| Fluorescence imaging technology plays a pivotal role in the biomedicine field,especially in the visualization therapy of cancer.With the red-shift of the fluorescence emission wavelength,especially locating the second near-infrared range,imaging has prominent biological penetration and resolution enhancement.Among the numerous NIR-II fluorescent molecules,organic cyanine dyes have been widely reported due to their excellent fluorescence imaging property and considerable biosafety.However,in practical biological applications,small molecule fluorescent reagents only stay for a short time in vivo,and they are easy to be removed from the body.In order to realize the prolonged blood circulation of the probes in vivo,it is necessary to utilize the macromolecular matrix,especially the polymer nanocarriers,represented by the amphiphilic polypeptide,to load them.This paper mainly focused on applying amphiphilic polypeptide-loaded NIR-Ⅱ small molecule probes in tumor imaging and photothermal therapy.In Chapter I of the thesis,we first reviewed the NIR-Ⅱ fluorescence imaging technology and its applications,including the design strategies of NIR-Ⅱ organic fluorescent molecules,NIR-Ⅱ inorganic material imaging reagents,and various applications based on NIR-Ⅱ fluorescence imaging techniques(surgical pilotage,angiography,NIR-Ⅱ phototherapy,drug delivery,etc.).Then,the research progress of photothermal therapy,including the PTT mechanism,various NIR-Ⅱ photothermal reagents,and PTT accuracy enhancement,were described.Finally,we introduced the research on Nano-carrier delivery systems,especially polymer Nanocarriers and tumor microenvironment(TME)responsive polymer Nano-diagnostic and therapeutic systems.Under irradiation,in addition to returning to the ground state by radiative transition(such as fluorescence),the NIR-Ⅱ probes in the excited state also release part of their energy to exchange thermal energy with the surrounding medium by the nonradiative transition.The generated heat can be used in tumor phototherapy inhibition.Compared with photodynamic therapy,PTT is highly efficient and non-invasive.It can inhibit the tumor effectively with only a single dose and irradiation.The fluorescence imaging performance of the probe itself also offers accurate tumor localization and realtime drug enrichment thus providing an accurate timing for subsequent photothermal therapy.Therefore,a NIR-Ⅱ photosensitizer that integrates diagnostic and therapeutic properties can be used for fluorescence imaging-guided tumor photothermal therapy.Based on this,in Chapter Ⅱ,we used an amphiphilic polypeptide(POEGMA-PLys)to encapsulate the small molecular fluorescent probe(FD-1080)to prepare a NIR-Ⅱmacromolecular fluorescent probe(PFD).Under the excitation of 808 nm,PFD possessed well photothermal conversion efficiency(40.69%)and stability.PFD nanoparticles could accumulate at the tumor site through the EPR effect after intravenous injection and exhibited significant photothermal inhibition on the tumor under irradiation.At the same time,the entire treatment process was monitored by NIRⅡ fluorescence and infrared thermal dual-mode imaging.NIR-Ⅱ polymethine cyanine dyes have a prominent fluorescence signal in the monodisperse state(such as in the organic phase),but their unique π-conjugated structures make them poorly soluble in aqueous solutions,resulting in the inevitable fluorescence quenching phenomenon.Improving the fluorescence quantum yield of such probes in the aqueous phase and their application in high-resolution biological imaging has always been a complex problem that people are eager to solve.In the work of Chapter Ⅲ,we effectively prevented the π-π stacking of the dye itself through the steric structure modification of the small molecule probe and the covalent coupling strategy with the polypeptide Nano-carrier,thereby exhibiting excellent anti-quenching property in aqueous solution(QY=0.178%).The synthesized NIR-Ⅱ macromolecular probe(MPAE)had good biocompatibility and negligible systemic side effect,and possessed deeper tissue penetration than ICG and high-contrast NIR-Ⅱ tumor fluorescence imaging.Due to the limited tissue penetration of the NIR-I light source during the PTT,effective photothermal inhibition cannot be performed on the deep tissue of the tumor,thereby increasing the probability of tumor recurrence in the later stage of treatment.It was worth mentioning that,based on the adequate enrichment of MPAE nanoparticles in the tumor site and the significant NIR-Ⅱ photothermal conversion efficiency(40.07%)under 1064 nm irradiation,MPAE Nano-drug could exhibit effective photothermal ablation at deep tumor site without any rebounding or recurring.The design of MPAE provided a new idea for the development of an antiquenching fluorescent probe and photo diagnostic and therapeutic system in the NIR-Ⅱwindow.In tumor PTT research,the improved targeting of Nano-diagnostic and therapeutic reagents can help reducing Nano-drug dosage while enhancing the limited property of photothermal reagents,thereby improving the tumor treatment effectively and reducing the potential biological toxicity of Nano-drug.The tumor microenvironment(TME)has always been a breakthrough in designing intelligent and responsive Nano-diagnostic and therapeutic systems.However,the design of this strategy is mainly limited to the traditional visible and NIR-Ⅰ regions,and it needs to be further expanded to the NIR-Ⅱregion.In Chapter Ⅳ,we designed and synthesized a disulfide-modified,polyethylene glycol-conjugated macromolecular probe(MPSS).MPSS could self-assemble into core-shell micelles in an aqueous solution,while inside the micelles,the small molecule probes were in a highly aggregated arrangement.The pronounced aggregation quenching(ACQ)effect caused them to the "sleeping" state.After entering the tumor cells,the disulfide bonds in MPSS were broken in response to the high concentration of glutathione(GSH)in TME.The small molecule probes were slowly released from the interior,and the highly aggregated state was effectively alleviated,resulting in the enhancement of absorption in the near-infrared region.Therefore,the fluorescence signal was recovered,the photothermal performance was also enhanced,and the tumor was continuously lightened up for a long time,thus providing sufficient treatment opportunities for subsequent photothermal therapy.In summary,we designed and synthesized a variety of polypeptide and NIR-Ⅱcyanine-based Nano-diagnostic and therapeutic systems for imaging-guided tumor PTT.The designed strategies included polymer-encapsulated dyes,NIR-Ⅱ PTT,antiquenching,and reduction response design.Whether it is the loading of the macromolecular matrix,the improvement of the fluorescence performance of the probe itself,or the optimization of the near-infrared light source and the design of the responsive structure,we are aiming at the improvement of the biocompatibility and biosafety for the Nano-medicine,as well as its better enrichment at the tumor site.Finally,we hope that our Nano-diagnostic and therapeutic systems could be promoted and strengthened,which would provide a new direction for the research of anti-tumor photo Nano-diagnostic and therapeutic system. |
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