Cationic Phenosafranin Photosensitizers Based on Polyhedral Oligomeric Silsesquioxanes for Inactivation of Gram-Positive and Gram-Negative Bacteria.

Krystyna Rozga-Wijas,Irena Bak-Sypien,Katarzyna Turecka,Krzysztof Waleron,Magdalena Narajczyk

doi:10.3390/ijms222413373

Abstract

The high photodynamic effect of the Newman strain of the S. aureus and of clinical strains of S. aureus MRSA 12673 and E. coli 12519 are observed for new cationic light-activated phenosafranin polyhedral oligomeric silsesquioxane (POSS) conjugates in vitro. Killing of bacteria was achieved at low concentrations of silsesquioxanes (0.38 µM) after light irradiation (λem. max = 522 nm, 10.6 mW/cm2) for 5 min. Water-soluble POSS-photosensitizers are synthesized by chemically coupling a phenosafranin dye (PSF) (3,7-diamino-5-phenylphenazine chloride) to an inorganic silsesquioxane cage activated by attachment of succinic anhydride rings. The chemical structure of conjugates is confirmed by 1H, 13C NMR, HRMS, IR, fluorescence spectroscopy and UV-VIS analyzes. The APDI and daunorubicin (DAU) synergy is investigated for POSSPSFDAU conjugates. Confocal microscopy experiments indicate a site of intracellular accumulation of the POSSPSF, whereas iBuPOSSPSF and POSSPSFDAU accumulate in the cell wall or cell membrane. Results from the TEM study show ruptured S. aureus cells with leaking cytosolic mass and distorted cells of E. coli. Bacterial cells are eradicated by ROS produced upon irradiation of the covalent conjugates that can kill the bacteria by destruction of cellular membranes, intracellular proteins and DNA through the oxidative damage of bacteria.

Highlights

The rapid acquisition of antibiotic resistance makes it difficult to develop effective methods of eliminating pathogenic bacteria that multiply rapidly under appropriate conditions and can cause infectious diseases on a large scale [1,2,3]
The positively charged conjugates composed of covalently linked inorganic polyhedral oligomeric silsesquioxane (POSS) cage and phenosafranin dye may increase the accumulation of the photosensitizer inside bacterial cells, as observed with POSSPSF conjugate, or the accumulation in the bacterial cell membrane or cell wall, as observed with iBuPOSSPSF and POSSPSFDAU
Bacterial cells were eradicated by reactive oxygen species (ROS) produced upon irradiation of the covalent conjugates with light that can kill the bacteria by destruction of cellular membranes, intracellular proteins and DNA through the oxidative damage of bacteria

Summary

Introduction

The rapid acquisition of antibiotic resistance makes it difficult to develop effective methods of eliminating pathogenic bacteria that multiply rapidly under appropriate conditions and can cause infectious diseases on a large scale [1,2,3]. Particular interest may be attributed to situations wherein small molecules are safe for humans and their toxicity increases under conditions of irradiation with light of a specific wavelength [5] Such conditions are achieved by antimicrobial photodynamic inactivation (APDI), which is a potential alternative for antibiotics to kill bacteria and importantly, such resistance mechanisms have not yet been observed [6]. Most of the phenothiazine, phthalocyanine and porphyrin photosensitizers reported so far are hydrophobic and tend to form aggregates when they interact with bacteria in physiological hydrophilic conditions [8] Such molecular aggregation and π-π stacking interactions can cause the quenching of the singlet state, quenching fluorescence, as well as reducing ROS production and attenuating the effects of both imaging and therapy [9]

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