Synthesis And Biological Application Of Functional Thermally Activated Delayed Fluorescence Dyes

Specific diagnosis and therapy of malignant cancer is still a challenge in biomedical research.Fluorescence analysis is a quick and convenient method for biological diagnosis.The fluorescence signal of the fluorescence probe responding to the targets in the biological samples can directly indicate the information of the physical activities in tumor cells or tissues.Photodynamic therapy(PDT)has become an effective cancer treatment approach with the advantages of non-invasion.In this paper,we developed a series of fluorescent probes or theranostic molecules for cancer diagnosis and treatment based on fluorescein derivatives which have thermally activated delayed fluorescence(TADF).A fluorescence resonance energy transfer(FRET)ratiometric probe FL-CyN was developed for hypochlorite.The donor of FL-CyN was a TADF fluorescein derivative,and the acceptor was a cyanine dye.FL-CyN has a large Stokes shift,two photon excitation and microsecond luminescence life,which enables the probe to be suitable for ratiometrically detecting hypochlorous acid in vivo.Meanwhile,using the long-lived emission feature of FL-CyN,time-resolved luminescence detection of hypochlorite in zebrafish was realized,which can overcome the autofluorescence interference from biological matrix.All above characters implied that this probe have potential to be applied in hypochlorite detection in vivo.Two activatable theranostic molecules DCF-MPYM-N1 and DCF-MPYM-N2 were synthesized based on a TADF fluorescein derivative with microsecond triplet lifetime.Nitroreductase(NTR)induced by mild hypoxia microenvironment of solid tumor was used to activate the fluorescence and photodynamic therapy(PDT)efficiency by employing the intramolecular photoinduced electron transfer(PET)mechanism.A high PDT efficiency under 10%oxygen concentration was achieved in DCF-MPYM-N2,which is better than that of porphyrin(PpIX),a traditional photosensitizer.Such an excellent PDT efficiency can be attributed to lysosomes disruption,because the theranostic molecule can specifically enter the lysosomes of cells.Importantly,the strategy of targeting the mild hypoxic cells in the edge of tumor tissue could overcome the limitation of oxygen dependence of traditional PDT.The results of fluorescence diagnosis and photodynamic therapy experiments in tumor-bearing mice demonstrated the potential of DCF-MPYM-N2 for diagnosis and treatment of cancer.A dual-targeted theranostic photosensitizer FL-RGD was synthesized by covalently conjugating a lysosome targeted TADF fluorescein derivative and a tumor marker cyclic arginine-glycine-aspartic acid tripeptide(RGD).FL-RGD can target tumor tissues and further locate lysosomes of tumor cells to concurrently achieve the cancers' specific diagnosis and efficient treatment.Meanwhile,it possessed low dark toxicity,high phototoxicity,high singlet oxygen quantum yields.Indeed,FL-RGD has much higher PDT efficiency than that of the commercial photosensitizer PpIX.The actual diagnosis and therapy performance of FL-RGD was proved by fluorescence imaging and PDT experiments of living cells and tumor bearing mice.Besides,FL-RGD has the potential to be utilized in depth imaging and treatment by two-photon excitation.These results indicate that FL-RGD has the potential in tumor diagnosis and treatment.