The Preparation Of BODIPY-loaded Liposomes And Its Mitochondria-targeted Photodynamic Therapy

Photodynamic therapy(PDT)has become a novel method for cancer treatment.The treatment principle of PDT is:the photosensitizer has administrated into the human body,the photosensitizer can accumulate at tumor tissue;a near-infrared wavelength of light is required to excite the photosensitizer to produce reactive oxygen species(mainly singlet oxygen,1O2);the reactive oxygen species can oxidize the biological macromolecules,causing oxidative damage to tumor cells and finally inhibit the growth of cancer cells.Mitochondria are energy factories of biological systems and play important roles in energy metabolism of various biochemical processes,and they are also the executioners of programmed cell death.Thus,it is great significance to develop the mitochondria-targeted photosensitizers and apply them for PDT of tumor.Because the transmembrane potential of mitochondria is negative,many studies have shown that lipophilic cations photosensitizers can easily bind to the mitochondrial membrane and subsequently enter the interior of mitochondria for enhanced PDT.At present,most studies use triphenylphosphine as a lipophilic cation,which is connected to photosensitizers via covalent bonds,resulting in the photosensitizers can be easily endocytosed into mitochondria of tumor cells.However,triphenylphosphine-modified photosensitizers are positively-charged hydrophobic molecules,which binds easily to negatively-charged proteins in the blood and will be recognized by the reticular endothelial system or macrophage system,leading to accelerate the clearance rate from the body before reaching tumor sites.To develop a mitochondria-targeted photosensitizer and increase its effective dose at tumor sites,we have synthesized four pyridine-modified boron-dipyrromethene(BODIPY)photosensitizers,and developed a novel technology that use liposomes to encapsulate BODIPY photosensitizers.The research contents and results in detail as follows:(1)Based on the molecular design of the BODIPY photosensitizers,four pyridine-decorated BODIPY photosensitizers were obtained through chemical synthesis,namely BDP-1,BDP-2,BDP-3 and BDP-4.These compounds have characterized through 1H-NMR,13C-NMR and HRMS.(2)The efficiency of four BODIPY photosensitizers to produce 1O2 under 660 nm light was studied,the results have shown that four BODIPY photosensitizers can effectively produce 1O2.BDP-1 and BDP-2 are hydrophobic in water,while BDP-3 and BDP-4 are capable of forming nanoparticles in aqueous solution.Transmission electron microscopy(TEM)results showed that the average particle size of BDP-3 and BDP-4 was 24.1±0.9 nm and 3.4±1.1 nm respectively.Dynamic light scattering(DLS)results showed that the hydrodynamic diameters of BDP-2,BDP-3 and BDP-4 are 825.0 nm,220.2 nm and 43.8 nm,respectively.The zeta potentials on the surface of nanoparticles are+25.8 mV,+25.4 mV and+30.7 mV,respectively.(3)The conditions that four photosensitizers were encapsulated into liposomes were investigated.It was found that BDP-3 could be loaded into liposomes with regular shape and uniform size(the average size is 113.3±10.07 nm),Zeta potential is-0.284 mV,and have good stability in aqueous solution.(4)In vitro experiments of human breast cancer MDA-MB-231 cells and human normal breast normal MCF-10A cells have shown that nanoparticles are taken up by cancer cells and enter the lysosome,leading to the destruction of the liposome structure and subsequently target mitochondria.Under 660 nm light irradiation,BDP-3 can effectively produce singlet oxygen within mitochondria,causing obvious photodynamic killing effects on cancer cells.In addition,nanoparticles have low dark toxicity and high light toxicity to cancer cells.