Polypeptide Nanoparticles Loaded With BODIPY For Near-Infrared Imaging-Guided Phototherapy

In the past few years,light therapies such as photothermal therapy(PTT)and photodynamic therapy(PDT)have been rapidly developed in cancer treatment.Nearinfrared fluorescence imaging is used to monitor drug enrichment and metabolism at the tumor site in real time,and near-infrared laser excitation guided by fluorescence imaging is used to precisely control phototherapy at the tumor site.Combined precision imaging-phototherapy for tumor eradication is an important tool for tumor treatment.However,there are still many problems for imaging-guided optical therapy:such as hydrophobicity of probes,poor targeting,low signal-to-noise ratio and shallow tissue penetration depth.Due to their excellent properties,nanomaterials can combine chemical molecules with various functions to construct multifunctional water-soluble nanoprobes for the visual delivery of drugs in vivo as well as for efficient optical therapy.Fluoroboron dipyrrole(BODIPY)derivatives are an important class of organic dyes that have been widely used in in bio-imaging and treatment of cancer due to their unique chemical and physical properties and rich structural modifications.In this thesis,by introducing different modification groups in the BODIPY backbone,on the one hand,superior fluorescence imaging performance was achieved;On the other hand,by changing the excited state relaxation path of BODIPY molecules,reactive oxygen species or heat is generated for PDT and PTT,respectively.Intelligent nanoparticles with imaging and phototherapeutic properties constructed by combining responsive amphiphilic polypeptides have promising applications in tumor imaging and therapy.Fluorescence imaging of most fluorophores is interfered by non-specific background signals outside the specified area,and poor imaging contrast can affect the accuracy of tumor treatment.In Chapter 2 of the thesis,we designed the BODIPY dye(BDPI)that activates fluorescence and PDT efficacy under acidic conditions by introducing dimethylaminophenyl in the neutral position of the BODIPY backbone.The introduction of heavy atomic iodine resulted in a single-state oxygen(1O2)quantum yield of 0.818 for BDPI.BDPI was then wrapped with the pH-sensitive amphiphilic polypeptide POEMA23-PE9 to obtain dual pH-responsive smart nanoparticles(BDPI NPs).In vivo studies have shown that BDPI NPs can disintegrate and release BDPI molecules in the acidic environment of tumors,and that BDPI can be protonated in lysosomes(pH=4.0-5.5)to achieve "off-on" conversion of NIR fluorescence in tumors.It also promotes the production of 1O2,which enables tumor-specific and selective imaging and treatment.Near-infrared second window(NIR-Ⅱ,1000-1700 nm)imaging enables higher fluorescence imaging contrast and deeper penetration depth than near-infrared light(NIR,650-1700 nm)imaging.Tuning the dye aggregation behavior proved to be an effective strategy to achieve redshift in both absorption and emission spectra.In Chapter 3,by galactose-modified BODIPY(Gal-BDP)using intermolecular hydrogen bonding(H-bond)and π-π interactions,we successfully constructed J-aggregates of BODIPY(J-NPs)in aqueous phase and J-NPs have longer absorption(λabs=815 nm)and emission(λem=1060 nm)wavelengths.The photothermal conversion efficiency(PCE)of J-NPs was as high as 55%under 808 nm laser.In addition,faster uptake was observed at the cellular level by NIR-Ⅱ fluorescence due to the targeting of galactose to hepatocellular carcinoma cells.Photothermal treatment of hepatocellular carcinoma tumors assisted by NIR-Ⅱ fluorescence imaging was achieved by injecting J-NPs into tumors.However,The stability problems of Gal-BDP J-NPs limit their further applications.Meanwhile,we found that the aggregation mode of Gal-BDP can be regulated by the pH of the solution.Therefore,in Chapter 4,we formed P-ipr@Gal NPs with Haggregation-based and PAsp@Gal NPs with J-aggregation-based after wrapping with different polymers,respectively.Under the acidic tumor environment,the P-ipr@Gal NPs achieved the transition from H-aggregates to J-aggregates due to the acid pH sensitivity of the polymeric carrier P-ipr and the dye molecule Gal-BDP.This process significantly enhanced red-shifted absorption and fluorescence emission(λabs=830 nm,λcm=1060 nm),accompanied by improved PCE,enabling specific NIR-Ⅱ imaging of acidic tumor regions in mice and their guided photothermal therapy.In addition,PAsp@Gal nanoparticles have excellent J-aggregation properties and have good applications in NIR-Ⅱ fluorescence imaging of tumors and PTT(PCE=46%).For PTT,it is usually necessary to raise the tumor tissue temperature above 50℃,and such a high temperature may cause damage to the normal tissues.Therefore,the relatively low temperature mild photothermal therapy(MPTT)is gaining attention.In Chapter 5,we prepared multifunctional nanoparticles pDG@Ahx by co-introducing Ahx-BDP,a probe with good NIR-Ⅰ/Ⅱ fluorescence and phototherapeutic properties,and 2-deoxy D-glucose(2DG),an anti-glycolytic reagent,into amphiphilic polypeptide side chains.The nanoparticles can not only achieve synergistic PDT/PTT treatment at different excitation wavelengths(730 nm,808 nm)guided by NIR-Ⅱ fluorescence,but also enhance the thermal sensitivity of tumors to temperature under acidic conditions with 2DG release to achieve synergistic starvation/MPTT/PDT efficacy.In vivo experiments have shown that pDG@Ahx can achieve effective tumor treatment under mild photothermal conditions under 730 nm light illumination.Throughout the paper,we have prepared a series of smart nanosystems with excellent imaging and therapeutic properties through the design of BODIPY backbone and amphiphilic polypeptide carriers,which have promising applications in real-time visualization and in situ treatment of tumors.