Construction Of Molecular Imaging Probes Based On Photo-click Chemistry

Molecular imaging to visualize disease releated imaging targets through a variety of imaging techniques is becoming more and more important in the diagnosis and monitoring of diseases such as tumor.Molecular imaging probes are one of the key components in molecular imaging.Rational design and construction of molecular imaging probes that allow sensitive and specific imaging of biological targets has attracted more and more research interests from chemical biologists.Photo-click reaction of tetrazoles with alkene proceeds rapidly upon mild light irradiation to induce the formation of nitrilimine dipole and subsequent 1,3-dipolar cycloaddition to form corresponding pyrazoline products.The photo-click reaction of tetrazoles with olefins is being developed into a bioorthogonal reaction with unique applications in chemical biological studies.Based on the fluorogenic feature of the pyrazoline products in photo-click reactions of biaryl-substituted tetrazoles as well as the fast kinetics of the reaction under physiological conditions,we tried to construct various molecular imaging probes in the work described in this Ph.D dissertation.In the first part of this dissertation,we described the construction of two-photon fluorescent probes that were able to be used in the two-photon fluorescent imaging at cellular and tissue level.The two-photon 1,3-dinaphthalene substituent pyrzoline fluorophore was obtained through the photo-click reactions of dinaphthalene substituent tetrazoles with dimethyl fumurates.With a large two-photon cross section and good photo-stablility,the two-photon probe showed strong fluorescence signal from cells upon two-photon excitation.By the modification of methyl fumarate with subcellular targeting group,different subcellular targeted two-photon probes were obtained.Moreover,an activatable two-photon probe containing both cyclic RGD(cRGD)for tumor targeting and a quencher-bearing peptide substrate that was recoganized by caspase-3 for cleavage was also constructed through photo-click reaction.The simutaneous generation of the two-photon fluorophore and the integration of multiple functional peptides into one probe were achieved through the highly-efficient photo-click reaction,which demostrated the potential applications of photo-click reactions in the construction of various two-photon imaging probes.In the second part of this dissertation,we systematically investigated the influence of substituted aryls of 1,3-diarylpyrazolines on the fluorogenic proerties of the pyrazoline.The electron-withdrawing or pushing properties of the sustitution groups on the aryls of the 1,3-diarylpyrazolines was found to highly-related to the fluorogenic nature of the 1,3-diarylpyrazoline fluorophore.Based on the effect of susbtitution groups,we were able to construct a ratiometric fluorescent probe with specific response to sulfite as well as an activatable fluorescent probe whose fluorescence can be turned on by bio-thiols in live cells such as H2S,cysteine,homocysteine and GSH.The third part of this dissertation described our efforts to use photo-click reaction as ligation method to construct the optical/MRI dual-modality nanoprobe for the imaging of tumors with over-expression of firbroblast activation protein alpha(FAPoc).Maleimide groups were firstly modified on the surface of magnetic nanoparticles.Then the photo-click reaction of tetrazole with the maleimide group on the nanoparticle surface was used for the attachment of the activatable NIR probe of FAPa to the naoparticle surface.Meanwhile,the thiol-ene reaction of thiol group with the maleimide group on the nanoparticle surface was used for the introduction of cRGD linked with cystein to the nanopartical surface.The nanoprobe constructed by this method thus was able to target ?v?3 which is overexpressed in tumor under MRI imaging and its NIR fluorescence was able to be activated by FAPa that over-expressed in tumor tissue.In vitro enzyme assays showed that this nanoprobe responded to FAPa selectivity and specificity.Cellular assays using FAPa-positive cells and FAPa-negative cells showed that this nanoprobe was selectively activated with NIR fluorescence in FAPa-positive cells.In the fourth part of this dissertation,we did preliminary work to develop a new method to construct optical/PET dual-modality probe targeting tumor.New F-labeling method for PET imaging was developed through the photo-click reaction of F-substituted diaryl-tetrazoles with olefins.2-bromopyridine was linked to the carbon atom in the tetrazole ring,which allows F to replace the bromo atom rapidly under relatively mild condition to generate tetrazole containing the 2-fluoropyridine substitution group.Followed by photo-click reaction,the probe was then able to be integrated with other functionalities for targeted or multi-modality imaging.