Design and Synthesis of H2S Responsive Molecular Probes Based on Cyanine Dyes for Biological Application

Author:Li Xiang

Supervisor:fan qu li


Degree Year:2019





Cyanine dyes are the most studied class of commercial organic dyes.They are widely used in the fields of science,technology engineering and biomedicine.Cyanine and its derivatives possess excellent photophysical properties,such as high molar absorption coefficient,high fluorescence quantum yield and relatively long absorption and emission wavelengths,making them excellent fluorescence/photoacoustic molecular probes for biomaging and biosensor applications.In recent years,using the optical and chemical reactivity of cyanine dyes to develop responsive molecular probes for the detection of biologically relevant molecules and real-time visualization of specific physiological processes has become a research hotspot.A large number of responsive molecular probes based on cyanine platforms(especially cyanine,hemicyanine and squaraine structures)have been reported to date.However,there is still much scope for improvement.In terms of structual design,the low photostabiliy of cyanine dyes need to be improved;the relatively short excitation and emission wavelengths of hemicyanines limit their biological applications;most probes are based on fluorescence mechanisms,and novel probes based on other imaging modalities need to be developed.In terms of application,cyanine-based molecular probes used for subcellular imaging and in vivo imaging are still very limited,and the application of cyanine dyes in medical diagnosis and disease treatment also needs more attention.Therefore we purpose to develop novel cyanine-based responsive probes with near-infrared absorption,high photostability and new imaging modalities,and study its application in subcellular and in vivo imaging and tumor theranostic.The specific researches are as follows.1.Hemicyanine-based organic-inorganic hybrid nanoprobe for ratiometric upconversion luminescence imaging of mitochondrial hydrogen sulfideIn this section,a hemicyanine derivative possessing both hydrogen sulfide(H2S)response and mitochondrial targeting properties is synthesized.And a ratiometric upconversion luminescence nanoprobe with an acid-activated targeting strategy is developed dye-modified upconversion nanophosphors(UCNPs)for detecting and bioimaging of mitochondrial H2S.The hemicyanine TPAMC-modified UCNPs,acting as the targeting and response component,are encapsulated into a pH-sensitive husk,composed of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy-(poly(ethylene glycol))-2000](DSPE-PEG)and poly(L-histidine)-b-PEG,which improved the nanoprobe’s stability during transport in vivo.Under lysosomal pH,the PEG shell is interrupted and the targeting sites are exposed to further attach to mitochondria.Cellular testing reveals the precise targeting to mitochondria via a lysosome delivery process.Taking advantage of the luminescence resonance energy transfer process between TPAMC and upconversion nanophosphors,the ratiometric detection of mitochondrial H2S can be achieved with high selectivity and sensitivity.Such structural design overcomes the photobleaching and short excitation wavelength issues of hemicyanine.Therefore,the nanoprobe can be used for monitoring mitochondrial H2S levels both in living cells and colon cancer mouse models.2.Cyanine-based near-infrared absorptive small-molecule probe for ratiometric photoacoustic imaging of hydrogen sulfide in living miceIn order to explore the in vivo application of cyanine-based probes,a small-molecule ratiometric photoacoustic(PA)probe is developed for PA imaging of H2S in living mice.The probe is constructed based on water-soluble cyanine dyes by taking advantage of the nucleophilic substitution of H2S to the active chlorine.The addition of H2S causes significant changes in the charge distribution of the probe molecule,thereby enabling the regulation of intramolecular charge transfer processes(ICT).CyCl-1 exhibits rapid and selective reponse to H2S with a ratiometric PA signal at 720 nm(enhancement)to 800 nm(attenuation),which permits the real time imaging of H2S in living mice with high resolution and fidelity.Furthermore,the probe provides more stable ratio PA signal and lower potential toxicity compare with traditional multi-composition ratiometric nanoprobes.Pharmacokinetics studies revealed the rapid clearance of CyCl-1 through the hepato-biliary excretion pathway.The successful development of this small-molecule ratiometric PA probe will be helpful in facilitating the application of advanced PA imaging technology in H2S relevant biomedical researches and the process of clinical translation.3.Cyanine-based photoacoustic nanoprobe for tumor imaging and controlled release of hydrogen sulfideHydrogen sulfide(H2S)is an endogenously generated signaling agent,which played significant roles in physiological and pathological processes.However,excessive H2S also shows cytotoxicity.Based on this,a hydrophobic cyanine molecular probe(CY)is synthesized and combined with a H2S donor to prepare a theranostic nano-platform for PA imaging guided H2S therapy.As the PA probe,CY showed favorable responsibility on H2S with ratiometric PA signal changes.Attributed to enhanced permeability and retention effect,the nanocomposite of CY and PSD(CY-PSD)can enrich in the tumor region of living mice.H2S generated from PSD via the glutathione-initiated thiol-polysulfide cleavage in vivo was effectively sensed by CY which simultaneously maps the tumor region.The release of H2S is is closely related to the bio-thiol content in the cells,which provid a cytotoxicity difference between cancer cells and normal cells.The development of this nanoprobe lays the foundation for further cancer treatment studies.