT?and photothermal therapy?PTT?.PDT for cancer is that photosensitizer can absorb energy and reach to excited state upon irradiation,which is not stable and will transitions to a more stable ground state.During this process,it will transfer energy to its surrounding oxygen molecules to generate reactive oxygen species?ROS?,which can be employed to destroy biomolecules?e.g.proteins,nucleic acid,etc.?for cancer therapy.PTT for cancer is that upon irradiation,materials absorb energy to generate heat through photothermal conversion,which will raise the temperature of tumor region.When the temperature is high enough,cancer cells will be destroyed or the tumor will be eliminated through thermal ablation.Because of the minimal invasiveness,fast healing process,relative high therapeutic efficiency and potential repeatability,PDT and PTT have attracted more and more attention,and been investigated intensively.However,there are obvious drawbacks in traditional PDT.First,the exited lights used in traditional PDT are usually ultraviolet or visible light,which have a poor skin penetration and may cause side effects to normal cells.Second,the low therapeutic efficiency caused by the extremely short lifespan?<40 ns?and severely limite diffusion distance?<20 nm?of ROS also limits its application.Then,the hypoxia in tumor region reduces the ROS generation in PDT.Finally,the efflux of the photosensitizers by drug resistant cancers will cause the reduction of intracellular concentration,which results in the insufficient ROS generation and poor therapeutic effects.As PTT is not tumor selective,the realization of PTT function to cancer depends on precise targeting of the materials with photothermal conversion capability.The premature entrance into normal cells will also cause side effects.These are the main challenges faced by the PDT and PTT needed to be addressed urgently.Recently,with the rapid development of nanotechnology,nanomaterials have been widely used in various fields such as chemistry,biology and medicine,etc.Due to the unique physical and chemical properties,nanomaterials also play important roles in cancer therapy.?1?Unique optical properties.For example,upconversion nanoparticles?UCNPs?can be excited upon NIR irradiation and emit ultraviolet or visible light,which are tunable by the doping of different rare earth ions.Gold nanoparticles with different size scale have different adsorption,which can be employed for fluorescence quenching and photothermal conversion.?2?Easy modification.There always are active groups on the surface of the nanoparticles or they are negative or positive charged after synthesis and treatment,which can be used for the conjugation of targeting groups,fluorescence dyes and other functional groups to improve the biocompatibility,function of targeting and labelling,etc.?3?Tunable morphology and size.As nanoparticles with different morphology and size have different behavior in the biological system,we can prepare them according to what we need.So nanotechnology and nanomaterials provide new methods and sights for solving the problems we meet in the clinic application of PDT and PTT.To sum up,it is an ideal candidate to develop NIR triggered,organelle targeted and drug resistant nanophotosensitizer for PDT and precise targeted or tumor specific activated photothermal nanoagents for PTT.This is because that NIR possesses nice penetration ability;organelle targeting can make the ROS generation close to biomolecules;materials with nanometer size can prevent from efflux outside cell to some extent;and nanoparticles with precise targeted ability can reduce side effects significantly.In this dissertation,a variety of nanoparticles were designed and prepared to solve the problems in traditional PDT and PTT and improve their therapeutic effects based on UCNPs,titanium dioxide?TiO₂?,gold nanoparticles,molecular photosensitizer,DNA and peptides,etc.It mainly includes the following sections:1.We presented a novel strategy to construct an NIR-responsive nanophotosensitizer for PDT based on mitochondria targeted TiO₂-coated UCNPs.The Tm³⁺-doped UCNPs can emit UV light with 980 nm laser excitation and activate TiO₂ to produce a flux of ROS,especially superoxide anion radicals(O₂^·-).The triphenylphosphine?TPP?,a mitochondria-targeted group,was then anchored on the surface of TiO₂ to selectively trigger the localized ROS burst in the mitochondria,resulting in initiation of mitochondria-mediated intrinsic apoptotic pathway,which was associated with cascade reactions,such as the activation of an inner membrane anion channel?IMAC?,the opening of mitochondrial permeability transition pores,the decrease in mitochondrial membrane potential???_m?,the release of cytochrome C to cytoplasm.The released cytochrome C will activate the caspase-3 and caspase-7 to induce apoptosis.These caspases can,in return,disturb the mitochondrial electron transport chain,induce the domino effect on ROS burst and cause irreversible cell death.2.We firstly designed and fabricated a nuclear targeted dual-photosensitizer for photodynamic therapy against multidrug resistant caner.Molecule-photosensitizer Ce6 was selected and modified on the surface of core/shell structure nano-photosensitizer upconversion@TiO₂ and then nuclear targeted peptides TAT were anchored for nuclear targeting.Through selective doping rare earth elements Er and Tm,multiple ROS(?OH,O₂^?-,and ¹O₂)can be generated for the dual-photosensitizer and realize their function synergistically by single 980 nm NIR excitation.The nano-sized photosensitizer accompanied with nuclear targeting can effectively generate multiple ROS in the nucleus regardless of the P-glycoprotein and directly break DNA double strands,which is considered as the most direct and serious lesion type for the cytotoxic effects.Therefore,enhanced photodynamic therapy can be achieved against multidrug resistant cancer.3.We developed a tumor targeted,chemical engery triggered PDT system for the the metastatic tumor therapy based on hollow mesoporous silica nanoparticles?HMSNs?,glucose oxidase?GOx?,cancer cell membranes.HMSNs were filled with perfluocarbon and bis?2,4,5-trichloro-6-carbopentoxyphenyl?oxalate?CPPO?,then modified with GOx and Ce6 on the surface and finally coated cancer cell membrane.Cancer cell membarane coated nanoparticles possessed tumor targeting ability.Perfluocarbon could carry O₂,which would improve the hypoxia condition in tumor region.When they entered into cancer cells,GOx would catalize glucose to generate H₂O₂,which would further react with CPPO in the cavity of HMSNs.The reaction will produce chemical energy,which could excite Ce6 to generate ROS for cancer therapy.This approach with no extra irradiation light sourse could solve the problem of limited penetration of excitation light completely and can be used for metastatic tumor therapy.4.We designed an intelligent alpha-cyclodextrin??-CD?-based gold nanomachines for efficient and tumor-specific retention,PA imaging and PTT.Complementary pyridine-2-imine-terminated single-strand DNAs were modified on the two groups of the gold nanoparticles through gold-thiol bonds.Then,?-CD rings encircled the pyridine-2-imine on the DNA via noncovalent bonding interactions under neutral pH conditions.Thus,the?-CD caps could prevent the hybridization between DNA on gold nanoparticles and help maintain the stability during blood circulation.Once the gold nanomachines reach the tumor microenvironment via the enhanced penetration and retention?EPR?effect and the pH decreases to approximately 6.5-6.8,the?-CDs separate from the DNA ends immediately due to the protonation of the pyridine-2-imine,which reduces the noncovalent forces.Subsequently,the gold nanoparticles?AuNPs?self-aggregate via complementary base pairing.The aggregates with large sizes not only exhibit better tumor retention but also have a near-infrared absorption capacity that can be used for cancer diagnosis and therapy through PA and PTT.Therefore,special retention in the tumor and tumor-activated PA and PTT were realized,which can improve the selectivity,enhance the signal-to-noise ratio,and greatly reduce the side effects.