Stable synthetic cationic bacteriochlorins as selective antimicrobial photosensitizers

Liyi Huang, Ying Ying Huang, Pawel Mroz, George P. Tegos, Timur Zhiyentayev, Sulbha K. Sharma, Zongshun Lu, Thiagarajan Balasubramanian, Michael Krayer, Christian Ruzié, Eunkyung Yang, Hooi Ling Kee, Christine Kirmaier, James R. Diers, David F. Bocian, Dewey Holten, Jonathan S. Lindsey, Michael R. Hamblin

Research output: Contribution to journalArticlepeer-review

119 Scopus citations


Photodynamic inactivation is a rapidly developing antimicrobial treatment that employs a nontoxic photoactivatable dye or photosensitizer in combination with harmless visible light to generate reactive oxygen species that are toxic to cells. Tetrapyrroles (e.g., porphyrins, chlorins, bacteriochlorins) are a class of photosensitizers that exhibit promising characteristics to serve as broad-spectrum antimicrobials. In order to bind to and efficiently penetrate into all classes of microbial cells, tetrapyrroles should have structures that contain (i) one or more cationic charge(s) or (ii) a basic group. In this report, we investigate the use of new stable synthetic bacteriochlorins that have a strong absorption band in the range 720 to 740 nm, which is in the near-infrared spectral region. Four bacteriochlorins with 2, 4, or 6 quaternized ammonium groups or 2 basic amine groups were compared for light-mediated killing against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli), and a dimorphic fungal yeast (Candida albicans). Selectivity was assessed by determining phototoxicity against human HeLa cancer cells under the same conditions. All four compounds were highly active (6 logs of killing at 1 μM or less) against S. aureus and showed selectivity for bacteria over human cells. Increasing the cationic charge increased activity against E. coli. Only the compound with basic groups was highly active against C. albicans. Supporting photochemical and theoretical characterization studies indicate that (i) the four bacteriochlorins have comparable photophysical features in homogeneous solution and (ii) the anticipated redox characteristics do not correlate with cell-killing ability. These results support the interpretation that the disparate biological activities observed stem from cellular binding and localization effects rather than intrinsic electronic properties. These findings further establish cationic bacteriochlorins as extremely active and selective near-infrared activated antimicrobial photosensitizers, and the results provide fundamental information on structure-activity relationships for antimicrobial photosensitizers.

Original languageEnglish (US)
Pages (from-to)3834-3841
Number of pages8
JournalAntimicrobial agents and chemotherapy
Issue number9
StatePublished - Sep 2010


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