Discovery of Meso-(meta-Pyridinium) BODIPY Photosensitizers: In Vitro and In Vivo Evaluations for Antimicrobial Photodynamic Therapy

Antimicrobial photodynamic therapy (aPDT) has emerged as a novel and promising approach for the treatment of pathogenic microorganism infections. The efficacy of aPDT depends greatly on the behavior of the photosensitizer. Herein, we report the design, preparation, antimicrobial photodynamic activities, as well as structure–activity relationships of a series of photosensitizers modified at the meso position of a 1,3,5,7-tetramethyl BODIPY scaffold with various pyridinyl and pyridinium moieties. The photodynamic antimicrobial activities of all photosensitizers have been tested against Staphylococcus aureus, Escherichia coli, Candida albicans, and Methicillin-resistant S. aureus (MRSA). The methyl meso-(meta-pyridinium) BODIPY photosensitizer (3c) possessed the highest phototoxicity against these pathogens at minimal inhibitory concentrations (MIC) ranging from 0.63 to 1.25 μM with a light dose of 81 J/cm2. Furthermore, 3c exhibited an impressive antimicrobial efficacy in S. aureus-infected mice wounds. Taken together, these findings suggest that 3c is a promising candidate as the antimicrobial photosensitizer for combating pathogenic microorganism infections.