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meso-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers.

ABSTRACT: A new category of cationic meso-thiophenium porphyrins are introduced as possible alternatives to the popular meso-pyridinium porphyrins. Combinations of cationic porphyrins bearing meso-2-methylthiophenium and meso-4-hydroxyphenyl moieties T₂(OH)₂M (A₂B₂ type) and T(OH)₃M (AB₃ type) along with their zinc(II) complexes T₂(OH)₂MZn and T(OH)₃MZn, are reported. The increase in the number of thienyl groups attached to the meso-positions of the porphyrin derivatives (A₂B₂ frame) has been shown to impart longer fluorescence lifetimes and stronger photocytotoxicity toward A549 lung cancer cells, as evident with T₂(OH)₂M and its corresponding diamagnetic metal complex T₂(OH)₂MZn. The photoactivated T₂(OH)₂MZn imparts an early stage reactive oxygen species (ROS) upregulation and antioxidant depletion in A549 cells and contributes to the strongest oxidative stress-induced cell death mechanism in the series. The DFT calculations of the singlet-triplet energy gap (ΔE) of all the four hydrophilic thiophenium porphyrin derivatives establish the potential applicability of these cationic photosensitizers as PDT agents.

SUBMITTER: Mazumdar ZH

PROVIDER: S-EPMC7549270 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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 microM 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.

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meso-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers.

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