Synthesis And Biological Evaluation Of Cyanine-based Targeting Probes

In China,about 3.929 million people were diagnosed with cancer and 2.378 million people died from cancer every year.Early diagnosis and treatment of cancer could improve the survival rate of patients.Molecular imaging technology can detect abnormalities at the cellular and molecular level,which has been widely used in clinical.Particulary,Optical imaging and PET imaging are widely used in clinical monitoring of tumors.Near-infrared fluorescence（NIRF）imaging had a deep tissue penetration and weak background signal.Animal experiments demonstrated that biotin-tagged NIRF probes could be specifically taken up by tumor cells.Moreover,a NIR/PET bimodal molecular probe could be conducted by introducing positron radioactive imaging nuclides to the NIRF probe.The bimodal molecular probe could combine the imaging advantages of two modalities to fully monitor the tumor.Besides,radiotherapy probes could be developed by introducing radiotherapeutic nuclides to the NIRF probe.Radiotherapy probes could accurately detect tumors and inhibit the growth of tumor cells.In our work,three types of probes were developed,including NIRF probe,NIR/PET bidmoal probe and radiotherapy probe.A series of in vitro cell experiments and in vivo animal experiments were performed to evaluate the biological properties and clinical application prospects of these probes.（1）Design and synthesis of NIRF probes G₁ and G₂.Biotin-PEG5-N₃ was introduced to G₀ via a copper（Ⅰ）-catalyzed alkyne–azide cycloaddition（CuAAC）reaction.The PEG group could enhance the hydrophilicity and reduce the aggregation tendency of the probes.G₁ and G₂ possessed higher molar absorption coefficient and light quantum yield than G₀.And the conjugated biotin could enhance the targeting specificity of probes.The absorption spectrum and fluorescence emission spectrum demonstrated that G₁ and G₂ were new NIRF cyanine probes with low aggregation.In vitro cell experiments showed that G₁ and G₂ can specifically recognize He La tumor cells.In tumor-bearing mice,G₁ and G₂ can be specifically taken up by tumor tissues and the fluorescence signal could last for about 7 days in the tumor.（2）Design and synthesis of a NIR/PET bidmoal probe ¹⁸F-Bim-H₁.Am BF₃ was conjugated with G₁ through CuAAC reaction to afford Bim-H₁.Bim-H₁ could be labeled with ¹⁸F to get ¹⁸F-Bim-H₁ through the ¹⁸F-¹⁹F isotope exchange method.The radiochemical purity of ¹⁸F-Bim-H₁ was over 90%.Besides,¹⁸F-Bim-H₁ displayed good stability in PBS.Bim-H₁ could specifically target tumors in He La tumor-bearing mice.Unfortunately,PET imaging experiments showed that the tumor uptake of the probe was low and the background signal was high.Therefore,the structure of the probe should be further optimized.（3）Design and synthesis a radiotherapy probe(¹³¹I-RT-H₂).4-（2-Bromoethyl）-phenol was introduced to G₁ to afford RT-H₂.RT-H₂ could be labeled with ¹³¹I to obtain ¹³¹I-RT-H₂under the catalyzation of Iodogen.The cyanine skeleton was retained in probe ¹³¹I-RT-H₂ and hence it still possessed good NIRF prosperties.By optimizing the labeling conditions,the optimal conditions for ¹³¹I labeling of cyanine probes were explored.The optimal conditions for ¹³¹I labeling of cyanine probes were summarized in our study.The conversion rate of ¹³¹I^-was 74%and the radiochemical purity of ¹³¹I-RT-H₂ was over 95%.Preliminary biological experiments showed that probe ¹³¹I-RT-H₂ had a good tumor targeting specificity and could inhibit the growth of tumor cells.