Design And Mechanistic Study Of A Pentapeptide-protected Gold Nanocluster-Based Drug Delivery System

Stimuli-responsive drug delivery systems hold great promise for the treatment of disease as the nature of trigger induced drug release can improve clinical efficacy and reduce the amount of drug needed,which can mitigate side effects.However,the clinical use of drug delivery systems is limited by the complexity of their structural designs and their potential cytotoxicity.Accordingly,readily accessible,stimuli-responsive nanocarriers with self-regulated release systems and good biocompatibility are urgently needed.Recently,peptide-protected gold nanoclusters are attracting people’s attention as a promising bio-nanomaterial.This is attributed to its ultrasmall size(<2 nm),uniform morphology,stable photoluminescence and high biocompatibility.More attractively,the diversity and versatility of peptide sequences make it possible to design nanoclusters with specific recognition functions.When peptide nanoclusters are designed as nanocarriers,drugs can be identified and loaded by functional peptides on their surfaces,and this weak interaction can be easily broken to release drugs.Therefore,in this scenario,people only need to pay attention to the specific biological functions they want to achieve,such as specific targeting to cells,drags loading and so on,and then design the peptides with corresponding biological functions to synthesize nanoclusters without the need for complex structural design of nanomaterials themselves.Compared with the time-consuming and laborious post-synthetic modification method,this method is much simpler and more efficient.In conclusion,high biocompatibility,intrinsic fluorescence and simple synthesis methods make polypeptide clusters have the potential to become nano-drug delivery systems.In this work,vancomycin is chosen as a model drug,which has been widely used as a common antibiotic in the clinical treatment of inflammation and infection caused by multidrug-resistant Gram-positive bacteria.With vancomycin as the target molecule,the sequence of the peptide was designed reasonably.That is,the peptide was divided into two domains,one domain was used to bind the nanocluster which can be realized by introducing the glutathione sequence;the other domain was used to bind vancomycin,which could be achieved by adding the D-alanine-D-alanine sequence.Using this peptide as ligand,water-soluble gold nanoclusters with strong fluorescence were synthesized.It was found that the fluorescence of the nanoclusters could be enhanced several times by adding vancomycin.Dynamic light scattering showed that the fluorescence enhancement was accompanied by the increase of the hydrodynamic radius of the nanocluster.Combined with the thermodynamic parameters obtained by isothermal calorimetric titration,it can be proved that the nanocluster and vancomycin interacted through hydrogen bond and hydrophobic interaction.Unlike the traditional drug delivery system,the gold nanoclusters based on the designed pentapeptide ligand can spontaneously load vancomycin through the specific recognition between the peptide and vancomycin.Antibacterial experiments showed that gold nanoclusters loaded with vancomycin could effectively inhibit the growth of Gram-positive bacteria,and their antimicrobial effects were comparable to those of vancomycin itself.Unlike the direct addition of vancomycin,this nanocluster-based drug delivery system can release a suitable amount of vancomycin according to the content of bacteria,effectively improving the utilization rate of drugs and reducing side effects.Further studies have shown that the controlled release of vancomycin is mainly due to the binding affinity between vancomycin and bacteria is stronger than that between vancomycin and gold nanoclusters,which results in the transfer of vancomycin from nanoclusters to bacterial surface and finally cause the death of bacteria.In addition,the fluorescence of the gold nanoclusters will change linearly and reversibly with the change of temperature,which indicates that the gold nanoclusters have potential value for constructing temperature sensors.In addition,fluorescence imaging in vitro and in vivo were also achieved by using these nanoclusters with strong fluorescence.