Fluorescence Imaging Study, The Mechanism Of Action Of Some Anti-schistosome Drugs And Schistosoma Japonicum Cercariae

The niclosamide and praziquantel were efficacious for killing Schistosoma japonicum cercariae, but the action mechanism of niclosamide and praziquantel in Schistosoma japonicum cercariae was unknown. In this thesis, a series of fluorescent derivatives of niclosamide and praziquantel were synthesized, and we elucidated the preliminary interaction of niclosamide and praziquantel with Schistosoma japonicum cercariae by fluorescence imaging technology.To match water-floating habit of Schistosoma japonicum cercariae, two novel niclosamide derivatives containing compound NI-2a and NI-2b were synthesized. Compound NI-2b possesses properties of self-diffusion and the water-surface floating which was sufficient for killing cercariae. The MTT assay data show that the NI-2a and NI-2b exhibit low cytotoxicity to HeLa cells. To investigate the interaction between the medicine and Schistosoma japonicum cercariae, a fluorescent niclosamide derivative (compound NI-3) based on compound 2a was further designed and synthesized. Confocal fluorescence imaging results show that compound NI-3 could penetrate into cercarial body and it can be transformed by the cercariae. These facts indicate that novel NI-2a can destroy the circulatory system of cercariae leading to the rapid death of cercariae.Two praziquantel derivatives PZQ-2 and PZQ-3 were synthesized by means of nitration and reduction reaction. The cytotoxicity of PZQ-2 is lower than that of PZQ-3. When incubating HeLa cells with 200μM PZQ-2 and PZQ-3, the cell validity is assigned to 86% and 80%, respectively. To investigate the interaction between the PZQ-3 and Schistosoma japonicum cercariae, a fluorescent derivative (compound PZQ-5) based on PZQ-3 was designed and synthesized. Fluorescence imaging experiments reveal that PZQ-5 is mainly located at cercarial tegument. It is concluded that the praziquantel can influent or demolish the cercariae tegument, which leads to a series of change of osmolality, calcium(Ca²+) balance and metabolism for cercariae.Five iridium complexes (Ir-1 to Ir-5) containing acetonitrile ligand (CH₃CN) were synthesized. The structure of Ir-5 was confirmed by X-ray crystal diffraction. Photophysical data show that complex Ir-5 can emit yellow phosphorescence. Some complexes were used for phosphorescence imaging of Schistosoma japonicum cercariae. Interestingly, the iridium complexes having higher conjugation ligands and appropriate partition coefficients could contribute to cercariae phosphorescence labeling.