| Early diagnosis and treatment of tumor is crucial to prolong the survival time for cancer patients. Thus, the development of tumor-imaging techniques with sufficient specificity and sensitivity is necessary for cancer diagnosis. Optical imaging has recently become an ideal method for tumor diagnosis by virtures of noninvasive, real-time imaging, high sensitive, convenient and visualized. The development of efficient contrast agents is the key of this technology. Compared to the fluorescence always on probes, pH-activated contrast agents which were designed according to the acidic feature of tumor have high signal to noise ratio in tumor imaging and can avoid the “false positive†results. However, to date, how to obtain the contrast agents with good biocompatibility and suitable responsing pH range to tumor microenvironment remains urgent problem. Moreover, intracellular pH plays important roles on cell growth, proliferation and intracellular enzyme activity, and so on. Therefore, developing excellent pH-sensitive fluorescent probes for tumor specific imaging or real-time, accurate monitoring of the fluctuation of intracellular pH is significantly meaningful.Based on this, this thesis aims to construct a series of pH-activated fluorescent probes for recognition and detection of pH variation and weakly acidic substances in vivo, and then screen out the probes with suitable responsing p H range to tumor microenvironment to construct tumor-targeted and specificity multifunction contrast agents.(1) Considering the near-infrared fluorescent probe’s excitation wavelengthand emission wavelength located in the region of biological window, advantages of deeper tissue penetration, lower optical absorption and autofluorescence interference from biological tissuesand so on, a series of pH-activated near-infrared cyanine fluorescent probes were designed and synthesized. It has been proved that these probes display strong pH sensitive characteristic through the studies of the optical properties upon pH value and the structure-activity relationships of probes. The results also showed that the responsing pH range was influenced by the electronic effect of the substituent. Furthermore, one of the probes has been successfully applied for the specific detection of two kinds of acidic amino acids(glutamic acid and aspartic acid) in living cell with no obvious cytotoxicity under the experimental conditions.(2) Two kinds of tumor-targeted and specificity contrast agents were designed and synthesized by modification of the pH-activated reversible fluorescent probessynthesized by us with tumor-targeted group folic acid or a quaternary ammonium cations(with target bindingproperties oftumormitochondria), further modification of the probes with glucosamine for enhancing their biocompatibility and aqueous solubility. The pH-activated contrast agent modified by quaternary ammonium cations has been successfully applied for the specific imaging of tumor cells and tumor-bearing nude mice with high signal-to-noise ratio. Moreover, this design strategy provides newideas and approaches for the construction of tumor specific contrast agents.(3) Since thecredibility andaccuracy of thefluorescence analysismethodbased on the fluorescent variation of single wavelengthneedto be improved, a noveltwo-colorratiometricpH-activatedprobe was designed and synthesized by introduction of dansylasanotherchromophore to glucosamine modified p H-activated reversible fluorescent probes. Thisprobehas been successfullyapplied fortumorcells dual-color and specific imaging. Furthermore, a linear correlation is found between the ratio of the fluorescenceintensity at twowavelengthsand pH value withinthe pH range of6.11 ~ 7.14. Therefore, thisprobe isalsoexpected to realizequantitative detectionof weakly acidicmicroenvironment andweak acidicsubstances in vivo. |
