Design And Synthesis Of Novel Photosensitizers Or Multifunctional Prodrugs And Their Antitumor Activity

Photodynamic therapy,as an emerging treatment method,has the advantages of high selectivity,minimally invasiveness,and less side effects compared with traditional chemotherapy and radiotherapy compared with traditional chemotherapy and radiotherapy,and has become a hotspot of current research.Oxygen,light and photosensitizer are the basic elements of photodynamic therapy.However,due to the low oxygen concentration in solid tumors,it is unable to provide sufficient oxygen to support the photodynamic process,which seriously hinders the effectiveness of photodynamic therapy.In addition,because biological tissues have strong absorption and scattering of ultraviolet and visible light,traditional photosensitizers with shorter excitation wavelengths cannot penetrate the tissues to reach deep tumors,making it difficult to achieve deep tumor treatments.In addition,monitoring the level of reactive oxygen production during the treatment process has important reference value for controlling the treatment progress and adjusting the treatment plan in time.Focusing on the above problems,we designed and synthesized a series of new photosensitizers in this thesis,and the therapeutic effect was significantly improved through the effective combination of photodynamic therapy with chemotherapy and photothermal therapy,respectively.The specific contents are as follows:1)At present,near-infrared small molecular dyes(such as ICG)have been developed and applied in photodynamic therapy and photothermal therapy,but they all have the disadvantage of photobleaching,which limits their application in the f ield of tumor phototherapy.In order to solve this problem,IR805,an ICG analogue,with photobleaching resistance was synthesized through reasonable structural design.Under 808 nm irradiation,compared with ICG,laser,IR805 not only has better photostability,but also exhibits higher photothermal conversion efficiency and reactive oxygen generation ability.The photothermal conversion efficiency of IR805is nearly 5 times higher than that of ICG.Then,the Nano IR805-PEG with good water solubility and biocompatibility was prepared by nano-modification of IR805.The results of in vivo phototherapy studies showed that the tumor volume of the treatment group was 22 times smaller than that of the blank group,indicating that Nano IR805-PEG can be used in near-infrared II fluorescence imaging guided photodynamic/photothermal synergistic therapy,and can significantly inhibit tumor growth.2)Singlet oxygen produced in photodynamic process will be consumed by overexpressed GSH in tumor cells,thus weakening the ef fect of photodynamic therapy.In addition,due to the lifetime and the limited diffusion distance of singlet oxygen,locating the photosensitizer on subcellular organelles is beneficial for the singlet oxygen produced by the PDT process to act directly on the biological macromolecules and improve the PDT effect.Considering the above problems,we designed and synthesized a multifunctional small molecule prodrug(D-bpy),which consists of a hydrophilic photosensitizer and a lipophilic prodrug.Cell membrane localization imaging showed that D-bpy could selectively remain in the tumor cell membrane.When irradiated by 800 nm two-photon laser,D-bpy could produce ¹O₂ on the cell membrane,and could transfer from the cell membrane to the cell with the prolongation of irradiation time.It is suggested that D-bpy could produce ¹O₂ on cell membrane under light irradiation,destroy the structure of cell membrane,and then promote cell uptake of more drug molecules.The results of comparative imaging experiments of tumor tissue before and after illumination showed that the photodynamic process induced tumor hypoxia,which promoted the azo bond breakage of D-bpy and released chemotherapeutic drugs.The results of in vivo and in vitro treatment showed that D-bpy had more obvious cell lethality and tumor growth inhibition ability than photodynamic therapy(Bpy)or chemotherapy(R-drug)alone.3)In the previous chapter,we used two-photon photodynamic therapy to effectively realize the ablation of living tumors.However,th e excitation wavelength of the photosensitizer is still in the UV-visible region,thus when treated by intravenous injection,the drug will spread all over the body,resulting in certain phototoxic side effects under sunlight.To solve this problem,a new hypoxia-activated small molecular prodrug CS-P was prepared based on the near-infrared dye NIR-NH₂developed by our research group.The results of fluorescence and photoacoustic dual-mode imaging experiments showed that CS-P could be activated at the tumor site,and simultaneously release the near-infrared photosensitizer CS-I and chemotherapeutic drugs(aromatic nitrogen mustard).Under 660 nm laser irradiation,CS-I could produce photodynamic effect,resulting in more hypoxia of the tumor,and promote the further release of photosensitizer and chemotherapeutic drug.In vivo and in vitro treatment experiments showed that under light conditions,CS-P has stronger ability to kill tumor cells and inhibit tumor growth than single ch emotherapy prodrug or photosensitizer.However,its toxicity was negligible without light irradiation.Biosafety experiments also proved its good biosafety,indicating that CS-P has great potential for therapeutic application.4)With the increasing interest in photodynamic therapy,the assessment of the level of reactive oxygen species produced during photodynamic therapy has also become increasingly important.However,most of fluorescent probes for ROS evaluation were separated from photosensitizers in P DT process,resulting in ectopic and asynchronous treatment feedback.Additionally,the consumption of ROS by these fluorescent probes themselves will inevitably affect the therapeutic effect.Herein,inspired by the redox balance in the cell,we developed a multifunctional hydrogen sulfide(H₂S)probe Ru-NBD for reporting the therapeutic effect during PDT process by detecting hydrogen sulfide.The probe Ru-NBD not only can be served as an effective PDT reagent both before and after H ₂S activation,but also could be real-time and in-situ monitoring of the therapeutic effect via restored fluorescence during the PDT process.As the phototherapy process progresses,the fluorescent signal of the Ru-NBD changes accordingly.The experimental results show that ther e is a certain correlation between the fluorescence intensity and the cell inhibition rate,thus we can monitor the phototherapy process by detecting changes in the probe's fluorescence signal.