Singlet Oxygen Delivery System For Targeted Treatment Of Profound Multidrug-Resistant Staphylococcus Aureus Infections

Bacterial infections are one of the most serious health problems facing humans today,and among the diseases caused by bacterial infections,pneumonia caused by Staphylococcus aureus（S.aureus）infection is the disease with high morbidity and mortality worldwide,but traditional treatment has led to the continued evolution of bacterial resistance,and the high virulence and as well as resistance of evolved multidrug-resistant Staphylococcus aureus（MRSA）has increased the threat of this pathogen,which has become one of the most common pathogens of nosocomial and community infections.Antimicrobial photodynamic therapy（aPDT）is popular because of its broad antimicrobial spectrum as well as being not susceptible to drug resistance,but the production of its main antimicrobial substance reactive oxygen species is light source dependent and there is a defect of insufficient depth of light penetration for deep level infection applications,in the meanwhile,the short half-life and short diffusion distance of reactive oxygen species also limit its application in deep level delivery.However,it has been reported that pyridones is able to react with singlet oxygen in reactive oxygen species to generate endoperoxides,and release singlet oxygen continuously without relying on oxygen and light,thus prolonging the half-life of reactive oxygen species,which is an ideal singlet oxygen donor,but the lack of targeting with bacteria makes its utilization efficiency low when used alone,and there is a potential cytotoxicity problem if used in large quantities.Based on the above problems,we designed a targeted singlet oxygen delivery system for S.aureus,CARG-Py,to address the limitation of reactive oxygen species delivery at deep infection sites and to improve the low utilization and cytotoxicity of pyridones when used alone,by using the targeting property of peptide CARGGLKSC for S.aureus.First,We analyzed the characteristic hydrogen area integrals of singlet oxygen on pyridone structure loading under different light conditions by ¹H NMR,and screened out the light conditions with higher singlet oxygen loading rate,and then the ability of CARG-Py to load and release singlet oxygen was verified using ¹H NMR as well as electron spin resonance spectrometer.Further,we compared the antibacterial effect of the constructed targeting system CARG-¹O₂ with Py-COOH,we found that CARG-¹O₂ has lower bactericidal concentration,thus confirming the good targeting performance of the material and providing basis for its further application.In addition,a series of mechanism experiments have verified that CARG-¹O₂ disrupts the bacterial inner membrane,enhance the level of reactive oxygen species inside the bacteria,and at the same time destroy the internal proteins and DNA of the bacteria and thus causes bacterial death.Finally,in the MRSA-infected mouse pneumonia model,CARG-¹O₂ reduced the inflammatory response in mice and did not cause systemic toxicity compared to the negative control group,demonstrating good antibacterial effects in vivo.Overall,a series of studies have demonstrated that CARG-Py,as a singlet oxygen delivery system,effectively improves the deficiency of a PDT in deep-level treatment,and provides a new strategy to address the lack of penetration depth of light source,short half-life of reactive oxygen species,and achieve deep-level delivery of reactive oxygen species.