Study On Poly(L-Lysine)-drug Complexed Nanosystems

As a class of protein-mimicking synthetic polypeptides,poly（amino acid）s show excellent biocompatibility and biodegradability.In particular,amphiphilic poly（amino acid）s can self-assemble into various morphologies such as micelles,nanofibers,vesicles and membranes.Compared with conventional biodegradable polymeric materials,poly（amino acid）s can form unique secondary conformations（e.g.,α-helix,β-sheet,β-turn,et al.）as well as hierarchically assembled structures in aqueous solution.Moreover,there are a good variety of active sites on the side chains of poly（amino acid）s for further modification and functionalization,which could also be used to immobilize drugs,proteins and nucleic acids through electrostatic interaction.Therefore,these materials hold great promise in drug delivery applications.The purpose of this study is to improve the water solubility of hydrophobic drugs by complexation with poly（amino acid）s via electrostatic interaction.Particularly,the interaction of complexed drugs with polymers and the hierarchical self-assembly behavior of the polymeric complexs were investigated by changing the types and loading contents of the drugs.In addition,the drug release profiles,cell internalization property and anti-tumor performance in vitro were evaluated to explore the potential of nanosystems in drug delivery applications.This work provides a new strategy for the development of smart polymeric drug carriers.The main findings are as follows:（1）Poly（ethylene glycol）-poly（L-lysine）（PEG-PLL）was successfully prepared by ring-opening polymerization ofε-carbobenzoxy-L-lysine-N-carboxyanhydride（ZLL-NCA）initiated by methoxypolyethylene glycol amine（PEG-NH₂）,followed by the deprotection of the Z groups.Small molecule cinnamic acid（tCA）was used as a model drug to electrostatically complex with PEG-PLL.It was found that PEG-PLL-tCA with different drug loading contents could self-assemble into different morphologies.PEG-PLL-tCA assembly is stable in aciditc,neutral and ionic conditions,but destabilized under UV irradiation,resulting in an accelerated drug release.The cell internalization and antitumor capacity of PEG-PLL-tCA nanosystems was tested.It was found that PEG-PLL-tCA showed higher cell entry efficiency than PEG-PLL and an enhanced anti-tumor effect under UV irradiation.（2）PEG-Cys-PLL bearing a disulfide bond was successfully prepared by NCA ring-opening polymerization.The hydrophobic antitumor drug gambogic acid（GA）was used as a model to electrostatically bind with polylysine segment.The drugs was found to interact with polymeric chains and inhibit the crystallization of PEG segment,as evidenced by DSC,XRD and 2D-NOESY experiments.Interstingly,the PEG-Cys-PLL-GA complexes with lower drug loading content could self-assemble into spherical micelles,while those with higher loading form vesicles.All the aggregates display stableα-helical conformation.The PEG-Cys-PLL-GA nanosystem is stable under neutral condition,and can response to acidic and reductive environments for triggered drug release.（3）The cell internalization antitumor effect of PEG-Cys-PLL-GA nanosystem were tested.Both flow cytometry and confocal laser scanning microscope（CLSM）show that PEG-Cys-PLL-GA nanocomplex has higher cell entry efficiency than PEG-Cys-PLL formulation.MTT assay indicates that the drug-free PEG-Cys-PLL is cytocompatible against L929 fibroblasts,while PEG-Cys-PLL-GA@DOX electrostatically complexed with gambogic acid and physically loaded with DOX exhibit excellent drug efficacy toward MCF-7 tumor cells.In particular,the cooperativity index（CI）of the two drugs is less than1,suggesting a cooperativity therapeutic effect in vitro.