Monosubstituted tricationic Zn(II) phthalocyanine enhances antimicrobial photodynamic inactivation (aPDI) of methicillin-resistant Staphylococcus aureus (MRSA) and cytotoxicity evaluation for topical applications: in vitro and in vivo study

Abstract

Antimicrobial photodynamic therapy (aPDT) has recently been proposed as an innovative approach to combat multi-drug resistant bacteria. It is known that cationic Zn(II) phthalocyanines (ZnPc) are effective in mediating aPDT against methicillin-resistant Staphylococcus aureus (MRSA). Here we have synthesized a ZnPc-based photosensitizer named ZnPcE previously reported by our research group to evaluate its aPDT efficacy against clinically relevant MRSAs including 4 ATCC type strains (ATCC 43300, ATCC BAA-42, ATCC BAA-43, ATCC BAA-44), two strains carrying specific antibiotic resistance mechanisms [AAC(6)’APH(2)” and RN4220/pUL5054] and 5 each from hospital- and community-associated MRSAs of important clonal types ST239, ST30 and ST59 which were previously documented to be prevalent in Hong Kong and its neighbouring countries. Remarkably, in vitro anti-MRSA activity was achieved using near infrared (NIR, >610 nm) light with minimal bactericidal concentrations ranging <0.019-0.156 µM against the panel of MRSAs. ZnPcE was not only significantly (p < 0.05) more potent than methylene blue, which is a clinically approved photosensitizer, but also demonstrated low cytotoxicity against human fibroblasts cell line (Hs-27) and human immortalized keratinocytes cell line (HaCaT). The toxicity was further evaluated on human 3-D skin constructs and found ZnPcE did not manifest in vivo skin irritation <7.8 µM concentration. In the murine MRSA wound model, ZnPcE with PDT group demonstrated > 4 log10 CFU reduction and the value is significantly higher (p < 0.05) than all test groups except positive control. To conclude, results of present study provide a scientific basis for future clinical evaluation of ZnPcE-PDT on MRSA wound infection.