Construction Of PH Responsive Drug Delivery System Based On Polysaccharides From Bletilla Striata/nano ZnO Composite Carrier And Evaluation Of Anticancer Activity Of Resveratrol Loaded On It

Cancer is one of the deadliest diseases in the 21st century.However,the chemical drugs used in cancer treatment have universal cytotoxicity and will bring toxic and side effects to normal cells.Therefore,it is necessary to construct a novel drug delivery system with important practical significance,which can not only effectively kill cancer cells,but also reduce the toxic side effects on normal cells.Nano zinc oxide（ZnO NPs）not only has the physical characteristics of high drug loading and easy modification,but also can quickly dissolve in the microenvironment of cancer tissue（pH<6）,and effectively kill cancer cells by producing cytotoxic zinc ions and reactive oxygen species.However,the preparation of ZnO NPs mainly uses volatile solvents and toxic synthetic polymers,which do not conform to the concept of green chemistry and limit the application of ZnO NPs in the biomedical field.Therefore,it is necessary to design an environmentally friendly preparation method of ZnO NPs to control the release of drugs in ZnO NPs in an environmentally sensitive manner.Based on this,a pH responsive delivery system based on polysaccharides from Bletilla Striata/nano zinc oxide composite carrier（BSP-ZnO NPs）was constructed with polysaccharides from Bletilla Striata（BSP）as stabilizer,and the anticancer activity of resveratrol（RES）loaded on it was evaluated.Firstly,BSP-ZnO NPs were synthesized by coprecipitation method,and the particle size of BSP-ZnO NPs was used as the optimization condition.The response surface experiment was designed based on single factor to determine the optimal preparation process conditions.BSP-ZnO NPs were characterized by dynamic light scattering,field emission scanning electron microscopy,ultraviolet spectrophotometer,Fourier transform infrared,and fluorescence spectrophotometer.The results showed that the optimum preparation conditions of BSP-ZnO NPs were as follows:drying time 3.5 h,precipitant addition 0.3 mol/L and stabilizer addition 0.3 g.under these conditions,the average particle size of BSP-ZnO NPs was 233.05 nm.Furthermore,we observed that ZnO NPs were aggregated flower-like structures composed of nano cones with tip units,which were evenly distributed on the substrate of BSP,the BSP-ZnO NPs exhibited good pH responsiveness.Secondly,RES was used as the model drug.The drug loading,chemical stability,physical stability and in vitro release ability of BSP-ZnO NPs under different pH conditions were investigated by dynamic light scattering and ultraviolet spectrophotometer.The results showed that RES and BSP-ZnO NPs were self-assembled into stable RES-BSP-ZnO NPs through electrostatic interaction,and the drug loading reached 30.8%.After RES was irradiated with ultraviolet for 10 h,the DPPH radical scavenging rate decreased by 45.70%,and the DPPH radical scavenging rate of RES-BSP-ZnO NPs decreased by only 6.2%.RES-BSP-ZnO NPs remained stable for 4 d under physiological conditions（pH 7.4）,and gradually formed aggregation and released RES in the microenvironment of cancer tissue（pH<6）.At pH 5.0,the cumulative release rate of RES-BSP-ZnO NPs within 36 h was as high as 87.1%,and the drug diffusion model conformed to the Fickian diffusion mechanism.Finally,the safety of BSP-ZnO NPs was evaluated by bovine serum albumin adsorption test and hemolysis test.The potential anticancer activity of RES-BSP-ZnO NPs on Caco-2 cells was evaluated by qualitative uptake,cytotoxicity,and intracellular reactive oxygen species levels.The results showed that compared with zinc oxide（ZnO）,the adsorption capacity of bovine serum albumin of BSP-ZnO NPs decreased by 5.03%and the hemolysis of red blood cells decreased relatively.After loading RES,BSP-ZnO NPs could enter Caco-2 cells through endocytosis,and were mainly distributed around the nucleus.RES-BSP-ZnO NPs exhibited a dose-dependent inhibitory effect on Caco-2cells in the concentration range of 75 to 200μg/m L,and the IC₅₀ of RES-BSP-ZnO NPs was about 47μg/m L based on RES,which was lower than RES（88μg/m L）,meanwhile,the intracellular reactive oxygen species level of RES-BSP-ZnO NPs was higher than that of RES.Therefore,the pH responsive delivery system（BSP-ZnO NPs）constructed in this subject not only met our expectations for the pH responsive release of RES,but also exhibited good biocompatibility and synergistic anticancer activity in vitro.