Design And Synthesis Of Functional Nano-photosensitizers For Photodynamic Therapy Applications

The incidence rate and mortality rate of cancer are increasing every year,posing a great threat to human health and survival.Photodynamic therapy(PDT),a new method of using light source for activating photosensitizers(PSs)to produce toxic reactive oxygen species(ROS)and kill tumor cells,has the advantages of high spatiotemporal controllability,non-invasive and repeatability.Thus,PDT is considered as a new cancer treatment strategy in clinical application.However,the clinical application of PDT has been hampered by several inherent limitations,such as PSs are poorly targeted and damage normal tissues,the short excitation wavelength of PSs makes it impossible to treat deep tumors,and the ROS generated by the PS has the extremely short lifetime(<4?s)and finite diffusion distance(<20 nm),reducing the efficacy of PDT.Threrfore,developing the new functional PSs is a key problem to promote the clinical application of PDT.Based on different strategies,a series of functionalized nano-PSs were designed to achieve high-efficiency PDT in this paper.The research content was divided into the following foure parts.In the first part,in order to overcome the damage of PSs to normal tissues,a new type of nano-PS named P-s-s-Pp? NPs with tumor-specific reduction-activatable property was designed and synthesized based on the self-quenching property of aggregative protoporphyrin(Pp?).Under normal physiological conditions,the stable P-s-s-Pp? NPs presented as the photo-inactive state with no fluorescence emission and no singlet oxygen generation,once the P-s-s-Pp? NPs entered into the cancer cells,the high concentration of GSH would rapidly break the disulfide linkers via the reductive cleavage to release the Pp? with the significant recovery of fluorescent emission and singlet oxygen generation,achieving effective killing of cancer cells and avoiding damage to normal cells.Results demonstrated that P-s-s-Pp? NPs display higher photodynamic cytotoxicity of tumor cells with light irradiation treatment when compared with the non-reducible P-Pp? NPs with stable amide linkages.In the second part,in order to overcome the problem of PSs such as short excitation wavelength,limited treatment depth and poor targeting,a new type of tumor targeted nano-PS(U-C/A NPs)with near-infrared excitation was designed and synthesized by upconversion nanoparticles(NaYF4:Yb3+,Er3+@NaYF4),PSs[dihydroporphyrin e6(Ce6)]and cancer cell membrane nucleolin-targeting aptamer AS1411,based on the resonance energy transfer effect.The physical and chemical property,spectral property,targeting property and photodynamic property of U-C/A NPs were investigated.Under the irradiation of 980 nm light source,the U-C/A NPs produced singlet oxygen for PDT.Compared with 660 nm light source,the nano-PSs could be excited at the NIR wavelength of 980 nm for the PDT with the deep tissue penetration of 5 mm,largely improving the photodynamic effect of deep solid tumors.Furthermore,compared with non-targeted U-C/R NPs,U-C/A NPs has the better tumor targeting and enrichment ability.Under the same light condition and PS dosage,U-C/A NPs could produce more singlet oxygen within cancer cells and induce an increased proportion of apoptotic cells,indicating the improved photodynamic effect against tumor.In the third part,in order to compensate for the limited photodynamic efficacy resulted from the short life span and limited diffusion distance of the toxic ROS,a new type of mitochondrial targeting nano-PS(U-C/T NPs)with high-efficiency mitochondria-targeting photodynamic damage was designed and synthesized.The mitochondrial localization ability and the photodynamic effect of U-C/T NPs were investigated.Compared with mitochondrial-untargeted U-C NPs,U-C/T NPs could target the mitochondria and produce singlet oxygen in the mitochondria,triggering mitochondrial functional dysfunction and resulting in reduced mitochondrial membrane potential.The photodynamic action of low dose U-C/T NPs could induce the rapid apoptosis of cells,exhibiting high tumor inhibition efficiency in vivo and in vitro.In the fourth part,in order to prolong the blood circulation time and enhance the cancer cell enrichment ability of U-C/T NPs,the novel nano-PSs(U-C/T-DM NPs)with acid-sensitive?-carboxylamide bond were designed and synthesized by covalently modifying 2,3-dimethylmaleic anhydride(DMMA)on the surface of U-C/T NPs.The physical and chemical property,spectral property,target enrichment ability and photodynamic property of U-C/T-DM NPs were investigated.The designed U-C/T-DM NPs were negatively charged and showed"stealth-like" long circulation in blood compartments without specific recognition capacity.However,once the U-C/T-DM NPs entered into interior of the solid tumor,the nanostructures would be switched to be positively charged under slightly acidic conditions and show enhanced internalization and retention against cancer cells.Compared with the U-C/T-SA NPs without charge reversal ability,U-C/T-DM NPs could largely accumulate in tumor site.Furthermore,the U-C/T-DM NPs were able to precisely target and strike at mitochondria,showing improved photodynamic therapeutic efficacy of cancer in vitro and in vivo under tissue-penetrating 980 nm light.