Sialic Acid-Functionalized Ph-Triggered Micelles For Hierarchical Taregeting Drug Delivery

The eventual aim of Drug Delivery Systems?DDSs?for targeted tumor therapy is to increase drug concentration in tumor cells,thereby enhancing efficiency and decreasing toxicity.At present,substantial targeted DDSs were developed based on receptor-mediated recognition?ligand receptor,antibody antigen?on the surface of tumor cells,only after passive accumulation into tumor tissue can they be actively transported into tumor cells.However,study on tumor tissue targeting is still inadequate.Therefore,enhanced targeting efficiency in tumor tissue of DDSs is one of the key issues that need to be addressed.In this study,sialic acid-modified pH-sensitive micelles?Sialic acid-PEG-hydrazone-doxorubicin,SPD?were synthesized based on the characteristics of sialic acid that specifically bind to E-selectin overexpressed on inflammatory vascular endothelial cells around tumor tissues and tumor cells.1H-NMR and IR were used to confirm the chemical structure of SPD.The SPD polymer could form micelles by self-aggregation in an aqueous medium with a small critical micelle concentration?26.52 ?g/mL?.The prepared SPD micelles were spherical in shape and have a particle size of 41.8±7.5 nm,which can further effectively load DOX with 40%of drug loading efficiency.DO-loaded SPD micelles?SPDD?showed a sustained release for 72 h,which was pH-dependent.As the pH decreased,the drug release accelerated.Both MTT assay and alive cell staining showed that the anti-tumor efficacy of SPDD?IC₅0:0.805 ?g/mL?was significantly higher than that of non-sialic acid-modified pH-sensitive micelle PDD?IC₅0:2.357 ?g/mL?,and the antitumor effect of PDD is enhanced than that of the non-sialic acid-modified non-sensitive micelle PPD?IC₅0:5.5549 ?g/mL?.Intracellular release studies showed that Nile Red released by SPD was significantly faster than that released by PD in Bel-7402 cells,and the intracellular release rate of non-sialic acid-modified pH-sensitive micelles is greater than that of non-sialic acid modified non-sensitive micelles.Subcellular co-localization results showed that both SPD and PD micelles could be internalized into lysosomes of Bel-7402 cells,which laid the foundation for the breakage of pH-sensitive linker.Both qualitative and quantitative results indicated that SPD can specifically target Bel-7402 cells,and this targeting ability is mainly mediated by sialic acid and E-selectin highly expressed on the surface of tumor cells.In vivo targeting study demonstrated that SPD micelles showed 2.3-fold higher accumulation in tumors after 48h compared to the micelles lacking the SA moiety.The overexpression of E-selectin on the inflammatory vascular endothelial cells around tumors increased the accumulation of SPD micelles in tumor tissues,while that on the tumor cells increased the internalization of micelles.Accordingly,SPDD exhibited prior suppression on Bel-7402 tumor growth to PDD micelles?the tumor inhibition:86.47%vs 73.80%?.In addition,after treatment of SPDD micelle for 25 days,the hematopoietic function of the mice was normal,and no obvious lesions appeared in the liver and heart,which verified the biosafety of SPD micelles.This study indicated that SPD can realize hierarchical targeting drug delivery via specifically bind to E-selectin upregulated on inflammatory vascular endothelial cells surrounding tumors and tumor cells.Furthermore,due to the acid-sensitive hydrazone linker between PEG and DOX,the drug will be quickly released upon internalization and accumulation inside the tumor cells in a short period of time,thereby having great potential in treatment for liver cancer.