Design,Synthesis And Properties Of Novel Two-Photon Organic Small Molecules Based On Porphyrin Skeleton

Due to their unique photophysical and photochemical properties,porphyrins have been widely applied in many frontier fields,especially in fluorescence imaging and photodynamic therapy.However,conventional porphyrin PSs have some limitations,which restrict their application in bioimaging and photodynamic therapy.On one hand,the absorptions of conventional porphyrin PSs are mainly located in the visible region,which is a major drawback as conventional one-photon excited PDT cannot penetrate deep tissue.On the other hand,conventional porphyrin PSs have insufficient specificity for cancer cells,which can cause photodamage to both normal cells and cancerous cells.Two-photon excitation uses infrared or near-infrared light as the excitation source.Under this long-wave excitation with strong penetration,deep lesions could be treated,and the autofluorescence of biomolecules and the interference from scattered light could be effectively avoided.Fluorescence resonance energy transfer(FRET)is a nonradiative process by which an excited donor transfers energy to an acceptor in the ground state through long-range dipole-dipole interactions.Our goal is to indirectly excite porphyrin moiety through FRET from a two-photon excitable energy donor.This approach permits retention of the established photophysical advantages afforded by the porphyrin while allowing excitation in biological transparency window within the range from 700 to 1000 nm.In addition,the targeting strategies,including tumor-targeting and organelle-targeting,are expected to significantly enhance the accuracy of diagnosis and the efficacy of PDT of cancers while reducing the adverse side effects.In this thesis a series of two-photon organic small molecules based on porphyrins have been designed and synthetized,with their application potential in bioimaging and photodynamic therapy explored.The main research contents are as follows:1 An AceDAN-porphyrin(Zn)dyad for fluorescence imaging and photodynamic therapy via two-photon excited FRETThe recent development of two-photon technique offers a unique opportunity to improve the depth of imaging and treatment in photodynamic therapy(PDT).However.the conventional photosensitizers,such as porphyrins,exhibited low two-photon absorption cross section(<50 GM),limiting their clinical utility.In the design and synthesis of novel two-photon photosensitizers,the larger two-photon absorption cross-section and the higher singlet oxygen quantum yield are difficult to be combined simultaneously.In Chapter 2 of this thesis,we designed a fluorescence resonance energy transfer(FRET)based AceDAN-Porphyrin(Zn)dyad for two-photon excited fluorescence imaging and PDT of cancer cells simultaneously,in which the AceDAN moiety was selected as the two-photon absorption donor,and the porphyrin(Zn)moiety served as the energy acceptor.Upon one-photon or two-photon excitation,the excited state energy of AceDAN donor was transferred to the porphyrin(Zn)acceptor with high efficiency(?EET=98%),where red fluorescence and singlet oxygen were generated.Dyad 1 exhibited high photocytotoxicity towards A549 cells(IC50 = 4.3 ?M)with rapid cellular uptake while displayed low dark-cytotoxicity.Furthermore,by combining the advantages of two-photon excitation with porphyrin(Zn)photosensitizer,the AceDAN-Porphyrin(Zn)dyad has been successfully applied to A549 cells for imaging and photodynamic therapy under two-photon laser irradiation.2 Lysosome-targeting two-photon excited FRET dyads for fluorescence imaging and photodynamic therapyTwo-photon excitable fluorescent dyes with integrated functions of organelle targeted imaging and photodynamic therapy(PDT)are highly desired for the development of cancer theranostic agents.PDT-induced apoptosis is affected by subcellular localization of photosensitizers.Lysosomes are a common organelle in eukaryotic cells containing more than 50 hydrolases,which can determine the decomposition of various exogenous and endogenous macromolecules.Singlet oxygen can induce lysosomal damage and release hydrolytic enzymes into the cytoplasm,thereby leading to cell necrosis.In Chapter 3,fluorescence resonance energy transfer(FRET)dyads,AceDAN-H2Por-Lyso(la)and AceDAN-ZnPor-Lyso(1b),were developed for two-photon excited(TPE)lysosome-targeted fluorescence imaging and PDT of cancer cells.Under one-photon or two-photon excitation,the AceDAN donor can effectively transfer the excited state energy to the porphyrin acceptor via high efficient FRET,leading to the generation of deep-red fluorescence and singlet oxygen for cell imaging and PDT respectively.la and 1b exhibit high photocytotoxicity and low dark cytotoxicity,in addition to strong lysosomal targeting capability in living cells.By taking the advantages of the two-photon absorption properties of the AceDAN donor and the properly distributed S1 and T1 states of the porphyrin acceptor,the AceDAN-porphyrin dyads la and 1b have been successfully applied to TPE-fluorescence imaging and PDT for tracking the significant morphology changes of cancer cells under two-photon laser irradiation.3 A tumor and lysosome dual-targeted photosensitizer for fluorescence imaging and photodynamic therapySelective imaging and photodynamic therapy(PDT)through targeted delivery of photosensitizer(PS)offers a unique opportunity for precise diagnosis and therapy of cancer.On the other hand,due to the limitations in lifetime and diffusion range,the effective damage caused by singlet oxygen(1O2)requires precise localization of the photosensitizers to the subcellular organelles.In Chapter 4,a novel tumor-targeting and lysosome-specific porphyrin-based photosensitizer(BMP)were developed for fluorescence imaging and PDT of cancer cells.Biotin was employed as the tumor-targeting module,and the morpholine group was selected as the lysosome-specific unit.Due to the proper distribution of the S1 and T1 states,porphyrin could generate red fluorescence emission and singlet oxygen(1O2)for the dual functions of cell imaging and PDT,respectively.In confocal microscopy studies,the dual-targeted photosensitizer BMP could preferably accumulate in cancer cells and subsequently locate in the lysosome organelles.Cell viability assays suggest that BMP exhibits much higher photocytotoxicity toward the cancer cells(A549 cells)than normal cells(BEAS-2B cells).Under illumination conditions,the singlet oxygen generated by BMP causes oxidative damage to lysosomes and subsequently leads to the necrosis of cells,as evidenced by the loss of morphological integrity and cell rupture.