Effect Of The Structure Of Lipidated Peptide Amphiphiles On Cell Membrane Affinity,Drug Delivery,and Cell Imaging

Amphiphilic peptides are a class of peptides which are widely used.They are easy to be modified,highly designable,and have structural and functional diversity.Lipidated peptide amphiphiles have compositional and structural similarity to phospholipids in cell membranes.They are biocompatible and biodegradable,and the degradation products are environmentally friendly.These advantages make lipidated peptide amphiphiles attractive in biomedical fields.The interaction between lipidated peptide amphiphiles and cell membranes determines the biological application of lipidated peptide amphiphiles.However,it is still challenging to enhance the interaction between lipidated peptide amphiphiles and cell membranes,as well as the affinity of lipidated peptide amphiphiles to cell membranes.In this thesis,we synthesized a series of lipidated peptide amphiphiles molecules with different structures.Then,the effect of structure on their self-assembly behavior of lipidated peptide amphiphiles was systematically studied.We further explored the effect of structure on the affinity to cell membranes.Finally,we expanded the application of lipidated peptide amphiphiles to drug delivery and cell imaging.Main results are as follows:（1）In order to improve the cell membranes affinity of lipidated peptide amphiphiles,a gemini lipidated peptide amphiphile（PA2）with high cell membranes affinity was designed,and antitumor drug camptothecin was loaded in their assemblies for antitumor research.Inspired by the structure of a phospholipid molecule,we synthesized a gemini lipidated peptide amphiphile with a peptide side chain modified with rhodamine group and two dodecyl chains as the hydrophobic end,and a targeting active peptide sequence（GRGDS）as hydrophilic end.In addition to the fluorescent imaging function,the rhodamine group also improves the drug loading capacity of the lipidated peptide amphiphiles carrier throughπ-πstacking effect with the chemotherapy drug camptothecin.Based on the hydrophobic interaction of the alkyl chains and theπ-πstacking effect of the rhodamine group,the gemini lipidated peptide amphiphiles and camptothecin are co-assembled in solution to form nanodrugs with small size and stable structures.Besides,an active peptide sequence（GRGDS）with targeting function can target tumor cells,thereby achieving efficient uptake of nanodrugs by cancer cells.These nanodrugs could inhibit tumor cells proliferation.Our results provide a new idea for the application of gemini lipidated peptide amphiphiles with high cell membranes affinity in tumor treatment.（2）To understand the effect of lipidated peptide amphiphiles structure on aggregation behavior,we prepared diacetylene lipidated peptide amphiphiles（PA-NH₂and PA-COOH）with different charge properties.The molecular structures of these two diacetylene lipidated peptide amphiphiles are similar,with four cationic lysine sequences at the hydrophilic end and one 10,12-docosacosynic acid at the hydrophobic end.The difference is that the C-terminus of PA-NH₂is amide,while the C-terminus of PA-COOH is carboxyl.Diethynyl can undergo photo-initiated polymerization,resulting in red-blue phase transition accompanied by red fluorescence.We studied the polymerization behavior of two diacetylene lipidated peptide amphiphiles in solution and intracellularly by UV-vis and up-conversion scanning laser confocal microscope（CLSM）.Red fluorescence signal could be detected in the cells after phagocytosis.The results showed that PA-NH₂had no characteristic absorption peak in solution and had strong red fluorescence signal in the cell,PA-NH₂and PA-COOH showed completely opposite polymerization behavior in solution and intracellular.The above design provides a new idea for the effect of lipidated peptide amphiphiles structure on aggregation behavior and affinity of cell membranes,and expands the application of diacetylene lipidated peptide amphiphiles in cell imaging.