Redox-responsive Photosensitizer Assembled By Ursolic Acid For Photochemical Synergistic Anti-cancer Research

Active natural small molecule assembled supramolecular photosensitizers have emerged as an innovative and promising strategy for combination tumor therapy.The hydrophobicity of the photosensitizer has become the main problem that restricts PDT from exerting the best tumor treatment effect,and a single PDT cannot achieve an effective anti-tumor effect.The active natural small molecule-mediated supramolecular co-assembly photosensitizer can effectively solve the above problems and become a new strategy of combined photochemical treatment of tumors.At the same time,based on the endogenous characteristics of high-concentration glutathione in the tumor microenvironment,we introduced groups that respond to GSH stimulus to achieve the selective release of drugs at the tumor.In this paper,3,3'-dithiodipropionic acid is grafted to ursolic acid with introducing disulfide bonds to make it responsive to glutathione stimuli,and then a nano-system is constructed by co-assembly with the photosensitizer.This is a new and simple method for combined photodynamic therapy,and we studied this system in vitro performance and anti-breast cancer effect in vivo and in vitro.The main research contents and results are as follows:The C3 hydroxyl group of ursolic acid is combined with one end carboxyl group of3,3'-dithiodipropionic acid to synthesize a ursolic acid derivative(UAD)through ester condensation reaction.Column chromatography and nuclear magnetic resonance spectroscopy were used for separation,purification and structural identification,which proved that UAD was successfully synthesized.The co-precipitation method of preparing nanoparticles was confirmed by observing the morphology of nanoparticles,and finally the coprecipitation method was used to prepare nanoparticles.We further evaluated the particle size and potential of nanoparticles formed under different ratios of UAD and Ce6 to confirm the best nanoformulation.And the prepared UAD-Ce6 NPs were fully characterized.The spherical nanoparticles with regular morphology and uniform distribution were seen under the scanning electron microscope.The average particle size measured by the particle size analyzer was about 212±4.87 nm,and the surface charge was-13.7±0.2 m V.Ultraviolet absorption spectrum and fluorescence emission spectrum indicate that the successful assembly of UAD-Ce6 NPs and the formation of nanoparticles have improved the water solubility and the bioavailability of the of Ce6.The drug loading of nanoparticles was determined to be 6.2% byultraviolet-visible absorption spectroscopy.According to the redox response drug release experiment in vitro,it was found that UAD-Ce6 NPs have excellent stimulus response drug release performance to GSH,and also have good physical stability and light stability,indicating that the nanoparticles have high stability and have physiological characteristics of medical drugs.In vitro cell experiments showed that UAD-Ce6 NPs had significant phototoxicity to cancer cells4T1 at a dose of 2 ?g/m L: tumor inhibition rate was 87.05%.And UAD-Ce6 NPs had a strong ability to generate reactive oxygen species.UAD-Ce6 NPs in vivo photochemical combined treatment of breast cancer was conducted by a mouse animal model of breast cancer.The tissue distribution of the nanoparticles was detected by the animal fluorescence imaging system,and it was found that the nanoparticles were mainly distributed in the liver and tumor,and the fluorescence signal was time-dependent,reaching the strongest at 6 h compared to the slow accumulation of Ce6,which proved the passive targeting of nanoparticles.After 14 days of treatment,the weight of the mice and the volume of tumor were recorded to evaluate the anti-tumor effect.It was found that the nanoparticles had a significant inhibitory effect on the tumor,which may be attributed to the nanoparticles and combination therapy.During the entire treatment,there was no significant change in the weight of the mice,and the biochemical measured values of the serum of the mice were not significantly different from the normal healthy mice,proving that the nanoparticles were safe and low toxicity.Therefore,in this study,UA,as a raw material,co-assembled with Ce6 to construct a nano-pharmaceutical system with glutathione stimulus responsiveness to achieve chemotherapy-photodynamic synergistic therapy,which has both good therapeutic effects and low toxic and side effects.