Studies On Construction And Antibacterial Activities Of Peptide-based Polymers

The value of antibiotics to human health is beyond doubt.Antibiotics have changed the vulnerability of human beings in the long-term struggle against bacterial infectious diseases,but the abuse of antibiotics has led to the emergence of bacterial resistance,which poses a major threat to human health,especially,the development of superbugs.Thus,we designed a class of antimicrobial agents to conquer drug resistance,which are different from antimicrobial mechanisms of traditional antibiotics.Cationic antimicrobial peptides（AMPs）,the important defense line of the immune system,have broad-spectrum antibacterial activities and are not easy to lead to drug resistance.However,the application of natural antimicrobial peptide is greatly limited due to the low bactericidal activity and yield.In order to effectively overcome the increasingly severe drug resistance,we envisaged to construct a class of peptide-based polymers which are not easy to induce the emergence of drug resistance.Specific study contents include the following three parts:（1）The amino acid N-carboxyanhydrides（NCAs）were synthesized by ring-forming reaction of amino acids with triphosgene.Followed,the peptide-based polymers were successfully prepared via the ring-opening polymerization of NCAs.SEM and DLS studies showed that the polymers could spontaneously self-assemble into nanoparticles with good dispersion and stability.Structure-activity assays suggested that the p2 with pectinate structure exhibited excellent broad-spectrum antibacterial activities with MIC of 16μg/mL,showing sterilization rate of more than 94%against S.aureus and E.coli.Especially,the nanoparticles didn’t easily result in the development of drug-resistance.The investigation of antibacterial mechanism suggested that the positively charged nanoparticles initially bound to the surface of bacteria,and disrupted the membranes,eventually causing cytoplasmic leakage and bacterial death.（2）The positively charged PCL-b-AMPs was constructed by ring-opening polymerization of the monomersε-caprolactone,Lys-NCA and Phe-NCAs.Subsequently,the AgNPs@PCL-b-AMPs was prepared by coordination with Ag⁺and in situ reduction.UV-Vis,XPS and XRD studies confirmed the formation of AgNPs.SEM,TEM and DLS studies showed that AgNPs@PCL-b-AMPs is nanocomposite with good dispersion.The biological assays revealed that the nanocomposite with 2:1 molar ratio of-NH₂ to Ag⁺exhibited strong antibacterial activities and no drug resistance,exhibiting a MIC value range in 2～8μg/mL.The investigation of antibacterial mechanism showed that the nanocomposite can physically damage the membranes structure and subsequently induce generation of the reactive oxygen species（ROS）.Also,in vivo anti-infective assays showed that the nanocomposite was also able to effectively kill bacteria.（3）The amphiphilic cationic PCL-b-Lys was successfully constructed by ring-opening polymerization ofε-caprolactone and Lys-NCA.Subsequently,the drug-loaded nanoparticles（PM-Cur）were afforded by encapsulating curcumin for achieving synergistic bactericidal effect.UV-Vis study confirmed the successful load of curcumin,by which could effectively improved the solubility of curcumin.The biological assays demonstrated that the PM-Cur showed effective antibacterial activities with MIC value range in 16～32μg/mL and the bactericidal rate are more than 90%.SEM,SPR and fluorescent staining studies suggested that PM-Cur can tightly attach to the surface of cell membranes,destroying the integrity of membrane and inhibiting the transmission of bioelectronic signals.