The Combination Of "On-site Activated" Antimicrobial Peptides And Antibiotics For The Treatment Of Bacterial Infections

Antibiotic therapy applied for bacterial infectious diseases faces problems,such as drug resistance and unsatisfactory bactericidal effect against intracellular bacteria in latent or dormant states.It is urgent to develop new strategies to improve the efficacy of antibiotics Studies have shown that antimicrobial peptides(AMPs)can significantly enhance the efficacy of conventional antibiotics.However,AMPs exhibit strong cytotoxicity to normal tissue cells It is critical challenge to effectively enhance antibiotics’ efficacy and with low toxicity to normal tissues for the combination therapy.The thesis developed infectious microenvironment-associated AMPs,including reactive oxygen species(ROS)-activated colistin prodrugs and lysosomal acid-activated antimicrobial polypeptides,presenting an inactive form with low toxicity in normal tissues and converting into an active form in infected tissues,for improving the efficacy of antibiotics.The research contents and main discussions of this thesis are divided into two parts(1)ROS-activated colistin prodrug(ABE-COL)was developed for the enhancement of the efficacy of antibiotics.Hemolysis test,cell proliferation(MTT)test,lactate dehydrogenase(LDH)and other experiments proved that that ABE-COL exhibited low toxicity to normal tissue cells,and didn’t cause mice death at a dose of 75 mg/kg,while MTD for free COL was 10 mg/kg.In the presence of ROS(hydrogen peroxide mimetic),ABE-COL restored antibacterial activity and significantly enhanced bactericidal effect of antibiotic rifampicin(RFP).The co-encapsulated nanoparticles(Co-NP)were obtained through co-encapsulating ABE-COL and RFP with mPEG-PLA by nanoprecipitation method,.The particles were characterized for drug loading and entrapment efficiency by high-performance liquid chromatography(HPLC),particle size by dynamic light scattering(DLS).The results of bactericidal kinetics experiments and intracellular infection treatment experiments indicated that Co-NP had a synergistic antibacterial effect.Treatment experiments in mouse pneumonia models suggested that in vivo therapeutic effects with Co-NP was better than that of monotherapy.This study provides a new idea for designing ROS-activated prodrugs in the infection microenvironment and provides a strategy to enhance the efficacy of antibiotic therapy.(2)Lysosomal acidity-activated helical polypeptide P3 was used to enhance the efficacy of antibiotics against intracellular infection.P3 presents as a non-helical structure with low cytotoxicity at physiological environment and converts into a helical structure at lysosomal acidity with strong antibacterial activity.P3 could enhance the bactericidal activity of cephalosporins under lysosomal acidic conditions whose activity was weakened under acidic conditions in vitro lysosomal acidity.In intracellular infection treatment experiments,P3 enhanced the bactericidal activity of cephalosporins against intracellular survival bacteria P3 was then encapsulated by mPEG-PLA to obtain stable nanoparticles P3(NPP3).NPP3 could be phagocytosed and taken up by macrophages and enriched in lysosomes according to flow cytometry and confocal laser microscopy(CLSM).NPP3 could enhance the bactericidal activity of cephalosporins against intracellular survival bacteria.And in mouse pneumonia models,the combination of NPP3 and cephalosporin was better than monotherapy.This study provides a new idea for the enhancement of the therapeutic effect of antibiotics on intracellular bacterial infectionsIn this thesis,we used the infection microenvironment-activated antimicrobial peptides for the enhancement of the therapeutic efficacy of conventional antibiotics,providing new strategies for treatment of bacterial infectious diseases.