Application Of Isoquinolinium In Mitochondrial Targeted Fluorescence Imaging And Photodynamic Therapy

Early diagnosis and treatment of cancer are high benefit for improving the cure rates and reducing the suffering of patients.Compared with traditional detection methods,fluorescence probe illuminates great advantages in visual inspection and clinical diagnosis with superiorities of non-invasive nature,easy synthesis,excellent photostability,tunable excitation and emission wavelengths,spatio-temporal resolution as well as real-time imaging.Mitochondria have been considered as one of the biomarkers to distinguish tumor cells from normal cells due to the huge potential difference between their inner and outer membranes.Moreover,mitochondria not only act as energy suppliers,but also work as reactive oxygen species generators which can trigger programmed cell death.Targeting mitochondria has been considered as an effective way to promote tumor treatment.Therefore,developing mitochondrial targeted fluorescent probes for rapid tumor detection and photodynamic therapy are of great significance.In the thesis,a series of isoquinolinium-based mitochondrial targeted fluorescent probes were designed and synthesized.These probes demonstrated excellent fluorescent characteristics with high fluorescence quantum yield and good biocompatibility which could be used for high fidelity imaging of mitochondrial or mitochondrial targeting photodynamic therapy.The detailed work was described as follow:1.Synthesis and optical properties of isoquinolinium-based fluorescent probes:20isoquinolinium-based fluorescent probes were designed and synthesized through Rh-catalyzed[4+2]cyclization reaction,which were characterized by ¹H NMR,¹³C NMR,¹⁹F NMR and HRMS.The optical properties of the above probes were investigated by UV-Vis and fluorescence spectra.The results demonstrated that probes modification with strong electron-donating group at the A ring（R₁）position of isoquinolinium can lead to the absorption and emission spectra red-shifted with quantum yield increase.Modification of the electron-donating group at C ring（R₂）resulted in the absorption and emission spectra shifting to shorter wavelength,while electron-withdrawing group led to a red-shifted for the absorption and emission spectra of the probe.The quantum yield decreased both for electron-donating and electron-withdrawing in R₂.For the D ring（R₃）position of isoquinolinium,it has little effect on the absorption and emission spectra of isoquinolinium.Among them,LIQ-3 showed the highest quantum yield in both solution and solid state.2.Ultrafast labeling and high-fidelity imaging of mitochondria in cancer cells:The cytotoxicity of the LIQ probes were firstly investigated by MTT assays.The results indicated that most of the probes have good biocompatibility.However,probes modified with conjugated group at R₂ and Br at R₃ would increase the cytotoxicity,while the electron-donating group（-OCH₃）at the R₁ could decrease the cytotoxicity.Then,co-localization experiments were conducted with mitochondrial targeting probe TPE-Ph-In as a reference.The Pearson correlation coefficient of most probe molecules was higher than0.85,demonstrating their mitochondria-specificity,while probes substituted R₂ or R₃ with electron-withdrawing group could change positive charge distribution of isoquinolinium,which led to a badly mitochondria targeting ability.Among them,LIQ-3 can selectively image cancer cells from normal cells,and revealed excellent mitochondrial targeting imaging capabilities in different cancer cell types.Moreover,LIQ-3 not only could achieve ultrafast labeling of mitochondria within 1 min but also showed good mitochondrial specificity and high signal-to-noise ratio in 3D imaging,which made LIQ-3 perform high fidelity and spatiotemporal tracking of mitochondria.3.Mitochondrial targeted photosensitizers for monitoring photo-induced apoptosis,photodynamic antitumor and antibacterial:After investigating the phototoxicity,probes with enhanced D-π-A structure（LIQ-5,LIQ-9,LIQ-10）revealed significant photo-induced reactive oxygen species production and cell phototoxicity.These photosensitizers have photodynamic anticancer effects on different cancer kinds of cells.Especially LIQ-9,the inhibition rate on 4T1 cancer cells can reach as high as 90%under white light irradiation for2 h with low power intensity.LIQ-9 could perform as an efficient photosensitizer in the PDT treatment of mouse breast cancer model in vivo.During the treatment,the PDT treatment group showed a significant cancer growth inhibition compared to other groups with light or LIQ-9 alone.At the same time,LIQ-9 was also used in the photodynamic ablation of bacteria in vitro,and showed good inhibitory effects on both S.aureus and P.aeruginosa.Furthermore,a model of S.aureus skin infection mice was constructed which exhibited an excellent photodynamic antibacterial efficiency in wound healing process after 14 days PDT treatment.