Development Of Antibiotic-crosslinked Micelle And Its Application For The Treatment Of Drug-resistant Bacterial Infections

The daunting problem of bacterial resistance is posing a serious threat to human health and safety.The"post-antibiotic era"may result in a situation that no antibiotics are available and more people lose their lives due to bacterial infections.Antimicrobial nano-materials have provided solutions to solve the problem of deadly bacterial infections because of their superior biocompatibility,ability of overcoming the mechanism of action of drug-resistance and targeted bactericidal effect.An important strategy is use of nanomaterials to address the drug-resistant bacterial infections and the side effects of toxicity of existing available drugs.In this thesis,a series of functionalized nano-micelles with high safety profile were designed using antibiotic colistin-crosslinked Pluronic micelles for the treatments of drug-resistant bacterial infections,intracellular bacterial infections,and bacterial biofilm infections.“Superbugs”resistant to multiple antibiotics recently are spreading dramatically,especially the gram-negative pathogens such as Acinetobacter baumannii,Pseudomonas aeruginosa,and Enterococcus.To combat multi-drug resistant bacteria,we developed a nanoplatform named antibiotic-crosslinked micelles（ABC-micelles）in Chapter 2.Colistin,as the last-resort of antimicrobial defense,could be encapsulated into FDA-approved Pluronic F127（F127）micelles also using colistin itself as crosslinker,forming safe and stable ABC-micelles with 80%drug encapsulation rate.ABC-micelles increased the maximum tolerated dose（MTD）of colistin by 16-fold and significantly reduced the nephrotoxicity and neurotoxicity caused by free colistin.In addition,ABC-micelles maintained superior bactericidal activity,with a mechanism of rapid and complete disruption of bacterial cell membranes to kill bacteria.Furthermore,the colistin and rifampicin co-loaded ABC-micelles（CR-ABCs）exhibited synergistic antibacterial effects against multi-drug resistant gram-negative pathogens.In a murine sepsis model,ABC-micelles showed equivalent antimicrobial efficacy to that of free colistin.It was shown that drug-crosslinked-micelles based on existing antibiotics can be used for novel antibacterial materials.Generally,intracellular bacteria are prone to cause more recurrent and persistent infections.However,small molecules of antibiotics are not able to enter the cell,hence how to effectively deliver antibacterial drugs to intracellular bacterial pathogens is a major bottleneck for the treatment of intracellular bacterial infections.In Chapter 3,we developed a delivery system denoted as SIR-micelles（+）,that can targeted deliver antibiotic-crosslinked micelles to macrophages where most intracellular bacteria reside.SIR-micelles（+）were responsive to the stimuli in intracellular environment,resulting in rapid self-immolation and release the pristine drug.After phagocytosis by macrophages,SIR-micelles（+）was able to undergo rapid self-immolation and traceless release the pristine drug in response to intracellular glutathione（GSH）,achieving the antibacterial effect of 100%clearance of intracellular E.coli within 15 min.In a mouse pneumonia model,SIR-micelles（+）significantly reduced the number of intracellular bacteria in lung tissues infected with multidrug-resistant Klebsiella pneumoniae,greatly increased the survival rate and reduced the intracellular bacterial burden in mice infected with homologous intracellular bacteria.SIR-micelles（+）provides a strong foundation and new strategy for the targeted treatment of intracellular drug-resistant pathogens.In medical conditions such as wound infections or medical device surfaces,Pseudomonas aeruginosa is prone to forming a thick biofilm,preventing small molecule drugs penetrating bacteria in biofilm,which causes drug resistance.In Chapter 4,a triple-stimulus-responsive bactericidal biomaterial,referred to as Ce6@Zn FeO4@Si ABC-micelles was developed by employing colistin-crosslinked micelles as a carrier,encapsulating magnetic metal oxide Zn FeO₄and photosensitizer dihydroporphyrin（Ce6）in the core of micelles.Driven by an external magnetic field,the nano-micelles were able to penetrate the external barrier of the biofilm,then the trigger-released active colistin under highly reduced conditions.And the photosensitizer Ce6 was able to be uniformly distributed deep in the biofilm.A clearance rate of 99.5%of bacteria was achieved under the combined effect of chemotherapy and photodynamic therapy with light irradiation.In animal wound infection,owing to the targeted driving effect of external magnetic field,along with the chemotherapeutic effect of colistin and photodynamic effect of Ce6,Ce6@Zn FeO4@Si ABC-micelles were able to effectively accumulate at the site of bacterial infection and remove the bacteria.This design provides a novel therapeutic strategy to address biofilm infections.