Application Of Polypeptide Nanoparticles Loaded With BODIPY Dye In Near Infrared Phototheranostic

As an emerging theranostic modality,near-infrared fluorescence imaging-guided photodynamic therapy(PDT)and photothermal therapy(PTT)are attracting widespread interests.Organic light-emitting nano-assemblies are becoming ideal choices for optical therapeutic reagents due to their good biocompatibility as well as abundant structural and property flexibility.However,current optical therapeutic reagents with short absorption and emission wavelengths suffer from low penetration depths,poor photodynamic and photothermal effects,unsatisfactory imaging and poor chemical or photostability,and it is crucial to develop stable therapeutic reagents with long-wavelength absorption and emission as well as excellent photothermal and photodynamic properties.Boron-dipyrromethene(BODIPY)dyes display excellent optical properties and stability due to their rigid conjugated backbone,and the rich structure variation of BODIPY brings great tunability to its photophysical properties.Herein,we aim to introduce different groups to the rigid backbone of BODIPY to tune its photophysicalchemical properties,and construct biocompatible nanoparticles in combination with amphiphilic polypeptides to overcome the hydrophobicity of the dye,achieving outstanding tumor imaging and therapeutic effects.In the second chapter of the dissertation,we have successfully synthesised two organic NIR BODIPY photosensitizers with reactive group by introducing pyrrole and atomic iodine substitutions in the BODIPY backbone.NO2-BDPI can be converted to NH2-BDPI upon reaction with hydrogen sulphide in solution and brings about a significant color change.Both dyes exhibit strong NIR absorption(650-750 nm)and excellent singlet oxygen production capacity(ΦΔ=0.629 for NO2-BDPI and ΦΔ=0.688 for NH2-BDPI).After assembly with amphiphilic polypeptides to form nanoparticles,the obtained NH2-BDPI nanophotosensitizers(nano-NH2-BDPI)exhibited good water dispersion and stability.In vitro experiments revealed that nano-NH2-BDPI could be well taken up by cells and abundant reactive oxygen species were generated under NIR irradiation.At a low dose(0.24 μM)and weak laser power(660 nm,10 mW/cm2),nanoNH2-BDPI showed excellent photodynamic therapeutic effects on both 4T1 and HeLa cells.After intravenous injection of nano-NH2-BDPI into mice,the nanoparticles could be passively targeted to the tumor region through enhanced permeability and retention(EPR)effect and exhibited efficient tumor inhibition and ablation under 660 nm NIR light(40 mW/cm2).Fluorescence imaging in the NIR-Ⅰ region(650-900 nm)has been widely studied and applied,but their imaging results was unsatisfactory due to the interference from strong tissue scattering and autofluorescence.In contrast,fluorescence in the second near-infrared region(1000-1700 nm)can effectively attenuate the interference of tissue scattering and autofluorescence,thereby enhancing the penetration depth and resolution of imaging.In Chapter 3,we synthesised an aza-BODIPY dye(TAB)with NIR-Ⅱfluorescence emission through simple procedures and economical substrates.Subsequently,the halogen atoms(Br,I)were introduced at the 2,6 position of the TAB molecule to enhance the singlet oxygen production capacity.Due to a larger atom volume at the 2,6 position,the TAB-2Br and TAB-21 molecules exhibit a more distorted conformation as well as a larger Stokes shift(around 300 nm).After co-assembly of TABs with amphiphilic polypeptides,the obtained P-TAB,P-TAB-2Br and P-TAB-2I nanoparticles exhibit significant photothermal conversion efficiencies(over 40%)as well as excellent photobleaching,thermal and H2O2 tolerance.Fluorescence imaging of tumor was successfully achieved in vivo with all three nanoparticles under 808 nm laser irradiation,and P-TAB-2I exhibited significant intracellular ROS production.In addition,we successfully achieved NIR-Ⅱ fluorescence imaging-guided photothermal and photodynamic synergistic therapy in mice using P-TAB-2I nanoparticles.Based on the work in Chapter 3,we hope to continue to extend the absorption wavelength of the dye to achieve photothermal treatment under longer excitation light.Constructing supramolecular J-aggregates is a much simpler and subtler strategy than extending the conjugation of molecules.Adjusting the balance between steric hindrance and conjugation interactions is an effective way to induce molecular J-aggregation.In Chapter 4,we successfully obtained dye molecule with J-aggregation behavior by introducing thiophene groups to enhance the conjugation effect of triphenylaminesubstituted aza-BODIPY molecule.In the THF/H2O solvent mixture,supramolecular Jaggregates with a regular stacking structure could quickly be formed by the dyetemplated self-assembly and longer absorption(λmax=939 nm)and emission(λmax=1039 nm)bands were observed.After assembly with amphiphilic polypeptides,the acquired J-aggregated nanoparticles(J-NPs)exhibit considerable photothermal conversion capacity(η=35.6%)as well as excellent resistance to pH,H2O2,and photobleaching.In vitro and in vivo experiments revealed that the J-NPs shown great NIR-Ⅱ fluorescence imaging capability and anti-tumor effect under 915 nm irradiation(1 W/cm2).In this dissertation,we have obtained a series of nanoparticles with near-infrared luminescence for tumor imaging and therapy by modification of the dye chemical structure or adjustment of the aggregation behavior to inducing bathochromic-shift in the absorption and emission wavelengths of BODIPY dyes,enhancing their performance in fluorescence imaging as well as phototherapy and expanding the application of BODIPY dyes in tumor theranostic.