Selective Photodynamic Inactivation of Bacterial Cells over Mammalian Cells by New Triarylmethanes

Three new triarylmethane dyes (TAMs), MPCV, DPCV, and AEV, were synthesized and their photodynamic inactivation abilities against E. coli and human pulmonary carcinoma A549 cells were compared to two commercial TAMs, CV and EV. The enhanced hydrophilicity of MPCV and AEV decreases their cellular uptake to A549 cells dramatically. However, their binding affinity toward E. coli cells are comparable to that of CV and EV by virtue of the improved electrostatic attraction with highly negatively charged E. coli outer membranes. MPCV and AEV were also found to generate hydroxyl radicals more efficiently upon irradiation than CV and EV. Consequently, MPCV and AEV exhibited markedly improved photodynamic inactivation of E. coli cells but remarkably diminished photodynamic inactivation of A549 cells than CV and EV. The photodynamic inactivation ability of DPCV was much lower than that of CV due to its high propensity for bleaching in neutral aqueous solution. Our work demonstrates that the introduction of protonatable groups in a proper manner into the structures of TAMs may lead to selective binding and photodynamic inactivation toward bacterial cells over mammalian cells. This strategy may be extended to other types of photodynamic antimicrobial chemotherapy (PACT) agents to improve their clinical potential.